As was shown in [170,172], even for moderate RF frequencies, GaAs HEMTs,
and pseudomorphic AlGaAs/InGaAs HEMTs (PHEMTs) on GaAs substrates offer the highest PAE, output
power and gain on the FET side in this frequency range. Extremely high-power amplifiers at 2 GHz
using three terminal devices with saturated output power
= 200 W [136] have been
realized. By introducing a fourth terminal output powers up to
= 230 W [172] have
been achieved. In the X-band (8-12 GHz) amplifiers up to
= 39 dBm have been demonstrated,
e.g. by TNO in [74]. Combining these circuits in modules up to 70 W of output power have
been realized [283].
In the K-band (18-26.5 GHz) PAE is a major concern especially for satellite communication. A PAE of 68% was demonstrated at 18 GHz using PHEMTs [245], where also a compilation of data on K-band power amplifiers is given.
High-power amplifiers have been developed for radar applications at 35 GHz to replace
traveling wave tube (TWT) amplifiers. Recently, however, the Ka-band (26.5-40 GHz) has been faced
with growing attention due to the interest in high bandwidth, high-speed digital data transmission
applications such as Local Multipoint Distribution Services (LMDS) or Multichannel-Multipoint
Distribution Services (MMDS). The highest overall output power for a Ka-band high-power amplifier
on a single chip was realized by both [150] and [261] with
= 5 W at
27.5 GHz to 29 GHz and
= 4 W for
= 29 GHz and 31 GHz, respectively. Very recently,
= 6 W at 30 GHz on a single chip have been published in [86]. LMDS chip
solutions for mixers have been proposed, see e.g. [27,301]. An overview for LMDS
modules is given in [11]. Module solutions up to
= 6 W have been demonstrated by TRW
in [133]. A space qualified process for this frequency has been reported by UMS
in [125], or in a more complete description in [227]. Low noise amplifiers at
38 GHz were demonstrated by Ali et al. in [157].