The desired 0° and 180° phase characteristics of the RRC are realized by the inherent in‐phase and out‐of‐phase electromagnetic fields of the dual‐mode CSIW cavity. The FRRC is developed in a single CSIW cavity embedded with four CPW resonators and four feeding ports, featuring miniaturized size. In this paper, an approach to designing filtering rat‐race coupler (FRRC) with hybrid circular substrate integrated waveguide (CSIW) and coplanar waveguide (CPW) resonators is proposed. Moreover, the first spurious response for the proposed filter topologies was pushed to 3fo, resulting in a wide stopband. Minimum insertion loss of 1.7 dB and 1.5 dB was observed for the two trisection filters, respectively, while the hybrid configurations caused significant size reduction in the overall filter size. The first filter generates a TZ below the passband, while the second one produces a TZ above the passband. To validate the proposed hybrid configurations, two X‐band trisection filters with 6.5% and 6.2% fractional bandwidth were designed. The main‐line couplings, on the other hand, are formed by mixed‐coupled λ/4 and λ/2 resonators.

The desired cross‐couplings for transmission zeros (TZs) are realized by parallel‐coupled transmission‐line sections (J‐inverter) or coupled via sections (K‐inverter) of λ/4 resonators.

This paper presents the design of compact cross‐coupled microstrip trisection bandpass filters based on the hybrid structures of quarter‐wavelength (λ/4) and half‐wavelength (λ/2) resonators.

Tz designbox