Ultra-wideband Microwave Mixer

The mixers with RF band overlapping with IF band are necessary for the wideband receiver, especially the channelized receiver of the communication system and the electronic countermeasure system, they need mixers to realize frequency conversion from the wideband microwave signals to base-band signals. The early single-ended mixer, single-balanced mixer, double-balanced mixer are restricted in these fields because of their shortcoming. The problem is solved by the invention of double-double balanced mixer. The double-double mixer circuit can be expected to have application in ultra broadband frequency mixer with IF band overlapping with the RF band. It is significant to manufacture double-double balanced mixer with good performance.This thesis overall views the historical development,mixer diodes,specification definitions and configurations of microwave mixers, and then discuss the advantage and shortcoming of several kinds of mixers and mixer diodes.The thesis presents a design procedure of double-double balanced mixer. The double-double balanced mixer consists of two schottky ring quad diodes and baluns. The balun is one of the most important elements of double-double balanced mixer, the microstrip tapered balun is employed, the thesis describes the theory in details of baluns. The thesis presents a novel design method of the tapered balun, the balun configuration is looked as three section: the first section is unbalanced port; the middle section is mode conversion section; the third is balanced port. The thesis presents a accuracy design method of tapped balun utilizing theory of non-standard microstrip line, theory of tapped line and theory of even and odd mode of broadside-coupled striplines. By using high frequency electromagnetic simulation software (HFSS) to simulate balun, the accuracy is certified.The thesis describes the theory of double-double balanced mixer in details and presents a design procedure of it. A 2-18GHz ultra-wide microwave double-double balanced mixer has been successfully developed. The RF balun and LO balun are mounted orthogonally, this method made it easy of the mixer mounted and can decrease leakage from LO large-signal to RF small signal, enhance the isolation of the mixer. The wide-band mixer exhibits RF, LO and IF bandwidth of 2-18GHz, 2-18GHz and 0.3-5GHz respectively with conversion loss less than 8dB, and LO to RF, LO to IF isolations all greater than 17dB. Double-double balanced mixers usually offer wider frequency conversion characteristic, better isolation, and broader IF port bandwidth than the other mixers. The mixer can be used in engineering and substitute some foreign mixers.