Performance and Stability of Schottky Barrier Mixers

Vol. 51, No. 10, December, 1972 Printed in U.S.A. Performance and Stability of Schottky Barrier Mixers By C. DRAGONE ( M a n u s c r i p t received J u n e 2 1 , 1 9 7 2 ) We discuss the -performance of a Schottky barrier diode as a mixer when the barrier of the diode is open-circuited at the harmonics 2u>0 , 3w,, , etc. of the pump frequency u,, . Such a mixer is shown to be capable of arbitrarily high conversion gain provided coc ^ T]U0 , where is the cutoff frequency of the diode and ?7 is a parameter that is typically less than 6.25 and approaches 4 under certain ideal conditions. It is shown that the limit imposed by the series resistance of the diode on the double-sideband noise figure of the mixer is given by An experiment is described at 1.25 GHz on a room temperature mixer whose double-sicleband noise figure Fm as a function of gain has a minimum of about 0.7 dB (for gain less than unity) and a maximum of about 2.3 dB (for high gain). I . I N T R O D U C T I O N In the past five years the performance of microwave mixers has been substantially improved with the advent of high quality Schottky barrier diodes.1 The noise figures obtained so far are better by a factor of approximately 2 than those obtained previously using point-contact diodes. 1-4 The ultimate microwave noise figure obtainable with these devices is not yet known, but there is reason to believe that, at room temperature, a figure well under 3 dB is possible. Calculation in a previous article 5 showed that a Schottky barrier diode with suitable characteristics should have a noise figure well under 1 dB provided the barrier of the diode is open-circuited at the harmonics 2169 2170 T H E BELL SYSTEM TECHNICAL JOURNAL, DECEMBER 11)7*2 2oo,, , 3w,, , etc.