RF Waveguide Assemblies Information
RF waveguide assemblies consist of RF waveguide components, devices through which electromagnetic waves are propagated in radio frequency (RF) communications. The wave passing through the medium is forced to follow the path determined by the physical structure of the guide. There are several basic types of RF waveguide assemblies. Devices with formed bends do not have miters in the elbow and are built by bending one straight section. Mitered bends are built by connecting two straight sections with a joint that forms the elbow of the bend. Twists are used to change the polarization of the wave inside the waveguide. Straight sections provide linear transitions between waveguide components. Offset sections are used to connect two non-aligned waveguides. Common bending or twisting angles for RF waveguide assemblies are 30°, 45°, 60°, and 90°. Most waveguides are made of aluminum, brass, bronze, copper, or silver. Waveguide cross-sections are usually rectangular, circular, or elliptical.
Flanges are used to connect waveguide sections to one another or terminate waveguide components. They have circular, rectangular, or square profiles and are often plated with cadmium, nickel, rhodium, silver, or tin. There are several basic types of flanges. Union guide (UG) is the military standard MIL-DTL-3922 for a range of flange types. Cover or plate flanges are flat, square UG-style flanges. Choke flanges are UG-style devices with an O-ring groove and choke cavity. They are often used to minimize the effects of flange discontinuity. Connector pressurized rectangular (CPR) flanges meet Electronic Industry Association (EIA) specifications and are used in many non-military applications. CPR variants include miniature (CMR), grooved (CPRG), and flat (CPRF) flanges. Mill-back flanges are made with the opening of the flange face equal in size to the inside of the waveguide, which is soldered into a larger milled opening at the rear of the flange.
Performance specifications for RF waveguide assemblies include operating frequency range, EIA waveguide size, voltage standing wave ratio, length or height, and width or radius. Operating frequency range is the range for which RF waveguide assemblies meet all guaranteed specifications. EIA waveguide sizes have a prefix of WR and indicate the widest inside dimension of the waveguide in hundredths of an inch. For example, WR650 is 6.50 in. wide, WR90 is 0.90 in. wide, and WR75 is 0.75 in. wide. Voltage standing wave ratio (VSWR) is a unit-less ratio ranging from 1 to infinity that expresses the amount of reflected energy at the input or output of the device. A value of one indicates that all energy passes. Any other value indicates that a portion of the energy is reflected. Bend type is an additional consideration when selecting RF waveguide assemblies. E-plane bends change the direction of the electric field lines. By contrast, H-plane bends change the direction of magnetic field lines.