Q-band GaAs bandpass filter designs for ALMA band-1

We report on the design and experimental results of Q-band GaAs bandpass filters (BPFs) for the Atacama Large Millimeter/submillimeter Array (ALMA) band-1 receiver. The BPF is required to reject the lower side band from 15.3 to 29 GHz while retain minimum insertion loss across the passband of 31.3 to 45 GHz. In order to reduce the size and weight of receiver module effectively, on-chip BPF designs using the commercial GaAs process are proposed. The parallel-coupled BPF with quarter-wavelength resonators is adopted to achieve a wide fractional bandwidth of about 37%. In addition, the capacitive/inductive loaded coupled-line and the stepped-impedance resonator are used to largely reduce the filter size. Moreover, the cross-coupling effect is introduced to create transmission zeros, such that the required 25 dB stopband rejection below 29 GHz can be achieved. Specifically, two GaAs BPFs with sizes less than 1.24 X 0.8 mm₂ are demonstrated. They will be applied to the multi-chip-module version of ALMA band-1 receiver prototype for further system evaluation and feasibility studies.