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Amplification is almost always needed in high-frequency systems, whether transmitting or receiving. When broadband amplification is needed, finding a solution can be most challenging, since a large number of simultaneous amplifier performance parameters, such as output power, gain, and even noise figure, must be satisfied over a wide frequency bandwidth.

Fortunately, the new model ZHL-5W-422+ coaxial amplifier from Mini-Circuits is an example of a broadband amplifier that not only delivers outstanding electrical performance with 5-W CW output power from 500 to 4200 MHz, but includes protective circuitry and numerous features to make its installation and use almost foolproof. The 50-Ω amplifier is well suited for military, commercial, test, and even amateur-radio applications, and can be supplied with or without a heat sink.

Model ZHL-5W-422+ designates a coaxial amplifier with fan and heat sink, which is also available as model ZHL-5W-422X+ as the coaxial amplifier in its housing alone, without fan and heat sink (Fig. 1). The Class-A linear amplifier, which is based on GaAs FET active devices, provides adequate continuous output power for a variety of transmit operations. These include frequency-modulated (FM) radios, television transmitters, point-to-point radio transmitters, amateur radio, and laboratory use.

Model ZHL-5W-422+

This is an amplifier with instrument-grade gain performance, with 20-dB minimum gain and 25-dB typical gain across its frequency range. Although these are not staggering gain numbers, what is impressive is the flatness of the gain with frequency, typically holding well within ±1 dB gain from 500 to 4200 MHz (Fig. 2). The amplifier is rated for worst-case gain flatness of ±1.7 dB across its operating frequency range.

Small-signal gain

Perhaps not as apparent, this is an amplifier that also features impressive directivity of better than 50 dB across its full operating frequency range (exceeding 60 dB at some frequencies). In addition, it is well matched for use in a wide range of applications, with a low input VSWR of no worse than 2.3:1 and typically at 1.70:1.

The low-input VSWR enables well-matched connections between signal sources, such as a feedline from an antenna, and the input port of the amplifier. Such “compatible impedances” help minimize mismatches and irregularities in amplitude and phase performance. As a result, with low-VSWR amplifier input ports that are well matched, the specified gain flatness can actually be achieved. In addition, for applications where phase irregularities due to impedance mismatches might be a problem—such when amplifying phase-modulated signals—these amplifiers help to minimize phase deviations across a wide bandwidth.

With or without the heat sink, the amplifier is rated for reasonable 5 W output power from 500 to 4200 MHz, with +35 dBm typical output power at 1-dB compression and +37 dBm typical output power at 3-dB compression. The linear amplifier boasts output third-order intercept point of at least +40 dBm and typically +45 dBm, and output second-order intercept point of at least +50 dBm and typically +55 dBm (Fig. 3). Two-tone output levels were measured with high-quality commercial test equipment, using two test tones set 1 MHz apart in frequency.

Output power

With its generous output-power levels, it also achieves high efficiency, boasting 30% typical operation under saturated output-power conditions and respectable noise figure across its frequency range (typically at 7 dB). The amplifier is designed for use from a 2-A supply at +28 VDC. It can handle input power levels as high as +20 dBm without damage. Models ZHL-5W-422+ and ZHL-5W-422X+ are RoHS compliant and supplied with SMA connectors.

Download this article in .PDF format
This file type includes high resolution graphics and schematics when applicable.