A compact Ku band microwave diplexer configured as a three port surface mount component on a miniature alumina substrate. Input signals occurring at a common port having frequencies within a first pass band are passed to a second port while being isolated from signals occurring at a third port. Signals occurring at the third port are passed to the common port while being isolated from the signals at the second port. A microstrip dual spur line filter is used combined with open circuit stubs to provide enhanced second harmonic suppression on the transmit side, while using a coupled line microstrip filter on the receive side. This approach allows for compact size and automated component assembly through pick and place and reflow manufacturing techniques.