A diplexer is a three port device that combines or divides a common signal according to frequency, into low pass and high pass ports. Unlike a duplexer, which combines two bandpass filters, diplexers are very broadband. Important specifications include frequency coverage, out of band rejection for the high/low pass filters, isolation between the high/low pass filters, insertion loss, and return loss. Marki diplexers offer extremely broad, resonance free passbands. Diplexers can be used as low loss combiners or dividers for signals with different frequencies or as reflectionless filters (with one port terminated) at the output of mixers and other nonlinear devices with many harmonics. Marki offers two types of diplexers: CAD-optimized microstrip filters built on a low-loss substrate offered in surface mount and connectorized packages, and GaAs MMIC filters with tight fabrication tolerances offered as bare die. Both offer low loss and extremely broad rejection bands.