Application of RF radio frequency simulation system based on vector network analyzer

I. Introduction

The antenna array and feed system, a subsystem of the RF simulation system, is mainly used to simulate the angular motion of the line of sight between the missile and the target. In order to ensure the simulation accuracy of the angular position of the antenna array and the feed system, the antenna array system must be calibrated. The so-called calibration refers to obtaining project data from the tables stored in the array control computer. These tables are used to compensate and control the antenna array system. In essence, it is to measure the tables of the programmable microwave devices in the antenna array system, that is, the insertion attenuation and insertion phase shift.

2. Vector Network Analyzer Wiltron360B

The vector network analyzer Wiltron360B consists of independent instruments such as vector network analyzer, signal source, test socket, test socket converter, etc., which form a complete measurement system through GPIB interface and special interface. It can control two test sockets and two signal sources. It is a measurement instrument with high measurement accuracy, high degree of automation, fast measurement speed and powerful functions.

3630A is a frequency converter test socket, which is a four-channel receiver that can measure the amplitude and phase of mixers, multi-port devices, antennas, etc. The structure of its front panel is shown in Figure 1. The signal of the signal source is provided to the 3630A test socket from the RF  IN terminal, and then divided into two, one is output through RF OUT as the test signal of the device under test; the other is output through SOURCE LOCK OUTPUT and connected to RA or RB as the phase-lock reference signal.

Figure 1 Schematic diagram of the front panel of 3630A III. Technical requirements of the RF simulation system for measurement

In array RF simulation systems, the calibration of antenna arrays and their feeding systems is a very important task. Calibration is essentially the same as the measurement of amplitude and phase of common microwave devices, but it has its own characteristics:

⑴The signal source is placed far away from the vector network analyzer, even not in the same laboratory;

⑵The measured signal needs to be sent to the vector network analyzer after down-conversion;

⑶ Requires higher relative amplitude and relative phase measurement accuracy;

⑷Higher amplitude and phase stability is required;

⑸Measure the amplitude and phase between two signals.

Therefore, it is the best choice to select a vector network analyzer as the amplitude and phase measurement device, and to use it together with necessary peripheral equipment to form a calibration test system. The key is that the frequency of the measurement signal required by the DUT is different from the test frequency of the vector network analyzer.

3630A was selected as the test socket for calibrating the antenna array and its feeding system. The composition principle of the entire system is shown in Figure 2.

Figure 2 Test system block diagram

The signal source outputs a signal with a frequency of f1, which is radiated by the antenna after passing through the antenna array feeding system. The received signals of the two receiving antennas are mixed into signals with a frequency of f2, and then filtered and amplified before being fed into the TA, and RA terminals of 3630A respectively.

Considering that the frequency of the measured signal is different from the test frequency of the vector network analyzer and the DUT is far away, the test signal is provided by a separate frequency synthesizer located near the DUT. In order to ensure the coherence of the entire test system, the Wiltron360B, signal source, and local oscillator use the same 10MHz signal as the reference signal .

Connect the ROURCE LOCK OUTPUT terminal to the RB terminal directly. Set the test socket of Wiltron360B to 3630A and the test frequency to f2. Since this system only tests TA/RA, and S11 is defined as TA/RA, set Wiltron360B to single channel display (SINGLE CHANNEL) and activate channel 1 (CH1). At this point, the main settings are completed and the test can be carried out.

In order to automate the test process, the computer remotely controls the vector network analyzer Wiltron360B through the GPIB interface. All settings and test data reading of Wiltron360B are automatically completed by the computer.

V. Conclusion

This test system is not concerned with the insertion loss and insertion phase shift of the DUT itself, but with the change in insertion loss and insertion phase shift when the state of the DUT changes. This is a relative measurement. The calibration system formed according to the above scheme can meet the required higher technical indicators and has been used in RF simulation tests.