Planar Millimeter-Wave Shared-Aperture Self-Diplexing Antenna with Small Frequency Ratio and High Isolation

This communication proposes a shared-aperture self-diplexing antenna using the composite parallel-plate waveguide (PPW). The long-straight slots (LSSs) etched on the top surface of the PPW are utilized as the common radiation aperture for two operating bands. At the high frequency band, the proposed antenna, excited by the alternative-phase TE 10 -mode wave, operates as a leaky-wave antenna (LWA). Meanwhile, it serves as a continuous transverse stub (CTS) array antenna when excited by the TEM wave at the low-frequency band. Two kinds of feeding networks are adopted to generate the alternative-phase TE 10 -mode wave and TEM wave, respectively. To verify the proposed method, a millimeter-wave prototype is designed, fabricated, and measured. The measured results show that −10 dB fractional bandwidths (FBWs) are 3.42% (76.25–78.9 GHz) and 14.5% (83.2–96.2 GHz), respectively, and the port isolation is higher than 40 dB. Additionally, the peak gains are 27.1 dBi at 78.5 GHz and 25.3 dBi at 90 GHz, respectively. The proposed antenna can be used to develop compact frequency-division system without using duplexers and multiband wireless systems.