Comparative Study of Electromagnetic Transparent Structures for Design of Aperture Shared Antenna Arrays

In this paper, three different geometries applied on low-band (LB) dipoles to suppress cross-band interference at High-band (HB) frequencies were compared. The radiation pattern of a HB dipole in the proximity of a LB dipole is usually negatively affected, likewise is port isolation and impedance matching. The results show a reduction of cross-band interference in the HB, compared to a regular LB dipole. A split-ring resonator (SRR) geometry was selected and the dimensional parameters were optimised for the targeted band. A prototype of the optimised design was manufactured to verify the simulated results. The measurement of the SRR showed a deviation less than 1 dB from the reference in both transmission and directivity over a fractional bandwidth of 19% with the centre frequency at 5.2 GHz. However, by shifting the centre frequency to 5.54 GHz the same metric would increase to 30% in the band 4.7−6.37 GHz. In the same frequency band, the difference in half-power beamwidth (HPBW) never exceeds 15◦ for the SRR, averaging 5.4◦ and 6.2◦ in the E-plane and H-plane, respectively. In comparison, the regular dipole reached 22.8◦ and 32.8◦ in the same band. At the higher end of the HB, the SRR LB antenna acts as a director, thus providing higher directivity than the reference. The increased directivity presents some problems by creating new side lobes at these frequencies.