The performance of backward diodes as mixers and detectors at microwave frequencies

Abstract

The physical properties of a backward diode, together with the parameters of a microwave mixer and low-level detector are briefly reviewed, indicating the choice of a bonded-contact structure and n-type germanium. The microwave performance of such a diode is discussed with particular emphasis on optimizing the diode for low-level detector and Doppler mixer applications.Results of r.f. performance at X-band frequencies are illustrated. These show that bonded backward diodes may be fabricated with improved detector and Doppler mixer characteristics compared with conventional point-contact microwave diodes. Further, the desirability to optimize their characteristics for a particular application is examined. Zero-bias tangential sensitivities of -62 dBm (1 Mc/s video bandwidth) have been achieved. The low-frequency noise properties of the backward diode indicate a potential receiver noise figure performance of about 16 dB at 3 kc/s intermediate frequency. The ability of the bonded backward diode to operate satisfactorily as a mixer (i.f. = 45 Mc/s) with very low local-oscillator power is shown.Finally, the performance of a bonded backward diode under development primarily as a detector is discussed. Measurements at zero bias indicate tangential sensitivities of -56 dBm (1 Mc/s video bandwidth) and video impedance about 800 Cl, whilst maintaining a mixer performance of about 8 dB. Further, this performance is shown to be substantially independent of temperature. The resistance of these devices to damage by electrical overloads is shown to be comparable with conventional point-contact microwave diodes.

A Study and Design of a Rat-Race Coupler based Microwave Mixer

“…A microwave mixer [1][2][3][4][5][6][7][8] is a device that up-concerts low frequency signal to microwave signal, and down-converts microwave signal to a corresponding base-band signal. The most usual application of mixers is in transceiver where two frequency beat together to generate two different frequencies, i.e., sum and difference of the two frequencies.…”