Microwave rotary joint for very-high-power satellite tracking

July 23, 2019 //By Jean-Pierre Joosting
Microwave rotary joint for very-high-power satellite tracking
Link Microtek has developed an X-band microwave rotary joint to meet the extremely demanding requirements of a satellite tracking system that transmits at a high pulsed power of 100 kW, with a mean power of 4 kW, over a wide frequency band of 2 GHz.

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

Steve Cranstone, managing director of Link Microtek, takes up the story: “While single-channel rotary joints in themselves aren’t particularly tough to make, when you have that frequency bandwidth and those levels of power, it becomes a massive challenge.

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

Drawing on years of experience in this field, Link Microtek’s engineering team used CST electromagnetic simulation software to model those crucial aspects of the design and eventually came up with a rotary joint that could satisfy the stringent requirements of the customer’s specification.

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

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