X-Band Quasi-Reflectionless MMIC Bandpass Filters With Minimum Number of Components

This article reports on the RF design and implementation of monolithic microwave integrated circuit (MMIC) bandpass filters (BPFs) with broadband symmetric quasi-reflectionless characteristics. They are based on in-series cascaded quasi-reflectionless stages that comprise one bandpass (BP) and two resistively terminated bandstop (BS) sections with approximately complementary transfer functions. This allows the resistors to absorb the reflected RF signal energy, and a quasi-reflectionless behavior is obtained at both the input and output ports of the BPF. The frequency selectivity of the BPF can be increased by: 1) introducing out-of-band transmission zeros (TZs) through inductive, capacitive, or resonant source-to-load couplings and/or by 2) increasing the number of stages in the overall filter. An on-chip integration scheme with minimum number of components is proposed using the commercially available PIH-110 GaAs MMIC process from WIN Semiconductors. Three prototypes were designed, manufactured, and measured at X-band. They demonstrated ultra-compact physical size and ultrawide >9:1 quasi-reflectionless characteristics.