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This paper presents a novel sequentially rotated patch array antenna with dual circular polarizations (CP). The present design has the advantages of compact size, simple feed networks, low cross polarization, and high isolation. The radiating elements are dual linearly polarized (LP) equilateral triangular patches with hybrid feeds. The vertical polarization (VP) of the patch antenna is obtained by using an aperture-coupled feed and the horizontal polarization (HP) is obtained by using a proximity feed. These two feeds are orthogonally positioned and are printed on different PCB layers, which leads to the high isolation between these two ports and facilitates the design of the feed networks. The array antenna consists of six such dual-LP triangular patches sequentially rotated by 60 ^\circ and fed by separated feed networks. Since LP antenna elements are used, the design of the feed network is much simplified. Through sequentially varying the feeding phase by \pm 60^\circ, dual circular polarizations are obtained. The operation principle of the array antenna is also analytically explained in this paper. To verify the design concept, one dual LP equilateral triangular patch and one dual CP equilateral triangular patch array resonating at 10.5 GHz are designed, fabricated, and tested. There is a good agreement between the simulation and measurement results, both of which show that the array antenna exhibits high port isolation and good circular polarizations with low cross polarization at different planes. The proposed design technique can be applied to the design of dual CP array antennas operating at other frequency bands. [ABSTRACT FROM PUBLISHER]

Low-profile wideband circularly polarized (CP) array antennas using integrated half-power quadrature power divider (HP-QPD) are presented. A novel HP-QPD is first proposed as an important design concept for CP radiation. Detailed analyses show that the proposed HP-QPD can have half-power CP radiation and the remaining half-power transmission with equal-magnitude but quadrature phase difference. Therefore, it can be utilized for designing a 1 $\times $ 2 CP array antenna. Compared to the traditionally designed single-feed or dual-feed CP counterparts, this 1 $\times $ 2 array antenna can have more than four times wider axial ratio (AR) bandwidth with three CP modes and a simple feed network. This 1 $\times $ 2 array antenna was then designed, fabricated, and measured for performance verification. Both measured and simulated results show that this array antenna can have a wide overlapped impedance and AR bandwidth of 7.9% with a thin dielectric thickness of $0.031\lambda _{0}$. The 1 $\times $ 2 array antenna was further extended to a 1 $\times $ 8 linear array antenna for high gain CP radiation. Measured results show that unidirectional and symmetrical radiation patterns are achieved with high peak realized gain of 15.4 dBic, low profile, and simple feed network. [ABSTRACT FROM AUTHOR]

In this article, a novel millimeter-wave dual-polarized 2-D multibeam antenna array incorporating differentially fed antenna elements is proposed to achieve high cross-polarization discrimination (XPD) when the beams scan to the maximal pointing angles. The antenna element is composed of an SIW cavity with four shorted patches placed inside, and it is differentially excited for dual-polarization by a pair of feeding strips and transverse slots beneath the patches. Differential excitation is realized by a power divider designed on two laminate layers. Two Butler matrices placed perpendicularly with each other in different laminates are employed to generate four tilted beams with dual-polarization. A $2\times 2$ dual-polarized 2-D multibeam antenna array working at 28 GHz is designed, fabricated, and measured. The operation bandwidth of the antenna is 26.8–29.2 GHz. The improvement in the XPD is experimentally demonstrated by far-field measurement. When the beams scan to 30° off the boresight, the measured XPDs are 28 dB at the center frequency and higher than 25 dB over the operation bandwidth, which confirms that the cross-polarized radiation in the 2-D multibeam antenna array is suppressed by using the differential-feeding technique. The measured gain is in the range from 7.6 to 10.5 dBi. [ABSTRACT FROM AUTHOR]

A new method to design wideband differentially driven dual-polarized antenna with high common-mode suppression and high port isolation is presented. The presented antenna can be equivalent as a combination of a six-port power divider and four crossed folded dipoles. The six-port power divider is composed of two orthogonal input ports and four equal magnitude output ports. Detailed analysis illustrates that the six-port power divider can have wide bandwidth and high isolation under odd-mode excitation and high common-mode suppression under even-mode excitation. Therefore, based on the wideband and high even-mode suppressed six-port power divider, a wideband differentially driven dual-polarized antenna is developed with high common-mode suppression. To validate the design concept, the proposed antenna was designed, fabricated, and measured. The measured results prove that the antenna has a wide impedance bandwidth of 1.64–3.0 GHz (58.6%) for the return loss higher than 15 dB and isolation higher than 35.4 dB. In addition, very high common-mode suppression is achieved for the measured common-mode reflection coefficient higher than −0.87 dB over the entire bandwidth. With stable antenna gain and half-power beamwidth, the developed antenna is suitable for base station applications. [ABSTRACT FROM AUTHOR]

A novel differentially driven dual-polarized patch antenna is presented in this communication. The proposed antenna is a low-cost design with a simple configuration, which avoids using the conventional high-cost multilayer PCB technology. The antenna is composed of two intersected open-loop resonators, which are connected to each other at the center. By using the electric coupling from the intersected resonators, two orthogonal radiating modes are excited from the top radiating patch. With the even- and odd-mode current distributions on the intersected resonators, high port isolation and low cross-polarization level are obtained. The external quality factor of the resonator is illustrated by using the analytical model of a double-loaded resonator. To demonstrate the design method, the proposed antenna and array are designed, fabricated, and measured. Compared to the traditionally designed capacitively coupled antenna, two times wider impedance bandwidth is obtained for the proposed antenna with high isolation (>38.5 dB) and low cross-polarization level (< −33 dB). The antenna array is designed for 5G base stations, which features the compact size and low reflection coefficient (< −15 dB). In addition, beam scanning performance of the antenna array is also investigated for base-station applications. [ABSTRACT FROM AUTHOR]

A novel broadband circularly polarized (CP) antenna with wide axial ratio (AR) beamwidth is proposed. It is composed of two curved arms shaped like an inverted “S.” The mechanisms of wideband CP operation and wide AR beamwidth are explained. To validate the concept, a prototype at C-band is manufactured and measured. Experimental results confirm that the antenna achieves an impedance bandwidth of 63% and a CP bandwidth of 42%. Furthermore, maximum AR beamwidth of 140° is achieved and wide AR beamwidth can be maintained in a frequency bandwidth of 35% in nearly all elevation planes. In addition, the antenna has the advantage of being easily extended to arrays. A four-element array using the proposed antenna is investigated through both simulations and experiments, and achieves 60% CP bandwidth and wide AR beamwidth. The proposed inverted-S antenna can realize wide CP bandwidth and wide AR beamwidth, and can easily form wideband CP arrays. [ABSTRACT FROM PUBLISHER]

A novel planar ultrathin electronically steerable parasitic array radiator (ESPAR) is presented in this paper. Through theoretical analysis of the electric fields of orthogonally crossed dipoles in phase quadrature, it is found that the crossed dipoles radiate linearly polarized wave with a rotational electric field in the azimuth plane. This characteristic is then utilized to design a planar crossed dipole ESPAR, termed as “CD-ESPAR.” Furthermore, a simple but effective impedance matching method is also proposed and analyzed. To verify these concepts, a prototype with compact size and very low profile ( 0.42~\lambda 0 \times 0.42~\lambda 0\times 0.006~\lambda 0) resonating at 2.3 GHz is designed, fabricated, and measured. The measured results indicate that the proposed antenna achieves more than 17.8% impedance bandwidth and can produce four directional beams, covering the whole azimuth plane. Owing to its planar ultrathin structure, compact size, electronically beam-switching ability, low power, and low cost characteristics, it is promising for applications in wireless communications. [ABSTRACT FROM PUBLISHER]

This communication presents a single-feed ultra-wideband circularly polarized (CP) antenna with high front-to-back ratio (FBR). The antenna is composed of two orthogonally placed elliptical dipoles printed on both sides of a substrate. To realize high FBR, a novel composite cavity is also proposed and integrated with the presented crossed dipoles, which effectively reduces the backlobe of the crossed dipoles. Simulation results are in good agreement with the measured results that demonstrate an impedance bandwidth from 0.9 to 2.95 GHz (106.5%) and a 3-dB axial ratio (AR) bandwidth from 1 to 2.87 GHz (96.6%). The measured FBR is about 30 dB across the whole global navigation satellite system (GNSS) band. Compared with other reported single-feed wideband CP antennas, the antenna has advantages such as a wider CP bandwidth and lower backlobe radiation. [ABSTRACT FROM AUTHOR]

A wideband differentially-fed slot antenna is presented for millimeter-wave (mmWave) applications. A novel method of using stepped corner-shaped slot is first utilized to establish the wideband circularly polarized (CP) radiation. In the configuration of corner-shaped slot, two wide open slots at the ends are utilized for effective orthogonal radiation, while the narrow slot at the center is utilized for power transmission and quadrature phase delay. An equivalent circuit is given to illustrate the inner working principle for CP radiation. In addition, square cuts are etched on the four corners of the radiating patches to further increase the axial ratio (AR) and impedance bandwidth. Based on this design concept, the antenna element was first designed and fabricated for performance verification. Then, a $1\times $ 4 linear array with beam-scanning performance and a $4\times $ 4 planar array with high gain and stable radiation were designed and fabricated. Both the simulated and measured results show that the $1\times $ 4 linear array and $4\times $ 4 planar array can have the wide overlapped impedance and AR bandwidths of 30.6% and 33.6% with a thickness of $0.16\lambda _{0}$ , respectively. The advantages of compact size and wide bandwidth make the presented antenna a good candidate for mmWave applications. [ABSTRACT FROM AUTHOR]

This article presents a novel design concept to realize a wideband circularly polarized (CP) antenna by using single-arm coupled asymmetric dipoles (SCADs). First, an impedance compensation method is developed to obtain flat antenna input impedance by designing different arm lengths of the asymmetric dipole. Then, a single-arm coupling method is introduced to improve the antenna bandwidth. Four asymmetric dipoles are bent and sequentially coupled to each other among the long arms of the dipoles. By elaborately adjusting the coupling among the long arms, improved bandwidth and compact radiator size are achieved simultaneously. In addition, to further enhance and optimize the operating bandwidth of the antenna implementation, impedance matching strip and interdigital structure are introduced into SCADs. To verify the design concept, a prototype of the SCAD antenna was designed, fabricated, and measured. Experimental results agree well with the simulations, showing a wide impedance bandwidth of 108% (1.53–5.12 GHz) and an axial ratio (AR) bandwidth of 96% (1.78–5.06 GHz). To the best of our knowledge, the proposed design concept of SCADs is first used to design a wideband CP antenna. Both the simulated and measured results prove that the proposed antenna is a promising candidate for modern broadband CP applications. [ABSTRACT FROM AUTHOR]