Design and implementation of intelligent debugging platform for cavity filters

0 Introduction

Microwave filters are widely used in satellite communications, relay communications, radar, electronic countermeasures and microwave measuring instruments. In satellite communication systems, the performance of microwave filters directly affects the communication quality of the repeater channel; for wireless communication systems, filters are a crucial microwave radio frequency device, and their use is of great significance for separating spectrum information, improving communication quality and preventing signal crosstalk. In today's increasingly complex electromagnetic environment and increasingly crowded spectrum range, microwave filters that realize important functions such as frequency selection and noise removal are increasingly valued by users.

Generally speaking, manual debugging of filters is actually a real-time iterative optimization process. In order to facilitate debugging, there will be tuning screws for debugging on the filter structure, or other forms of tuning elements, so that debugging technicians can change the resonant frequency of the filter resonant unit and the coupling amount between the resonant units during debugging. When debugging, the debugging technician repeatedly tightens the tuning screw according to the changes in the vector network analyzer graph until the performance of the filter meets the design requirements. For many debugging technicians, the manual debugging process is more like a craft than a science. Therefore, manual debugging of complex structure micro filters is generally completed by very experienced debugging technicians.

In the process of mass debugging and production, power capacity, temperature effect, material mechanical properties, passive third-order intermodulation and size restrictions are all important factors to consider in the actual processing of filters. The debugging of microwave filters has become a bottleneck problem in the industrialization process. At present, a large number of projects still rely on vector network diagnosis and manual debugging, which is difficult to achieve fast and accurate debugging, especially for inexperienced filter debuggers.

1 Principle and process of filter intelligent debugging

The purpose of developing a filter intelligent debugging platform is to continuously improve the debugging efficiency of microwave filters, greatly reduce the dependence of debugging on engineering experience, and reduce human labor as much as possible. The goal of the filter intelligent debugging platform is to establish an automated debugging platform with computers as the core, let the computer play the role of repetitive work and give it a certain level of intelligent judgment to guide the work of debuggers.

At present, intelligent debugging methods based on computer control are mainly divided into two categories: frequency domain method and time domain method:

(1) Time domain debugging method: This method mainly uses the frequency-time domain conversion of the signal to obtain the time domain response of the filter, find the change law between each adjustable component and the time domain response, and perform corresponding debugging. Among them, the more prominent one is the time domain debugging method proposed by Agilent. The disadvantage of this debugging method is that it requires an ideal time domain response of a well-debugged filter as a template. Moreover, for cross-coupled filters, there is no obvious relationship between the filter debugging parameters and the time domain response curve.

(2) Frequency domain debugging method: The basic idea of ​​this method is to apply various numerical calculation methods to the frequency domain response curve of the filter S parameters, extract the filter model parameters, find out the gap with the ideal model parameters, and perform corresponding debugging. This system adopts the frequency domain debugging method.

As shown in Figure 1, both methods are based on the equivalent circuit parameters, and the main steps are as follows:

① Test the response of the filter to be adjusted;

② Use the equivalent circuit model to extract parameters;

③ Compare the difference between the actual response extraction parameters and the ideal response ideal parameters;

④ According to the above differences, obtain the direction and amplitude of the next step of debugging, and change the actual position of the adjustable component;

⑤ Repeat the above steps ① to ④ until the measured response reaches the index.

2 Intelligent debugging platform for filters

As shown in Figure 2, the intelligent debugging platform for filters is mainly composed of computers, debugging machinery (such as motors), vector network analyzers, and filters to be debugged. Its basic workflow is: first, the vector network analyzer tests the filter parameters, and then collects the parameters into the computer, and through software analysis, the physical quantity that needs to be debugged is obtained, and then the computer controls the DC motor to drive the special debugging equipment to debug the debugging screws of the filter until the vector network analyzer tests that the filter parameters meet the design requirements.

2.1 Vector Network Analyzer

The vector network analyzer can fully evaluate RF and microwave devices. It includes an integrated synthetic source, test set and tuned receiver. The built-in S parameter test set provides full range amplitude and phase measurements in forward and reverse directions, as shown in Figure 3.

2.2 Debugging machinery

This solution uses a DC motor to drive a special debugging device to adjust the debugging screw to the best position. The current console is controlled by five motors, namely the x-axis, y-axis, z-axis, DM (motor for locking the nut), and DT (motor for tuning the screw); x, y, and z use stepper motors, and DM and DT use servo motors.

2.3 Industrial control computer

Run the corresponding software on the industrial control computer to read the test parameters of the network analyzer, analyze and calculate the physical quantities that need to be debugged, and then control the DC motor debugging equipment for debugging. As shown in Figure 4, the user only needs to click Start debugging in the software interface, and the debugging platform can automatically complete the debugging process, and can also provide friendly prompts for abnormalities that occur during the debugging process.

3 Conclusion

Microwave filters are widely used in the fields of communication, radar and measurement. With the development of society, their demand is also increasing. The debugging of microwave filters is a complex task, which requires rich practical operation experience. With the increase of the number of filter sections, the number of parameters involved in debugging also increases, and the difficulty of debugging also increases greatly. The introduction of intelligent computer-aided debugging technology can not only reduce the workload of debuggers, but also improve production efficiency, and has a good application prospect.

The intelligent debugging platform for cavity filters proposed in this paper can realize computer automatic debugging of filters. It can reduce the difficulty of experimental debugging of microwave components, shorten the debugging cycle, and greatly reduce the requirements for operator debugging experience. It is a very good way to improve the mass production capacity of microwave filters.