The system makes full use of the control and calculation ability of 89C51 single-chip microcomputer, and adopts MCS-51 assembly language to design a microwave pulse test system based on average power method.
The average power method measures the average power of the RF pulse complex cycle and uses an auxiliary method to measure the duty cycle of the pulse. Let the pulse be a rectangle with a width of Ï„ and a repetition period of T. Then the pulse peak power is:
In the above formula, Q = Ï„ / T is the duty cycle of the radio frequency pulse.
When measuring, the pulse waveform is displayed with an oscilloscope, and the pulse repetition period T and the width Ï„ are measured. The average power Pav of the pulse is measured by the method of measuring the continuous wave power.
When using the attenuator and directional coupler, if the attenuation of the attenuator is A (dB), the directional coupler's transition attenuation is C (dB), and the directionality is infinite, then the pulse peak power is
When the pulse is a non-ideal rectangle, it must be multiplied by the correction factor K to correct, that is, Ppp = (KPavT / τ) & TImes; 10 (A + C) / 10. K is equal to the ratio of the peak power level of the actual pulse to the equivalent rectangular pulse level of the same width and area. K is often estimated, ideally rectangular pulse K=1. 
2 hardware componentsThe hardware of the system is mainly composed of a measurement module and a control module.
2.1 Measurement Module
In the measurement module, the microwave signal is converted into an electrical signal that is easily transformed and measured with a low frequency device. The measurement module is mainly composed of adjustable attenuator, directional coupler, matching load, peak detector, oscilloscope, thermocouple, etc., as shown in Figure 1.
The microwave power is first attenuated by the adjustable attenuator, and then the directional coupler couples part of the energy to the thermocouple and the peak detector respectively, and most of the remaining energy is absorbed by the matching load. The signal sent to the peak detector is displayed by the oscilloscope with its pulse waveform and the pulse repetition period T and width Ï„ are measured. The signal sent to the thermocouple is converted to a voltage signal by a thermocouple and sent to the control module for processing.
2.2 control module
The control module processes and displays the output signal of the measurement module and controls the operation of the whole system. The function is realized by the 89C51 single-chip microcomputer system, which is divided into four parts: human-machine interface, signal acquisition channel, serial communication and microprocessor. The composition is shown in Figure 2.
The microwave signal is converted into a voltage signal by the measurement module, sent to the input circuit for analog-to-digital conversion, and then the data is collected, saved, processed by the 89C51, and finally displayed on the display. Using the 89C51 serial communication resource, it can communicate with the PC via RS232 level conversion. Parameter settings and operational controls are available using the keyboard.
2.2.1 Human Machine Interface Section
The system uses a universal programmable keyboard and LED display dedicated intelligent control chip HD7279A, while managing 8-bit common cathode LED display and up to 64-key keyboard, it has automatic scanning display, automatic identification of key codes, automatic elimination of jitter and other functions. The serial communication between HD7279A and the microprocessor uses only 4 port lines, and the interface circuit between the microprocessor and the microprocessor is simple. The chip has a driving circuit inside, which can directly drive LED digital tubes of 1 inch or less. Two decoding methods of decoding circuit, the peripheral circuit is also simple and reliable. The keyboard is mainly composed of function keys and numeric keys. The display consists of 6 digital tubes, the first 4 displays the value, and the last 2 display units.
2.2.2 signal acquisition channel
The main component of the signal acquisition channel is the A/D converter MC1433. It is a 3-bit half (BCD code) monolithic dual-integration A/D converter with zero drift compensation. The chip can realize A/D conversion function with only 2 capacitors and 2 resistors. The signal acquisition channel also includes a range switching circuit, a zeroing circuit, and the like.
2.2.3 Serial communication
The system uses the serial port resources and clock resources in the 89C51 to realize serial communication with the PC, and realizes level conversion by using RS232.
2.2.4 microprocessor
The MCS-51 single-chip microcomputer used in this system adopts single bus structure, with on-chip oscillator, which can output clock signal; 1 full-duplex serial I/O interface, which can communicate with multiple machines; it has 16-bit address bus, Wide range of addresses, strong bit addressing, bit processing capabilities; rich and concise instruction system.
3 software expressionThe system software is written in MCS-51 assembly language, and the Cygnal integrated development environment (IDE) is used for download debugging. The system software mainly consists of the following two parts: the monitoring module and the data acquisition and processing module.
3.1 monitoring module
This part implements human-computer interaction functions, system initialization, system self-test, system zeroing, and control of the entire system, including keyboard analysis programs, zero adjustment procedures, and so on. The keyboard analysis program is written by state analysis method, which recognizes the operation of the keyboard and calls the corresponding function program module to complete the predetermined task. The basic block diagram is shown in Figure 3(a).
3.2 data acquisition and processing module
This module controls the I/O interface circuit for data acquisition and storage according to the functions and working modes set by the system; performs related processing on the collected data according to the parameters set by the system; manages the communication interface to realize remote management. Including automatic range conversion program, A/D conversion program, over limit alarm program, display program, etc. The basic block diagram is shown in Figure 3(b).
4 Error analysis The error of this system mainly includes the following components: (1) error of measuring power average; (2) measuring pulse width error; (3) measuring pulse repetition frequency error; (4) determining adjustable attenuation The error of the attenuation of the device; (5) determine the error of the transmission coefficient of the directional coupler.
Error processing method: The first three errors are mainly the error of the measurement part (ie, the instrument error). It can be processed by mathematical methods, and the correction can be performed by using a more accurate external indicator. The correction amount can be introduced to reduce the error of the measurement part. The last two errors can be reduced by using more sophisticated components.
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