A Compact Multi-Mode Reconfigurable Filter with Coarse- and Fine-Tunable Pole–Zero Characteristics for Ku/Ka Multi-Band Applications

This work presents a compact, multi-mode reconfigurable filter fabricated in a 65-nm CMOS process for Ku-/Ka multiband applications. The filter employs lumped-element LC series and parallel resonant networks to realize two transmission zeros (TZs) and two poles, with the TZs intrinsically clamped between the poles. Coarse-tuning is achieved by controlling voltage-controlled switches, enabling wide-range relocation of the pole–zero frequencies, while voltage-controlled varactors provide continuous fine-tuning. This pole–zero tracking mechanism allows the filter to suppress high-frequency image signals in Ku-band satellite communication terminals and low-frequency image signals in Ka-band applications. Measurements demonstrate 15-dB stopband fractional bandwidths of 58% and 58.3% in the coarse-low and coarse-high modes, respectively, with maximum attenuations exceeding 33 and 40 dB. Fine-tuning shifts the stopband center frequencies continuously from 14.5–19.7 GHz and 24.1–26.9 GHz, respectively, in close agreement with electromagnetic simulations. The measurement results confirm its suitability for multi-band and tunable image-rejection applications.