Phase Locked Loop Oriented Research Of MEMS Microwave Phase Detectors

In the field of microwave technology, microwave phase is an important characteristic parameter of microwave signals. Microwave phase detection devices and circuits are widely applied in phase locked loops, phased-array radars, antennas as well as electronic countermeasures systems.Conventional phase detectors based on diodes and Gilbert multipliers are suffered from disadvantages such as complicate structures and small dynamic ranges. In comparison, MEMS phase detection structures based on vector combination are featured with simple structure, low power consumption and large detection range. For these reasons, this phase locked loop oriented research of MEMS microwave phase detectors is carried out in this paper, the main works and the innovations are described as follows:1. In terms of broadband demandsA broadband power combiner for X-band application based on GaAs MMIC technology is presented. In the structure, cascaded two sections of ACPSs are adopted for broadband performance.Design equations for structure parameters are obtained through even/odd-mode analysis.Simulations are taken out for structure optimization. Experiments demonstrate that the measured return losses is less than -14.9dB across the whole X-band; isolation is better than -10.7dB and insertion loss is around -3.7dB. More importantly, discrepancies of the S-parameters at different frequencies are small, which is verification for broadband performance.As a large chip size is resulted from the cascaded-line structure, a miniaturized broadband power combiner is presented based on capacitive loadings. Even/odd-mode analysis and HFSS simulations are also taken out for the design. A size-reduction of 60% is obtained. Broadband properties for X-band are demonstrated through measurements.2. In terms of modeling and third-order intermodulation distortion research of the capacitive MEMS microwave power sensorA capacitive MEMS microwave power sensor based on GaAs technology is presented. The conversion mechanism between microwave, force and capacitive is derived through multi-reflection theory. The the relationship between the membrane displacement and the input microwave power is obtained. Measurement results show that return loss is less than -49.1dB and insertion loss is around-0.1 dB over X-band. Power detection sensitivities for different operating frequencies are measured to be 11.4aF/mW at 8GHz, 11.1 aF/mW at 10GHz and 10.9aF/mW at 12GHz.In addition, the third-order intermodulation distortion of the presented capacitive MEMS microwave power sensor is also studied. Experiments show that the intermodulation distortion is rather small when the frequency interval is larger than 10kHz.3. In terms of modeling and temperature effect research of the thermoelectric MEMS microwave power sensorThe conversion mechanism between microwave, force and capacitive is analyzed for thermoelectric MEMS microwave power sensor. A new analytical method which can support full computer-aided circuit design is presented. A reduced dimensional form of heat transfer equation is built in radial direction based on point heat source approximation and precise volume mesh of the sensor. A computer-aided equivalent circuit model is established base on analogies between thermal and electrical variables, laying a good foundation for the application research of phase locked loops.Based on the experiments of temperature effect of the thermoelectric MEMS microwave power sensor, a temperature compensation approach is proposed by connecting an extra resistor with negative temperature coefficient at the output port of thermoelectric sensor. Its validity is confirmed by simulation.4. In terms of possibility exploration of MEMS microwave phase detection structures in the application of phase locked loopsIn order to explore the phase locked loop oriented application potential of MEMS microwave phase detection structures, computer-aided equivalent circuit models are established for power combiner, capacitive MEMS microwave power sensor and thermoelectric MEMS microwave power sensor. Two different kinds of phase detection structures can be established, the first kind is based on power combiner and capacitive MEMS microwave power sensor, and the second kind is based on power combiner and thermoelectric MEMS microwave power sensor. Equivalent circuit models of phase locked loops based on these two different phase detection structures are presented and studied. Based on comparison, the structure based on power combiner and thermoelectric MEMS microwave power sensor is chosen to be better suitable for the application in phase locked loops.5. In terms of performance research of MEMS microwave phase detectorsBased on the above research, a broadband MEMS microwave phase detector for X-band is presented. The fabrication process is compatible with the GaAs MMIC technology. Cosine tendency relations are revealed between the output voltages and the phase differences through measurements.The detection sensitivities at 200mW are 62.8?V/degree for 8GHz, 56.2?V/degree for 9GHz,52.4?V/degree for 10GHz, 55.0?V/degree for 11GHz and 50.9?V/degree for 12GHz. Broadband performance is verified.Meantime, a miniaturized broadband MEMS microwave phase detector is presented. Its occupied size is reduced by 60%. The measured sensitivities at 200mW are 116.9?V/degree for 8GHz,116.4?V/degree for 9GHz,109.3?V/degree for 10GHz,118.8?V/degree for 11 GHz and 101.2?V/degree for 12GHz. As can be seen, this miniaturized broadband MEMS microwave phase detector show superiority both in size and sensitivity.Furthermore, in order to fully reveal the application potential of this miniaturized broadband MEMS microwave phase detector, phase detection for large signals up to 1W are measured and cosine tendency is also seen. On the other hand, measurement is also conducted in case that the two input signals are not equal in magnitude.