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A recent trend in characterizing coaxial and waveguide adapters stresses the importance of PIM performance, a parameter not included in product comparisons just a few years ago. Because of the impact that high PIM levels can have on wireless communications systems, such as degradation of bit error rate (BER), the PIM levels of newer coaxial and waveguide adapters have come under closer scrutiny in recent years. Many suppliers now offer components with low PIM levels of -165 dab or better for coaxial-to-coaxial adapters.

Although there is some debate within the industry on the preferred composition of connector materials for optimum PIM performance, including silver-plated brass, some manufacturers recommend the use of white bronze to achieve minimal PIM levels. White bronze is actually a blend of copper, tin, and zinc, combined to form a smooth, stainless-steel-like finish. In all cases, the finish as well as the composition of the materials for low-PIM adapters should be carefully engineered to achieve the lowest PIM levels within high-frequency coaxial connectors.

As an example of a low-PIM coaxial adapter, model ANN-NM-M03 from MECA mates Type-N male to Type-N male connectors from DC to 12.4 GHz with better than -165 dBc typical PIM performance. The adapter, with 1.60 in. length and 0.82 in. diameter, is formed with nickel adapters and silver-plated brass connector pins and cables.

Couplers for RF/microwave applications come in many shapes and sizes, including with waveguide and coaxial terminations. Couplers can be designed in various configurations, including as quadrature hybrid couplers, where input signals are split into two equal-amplitude (3-dB split) output signals offset by 90 deg., and as stripline directional couplers, where a small amount of an input signal is available at a coupled port for analysis or testing, with the remainder of the input signal passed to an output port for normal system use.

Krytar's couplersDirectional couplers usually have four ports: input, output, coupled, and isolated. The coupled port contains a portion of the power applied to the input port, with most of the input port power appearing at the output port, while the isolated port contains an amount of power typically symmetrical to the amount of power at the coupled port. This isolated port is usually terminated in a matched load.

As an example, model 104020030 is a coaxial directional coupler from Krytar, Inc. with a 30-dB coupled port (Fig. 2). This stripline coupler is designed for use from 4 to 20 GHz, with maximum VSWR of 1.35:1 and less than 0.60 dB insertion loss across the full frequency range. It can handle 20 W average input power and 3 kW peak (short pulses) input power at temperatures from -54 to +85°C. The coupling remains within ±1 dB across the frequency range in a package that is only 1.40 × 0.40 × 0.66 in. and weighs 1 oz. It is supplied with SMA female connectors (SMA male connectors as an option).

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