A bulk micromachined tunable dual-mode ku-band bandpass filter

This paper proposes a bulk micromachined tunable dual-mode bandpass filter. Splitting of odd and even degenerate modes in its resonators by perturbation, is utilized for bandpass filtering. Thus, the filter, with 4% bandwidth and 17 GHz midband, requires only half resonators of conventional micromachined devices, resulting in a more compact configuration. CPW (coplanar waveguide) and CPS (coplanar stripline) square-ring resonators and an open- circuited perturbation stub dominating passband are used. Actuation of two bulk micromachined switches placed symmetrically along resonator diagonal, may vary its electrical length, and shift both degenerate frequencies and tune filter mid-band frequency. Theoretical and finite-element fullwave tools are used to analyse the filter performance. A frequency shift of 0.6 GHz is seen, which is in good agreement with analytical solution of 0.58 GHz. Both original and tuned states present satisfying microwave performance, i.e. low passband insertion-loss (< 0.5 dB) and return-loss (<-15 dB) and high stopband rejection (>30 dB). The bulk micromachining is simpler than conventional ones for microswitches. Among the advantages, little mismatch between the micro bridges and the Pyrex glass substrate is demonstrated, and thus reliability at elevated temperature is greatly improved. Tested results of fabricated switch samples shows that the device may be a good candidate for novel Ku-band inter-scientific satellite, and handheld wireless gadgets.