A Compact Impedance Measurement Solution for Systems Operating in Load Varying Scenarios

Abstract

This paper presents a compact solution for impedance calculation obtained from low phase resolution stationary wave measurements, for RF power systems operating in load varying scenarios. The implemented system is based on a bi-directional coupler and makes use of the stationary wave periodicity, which is synthesized and measured via a digital phase shifter, a power combiner, and an envelope detector, in a specific arrangement. Instead of sampling a transmission line at various spatial points (sampled line architectures), both incident and reflected waves are sampled at one specific position, the stationary wave is obtained by sweeping the incident or reflected waves' phase, mimicking the slotted line principle and, from there, the impedance is obtained using a new signal processing algorithm that is now presented. Taking advantage of the developed technique, this can be done for only three phase shifter states, making the measurement fast and accurate. This compact measurement solution can compute the impedance of both real and complex loads inside a 2.1 voltage standing wave ratio circle with high accuracy (-28.8 dB) at a rate of 1 kHz and is appropriate for high power systems due to its simple architecture and very low total losses (0.075 dB).

Keywords

• Impedance measurement
• impedance mismatch
• power systems
• stationary waves