Design and Implementation of a Reconfigurable Wideband Radio Frequency Spectrum Analyzer with Image Rejection in the Digital Domain

Abstract

Most existing radio frequency (RF) spectrum analyzers use conventional superheterodyne architecture to remove images associated with the down conversion of RF input frequency to some intermediate frequency (IF) for further processing, and their complexity increases as the frequency range of interest is extended. This article describes a novel digital system architecture for spectrum analyzers based on quadrature down conversion. Quadrature down conversion architectures where image responses are inherently rejected are normally used to analyze a single frequency or a very narrow frequency spectrum. This article proposes using quadrature architecture in an ultrawideband spectrum analysis application. A wideband spectrum analyzer receiver with compensation for gain and phase imbalances in the RF input range, as well as compensation for gain and phase imbalances within the IF passband complete with resolution bandwidth (RBW) filtering, video bandwidth (VBW) filtering, and amplitude detection, is implemented in a low-cost field-programmable gate arrays (FPGAs). The proposed method still achieves the desired image rejection performance specification, is power-efficient, and significantly simplifies the RF front-end hardware in comparison to state-of-the-art methods.