Design of Compact GaAs-Based On-Chip Filter and Duplexer With High Selectivity and Wide Stopband

In this letter, an on-chip filter and duplexer with compact size and wide stopband are proposed. A novel design methodology is proposed to improve the performance of the lumped-element circuits by judiciously analyzing and applying the distributed-element resonators. First, a half-wavelength stepped impedance resonator (SIR) is embedded into a third-order Chebyshev LC filtering circuit, bringing two additional poles and two transmission zeros (TZs). Then, it is substituted by equivalent lumped-element section for size reduction and spurious-mode elimination. The operating mechanism of the fifth-order filter is revealed by its even-and odd-mode equivalent circuits, and the design procedure is also summarized. Two types of modified loading structures are investigated to achieve responses with specified TZs located on either the left or right sides of the passband. By simultaneously utilizing the two unique bandpass filters (BPFs) as two channels, a duplexer with high isolation and wide bandwidth is implemented. The BPF and duplexer are realized by the GaAs technology for 5G and WIFI 6E wireless systems. These on-chip integrated passive device (IPD) devices show advantages in compact size, high isolation, and deep rejection.