Compact, wideband impedance tuner using a three‐line‐microstrip structure

Abstract

A novel three-line-microstrip compact impedance tuner is presented. It is based on a multimodal structure wherein six variable capacitances, implemented with two parallel-connected varactors each, create multiple interactions among the three-line-microstrip modes in a reduced circuit area. Experimental results show better-than-70% coverage of the Smith chart in an 85% frequency bandwidth from 1.4 to 3.2 GHz.Introduction: Impedance tuners are extensively used to implement tunable matching networks in power amplifiers [1] or antennas [2], and for load-pull or noise-parameter characterisation [3]. To provide flexibility in reconfigurable systems, the tuner should be compact in size, with a wide Smith-chart coverage and large fractional frequency bandwidth (FBW). Recent MOS and BiCMOS mm-wave tuners [2,3] exhibit a very small area, but limited (an estimated 35%) Smith-chart coverage. In [4] a small-size, low-power-consumption tuner for RFID applications using varactors is proposed featuring a 50% FBW (1.8-3 GHz), moderate (an estimated 64.3%) Smith-chart coverage, with complete coverage of all reflection coefficients with voltage standing-wave ratio (VSWR) lower than VSWR CC = 4.6 (and any phase) at 2.2 GHz. The integrated-passive device tuner using ferroelectric varactors in [5] features small size, and a 40% FBW (2-3 GHz) for an estimated 40% Smith-chart coverage and VSWR CC = 1.8. In [1] a substrate-integrated-cavity technology with piezoelectric actuated dishes is used to achieve a 37% FBW (2.5-3.9 GHz) with a 50% Smith-chart coverage, and VSWR CC = 2 in the 2.53.7 GHz frequency range.Multimodal circuits use multimodal waveguides to allow the propagation of more than one fundamental mode in the same circuit area. The additional modes increase the equivalent electrical length of the circuit, allowing for designs that are more compact. Multimodal circuits have demonstrated compact size and reconfiguration capabilities in structures such as filters [6].In this Letter, a novel varactor-loaded multimodal threeline-microstrip (TLM) structure is used to implement a wideband impedance tuner with a wide, uniform Smith-chart coverage in the whole operation band.

A 125–143-GHz Frequency-Reconfigurable BiCMOS Compact LNA Using a Single RF-MEMS Switch

“…propagation of more than one mode in the same circuit area. These additional modes increase the equivalent electrical length of the circuit and result in compact-size designs [10].…”