Lumped Dual-Band Transformer with Chebyshev and Quasi-Elliptic Responses Based on GaAs-IPD

In this article, the design method of dual-band (DB) transformers with Chebyshev and quasi-elliptic responses has been proposed. This method not only enables arbitrary combinations of bandwidth and impedance transformation ratio but also achieves typical Chebyshev responses or conveniently introduces arbitrary transmission zeros (TZs) for quasi-elliptic responses, compared to conventional transformers. Ultra-compact lumped prototypes, fabricated using GaAs integrated passive device (IPD) technology, successfully realize DB Chebyshev transformer (DB-CT) and DB quasi-elliptic transformer (DB-QET) with impedance transformations from 10 to $50~\Omega $ , operating at 2.25 and 3.1 GHz, respectively. The devices achieve a bandwidth of 22% in both operating bands, with minimum in-band insertion losses of 1.3 and 1.45 dB, respectively. Due to the lumped form and the introduced TZs of DB-QET, up to seventh-order harmonic suppression and rapid out-of-band attenuation can be observed. Additionally, the grounded-shielding metal fence (GSMF) structure added to the devices demonstrated excellent electromagnetic (EM) interference shielding performance. The simulated and measured results of the proposed devices exhibit good consistency.