| Summary: | 碩士 === 國立中央大學 === 電機工程學系 === 102 === In this study, in order to cooperate with the development of ALMA (Atacama Large Milli- meter/Submillimeter Array) Band-1 receiver front-end, novel absorptive bandstop filter (ABSF) implemented using GaAs semiconductor process is proposed. The proposed ABSF can help minimize the impact of LO-to-RF leakage on the conversion loss degradation of mixer in the ALMA Band-1 receiver.
First, novel design method of ABSF is proposed and a complete design procedure and formulae are established. The proposed ABSF structure is based on introducing resistor to the bandstop resonator appropriately so as to dissipate the reflected signals in the stopband. The design of a 3rd-order ABSF is presented to demonstrate the achieved performance, and it is used for verifying the proposed design formulas. The ABSF is designed with a fractional bandwidth of 5% and a center frequency of 2 GHz. The measured return loss is better than 17.92 dB in the passband. The measured rejection at stopband center frequency is 34.83 dB, and the maximum stopband power dissipation is 99.8%.
Second, the Q-Band ABSF for ALMA Band-1 receiver application is proposed. The stopband frequency is from 31 to 33 GHz, which corresponds to a stopband fractional bandwidth of about 7%. The passband frequency is from 35 to 52 GHz. The ABSF is implemented in GaAs using the WIN 0.15 um pHEMT process, and the chip size is 2.5 mm×2 mm. In the measured results, more than 93.4% of the power within the stopband can be dissipated by the proposed ABSF, and the rejection at the stopband center frequency is 35.6 dB. The insertion loss is better than 2.44 dB and the return loss is better than 15.23 dB in the passband. To facilitate the receiver system integration, the proposed ABSF is then integrated with the bandpass filter on the same chip.
Compared with other related previous works, the proposed ABSF features a complete and simple design procedure with better design flexibility. The stopband bandwidth, filter selectivity and passband ripple can all be designed according to the specifications. The proposed ABSF is easy to realize such that it is helpful for applications in front-end receiver designs.
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