Reseach Of Phase Shifter Based On Microshield Transmission Line

Microwave and Millmeter wave phase shifter is the key part of phased array in the communication and radar application, including analog phase shifters and digital phase shifters. Compared with analog phase shifter, the digital phase shifter is easy to adjust, and also has advantages like small phase deviation and short response time. Due to the large bulk and narrow operating frequency, digital phase shifter taking MEMS technology is arising gradually.This thesis researches a novel transmission line – MEMS microshield transmission line, aimed at theoretical analysis and three dimensional full-wave simulation. We analyzed basic operation principle of direct contact RF MEMS SPDT switches. Establishment of RLC circuit model of the switches is done and the circuit parameters are extracted, a measurement system of RF MEMS direct contact switches is then setup. Finally a 4-bit phase shifter based on RF MEMS direct contact switches is designed, manufactured and tested. The main content of the thesis includes the following:1.Transmission characteristics of Microshield line are studied. Conformal mapping method is employed to analyze microshield line quasi-statically, the numerical calculation and simulation are used to analyze transmission characteristics, including characteristic impedance and relative permittivity. The characteristic impedance has wide variation range and the relative permittivity approach to 1, which is good for transmission. At last, structure parameters(depth and width) of microshield line cavity is analyzed, and influence brought by changes of these parameters is investigated.2.Basic operation principles of RF MEMS SPDT switches are presented. According to actual size and test data, RLC circuit model of switches is established and the circuit parameters are extracted afterwards, complete RF MEMS SPDT switches equivalent circuit model is hence obtained. Fitting the analysis result and test data of switches, verifying the accuracy and precision of circuit model, the equivalent model is simulated using ADS. Finally a measurement system of RF MEMS direct contact switches is designed, we can test switching speed, S-parameter, lifetime, et al.3.A 4-bit phase shifter based on RF MEMS SPDT switches is designed. After determining the topological structure, size and shape of phase shifter reference line, delay line, T-stub and transmission line bend is designed. Simulation results show that insertion loss of each phase shift state at 1.7 GHz to 2.7 GHz is better than-1 dB, return loss is better than-17 dB, the precision of phase shifting is less than 1°. Practical test result shows that insertion loss of each phase shift state at 1.7 GHz 2.7 GHz is better than-2 dB, return loss is better than-8 dB, the precision of phase shifting is less than 2°, this basically achieves the goal. But in the phase shift state of 40°~75°, phase shifting degree of phase shifter raised 5° entirety, we then analyzed the error and proposed improving methods.