A Continuously Tunable Wideband Differential Phase Shifter With Filtering Function and Passband Alignment

Wideband differential phase shifters with tunable phase shift and filtering passband alignment are proposed based on the varactor-loaded transversal interference structure. To overcome the problem of uncontrollable passband shifts while tuning the phase shift, a design method using the shorted stubs to align the position of transmission zero and isolate interference of varactors is proposed first. To further improve the alignment of the passbands corresponding to different phase shift values, coupled lines are adopted at transversal paths, resulting in additional transmission poles (TPs) to align the passband edges. Moreover, an evaluation formula is proposed to show the alignment performance. For verification purposes, two design examples are fabricated and measured, working from 0.75 to 1.65 GHz. The measured results show that the passband alignment rates (PARs) are 72% within a tunable phase shift range of 7°–127° and 95.9% within 0°–80°, respectively. A good agreement between measurement and simulation is verified. The proposed scheme is valuable for RF communication systems from a high integration and multifunction of view.

I. Introduction

Phase shifter is one of the critical elements in various RF/microwave systems, such as phased arrays [1] and beamforming networks [2], [3], and can improve the efficiency and linearity of active circuits [4]. The differential phase shifter was first proposed by Schiffman [5], which consists of a uniform transmission line and a coupled line using an edge coupling strategy. To support multiple wireless communication standards simultaneously within a system, wideband phase shifters utilizing cascaded or parallel connected coupled lines [6], [7] and broadside coupling structures [8] are proposed. With the development demand for miniaturization and integration of RF devices, the requirements of phase shifters for integration and multifunction become prominent.