Broadband Tunable Phase Shifter and Attenuator Using Bandwidth Expansion Property of Dual Microstrip Stubs Loaded Slotline Structure

This article proposes the design methods for broad-band 90° phase shifter (PS) and continuously tunable phase shifter (CTPS) using bandwidth expansion property of dual microstrip stubs loaded slotline structure. Firstly, the matching characteris-tics and phase shift characteristics of the dual λ/4 microstrip stubs loaded λ/4 slotline structure are theoretically analyzed, and the principle of expanding the bandwidth of the phase shifter by in-troducing transmission poles and zero points of the phase shift slope is clarified. Secondly, a CTPS is designed based on a new mechanism of varactor-loaded slotline, which utilizes the band-width expansion characteristics of the dual λ/2 microstrip stubs loaded two λ/4 slotline structure and theoretically achieves a band-width of 42.6% and a low in-band phase error of ±2.9° with more than 90° phase shift range (PSR). In order to verify the correctness and practicality of the theoretical analysis, the above PSs are em-ployed as constituent units to design two applications: 1. A 360° PS is implemented using the hybrid structure. 2. A variable attenua-tor (VA) is designed by a new method of vector-sum. Benefiting from the broadband and low phase error features of the CTPS, the proposed 360° PS achieves a 10 dB return loss (RL) and ±5.4° in-band phase error in a wide fractional bandwidth (FBW) of 40%, which is highly competitive compared to other works. The pro-posed VA can realize an attenuation range of 18 dB from 2 to 3 GHz, and it has the advantage of low insertion phase error.