Improvement on the image rejection ratio via phase error equalization and adaptive DC tuning in Hartley receivers: A practical approach

This paper presents a novel tunable method to improve the image rejection ratio in image-reject down-converters. The proposed technique is based on the phase equalization and amplitude error mitigation through proper biasing of mixers. With the aid of the proposed technique, amplitude, and phase imbalances, resulting in unwanted images, were minimized. Therefore, significant improvement in the image rejection ratio was attained without using complex filter banks. Phase equalization is accomplished by introducing a delay line to force the phase error to be zero at the center of the frequency band. A frequency down-converter was designed and built with discrete components for an L-band Hartley receiver, which operates over 950–1450 MHz. Image rejection performance of the proposed technique was shown by simulation and prototype-measurements. It is exhibited that the proposed easy to apply technique provides a considerable improvement in the entire band without disturbing the system. Consequently, an average of 50 dB and a maximum 77 dB image rejection ratio can be obtained in Hartley image rejection and dual-IF receivers without using traditional filters.