A metasurface-based circularly polarized (CP) microstrip patch antenna with high performance in terms of the global bandwidth and gain is presented. The antenna configuration was a square modified microstrip patch that was sandwiched between a metasurface and the ground plane. The metasurface comprised a 4 × 4 array of square patches, while the single-feed radiating microstrip patch had axial ratio (AR) tuning stubs and a crossed slot. Under excitation, the microstrip patch and crossed slot, in conjunction with the metasurface, generated multiple resonances and AR minimum points that combined to produce large global bandwidths with regard to the impedance, AR, and 3-dB gain. Using a stacked layout, a low-profile design with the dimensions of 54 mm×54 mm×3.1 mm (1.2 λ0×1.2 λ0×0.07 λ0 at 6.8 GHz) was obtained, which generated a highly stable broadside gain above 10 dBic throughout the entire operating AR bandwidth. This antenna had a measured −10 dB impedance bandwidth of 5.62–11.04 GHz (65.06%) and a 3-dB AR bandwidth of 5.64–7.89 GHz (33.25%). Additionally, it had a measured 3-dB gain bandwidth of 5.17–8.2 GHz (45.32%), with a measured peak gain of 12.17 dBic.

In this paper, we have proposed a non-uniform series-fed angled dipole array antenna with a high gain, a wide bandwidth, a good sidelobe level (SLL), and a high front-to-back ratio characteristics. The proposed array antenna structure consisted of eight dipole elements, and each dipole was connected to a parallel stripline printed on the front and back sides of the substrate. From the first dipole element near the ground plane to the eighth dipole element at the end of the parallel stripline, the length of each dipole was reduced by ΔLd. As with dipole length, the spacing between the dipole elements decreased by ΔSd from each previous dipole spacing. Compared to uniform array antennas, the impedance and gain bandwidths were greatly increased, and the SLL and front-to-back (F/B) ratio characteristics were improved. The proposed array antenna had an |S11| < –V10 dB, an impedance bandwidth of 23.3–V51.0 GHz, and a 3-dB gain bandwidth of 22.0–V44.0 GHz. At 28 GHz, the E-and H-plane SLLs of the proposed array antenna were –V24.1 dB and –V18.8 dB, respectively. The F/B ratio of the proposed antenna was less than –V30 dB.

This paper proposes two reduced-size crossed-dipole antennas that comprise two printed crossed-dipole arms and a pair of vacant-quarter printed rings to generate circularly polarized (CP) radiation. The T-shaped crossed-dipole antenna is similar to a conventional crossed-dipole antenna but differs that half of the crossed dipole is rotated 90°. This rotation reduces the dipole’s area coverage by nearly half, resulting in a compact antenna that generates CP radiation with performance similar to that of a conventional crossed-dipole antenna. A compact folded E-shaped crossed-dipole with good CP radiation characteristics is formed by folding the arms of the T-shaped antenna. The performance of these compact reduced size crossed-dipole antennas is discussed. The T-shaped antenna with an overall radiator size of 30.3 mm × 51.4 mm × 0.508 mm (0.29λo × 0.5λo × 0.005λo at 2.97 GHz) has an |S11| < −10 dB bandwidth of 2.58–3.42 GHz (28%) and a 3 dB AR bandwidth of 2.78–3.16 GHz (12.8%). The folded E-shaped crossed-dipole antenna with overall dimensions of 19.6 mm × 31 mm × 0.508 mm (0.21λo × 0.33λo × 0.0055λo at 3.25 GHz) has an |S11| < −10 dB bandwidth of 2.92–3.44 GHz (16.4%) and a 3-dB AR bandwidth of 3.06–3.44 GHz (11.7%).

In this paper, a method to reduce mutual coupling between an E-plane and H-plane coupled microstrip patch antenna is presented. Two dual differentially fed square patches are designed in a 1 × 2 antenna array configuration. To minimize mutual coupling and its effects, coupled split-ring resonators (SRRs) are designed, characterized and positioned between the patches. Circular SRRs are designed and coupled to produce a band-stop response to suppress surface waves propagating within the dielectric substrate while enhancing isolation. Mutual coupling interactions and the suppression mechanism are discussed in relation to the patches and SRRs. The patch radiators are dual differentially fed to achieve polarization diversity. E- and H-planes decoupling is achieved between the two patches throughout their bandwidth while maintaining good antenna performance. A prototype of the antenna array and the SRR is fabricated and measured to validate the decoupling approach. With a separation distance of 0.49$\lambda$ between the patches, the measured S-parameters show an impedance bandwidth of |S11|≤−10 dB, covering 9.27–9.46 GHz, and −38 dB and −35 dB mutual coupling for E- and H-planes, respectively, are observed throughout the antenna operating bandwidth.