Design of a New Dual-Band Balanced-to-Balanced Filtering Power Divider Based on the Circular Microstrip Patch Resonator

A novel compact dual-band balanced-to-balanced (BTB) filtering power divider (FPD) based on the circular microstrip patch resonator is presented, for the first time in this brief. Firstly, in order to elucidate its principle of operation, the resonant property of the circular microstrip patch resonator is researched. After that, a prototype of the dual-band BTB FPD is developed. It is mainly constructed by two coupled circular patch resonators, two impedance matching ports, and three pairs of balanced ports. Its operating mechanism can be strictly illustrated by the field distributions of the concerned resonant modes. Hereinto, desired dual-band balanced filtering response is attained by elaborately exploiting TM₁₁ and TM₃₁ modes while suppressing other modes from the patches. Ultimately, for validation, a dual-band BTB FPD centered at 4.2 GHz and 9.4 GHz is designed, fabricated, and tested. Good agreement between simulated and measured results validates that expected differential mode (DM) response, prominent DM isolation, nice common-mode (CM) suppression, high selectivity, and satisfactory harmonic suppression.

I. Introduction

With the development of modern communication systems, microwave devices have been widely used. Compared with traditional single-ended devices, balanced components have higher immunity to environmental noise, better dynamic range, and lower electromagnetic interference. Due to these advantages, balanced components are becoming more and more attractive in modern wireless communication systems. Among them, balanced-to-balanced (BTB) bandpass filters (BPFs) and BTB power dividers (PDs) have been widely explored [1]–[8]. For example, a BTB PD and a balanced-to-unbalanced (BTU) PD based on DM-CM converter with wideband DM passband and CM suppression was proposed in [4]. Another differential wideband BPF is also implemented by coupled microstrip line in [7]. In addition, a balanced BPF with high CM suppression and high selectivity is also introduced in [8]. Recently, in order to better meet the requirement of the modern wireless communication system for components miniaturization, a novel component called BTB filtering PDs (FPDs) are put forward, in which both functions of BTB PDs and BPFs can be achieved simultaneously [9]–[13]. For instance, in [9], a new BTB FPD is designed based on the square patch resonator. Besides, the balanced dual-band FPDs are presented in [11] and [13] with good isolation and high wide stopband, respectively.