Design of Balanced and Balun Filters Using Dual-Mode Cross-Shaped Dielectric Resonators

In this paper, a dual-mode cross-shaped dielectric resonator (DR) that consists of two identical rectangular DRs is investigated to design balanced and balun bandpass filters (BPFs) for the first time. According to the dominant TE11δ-mode electromagnetic field of a single rectangular DR, the driven signals for the DR through two probes on the two sides of the DR should be antiphase. Equivalently, the extracted signals from the DR operating at TE11δmode are positively out-of-phase. Based on this, a four-port balanced TE11δ-mode BPF using a single dual-mode DR cavity can be constructed. Furthermore, by converting the balanced BPF into a three-port device, a novel balun BPF using the same DR cavity is designed, showcasing excellent performance of amplitude balance and 180° phase difference. To validate the proposed idea, the balanced and balun BPFs are designed and implemented, respectively. Both of them have a miniaturized circuit size due to the adoption of the dual-mode DR. Good agreement can be obtained between their respective simulated and measured results.