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We present a circularly polarized (CP) endfire leaky wave antenna with a high gain, low profile, wide axial ratio bandwidth, and high gain-to-length ratio in this communication. The proposed CP endfire leaky wave antenna comprises CP nonresonant radiation elements and double-sided parallel strip lines (DSPSLs). The DSPSLs feed CP radiation elements through spatial coupling, leveraging the identical E-field modes of DSPSLs and elements. The antenna achieves a low profile due to the same height of DSPSLs and elements. The enhanced CP nonresonant radiation elements are adopted to extend the aperture, achieving a high gain. Moreover, the amplitudes and phases of the orthogonal E-fields generated by the CP nonresonant radiation elements vary linearly with frequency, ensuring a wide axial ratio bandwidth. Energy propagation through two paths, including DSPSLs and spatial coupling of elements, results in a uniform aperture and a high gain-to-length ratio. The fabricated antenna demonstrated a maximum gain of 13.9 dBic, a gain-to-length ratio of 8.13, and an axial ratio bandwidth of 18.57%, with a low profile of $0.04~\lambda _{0}$ .

In this article, a novel circularly polarized (CP) phased array is proposed with the augmented feature of high-precision beamforming with low axial ratio (AR) and wide AR bandwidth. First, the two-stage sequential rotation feed (SRF) technique is adopted in the CP phased array, broadening the AR bandwidth. Then, the innovative 180°–90°/90°–180° combined SRF network is implemented in the CP phased array, to perform a high-precision beamforming, ensuring low AR and AR bandwidth of scanning beams. Utilizing the proposed SRF topology, output phase differences of the feed network are kept constant over the operating band with an effective improvement of port isolation. Moreover, the coupling transition with filtering responses is applied to reduce the cost and complexity of fabrication. Long blind vias that require the back-drilling process are avoided. Finally, a prototype of the CP phased array for Wi-Fi applications is fabricated. The 180°–90°/90°–180° combined SRF beamforming network is measured separately, with highly stable output phase differences and isolation at output ports of higher than 12.17 dB over the operating band from 2.30 to 2.60 GHz. With the proposed SRF beamforming network, the CP phased array supports a wide-angle scanning of ±50°, with high precision of pointing error $\le 1^{\circ }$ . The AR of beams is lower than 1.31 dB at 2.45 GHz. The AR bandwidth (AR $\le 3$ dB) of steered beams is 28.6%, from 2.15 to 2.85 GHz.

In this letter, a novel planar all-metal single-conductor planar ladder endfire antenna is introduced for the first time. The proposed antenna has the advantages of stable endfire radiation, broad bandwidth, low-cost, and easy assembly. By adopting the air-substrate feeding structure, the antenna achieves a moderate phase constant, leading to a stable endfire radiation pattern. Meanwhile, choosing a longer radiating element can produce a larger radiating aperture and thus attain a wider bandwidth. Moreover, by differentially feeding the radiating elements on both sides, the whole configuration has an integrated single-conductor design. Due to the novel single-conductor structure, the proposed antenna is low-cost and easy to assemble. Finally, the prototype is simulated, fabricated, and tested to validate its performance. The measured impedance bandwidth is 20% from 2.7 to 3.3 GHz. The measured 1 dB and 3 dB gain bandwidths are 13.3% and 28.3%, respectively.

A 1-D wide-angle scanning phased antenna array with enhanced gain and reduced mutual coupling by using a thin dielectric superstrate (DS) is presented. The DS can enlarge the effective aperture in the ${H}$ -plane and improve the directivity without sacrificing the wide scan range in the ${E}$ -plane. The directly coupled waves between the antenna elements can be cancelled out by the partially reflected waves from the DS, giving reduced mutual coupling. To demonstrate the idea, a $1\times 8$ phased patch antenna array loaded with a 3-D printed DS was designed, fabricated, and measured at 10 GHz. The DS has a small thickness of $0.16~\lambda _{0}$ , where $\lambda _{0}$ is the wavelength in free space. The measured realized gain is enhanced by 1.6–3 dB in the scan range of ±48° with the scan loss being less than 3.2 dB. The measured port isolation is improved by 7.4 dB.

This letter introduces a multifunctional low-profile wideband dual-polarized dipole antenna and its 4-element array. The proposed antenna and array can be applied to the WiFi (2400–2497 MHz, 5150–5350 MHz) and 5G (2515–2675 MHz, 3400–3600 MHz, 4800–4960 MHz) indoor base station applications. Unlike the existing literature, this design adopts a new balun design and optimization method to improve the antenna performance. Under the simple typical single-layer dipole radiation structure, the balun is designed using the key parameters extraction joint particle swarm optimization algorithm. The proposed dipole antenna can simultaneously realize the advantages of wide band, low profile, and easy machining. At the lowest frequency of 2400 MHz, the profile of the antenna is only 0.14λ0. Furthermore, by cleverly synthesizing the radiation pattern of active elements, precise patterns and gain performance of the antenna array are obtained without the feeding network. The maximum measured gain of the 4-element array can reach 14.2 dBi, demonstrating good agreement with simulation results. Based on the proposed balun design method, further optimizing the radiator promises to achieve superior performance for both dipole antennas and arrays.

In this article, a dual-polarized 2-bit electronically reconfigurable reflectarray (RRA) is proposed for 5G beam scanning applications. By introducing two parallel transmission lines and a T-junction, only two p-i-n diodes are used to generate 2-bit phase quantization is analyzed and verified. Based on this concept, a novel 2-bit dual-polarized RRA element is presented that makes use of an aperture-coupled patch and microstrip delay lines behind its ground plane. Only two p-i-n diodes are loaded on each delay line to realize the 2-bit phase quantization. Two orthogonal linear polarizations are independently controlled by deploying two perpendicular coupling slots and two delay lines. A $16\times16$ RRA prototype is fabricated and tested at 3.6 GHz. The measurement and simulation results show good agreement. Both polarizations can provide a ±60° 2-D beam scanning range with a maximum scanning gain drop of 2.75 dB. The maximum measured gain is 23.11 dBi, which corresponds to an aperture efficiency of 40.56%. A 1-dB measured gain bandwidth of 8.06% is also achieved.