Waveguide rotary joints (WRJ) are waveguide components used to transmit microwave energy from stationary lines to rotating lines. They are also known as rotating couplers and RF rotary joints. Waveguide rotary joints are made of two waveguide-to-coaxial transitions connected by a coaxial line. Because this coaxial line is circular, the WRJ can rotate about it without affecting performance. If the inner conductor of the coaxial line is hollow, two coaxial cables can be inserted to build dual-channel waveguide rotary joints. Swivel waveguide joints can be rotated +/- 60 degrees (+/-90 degrees mechanically).

Differences Between Waveguide Rotary Joints

Waveguide rotary joints differ in terms of cross-section, materials of construction, and physical dimensions. Most rotating couplers and RF rotary joints have rectangular, circular, or elliptical cross-sections. Common materials for waveguide rotary joints include aluminum, brass, bronze, copper and silver. These waveguide components are also made of stainless steel, specialty steels, and specialty clad or bi-metallic alloys. Length or height and width are important dimensional parameters to consider when specifying products.

Performance Specifications

Performance specifications for waveguide rotary joints include operating frequency range, EIA waveguide size, voltage standing wave ratio (VSWR), insertion loss, peak power, average power, and isolation. The Electronic Industry Alliance (EIA) approves specific waveguide sizes. Insertion loss is defined as the measured power loss through the waveguide component. Peak power is the maximum power in watts (W) that waveguide rotary joints are designed to support. Average power is also measured in watts. By contrast, isolation is measured in decibels (dB) between any set of output ports.   

Waveguide rotary joints are manufactured in accordance with U.S. military specifications such as MIL-W-85 and BS 9220 N001, a detail specification for ordinary rectangular (2:1) rigid waveguide tubing. The International Electrotechnical Commission (IEC) also maintains standards that apply to waveguide rotary joints, such as IEC 60153 regarding hollow metallic waveguides. Depending on the markets that they serve, RF rotary joint suppliers may also meet other may also meet other military and civilian specifications.

Features

General features are important to consider when selecting waveguide rotary joints (WRJ). Single-ridge, double-ridge, and quad-ridge devices have 1, 2, or 4 apertures, respectively. Some waveguide components are flexible. Others are twistable. The waveguide rotary joint’s interface to other components may be a coaxial connector or another waveguide.