Digital Processing for Accurate Frequency Extraction in IFM Receivers

Abstract

Extracting the unknown frequency of a radar pulse has been one of the most challenging aspects of instantaneous frequency measurement (IFM) receivers. The conventional IFM receivers are limited in accurate frequency extraction by their design. In this article, a digital processing unit is added to the conventional IFM to extract the frequency with higher accuracy. A 2–4 GHz IFM has been designed combining the compact conventional RF section with the new digital processing unit using a novel efficient frequency extraction algorithm. The algorithm of minimum mean square error (MMSE) estimator is explored for use within the IFM, and it is proven that it can achieve much higher frequency accuracy. The novelty of this article includes both investigation and development of the algorithm to be a good fit for the frequency extraction in IFM receivers and also a digital implementation of the algorithm which meets the minimum requirements of an industrial IFM. The design has been implemented using microstrip filters on Rogers substrate and a Spartan-3E field-programmable gate array (FPGA) processor. The measurement results show promising achievements and verify the principle idea of digital processing for accurate frequency extraction in IFM receivers. The designed and fabricated receiver reaches 1.7 MHz rms frequency error in the frequency band of 2–4 GHz, which is at least $10\times $ improvement with respect to the state-of-the-art works.