CN104849592A - Radio telescope broadband electromagnetic shielding effectiveness detection system and detection method thereof - Google Patents

Abstract

The invention discloses a radio telescope broadband electromagnetic shielding effectiveness detection system and a detection method. The detection system includes a transmitting module and a receiving module; the transmitting module includes a signal source and a transmitting antenna. The antenna sends out; the receiving module includes a spectrum analyzer and a receiving antenna, the receiving antenna is used to receive the electrical signal sent by the signal source, and transmits the received electrical signal to the spectrum analyzer; the spectrum analyzer is electrically coupled with the signal source to ensure that both send and receive Synchronization of electrical signals; the spectrum analyzer respectively receives the electrical signals sent by the signal source before and after the shielding body is placed, and then calculates the shielding effectiveness of the shielding body. The application can detect multiple frequency points in the frequency band, has high detection efficiency, avoids the influence of manual testing on testers, and automatically generates a test result report, saving time and effort.

Description

A radio telescope broadband electromagnetic shielding effectiveness detection system and detection method

technical field

The invention relates to the field of electromagnetic shielding effectiveness detection, in particular to a radio telescope broadband electromagnetic shielding effectiveness detection system and detection method.

Background technique

Radio astronomy telescopes observe very weak radio signals from the universe, and the receiving frequency band can cover the frequency range from tens of MHz to hundreds of GHz. Due to the extremely high sensitivity of the radio telescope, it is very easy to receive radio interference from the outside world and itself, thus affecting normal operation and scientific output. Take the 500-meter Aperture Spherical Radio Telescope (FAST), a national major scientific and technological infrastructure, as an example. Its operating frequency is 70MHz-3000MHz. After completion, it will become the largest radio telescope in the world. Also very high, radio interference from the ground can affect the work of radio astronomy telescopes. Therefore, for the electromagnetic shielding room and shielding cabinet in the FAST station, the requirement that the shielding effectiveness in the 70MHz-3000MHz frequency be greater than 120dB is required, which requires strict electromagnetic shielding effectiveness testing.

Existing methods for testing the electromagnetic shielding effectiveness of shielding bodies are usually based on manual testing, single-frequency point testing, manual recording, sorting, and compliance judgment; there are the following problems:

1. The test results are incomplete; since the observation frequency range of the radio telescope is very wide, if a limited frequency point is selected for detection, for example, the frequency points of the conventional test only measure four frequency points of 100MHz, 450MHz, 950MHz, and 3GMHz within the range of 70MHz-3GMHz. As a result, the test results are incomplete, and some frequency points cannot meet the requirements, thereby interfering with the normal operation of the radio telescope.

2. The test efficiency is low; since there are many shields to be tested, if the test frequency is increased, the workload of manual testing will increase greatly, and the test efficiency will be low.

3. Radiation affects the health of the testers; the testers will be exposed to the radiation field due to manual operation, which is not good for the health of the testers.

4. It is time-consuming and labor-intensive to sort out test results; it takes a long time to make test reports manually, and it is easy to cause unobjective test results.

Therefore, solving the above-mentioned problems becomes a technical problem urgently needed by those skilled in the art.

Contents of the invention

For the problems existing in the background technology, the object of the present invention is to provide a radio telescope broadband electromagnetic shielding effectiveness detection system and detection method, the application can detect multiple frequency points in the frequency band, the detection efficiency is high, and manual testing is avoided. The impact of testers and automatic generation of test result reports, saving time and effort.

The purpose of the present invention is achieved through the following technical solutions:

A radio telescope broadband electromagnetic shielding effectiveness detection system, the detection system includes a transmitting module and a receiving module; sent by the antenna; the receiving module includes a spectrum analyzer and a receiving antenna, the receiving antenna is used to receive the electrical signal sent by the signal source, and transmit the received electrical signal to the spectrum analyzer; the spectrum analyzer and the The signal source is electrically coupled to ensure the synchronization of the two sending and receiving electrical signals; the spectrum analyzer respectively receives the electrical signals sent by the signal source before and after being placed in the shielding body, and then calculates the shielding effectiveness of the shielding body.

Further, the spectrum analyzer and the signal source are electrically coupled through an optical fiber, and there is no metal connection between the two, so as to avoid the impact of the metal connection on the accuracy of the shielding effectiveness test.

Further, the detection method based on the detection system includes the following steps:

1) use an optical fiber to connect the spectrum analyzer and the signal source, so that the signal source sends a signal and the spectrum analyzer receives the signal synchronously, and the spectrum analyzer is connected with a receiving antenna, and the signal source is connected with a transmitting antenna;

2) controlling the signal source to output signals according to the set power and frequency;

3) control the frequency of the signal received by the spectrum analyzer to be consistent with the frequency of the signal sent by the signal source;

4) The spectrum analyzer receives the electrical signals sent before and after the signal source is put into the shielding body respectively, and automatically stores the received data;

5) Use the data in step 4) and calculate the shielding effectiveness of the shielding body according to the shielding effectiveness calculation.

Further, the step 3) is specifically: first set the start frequency and stop frequency of the frequency band to be detected, the number of detection frequency points in the frequency band and the output power of the signal source, and then control the signal source according to the set power and frequency output signal.

Further, the detection method also includes step 6): after the shielding effectiveness of the shielding body is calculated, a shielding effectiveness report is automatically generated.

The present invention has following positive technical effect:

The application can detect multiple frequency points in the frequency band, has high detection efficiency, avoids the influence of manual testing on testers, and automatically generates a test result report, saving time and effort.

Description of drawings

Fig. 1 is the structural representation of detection system of the present invention;

Fig. 2 is a schematic diagram of the structure of the transmitter module of the present invention placed inside the shield.

Detailed ways

The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

For ease of description, spatially relative terms such as "upper," "lower," "left," and "right" may be used herein to describe the relationship of one element or feature relative to another element or feature shown in the figures. It will be understood that the spatial terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "below" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "lower" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative specifications used herein interpreted accordingly.

The basic principle of electromagnetic shielding effectiveness test is as follows:

Shielding is a measure to prevent or reduce the transmission of electromagnetic energy by means of a shield. A shield is a barrier used to enclose equipment or devices.

The performance of the shielding body is expressed by shielding effectiveness. The definition of shielding effectiveness is: when shielding a given external source, the ratio of the electric field strength or magnetic field strength before and after the shielding body is placed at a certain point, that is:

$\mathrm{<span\; class="notranslate">\; SE</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}$

In the formula, SE——shielding effectiveness, multiple;

E0——Electric field strength or magnetic field strength at a certain point when there is no shield;

E1——Electric field or magnetic field intensity at the same point behind the shielding body.

According to the above definition of shielding effectiveness, as long as the same incident field power is maintained, the field strength before and after shielding at the same point is measured respectively, and the ratio is the shielding effectiveness, usually expressed in decibels:

${\mathrm{<span\; class="notranslate">\; SE</span>}}_{\mathrm{<span\; class="notranslate">\; dB</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 20</span>}\mathrm{<span\; class="notranslate">\; lg</span>}\frac{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; E.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}$

It is difficult to measure the absolute field strength at a point. In the measurement of shielding effectiveness, it is often necessary to select the corresponding probe according to the size of the shielding body to be tested and the nature of the shielding, and such probes are generally untested, even if an electromagnetic interference measuring instrument is used as an indicating instrument. Only the induced voltage can be measured.

Generally, the probes used for shielding measurement are linear components, that is, the induced voltage of the probe is proportional to the external field strength, and the measurement reading is:

U ₀ =KE ₀ U ₁ =KE ₁

In the formula, U0 - the induced voltage on the probe before shielding;

U1 - the induced voltage on the probe after shielding;

K—the constant related to the probe parameters.

In this way, the shielding effectiveness can be expressed by the ratio of the induced voltage value on the probe before and after shielding, namely:

${\mathrm{<span\; class="notranslate">\; SE</span>}}_{\mathrm{<span\; class="notranslate">\; dB</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 20</span>}\mathrm{<span\; class="notranslate">\; lg</span>}\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}$

The indication scale of the voltage interference measuring instrument is in dBμV, and the shielding effectiveness is:

SE _dB = U _0dB -U _1dB

Thus, shielding effectiveness is the difference in decibel counts on an EMI meter before and after shielding.

The above is the basic principle of shielding effectiveness measurement. However, for shields of different sizes, the measurement methods are different according to the selected electric field sensor, the transmitting source and the receiving device. At present, there are different standards for the measurement of shielding effectiveness of shielded rooms or small shielded boxes in China:

Large shielded room: GB/T 12190-2006

Small shielding box: GJB 5185-2003, GB/T 18663.3-2007

As shown in Figure 1-2, a radio telescope broadband electromagnetic shielding effectiveness detection system of the present application, the detection system includes a transmitting module and a receiving module; wherein, the transmitting module includes a signal source and a transmitting antenna, and the signal source is used to send a specified frequency The electrical signal is sent out through the transmitting antenna; the receiving module includes a spectrum analyzer and a receiving antenna, the receiving antenna is used to receive the electrical signal sent by the signal source, and transmit the received electrical signal to the spectrum analyzer; the spectrum analyzer is electrically coupled with the signal source to Ensure the synchronization of the two sending and receiving electrical signals; the spectrum analyzer respectively receives the electrical signals sent by the signal source before and after the shielding body is placed, and then calculates the shielding effectiveness of the shielding body. Among them, Agilent N9020A is selected for the spectrum analyzer (the instrument comes with Windows XP operating system, so the control computer is no longer configured separately); Windows XP operating system: realizes hardware driver management, file operation processing and network communication services, and provides underlying support for Matlab software. Matlab: Realize the core functions of the broadband electromagnetic shielding effectiveness automatic test system, including signal source control, spectrum analyzer control, test data processing, algorithm, and automatic generation of data reports. Agilent N5181B is selected as the signal source.

Preferably, the spectrum analyzer and the signal source are electrically coupled through an optical fiber, and there is no metal connection between the two, so as to avoid the influence of the metal connection on the accuracy of the shielding effectiveness test. Spectrum analyzers and signal generators work together. The signal source is placed in the shielded room, and the spectrum analyzer is placed outside the shielded room. The two use optical fiber network communication, no metal connecting wires, which can ensure that the real shielding effectiveness of the shielding room will not be disturbed. Both the spectrum analyzer and the signal source support the LXI (LAN eXtension for instrumentation) protocol, run on top of the Ethernet, and completely use the Ethernet protocol at the network layer, so that it can be easily transformed into a general network link based on optical fiber, and the command transmission delay is less than 1ms .

The spectrum analyzer itself runs an operating system, which is equivalent to a computer. It can use the LXI protocol to control the spectrum analyzer itself and the signal source at the same time, so that the two can work together at high speed. At the same time, the integration of the work that needs to be completed by three instruments, the spectrum analyzer, the signal source, and the control computer, is completed by two instruments.

Use network communication to quickly change the frequency of the signal source. After setting a frequency, use the spectrum analyzer to measure the received power at that frequency. It takes about 3 seconds to measure a frequency point, which is much shorter than the traditional method.

Take the FAST working band as an example: the frequency selection is 100 frequency points, which are approximately proportional to the number sequence, and can cover the 70MHz to 3GHz band very densely, and the measurement time used is less than 5 minutes. The number of frequency points and the start and end frequencies can be freely adjusted according to specific test requirements. Compared with the traditional method, which only measures four frequency points of 100MHz, 450MHz, 950MHz, and 3GHz, it covers the FAST band more comprehensively and quickly. After automatically measuring the generated frequency points, measure the environmental interference again, and remove the interference frequency points in the frequency bands such as mobile phone communications. This provides dense coverage of the test frequency band while minimizing environmental interference.

Then subtract the received power of the shielding effectiveness test from the received power of the first step reference level test to obtain the shielding effectiveness. Because it is a relative measurement, there is another convenience: the cable attenuation and the amplifier do not need to be strictly calibrated, just use the same cable and amplifier.

Preferably, the detection method based on the detection system comprises the following steps:

1) Use an optical fiber to connect the spectrum analyzer and the signal source, so that the signal sent by the signal source is synchronized with the signal received by the spectrum analyzer, and the spectrum analyzer is connected to a receiving antenna, and the signal source is connected to a transmitting antenna;

2) The control signal source outputs signals according to the set power and frequency;

3) Control the frequency of the signal received by the spectrum analyzer to be consistent with the frequency of the signal sent by the signal source;

4) The spectrum analyzer respectively receives the electrical signals sent by the signal source before and after being placed in the shielding body, and automatically stores the received data;

5) Use the data in step 4) and calculate the shielding effectiveness of the shielding body according to the shielding effectiveness calculation.

Preferably, step 3) is specifically: firstly set the start frequency and stop frequency of the frequency segment to be detected, the number of detection frequency points in the frequency segment and the output power of the signal source, and then control the signal source according to the set power and frequency output signal.

Preferably, the detection method also includes step 6): automatically generate a shielding effectiveness report form after calculating the shielding effectiveness of the shielding body.

The source code of this application is as follows:

The radio telescope broadband electromagnetic shielding effectiveness automatic test system has been specifically applied in the FAST engineering EMC test, and the shielding effectiveness has been measured many times. The following is an application example of shielding effectiveness measurement at the Dawodang site in December 2014.

Test equipment layout: the distance between the indoor transmitting antenna and the outdoor receiving antenna is 2 meters, with the same horizontal height and polarization. The optical fiber connection control signal source uniformly selects 100 measurement points on the exponential coordinates within the test range of 70-3000MHz. Spectrum analyzer synchronous reception test.

Cable drive 7H electrical shielding room shielding effectiveness test results: The design index of the shielding room is 70MHz-3000MHz greater than or equal to 120dB, and the test shows that 200MHz-2GHz has met the requirements. Due to the limitation of the test antenna, the measurement sensitivity of 70-200MHz is not enough, and the low-frequency antenna can be replaced here. The part above 2GHz does not meet the requirements due to reasons such as the welding seam of the shielding room and the shielding door, and needs to be rectified.

The high dynamic range, broadband electromagnetic shielding effectiveness automatic test system has been put into the actual measurement application of FAST engineering. The system is easy to use, efficient in testing, can test 120dB shielding effectiveness, and the test results are objective and accurate. It solves the problems existing in traditional manual testing of shielding effectiveness. It meets the requirements of broadband and high dynamic range electromagnetic shielding effectiveness testing required by radio astronomy telescopes.

The above is just to illustrate the present invention, and it should be understood that the present invention is not limited to the above embodiments, and various modifications conforming to the idea of the present invention are within the protection scope of the present invention.

Claims (5)

1. a radio telescope wideband electromagnetic shield effectiveness detection system, is characterized in that, described detection system comprises transmitter module and receiver module; Described transmitter module comprises signal source and emitting antenna, and described signal source is for sending the electric signal of assigned frequency and sending through described emitting antenna; Described receiver module comprises frequency spectrograph and receiving antenna, the electric signal that described receiving antenna sends for receiving described signal source, and the electric signal transmission extremely described frequency spectrograph that will receive; Described frequency spectrograph and described signal source electric coupling, to ensure that the two sends and receive the synchronous of electric signal; Described frequency spectrograph receives described signal source respectively and puts into the electric signal sent before and after shield, and then calculates the shield effectiveness of shield.

2. detection system according to claim 1, is characterized in that, described frequency spectrograph and described signal source realize electric coupling by optical fiber, connects therebetween without metal, to avoid the impact of metal connection on shield effectiveness test accuracy.

3. based on the detection method of detection system described in claim 1 or 2, it is characterized in that, described method comprises the steps:

1) use Fiber connection frequency spectrograph and signal source, makes described signal source send signal and described frequency spectrograph Received signal strength is synchronous, and frequency spectrograph is connected with receiving antenna, and signal source is connected with emitting antenna;

2) described signal source is controlled according to the power set and frequency output signal;

3) frequency controlling described frequency spectrograph Received signal strength is consistent with the frequency that described signal source sends signal;

4) described frequency spectrograph receives described signal source respectively and puts into the electric signal sent before and after shield, and the data that autostore receives;

5) utilize the data in step 4) and calculate the shield effectiveness of shield according to shield effectiveness.

4. detection method according to claim 3, it is characterized in that, described step 3) is specially: the output power first arranging the initial frequency that will detect frequency band and the detection frequency number stopped in frequency, frequency band and signal source, then controls described signal source according to the power set and frequency output signal.

5. detection method according to claim 3, is characterized in that, described detection method also comprises step 6): automatic generating masking usefulness form after calculating the shield effectiveness of shield.