Diplexers are three-port frequency-dependent devices that may be used as a separator or a combiner of signals. The device consists of two fixed tuned bandpass filters sharing a common port. The common port and the output of the two filters (RX and TX) form the three terminals of the diplexer. Signals applied to common port are separated in accordance with their passband frequencies of the filters. Signals applied to either uncommon port are isolated from the other uncommon port and are combined at the common port. Diplexers are the simplest form of a multiplexer.  Duplexers allow a transmitter operating on one frequency and a receiver operating on a different frequency to share one common antenna with a minimum of interaction and degradation of the different RF signals.

Choices for Package Types

Choices for package types for diplexers and duplexers, RF, include surface mount, flat pack, through hole or plug-in, connectorized, and waveguide assembly.  In Surface Mount Technology (SMT), components are mounted on printed circuit boards by soldering the component leads or terminals to the top surface of the board.  A flat pack is an IC package with gull wing or flat leads on two or four sides.  In Through Hole Technology (THT), components are mounted on printed circuit boards by inserting component leads through holes in the board and then soldering.  A connectorized components is attached to the system by means of connectors such as coaxial or other type.  A waveguide assembly is used in a microwave waveguide system. A waveguide normally consists of a hollow metallic conductor, usually rectangular, elliptical, or circular in cross section. Under certain conditions it may contain a solid or gaseous dielectric material.  Choices for connector type include BNC, MCX, Mini UHF, MMCX, SMA, SMB, SMP, TNC, Type F, Type N, UHF, 1.6/5.6, and 7/16.

Performance Specifications

Important performance specifications to consider when searching for diplexers and duplexers, RF, include RX (low), TX (high), RX rejection (over TX), TX rejection (over RX), insertion loss, and VSWR.  RX is the passband of the RX or Receive port (lower port) bandpass filter of the diplexer.  TX is the passband of the TX or Transmit port (higher port) bandpass filter of the diplexer.  RX rejection is the attenuation of the RX filter over the passband of the TX filter.  TX rejection is the attenuation (in dB) of the TX filter over the passband of the RX filter.  Insertion loss (in dB) is the total RF power transmission loss resulting from the insertion of a device in a transmission line. It is defined as the ratio of signal power at the output of the inserted device to the input signal power at the input of the inserted device.  VSWR (Voltage Standing Wave Ratio) is a unitless ratio ranging from 1 to infinity, expressing the amount of reflected energy at the input of the device.  A value of one indicates that all the energy will pass through, while any other value indicates that a portion of the energy will be reflected.