High-selectivity IPD bandpass filter based on multi-path transmission and transmission-zero control

To meet the demands of RF front-ends for out-of-band suppression and miniaturization, a high-selectivity filter topology based on multi-path transmission is proposed. The structure incorporates coupling matrix theory to construct multiple signal transmission paths and introduces multiple transmission zeros through phase cancellation at specific frequencies, thereby enhancing out-of-band suppression and frequency selectivity. The filter is miniaturized using IPD technology. Measurement results show that the filter has a center frequency of 6.2 GHz with an insertion loss of approximately 1.48 dB at the center frequency. The port reflection coefficient |S11| is better than −20 dB within the passband of 5.2–7.2 GHz. Transmission zeros are generated at 4.2 GHz, 9 GHz, and 9.4 GHz. An out-of-band suppression of about 20 dB is achieved at 1.66 f₀, with a shape factor of 1.63. The chip size is approximately 770 um × 620 um (0.0159 λ₀ × 0.0128 λ₀). These results demonstrate that the proposed filter possesses the advantages of high selectivity, good suppression, and miniaturization.