GaAs and GaN MMIC Power Amplifiers Support Military and Test Applications to 48 GHz
By Hittite Microwave

Introduction
The increasing demand for bandwidth, as well as the search for robust sensors and communications equipment for military applications, continues to push transceiver operating frequencies ever higher. Interest from military leaders in high resolution targeting, remotely piloted vehicles, and integrated defense networks continues to require higher data throughput. Higher operating frequencies enable faster communications, while the associated narrower antenna beamwidths can be exploited to stay ahead of threats and eaves dropping counter measures. Similarly, test and measurement equipment manufacturers need to stay ahead of designers’ activities so that these systems can be characterized and optimized for their intended missions. Furthermore, power consumption characteristics which were not so important in the past have become a top priority, as defense related systems and sensors go remote and mobile.

Hittite has made significant advances in Monolithic Microwave Integrated Circuit (MMIC) technology over the company’s 26 year history, and continues to support the requirements of military, microwave radio, and test and measurement equipment OEMs. MMIC technology has enabled design engineers to steadily miniaturize microwave transceivers and sensors, and to bundle more capability into a given chip area. The end results are increased functionality and more robust system performance for cellular, broadband and microwave applications.
While much effort has been spent developing integrated circuits for specific consumer applications, many high performance systems require wide operating bandwidth in order to perform complex tasks in RF and microwave modules for telecom, test equipment, industrial, laboratory, military and space end-use applications.

The HMC999 (Figure 1) is a GaN pHEMT MMIC Wideband Distributed Power Amplifier Chip, which operates from 10 MHz to 10 GHz. This wideband power amplifier provides 11 dB of gain, +38 dBm of output power at 1 dB gain compression and up to +40 dBm of saturated output power. When biased for maximum output power, the HMC999 consumes 1100 mA of quiescent current from a +48V supply, and achieves approximately 18% power added efficiency at saturation. For less demanding applications, the HMC999 can be operated from a drain voltage as low as +28V while still producing 5 Watts of saturated output power.

This compact GaN MMIC power amplifier delivers 10 Watts of saturated output power in a chip area of only 7 mm2, which equates to a power density of 1.5 W/mm2 across three decades of bandwidth. When required, the RF outputs of several HMC999 devices can be connected via an external power combining network to achieve extremely dense and wideband output power levels.

The HMC999 also provides an industry leading +47 dBm output IP3 with output tone power levels of +26 dBm, making it ideal for applications requiring high linearity at power levels below saturation. In addition, the second harmonic performance of -40 dBc at +26 dBm output power makes the HMC999 ideal for replacing Travelling Wave Tube (TWT) amplifiers in applications where wideband performance and low second harmonic content are desirable.

The HMC999 is extremely robust and is designed to reliably operate into partially reflective loads and to tolerate very high incident power levels. This GaN pHEMT MMIC also exhibits a very low thermal resistance coefficient of 1.37° C/W, while the maximum junction temperature is rated at 225° C. For ease of integration within higher level assemblies, the HMC999 can be attached to a heat sink with a good quality thermally conductive epoxy; eutectic die mounting is not a necessity. The HMC999 is unconditionally stable and rated for operation over the full temperature range of –55° C to +85° C.

For test and measurement and military applications which require extreme bandwidth coverage, Hittite Microwave has also released four new GaAs pHEMT MMIC distributed power amplifiers which are summarized in Table 1.

The HMC930, HMC994, HMC998 and HMC1022 distributed amplifiers cover various frequency ranges from DC to 48 GHz. Across the line, these amplifiers deliver small signal gain levels from 12 to 14 dB, output IP3 from +32 to +41 dBm, and output power levels at 1 dB compression from +22 dBm to +31 dBm.

This family of wideband GaAs pHEMT distributed power amplifiers are internally matched to 50 Ohms facilitating integration into multi-chip-modules (MCMs). In addition, each of these amplifiers exhibits a slightly positive gain slope across a portion of its operating band, making them ideal for EW, ECM, radar and test equipment subsystem applications.

Hittite Microwave offers a broad range of wideband components which are found in some of the world’s most demanding military and test equipment applications, including those used for wideband noise generation and for jamming electronic adversaries.

The simplified functional block diagram shown in Figure 4 is an example showing how the HMC999 GaN pHEMT distributed power amplifier can be combined with other wideband amplifiers, frequency generation and control products from Hittite to assemble a wideband frequency jamming subsystem with up to 10 Watts of saturated output power from 25 MHz to 10 GHz.

The HMC830LP6GE fractional-N PLL with integrated wideband VCO is used as the core of the frequency generation section. The HMC830LP6GE, capable of sweeping from 25 to 3000 MHz, features industry leading phase noise and spurious performance, and delivers up to +5 dBm of output power.

Following the HMC830LP6GE is a switched multiplier bank, which is comprised of two Single Pole Four Throw (SP4T) switches, two frequency multipliers and an HBT gain block amplifier. By selecting the direct path between the HMC241LP3E and the HMC641LP4E SP4T non-reflective switches, the fundamental frequencies between 25 and 3000 MHz are sent to the amplification chain. By selecting the path through the HMC589ST89E GaAs HBT gain block amplifier and the HMC188MS8E passive frequency doubler, the frequency range between 3000 and 6000 MHz is generated. Finally, by selecting the path through the HMC917LP3E x4 active multiplier, the frequency range of 6 to 10 GHz can be realized.

The amplifier line-up shown in Figure 4 consists of the HMC788LP2E DC to 10 GHz pHEMT gain block amplifier and the HMC998 DC to 22 GHz pHEMT MMIC power amplifier, which are used in this example as driver stages. Meanwhile, the HMC999 GaN pHEMT power amplifier is used as the final output stage in order to generate signal levels as high as +40 dBm. Additional components from Hittite such as linear voltage regulators, variable gain amplifiers and tunable filters could also be used to further improve spectral performance.

Summary
A new series of GaAs and GaN based MMIC power amplifiers have been developed by Hittite Microwave Corporation. These amplifiers will enable the next generation of test and measurement equipment, as well as broadband electronic warfare subsystems. Design engineers who are in need of surface mount packaged versions of the amplifiers discussed in this article should contact Hittite for further information.

phone (978) 250-3343
sales@hittite.com

Hittite Microwave
www.hittite.com
Email this article to a friend!