Coax Cables Improve Receiver Performance

Sept. 20, 2005
These unique coaxial cable assemblies cover the frequency range 0.5 to 18 GHz and feature integrated active components to provide an almost lossless coaxial cable link between antennas and receiver equipment.

Coaxial cable assemblies provide the vital link between antennas and receivers for high-performance avionics systems. Unfortunately, the signal attenuation caused by these coaxial cable assemblies has historically resulted in a significant degradation in the overall installed system performance.

This long-standing limitation has now been virtually eliminated due to the introduction of a new product from Times Microwave Systems (Wallingford, CT)—a Zero dB™ coaxial cable assembly.

Zero dB now gives the system design engineer an additional degree of design freedom. This unique solution consists of an active coaxial cable assembly that features an integrated broadband low-noise amplifier (LNA) at the antenna end and a bias tee at the receiver end with a low loss cable in between. Capable of operation to 18 GHz with ±1 dB amplitude flatness, the integral LNA has a low noise figure (approx 3 dB) in order to maintain excellent receiver sensitivity and the gain is tailored to the loss of any specific cable.

The active Zero dB cable assemblies (see figure) provide operating voltages to the monolithic-microwave-integrated-circuit (MMIC) amplifier by means of the bias tee (or this voltage can be provided by the receiver itself). These voltages are sent to the amplifier via the cables center and outer conductors. If a separate Bias-T is used, it features a minimum isolation of 60 dB or better between the DC and the RF paths.

The MMIC amplifier provides broadband gain of 20 dB or more over selected bands from 500 MHz to 18 GHz with a 3 to 4 dB noise figure. It is rated for a mean time before failure of (MTBF) of over 100,000 hours per MIL-STD-810 requirements. An integral amplifier connector/package protects the component from vibration and from the various fluids and contaminants encountered on aircraft. Coaxial cable assemblies are available with amplifiers for single-direction operation, dual direction operation that sense power and switch off the amplifier to allow transmit pulses to pass in the reverse direction, and even with amplifiers that allow full-duplex operation with different transmit and receive frequencies.

The Zero dB coaxial cable assemblies include an input power limiter to protect the integral LNA from damage at RF power levels of up to 1 W (+30 dBm). Additional options include lightning protection between the amplifier and the antenna, blind mating of the antenna itself, filters to eliminate unwanted signals, and even integrated fault isolation. The Zero dB cable assemblies are designed to operate with aircraft supplies of +28 VDC with a typical current consumption of 250 mA. Times Microwave Systems, A Smiths Group plc Co., 358 Hall Ave., Wallingford, CT 06492; (203) 949-8400, (800) 867-2629, FAX: (203) 949-8423, e-mail: [email protected], Internet:

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