RF waveguide transition adapters are used to connect waveguide components with different cross sectional sizes. They are made of aluminum, brass, bronze, copper or silver and are used with both small and large waveguides. There are several types of products. Rectangular-to-rectangular RF waveguide transition adapters are designed to connect one rectangular waveguide to another rectangular waveguide. Similarly, circular-to-circular adapters are used to connect one circular waveguide to another circular waveguide. Circular-to-rectangular waveguides that change a circular waveguide to a rectangular waveguide are also available. Single-ridge to double-ridge RF waveguide transition adapters are designed to change a single-ridge waveguide to a double-ridge waveguide. Conversely, double-ridge RF waveguide transition adapters are used to change a double-ridge waveguide to a single-ridge waveguide.
RF waveguide transition adapters use flanges to connect waveguide sections or terminate waveguide components. Most flanges are square, circular, or rectangular in shape and plated with cadmium, nickel, rhodium, silver, or tin. 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 transition adapters include EIA waveguide size, length, insertion loss, and voltage standing wave ratio. 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. Length is also measured in inches. Insertion loss is defined as the measured power loss through the device. It is calculated as the ratio of power output to power input and is expressed in decibels (dB). 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.