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Broadband RF/microwave components are typically associated with test-and-measurement applications, although they are also very much a part of different defense and aerospace systems. From active components, such as broadband amplifiers, to passive components, such as terminations, broadband RF/microwave components enable the operation of many different electronic systems for military users, including electronic-warfare (EW), radio, radar, and surveillance systems. Successfully specifying these components for such applications relies on reviewing some of the essential specifications connected to broadband performance, for both active and passive components.

Fig. 1In most military and aerospace systems that are meant to operate over broad bandwidths, such as 500 MHz to 18 GHz, the amplitude and phase performance levels of active and passive components can play a hand in the system-level performance that is possible with a particular design. Even the amplitude and phase flatness of often-overlooked components in these systems, such as antennas and coaxial cable assemblies, can set limits on the ultimate performance possible from a system.

Investments by the Defense Advanced Research and Projects Agency (DARPA) and other research-minded organizations within the Department of Defense (DoD) have sought higher performance levels with greater reliability and accuracy from the active and passive components used in broadband systems. For active components, such as amplifiers, advances have often come at the device level, with such devices as gallium-nitride (GaN) high-electron-mobility transistors and other semiconductors providing new levels of performance from compact-sized components. For passive components, advances often come at the material level, by gaining improved knowledge of often-used materials, including printed-circuit-board (PCB) laminates, and experimenting with newer materials, including superconducting circuit materials that must be maintained at cryogenic temperatures for optimum performance.

Specifying a broadband component, whether active or passive, usually starts with the amplitude or gain flatness with frequency, since it is normally assumed that the components used in a system should have as little impact as possible on the amplitude accuracy of the system. Typically, radar and EW systems are developed with target amplitude-with-frequency flatness of ±1 dB or better, which becomes more challenging to achieve (and measure) as the bandwidth increases. Similarly, phase-with-frequency deviations must be minimized as much as possible, especially in phase-sensitive systems. Both specifications are subject to added deviations with temperature, so that specifying a broadband component also requires knowledge of the product’s amplitude and phase performance across the full operating-temperature range.

Suppliers of broadband active and passive components for defense-related applications are numerous. As an example, Krytar, a long-time supplier of broadband passive components for commercial and defense applications, and a scheduled exhibitor at the upcoming IEEE International Microwave Symposium (IMS) in Phoenix, Ariz., has developed lines of test equipment and broadband passive components, including adapters, terminations, hybrid couplers, and power dividers. The company’s model 4100400 180-deg. hybrid coupler, with a bandwidth of 10 to 40 GHz, is well suited for defense and test applications, providing excellent amplitude and phase matching across its 30-GHz bandwidth. It features amplitude balance of ±1 dB across its frequency range and phase balance within ±12 deg. across the full frequency range. Additional specifications include insertion loss of less than 1.7 dB across the frequency range, isolation of better than 12 dB, and full-band VSWR of 1.80:1 or better.

Model 4100400 (Fig. 1) handles 20 W average power and 3 kW peak power across the wide frequency range. It measures 0.86 in. × 1.10 in. × 0.5 in. and weighs 1.2 oz. This hybrid coupler, and other couplers in the firm’s line, is designed for operating temperatures from -54° C to +85° C. It is supplied with 2.4-mm female connections, but available with 2.92-mm coaxial connections as an option. It can be manufactured to meet full military specifications for defense-related applications.

Fig. 2A company known for components with high performance at low cost, Mini-Circuits, recently announced a line of low-cost broadband mixers, the Ultra-Rel MAC mixers. Current units are available from 300 MHz to 12 GHz, with models in development through 18 GHz. What makes these mixers unusual are low prices with outstanding electrical performance, in hermetic low-temperature-cofired-ceramic (LTCC) housings that provide high reliability over an operating temperature range of -55° C to +125° C. 

In spite of the low cost, these packaged mixers are qualified to an extensive series of military testing for gross leak, fine leak, thermal shock, vibration, acceleration, and mechanical shock, including MIL-STD-202 and MIL-STD-883. Supplied in hermetic LTCC surface-mount housings measuring just 0.3 in. × 0.25 in. × 0.06 in., the mixers boast extremely high unit-to-unit and lot-to-lot consistency, with excellent amplitude and phase repeatability.

As an example, the firm’s MAC-60 line of mixers operate at RF and local oscillator (LO) frequencies from 1.6 to 6.0 GHz and provide intermediate-frequencies (IFs) from DC to 2 GHz. The models MAC-60+, MAC-60LH+, and MAC-60MH+ operate at LO levels of +7, +10, and +13 dBm, respectively, with 6.5-dB conversion loss and 35-dB typical LO-to-RF isolation.

In terms of mixers for higher-frequency use, Marki Microwave recently introduced its highest-frequency broadband mixer, the model MM1-2567LS GaAs MMIC mixer with an RF/LO frequency range of 25 to 67 GHz. It features an IF range of DC to 30 GHz with 9-dB typical conversion loss in a compact housing. It is designed for an operating temperature range of -55° C to +100° C.

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