A high-performance 5.8-GHz diplexer, designed for point-to-point and wireless-radio systems, can be tuned for operation at any point along the popular 5.7-to-5.9-GHz frequency band. For example, a diplexer with channel 1 center frequency of 5,738 MHz and channel 2 center frequency of 5,798 MHz exhibits minimum 1-dB passband of 22.5 MHz with 2 dB or less insertion loss at each center frequency and 2.5 dB or less insertion loss within the channel passbands. The return loss within the passbands is 15 dB or better. These diplexers, which measure 0.67 × 3.5 × 4.5 in., with make SMA input connectors and female SMA output connectors, provide signal rejection (attenuation) of better than 85 dB removed 48 MHz from each center frequency, and better than 85 dB removed 65 MHz from the center frequency. The channel-to-channel isolation is better than 95 dB.