Application of time domain technique in antenna measurement

With the development of antenna testing technology, its measurement methods have been involved in the frequency domain, time domain, space domain, and digital domain. But still commonly used method in frequency domain is given priority to, and the index of frequency domain testing is comprehensive response of corresponding to the frequency of the index, to analyze and differentiate, other factors such as joint, a transmission line feed point, test environment reflection on its impact and interference degree, can also be difficult to remove these affect the accuracy of the test.
Along with the development of digital technology, the function of software process, network analyzer, began to have strong time-domain features, such as time-domain measurement technology began in the sights of practitioners, the technology used in the test field of antenna pattern, can effectively solve the pursuit of low reflection in test in order to ensure the accuracy and caused the defect of high construction cost. It has the characteristics of low cost and good effect. At the same time, time-domain tests can also effectively solve the problem of reflection and interference, and fault location and other problems.

1. Time-domain measurement technology
In the time domain test method, a continuous frequency sine wave is adopted for excitation. First, the characteristic data of the measured object in the frequency domain are measured, and then the data are transformed into the domain by Fourier transform. “gate” is applied in the time domain to exclude the undesired response and separate the required response, and then the non-interference measurement data are obtained by returning to the frequency domain.
The important test parameters in time domain measurement include test distance, response resolution, and time resolution.
2. Time-domain test of direction diagram
When testing the antenna pattern, various kinds of reflection and refraction waves will affect the accuracy of the test. For frequency-domain antenna testing, a low reflectivity testing environment is often pursued, which brings high cost of environment construction. Due to its computing characteristics, the time-domain pattern testing method can largely eliminate the testing errors caused by the reflection environment and restore the actual radiation performance of the antenna.
The vector network analyzer with a time-domain function is used to test the direction diagram in the time domain.
The time-domain method is of great practical value for high-precision directional map measurement. Using this technique, the test accuracy can be improved by at least one grade. Therefore, it is more economical and practical than the construction of high performance and low reflectivity test field.
3. Standing wave ratio time-domain test and fault location
For the antenna feeder system test, the influence degree and position of standing wave on the system at various discontinuities can be distinguished by using time-domain measurement. Input frequency sweep width (bandwidth), get frequency response curve; Enter the time domain and adjust the width of the gate according to the need so that the required response is within the gate. The influence degree and position of each reflection point can be seen in the time domain response curve. The relation curve between standing wave response and frequency can be obtained by returning to the frequency domain.
In the development and debugging and analysis of antenna and RF transmission systems, time-domain technology will be used to quickly know the location of main reflection problem points such as joints, nodes, power dividers, and radiation units, to facilitate targeted analysis and improve the efficiency of problem-solving.

From：http://www.hj-antenna.com/application-time-domain-technique-antenna-measurement/