Switch-extender and a method for calibrating

Abstract

A switch-extender is connected to a measurement system and to several DUTs. It splits a signal from the measurement system into several signals so that the several DUTs receive the same signal and can therefore be tested in parallel. The switch-extender further includes at least one amplifier and/or at least one attenuator for every output port so that every signal has the same signal level no matter what the individual attenuation factor of the signal connectors or of the internal printed circuit board is. Furthermore a method for calibrating the measurement system as well as for the switch-extender and the signal connectors describes how to obtain the needed calibration values both for the downlink path and for the uplink path without changing the signal connector.

Claims

1. A method for calibrating a system comprising a measurement system, a switch-extender, signal connects, attenuators and one calibration system comprising a first measurement unit, a second measurement unit, and a signal splitter, wherein the method comprises the steps of: connecting a first output of the signal splitter to the first measurement unit; connecting a second output of the signal splitter to the second measurement unit; connecting the first and the second measurement unit; connecting the switch extender to the measurement system; connecting each one end of the several signal connectors to the switch extender; connecting the other end of one of the several signal connectors with an attenuator to an input of the signal splitter; generating a signal with a specific signal level and/or a specific signal frequency with the measurement system; measuring a signal level and/or a signal frequency with the calibration system at the first output of the signal splitter, measuring a signal power at the second output of the signal splitter and transmitting measured values to the first measurement unit; determining a difference between the measured signal level and/or the measured signal frequency and the generated signal with the specific signal level and/or the specific signal frequency; and calculating calibration data by using the determined difference between the measured signal level and/or the measured signal frequency and the generated signal with the specific signal level and/or the specific signal frequency.

2. The method according to claim 1, further comprising the steps of: generating a signal with a second specific signal level and/or a second specific signal frequency with the calibration system; measuring a second signal level and/or a second signal frequency with the measurement system; determining a difference between the measured signal level and/or the measured signal frequency and the generated signal with the specific signal level and/or the specific signal frequency; and calculating second calibration data by using the determined difference between the measured signal level and/or the measured signal frequency and the generated signal with the specific signal level and/or the specific signal frequency.

3. The method according to claim 1, wherein the switch-extender further comprises at least one attenuator or the at least one first attenuator and a second attenuator in series and for every output port a signal connector is connected to the switch-extender, and wherein the method further comprises the step of: adjusting the attenuation value of the at least one first attenuator or adjusting the attenuation value of the at least one first attenuator and the second attenuator so that the measured signal level and/or signal frequency of the signal is equal to the generated signal with the specific signal level and/or the specific signal frequency.

4. The method according to claim 3, further comprising the steps of: repeating the generating step, the measuring step, the determining step and the calculating step for another signal frequency and/or signal level, or repeating the generating step, the measuring step, the determining step, the adjusting step and the calculating step for another signal frequency and/or signal level.

5. The method according to claim 3, wherein a signal connector is a cable, and wherein the method further comprises the steps of: connecting the other end of another signal connector with another attenuator to the calibration system; and repeating the generating step, the measuring step, the determining step and the calculating step for another signal frequency and/or signal level, or repeating the generating step, the measuring step, the determining step, the adjusting step and the calculating step for another signal frequency and/or signal level.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Different embodiments of the present invention are described exemplary in the following in reference to the description. This is done by the way of example without limitation. The same subject matter has the same reference signs. The figures in the drawings show in detail:

(2) FIG. 1 a measurement system, a switch-extender and several DUTs according to an embodiment of the present invention;

(3) FIG. 2 a measurement system, another switch-extender and several DUTs according to an embodiment of the present invention;

(4) FIG. 3 a detailed configuration of the plurality of first MUX/DEMUX-units according to an embodiment of the present invention;

(5) FIG. 4 a detailed configuration of the plurality of second MUX/DEMUX-units according to an embodiment of the present invention;

(6) FIG. 5 a 3-dimensional view of the exemplary embodiment of the switch-extender 4 according to the present invention;

(7) FIG. 6 another detailed configuration of the plurality of second MUX/DEMUX-units sharing the output ports of each other according to an embodiment of the present invention;

(8) FIG. 7 a flow chart diagram of a test routine according to an embodiment of the present invention;

(9) FIG. 8 a measurement system, a switch-extender and a calibration system according to an embodiment of the present invention;

(10) FIG. 9 a flow chart diagram of a calibration routine according to an embodiment of the present invention;

(11) FIG. 10 another flow chat diagram of a further calibration routine according to an embodiment of the present invention;

(12) FIG. 11 another flow chat diagram of a further calibration routine according to an embodiment of the present invention;

(13) FIG. 12 another flow chat diagram of a further calibration routine according to an embodiment of the present invention; and

(14) FIG. 13 another flow chat diagram of a further calibration routine according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

(15) In the following some preferred embodiments of the present invention are described in detail.

(16) FIG. 1 shows the basic principle of the present invention. It shows a measurement system 1 which is used for generating a test signal (downlink signal) and which is also used for measuring a signal transmitted from the DUTs (uplink signal). Therefore, the measurement system 1 comprises a TRX unit 2 (transmit receive) which is used for generating the base band and/or the RF (radio frequency). Furthermore the measurement system 1 also comprises a frontend 3 which comprises a reference circuit and which divides the signal from or to the TRX unit 2 into three input or output ports. For example, there is a first port RF1Out which is used to output the test signal (downlink signal) that is normally a high frequency signal, like a GSM or UMTS (CDMA signal in generally). Furthermore, there is a second port RF1COM which is used to output the test signal (downlink signal) or which can be used as an input port for a signal (uplink signal) that is transmitted by the mobile communication system to be measured by the measurement system 1. Furthermore, there is a third port RF2COM which can also be used to output the test signal (downlink signal) and which can also be used to input a signal (uplink signal) transmitted from the mobile communication system 7 (device under test-DUT).

(17) However, all three ports RF1Out, RF1COM and RF2COM are connected to a switch-extender 4 according to the embodiment of the present invention. The switch-extender 4 comprises a first MUX/DEMUX-unit 5 having a ratio of one to eight. The switch-extender 4 according to the present invention may also have a second MUX/DEMUX-unit 6 which has a ratio of one to four. The second MUX/DEMUX-unit 6 is optional. However, other ratios are also possible. The switch-extender 4 will be described in the following in detail.

(18) Furthermore, the switch-extender 4 is preferably connected to several mobile communication systems 7, also called devices under test (DUT). This connection is done by using a cable connection. In this case, there are four devices under test, also called DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4. As mentioned before, the DUTs can be a mobile phone or a handheld PC or a tablet PC or a pocket PC or even a WLAN router. For this example, each of the DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 has at least three antennas. However, it is possible that a DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 has also more or less than three antennas. FIG. 1 also shows that two antennas of each DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 are connected to the MUX/DEMUX-unit 5 of the switch-extender 4. Those antennas are used for communication by using the MIMO (Multiple Input, Multiple Output) technique. A third antenna of each DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 is connected to the second MUX/DEMUX-unit 6. The third antenna can be used for GPS or WLAN. It can also be used for Bluetooth or other communication standards.

(19) The antennas of the DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 and the cable connection are not matched. Therefore, an attenuator is used between the cable and the antenna. Normally a 3 dB attenuator is used as shown in FIG. 1. Using a 3 dB attenuator, the reflected wave from the antenna of the DUT has a signal level which is 6 dB lower than the signal level of the signal (downlink) which is transmitted from the measurement system 1 over the switch-extender 4 to the antennas of the DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4.

(20) The second MUX/DEMUX-unit 6 is only used for none-cellular applications like WLAN, Bluetooth or GPS or the like. If the DUT uses only one antenna for cellular applications (none-MIMO) the switch-extender 4 can support up to eight DUTs.

(21) If the second MUX/DEMUX-unit 6 is used, the none-cellular applications (WLAN, Bluetooth and/or GPS) are tested first, since the cellular chips (CDMA-chips) need more time to come up. The measurement system 1 generates a base band-signal (downlink) in the TRX-unit 2. This signal (downlink) is then sent to the MUX/DEMUX-unit 6 using the third port RF2COM of the second MUX/DEMUX unit 6. The second MUX/DEMUX-unit 6 connects the third port of the measurement system 1 to the third antenna of the first DUT 7.sub.1. After the test signal is sent, the first DUT 7.sub.1 is processing it. After the first DUT 7.sub.1 has processed the test signal, it outputs the results, for example the current GPS-position using the third antenna or a data bus which is not shown. The second MUX/DEMUX-unit 6 still connects the third antenna to the third port RF2COM of the measurement system 1. The measurement system 1 can analyze if the calculated results of the first DUT 7.sub.1 are correct. If the none-cellular applications are tested for the first DUT 7.sub.1, the second MUX/DEMUX-unit 6 connects the third port of the frontend 3 of the measurement system 1 to the third antenna of the second DUT 7.sub.2.

(22) The second MUX/DEMUX-unit 6 connects all DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 one after another to the third port of the measurement system 1. The second MUX/DEMUX-unit 6 can also connect DUTs to another port of the measurement system 1 as long as this port can also be used for transmitting and receiving signals. In this case, the second MUX/DEMUX-unit 6 can also be connected to the second port RF1COM of the measurement system 1.

(23) If the measurement of the none-cellular applications of the DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 is done, the cellular chips of the DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 are up for operation. Now the measurement system 1 generates and transmits test signals to the first MUX/DEMUX-unit 5. The signals are generated in the TRX-unit 2 and are sent by using the first port RF1OUT of the frontend 3. This test signal is then split into eight signals and transmitted to the first and to the second antenna of each of the four DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4. The test signal can comprise a really long sequence that is used to calculate the bit error rate (BER) of each of the DUTs. So each of the DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 receives a long sequence which is used to calculate the bit error rate. If the DUTs have calculated the bit error rate, the first MUX/DEMUX-unit 5 connects one DUT after another to the second port RF1COM of the measurement system 1. The measurement system 1 then measures the uplink signal from each of the DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4.

(24) FIG. 2 shows a measurement system 1 which comprises two separate TRX-units 2, 8 and two separate frontends 3, 9. Furthermore, the switch-extender 4 also comprises a first MUX/DEMUX-unit 5 and optionally a second MUX/DEMUX-unit 6 as described above. Furthermore, the switch-extender 4 comprises also a further MUX/DEMUX-unit 10 having also a ratio of one to eight and a MUX/DEMUX-unit 11 having a ratio of one to four. The MUX/DEMUX-unit 11 is also optional. Therefore, several other DUTs 12.sub.1, 12.sub.2, 12.sub.3, 12.sub.4 are connected to the further MUX/DEMUX-unit 10 and to the MUX/DEMUX-unit 11 as described above referring to the DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4.

(25) FIG. 3 shows a detailed schematic diagram of the first MUX/DEMUX-unit 5 according to the present invention. It can be seen that the first MUX/DEMUX-unit 5 is divided into two parts. The first part is the transmission path and the second part is the receiving path. The transmission path is used to transmit a signal (downlink signal) from measurement system 1 to the DUTs 7.sub.1 to 7.sub.4 in parallel and the receiving path is used to transmit a signal (uplink signal) from the DUTs 7.sub.1 to 7.sub.4 to the measurement system 1. The transmission path is connected to the first port RF1Out of the frontend 3 of the measurement system 1.

(26) The downlink signal is split using a signal splitter 30, like a Wilkinson divider, into two signals, both having preferably the same signal level. Each output port of the signal splitter 30 is then connected to a switch 31.sub.1, 31.sub.2. One output port of each switch 31.sub.1, 31.sub.2 is not connected to anything, so the switch can be used to decouple the specific signal path at all. Normally the other output port of the switch 31.sub.1, 31.sub.2 is used to connect each output of the signal splitter 30 to an amplifier 32.sub.1, 32.sub.2. The amplifiers 32.sub.1, 32.sub.2 can be used to amplify the signal by 0 to +20 dB. The output of each of the amplifiers 32.sub.1, 32.sub.2 is then connected to another signal splitter 33.sub.1, 33.sub.2. Each output port of the further signal splitters 33.sub.1, 33.sub.2 is then connected with another signal splitter 34.sub.1, 34.sub.2, 34.sub.3, 34.sub.4. The downlink signal which is generated by the TRX-Unit 2 is split up and amplified into eight equal signals. Those signals can be used for four DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4, each of them having up to two cellular antennas operating in MIMO-mode.

(27) However, before the eight individual downlink signals can be sent to the DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 they are applied to a level adjustment unit 35. The level adjustment unit 35 is very important, because it comprises several attenuators. Each signal path that is used for carrying one of the split downlink signals comprises two attenuators arranged in series. Therefore, each output port of the further signal splitters 34.sub.1, 34.sub.2, 34.sub.3, 34.sub.4 is connected to a first attenuator 36.sub.1, 36.sub.2, 36.sub.3, 36.sub.4, 36.sub.5, 36.sub.6, 36.sub.7 and 36.sub.8. Those first attenuators 36.sub.1 are 36.sub.8 are also called step-attenuators. Those attenuators can be used to attenuate the split downlink signal in steps of approximately dB from 0 to 31 dB. The output port of each the first attenuators of each signal path is then connected to a second attenuator 37.sub.1, 37.sub.2, 37.sub.3, 37.sub.4, 37.sub.5, 37.sub.6, 37.sub.7 and 37.sub.8. The second attenuators are also called fine attenuators. They allow attenuating the split downlink signal in steps of approximately a 2 mdB.

(28) Each output port of the level adjustment unit 35 or, to be more precise, each output port of the second attenuator is connected to one coupling-unit 38.sub.1 to 38.sub.8. The use of each coupling-unit is that the downlink signal which is split into up to eight individual downlink signals is transmitted to the first and to the second antenna of each DUT and that the uplink signal which is transmitted from the first and the second antenna of each DUT is transmitted back to the second output port RF1COM of the measurement system 1. Therefore, the coupling-unit 38.sub.1 to 38.sub.8 prevents an uplink signal which is transmitted from the DUTs to travel across the downlink signal path. The coupling-unit 38.sub.1 to 38.sub.8 is preferably a directional coupling-unit 38.sub.1 to 38.sub.8, so that the uplink signal exits the directional coupling-unit 38.sub.1 to 38.sub.8 through another port. The directional coupling-unit 38.sub.1 to 38.sub.8 comprises three attenuators and three resistors, for example connected in a T-structure. Each output port RF1 to RF8 is connected to the first or to the second antenna of each DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 using a cable and several connectors.

(29) The task of the switch-extender 4 according to the present invention is that the downlink signal at the first and the second antenna of each of the DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 has the same predetermined signal level. So all downlink signals that apply at the cellular antennas of each DUT have the same level. In order to obtain this object, the attenuation of the cable and the connectors have to be taken into account. This object is solved by the use of the level adjustment unit 35. The level adjustment unit 35 allows a coarse and a fine tuning of the split downlink signals. Since the first and the second attenuator within the level adjustment unit 35 are built by using transistors or the like, the signal can be attenuated within 300 microseconds or less. Relays which are used in the state of the art are preferably not used within the present invention at all.

(30) The signal level of the downlink signal is very low, for example 100 dBm. The third output ports RX1 to RX8 of each of the coupling-units 38.sub.1 to 38.sub.8 are connected to a multiplexer 39.sub.1, 39.sub.2. Each of the multiplexers 39.sub.1, 39.sub.2 have four input ports for example and one output port. Therefore, the uplink signal which is transmitted from the first and the second DUT 7.sub.1, 7.sub.2 is available at the first multiplexer 39.sub.1 and the uplink signal which is transmitted from the third and the fourth DUT 7.sub.3, 7.sub.4 is available at the second multiplexer 39.sub.2. This is done by using the coupling-units 38.sub.1 to 38.sub.8 as described above.

(31) The output port of each multiplexer 39.sub.1, 39.sub.2 is connected to another attenuator 40.sub.1, 40.sub.2. These attenuators 40.sub.1, 40.sub.2 are able to attenuate an uplink signal coarsely. In this example according to the present invention the attenuators 40.sub.1, 40.sub.2 can attenuate an uplink signal in steps of 0 dB, 13 dB and 26 dB. It is also possible to use an attenuator 40.sub.1, 40.sub.2 which attenuates an uplink signal in much smaller steps. If the DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 transmits an uplink signal having a signal level of 33 dBm for example, the attenuation factor of the attenuator 40.sub.1, 40.sub.2, is selected to the highest possible value, in this example 26 dB. If the DUT transmits an uplink signal with a signal level of 0 dBm the attenuator 40.sub.1, 40.sub.2 selects the lowest possible attenuation factor, in this example 0 dB.

(32) The output port of each of the attenuators 40.sub.1, 40.sub.2 is connected to an amplifier 41.sub.1, 41.sub.2. Each amplifier 41.sub.1, 41.sub.2 amplifies the input signal to an output signal having a desired signal level. The amplifier factor is chosen so that the measurement system 1 measures the uplink signal with the highest possible precision.

(33) The output port of each amplifier is connected to a switch 42. By using the switch 42 and one of the multiplexer 39.sub.1, 39.sub.2 a control unit within the switch-extender 4 or within the measurement system 1 selects the uplink signal from one antenna of one of one DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 to be measured within the measurement system 1. The output port of the switch 42 is then connected to the second port RF1COM of the measurement system 1. It can also be connected to the third port RF2COM or to any port within the measurement system 1 which allows inputting an uplink signal for further analyses.

(34) However, the schematic diagram of FIG. 3 can also be used within the further MUX/DEMUX-unit 10 as shown in FIG. 2.

(35) The level adjustment unit 35 selects an attenuation value for the first attenuators 36.sub.1 to 36.sub.8 and for the second attenuators 37.sub.1 to 37.sub.8 which is based on the individual cable and connectors as well as on the individual signal path. The correction data is obtained for each frequency point for each signal path as well as for each cable and connector. Therefore, if the frequency band for which the downlink signal is transmitted is changed, all attenuators within the level adjustment unit 35 have to be set for their new attenuation factor.

(36) Furthermore, the amplifiers 32.sub.1, 32.sub.2 and 41.sub.1, 41.sub.2 as well as the attenuators 40.sub.1, 40.sub.2 may also need to be set for the new frequency. This is done preferably very fast in less than 300 microseconds. The control of the level adjustment unit 35 as well as of the amplifiers 32.sub.1, 32.sub.2, as well as of the amplifiers 41.sub.1, 41.sub.2 and as well as of the attenuator 40.sub.1, 40.sub.2 can be done in three different ways.

(37) First of all, the aforementioned components can be connected to the measurement system 1 directly. However, only very fast connection types are recommended. This could be done by an interface with a lot of parallel data lines applying a high clock rate. The measurement system 1 selects all attenuation factors as well as all amplifier factors for the selected frequency of operation of the downlink signal. This information can be extracted from calibration data which will be discussed below. SPI-commands allow those components to be programmed by the measurement system 1.

(38) A more preferred second possibility for adjusting the aforementioned components can be done by incorporating a processing unit 45 within the switch-extender 4. The processing unit is connected to the level adjustment unit 35 and therein with the first attenuators and the second attenuators. The processing unit 45 is further connected to the amplifier 32.sub.1, 32.sub.2, 41.sub.1, 41.sub.2 as well as to the attenuators 40.sub.1, 40.sub.2 and optional to the multiplexers 39.sub.1, 39.sub.2 and the switches 31.sub.1, 31.sub.2, 42. Furthermore, the processing unit is also connected to the measurement system 1. The measurement system 1 then signals the processing unit 45 the values of the attenuation and/or the amplification factors to be set and optional the position of the switches and the multiplexers. The communication itself between the processing unit 45 and the components within the switch-extender 4 is done without any knowledge of the measurement system 1. For example, the processing unit 45 can communicate by using the SPI-commands on a single line or by using parallel data lines.

(39) A third possibility is that the processing unit 45 only receives the frequency and the signal level of the downlink signal which is transmitted by the measurement system 1. The processing unit 45 then alternates all attenuation factors or amplification factors by itself. Therefore, besides the processing unit 45 a further storage unit 46 is needed where all calibration data are stored. This could be done by using a lookup-table comprising all attenuation factors and/or amplification factors needed for an individual signal level as well as for an individual signal frequency. The processing unit 45 then reads out the storage unit 46 and alternates those factors as required.

(40) As shown in FIG. 3 it is possible to transmit a downlink signal on eight signal paths in parallel. On the other hand, it is only possible to receive one uplink signal which is transmitted from one antenna of one DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 at one time. In order to receive the uplink signal from the other antenna or from other DUTs the multiplexer 39.sub.1, 39.sub.2 or the switch 42 have to be changed. This can also be done by the processing unit 45 or by the measurement system 1 directly. Therefore, the multiplexer 39.sub.1, 39.sub.2 as well as the switch have to be connected to the processing unit 45 and/or to the measurement system 1. This can also be done by well known data connection types or by a parallel interface. The same also applies for the further MUX/DEMUX-unit 10.

(41) FIG. 4 shows a schematic diagram of the second MUX/DEMUX-unit 6 as well as of the MUX/DEMUX-unit 11 according to the present invention. As already described, the second MUX/DEMUX-unit 6 is used to measure the none-cellular applications within the DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4. As already explained, the measurement system 1, in particular the TRX-unit 2 and the frontend 3 generate a downlink signal which is output at the third output port RF2COM. For the second TRX-unit 8 and the second frontend 9 the subject matter as explained in detail above stays the same. It only differs in the names used for the reference signs. As already said, the third port RF2COM can be used to output a downlink signal or to input an uplink signal. In the following the case where a downlink signal is transmitted to the third antenna of the DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 is described. The output port RF2COM is connected to a switch 50. One output port of the switch 50 is connected to another switch 51. One output of the switch 51 is connected to an amplifier 52. The amplifier 52 is used to amplify the downlink signal by 0 to +20 dB. The output of the amplifier 52 is connected to a signal splitter 53. The signal splitter 53 can be a Wilkinson divider.

(42) Each output port of the signal splitter 53 is connected to an input port of another signal splitter 54.sub.1, 54.sub.2. Each output port of the further signal splitters 54.sub.1, 54.sub.2 is connected to the second level adjustment unit 55. The second level adjustment unit 55 comprises the same structure as the level adjustment unit 35 as described in FIG. 3. In contrast to the level adjustment unit 35 as described in FIG. 3, the second level adjustment unit 55 only comprises four signal paths. In each signal paths, there are two attenuators arranged in series. A first attenuator 56.sub.1, 56.sub.2, 56.sub.3, 56.sub.4 is used to attenuate the split downlink signal in a coarse step. For example, the first attenuator 56.sub.1 to 56.sub.4 can attenuate the split downlink signal in steps of dB over a range from 0 to 31 dB. The output port of the first attenuator 56.sub.1 to 56.sub.4 is then connected to an input port of a second attenuator 57.sub.1, 57.sub.2, 57.sub.3, 57.sub.4. The second attenuator is used to attenuate the split downlink signal in finer steps. For example, the second attenuators 57.sub.1 to 57.sub.4 can attenuate a signal in steps of 2 mdB or the like. The output port of the second attenuators 57.sub.1 to 57.sub.4 is then connected to a coupling-unit 58.sub.1 to 58.sub.4. The design of the coupling-unit 58.sub.1 to 58.sub.4 as shown in FIG. 4 is the same as the design of the coupling-unit 38.sub.1 to 38.sub.8 as shown in FIG. 3 so that a reference is made to the description above. The second output port RF1 to RF4 of the coupling-unit 58.sub.1 to 58.sub.4 is connected to the third antenna of the DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4.

(43) If the measurement system 1 generates and transmits a downlink signal to the third antenna of all DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 the second level adjustment unit 55 makes sure that the level of the downlink signal is the same for all signal paths at the third antenna of each DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4. This is done by using calibration data of the cable and the connector as well as of each individual signal path. The amplification as well as the attenuation value of each attenuator is selected in such a way that different frequency behaviors over a frequency span are compensated. This also applies for different signal levels. Therefore, every downlink signal frequency and every downlink signal level corresponds to a separate data set which includes the calibration data that is used for setting the amplifier 52 and the first attenuator 56.sub.1 to 56.sub.4 and the second attenuator 57.sub.1 to 57.sub.4 properly.

(44) The same also applies for every uplink signal. The uplink signal transmitted from the third antenna of each DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 is decoupled within the coupling-unit 58.sub.1 to 58.sub.4 to the third output port RX1 to RX4. The third output port RX1 to RX4 of all coupling-units 58.sub.1 to 58.sub.4 are connected to a multiplexer 59. The multiplexer has four input ports connected to each of the coupling-units 58.sub.1 to 58.sub.4 and one output port connected to an attenuator 60. The attenuator 60 attenuates the uplink signal in a coarse way. For example, an attenuation factor of 0, 13, 26 dB can be selected. However, also other attenuators can be used which allow the selection of an attenuation factor having finer steps. The output port of the attenuator 60 is then connected to the input port of an amplifier 61. The amplifier 61 is then connected to the second output port of the switch 50. The switch 50 then connects the output port of the amplifier 61 to the third port RF2COM of the measurement system 1. The attenuator 60 is thereby selected to attenuate a strong signal with a higher attenuation factor than a weak signal. For example, if the DUT transmits an uplink signal having a signal level 30 dB, the attenuator 60 attenuates this signal by 26 dB. On the other hand, if the DUT transmits a signal having a signal level of 0 dB, the attenuator 60 attenuates this signal with 0 dB. Other values are also possible.

(45) As already described in FIG. 3 the amplifiers 52, 61 and the attenuators 56.sub.1 to 56.sub.4 and 57.sub.1 to 57.sub.4 and 60 are controlled by the measurement system 1 directly or by the processing unit 45. The same also applies for the switch 50, the switch 51 and the multiplexer 59. The switch 51 can be used to separate the transmitting path from the receiving path in order to increase the isolation between them.

(46) As already explained, the components can be controlled by the measurement system 1 directly. In this case, the measurement system 1 sets all switch positions and/or all attenuation and/or amplification factors. On the other hand, the measurement system 1 can signal the processing unit 45 the switching positions and the amplification and/or attenuation factors. The third possibility is that the measurement system 1 only informs the processing unit 45 about the frequency and the signal level of the downlink signal and/or the number of the DUT which has to be measured in the uplink path. The processing unit 45 then reads the settings from a storage unit 46 and makes the needed adjustments.

(47) The same also applies for the MUX/DEMUX-unit 11 as also shown in FIG. 4. For those components no reference signs are placed. However, all explanations made to the second MUX/DEMUX-unit 6 are also valid for the MUX/DEMUX-unit 11.

(48) FIG. 5 shows a 3-dimensional view of the exemplary embodiment of the switch-extender 4 according to the present invention. The switch-extender 4 comprises a series of input and/or output ports. The ports for connecting the switch-extender 4 to the measurement system 1 are located on the right side of the switch-extender 4. FIG. 5 shows the ports RF1Out, RF1COM and RF2COM for connecting the switch-extender 4 to the first frontend 3 within the measurement system 1. Furthermore, FIG. 5 also shows the ports RF3Out, RF3COM and RF4COM for connecting the switch-extender 4 to the second frontend 9 within the measurement system 1. In this exemplary embodiment, the ports for connecting the switch-extender 4 to the measurement system 1 are shown on the right, but they can also be located anywhere on the front or the rear-panel of the switch-extender 4.

(49) The other ports are used for connecting the switch-extender 4 to the series of antennas of the DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 and 12.sub.1 to 12.sub.4. For example eight ports on the bottom row from left to right represent the output and/or input ports of the MUX/DEMUX-unit 5 as shown in FIG. 3. Within FIG. 3 these ports are named RF1 to RF8. The top row comprises the input and/or output ports for the further MUX/DEMUX-unit 10 which is connected to the second frontend 9. With respect to FIG. 2, also eight ports are used therefor. The row in the middle is used for the second MUX/DEMUX-unit 6 as well as for the MUX/DEMUX-unit 11. In this exemplary embodiment the four ports from left to right represent the output and/or input ports of the second MUX/DEMUX-unit 6, whereas the four ports following on the right represent the input and/or output ports of the MUX/DEMUX-unit 11. However, it is obvious that the input and/or output ports can be arranged in different ways. Beside every port, there are two LEDs 70.sub.1, 70.sub.2. Those LEDs 70.sub.1, 70.sub.2 indicate whether the individual port is used as an output port or an input port.

(50) All ports are mounted directly on a printed circuit board. Preferably there are no cable connections. There is normally one printed circuit board for each row using connectors to connect the individual printed circuit boards together. All printed circuit boards are controlled by a central processing unit 45. However, as described above, the ports can also be controlled by the measurement system 1 itself.

(51) FIG. 6 shows a further exemplary embodiment of a schematic diagram according to the present invention. According to FIG. 5 the output and/or input ports in the middle of the row are shared between the first frontend 3 and the second frontend 9. One possibility on how to connect these ports with the measurement system 1 is shown in FIG. 4. As already described above, it is not possible for the first frontend 3 and for the second frontend 9 to use the output ports of the switch-extender 4 from each another. This means that the first frontend 3 can only address four DUTs 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 each having one third antenna. The same applies for the second frontend 9. The second frontend 9 can also only address four DUTs 12.sub.1 to 12.sub.4 each having one third antenna. However, some DUTs may have more than three antennas. Therefore, it would be desirable if the first frontend 3 could also use the output and/or input ports of the switch-extender 4 linked to the second frontend 9.

(52) FIG. 6 describes a possibility that allows the first frontend 3 to use the input and/or output ports of the second MUX/DEMUX-unit 6 as well as the input and/or output ports of the MUX/DEMUX-unit 11. On the other hand, FIG. 6 also shows the possibility for the second frontend 9 to use the input and/or output ports of the MUX/DEMUX-unit 11 as well as the input and/or output ports of the second MUX/DEMUX-unit 6.

(53) As shown in FIG. 6, the port RF2COM is connected to a multiplexer 80 and the port RF4COM is connected to a multiplexer 81. It is noted that the ports RF2COM and RF4COM are bidirectional ports which can be used as output ports as well as input ports. Therefore, the wording multiplexer is always used instead of the wording demultiplexer. One output port of the multiplexer 80 can be connected to the transmit path as shown in FIG. 4. The transmit path comprises another switch 82 and the well-known circuit elements 52, 53, 54.sub.1, 54.sub.2, 55 and 58.sub.1 to 58.sub.4.

(54) A second output of the multiplexer 80 can also be connected to the second transmit path which was only used in FIG. 4 by the second frontend 9. The second output of the multiplexer 80 is therefore connected to a switch 83 and in row to the switch 83 to a signal splitter 84. One outfit of the splitter 84 is connected to the switch 82 and the other output of the signal splitter is connected to the switch 85. The output of the switch 85 is thereby connected to the second signal path. The circuit elements of the second signal path are the same as the circuit elements of the first signal path.

(55) The same applies for the uplink signal, namely the signal which is transmitted from the third antenna of the DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 as well as for the uplink signal which is transmitted from the third antenna of the DUT 12.sub.1 to 12.sub.4. As described in FIG. 4, coupling-units 58.sub.1 to 58.sub.4 are used to decouple the uplink signal transmitted by the third antenna of the DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4. The uplink signal is decoupled at the third port of the coupling-unit 58.sub.1, to 58.sub.4. These ports are called RX1 to RX4. These ports are connected to a multiplexer 59. The multiplexer 59 selects one uplink signal at the same time and forwards it to an attenuator 60. The output of the attenuator 60 is connected to an amplifier 61. This subject matter is also described with respect to FIG. 4. Within FIG. 6 the output of the amplifier 61 is connected to a switch 86. The output of the switch 86 is connected to the multiplexer 80.

(56) The same also applies for the uplink path of the DUTs 12.sub.1 to 12.sub.4. The uplink signal transmitted from the DUTs 12.sub.1 to 12.sub.4 is decoupled by the coupling-units 87.sub.1 to 87.sub.4. Those coupling-units are integrated within a switch-extender 4 in the MUX/DEMUX-unit 11. The uplink signal is then fed to a multiplexer 88. The multiplexer 88 selects one uplink signal at the same time and forwards it to another attenuator 89. The output port of the attenuator 89 is then connected to an amplifier 90. The output of the amplifier 90 is further connected to switch 91. One output of the switch 91 is also connected to the multiplexer 80. The multiplexer 88 is the same multiplexer as the multiplexer 59. The attenuator 89 is the same attenuator as the attenuator 60. The amplifier 90 is the same amplifier as the amplifier 69. This also applies for coupling-units 87.sub.1 to 87.sub.4 with respect to the coupling-units 58.sub.1 to 58.sub.4.

(57) The aforementioned structure allows the first frontend 3 to address the third antenna of the DUTs 7.sub.1 to 7.sub.4 and 12.sub.1 to 12.sub.4. The first frontend 3 can transmit a downlink signal to all third antenna ports of the DUTs 7.sub.1, to 7.sub.4 and 12.sub.1 to 12.sub.4 at the same time. However, the uplink signal from the third antenna of every DUT 7.sub.1, 7.sub.2, 7.sub.3, 7.sub.4 and 12.sub.1 and 12.sub.4 can be fed through the input port RF2COM to the first frontend 3 one after another. The same also applies for the second frontend 9. The bidirectional port RF4COM is connected to the multiplexer 81 as described above. The output ports of the multiplexer 81 are connected to the switch 83 as well as to the switch 85 as well as to the switch 86 and to the switch 91. Therefore, it is also possible for the second frontend 9 to address all third antenna ports of all DUTs 7.sub.1 to 7.sub.4 and 12.sub.1 to 12.sub.4. The second frontend 9 can therefore transmit the downlink signal to all DUTs 7.sub.1 to 7.sub.4 and 12.sub.1 and 12.sub.4 at the same time. The uplink signal transmitted from each DUT at the third antenna board can be measured one after another by switching the multiplexer 59 and 88 as well as the switches 86 and 91 as well as the multiplexer 81 accordingly.

(58) To sum it up, the above described structure of the switch-extender 4 having further multiplexers 80, 81 for each of the plurality of the second MUX/DEMUX-units 6 that are connected to every downlink path and to every uplink path used by the second MUX/DEMUX-units 6 allows the plurality of the second MUX/DEMUX-units 6, 11 to access all components within the uplink path as well as within the downlink path of each other thereby doubling the available output ports.

(59) However, all components like the switches, the amplifiers, the attenuators, the multiplexers can be controlled directly by the measurement system 1 or they can be controlled by a processing unit 45. The subject matter is described in detail above so that a reference is made thereto.

(60) FIG. 7 shows a flow chart diagram that describes the proceeding for testing several DUTs with the switch-extender 4 and the measurement system 1 according to the present invention. After all DUTs are connected to the switch-extender 4, the procedural step S.sub.1 is executed. Within the step S.sub.1 all DUTs are powered up and the non-cellular components of all DUTs are tested. As described above, those components are connected to the third antenna of each DUT. For example, in the step S.sub.1 Bluetooth services, GPS services or WLAN services can be tested. As already explained in detail, it is also possible that the measurement system 1 transmits a downlink signal to all DUTs 7.sub.1 to 7.sub.4 and/or 12.sub.1 to 12.sub.4 simultaneously. After that the third antenna of each DUT is connected one after another with the measurement system 1 for measuring the uplink signal.

(61) If the non-cellular components are tested, the procedural step S.sub.2 is executed. The procedural step S.sub.2 is preferably executed when the cellular components are booted. The cellular components comprise for example CDMA-chips. Those chips have a longer boot time than the non-cellular components. Within the procedural S.sub.2 a downlink signal is sent from the measurement system 1 to all DUTs 7.sub.1 to 7.sub.4 and 12.sub.1 to 12.sub.4 which comprises a long data sequence. This sequence is well known and allows the DUTs to calculate the bit error rate for example. In order to obtain a good statistic, the sequence is transmitted over a longer period, for example 10 seconds.

(62) After the bit error rate is calculated by all DUTs in parallel for a desired frequency and/or for desired signal level, the procedural step S.sub.3 is executed. Within the procedural step S.sub.3 the procedural step S.sub.2 is repeated for all desired frequency bands and/or for all desired signal levels. The DUTs further calculate the bit error rate.

(63) Afterwards the procedural step S.sub.4 is executed. Within the procedural step S.sub.4, the measurement system 1 collects all calculated BER-values for one DUT after another. This is done by decoupling the uplink signal which is transmitted from the DUT by using the coupling-unit 58.sub.1 to 58.sub.4 and 87.sub.1 to 87.sub.4. As already described each frontend 3, 9 can only receive one uplink signal at the same time. However, the time for collecting the calculated BER-values is much shorter than the time for sending the sequence to all DUTs. Therefore, it does not matter that all DUTs cannot transmit the uplink signal at the same time.

(64) In the following, the procedural step S.sub.5 is executed. Within the procedural step S.sub.5, the reception for every DUT is calibrated in parallel or one after another for the desired frequency. This is done by using the method and the system which is described in the U.S. patent application US 2009/0209249 A1 which is hereby incorporated by reference. The time between the steps wherein the signal level is lowered has to be as long as the time it needs to adjust the attenuators and the amplifiers. 300 microseconds should be enough.

(65) Afterwards, the procedural step S.sub.6 is executed. In the procedural Step S.sub.6, the step S.sub.5 is repeated for all desired frequency bands.

(66) After that, the procedural step S.sub.7 is executed. Within the procedural step S.sub.7 all DUTs are calibrated one after another for their transmission behavior. The method and the system that are used therefore are also described in the U.S. patent application US 2009/0209249 A1 which is hereby incorporated by reference. Each frontend 3, 9 receives only one uplink signal at the same time. The uplink signal is thereby stepped down continuously. However, the time for each step has to be chosen in such a way that the switch-extender 4 has enough time to adjust the settings for the attenuators, the amplifiers and the switches. This is done for all DUTs one after another.

(67) Afterwards, the procedural step S.sub.8 is executed. Within the procedural step S.sub.8 the former step S.sub.7 is repeated for all desired frequency bands.

(68) Last but not least, a Pass/Fail-analysis is performed within the procedural step S.sub.9.

(69) It has to be noted that procedural steps S.sub.1 to S.sub.9 need not to be executed in the described order. For example, it is also possible that the method is finished after the procedural step S.sub.1 or after the procedural step S.sub.3 or after the procedural step S.sub.8. The order can also be mixed.

(70) FIG. 8 shows a schematic diagram that describes how the measurement system 1, the switch-extender 4 and the cable connection 100.sub.1 to 100.sub.4 as well as the 3 dB attenuator 101.sub.1, 101.sub.2 are calibrated. The calibration is done by using a calibration system 102. The calibration system comprises a first measurement unit 103 and a second measurement unit 105. Both measurement units 1, 5 are connected together for example by using a USB-connection. Other connection methods can also be used. The calibration system 102 further includes a signal splitter 104. The signal splitter 104 divides an input signal into two equal output signals. The first measurement unit 103 is able to measure and to analyze a downlink signal as well as to generate a known uplink signal. In fact, the measurement unit 103 can be of the same type as the measurement system 1. The second measurement unit 105 is able to measure the signal power. The measured values are then transmitted to the first measurement unit 1 by using the USB-connection. However, it is also possible that the DUT 7.sub.1 to 7.sub.4 and 12.sub.1 to 12.sub.4 is directly connected with the cable 100.sub.1 to 100.sub.4, so that no 3 dB attenuator 101.sub.1, 101.sub.2 is needed.

(71) Furthermore instead of using a cable 100.sub.1 to 100.sub.4 for establishing the connection other signal connectors like wave guides for example can also be used.

(72) In the following it is described how the calibration is done. The object of the calibration is to determine the necessary settings within the measurement system 1 and the switch-extender 4 in order to generate a predefined signal level at the first or at the second or at the third antenna of the DUT. It has to be noted that all cables 100.sub.1 to 100.sub.4 as well as all connectors and the attenuators 101.sub.1, 101.sub.2 which are used within the calibration also have to be used in the later measurement steps.

(73) Thus it is very important that every output port of the switch-extender 4 has its own dedicated cable. The output ports of the MUX/DEMUX-unit 5 as well as of the second MUX/DEMUX-unit 6 are connected one after another with the calibration system 102. The same also applies to the further MUX/DEMUX-unit 10 as well as for the MUX/DEMUX-unit 11. FIG. 10 only describes the calibration method for the MUX/DEMUX-unit 5 within the switch-extender 4 having eight output ports. The first output port of the MUX/DEMUX-unit 5 which is labeled with RF1 according to FIG. 3 is connected to a cable 100.sub.1. The other end of the cable 100.sub.1 is connected to a 3 dB attenuator 101.sub.1. The attenuator 101.sub.1 would normally be connected with the first antenna of the first DUT 7.sub.1. In this case, the other end of the attenuator 101.sub.1 that is not connected to the cable 100.sub.1 is thereby connected with the calibration system 102. More exactly, the attenuator 101.sub.1 is connected with the input of the signal splitter 104 within the calibration system 102.

(74) In the first instance, the measurement system 1 generates a downlink signal which would normally be used to measure the proper functioning of the first antenna of the first DUT 7.sub.1. The measurement system 1 generates this downlink signal having a specific frequency as well as a specific signal level. The downlink signal is split within the signal splitter 104 into two equal signals. One signal is transmitted to the first measurement unit 103 whereas the other signal is transmitted to the second measurement unit 103. It has to be understood that the signal splitter 14 has to be well known when thinking of its attenuation or its diversity. However, the first measurement unit 103 and the second measurement unit 105 measure the downlink signal properties, for example the frequency as well as the signal at the input port of the signal splitter 104. This data is used in order to inform the measurement system 1 about the difference between the measured values of the downlink signal and the estimated values of the downlink signal. This information is then used within the measurement system 1 to generate calibration data in order to generate a downlink signal which has a predetermined frequency as well as a predetermined signal level at the antenna port of the DUT. The calibration data can also be generated the calibration system 102.

(75) After the calibration system 102 has generated the calibration data for the downlink signal, the calibration data for the uplink signal has also to be generated. The uplink signal as well as the downlink signal should be similar to the real signal. The uplink signal is generated by the first measurement unit 103. The first measurement unit 103 outputs the uplink signal to the signal splitter 104. One output port of the signal splitter 104 is still connected to second measurement unit 105 which is also connected the first measurement unit 103 by using a standard connection for data transmission, like USB or the like. The other output port of the signal splitter 104 is still connected with the cable 100.sub.1 over the 3 dB attenuator 101.sub.1. It is very advantageous that the cable connection has not to be changed for generating calibration data for the uplink signal. The second measurement unit 105 also measures the uplink signal generated by the first measurement unit 103 and makes sure that the uplink signal has the dedicated signal frequency as well as the dedicated signal level at the output port of the signal splitter 104. The uplink signal travels through the attenuator 101.sub.1 and the cable 100.sub.1 through the switch-extender 4 into the measurement system 1.

(76) The measurement system 1 measures the signal frequency as well as the signal level. Based on the difference between the measured uplink signal within the measurement system 1 and the measured uplink signal at the output port of the signal splitter 105, the calibration data is obtained by the calibration system 102 or by the measurement system 1. The calibration data takes into account the downlink signal path as well as the uplink signal path. The calibration data is obtained for several frequencies as well as for several signal levels. Based on the calibration data, the measurement system 1 as well as the switch-extender 4 know how to set the attenuators, the amplifiers as shown in FIG. 3 or FIG. 4 in detail. After the first cable 100.sub.1 is calibrated together with the attenuator 101.sub.1 and all connectors, the second cable 100.sub.2 together with the second attenuator 101.sub.2 is connected to the input port of the signal splitter 104 of the calibration system 102. Then the calibration data is obtained for the second cable 100.sub.2 as well as the attenuator 101.sub.2. This is done for the downlink signal as well as for the uplink signal as described above for a specific frequency as well for a specific signal level.

(77) The aforementioned steps are repeated for all cables 100.sub.1 to 100.sub.4 that are used for the MUX/DEMUX-unit 5 as well as for the second MUX/DEMUX-unit 6 and for the further MUX/DEMUX-unit 10 as well as for the MUX/DEMUX-unit 11.

(78) FIG. 9 shows a flow chat diagram of a calibration routine according to the present invention. The calibration routine has already been described to a certain extent. In a procedural step S.sub.10 the connections between the switch-extender 4 and the calibration system 102 are established. Those connections can be established by using a signal connector 100.sub.1 to 100.sub.4 like a cable 100.sub.1 to 100.sub.4 or a wave guide or the like. The signal connector 100.sub.1 to 100.sub.4 can be connected directly to the calibration system 102 or through an attenuator 101.sub.1, 101.sub.2 like a 3 dB attenuator.

(79) In the following the procedural step S.sub.11 is executed. In this step a signal with a specific signal level and/or a specific signal frequency is generated and output by the measurement system 1 for testing the downlink path. Since the measurement system 1 is connected through the switch-extender 4 and the signal connector 100.sub.1 to 100.sub.4 to the calibration system 102, the output signal can be measured by the calibration system 102.

(80) This is done within the procedural step S.sub.12. The calibration system 102 measures the signal level and/or the signal frequency at the output of the signal connector 100.sub.1 to 100.sub.4 or at the output of the attenuator 101.sub.1, 101.sub.2 if used.

(81) In the following the procedural step S.sub.13 is executed. Within the procedural step S.sub.12 a difference between the measured signal level and/or the measured signal frequency and the generated signal with the specific signal level and/or the specific signal frequency is determined. It is known by the calibration system 102 what signal level and/or signal frequency should be obtained so that a deviation can be calculated.

(82) In the next procedural step S.sub.14 calibration data are calculated by using the determined difference between the measured signal level and/or the measured signal frequency and the generated signal with the specific signal level and/or the specific signal frequency. This can be done by the calibration system 102 or even by the measurement system 1.

(83) FIG. 10 shows a flow chat diagram of a calibration routine according to the present invention. The calibration routine has already been described to a certain extent.

(84) In the following the procedural step S.sub.15 is executed. It has to be noted that the measurement system 1 and the switch-extender 4 are still connected to each other and to the calibration system 102. In this step a signal with a specific signal level and/or a specific signal frequency is generated and output by the calibration system 102 for testing the uplink path. Since the measurement system 1 is connected through the switch-extender 4 and the signal connector 100.sub.1 to 100.sub.4 to the calibration system 102, the output signal can be measured by the measurement system 1. The calibration system 102 can also still measure the generated signal by itself using the second measurement unit 105.

(85) This is done within the procedural step S.sub.16. The measurement system 1 measures the signal level and/or the signal frequency at the output of the signal connector 100.sub.1 to 100.sub.4 or at the output of the attenuator 101.sub.1, 101.sub.2 if used.

(86) In the following the procedural step S.sub.17 is executed. Within the procedural step S.sub.17 a difference between the measured signal level and/or the measured signal frequency and the generated signal with the specific signal level and/or the specific signal frequency is determined. It is known by the measurement system 1 what signal level and/or signal frequency should be obtained so that a deviation can be calculated.

(87) In the next procedural step S.sub.18 calibration data are calculated by using the determined difference between the measured signal level and/or the measured signal frequency and the generated signal with the specific signal level and/or the specific signal frequency. This can be done by the calibration system 102 or even by the measurement system 1.

(88) FIG. 11 shows another flow chat diagram of a further calibration routine according to the present invention. The switch-extender 4 further comprises at least one attenuator 36.sub.1, 36.sub.2, 36.sub.3, 36.sub.4, 36.sub.5, 36.sub.6, 36.sub.7, 36.sub.8 or the at least one attenuator 36.sub.1, 36.sub.2, 36.sub.3, 36.sub.4, 36.sub.5, 36.sub.6, 36.sub.7, 36.sub.8 and a second attenuator 37.sub.1, 37.sub.2, 37.sub.3, 37.sub.4, 37.sub.5, 37.sub.6, 37.sub.7, 37.sub.8 in a row for every output port a signal connector 100.sub.1 to 100.sub.4 is connected to the switch-extender 4. Thus a procedural step S.sub.18 can be executed. Within this step the attenuation factor of the at least one attenuator 36.sub.1 to 36.sub.8 or adjusting the attenuation factor of the at least one attenuator 36.sub.1 to 36.sub.8 and the second attenuator 37.sub.1 to 37.sub.8 can be adjusted so that the measured signal level and/or signal frequency of the signal is equal to the generated signal with the specific signal level and/or the specific signal frequency. The procedural step S.sub.18 and the procedural steps S.sub.12, S.sub.13 and S.sub.16, S.sub.17 are executed alternately until the difference is smaller than a predefined threshold.

(89) FIG. 12 shows another flow chart diagram of a further calibration routine according to the present invention. A procedural step S.sub.20 describes the previous steps are repeated for every desired frequency and/or signal level. The step S.sub.20 repeats the steps Generating, Measuring, Determining and Calculating for another signal frequency and/or signal level or Repeating the steps Generating, Measuring, Determining, Adjusting and Calculating for another signal frequency and/or signal level as described above.

(90) FIG. 13 shows another flow chart diagram of a further calibration routine according to the present invention. The procedural steps S.sub.21 and S.sub.22 describe that after the calibration of one signal connector 100.sub.1 to 100.sub.4 and the corresponding signal path for the downlink and the uplink within the switch-extender 4 and optional for the attenuator 101.sub.1, 101.sub.2 another signal connector 100.sub.1 to 100.sub.4 is connected at another output port of the switch-extender 4. After that the procedural steps S.sub.22 describes that the former steps Generating, Measuring, Determining and Calculating are repeated for another signal frequency and/or signal level or that the former steps Generating, Measuring, Determining, Adjusting and Calculating are repeated for another signal frequency and/or signal level.

(91) In general, it is very important that the transmission path as well as the receiving path comprise active components like attenuators or amplifiers which are built using transistors and/or discrete elements like diodes for example or the like to compensate the loss in the signal levels. Furthermore, it is very important that those components have very fast switching times so that the actual settings can be adjusted very fast. This reduces the needed measurement time. This also allows that the signal level as well the signal frequency can be switched very fast, since the correction of the attenuator as well as the amplifiers takes place in nearly no time.

(92) It is also possible that further switch-extenders are connected to the switch-extender 4 in order to obtain a measurement system 1 that allows measuring more than eight DUTs having two antennas used in parallel for cellular applications. However, the specific arrangement shown above is not limited to a measurement system 1 and a switch-extender 4 used for only four DUTs. All features shown above can be combined together in any order.