On-chip coupled-resonator filter with controllable transmission zeros based on hybrid coupling technique

A novel on-chip bandpass filter (BPF) design with controllable transmission zeros (TZs) for high out-of-band rejection is proposed using the hybrid coupling technique. The proposed hybrid coupling filter consists of two symmetrical hybrid coupling spiral structures where the mutual electric and magnetic couplings are introduced to generate two TZs in the high frequency band. The center frequency, bandwidth, and transmission zero position of the proposed filter can be well controlled. To illustrate the principle of this configuration, an equivalent circuit with odd- and even-mode analysis is discussed. Moreover, another transmission zero in the low frequency band can be further generated by loading a quasi-distribution structure. The proposed hybrid coupling filter is fabricated using commercial high resistance silicon technology. The measured results show that the proposed filter can achieve a 3 dB bandwidth from 1.85 to 2.33 GHz, which indicates a fractional bandwidth of about 26 %. In addition, more than 40 dB of suppression is achieved from 3.15 to 5.55 GHz. A return loss of 29 dB and a minimum insertion loss of 2.5 dB are achieved at the center frequency with a minimized size 1.6 mm × 0.8 mm. The simulated and measured results are in good agreement.