A compact semi-lumped tunable complex-impedance transformer

Abstract

-This article describes the design and performance of a compact tunable impedance transformer. The structure is based on a transmission line loaded by varactor diodes. Using only two pairs of diodes, the circuit is very small with a total length of only λ/10. Both the frequency range and the load impedance can be tuned by varying the varactor bias voltages. Our design provides a tunable operating frequency range of ± 40% and an impedance match ranging from 20 Ω to 90 Ω at 0.8 GHz and from 30 Ω to 170 Ω at 1.5 GHz. In addition, a new approach that considers losses for the simulation and measurement of this impedance transformer was investigated. The measured performance of a 1 GHz prototype design confirmed the validity of this new approach.

Power Amplifier Efficiency Enhancement Using Adaptive Load Transformation

“…Adaptive impedance transformers for load modulation are required for that purpose. Such impedance transformers using reverse biased varactor diodes are presented in [4,5]. The varactors are placed in lumped element transmission line equivalent networks or between line and ground metallization in coplanar waveguides.…”