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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]

This paper presents a single-layer circularly polarized reflectarray which achieves large bandwidth (BW) in terms of axial ratio (AR), gain, aperture efficiency (AE) and radiation pattern. By using a novel wideband S-shaped phasing element, an offset-fed reflectarray with 20° offset beam is designed based on the element angular rotation method. Theoretical analysis is given to analyze the effect of angular rotated elements on the performance of the reflectarray, which indicates that the AR BW of the reflectarray can exceed the AR BW of the feed horn. Furthermore, the influence of the differential spatial phase delay is analyzed quantitatively, and the performance of S-element-based reflectarrays with different aperture sizes are investigated and discussed. To verify these concepts, a 180 mm $\times180$ mm prototype with $15 \times 15$ elements is fabricated and measured. The measured results confirm that the proposed reflectarray achieves a 68.5% 3-dB AR BW (7 to 14.3 GHz) and a 47.8% 3-dB gain BW (8.6 to 14 GHz). Moreover, the AE is larger than 50% in a 33% BW and larger than 30% in a 64% BW. [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]

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]

A novel wideband four-arm sinuous antenna with dual circular polarizations (CPs) and unidirectional radiation is proposed. Different from the conventional designs, this sinuous antenna is realized in a conical form and no ground plane or absorptive cavity is required to obtain unidirectional radiation. The beamforming network for dual circularly polarized operations consists of a wideband quadrature coupler and two wideband baluns, and an auxiliary feeding patch is introduced to facilitate the connection between baluns and sinuous arms. The design of baluns and coupler is inspired from the printed exponentially tapered microstrip balun and broadside-coupled microstrip coupler, respectively. The dynamic differential evolution algorithm is employed to optimize the geometry of coupler for optimal performance. For both polarizations, the presented antenna has wide impedance bandwidth, good axial ratio, moderate realized gain, and front-to-back ratio within 2–5 GHz. An antenna prototype is fabricated and tested. The agreement between simulation and measurement results validates the proposed antenna framework. The demonstrated antenna has advantages of wide bandwidth, dual CPs, unidirectional radiation, lightweight, and low cost, and is promising for applications in wireless systems. [ABSTRACT FROM AUTHOR]

A novel polarization-reconfigurable planar antenna is presented. The antenna consists of an electronically reconfigurable polarizer integrated with a printed slot. By changing the states of the p-i-n diodes on the polarizer, the linearly polarized (LP) waves radiated by the slot can be converted into either right-hand circularly polarized (RHCP) or left-hand CP (LHCP) waves. The polarizer contains 16 unit cells arranged as a $4\times 4$ array. The antenna radiates RHCP waves if the p-i-n diodes on the top side of the polarizer are switched ON, while LHCP waves are radiated if the p-i-n diodes of the bottom side of the polarizer are switched ON instead. The physical mechanisms of the antenna are discussed and the parametric study is carried out by full-wave simulations. To verify the concept, one prototype at 2.5 GHz is designed, fabricated, and measured. Good agreement between the measured and simulated results is obtained. The antenna achieves a gain ≥8.5 dBic in both RHCP and LHCP with an aperture efficiency of 70%. Advantages of the proposed design include electronically reconfigurable polarizations for RHCP or LHCP, low profile, low cost, high isolation between the dc bias circuit and RF signals, high power handling capability, and easy extension to large-scale arrays without increasing the complexity of the dc bias circuit. To the best of our knowledge, this is the first report of an electronically polarization-reconfigurable CP antenna with a single-substrate polarizer. [ABSTRACT FROM AUTHOR]

A compact-size low-profile wideband circularly polarized (CP) omnidirectional antenna with reconfigurable polarizations is presented in this communication. This design is based on a low-profile omnidirectional CP antenna which consists of a vertically polarized microstrip patch antenna working in \textTM01/\textTM02 modes and sequentially bended slots etched on the ground plane for radiating horizontally polarized electric field. The combined radiation from both the microstrip patch and the slots leads to a CP omnidirectional radiation pattern. The polarization reconfigurability is realized by introducing PIN diodes on the slots. By electronically controlling the states of the PIN diodes, the effective orientation of the slots on ground plane can be changed dynamically and the polarization of antenna can be altered between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). The proposed antenna exhibits a wide-operational bandwidth of 19.8% (2.09–2.55 GHz) with both axial ratio below 3 dB and return loss above 10 dB when radiates either LHCP or RHCP waves. Experimental results show good agreement with the simulation results. The present design has a compact size, a thickness of only $0.024\lambda$ and exhibits stable CP omnidirectional conical-beam radiation patterns within the entire operating frequency band with good circular polarization. [ABSTRACT FROM PUBLISHER]