Passive methods such as wideband spectrum analysis, time-domain I/Q recordings, and relative gain measurements using a rotating platform can be employed. In an anechoic chamber or open-field environment, the received signal strength can be measured at various angles to obtain the relative radiation pattern, while polarization can be determined by rotating the receiving antenna.

These methods seem to be able to test the amplitude of the antenna, but how to measure its phase ？@Cem Güler

If you put a receiver at a fixed distance and direction to the antenna then you can receive a signal of constant phase and amplitude from the lo in the antenna and use this signal as a phase reference to do phase measurements from another receiver at various positions.

Hello,

To test an antenna under unknown coherent signal conditions, several steps are crucial. These involve understanding the signal environment, employing appropriate measurement techniques, and analyzing the data to extract relevant antenna characteristics. Here's a breakdown of the process:

1. Understanding the Signal Environment:

• Signal Coherence:Coherent signals have a fixed phase relationship, which can significantly impact antenna measurements, especially direction-of-arrival (DOA) estimation.
• Signal Characteristics:Determine the frequency, bandwidth, and modulation scheme of the coherent signals. This helps in selecting appropriate measurement equipment and analysis techniques.
• Source Number Estimation:Coherent signals can make it difficult to determine the number of signal sources. Techniques like spatial smoothing or deep learning-based methods may be needed.
• Interference:Identify any potential interference from other sources that could affect measurements.

2. Measurement Setup:

• Anechoic Chamber/Open Field:Choose an environment that minimizes reflections and provides a controlled environment for antenna measurements.
• Reference Antenna (Optional):If possible, use a calibrated reference antenna with known characteristics to compare against the antenna under test (AUT).
• Receiving System:Employ a wideband spectrum analyzer or a network analyzer to capture the received signals.
• Signal Generation:If needed, use a signal generator to transmit known signals for testing, or use the AUT as a transmitter to analyze its radiation pattern.
• Rotating Platform (Optional):If measuring radiation patterns, use a rotating platform to capture the antenna's response at various angles.

3. Measurement Techniques:

• Relative Gain Measurement:Measure the power received by the AUT and the reference antenna to determine the gain of the AUT relative to the reference.
• Radiation Pattern Measurement:Capture the received signal strength at different angles to create a 2D or 3D representation of the antenna's radiation pattern.
• Polarization Measurement:Rotate the receiving antenna to determine the polarization characteristics of the signal and the antenna.
• Time-Domain I/Q Recording:Record the in-phase (I) and quadrature (Q) components of the received signal to analyze phase information.
• Passive Methods:Utilize wideband spectrum analysis and time-domain I/Q recordings for signal analysis in echoic or anechoic environments.

4. Data Analysis:

• Signal Processing:Apply signal processing techniques to extract relevant parameters from the recorded data. This may include Fourier transforms, spectral analysis, and direction-of-arrival (DOA) algorithms.
• Coherent Signal Processing:For coherent signals, advanced techniques like spatial smoothing, eigen decomposition, or deep learning-based methods may be necessary to accurately estimate DOA and other parameters.
• Error Analysis:Account for measurement uncertainties and estimate the accuracy of the results.

5. Final Functional Test:

• Compare with Specifications:Compare the measured antenna characteristics with the manufacturer's specifications or desired performance parameters.
• Identify Deviations:Analyze any deviations from expected performance and determine the root cause.

By following these steps, you can effectively test an antenna under unknown coherent signal conditions, even without prior knowledge of the signal's characteristics. This allows for a thorough evaluation of the antenna's performance and identification of any potential issues.

Thanks,

لديك خيار معالجة الإشارة، أيا ما كان الإتجاه، إجعل الهوائي يستقبل تردد واحد و إبحث عنه ضمن حزمة الترددات المتراكبة بواسطة FFT.

could you supply more about this method, such as related papers、website link? Malcolm White

I don't know any links, but if you fix a small antenna on a long enough arm to the antenna under test, in a direction you aren't interested in, it should receive a constant signal in phase with the transmitted signal.

This antenna will change the measured antenna pattern a little. You can estimate its effect by repeating with it in a different direction.

It might work perfectly well just putting the receive antenna directly behind the test antenna, where it probably won't affect anything you are interested in.

It can also receive bounces off the chamber walls which will modulate the phase as the antenna moves, so you need to be careful to minimise these effects.