A method for measuring the noise figure of an active antenna

Abstract

The present invention discloses a method for measuring the noise figure of an active antenna, belonging to the field of antenna index measurement. First, the total gain of the active antenna is measured by the far-field comparison method in a microwave anechoic chamber; then, the equivalent gain of the low-noise amplifier of the active antenna is measured by the reference antenna method; then, the value of the active antenna is measured by the carrier-to-noise ratio method; finally, the noise figure of the active antenna is calculated from the measured total gain, equivalent gain and value of the active antenna. The method of the present invention is simple and feasible and has the value of popularization and application.

Description

Technical Field

[0001] The present invention relates to the field of antenna index measurement, and is particularly applicable to the measurement of the noise figure of an active antenna. Background Art

[0002] The noise figure is one of the important performance indicators of an active antenna, and its performance directly affects the sensitivity of the antenna receiving system. The radiation unit of the active antenna is integrated with the low-noise amplifier and cannot be separated. The traditional measurement methods for the noise figure of the low-noise amplifier are: the noise figure analyzer method, the Y-factor method, and the spectrum analyzer method. There are the following limitations in measuring the noise figure of the active antenna using the traditional methods:

[0003] 1. In the traditional noise figure analyzer method, the noise figure of a two-port device can be directly measured with a noise figure analyzer. The active antenna is a single-port device, and the noise figure of the active antenna cannot be measured with a noise figure analyzer;

[0004] 2. In the traditional Y-factor method, the noise figure of the low-noise amplifier can be measured using the hot and cold load Y-factor method. However, for the active antenna, since the antenna unit and the low-noise amplifier are integrated together, the noise figure measured by the Y-factor method is the equivalent noise figure of the antenna unit and the low-noise amplifier, and the influence of the antenna radiation unit cannot be deducted. Therefore, the noise figure of the low-noise amplifier cannot be determined;

[0005] 3. In the traditional spectrum analyzer method, the gain and noise power of the low-noise amplifier are measured with a signal source and a spectrum analyzer to determine the noise figure of the low-noise amplifier. However, for the active antenna, this method can measure the total gain of the active antenna and cannot measure the gain of the low-noise amplifier. Therefore, the noise figure of the active antenna cannot be determined. Summary of the Invention

[0006] The purpose of the present invention is to propose a method for measuring the noise figure of an active antenna to avoid the deficiencies in the above background art. The method of the present invention is simple, easy to implement, can effectively measure the noise figure of the active antenna, and the measurement result is accurate.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is:

[0008] A method for measuring the noise figure of an active antenna, comprising the following steps:

[0009] (1) In the far-field test field of the microwave anechoic chamber, measure the received signal power of the active antenna to be measured and the standard gain antenna for the same transmitting antenna respectively, and calculate the total gain of the active antenna to be measured using the following formula:

[0010] G ∑ =G SGH +P active -PSGH

[0011] In the formula:

[0012] G ∑ —Total gain of the active antenna, dBi;

[0013] G SGH —Gain of the standard gain antenna, dBi;

[0014] P active —Signal power level received by the active antenna under test, dBm;

[0015] P SGH —Signal power level received by the standard gain antenna, dBm;

[0016] (2) Replace the standard gain antenna with a reference antenna, measure the received signal power of the reference antenna for the transmitting antenna, and calculate the equivalent gain of the low-noise amplifier of the active antenna using the following formula:

[0017] G e =P active -P reference

[0018] In the formula:

[0019] G e —Equivalent gain of the low-noise amplifier of the active antenna, dB;

[0020] P reference —Power level of the signal received by the reference antenna, dBm;

[0021] (3) Replace the transmitting antenna with a standard gain antenna, replace the reference antenna with the active antenna under test, transmit a single-carrier signal with the standard gain antenna, and measure the magnitude of the carrier power received by the active antenna under test; then, rotate the azimuth of the active antenna under test by 90°, point it at the absorbing material on the side wall of the microwave anechoic chamber, receive the ambient noise of the microwave anechoic chamber, and measure the normalized noise power of the system; calculate the value of the active antenna system using the following formula:

[0022]

[0023] In the formula:

[0024] —Figure of merit of the active antenna system, dB / K;

[0025] C—Signal power level received by the active antenna under test, dBm;

[0026] N0—Normalized noise power output by the active antenna system, dBm / Hz;

[0027] — Normalized carrier-to-noise ratio output by the active antenna system, dB / Hz;

[0028] P T — Free space propagation loss, dBW;

[0029] G SGH — Gain of the standard gain antenna, dBi;

[0030] (4) From the measured total gain of the active antenna, the equivalent gain of the low-noise amplification, and the value of the active antenna system, calculate the noise figure of the active antenna using the following formula: The noise figure of the active antenna is calculated using the following formula:

[0031]

[0032] In the formula:

[0033] NF act-ant — Noise figure of the active antenna, dB;

[0034] T0 — Ambient noise temperature of the active antenna, K;

[0035] Complete the measurement of the noise figure of the active antenna.

[0036] Furthermore, the specific method of step (1) is as follows:

[0037] Establish an antenna far-field test system in the microwave anechoic chamber, install the transmitting antenna and the active antenna to be measured. The transmitting antenna and the active antenna to be measured are at the same height, and the distance between the transmitting antenna and the active antenna to be measured meets the far-field condition;

[0038] The signal source emits a single-carrier RF signal, which is radiated by the transmitting antenna, propagates through free space, and is received by the active antenna to be measured; adjust the azimuth and elevation of the active antenna to be measured to align the axes of the transmitting antenna and the active antenna to be measured and make the polarization match. Measure the magnitude of the signal power received by the active antenna with a spectrum analyzer, and use P active to represent it, with the unit of dBm;

[0039] Replace the active antenna to be measured with a standard gain antenna, keep the test distance and the output power of the signal source unchanged, adjust the alignment between the transmitting antenna and the standard gain antenna and make the polarization match. Measure the magnitude of the signal power received by the standard gain antenna with a spectrum analyzer, and use P SGH to represent it, with the unit of dBm;

[0040] Calculate the total gain of the active antenna to be measured.

[0041] Furthermore, the specific method of step (2) is as follows:

[0042] After completing the measurement in step (1), turn off the RF output of the signal source, replace the standard gain antenna with the reference antenna, then turn on the RF output switch of the signal source, keep the output power and frequency of the signal source unchanged, and keep the test distance between the transmitting antenna and the reference antenna unchanged.

[0043] Adjust the azimuth and elevation of the reference antenna to align the transmitting antenna and the reference antenna and make the polarization match.

[0044] Measure the signal power received by the reference antenna with a spectrum analyzer, denoted by P reference in dBm.

[0045] Calculate the equivalent gain of the low-noise amplifier of the active antenna.

[0046] Furthermore, the specific method of step (3) is as follows:

[0047] After completing the measurement in step (2), turn off the RF output of the signal source, replace the transmitting antenna with the standard gain antenna, replace the reference antenna with the active antenna under test, and transmit a single-carrier signal with the standard gain antenna.

[0048] Turn on the RF output switch of the signal source, adjust the standard gain antenna to align with the active antenna under test and make the polarization match, measure the carrier power received by the active antenna under test with a spectrum analyzer, denoted by C in dBm.

[0049] Turn off the RF output of the signal source, rotate the azimuth of the active antenna under test by 90°, point it to the absorbing material on the side wall of the microwave anechoic chamber, receive the ambient noise of the microwave anechoic chamber, and measure the normalized noise power of the system with a spectrum analyzer, denoted by N0 in dBm / Hz.

[0050] Calculate the value of the active antenna system.

[0051] Furthermore, the distance R between the transmitting antenna and the active antenna under test satisfies the far-field condition, i.e., R ≥ 2D 2 / λ, where D is the maximum size of the active antenna under test and λ is the operating wavelength.

[0052] Furthermore, the reference antenna and the active antenna under test have the same structure and the same radiation unit, i.e., the antenna gain of the reference antenna is equal to the antenna gain of the active antenna.

[0053] The present invention has the following advantages compared with the background art:

[0054] 1. This method can effectively measure the noise figure of the active antenna, the measurement method is simple, and the measurement result is accurate.

[0055] 2. This method can not only measure the noise figure of an active antenna, but also its measurement principle can be used for measuring the noise figure of a passive antenna. Therefore, the present invention has good popularization and application value. Description of the Drawings

[0056] Figure 1 It is a schematic diagram for measuring the total gain of an active antenna.

[0057] Figure 2 It is a schematic diagram for measuring the equivalent gain of the low-noise amplifier of an active antenna.

[0058] Figure 3 It is for measuring an active antenna value. Detailed Embodiment

[0059] A method for measuring the noise figure of an active antenna. This method first measures the total gain of the active antenna by the far-field comparison method in a microwave anechoic chamber; then measures the equivalent gain of the low-noise amplifier of the active antenna by the reference antenna method; then, measures the value of the active antenna by the carrier-to-noise ratio method; finally, calculates the noise figure of the active antenna from the measured total gain, equivalent gain and value of the active antenna.

[0060] Referring to Figures 1-3 , the test system consists of a signal source, a transmitting antenna, a standard gain antenna, a reference antenna, an active antenna, a radio frequency test cable and a spectrum analyzer. By measuring the total gain of the active antenna, the equivalent gain of the low-noise amplifier of the active antenna and the value of the active antenna, the noise figure of the active antenna is calculated therefrom.

[0061] In a specific embodiment, the antenna under test is a microstrip active antenna, with a working frequency of 3.4 GHz to 4.2 GHz, a polarization of linear polarization, a test frequency of 4 GHz, and the gain of the C-band standard gain antenna at 4 GHz is 19.5 dBi. The specific steps of the measurement method for the noise figure of the antenna under test are as follows:

[0062] Step 1: Measurement of the total gain of the active antenna. In the far-field test field of the microwave anechoic chamber, install the transmitting antenna and the antenna under test. Adjust the transmitting antenna and the antenna under test to be aligned and polarization-matched. Use a frequency analyzer to measure the magnitude of the received signal power of the antenna under test, represented by P active , with the unit of dBm; then replace the antenna under test with a standard gain antenna, keep the test distance and the output power of the signal source unchanged, adjust the transmitting antenna and the standard gain antenna to be aligned and polarization-matched, and use a spectrum analyzer to measure the magnitude of the received signal power of the standard gain antenna, represented by P SGH , with the unit of dBm. Calculate the total gain of the antenna under test using the following formula.

[0063] G ∑ = G SGH + P active - P SGH

[0064] In the embodiment, the signal power level received by the active antenna under test is measured as -30.2 dBm by a spectrum analyzer; the signal power level received by the standard gain antenna measured by the spectrum analyzer is -56.3 dBm. Then the total gain of the active antenna under test is:

[0065] G ∑ = 19.5 - 30.2 + 56.3 = 45.6

[0066] Step 2: Measurement of the equivalent gain of the low-noise amplifier of the active antenna. After completing the measurement of the total gain of the active antenna, turn off the RF output of the microwave signal source, replace the standard gain horn antenna with a reference antenna. The structure of the reference antenna is the same as that of the active antenna under test, and the antenna gain of the active antenna is equal to the gain of the reference antenna. Turn on the RF output switch of the signal source, keep the output power and frequency of the signal source unchanged, keep the test distance unchanged, adjust the transmitting antenna and the reference antenna to be aligned and polarization-matched, measure the magnitude of the signal power received by the reference antenna with a spectrum analyzer, and represent it with P reference in dBm. Calculate the equivalent gain of the low-noise amplifier of the active antenna using the following formula.

[0067] G e = P active - P reference

[0068] In the embodiment, the signal power level received by the reference antenna measured by the spectrum analyzer is -65.8 dBm. Then the equivalent gain of the low-noise amplifier of the active antenna is:

[0069] G e = -30.2 + 65.8 = 35.6

[0070] Step 3: Measurement of the value of the active antenna. After completing the measurement of the total gain of the active antenna and the equivalent gain of the low-noise amplifier, replace the transmitting antenna with a standard gain antenna, transmit a single-carrier signal with the standard gain antenna, adjust the standard gain antenna and the active antenna under test to be aligned and polarization-matched, measure the magnitude of the carrier power received by the active antenna under test with a spectrum analyzer, and represent it with C in dBm; then turn off the RF output of the signal source, rotate the azimuth of the active antenna under test by 90°, point it to the absorbing material on the side wall of the microwave anechoic chamber, receive the ambient noise of the microwave anechoic chamber, and measure the normalized noise power of the system with a spectrum analyzer, and represent it with N0 in dBm / Hz. Calculate the value of the active antenna using the following formula.

[0071]

[0072] In the embodiment, the free space loss between the standard gain antenna and the active antenna under test is 64.3 dB, and the input power of the standard gain antenna is -30 dBW. The carrier power received by the active antenna under test measured by the spectrum analyzer is -10.2 dBm; the normalized noise power of the spectrum analyzer system is -150.6 dBm / Hz. Then the active antenna value is:

[0073]

[0074] Step 4: Calculation of the noise figure of the active antenna. From the measured total gain of the active antenna, the equivalent gain of the low-noise amplification, and the system value, the noise figure of the active antenna is calculated using the following formula.

[0075]

[0076] In the embodiment, the ambient noise temperature of the microwave anechoic chamber is 300 K, and the noise figure of the active antenna under test is:

[0077] NF act-ant = 45.6 - 33.5 - 10×lg(300) + 13.4 = 0.73 dB

[0078] In summary, the present invention first measures the total gain of the active antenna using the far-field comparison method in a microwave anechoic chamber; then measures the equivalent gain of the low-noise amplifier of the active antenna using the reference antenna method; then measures the value of the active antenna using the carrier-to-noise ratio method; finally, calculates the noise figure of the active antenna from the measured total gain, equivalent gain, and value of the active antenna. The method of the present invention is simple and feasible, and has the value of popularization and application.

Claims

1. A method for measuring the noise figure of an active antenna, characterized in that, It includes the following steps: (1) In the far-field test field of the anechoic chamber, measure the received signal power of the active antenna under test and the standard gain antenna for the same transmitting antenna respectively, and calculate the total gain of the active antenna under test by using the following formula: G ∑ = G SGH + P active - P SGH In the formula: G ∑ — Total active antenna gain, dBi; G SGH — Gain of the standard gain antenna, dBi; P active — Signal power level received by the active antenna under test, dBm; P SGH — Signal power level received by a standard gain antenna, dBm; (2) Replace the standard gain antenna with the reference antenna, measure the received signal power of the reference antenna for the transmitting antenna, and calculate the equivalent gain of the low-noise amplifier of the active antenna by using the following formula: G e = P active - P reference In the formula: G e — Equivalent gain of the active antenna low-noise amplifier, dB; P reference — Power level of the signal received by the reference antenna, dBm; (3) Replace the transmitting antenna with a standard gain antenna, and replace the reference antenna with the active antenna under test. Transmit a single carrier signal with the standard gain antenna and measure the carrier power received by the active antenna under test. Then, rotate the azimuth of the active antenna under test by 90° so that it points to the absorbing material on the side wall of the microwave anechoic chamber, receive the ambient noise of the microwave anechoic chamber, and measure the normalized noise power of the system. Calculate the value of the active antenna system using the following formula: In the formula: — Quality factor of the active antenna system, dB / K; C—the signal power level received by the active antenna under test, dBm; N0—the normalized noise power output by the active antenna system, dBm / Hz; — Normalized carrier-to-noise ratio output by the active antenna system, dB / Hz; P T — Free space propagation loss, dBW; G SGH — Standard gain of the antenna, dBi; (4) From the measured total gain of the active antenna, the equivalent gain of the low-noise amplification, and the value of the active antenna system Calculate the noise figure of the active antenna using the following formula: In the formula: NF act-ant — Noise figure of the active antenna, dB; T0—the ambient noise temperature of the active antenna, K; Complete the measurement of the noise figure of the active antenna.

2. The method for measuring the noise figure of an active antenna according to claim 1, wherein The specific method of step (1) is: Establish an antenna far-field test system in the anechoic chamber, install the transmitting antenna and the active antenna under test. The transmitting antenna and the active antenna under test are at the same height, and the distance between the transmitting antenna and the active antenna under test meets the far-field condition; The signal source emits a single-carrier RF signal, which is radiated by the transmitting antenna, propagates in free space, and is received by the active antenna under test; Adjust the azimuth and elevation of the active antenna to be measured so that the axes of the transmitting antenna and the active antenna to be measured are aligned and polarization matched. Measure the magnitude of the signal power received by the active antenna using a spectrum analyzer, denoted by P active in dBm; Replace the active antenna to be measured with a standard gain antenna, keep the test distance and the output power of the signal source unchanged, adjust the transmitting antenna to be aligned with the standard gain antenna and polarization matching, measure the signal power received by the standard gain antenna with a spectrum analyzer, and use P SGH to represent, with the unit of dBm; Calculate the total gain of the active antenna under test.

3. A method for measuring the noise figure of an active antenna according to claim 1, characterized in that, The specific method of step (2) is: After completing the measurement of step (1), turn off the RF output of the signal source, replace the standard gain antenna with the reference antenna, then turn on the RF output switch of the signal source, keep the output power and frequency of the signal source unchanged, and keep the test distance between the transmitting antenna and the reference antenna unchanged; Adjust the azimuth and elevation of the reference antenna to align the transmitting antenna and the reference antenna and make the polarization match; Measure the signal power received by the reference antenna using a spectrum analyzer, denoted by P reference in units of dBm; Calculate the equivalent gain of the low-noise amplifier of the active antenna.

4. A method for measuring the noise figure of an active antenna according to claim 1, characterized in that, The specific method of step (3) is: After completing the measurement of step (2), turn off the RF output of the signal source, replace the transmitting antenna with the standard gain antenna, replace the reference antenna with the active antenna under test, and use the standard gain antenna to transmit a single-carrier signal; Turn on the RF output switch of the signal source, adjust the standard gain antenna to align with the active antenna under test and make the polarization match. Measure the magnitude of the carrier power received by the active antenna under test with a spectrum analyzer, denoted as C, with the unit of dBm; Turn off the RF output of the signal source, rotate the azimuth of the active antenna under test by 90°, point it at the absorbing material on the side wall of the anechoic chamber, receive the ambient noise of the anechoic chamber, and measure the normalized noise power of the system with a spectrum analyzer, denoted as N0, with the unit of dBm / Hz; Calculate the value of the active antenna system.

5. A method for measuring the noise figure of an active antenna according to claim 1, characterized in that, The distance R between the transmitting antenna and the active antenna under test satisfies the far-field condition, i.e., R ≥ 2D 2 / λ, where D is the maximum size of the active antenna under test and λ is the operating wavelength.

6. A method for measuring the noise figure of an active antenna according to claim 1, characterized in that, The reference antenna and the active antenna under test have the same structure and the same radiation unit, that is, the antenna gain of the reference antenna is equal to the antenna gain of the active antenna.

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