||In order to improve the high insertion loss of traditional silicon-based stack coupler and non-four-phase output characteristics. This thesis presents the planar suspended four-phase quadrature coupler utilizing surface micromachining technology to reduce insertion loss and compact size, and can be applied to the manufacturing of the front-end receiver for next-generation mobile communication systems.|
To achieve the four-phase quadrature coupler with four-phase output, low insertion loss and high isolation characteristics, the main fabrication processes in this thesis including: (i) utilize suspended structure to reduce the insertion loss caused by parasitic capacitance between device and substrate, (ii) construct of a tandem coupler with center-tapped balun to perform four-phase output, (iii) use the air dielectric layer of MIM capacitors input/output ports matching by employing high frequency simulation software (HFSS and ADS) to optimize the analysis of the coupler. The suspended four-phase quadrature coupler constructed of supported post, bottom electrodes, vias and top electrodes. The main fabrication processes including four thin-film depositions, four graphic definitions of photolithography, four copper electroplating and etching processes.
The chip size of the suspended four-phase quadrature coupler is 22 mm×12.8 mm×71 µm, and measured by network analyzer under frequency range from10 MHz ~ 4 GHz. First generation of suspended coupler result of measurement shows its center frequency is 825 MHz, the insertion loss of four output ports are -41, -44.7, -44.7 and -44.7 dB, the phases of four output ports are 88°, 21.7°, -74.7° and -175.3°, input return loss and isolation are -3.9 and -32 dB, respectively. Second generation of suspended coupler with the improvement of slotting cavities on the ground plane structure. The measurement results show the center frequency is 1.05 GHz, insertion loss of four output ports are -45, -47.9, -49.8 and -51.6 dB, input return loss of -4.53 dB, isolation of -37.7 dB, and the phase of four output ports are 138°, 56.1°, -25.9° and -145°. Obviously, the insertion loss and phase of bandwidth can be further increased and more close to the simulation.