Microwave rotary joint meets satellite tracking needs

Microwave and RF component specialist, Link Microtek, has developed an X-band microwave rotary joint to meet the extremely demanding requirements of a satellite tracking system. It transmits at a high pulsed power of 100kW, with a mean power of 4kW, over a wide frequency band of 2GHz.

Designed to transmit and receive at frequencies from 8.5 to 10.5GHz, the tracking system uses long runs of WR90 rigid waveguide, with six of the special single-channel rotary joints to provide movement for elevation, azimuth and tilt.

Steve Cranstone, managing director of Link Microtek, explains that single-channel rotary joints are not difficult to make but they can be a challenge at the frequency bandwidth and levels of power related to satellite tracking.

“Any losses, even tiny ones, will generate a significant amount of heat, so thermal modelling was key in preventing internal overheating of the devices,” he says. He adds, “The customer’s system was unpressurised, so that made it very difficult to keep breakdown voltages to acceptable levels.”

Link Microtek’s engineering team used CST electromagnetic simulation software to model those crucial aspects of the design and came up with a rotary joint that could satisfy the stringent requirements of the customer’s specification.

Incorporating a 10mm-thick heatsink to conduct the excess heat away, the rotary joints achieve a low insertion loss of less than 0.2dB and a VSWR of 1.2:1. They are manufactured from aluminium and measure 122mm in length with a heatsink diameter of 75mm.

The satellite tracking system is installed in an exposed coastal location, so the rotary joints have chromium-free passivation for corrosion resistance and IP65 sealing to prevent the ingress of moisture and dust.

Steve Cranstone observes: “You might expect to be dealing with a 100kW peak power level at lower frequencies, but at X-band we had to be very, very careful to minimise the losses at every stage of design and production.”


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