Design of High-Performance Filtering Balun Based on TE01δ-Mode Dielectric Resonator

This paper presents a fusion design approach of high-performance filtering balun based on the ringshaped dielectric resonator (DR) for the first time. According to the electromagnetic (EM) field properties of the TE01δmode of the DR cavity, it can be differentially driven or extracted by reasonably placing the orientations of the feeding probes, which answers for the realization of unbalanced-to-balanced conversion. As a result, the coupling between the resonators can refer to the traditional single-ended design, regardless of the feeding scheme. Based on this, a second-order DR filtering balun is designed by converting a four-port balanced filter to a three-port device. Within the passband, the excellent performance of amplitude balance and 180° phase difference at the balun outputs can be achieved. To improve the stopband rejection by suppressing the spurious responses of the DR cavity, a third-order filtering balun using the hybrid DR and coaxial resonator is designed. It is not rigorously symmetrical, which is different from the traditional designs. The simulated and measured results with good accordance showcase good filter and balun functions at the same time.