Monolithic microwave integrated circuits based on silicon-on-sapphire (SOS) and gallium arsenide technologies are being considered seriously as viable candidates for satellite communication systems, airborne radar, and other applications. The low-loss properties of sapphire and semi-insulating GaAs substrates, combined with the excellent microwave performance of metal-semiconductor FET's (MESFET's), allows, for the first time, a truly monolithic approach to microwave integrated circuits. By monolithic we mean an approach wherein all passive and active circuit elements and interconnections are formed into the bulk, or onto the surface of the substrate by some deposition scheme, such as epitaxy, ion implantation, sputtering, evaporation, and other methods. The importance of this development is that microwave applications such as airborne phased-array systems based on a large number of identical circuits and requiring small physical volume and/or light weight, may, finally, become cost effective. The paper covers in some detail the design considerations that must be applied to monolithic microwave circuits in general, and to gallium arsenide circuits in particular. The important role being played by computer-aided design techniques is stressed. Numerous examples of monolithic circuits and components which illustrate the design principles are described. These provide a cross section of the world-wide effort in this field. A glimpse into the future prospects of monolithic microwave circuits is made.

Design Considerations for Monolithic Microwave Circuits

We report a broadband, linear, push-pull amplifier that utilizes GaN-based HEMTs grown on SiC substrates. The high power density capabilities of these devices can be enhanced by the high efficiency achievable with push-pull operation. Good amplifier performance is facilitated by use of a new low-loss balun that is implemented with three symmetric coupled lines and which showed insertion loss of less than 0.5 dB per balun. The bias was injected through the baluns, thereby simplifying the amplifier design and reducing loss associated with dc decoupling capacitors. Using two 1.5 mm HEMTs with 0.35-/spl mu/m gate length, a push-pull amplifier produced a small-signal gain of 8 dB at 5 GH2, a 3 dB bandwidth of 3.5-10.5 GHz, and a PAE of 25%.

Broadband GaN HEMT push-pull microwave power amplifier

A monolithic W-band push-pull two-stage power amplifier has been developed using 0.1 pm AlGaAs-InGaAs-GaAs pseudomorphic T-gate power HEMT technology. This novel design utilizes the push-pull scheme to take the advantage of a virtual ground in a push-pull HEMT device pair which eliminates the via hole inductance, and improves the power amplifier performance at millimeter-wave frequency. The measurement results show that a small signal gain of 12 dB, an output power of 19.4 dBm, and a power added efficiency of 13.3% have been achieved at 90 GHz, and presents state-of-the-art performance for a monolithic power amplifiers at this frequency. To our knowledge, this is the first reported monolithic push-pull amplifier at millimeter-wave frequencies.

A novel W-band monolithic push-pull power amplifier

The design, fabrication, and characterization of three- and four-stage monolithic GaAs power FET amplifiers are described. Each of the amplifier chips measures 1 mm × 4 mm. Procedures for characterizing these monolithic amplifiers are outlined. Output powers of up to 1 W with 27-dB gain were achieved with a four-stage design near 9 GHz. The circuit topologies used were flexible enough to allow external bondwires to be used as shunt inductors for amplifier operation at C- or S-bands. An output power of 2 W with 28-dB gain and 36.6-percent power-added efficiency was achieved at 3.5 GHz, using a modified four-stage amplifier.

Design, fabrication, and characterization of monolithic microwave GaAs power FET amplifiers

We report a new planar low loss microstrip balun with radial stub RF grounding. This structure achieves a good RF ground for a Marchand-type balun and facilitates microstrip balun characterization. Moreover, a simplified biasing scheme for a push-pull amplifier was designed using this concept and this approach has been used successfully in a push-pull amplifier. The measured balun insertion loss was less than 0.5 dB over a 5-11 GHz band.

A low-loss planar microwave balun with an integrated bias scheme for push-pull amplifiers

The design, fabrication, and performance of several GaAs FET monolithic circuits are described. These include a two-stage, four-FET push-pull amplifier that has exhibited 1.4-W output power with 12.4-dB gain at 9.0 GHz, and a three-transistor monolithic paraphase amplifier (unbalanced input, balanced output) exhibiting 6-dB small-signal gain and a 1-dB gain compression point of 20 dBm. The amplifier chips utilize monolithically fabricated inductors, capacitors, and transmission lines to accomplish on-the-chip impedance matching.

V. Sokolov

Papers

Development of GaAs monolithic power amplifiers in X-band