Amplifiers for RF and microwave use are available in a range of packaged and unpackaged varieties to suit low-noise and power requirements through millimeter-wave frequencies.
High-frequency amplifiers are abundant in type and application, being used for everything from setting the noise figure of communications receivers to driving high-power signals to transmitter antennas. Types include broadband and narrowband power amplifiers, low-noise amplifiers (LNAs), logarithmic amplifiers (logamps), operational amplifiers (opamps), transimpedance amplifiers (TIAs), and voltage-variable amplifiers in configurations ranging from chips and surface-mount-technology (SMT) packaged devices to rack-mount systems based on solid-state and vacuum-tube devices. This short report does not pretend to cover the topic of RF/microwave amplifiers in any detail; it merely hopes to offer a sampling of recently announced products. Those needing a more comprehensive cross section of available amplifier products are invited to visit the online version of the Microwaves & RF Product Data Directory at www.mwrfpdd.com, where they can search through more than 30 different amplifier categories.
Among the smallest of RF/microwave amplifiers are the monolithic microwave integrated circuit (MMIC) devices often used as gain blocks to offset passive signal losses in systems and circuits. Suppliers of chip and packaged MMIC amplifiers are many, and include Agilent Technologies (www.agilent.com), Analog Devices (www.analog.com), Filtronic (www.filtronic.co.uk), Hittite Microwave (www.hittite.com), M/A-COM (www.macom.com), Mimix Broadband (www.mimixbroadband.com), Mini-Circuits (www.minicircuits.com), Microwave Technology (www.mwtinc.com), and RF Micro Devices (www.rfmd.com).
Hittite Microwave, for example, offers the model HMC-ALH444 LNA in chip form. Ideal for military and commercial applications from 1 to 12 GHz, it features a low noise figure of 1.75 dB at 10 GHz with 17 dB gain. The die measures a mere 2.64 x 1.64 x 0.1 mm. The company recently announced GaAs high-electron-mobility-transistor (HEMT) LNA chips for applications through 65 GHz (Fig. 1). Model HMCALH382 delivers 21 dB gain and 4 dB noise figure from 57 to 65 GHz. It yields +12 dBm output power at 1-dB compression while drawing 64 mA from a single +2.5-VDC supply.
Another chip amplifier, Microwave Technology's MMA-021015, leverages AlGaAs/InGaAs pseudomorphic- HEMT (PHEMT) technology to achieve 4.8 dB noise figure from 1 to 10 GHz. It provides +17 dBm output power and 18 dB gain with +/- 2.5 dB gain flatness over the full bandwidth. It is designed for +6-VDC systems. Last year, the company announced a series of broadband medium-power amplifiers that included the MMA-022020B with +22.5 dBm output power at 1-dB compression and 8 dB gain from 1 to 22 GHz.
In terms of pure bandwidth, few MMIC chip amplifiers can match the model HMMC-5025 from Agilent Technologies. The distributed amplifier covers a frequency range of 2 to 50 GHz with 8.5 dB small-signal gain and +12 dBm output power at 40 GHz. The noise figure is only 5 dB through 35 GHz and 7 dB through 50 GHz. The seven-stage distributed amplifier chip includes 30-dB gain control range. Each stage consists of two cascoded GaAs FET devices.
Many MMIC-amplifier suppliers also offer packaged amplifiers. For example, Mimix Broadband recently announced the model CMM9000-QT two-stage feedback driver amplifier for use from 1.5 to 6.0 GHz. Supplied in a 3 x 3 mm surface-mount QFN package, the amplifier delivers 15-dB small-signal gain and +15-dBm output power at 1-dB compression and includes on-chip matching circuitry, RF choke inductors, and DC blocking capacitors. Analog Devices recently introduced the ADL5320 and ADL5321 predriver and driver amplifiers. The former operates from 400 to 2700 MHz with 13.7-dB gain, 4.2-dB noise figure, and +25.6-dBm output power at 2140 MHz, while the latter operates from 2300 to 4000 MHz with 14-dB gain, +25-dBm output power, and 4-dB noise figure at 2600 MHz.
Mini-Circuits offers several lines of packaged MMIC amplifiers, including the ERA family. Among the many miniature SMT-packaged ERA amplifiers, model ERA-1 supplies more than 10 dB gain from DC to 8 GHz with +12 dBm typical output power at 1-dB compression. The versatile amplifier features a low noise figure of 4.3 dB and high linearity with a third-order intercept point of typically +26 dBm.
Because the power levels provided by these small MMIC amplifiers are rarely above about 0.5 W (+27 dBm), larger circuits and assemblies are needed to produce reasonably high power levels. On a slightly larger scale, many companies offer amplifiers in machined aluminum housings with coaxial connectors capable of producing higher power levels and (by means of the housings and heat sinks) dissipating more heat. CTT, Inc. (www.cttinc.com), for example, supplies extensive lines of narrowband and broadband power amplifiers for commercial and military applications, covering such bands as 0.5 to 2.0 GHz, 1.0 to 2.0 GHz, 2 to 4 GHz, 2 to 6 GHz, 2 to 8 GHz, 2 to 18 GHz, and 2 to 20 GHz with as much as +41 dBm output power. Higher-frequency models include the model APW/265-3036 with 36 dB gain and +30 dBm output power at 1-dB compression from 18.0 to 26.5 GHz.
The emergence of commercial widebandgap devices, such as those fabricated on silicon carbide (SiC) and gallium nitride (GaN) materials, has provided amplifier designers with very highpower- density devices. Last year, for example, the UK firm Milmega (www.milmega.co.uk) announced that it was producing UHF power amplifiers using SiC transistors from Cree, Inc. (www.cree.com). The SiC MESFETs boast greater power density than competing transistor technologies at those frequencies, allowing the design of higherpower amplifiers in smaller packages.
The model 1117-BBM3K5KEL power amplifier from EMPOWER RF Systems (www.empowerrf.com) employs GaN devices for high power density. It provides 20 W typical output power at 1-dB compression from 500 to 2500 MHz with 46 dB gain and +/-1.5 dB gain flatness.
Some power amplifiers rely on vacuum electronics rather than solid-state devices to generate their high output-power levels. For example, dB Control (www.dbcontrol.com) recently announced several contracts totaling almost $8 million for high-power traveling wave tube (TWT) amplifiers and microwave power modules (MPMs) for US defense contractors. Last year, the company announced additions to its MPM line that extended frequency coverage to 2 to 40 GHz. The new MPMs include the model dB-3757 with 1500-kW peak power from 6 to 18 GHz with sixpercent- duty-cycle signals. Additional suppliers of vacuum-tube amplifiers include AR Worldwide (www.ar-worldwide.com), Communications & Power Industries (CPI, www.cpii.com), Instruments For Industry (www.ifi.com), and MITEQ, Inc. (www.miteq.com).
AR Worldwide also has sought to make smaller power amplifiers for a variety of applications. One of the firm's more popular amplifiers is the modular model CMS1070 GaAs FET power amplifier, perhaps because of its intended use in WiMAX systems (Fig. 2). It delivers +43 dBm output power at 1-dB compression from 3400 to 3700 MHz with scalable gain from 20 to 50 dB. The amplifier module achieves a thirdorder intercept point of +54 dBm.
For satcom and other high-frequency applications, Endwave (www.endwave.com) supplies a series of solid-state amplifiers. The firm recently announced a pair of amplifier modules for satcom use (Fig. 3). The Ku-band unit delivers at least 40 dB gain with 0.5-dB gain flatness and +37 dBm typical output power at 1-dB compression. The Ka-band module provides at least 27-dB gain with 1-dB gain flatness and +36 dBm output power at 1-dB compression. The noise figures are low, at 4.5 dB for the Ku-band module and 6 dB for the Ka-band module.
In searching for amplifiers, some companies provide help on their websites. Mini-Circuits, for example, has the powerful Yoni2 search engine. Spectrum Microwave (www.spectrummicrowave.com) offers a useful search tool by which specifiers can enter frequency range, gain, noise figure, P1dB, and second and third-order intercept points and search for a product solution.