RF waveguide isolators and circulators permit a signal to pass in one direction while providing high isolation to reflected energy in the reverse direction. RF waveguide circulators are passive devices with three or more ports. General specifications for RF waveguide isolators and circulators include waveguide material and waveguide cross section. Common materials for RF waveguide isolators and RF waveguide circulators are aluminum, brass, bronze, copper, and silver. Typically, the waveguide cross-section is rectangular, elliptical or circular. RF waveguide isolators and RF waveguide circulators differ in terms of operating frequency, EIA waveguide size, and VSWR. Operating frequency is the range of frequencies over which products meet all guaranteed specifications. Typically, the Electronic Industry Alliance (EIA) approves sizes for RF isolators and circulators. Voltage standing wave ratio (VSWR), a unit-less ratio ranging from one to infinity, expresses the amount of reflected energy at the input or output of a RF waveguide isolator or RF waveguide circulator. A value of one indicates that all of the energy will pass through. Any other value indicates that a portion of the energy will be reflected.
Specifications for RF waveguide isolators and RF waveguide circulators include flange type, profile, and plating material. Union guide (UG) and connector pressurized rectangular (CPR) are the most common flange types. UG variants include choke and cover or plate. Choke flanges have an O-ring groove and choke cavity. Cover or plate flanges are square and flat. CPR flanges include variants such as connector pressurized rectangular flat (CPRF), connector pressurized rectangular grooved (CPRG), and connector miniature rectangular (CMR). Most RF waveguide isolators and circulators have a square, rectangular, or circle profile. Plating materials include cadmium, nickel, rhodium, silver and tin. Non-plated products are also available.
RF waveguide isolators and RF waveguide circulators that are sold in Europe must comply with the Restriction of Hazardous Substances (RoHS). RoHS requires all manufacturers of electronic and electrical equipment sold in Europe to demonstrate that their products contain only minimal levels of the following hazardous substances: lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyl and polybrominated diphenyl ether. RoHS became effective on July 1, 2006. By definition, lead-free devices contain less than 1000 ppm lead by weight. Some RF waveguide isolators and circulators are suitable for programmable devices. Others are designed for military applications.