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RF Adapters Gain Bandwidth While Lowering Return Loss

From laboratory test setups to the transmitting equipment connected to base-station antennas, coaxial and waveguide adapters have been guiding RF and microwave signals for a long time. These adapters have increased flexibility by establishing connections between different or dissimilar connectors. At the same time, they have steadily continued to make electrical and mechanical progress in order to meet new performance goals set by modern and emerging applications. RF connectors suppliers have been able to continuously augment adapter performance by using newer materials, improved manufacturing methods and plating techniques, precision assembly processes, and clever impedance transformer designs.

Traditionally, waveguide-to-coaxial adapters have been a right-angle solution for applications requiring transition. In many situations, however, it is desirable to have connectors inline with the waveguide. By employing the latest RF techniques coupled with precision assembly methods, RLC Electronics has developed in-line adapters also popularly known as end-launch adapters. According to RLC's Director of Marketing, Peter Jeffery, the only advantage here is mechanical and there is also a disadvantage: very narrow bandwidth. Further details on this customer-specific solution were unavailable.

Numerous firms have taken more standard approaches (see Table). Space Machine & Engineering Corp., for instance, has readied a standard series of end-launch waveguide-to-coaxial adapters that incorporate its proprietary matching structure into the waveguide. To obtain broader bandwidth, the company has developed double-ridge waveguide-to-coaxial endlaunch adapters covering sizes WRD750 through WRD200 (Fig. 1). The adapters boast a maximum voltage standing wave ratio (VSWR) of 1.5:1. Doubleridge waveguides for end-launch-style adapters also have been developed by AR RF/Microwave Instrumentation, Cobham Defense Electronic Systems, and QuinStar Technology. Both AR and QuinStar also offer these adapters with rectangular waveguides using a variety of coaxial connectors.

Among the additional proponents of end-launch-style waveguideto- coaxial adapters are Advanced Technical Materials, A-INFO, Flann Microwave, Maury Microwave, Microwave Engineering Corp., and Unique Broadband Systems. Aside from achieving a low profile with short length and low loss and VSWR, Microwave Engineering's design permits its end-launch adapters to operate over multi-octave bandwidths at high power levels.

Developers of end-launch adapters also provide right-angle models. RLC, for example, has been making standard waveguide-to-coaxial adapters in a variety of configurations for applications in the 3.3-to-40-GHz range with options for a broadband or band-specific model. Broadband waveguide-to-coaxial adapters maintain superior electrical specifications over the entire bandwidth. In contrast, band-specific models offer enhanced electrical performance for a specified bandwidth around the center frequency.

The firm's WAD series comprises 50-Ω coaxial-connector types including N, SMA, and K male or female. The adapters' average power-handling capability is 300 W for N, 60 W for SMA, and 25 W for K-type connectors with the waveguide flange as standard. Although insertion loss ranges to just 0.05 dB between 3.3 and 8.2 GHz, it begins to climb as the frequency goes higher. Hence, insertion loss rises to 0.1 dB between 10 and 18 GHz and climbs to 0.15 dB as frequency scales beyond 18 GHz. Likewise, VSWR is 1.2:1 between 3.3 and 8.2 GHz, but deteriorates to 1.35:1 with frequency ascending to 18 GHz and beyond.

The manufacturer also has introduced right-angle solder-free adapters that can handle frequencies to 11 GHz from -65 to 165C. The 50-Ω UG-27 C/U adapters are rated for operating voltages to 1000 V RMS with a maximum dielectric withstanding voltage of 2000 V RMS at 60 Hz at sea level. They flaunt a VSWR of 1.15:1 from DC to 6 GHz and 1.35:1 from 6 to 11 GHz, respectively. Featuring silver and gold center contact plating, the adapters come with albaloy, nickel, and silver body plating.

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