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A Discussion of Power Coupling Bandwidth Limitations of Planar Schottky Diodes at Submillimeter Wavelengths

Authors:
J. L. Hesler, B. Gelmont
Abstract:
Planar Schottky diodes can be used to build sensitive, rugged and reproducible mixers that operate at room temperature. Discrete-chip surface-channel planar Schottky barrier diodes have been used in the development of receivers at frequencies up to 700 GHz with performance comparable with that of the best whisker contacted diodes. However, the packaging parasitics of the planar diode geometry have limited the development of such mixers at higher frequencies. The planar diode chip can be modeled as a set of lumped capacitors (representing fringing fields around the diode) and inductors (representing the metal connection lines) that affect the coupling of power to the diode junction. Bode and Fano showed that there is an inherent limit to the bandwidth over which power can be coupled to a complex load of this sort using a lossless passive coupling circuit. We have extended the Bode-Fano theory to circuits with three or more elements, and have used this theory to examine limitations to mixer design caused by planar diode packaging at submillimeter wavelengths. In particular, we have examined the coupling bandwidth limitation for a discrete-chip surface-channel planar Schottky barrier diode mounted in a microstrip channel. The simulations indicate that for diodes chips with semi-insulating GaAs support substrates at frequencies around 500 GHz the coupling of power to the anode is not significantly limited by the chip parasitics. However, at frequencies above approximately 1000 GHz, the packaging parasitics impose tight limits on the power coupling bandwidth, thus complicating mixer design. The bandwidth limitation condition derived here is general and can be used to explore power coupling limitations for a variety of devices and structures.
Categories:
Mixers, Schottky Devices
Year:
1998
Session:
4
Full-text:
Download a PDF of this paper.
Page Number(s):
173-180