SHIELDING ATTENUATION MEASUREMENT

Abstract

A system for measuring the attenuation of electromagnetic shielding of an infrastructure as a function of the frequency, including a transmitter of a white noise signal with a constant power over a frequency band between a minimum frequency and a maximum frequency, a signal receiver, the transmitter and the receiver being capable of sending a signal and receiving a signal across the infrastructure, the receiver including a filter module capable of applying sliding filter on the received signal between the minimum frequency and the maximum frequency, and a double synchronous detection module capable of double synchronous detection on a signal output by the filter module.

Claims

1. A system for measuring the attenuation of electromagnetic shielding of an infrastructure as a function of the frequency, comprising: a transmitter of a white noise signal with a constant power over a frequency band between a minimum frequency and a maximum frequency; and a receiver of a signal, the transmitter and the receiver being capable of sending a signal and receiving a signal across the infrastructure, the receiver comprising: a filter module configured to apply a sliding filter on the received signal between the minimum frequency and the maximum frequency, and a double synchronous detection module configured to double synchronous detect on a signal output by the filter module.

2. The system for measuring the attenuation of electromagnetic shielding of an infrastructure according to claim 1, wherein: the transmitter is configured to transmit a signal that is chopped white noise comprising two alternating power levels, the receiver is capable of determining is configured to determine the difference between received powers corresponding to two power levels of the transmitted signal.

3. The system for measuring the attenuation of electromagnetic shielding of an infrastructure according to claim 1, wherein the receiver comprises a determination module configured to determine the shielding attenuation as a function of the results output by the double synchronous detection module determined following signal transmission and reception in the absence of the infrastructure and then on each side of the infrastructure.

4. A receiver for a system for measurement of the attenuation of electromagnetic shielding of an infrastructure as a function of the frequency, comprising: circuitry configured to receive a signal transmitted by a transmitter of a white noise signal with constant power over a frequency band between a minimum frequency and a maximum frequency, the transmitter and the receiver being configured to transmit and receive a signal on opposite sides of the infrastructure; a filter module configured to apply a sliding filter on the received signal between the minimum frequency and the maximum frequency; and a double synchronous detection module configured to double synchronous detect on a signal output by the filter module.

5. The receiver according to claim 4, comprising a determination module configured to determine the shielding attenuation as a function of the results output by the double synchronous detection module determined following signal transmission and reception in the absence of the infrastructure and then on each side of the infrastructure.

6. A method for measuring the attenuation of electromagnetic shielding of an infrastructure as a function of the frequency, comprising the following steps: transmitting a white noise signal with a constant power over a frequency band between a minimum frequency and a maximum frequency; receiving a signal, the signal transmission and reception taking place on opposite sides of the infrastructure; performing sliding filtering on the received signal between the minimum frequency and the maximum frequency; and performing synchronous double detection on a signal output by the filtering.

7. The method for measuring the attenuation of electromagnetic shielding of an infrastructure according to claim 6, further comprising preliminary steps of the transmitting and receiving of a signal in the absence of the infrastructure, and applying the sliding filter on the received signal and double synchronous detection on a signal output by the sliding filter step.

8. The method for measuring the attenuation of electromagnetic shielding of an infrastructure according to claim 7, further comprising a step of determining the shielding attenuation as a function of the results of the sliding filter and double synchronous detection steps performed following signal transmission and reception in the absence of the infrastructure and then on each side of the infrastructure.

9. (canceled)

10. A non-transitory storage medium that can be read by a computer, in which a computer program is stored containing instructions for execution of the sliding filter and double synchronous detection steps in the method according to claim 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Other characteristics and advantages will become clear after reading the following description of a preferred embodiment given as a non-limitative example, described with reference to the figures in which:

[0047] FIG. 1 represents a system for measuring the shielding attenuation according to one embodiment of this invention,

[0048] FIG. 2 represents a method for measuring the shielding attenuation according to one embodiment of this invention,

[0049] FIG. 3 represents a signal transmitted by the system for measuring the shielding attenuation according to one embodiment of this invention,

[0050] FIG. 4 represents a sliding filter performed on a signal received by the system for measuring the shielding attenuation according to one embodiment of this invention,

[0051] FIG. 5 represents a signal transmitted by the system for measuring the shielding attenuation according to one embodiment of this invention,

[0052] FIGS. 6a and 6b represent signals received by the system for measuring the shielding attenuation, according to one embodiment of this invention,

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

[0053] According to one preferred embodiment shown on FIG. 1, a system for measuring the shielding attenuation comprises a signal transmitter 10 connected to a transmission antenna 11. The transmitter 10 is capable of transmitting a signal that is described below.

[0054] The shielding attenuation measurement system also comprises a receiver 12 connected to a reception antenna 13.

[0055] The transmission and reception antennas may be of any type, for example: [0056] Directional or omnidirectional, [0057] Wide band or narrow band, [0058] Linear or circular polarisation, [0059] Electronic or mechanical directional control, [0060] Wire, aperture or planar, with progressive or stationary waves.

[0061] The receiver 12 is capable of receiving a signal received by the reception antenna 13. The receiver 12 comprises a filter module 121, a double synchronous detection module 122 and a measurement processing module 123 to determine the attenuation of a shielding. Processing done by the different modules is described below.

[0062] The shielding attenuation measurement system may be battery powered.

[0063] Note that the description only includes elements of the shielding attenuation measurement system that are useful for understanding the invention.

[0064] The shielding attenuation measurement system is used according to the double weighing principle. A first measurement, called the reference measurement, is made when the transmission antenna 11 and the reception antenna 13 are put into place in the absence of a structure for which the shielding attenuation is to be determined, at a determined distance and orientation. The transmission antenna and the reception antenna are then placed on each side of the structure for which the shielding attenuation is to be determined, at the same determined distance and orientation. A second measurement is made.

[0065] The signals transmitted for the two measurements have the same power.

[0066] The shielding attenuation is the ratio of the powers received during the two measurement operations. The attenuation measurement is made as a function of the frequency, typically of the order of 1 kHz to about 10 GHz.

[0067] FIG. 1 illustrates the configuration for making the second measurement in the case in which the structure is a wall 20 of a room in a building. The wall 20 comprises a door 21, the corners of which form potential shielding defects. The antennas 11 and 13 are thus located on each side of the wall 20.

[0068] FIG. 2 represents the operation of the system for measuring the shielding attenuation according to one embodiment of the invention. This operation is represented in the form of a flowchart comprising steps E1 to E5.

[0069] Step E1 is the transmission of a signal SE by the transmitter 10.

[0070] FIG. 3 represents the signal SE transmitted by the transmitter 10 as a function of the frequency. The transmitted signal SE is a white noise signal with a constant power over a frequency band between a minimum frequency F.sub.min and a maximum frequency F.sub.max.

[0071] The next step E2 is the reception of a signal SR by the receiver 12.

[0072] The next step E3 is a sliding filter applied to the received signal SR.

[0073] FIG. 4 represents the sliding filter applied to the signal SR received by the receiver 12. The signal SR is within the frequency band between frequencies F.sub.min and F.sub.max.

[0074] A sliding filter is applied between frequencies F.sub.min and F.sub.max. The sliding filter has a predetermined width LF around a frequency F.sub.0 that varies from F.sub.min to F.sub.max.

[0075] The next step E4 is determination of the received power at a given frequency within the frequency band of the transmitted signal SE. The received power is expressed in Watts. It is memorised in a memory (not shown) internal to the receiver or associated with the receiver.

[0076] As described above, a reference measurement is made when the transmission antenna and the reception antenna are put into place in the absence of the structure for which the shielding attenuation is to be determined, at a determined distance and orientation. Therefore steps E1 to E4 are performed for this first measurement. The memorised power is then a received reference power PR.sub.ref. It should be noted that this power depends on the distance between the transmission antenna and the reference antenna, the orientation of the antennas and the power of the transmitted signal. Therefore, provided that these parameters are respectively the same for several different shielding attenuation determinations, the same received reference power can be used later for these different shielding attenuation determinations.

[0077] The transmission antenna and the reception antenna are then placed on each side of the structure for which the shielding attenuation is to be determined, at the same determined distance and orientation. A second measurement is made from the same transmission signal SE. Therefore steps E1 to E4 are performed for this second measurement. The result of step E4 is then a received signal power PR for a given frequency within the frequency band of the transmitted signal SE.

[0078] Step E5 determines the shielding attenuation for one or more frequencies in the frequency band between the frequencies F.sub.min and F.sub.max.

[0079] The shielding attenuation is determined for a given frequency F. It is equal to the ratio between the power of the reference signal PR.sub.ref and the power of the received signal PR during the second measurement, at the given frequency F. Note that the powers are expressed in Watts. Step E5 is described in detail below.

[0080] Any variations in the environmental noise between the two measurements are taken into account as follows.

[0081] FIG. 5 represents the signal SE transmitted by the transmitter 10, as a function of time. The transmitted signal SE is a chopped white noise in the form of square wave with a cyclic ratio equal to . The cyclic ratio may be different.

[0082] The transmitted power is alternatively in a high state E.sub.high corresponding to a transmission time and a low state E.sub.low in which the transmitted power is null, corresponding to the transmission being cut off.

[0083] FIGS. 6a and 6b represent the signal SR received by the receiver 12 as a function of time, during the reference measurement and during the second measurement respectively.

[0084] In both cases, for the reference measurement and the second measurement, the received signal SR is also chopped in the form of square wave with a cyclic ratio equal to . The received power is alternatively in a high state corresponding to a transmission time and a low state in which the received power is low but not null, corresponding to the transmission being cut off. The power received in the low state corresponds to environmental noise and the power received in the high state corresponds to the sum of white noise received from the transmitter and environmental noise.

[0085] After the reference measurement, the difference between the power received in the high state RH.sub.ref and the power received in the low state RB.sub.ref is calculated, to cancel the contribution of ambient noise.

[0086] Similarly, after the second measurement, the difference between the power received in the high state RH and the power received in the low state RB is calculated, once again to cancel the contribution of ambient noise.

[0087] The module 122 uses double synchronous detection to measure the difference in power received between successive phases with and without transmission, without knowing the instant of the phase change controlled by the transmitter 10. This avoids the influence of a possible phase shift between the received signal SR at the modulation frequency Fm and a demodulation signal.

[0088] The processing done on the signal V.sub.in output from the sliding filter 121 is considered. The signal V.sub.in is applied to the input of the double synchronous detection module 122. The quantity V.sub.in is representative of the difference in received powers (RHRB) corresponding to the emission of white noise with cyclic ratio .

[0089] Compared with classical synchronous detection, the module 122 makes a first demodulation at the modulation frequency Fm and a second demodulation at frequency (Fm+/2). The quantities: 0.5.Math.V.sub.in.Math.cos() and 0.5.Math.V.sub.in.Math.cos(+/2)=0.5.Math.V.sub.in.Math.sin() are thus determined. These quantities are then squared and summated. The module 122 then outputs the quantity (0.5.Math.V.sub.in).sup.2.Math.(cos.sup.2()+sin.sup.2()). This quantity is equal to (0.5.Math.V.sub.in).sup.2.

[0090] Thus, the output signal obtained is (0.5.Math.V.sub.in).sup.2. The output signal is independent of a possible phase shift between the modulation signal used for transmission and the demodulation signal used for reception.

[0091] This quantity is an image of V.sub.in in which V.sub.in is representative of the difference in received powers (RHRB) corresponding to the emission of white noise with cyclic ratio % at the modulation frequency Fm.

[0092] The shielding attenuation is determined for a given frequency F, by the module 123. It is equal to the ratio of the difference calculated for the reference measurement and the difference calculated for the second measurement: (RH.sub.refRB.sub.ref)/(RHRB). Note again that all powers are expressed herein in Watts.

[0093] Processing done on the signal received by the receiver 12 can be repeated for all frequencies within the frequency band varying from F.sub.min to F.sub.max.

[0094] The range of the measurement system is increased by the use of an automatic gain control so as to work at constant power at the input to the detection diode.