Compact Diplexer Using Electromagnetic Bandgap Resonators for C and X Band Radar Systems

For wireless communication, it becomes necessary to employ frequency multiplexing to enable two devices to share a common channel. Diplexers are an example of such microwave devices that facilitate frequency multiplexing. This paper presents an electromagnetic bandgap (EBG) structure-based new diplexer with two closely located passband resonances at 6.9 and 9.1 GHz. The proposed diplexer displays insertion losses of < 1 dB and 2 dB, whereas the return losses of > 28 dB and 30 dB at the lower and higher frequencies in port-2 and port-3, respectively. Isolation at the output channels is improved by incorporating EBG as coupled resonators to create transmission notches at the two passband frequencies. The total size of the designed diplexer is 35 × 45 × 1.02 mm
³
or 0.8 × 1.03 × 0.02 λ
L
³
, where λ
L
is the free-space wavelength at the lowest resonance. The diplexer will have the potential application to operate at up-link and down-link frequencies of satellite communication, full-duplex, and a radar system in the C and X bands.