Antenna Status Remote Monitoring System

Abstract

An antenna monitoring unit for monitoring an RF transmission line and RF signal path to an antenna unit used in a distributed antenna system in a structure. The antenna is DC isolated from the RF transmission line through a current injector, allowing testing by sending a code from a base station to a remote antenna location and using a monitoring module to confirm reception of the code and transmit data to the base station relating to the antenna unit.

Claims

1. An antenna monitoring unit comprising: an antenna having a resistor connected to ground; a monitoring module; a DC injector for injecting a DC signal into the antenna, wherein the antenna is DC isolated from the RF transmission line through the DC injector; the monitoring module receiving a DC coded signal transmitted along the RF transmission line and the monitoring module comprises a saved code associated with the monitoring module and the monitoring module compares the received DC coded signal with the saved code.

2. The antenna monitoring unit of claim 1, wherein the DC injector includes: a capacitor having a first side connected to the RF transmission line and a second side connected to the antenna; and a first inductor coupled between the resistor and the monitoring module.

3. The antenna monitoring unit of claim 1, wherein the DC injector injects a DC signal through the first inductor to the antenna and the monitoring module measures the injected DC signal.

4. The antenna monitoring unit of claim 1, wherein the antenna system is configured to be coupled to a transceiver, and wherein when the monitoring module determines that the received code matches the saved code, the monitoring module transmits a confirmation signal along the RF transmission line to the transceiver.

5. The antenna monitoring unit of claim 4, wherein if no confirmation signal is received from the monitoring module after a threshold number of attempts to contact the monitoring module, a transmission alarm is generated by a master module.

6. The antenna monitoring unit of claim 5, wherein the transmission alarm includes information identifying the monitoring module associated with the transmission alarm.

7. The antenna monitoring unit of claim 6, wherein if a warning has been generated by the monitoring module, the warning will be transmitted to the transceiver and the master module will generate an antenna alarm, the antenna alarm including information identifying the monitoring module associated with the antenna alarm

8. The antenna monitoring unit of claim 7, wherein either the transmission alarm or the antenna alarm are transmitted via a network to a remote computer.

9. The antenna monitoring unit of claim 2, wherein the monitoring module compares a resistance of the current path of the injected DC signal to a stored value and if the comparison of values exceeds a threshold level, the monitoring module generates a warning.

10. The antenna monitoring unit of claim 9, wherein the resistor comprises a thermistor.

11. The antenna monitoring unit of claim 10, wherein the monitoring module measures the resistance of the current path of the injected DC signal and generates temperature data indicative of an ambient temperature around the antenna.

12. The antenna monitoring unit of claim 11, wherein the ambient temperature data is transmitted to a master module.

13. The antenna monitoring unit of claim 2, wherein the DC injector including further comprises: a second inductor coupled between the first side of the capacitor and the RF transmission line.

14. A method for monitoring an antenna used in an antenna system comprising the steps of: connecting an RF path of an antenna to ground through a resistor; connecting the RF path of the antenna to a RF transmission line through a capacitor; connecting a monitoring module to the RF path of the antenna through a first inductor; injecting a DC signal into an RF path of the antenna; measuring the DC signal; comparing the DC signal to a stored value; receiving a DC coded signal transmitted along an RF transmission line; and comparing the received signal with a saved code associated with the monitoring module.

15. The method according to claim 14, further comprising the steps of: generating a confirmation signal when the received code matches the saved code; and transmitting the confirmation signal along the RF transmission line to a transceiver.

16. The method according to claim 15, further comprising the steps of: generating a transmission alarm when no confirmation signal is received after a threshold number of attempts to contact the monitoring module; and transmitting the transmission alarm along the RF transmission line to the transceiver.

17. In a distributed antenna system including a transceiver connected to a building-wide distributed antenna system having a plurality of antennas, an antenna monitoring unit comprising: an antenna; a current injector coupled to the antenna and to an RF transmission line; wherein the antenna is DC isolated from the RF transmission line through the current injector; a monitoring module coupled to the current injector; wherein a master controller transmits a DC signal to the monitoring module via the RF transmission line, and the monitoring module compares the DC with saved information to determine if the DC signal matches the saved information and the monitoring module transmits a confirmation signal to the master controller when the DC signal is determined to match the saved information.

18. The antenna monitoring unit of claim 17, wherein the DC injector injects a DC signal to the antenna and the monitoring module measures the injected DC signal.

19. The antenna monitoring unit of claim 18, wherein the monitoring module compares a resistance of the current path of the injected DC signal to a stored value and if the comparison of values exceeds a threshold level, the monitoring module generates a warning.

20. The antenna monitoring unit of claim 19, wherein the resistor comprises a thermistor.

21. The antenna monitoring unit of claim 20, wherein the monitoring module measures the resistance of the current path of the injected DC signal and generates temperature data indicative of an ambient temperature around the antenna.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG. 1 is a block diagram illustrating a configuration of a distributed antenna system using the inventive antenna connected to a monitoring unit.

[0029] FIG. 2 is a block diagram of the antenna connected to a monitoring unit according to FIG. 1.

[0030] FIG. 3 is a schematic diagram of a DC signal path according to FIG. 2.

[0031] FIG. 3A is a schematic diagram of an alternative design according to FIG. 3.

[0032] FIG. 4 is a schematic diagram of various DC signal paths according to FIG. 2.

[0033] FIG. 5 is an illustration of the DC injector according to one configuration of FIG. 2.

[0034] FIG. 6 is an illustration of the DC injector according to another configuration of FIG. 2.

[0035] FIG. 7 is a block diagram of the monitoring module according to FIG. 2.

[0036] FIG. 8 is a block diagram of the antenna according to FIG. 2.

[0037] FIG. 9 is a Smith diagram of the antenna according to FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

[0038] Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views.

[0039] FIG. 1 is a system overview of a Radio Frequency Distributed Antenna System (RF-DAS system) 100.

[0040] The system 100 includes an RF signal generator 110, power dividers 120, and antenna units 130. The system further includes a component status monitoring system, which may include a master controller 140 located at a base station, current injectors 150, and monitoring modules 160. The antenna units 130 in the RF-DAS system may comprise inverted F antennas, such as illustrated in FIG. 8. An inverted F antenna is a planar monopole antenna with a shunt.

[0041] The RF signal generator 110 functions as a transceiver for the transmission of RF signals along the RF transmission line 170. The power dividers 120 are placed along the RF transmission line and various locations and function to split the RF signal to be transmitted to and from each of the various antenna units 130.

[0042] The current injectors 150 are coupled to the RF transmission line 170 and pass the RF signals through to an RF signal path 180 to their associated antenna units 130. The current injectors 150 also include a DC signal path 190 that is provided to transmit DC signals between the master controller 140 and the various monitoring modules 160.

[0043] A schematic diagram of one configuration of a fault detecting circuit for use in the system of FIG. 1 is illustrated in FIG. 2. FIG. 2 includes the antenna unit 130 that includes a resistance 132 corresponding to the shunt. The antenna unit 130 is coupled to a current injector 150 that includes a capacitance 152 that functions to DC isolate the antenna unit 130 from any DC signal transmitted along the RF transmission line 170.

[0044] Current injector 150 further includes an inductance 154, which functions to allow for the injection of a DC signal into antenna unit 130 to determine if antenna unit 130 is currently functional. Additionally, an inductance 156 is provided, which functions to allow for the transmission of DC signals between the master controller 140 along RF transmission line 170, through the current injector 150, along DC signal path 190 and to monitoring module 160.

[0045] In one configuration, the DC signal comprises a coded signal and the monitoring module 160 includes saved information in a storage 162 (FIG. 7) that identifies the monitoring module 160 from the other monitoring modules connected to the RF transmission line 170. In this manner, a particular monitoring module is able to receive a DC signal that includes a code, compare that received code with the saved information using circuitry 164 to identify that the DC signal is intended for that particular monitoring module 160.

[0046] It will be understood by those of skill in the art that the inductance 156 functions to block higher frequency signals but will pass through low frequency DC signals. The inductance 154 functions in the same manner, however, inductance 154 is connected on the other side of capacitance 152 to RF signal path 180 to antenna units 130. The monitoring unit 160 is capable, in one configuration, of injecting a DC signal onto RF signal path 180 to monitor the status of antenna unit 130.

[0047] FIG. 3 comprises a configuration for testing antenna unit 130. For example, FIG. 3 illustrates antenna 133, capacitor 134, inductor 135, resistor 136 and a ground connection 137. In one embodiment, resistor 136 is 200 (ohms) and is positioned in series with inductor 135 with a value of 300 nH (nano Henrys). Inductor 135 and resistor 136 are connected in series with each other between the positive conductor 182 of RF signal path 180 and ground connection 137 to which the negative conductor 184 of RF signal path 180 is also connected. Capacitor 134 has a value of 300 pF (pico Farads).

[0048] This component circuit provides a DC resistance of 200Ω at DC and very low frequencies. The impedance, however, becomes a virtual short circuit above 200 MHz. Therefore, an inverted F antenna (FIG. 8) is able to function as if the small component network was nonexistent.

[0049] Referring now to FIG. 3A, a variant circuit is illustrated in which resistor 136 is replaced with thermistor 139. In this configuration, thermistor 139 is placed in close vicinity to antenna 133 and is used to sense changes in temperature, such that, the complete system can be monitored for ‘hot spots.’ In such case, remote monitoring of the cabling and antenna could further include, an ambient temperature measurement of the area in the vicinity of the antenna. This embodiment could further include a threshold alarm setting, warning of dangerous temperature levels in the building, possibly adding early fire detection and warning.

[0050] In the above-described configuration, it is contemplated that the master controller 140 supplies a DC voltage having a low frequency (i.e., 9 kHz) coded square wave signal. The square wave signal is separated from the RF transmission line 170 by current injector 150. Current injector 150 forwards the DC signal to the monitoring module 160. The monitoring module 160, if it recognizes the coded square wave signal will transmit a confirming DC signal verifying the status of the RF transmission line 170. In one simple arrangement, the monitoring module 160 may simply DC switch the connection to the RF transmission line and/or direct the coded square wave signal back to the master controller 140. The monitoring module 160 may include a microprocessor 163 to allow signaling with an addressable memory to store information in storage 162.

[0051] FIG. 4 is an example of the DC injector that injects the DC signal according to one embodiment of the current invention. On one side of capacitor 152, arrows indicate an incoming signal (from master controller 140) received on RF transmission line 170 (172, 174) that is transmitted through inductor 156. Also shown are arrows indicating an outgoing signal (to master controller 140) that may comprise any of the types of signals described above.

[0052] On the other side of capacitor 152, arrows indicate an outgoing signal (from monitoring module 160) that travel toward antenna unit 130 where a value (such as resistance, or voltage or current) can be measured to determine if the RF signal path 180 (182, 184) is valid and/or provide temperature data per the embodiment of FIG. 3A.

[0053] FIGS. 5 and 6 illustrate two different configurations for current injector 150. In FIG. 5, the device is configured to allow for a DC signal to be transmitted on RF transmission line 170, but blocks any DC signal from reaching antenna unit 130. Alternatively, FIG. 6 allows for a DC signal to be sent on both RF transmission line 170 and RF signal path 180. Each of these will be discussed in further detail below.

[0054] Antenna. The antenna 133 in one form is monitored with a current loop and is capable of providing analog signals to a monitoring device including a constant resistance to prove the antenna is in place and ready to function or a variable resistance depicting a value which could relate to ambient temperature, RF signal level, or any variable the internal circuitry was designed to relay. In another form, the antenna could incorporate a microprocessor that could process information within the antenna and disseminate that information as it is processed or in response to a polling request triggered by the monitoring system. Referring to FIG. 1, a current injector 150 is placed at each antenna unit 130 location and provides the monitoring module 160 with a continuous DC path to the master controller 140 and an isolated DC path to the antenna unit 130 (isolated DC paths on each connector of the current injector 150). This allows monitoring of the antenna unit 130 itself. The monitoring module 160 may optionally be provided with a power source 165 (or with an external power source) that provides DC voltage and enough current to manage this feature. The current injector 150 and the monitoring module 160 are designed to allow for this feature. The antenna is designed for whatever operational RF band it is expected to operate within and as such, is available in various models. A broadband model is available, for example, where the UHF “public safety” band as well as all popular cellular bands from 700 MHz through 2700 MHz and above are effectively managed through a single radiating element. The components within the antenna itself responsible for the monitoring capability are not affected by the operational bandwidth of the radiating element of the antenna. Therefore, the invention can be incorporated into antennas designed for in-building DAS applications or any other RF antenna such as base station antennas, specialty applications, etc.

[0055] Power Divider. A reactive power divider 120 allows a DC path through all ports and provides equal 2-way, 3-way, and 4-way divisions typically (2-way dividers shown in FIG. 1). A reactive power divider 120 is a non-directional coaxial structure available in a variety of coupled values, which enables the RF system designer to balance the various antenna lines having differing lengths and to be able to split the power from main lines to branch lines to divide the power as needed. A reactive power divider 120 for this application may have the following attributes:

TABLE-US-00001 Parameter Specification Comments RF Passband freq. 376-2,200 MHz Passband insertion loss 0.15 dB Max Return loss >18 dB Measured at input RF power handling 100 W PIMD IM3 >155 dBc 2 × 20 W tones @ 850 MHz DC PASS yes All ports to all ports DC Voltage 3 V-36 V DC Current 2 A @ 36VDC Connectors N Type Female Coupling values 3, 4.8, 6 dB (2, 3, 4 way splits) Operating Temp 0 C.-45 C.

[0056] Current Injector The current injector 150 (shown in FIG. 5) is a bi-directional coaxial structure for RF power while allowing DC current to be placed on the coaxial line in one direction and blocking that DC current in the other direction. Blocking the DC in one direction protects circuits on the blocked side from being DC energized to prevent a shock hazard or the possibility of that DC current damaging a radio for example.

[0057] It should be noted, however, that this configuration does not allow the antenna unit 130 direct monitoring feature.

TABLE-US-00002 Parameter Specification Comments RF Passband freq. 350-960 MHz Passband insertion loss 0.2 dB Max Return loss >18 dB S11 and S22 RF power handling 100 W PIMD IM3 >150 dBc 2 × 10 W tones @ 850 MHz DC PASS yes DC Voltage 3 V-36 V DC Current 2 A @ 36VDC Connectors N Type Female DB9 for DC path Operating Temp 0 C.-45 C.

[0058] Current Injector allowing direct antenna monitoring. While similar to the current injector shown in FIG. 5, the unit shown in FIG. 6 permits monitoring the antenna directly. Current injector 150 comprises a second injector that is connected to the antenna unit 130, allowing an isolated DC path between the antenna and the monitoring unit. This configuration allows the antenna monitoring unit to be powered and polled by a DC current supplied elsewhere in the building such as at the master controller location as well as supply an isolated DC path directly into the antenna the monitoring unit is monitoring. This configuration negates the need for locally powering each antenna location which can be a real challenge in many installations.

[0059] Master Controller. The master controller 140 communicates with the monitoring modules 160 placed at each antenna unit 130 location. The master controller 140 supplies a DC current to each of the monitoring modules 160, polls the monitoring modules 160 to ensure they are still part of the RF transmission line 170 and provides information on the health of the system to an alarm monitoring center over a system wide network connection. Each monitoring module 160 can include a unique address within the network of remote monitoring modules that may be managed by master controller 140.

[0060] Monitoring Module. Each monitoring module 160 is a part of the system that communicates uniquely with master controller 140. The monitoring module 160, in this example, is fed DC current from the master controller 140 and has an address that the master controller 140 recognizes as associated with an antenna unit 130 position/physical location within the building. This could be accomplished, for example, by using a lookup table or other dataset system. The monitoring module 160 is located as close as practically possible to the antenna thereby monitoring the entire RF transmission line 170 and the RF signal path 180 directly into the antenna 133.

[0061] FIG. 9 is an Impedance View Smith Chart showing that the impedance of the fault detection circuit becomes a virtual short circuit to signal frequencies above 200 MHz, so that the antenna is able to function as if the small component network were not present.

[0062] Although the invention has been described with reference to a particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements or features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.