Compact IPD Bandpass Filters Based on Coupling-Enhanced Transformer and Metamaterial Lowpass Structure

Two compact bandpass filters (BPFs) based on the coupling-enhanced transformer and metamaterial lowpass structure are presented. The coupling-enhanced transformer is introduced to reduce the insertion loss in the desired passband. Moreover, for the first time, a new metamaterial lowpass structure is proposed to generate multiple transmission zeros (TZs) and can achieve high stopband suppression in a wide upper stopband. Its even-odd mode equivalent circuits are discussed, and its Bloch impedance and dispersion are analyzed. The first BPF operates at 1.85 GHz and the second BPF operates at 2.45 GHz, which can achieve an insertion loss of less than 1.0 and 0.8 dB, respectively. These two BPFs can achieve 30 dB attenuation from 4.7 to 7.5 GHz and 20 dB attenuation up to $7.2~f_{0}$ , respectively. Both designs have a compact size of less than $1.3\times 10^{-2}~\lambda _{0} \times 6.5\times 10^{-3}~\lambda _{0}$ . Two prototypes are fabricated using Si-based integrated passive devices (IPDs) technology and validated with measurements.