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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]

This paper presents a folded reflectarray designed for Ka-band satellite communication applications. The array element is a dual-polarized slot antenna with multilayered PCB structure and is designed to operate at 29.5–30.8 GHz band for both transmitting and receiving with single linear polarization. Vias are employed to suppress the surface wave propagation and reduce the mutual coupling between adjacent array elements, for achieving a reflectarray with a wide scan angle range. An equivalent circuit model for the array element is developed and it agrees well with the EM simulation results. Several passive demonstrators consisting of 116 elements spaced by 0.5\lambda 30\rm{GHz} were fabricated and measured. The experimental results show that the presented reflectarray is capable of steering the beam up to \pm 60^\circ in both E- and H-planes with low cross-polarization level. [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 article presents a new design of a differentially fed substrate integrated planar antenna array with dual-polarization. Compared with the traditional dual-polarized antenna arrays, the proposed array antenna has the advantages of simple configuration, high cross-polarization discrimination (XPD), and high gain. The 2 × 2-element subarray design with a via-loaded crossover structure is used, which reduces the complexity of the array antenna. The operation bandwidth is improved by generating three resonances in the subarray. An 8 × 8 antenna array is designed, prototyped, and tested to exemplify its potential applications in large dual-polarized antenna arrays. A planar orthomode transducer is used to achieve differential excitation for the antenna array. The measured results show that the proposed antenna array has an impedance bandwidth of 19.2–20.7 GHz for |S11|< −10 dB and port isolation higher than 20 dB. The array antenna exhibits a high XPD of 43 dB and a flat gain of about 22.2 dBi within the bandwidth. [ABSTRACT FROM AUTHOR]

This article presents a novel dual slant polarized antenna for millimeter-wave (mmWave) base stations. Compared with the traditional slant polarized mmWave antennas, the proposed antenna offers the advantages of high cross-polarization discrimination (XPD), good aperture efficiency, simple structure, and low profile. The corner-fed substrate integrated waveguide (SIW) cavity is adopted to improve the port isolation and XPD of this slot-coupled antenna. Four corner-truncated patches connected by a thin cross strip are placed over the SIW cavity to increase the operation bandwidth. Then, a $2\times 8$ antenna array is designed to exemplify the antenna element performance. To improve the impedance matching, a shorted patch is introduced in designing the series feeding network and the power divider. The experimental results show that the 2 dB-down gain bandwidth of the proposed antenna array reaches 6.0% and the port isolation is better than 20 dB. The gain and XPD of the antenna array measure 16.7 dBi and 25 dB at the center frequency, respectively. [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 novel dual-polarized crossed slot planar array antenna is presented in this communication. The proposed design integrates the antenna array with the feeding networks on a single laminate. The antenna element is developed by using a TE210 and TE120 mode cavity, which is constructed by inserting a number of metalized posts around the crossed region of two perpendicular substrate integrated waveguides (SIWs). The crossed slot is etched over the cavity and is excited from two orthogonal directions to realize dual-polarization. Owing to the orthogonality between the TE210 and TE120 mode, high isolation and low cross-polarization are achieved. A prototype of the designed antenna array operating at 25 GHz is fabricated and measured. The measured results confirm that the presented array antenna has high port isolation (>41 dB), high cross-polarization discrimination (XPD) (>26 dB), and high aperture efficiency (40%). With the advantages of simple configuration, good radiation performance, and easy fabrication, this proposed array antenna is a good candidate for millimeter-wave wireless systems. [ABSTRACT FROM AUTHOR]

A novel method of designing a wideband series-fed circularly polarized (CP) differential antenna by using crossed open slot pairs is presented in this article. The near-field distributions and input impedance analyses show that the closely spaced open slot-pairs can radiate as the crossed dipoles and have stable radiating resistance with a compact radiator size. Besides, a wideband half-power phase shifter using open slot is proposed and utilized to realize CP radiation. The proposed CP antenna is composed of a wide slot-pair and a narrow slot-pair. In the antenna design, the narrow slot-pair is not only excited as a radiator, but also elaborately loaded to provide wideband half-power output and quadrature phase excitation to the wide slot-pair. Both the proposed half-power phase shifter and CP antenna are illustrated by the corresponding equivalent circuits. Based on these analyses, the proposed antenna is designed, fabricated, and measured. Compared with the simulated traditionally designed counterpart, 2.1 times wider axial ratio (AR) bandwidth is achieved for the proposed antenna. The measured overlapped bandwidth for AR < 3 dB and return loss >10 dB is 1.95–3.45 GHz (55.6%). Also, the antenna gain and radiation patterns are measured, which agree well with the simulated results. [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 wideband differentially fed dual-polarized antenna with wideband harmonic suppression is presented. The radiating structure is composed of open slots, stair-shaped strips, and a square patch. Eight open slots are etched on the four corners of the square patch to realize symmetrical radiation and low cross-polarization for orthogonal polarizations. Stair-shaped strips are not only used to excite the open slots, but also introduce the monopole resonance. In addition, patch resonance is excited on the center square patch. For matching these different resonances, shorted microstrip lines are utilized to achieve the wide impedance bandwidth. Moreover, compact stepped impedance resonators are elaborately introduced on the top of the patch to achieve wideband harmonic suppression without any increase of the antenna footprint. The proposed antenna is designed, fabricated, and measured to verify the design method. The measured results demonstrate that the proposed antenna has the impedance bandwidth of 1.70–2.81 GHz for Sdd11 < −15 dB with high isolation of 39 dB. Moreover, wideband harmonic suppression is measured from 3 to 9 GHz with the Sdd11 higher than −2.2 dB, and the corresponding harmonic gain lower than −5.3 dBi. In addition, a stable gain of 7.2–7.9 dBi and beamwidth of 63°–71° are achieved for base station applications. [ABSTRACT FROM AUTHOR]

A compact wideband dual-polarized antenna with enhanced upper out-of-band suppression is presented in this paper. The proposed antenna is an equivalent configuration of two electric dipoles and two magnetic dipoles using the crossed shunt loops. The incorporation of the electric and magnetic dipoles enables the antenna to achieve wide impedance bandwidth and a compact radiator size. In addition, four parasitic strips are inserted near the inner edge of the four loops to enhance the antenna upper out-of-band suppression at 3.5 GHz with improved impedance bandwidth. The antenna is fed by the crossed coaxial baluns with high isolation. A shorting sheet is introduced into the baluns to enhance the upper out-of-band suppression further and create another rejection at 4.9 GHz. To demonstrate the design method, the proposed antenna prototype was fabricated and measured. Measured results show that the proposed antenna has a wide impedance bandwidth of 1.625–3.05 GHz (61%) for ${S}_{11} < -14$ dB with the isolation better than 38.3 dB. The upper out-of-band suppression of the antenna is also highly enhanced with measured ${S}_{11}>-2$ dB from 3.35 to 5.25 GHz. In addition, stable antenna gain and radiation patterns are achieved 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]

Crossed-dipole (CD) antennas have been widely employed for dual polarization in wireless communication systems in recent years. In this paper, a novel design concept of dual-polarized shared-dipole (DPSD) antenna is presented. Different from the traditional CD antennas, the arms of the DPSD antenna are shared for two orthogonal polarizations. This design technique leads to significant size reduction and high isolation compared to the traditional CD antennas. The operation principle of the proposed antenna is theoretically analyzed. To validate the presented design concept, two novel DPSD antennas are designed, fabricated, and measured. The first design is a four-port DPSD antenna, which is a straightforward demonstration of the operation principle of the DPSD antenna. The second design is a highly integrated DPSD antenna, which avoids the use of a feed network and provides a simple configuration to design the dual-polarized antenna. Both of the DPSD antennas are designed to operate at 1.7–2.7 GHz for base station applications. The simulated and measured results confirm that the two DPSD antennas have wide bandwidth with VSWR < 1.5 and isolation > 35 dB dB. In addition, stable gain and half-power beamwidth are obtained with the variance less than ±0.55 dB and ±3.5°, respectively. [ABSTRACT FROM AUTHOR]

Tightly coupled arrays (TCAs) have received considerable interests recently. Although various TCAs have been reported, they are generally limited to single or dual linear polarizations. Considering the importance of circularly polarization in various wireless systems, it is meaningful to design a circularly polarized (CP) TCA with a simple configuration. This communication presents a CP tightly coupled crossed dipole array (CP-TCCDA) with intrinsic CP feeding structure, which achieves wide overlapped impedance bandwidth and axial ratio (AR) bandwidth. An analysis is given to explain the principles of AR bandwidth improvement and is validated by the comparison of radiated E-fields between a CP-TCCDA and a conventional CP crossed dipole array. To verify the design concept, a $4 \times 4$ CP-TCCDA with elaborate feeding network is fabricated and measured. The measured results confirm that the proposed array achieves VSWR < 3 bandwidth from 2.06 to 6.46 GHz (3.14:1) and 3 dB AR bandwidth from 2.35 to 5.6 GHz (2.38:1), which are much wider than the bandwidth of an isolated element and a conventional array using the same element. [ABSTRACT FROM AUTHOR]

A novel ultra-wide-band tightly coupled dipole reflectarray (TCDR) antenna is presented in this paper. This reflectarray antenna consists of a wideband feed and a wideband reflecting surface. The feed is a log-periodic dipole array antenna. The reflecting surface consists of $26 \times 11$ unit cells. Each cell is composed of a tightly coupled dipole and a delay line. The minimum distance between adjacent cells is 8 mm, which is about 1/10 wavelength at the lowest operating frequency. By combining the advantages of reflectarray antennas and those of tightly coupled array antennas, the proposed TCDR antenna achieves ultra-wide bandwidth with reduced complexity and fabrication cost. A method to minimize the phase errors of the wideband reflectarray is also developed and the concept of equivalent distance delay is introduced to design the unit cell elements. To verify the design concept, a prototype operating from 3.4 to 10.6 GHz is simulated and fabricated. Good agreement between simulated and measured results is observed. Within the designed frequency band, the radiation pattern of the TCDR antenna is stable and the main beam of the antenna is not distorted or split. The side lobe levels of the radiation patterns are below −11.7 dB in the entire operating band. It is the first time a tightly coupled reflectarray is reported. [ABSTRACT FROM PUBLISHER]

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]

This paper presents a novel tri-band (X/Ku/Ka-band) planar antenna array with dual polarizations and shared aperture. Compared with traditional dual-polarized arrays, the proposed array has advantages of low cost, low profile, and high integration. Three types of antennas resonating at different frequencies, including the perforated patch, stacked patch, and slim crosspatch, are innovatively interleaved in the same aperture. The crosspatch fed by proximity coupling is presented as Ku-band element for its advantages of compact size, high isolation, and pure polarization. The techniques such as series feed and reverse feed are utilized to implement the six feed networks in a compact size with reduced cross polarizations. Measured results agree well with the simulations, showing three operation bands at X-, Ku-, and Ka-bands with the bandwidths of 3.6%, 6.7%, and 5.3%, respectively. The antenna also exhibits excellent radiation performance with the cross-polarization discrimination over 25 dB at the three bands. To the best of the author’s knowledge, this is the first shared-aperture X/Ku/Ka-band dual-polarized antenna array reported, which is useful for potential synthetic aperture radar applications. [ABSTRACT FROM AUTHOR]

A triband antenna with high gain and low profile is proposed. This antenna is based on the concept of Fabry–Perot cavity antenna (FPCA) and three resonances are obtained by employing two frequency selective surface (FSS) layers. Two FSS layers lead to two resonant frequencies by making each FSS layer satisfy the resonant condition of Fabry–Perot cavity. The third resonant frequency is obtained by exploiting the combined effects of the two FSS layers together. The operating principle of this proposed antenna is explained and the achievable frequency range is investigated. It is shown that the proposed method enables all three resonant frequencies to be independently tuned within certain frequency range. Because of the 0° reflection phase of the combined-FSSs, the present antenna has a low profile. To verify the design concept, one C-/X-/Ku-band FPCA is designed, fabricated and tested. Experimental results agree well with the simulated results. High gain with good impedance matching in three bands is obtained, which reaches a peak gain of 13.4 dBi at 5.2 GHz, 18.9 dBi at 9.7 GHz, and 20 dBi at 14.6 GHz. The overall height of the proposed antenna is approximately 0.36 wavelength at its lowest operating frequency. [ABSTRACT FROM PUBLISHER]

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 paper presents a novel shared-aperture dual-band dual-polarized (DBDP) high-gain antenna for potential applications in synthetic aperture radars (SARs). To reduce the complexity of SAR antennae, a DBDP high-gain antenna based on the concept of Fabry–Perot resonant cavity is designed. This antenna operates in both $C$ - and $X$ -bands with a frequency ratio of 1:1.8. To form two separate resonant cavities, two frequency selective surface layers are employed, leading to high flexibility in choosing desired frequencies for each band. The beam-scanning capability of this proposed antenna is also investigated, where a beam-scanning angle range of ±15° is achieved in two orthogonal polarizations. To verify this design concept, three passive antenna prototypes were designed, fabricated, and measured. One prototype has broadside radiation patterns, while the other two prototypes have frozen beam scanned to +15°. The measured results agree well with the simulated ones, showing that the high gain, high port isolation, and low cross-polarization levels are obtained in both the bands. Compared with the conventional high-gain DBDP SAR antennae, the proposed antenna has achieved a significant reduction in the complexity, mass, size, loss, and cost of the feed network. [ABSTRACT FROM AUTHOR]

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 dual-polarized filtering antenna with steep cut-off and compact size is developed for base-station applications. In this design, four controllable radiation nulls are obtained by utilizing split rings, slotted T-shaped branches, a single-stub tuner, and a parasitic loop. Split rings are first used as the dipole arms to obtain the first radiation null at upper out-of-band. Four T-shaped branches working as DGS are printed under the crossed dipoles to achieve the second radiation null. The connected outer conductors of the differential feed structure acting as a single-stub tuner can provide the third radiation null to further enhance the upper band rejection. Finally, a parasitic loop is incorporated around the split rings, and the out-of-band rejection of the lower band is further enhanced by the fourth radiation null. More importantly, the impedance bandwidth of the antenna can be expended with two newly introduced resonant modes. As a result, a compact filtering antenna with a wide operational bandwidth of 1.7–3.01 GHz (56%) is realized for $\vert \text{S}_{dd11}\vert < -15$ dB with the isolation higher than 38 dB. The out-of-band suppression is higher than 18.4 dB in 3.1–4.5 GHz and more than 47 dB in 0.8–1.1 GHz. [ABSTRACT FROM AUTHOR]

A novel method of designing a wideband high-isolated dual-antenna pair using dual-characteristic modes (CMs) is presented for fifth-generation (5G) multiple-input multiple-output (MIMO) smartphone applications. A set of orthogonal CMs resonating from the square-loop slot is first introduced and works for the lower band. Then, another set of orthogonal CMs resonating from the edge branches is introduced with a shared compact radiator and works for the higher band. In combination with two sets of degenerated CMs and a capacitive coupling feeding structure, the proposed dual-antenna pair achieves a broad impedance bandwidth and high isolation without the need for any external decoupling structures. Based on this dual-antenna pair, an $8\times $ 8 MIMO array is developed and integrated into the back cover of a smartphone, which realizes zero ground clearance on the system circuit board. To verify the design concept, prototypes of the antenna pair and MIMO array were fabricated and measured. It shows that experimental results agree well with the simulation results. More importantly, the presented $8\times $ 8 MIMO array has high isolation of more than 20 dB is achieved across the operating band of 3.3–3.8 GHz. [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 reflectarray (RA) with ultralow-profile and 2-bit phase quantization beam-steering ability is presented in this article. To reduce the profile, a Leaky-wave feed is used to excite the RA with enhanced illumination efficiency. Moreover, simultaneous sum and difference patterns are also obtained to provide beam flexibility. The entire thickness of the proposed RA is less than 3% of that of the conventional front-fed RA with the same aperture. To increase the efficiency of the RA, a novel unit cell consisting of a polarizer layer and a reflection layer is developed, which is configured to provide polarization rotation and 2-bit phase shifts by using a hybrid of tunable polarization and discrete resonator. The operation principle, theoretical explanation, and implementation of the proposed antenna are elaborated in this work. To prove the design concept and beam scanning performance, an array with $9 \times 7$ unit cells operating at Ka-band is designed and simulated first. Two-dimensional beam scanning within the range of ±30° has been verified. Then, a passive prototype with $9\,\,\times67$ unit cells is designed, fabricated, and measured. Experimental results show aperture efficiency of 35.1% and illumination efficiency of 43.4%. The developed RA is scalable, and it provides a viable low-cost solution to develop low-profile, high-gain and beam-steering array antennas for satellite 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]

A compact and wideband folded dipole antenna with multi-resonant modes is presented in this paper. Three resonant modes are obtained by using a modified planar folded dipole and its coupled feeding structure. Incorporating the shorting pins and parasitic patches, multiple resonant modes in the antenna are manipulated, shifted, and then combined to increase the impedance bandwidth. Using this concept, a prototype of a multi-mode folded dipole is designed, fabricated, and measured. The experimental results show that the proposed antenna achieves a bandwidth of 80% from 1.57 to 3.68 GHz, while occupying a compact size of $0.3\lambda _{0}\times 0.15\lambda _{0}\times 0.05\lambda _{0}$ ($\lambda _{0}$ is the wavelength in free space at the lowest operating frequency). Furthermore, a simple and effective design to achieve good omnidirectional radiation performance is developed by placing two proposed folded dipoles back to back. The antenna exhibits a flat gain variation of less than 1.27 dB over a broad bandwidth (82%) in the horizontal plane. Such a compact, wideband, planar antenna is a promising candidate for indoor signal coverage, wireless access points, and micro base stations in 2G/3G/4G/5G and WLAN/WiMAX wireless communication systems. [ABSTRACT FROM AUTHOR]

In this communication, a novel microstrip phased array with dual-polarized and wide-angle scanning in the 2-D space is proposed. The element antenna consists of a mushroom-shaped patch and two circular patches. Each circular patch is connected with one feeding port. The mushroom-shaped patch is excited via capacitive coupling through the gaps between the mushroom-shaped patch and the circular patch. The zeroth-order resonance and TM010 mode resonance are simultaneously generated in the mushroom-shaped patch. The 3 dB beamwidth of the element antenna in the 2-D space is in the range between 110° and 125°. One $6 \times 6$ phased array based on the antenna element is designed, fabricated, and measured. The phased array shows the dual-polarized wide-angle beam scanning in a range of ±66° in both $x {z}$ and $y {z}$ planes with the scan loss of 3.5 dB. [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]

In this paper, a novel dual-band dual-polarized array antenna with low frequency ratio and integrated filtering characteristics is proposed. By employing a dual-mode stub-loaded resonator (SLR) to feed and tune with two patches, the two feed networks for each polarization can be combined, resulting in the reduction of the feed networks and the input ports. In addition, owing to the native dual resonant features of the SLR, the proposed antenna exhibits second-order filtering characteristics with improved bandwidth and out-of-band rejections. The antenna is synthesized and the design methodology is explained. The coupling coefficients between the SLR and the patches are investigated. To verify the design concept, a C-/X-band element and a $2 \times 2$ array are optimized and prototyped. Measured results agree well with the simulations, showing good performance in terms of bandwidth, filtering, harmonic suppression, and radiation at both bands. Such an integrated array design can be used to simplify the feed of a reflector antenna. To prove the concept, a paraboloid reflector fed by the proposed array is conceived and measured directivities of 24.6 dBi (24.7 dBi) and 28.6 dBi (29.2 dBi) for the X-polarization (Y-polarization) are obtained for the low- and high-band operations, respectively. [ABSTRACT FROM PUBLISHER]

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]

This paper presents a compact-size, low-cost smart antenna with electronically switchable radiation patterns, and reconfigurable polarizations. This antenna can be dynamically switched to realize three different polarizations including two orthogonal linear polarizations and one diagonally linear polarization. By closely placing several electronically reconfigurable parasitic elements around the driven antenna, the beam switching can be achieved in any of the three polarization states. In this design, a polarization reconfigurable square patch antenna with a simple feeding network is used as the driven element. The parasitic element is composed of a printed dipole with a PIN diode. Using different combinations of PIN diode on/off states, the radiation pattern can be switched toward different directions to cover an angle range of 0° to 360° in the azimuth plane. The concept is confirmed by a series of measurements. This smart antenna has the advantages of compact size, low cost, low power consumption, reconfigurable polarizations, and beams. [ABSTRACT FROM PUBLISHER]