An analysis of the microwave (f > 1 GHz) properties of field-emitter arrays (FEAs) and several representative medium power (10-100 W) microwave amplifiers employing FEAs is presented. The FEA analysis is limited to parallel-plate structures having discrete pointlike vertical emitter tips and gate apertures aligned to each tip. A transmission line analysis of wave propagation in this structure is presented and used to evaluate the geometries and materials needed for microwave operation. This analysis is used to investigate the performance capabilities and emitter requirements of both modulated-emission linear beam tubes and microdevices based on FEAs. Specific microtriode designs are used to investigate practical problems such as space charge and thermal effects. Competitive performance should be achievable in gated-emission linear beam tubes by using FEAs that perform at levels previously reported by several laboratories. Existing FEA technology (currents of 10 muA per emitter, transconductances of 1 muS per emitter, 1 mum oxide thickness, and 3 mum emitter spacing) is suitable for use in cavity klystrodes(R) at frequencies through 10 GHz, and in moderately bunched beam (bunch width of 180-degrees), octave-bandwidth traveling-wave-tube applications through 3 GHz. Extending the operating frequency and/or reducing the bunch width will require a larger ratio of transconductance to current. Microtriodes operating at 10 GHz will benefit from a modified FEA structure and improved emitter performance. An extra acceleration electrode must be added above the gate aperture to alleviate problems due to space charge between the gate and collector, and the gate oxide thickness must be increased 10 at least 2 mum. A FEA incorporating these features and capable of producing 5 muS and 100 muA per emitter could generate 130 W from a 5-mm-wide device with 8.6 dB gain, 7% bandwidth, and 36% power added efficiency. To allow higher gain and wideband operation, the transconductance at a given current must be increased. A FEA capable of producing 5 muS at only 10 muA per emitter would result in a microtriode with more than 1 octave bandwidth, 45 W output power, 10 dB gain, and 34% power added efficiency. Anode-to-case temperature differences of less than 100-degrees-C appear possible in this device if BeO is used as the dielectric.
