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A novel windmill‐shaped metasurface (MTS) structure is firstly presented and applied to realise broadband antennas with stable radiation patterns. Different from conventional square MTS structure, the proposed windmill‐shaped MTS structure is formed by etching several triangular sawtooth slots instead of rectangular slots on the radiating square patch. Through the characteristic mode analysis, it can be found that the proposed MTS structure exhibits a much stable broadside radiation within a large bandwidth of 45.9%. Besides, the tapered edges resulted from the sawtooth slots can be regarded as smoother transitions, which would bring a better impedance matching. Based on above analysis, two antennas with different aperture sizes using the proposed windmill‐shaped MTS are well designed accordingly. Both antennas demonstrate the capability to achieve large impedance bandwidths over 40% and stable radiations (2‐dB gain bandwidth >33%). Compared with the conventional MTS‐based antenna, these proposed antennas improve the bandwidth and radiation performances effectively, showing great promises for modern wireless communication systems. [ABSTRACT FROM AUTHOR]

A low-profile and shared aperture dual-polarized (DP) omnidirectional antenna by reusing the structure of an annular quasi-dipole array is presented. The proposed antenna consists of a center-fed circular patch antenna, an annular quasi-dipole array, a wideband one-to-four power divider integrated with the center-fed circular patch antenna, and two annular strips. The center-fed circular patch antenna is utilized as the driven element for the vertically polarized (VP) radiation. The annular quasi-dipole array fed by the one-to-four power divider produces horizontally polarized (HP) radiation. Simultaneously, it also acts as the VP director to improve VP gain and bandwidth. Besides, the two annular strips enhance the HP omni-directivity and gain. In this way, the VP and HP share the same aperture to improve the profile utilization rate effectively. Due to the symmetry of the basic antenna structure, stable DP donut patterns are obtained within the entire operating bandwidth. For demonstration, a 4.1–5.0 GHz prototype is designed, fabricated, and measured. Under a low profile of $0.13\lambda _{0}$ , the prototype realizes a −10 dB overlapped bandwidth of 20%, high port isolation of above 35 dB, and stable DP donut patterns with horizontal gain larger than 1.8 dBi. [ABSTRACT FROM AUTHOR]

A planar bidirectional circularly polarized (CP) antenna using orthogonal magnetic dipoles (OMDs) without an extra phase shift line is proposed in this work. It consists of a rectangular microstrip magnetic dipole antenna (MMDA) and a loop radiator with two arms directly connected to the open edge of MMDA. The working principle is revealed by the equivalent sources model to provide a clear physical insight at first. The theoretical investigations imply that by controlling the width and the feed locations of the loop antenna on the aperture, the phase and magnitude for CP radiation can be realized in both endfire and backfire directions without introducing an additional phase shift line structure. For demonstration, one antenna prototype is designed and fabricated. The experimental results indicate that an overlapping bandwidth of 5.91% from 2.30 to 2.44 GHz is attained. Compared with the counterpart using OMDs, the proposed antenna exhibits a low design complexity and improved gains of 3.56/1.83 dBic in the endfire/backfire directions. [ABSTRACT FROM AUTHOR]

This communication presents a new multiband multiarray (MBMA) scattering suppression antenna configuration for a dual-band and dual-polarized antenna array with reduced radiation distortion. The proposed antenna array configuration consists of a low-band (LB) antenna element working in the 690–960 MHz band and four high-band (HB) antenna elements working in the 1.7–2.7 GHz band. The LB antenna introduces U-shape structures to the radiation element to neutralize HB scattering currents. On the other hand, the HB antenna involves an LC resonant structure between its radiation arm and feeding balun to suppress LB scattering currents. An antenna array using the proposed LB and HB elements is designed to achieve MBMA functions. Experimental results show that the radiation distortions in both LB and HB bands are improved significantly. The VSWR of less than 1.5, the isolation of more than 25 dB, and the symmetrical radiation pattern are obtained in both bands. [ABSTRACT FROM AUTHOR]

This article presents an antenna array to produce a circularly polarized (CP) isoflux beam for CubeSat earth coverage applications. Distinguished from conventional arrays formed by identical elements, the proposed one is based on sequential rotation-fed concentric annular aperture elements. By adjusting the excitation phase, magnitude, and polarization of each annular aperture element, the radiation patterns of the array can be shaped to form isoflux beams. Radiation pattern modeling method is developed to obtain array radiation parameters. Besides, to effectively characterize the impedance matching of the radiators of the array with multiple excitations, an overall reflection coefficient is deduced from signal decomposition. A prototype operating at $C$ -band (5 GHz) is designed, fabricated, and measured. It consists of a radiator and a feeding network. The radiator is formed by two annular aperture elements, of which the inner one is realized by a circular patch antenna while the outer one is formed by eight planar inverted-F antennas (PIFAs). The feeding network drives annular aperture elements in the manner of sequential rotation. In this way, a CP isoflux beam array with a low profile ($0.078~{\lambda }_{0})$ , lightweight, and ease-of-integration for CubeSat is realized. The proposed array can also be extended to realize other shaped beams. [ABSTRACT FROM AUTHOR]

An annular array antenna is proposed in this letter. The proposed low-profile antenna produces an enhanced gain with omnidirectional vertically polarized radiation patterns. Center-fed via-shorted circular patch antenna with omnidirectional radiation pattern can be low profile and wide bandwidth but suffers from tilted beam leading to a low gain in the azimuth plane. To improve the azimuth gain, instead of the traditional way of increasing the profile, a low-profile omnidirectional director is exploited, which is basically a passive magnetic dipole consisting of an annular side-coupling open-cavity. Several directors cooperating with the driven element form the proposed antenna, whose working principle is similar to the Yagi–Uda antenna. A prototype with a low profile of 0.11 ${\lambda _0}$ is designed and fabricated. Measured results show that the prototype can realize −10-dB impedance bandwidth of 13% (4.72–5.42 GHz) and gain of 3.72 dBi at 5.34 GHz with good omnidirectivity. Compared with that of the driven element only, the omnidirectional azimuth gain is significantly improved within the bandwidth, with the maximum gain being enhanced from −4.2 to 3.72 dBi at 5.34 GHz. The proposed antenna is designed for a portable 5G sub-6 GHz wireless channel measurement application. [ABSTRACT FROM AUTHOR]

In this paper, a novel filtering antenna based on periodic spoof surface plasmon polaritons (SSPPs) is proposed. Double-sided parallel-strip line (DSPSL) is used to realize the wideband property for the double-layer SSPPs. Filtering performance can be realized by adding via holes and ring resonators in the double-layer SSPPs. The simulated and measured results indicate the high gain of 9.38 dBi and bandwidth of 10.44% can be achieved for the antenna with via holes and ring resonators, the out-of-band rejection is over 17 dBi. Meanwhile, the gain variations are less than 1 dBi in the whole frequency band. Good agreements can be observed between the measured and simulated results, which indicate good potential applications in the communication systems and integrated circuits. [ABSTRACT FROM AUTHOR]

This study develops a differential‐fed filtering patch antenna, which features superior frequency selectivity, compact size, low cross‐polarisation, and symmetrical radiation patterns. The proposed antenna consists of a rectangular patch on the top layer, which is differentially fed by a balun bandpass filter on the bottom layer. A pair of rectangular coupling slots were etched on the middle layer for energy coupling. The patch antenna performs not only as the radiator but also as the last resonator of the whole filter circuit for compactness. A prototype of the proposed filtering antenna operating at 2.45 GHz was fabricated and tested. The measured in‐band peak gain is 5.9 dBi with steep roll‐off at band edges, and the out‐of‐band gain is less than − 25 dBi. Moreover, symmetrical radiation patterns and low cross‐polarisation levels of − 22 dB are also realised for the proposed filtering antenna. [ABSTRACT FROM AUTHOR]

In this paper, two 24 GHz horizontally polarized $1 \times 8$ patch antenna arrays were developed for automotive radar applications. The proposed antenna arrays offer the advantages of wide fan beams and high gain. The far-field radiation patterns are widened in the E-plane by disturbing the near-field distribution of each driven patch. In Design I, the driven patch is loaded with a parasitic loop, which functions as a director in the E-plane. Due to the directing effect, the E-plane beamwidth can be increased. The experimental verification prepared for Design I showed that a beamwidth of 130° and a gain of 12.2 dBi can be achieved through this method. To further enhance the beamwidth, another array with each patch loaded with parasitic mushroom-like elements was proposed by Design II. The PMLEs are 180° out of phase to their corresponding driven patch. The cancelation effects can be properly managed to slightly sacrifice the gain of the array in return for a wider beamwidth in the E-plane. Design II exhibits a wider beamwidth of 150° and a lower gain of 11.1 dBi. [ABSTRACT FROM AUTHOR]

A novel steerable dual-beam metasurface antenna (MSA) with controllable feeding mechanism is proposed. The proposed MSA consists of $7 \times 10$ square metasurface cells and is fed by a completely symmetrical controllable network, which includes three dumbbell-shaped coupling slots etched on the ground and two-port stepped impedance line beneath the ground. The network can flexibly control the magnitude and phase of the coupling energy from the feeding line to the radiated metasurface cells via the slots, so as to realize two desired symmetrical beams. Owing to good directional radiation of the MSA, the beams of the proposed MSA exhibit better front-to-back ratio, higher gain, and higher channel isolation than those of traditional traveling-wave slot antennas. Moreover, benefiting from the controllable feeding mechanism, impedance matching, sidelobe suppression, and isolation of the ports can be further improved. Consequently, the two achieved beams are, respectively, oriented at ±30°in azimuth plane with 10 dB beamwidth of about 120°, high-peak gains of 12.8 dBi and cross level at two beams junction of about −10 dB; meanwhile, the isolation of the two ports is over 15 dB within the band of interests (5.23 and 5.40 GHz). For demonstration of the design strategy, one $1 \times 2$ dual-beam MSA array with gain of 14.8 dBi and similar beam performance is designed and fabricated. Due to the controllable steerable beams and the simple mechanism without complex beamforming networks, phase shifters or large footprint, the proposed steering dual-beam MSA array can be expected to find potential applications in multibeam base stations. [ABSTRACT FROM AUTHOR]

A millimeter-wave series–parallel patch antenna array is presented, in which the dual-slot feeding structure is handily implemented using the intrinsic field distribution of TE20 mode in substrate-integrated waveguide (SIW). One 28 GHz patch antenna element fed by the TE20-mode SIW is first designed, achieving a 10 dB impedance bandwidth of 10.2% and a simulated peak gain of 6.48 dBi. Based on the antenna element, a $4 \times 4$ array with a compact series–parallel differential feeding network is developed accordingly. Due to the novel compact SIW-based series–parallel feeding network, the antenna array can achieve superior radiation performances, which is the highlight of this communication. The simulation and measurement results of the proposed antenna array are in good agreement, demonstrating a performance of 8.5% impedance bandwidth, 19.1 dBi peak gain, symmetrical radiation patterns, and low cross-polarization levels (−30 dB in E-plane and −25 dB in H-plane) in the operating frequency band of 26.65–29.14 GHz. [ABSTRACT FROM AUTHOR]

This paper presents a 60-GHz $4 \times 4$ differential -fed patch antenna array using low-temperature cofired ceramic (LTCC) process. Wideband patch with L-shaped feeding scheme is adopted as antenna element, while differential substrate integrated waveguide feeding network with low insertion loss is applied for the integration of antenna array. The differential-fed structure improves the symmetry of radiation patterns and reduces the cross-polarization level significantly. To further suppress the surface wave and improve the gain of the antenna array, one kind of soft surface structure is proposed. The equivalent circuit model of the soft surface is developed for calculating its dispersion diagram and analyzing stopband characteristics. The simulated results indicate that the antenna gain enhancement can be up to 2 dB because of the proposed soft surface. For demonstration, one prototype using LTCC process is fabricated and measured. The measured 10-dB impedance bandwidth of the antenna array is 11.7%. The measured antenna peak gain of 18.62 dBi at 61.5 GHz and symmetrical radiation patterns with a low cross polarization of −25 dB across the whole operating frequency are achieved. [ABSTRACT FROM AUTHOR]

A novel polarization-reconfigurable mechanism based on a polarization-rotation artificial magnetic conductor (PRAMC) structure is proposed. A new polarization-reconfigurable antenna is designed by combining a PRAMC-based multipolarized dipole antenna with a RFIC switch-based network, in which three polarization states of right-handed, left-handed circular polarization (RHCP, LHCP) and +45^\circ linear polarization (LP) can be realized by controlling the dc bias of the switches accordingly. The multipolarization antenna is well designed for offering three polarization states. A large 3-dB axial ratio (AR) bandwidth of 15.5%, a wide 3-dB AR beamwidth for CP states and a large cross-polarization isolation of more than 50 dB for LP state together with a broad impedance bandwidth of 20.5% are obtained. A switch network is used to generate three feeding modes, and the performance of the RF-integrated circuit (RFIC) switches is experimentally verified. A prototype of the proposed polarization-reconfigurable antenna is fabricated and tested. Good agreements between the measured and simulated results are observed, which indicates good performances of the proposed antenna. [ABSTRACT FROM PUBLISHER]

A novel polarization rotation technique based on an artificial magnetic conductor (AMC) structure is proposed. A new polarization rotating reflective surface (PRRS) is designed using a newly proposed AMC as the unit cell. The height of the so-constructed PRRS is only 0.04 \lambda0. Our theoretical analysis shows that the polarization rotation property of the new PRRS is due to an impedance imbalance which can be analyzed using an equivalent circuit model. In addition, two polarization rotation bands and a large polarization rotation bandwidth of 29.1% can be achieved by using the new PRRS. Moreover, the new PRRS is applied for the first time to design a low-profile dipole antenna for the generation of circular polarization radiation. Three polarization states are readily achieved. Both simulation and measurement results demonstrate good right-handed circular polarization with a broad axial ratio bandwidth and a large axial ratio beamwidth in both the x o z and y o z planes. [ABSTRACT FROM PUBLISHER]

A novel polarisation rotating reflective surface (PRRS) based on a tri‐via artificial magnetic conductor (AMC) structure is proposed. It has three polarisation rotation (PR) frequency points, which can be adjusted by the offset of vias loaded in the AMC structure. When a proper offset is chosen, two adjacent PR frequency points will come together to form a wide PR band. As a result, two PR bands can be obtained. Moreover, the new PRRS is applied to the design of a low‐profile dipole antenna for the generation of circular polarisation radiation. Simulation and measurement results both demonstrate good right‐handed circular polarisation. [ABSTRACT FROM AUTHOR]