Three-Port Reflectionless Down-Converter for Wideband and Multichannel Receiver With Flat Gain, Enhanced EVM, and High Stability

Abstract

This article presents a three-port reflectionless down-converter to achieve flat gain, enhanced EVM, and high stability for wideband and multichannel receivers. The downconverter consists of a mixer with three reflectionless filters at IF, RF, and LO ports. The analysis of the proposed reflection model demonstrates that the elimination of reflected signals alleviates the problems of gain fluctuation and harmonics generation. Meanwhile, reflectionless operation effectively improves the dynamic range of the receiving system. To verify the mechanism and operation mentioned above, a series of reflectionless down-converters is designed and fabricated. The measurement results fully confirm the theoretical analysis, in which the three-port reflectionless converter supports a 300 MHz 256-QAM signal with an error vector magnitude (EVM) of 3.02%. The EVM of 400 MHz 64-QAM signal is below 4.50% when overlap bandwidth varies from 0 to 400 MHz. For an eight-carrier signal of 40 MHz 256-QAM, the proposed three-port reflectionless converter maintains the EVM difference among each channel lower than 0.15%.