A 10W IMPATT Diode Amplifier for X-Band Communication Systems

Abstract

A two stage ITAPATT diode amplifier with an output power of 1OW has been developed for use in a digital radio relay system operating in the 10.7 to 11.7 GHz freauency band. The amplifier consists of a 6 dB gain out-put stage, combining the outputs of two 4W high efficiency IIVEPATT diodes, preceeded by a similar stage with 10 dB gain using two 1.5-2W TPb,TPATT diodes. The combining circuit is based on Rucker's [1 symmetrical multidevice combining circuit and is realised in coaxial troughline. The practical details of the combining circuit are discussed in a subsequent secti-on which also describes the RF performance of the circuit. DEVELOPMZENT OF HIGH EFFICIENCY INEPATT DIODESIn order to realise a 1OW output power with the minimuim number of active devices, it has been necessary to develop high efficiency IMIPATT diodes. Single diodes give output powers in the 2-3W range with 20% efficiency. However, if two or three diodes are bonded in parallel in one package, output powers of 4-5W can be obtained reproducibly. It is then a simple matter to use combining ci.rcuits to reach the desired 10W output power.The diodes are fabricated at the Post Office Research Centre[2] from GaAs material with a high-low dopitg profile,nd a drift region doping density of 6 + 0.5 x 10 atoms cm .The width of the high-doped region is adjusted chemically to yield a DC breakdown voltage of 28-32v. Such a tight specification is necessary to avoid discontinuous changes of amplifier gain with RF drive associated with the premature collection mode in the upper part of the 10.7 -11.7 GHz frequency band.Devices destined for the output stage of the amplifier consist of arrays of two 160m or three 140 eu-m diameter diodes capable of an output in the 4.5-5W range with a DC to RF conversion efficiency of at least 20%. The diodes are symmetrically interconnected by a perforated gold tape which is thermocompression bonded to the toD contacts of the diode and the metallised surface of a low profile ceramic ring package.The lower power requirements of the driver stage allow devices consisting of one 160 or 140 ,czm diameter diode to be used.