In this letter, we propose a broadband printed-dipole antenna and its arrays for fifth-generation (5G) wireless cellular networks. To realize a wide frequency range of operation, the proposed antenna is fed by an integrated balun, which consists of a folded microstrip line and a rectangular slot. For compactness, the printed dipole is angled at 45°. The single-element antenna yields an |S₁₁ | <;-10-dB bandwidth of 36.2% (26.5-38.2 GHz) and a gain of 4.5-5.8 dBi. We insert a stub between two printed-dipole antennas and obtain a low mutual coupling of <;-20 dB for a 4.8-mm center-to-center spacing (0.42-0.61 λ at 26-38 GHz). We demonstrate the usefulness of this antenna as a beamforming radiator by configuring 8-element linear arrays. Due to the presence of the stubs, the arrays resulted in a wider scanning angle, a higher gain, and a lower sidelobe level in the low-frequency region.

This letter proposes a compact wideband circularly polarized (CP) antenna array, which is a set of 2 × 2 metasurfacebased CP patch antennas fed by a sequential-phase (SP) network. The single element is composed of a truncated corner square patch sandwiched between the ground plane and the metasurface of a lattice of 4 × 4 periodic metal plates. These metasurface-based antennas are incorporated with the SP network of a sequentially rotated series-parallel feed to achieve wideband operation. The radiation pattern and operational bandwidth in the high-frequency region were improved by reducing the spacing between the driven patches while maintaining the structure and overall size of the metasurface. The final design, with an overall size of 64 × 64 × 2.34 mm ³ (approximately 1.26λ _o × 1.26λ _o × 0.046λ _o at 5.9 GHz), was fabricated and measured. The antenna array has a measured |Sιι| <; -10-dB bandwidth of 4.40-8.00 GHz (58.06%), a 3-dB axial ratio bandwidth of 4.75-7.25 GHz (41.67%), a 3-dB gain bandwidth of 4.8-7.0 GHz (37.3%), and a peak gain of 12.08 dBic at 6.0 GHz. In addition, the antenna array yielded a broadside, left-hand CP radiation with a symmetrical profile, low sidelobe level, and high radiation efficiency.

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.

A dual-wideband circularly polarized (CP) antenna was proposed based on the strategy of combining multimode resonances. The primary radiators were two barbed-shape dipoles and two bowtie dipoles printed on the same substrate. They were placed over an artificial magnetic conductor (AMC) for the low-profile antenna design purpose. Properly combining the fundamental mode of the barbed-shape dipole, the bowtie mode, the slot mode, the second mode of a barbed-shape dipole, and extra resonance generated by the AMC surface, a dual-wideband operation can be achieved. The final design with an overall size of 0.64λ _o × 0.64λ _o × 0.16λ _o at 2.4 GHz had measured impedance bandwidth of 40% (2-3 GHz) and 49.5% (3.8-6.3 GHz) for the lower and upper bands, respectively. The measured 3-dB axial-ratio bandwidths were 19.3% (2.25-2.73 GHz) and 33.8% (4.3-6.05 GHz) for the lower and upper bands, respectively. The antenna performed an average gain of about 6.6 dBic across the low CP region and 7.4 dBic across the high CP region.

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.

A method of using a simple single parasitic element to significantly enhance a 3-dB axial-ratio (AR) bandwidth of a crossed dipole antenna is presented. This approach is verified by introducing one bowtie-shaped parasitic element between two arms of crossed bowtie dipoles to generate additional resonance and thereby significantly broadening AR bandwidth. The final design, with an overall size of 0.79 λ _o × 0.79 λ _o × 0.27 λ _o (λ _o is the free-space wavelength of circular polarized center frequency), resulted in very large measured -10-dB impedance and 3-dB AR bandwidths ranging from 1.9 to 3.9 GHz (~68.9%) and from 2.05 to 3.75 GHz (~58.6%), respectively. In addition, the antenna also yielded a right-hand circular polarization with stable far-field radiation patterns and an average broadside gain of approximately 8.2 dBic.