In spite of the high power levels and broad bandwidths of TWTAs, however, the efficiency of solid-state RF/microwave amplifiers has resulted in a much greater demand for this type of power amplifier solution in recent years. This has proven to be the case even though with the cooling requirements at high power levels, the sizes of these high-power solid-state amplifier systems are often comparable to the sizes of TWTAs at considerably higher power levels. Some of the newer solid-state power amplifier systems are making use of newer device technologies, such as GaN power transistors, for their active-device circuitry.

As an example, model BPC318358-13000 from Comtech PST is very “tubelike” in terms of size and weight, in a package measuring 24.0 x 25.5 x 24.0 in. and weighing 230 lbs. But it is designed in a modular housing, with removable modules that simplify maintenance and upgrade operations. This S-band amplifier system (Fig. 1) operates from 3100 to 3500 MHz with 13 kW pulsed output power and 71-dB nominal RF gain. It is designed for signals having 2 to 200 μs pulse widths at 10% maximum duty cycle. The Class AB linear GaN amplifier system has better than -60 dBc spurious performance and runs on a 1.35-kVA supply. Designed for ground-based and laboratory applications, the amplifier system includes forced-air cooling and Ethernet remote control and can be enabled or disabled from active operation in less than 5 μs.

Amplifier Systems Gain In Power, Fig. 1

Empower RF recently unveiled its model 2141 solid-state Class AB linear amplifier based on GaN and LDMOS transistor technologies. It is suitable for CW signals and signals with modulation, such as AM and FM, over a range from 100 to 6000 MHz, with 500 W typical saturated output power to 1000 MHz and 125 W typical saturated output power to 6000 MHz. The four-unit stacked system measures 19 x 22 x 22 in. and weighs 220 lbs. It features a 20-dB gain-adjustment range, at least 47 dB power gain across the full frequency range, with better than ±2 dB gain flatness, and RS-422/485 remote control.

For broadband applications at lower power levels, numerous test-instrument manufacturers offer extremely linear amplifiers capable of covering broad bandwidths. The model GT-1020A instrumentation amplifier from Giga-tronics, for example, covers the broad frequency range from 100 MHz to 20 GHz, suitable for use with broadband signal generators, spectrum analyzers, and vector network analyzers. It provides about 600 mW (+28 dBm) output power from 100 MHz to 10 GHz and about 500 mW (+27 dBm) typical output power from 10 to 20 GHz, in a compact housing measuring 2.5 x 6.8 x 7.0 in. and weighing just 4.5 lbs with SMA connectors.

For both instrumentation and system use, Agilent Technologies offers its 83000A series of microwave system amplifiers for applications through 50 GHz. Some extremely broadband units are included, such as model 83006A, from 10 MHz to 26.5 GHz (20-dB gain and +13 dBm output power), and model 83051A, operating from 45 MHz to 50 GHz (23-dB gain at +12 dBm output power).

A company that supplies numerous power amplifiers for test applications, Instruments For Industry, has leveraged GaN device technology in its S61-50 series of broadband amplifiers, which provide as much as 50 W CW output power from1 to 6 GHz. The amplifiers are built into compact housings measuring just 5.25 x 19.00 x 24.00 in. They are well suited for electromagnetic-interference (EMI) compliance testing and electromagnetic-compatibility (EMC) testing requiring the wide bandwidth. The company also supplies power amplifiers that combine technologies, such as the ST181-50 series of amplifiers with as much as 50 W CW output power from 0.8 to 18.0 GHz, using TWTs and GaN transistors to achieve the final power levels.

Amplifier Systems Gain In Power, Fig. 2

Amplifier Research is another amplifier supplier well associated with solutions for test applications. Its recently introduced model 50S1G6 Class A power amplifier (Fig. 2) is supplied in a rack-mount case measuring 19.8 x 8.0 x 21.5 in. It delivers 50 W CW output power from 700 MHz to 6 GHz and 48-dB minimum gain with ±2 dB worst-case gain flatness. The amplifier includes an RF input leveling circuit to protect the amplifier from overdrive conditions by maintaining input levels at or below 0 dBm. It incorporates forced-air cooling and can be remote controlled by means of RS-232, GPIB, USB, and Ethernet interfaces.