Miniaturized Wide-band Power Detection Module Design And Realization

Microwave power measurement has an important academic and commercial value in many areas such as microwave communication, radar, remote sensing of environment and medical research. The modern technology of microwave power measurement is moving in small, modular, wide-band and other directions. After analyzing the development of microwave power measurement technology in today’s domestic and foreign, combined with the requirements of wide-band and high power microwave projects, this paper designed the overall indicators and plan of the miniaturized wide-band power detection module. It’s mainly composed of four parts, they are microwave power coupler, switch filter banks, microwave power detector and a display with protection circuit.The stripline directional coupler was designed in ADS09 and IE3 D to make the power measurement system be embedded in the system to detect in real time by using the directional measurement. The coupler’s frequency is 6GHz~18GHz, the degree of coupling is 20±0.7dB, the direction is better than 16 dB, SWR is less than 1.2, the insertion loss is less than 0.3dB and has a smaller size. In the engineering applications, the microwave signals are always mixed with harmonics. This system uses the switch filter banks to achieve the separation of the fundamental and harmonic waves, which is the innovation of this measurement system. The microwave switches are Agilent N1810 UL electromechanical coaxial switches with high performance, whose frequency is up to 26.5GHz, insertion loss is less than 0.7dB, SPDT. The filter banks are composed of 6GHz~10GHz, 10GHz~18GHz two channels band-pass filters, which have high Q value and low loss of suspended stripline. Two band-pass filters’ insertion loss is less than 0.5dB, reflection is greater than 15 dB, out of band rejection is greater than 40dB(offset 300 MHz), have a similar performance. The core of the system to detect microwave power is the microwave power detector module. A detector with a circuit model of wide-band matching in front-end and a low-pass filter in back-end was designed based on SMS7630-061 Schottky diode. Its reflection and insertion loss are simulated by S-parameter simulation, and the curve of input power-output voltage is simulated by harmonic balance simulation. The power range of the detector after processing and assembly is from-35 dBm to 10 dBm in the 6GHz ~ 18 GHz.As a back-end section of signal processing, the display and protection circuit module needs to convert the analog output of the power detection module to digital signal, then gets the corresponding power value after arithmetic average filtering, looking-up table, piecewise linear interpolation and other algorithms. The system uses a 24-bit ADC module ADS1220 with high sampling accuracy. The core controller is the STM32F103VCT6 in ARM series, which have rich integrated feature. The UART and LCD touching screen achieve Human-computer interaction of input and output in different occasions. In addition, when the comparator detects a power that exceeds a certain threshold, the MOSFET switch circuit selects, cutting off power to protect the signal chain and the key components of microwave system. At last, we analysis of the mismatch error and temperature error that present in the system, and raise the correction methods of these error.Finally, we completed the design of miniaturized wide-band power detection module, which has a small size(about 250mm*75mm*55mm), flexible connection form and low cost. The real-time system can detect the power(average power) of 6GHz~18GHz wide-band microwave signals accurately, and realize the measurement of fundamental and harmonic waves’ power dividually. Its power range is from-15 dBm to 30 dBm, the measurement error is less than ±0.4dB, with the characteristics of miniaturization, digitization, good accuracy and repeatability, etc. And it has an alarm of overload power and automatic protection of microwave circuitry.