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In the paper, a circularly polarized (CP) frequency beam-scanning antenna based on photonic crystal (PC) is proposed, which possesses the characteristics of eliminating open-stopband (OSB). In the microwave field, the PC is typically constructed by embedding the air or metal column into the material. However, it is difficult for the PC with perfect magnetic conductor walls to accomplish the degeneracy of eigenmodes at the Γ point. Additionally, antennas based on the PC with perfect electric conductor walls exhibit a narrow scanning angle. The proposed unit based on 1D PC possesses perfect electric and magnetic conductor walls. The unit can not only eliminate OSB but also has a wide scanning range. In addition, the unit breaks into the original symmetrical field distributions of 1D PC. Based on the perturbation theory, leaky-wave slots can be designed to generate electromagnetic waves with the CP characteristics. And a CP antenna based on the unit is designed. The antenna can achieve a 70° beam-scanning within the entire operating band (7.6–9.2 GHz), and the variation of the realized gains is below 1.0 dBi around the broadside frequency. Simultaneously, the antenna is fabricated and measured. The measured results are in accordance with the simulation, which validates the success of the design. [ABSTRACT FROM AUTHOR]

In this paper, a patch array antenna with wideband circular polarization and high gain is proposed by utilizing a hybrid metasurface (MS). A corner-cut slotted patch antenna was chosen as the source due to the possible generation of CP mode. The hybrid MS (HMS), consisting of a receiver MS (RMS) arranged in a 2 × 2 array of squared patches and a linear-to-circular polarization conversion (LCPC) MS surrounding it was then utilized as the superstrate driven by the source. The LCPC MS cell is a squared-corner-cut patch with a 45° oblique slot etched, which has the capability for wideband LCPC. The LCPC unit cell possesses wideband PC capabilities, as demonstrated by the surface current analysis and S-parameter simulations conducted using a Floquet–port setup. The LP EM wave radiated by the source antenna was initially received by the RMS, then converted to a CP wave as it passed through the LCPC MS, and ultimately propagated into space. To further enhance the LCPC properties, an improved HMS (IHMS) was then proposed with four cells cut at the corners, based on the original HMS design. To verify this design, both CMA and E-field were utilized to analyze the three MSs, indicating that the IHMS possessed a wideband LCPC capability compared to the other two MSs. The proposed antenna was then arranged in a 2 × 2 array with sequential rotation to further enhance its properties. As demonstrated by the measurements, the array antenna achieved an S11 bandwidth of 60.5%, a 3 dB AR bandwidth of 2.85 GHz, and a peak gain of 15.1 dBic, all while maintaining a low profile of only 0.09λ0. [ABSTRACT FROM AUTHOR]

In this paper, a circularly polarized millimeter-wave L-shaped dipole antenna based on low temperature cofired ceramic (LTCC) technology is proposed, which realizes compact size and low-profile performance. The designed antenna consists of radiation patches and the grounded coplanar waveguide-substrate integrated waveguide (GCPW-SIW) feeding structure, which connects each other by two via holes. The radiation patches include a pair of L-shaped patches and four parasitic patches. The simulated results show that the proposed antenna operates from 26.5 to 29.5 GHz for |S11| < -10 dB and AR < 3 dB with a peak gain of 6.7 dBic. The antenna element size is only 0.58-0×0.58-0×0.056-0, where -0 is free-space wavelength at the center frequency of 28 GHz. A sample of the antenna is fabricated and measured to verify the proposed design, which has a good agreement with the simulated ones, indicating that the antenna has potential applications for the fifth generation (5G) mm-Wave n257 (26.5 - 29.5 GHz) frequency band communications and satellite communication systems. [ABSTRACT FROM AUTHOR]

A broadband circularly polarized (CP) printed monopole antenna which fed by coplanar waveguide (CPW) is proposed in the paper. The structure of the novel antenna includes a quarter circular disc radiating monopole, a coupled circular patch, and a bent L-shaped microstrip stub line. The L-shaped microstrip stub line is used to widen the impedance bandwidth and generate a horizontal component of the electromagnetic wave. The adoption of the asymmetric ground coplanar waveguide structure with the single-feed technology and the coupled circular patch, simultaneously achieve wide impedance bandwidth and wide axial ratio (AR) bandwidth. The structure parameters and the surface current of the designed antenna are analysed. The simulation and the measurement are conducted, showing good characterizations of the designed antenna. The 10-dB impedance bandwidth is 7.57 GHz, the fractional bandwidth from 6.05 to 13.62 GHz is 76.9%, the 3-dB axial ratio bandwidth is 3.01 GHz, and the fractional bandwidth from 6.05 to 9.06 GHz is 39.8%. The antenna can generate right/left hand circularly polarized waves in the direction of ± z axis. The designed antenna has wide applications in the fields of Internet of Things (IoT), broadband dual-CP communication systems and polarization diversity systems, wireless personal area network and other advanced communication systems. [ABSTRACT FROM AUTHOR]

In this paper, a broadband circularly polarized (CP) antenna array with stable radiation pattern is proposed for satellite communication applications. The antenna array consists of a 2 $ \times $ × 2 planar antenna array and a feeding network. Based on the magneto-electric (ME) dipole antenna structure, the electric dipoles are modified, and a pair of shorting pins are introduced to adjust the surface current. The bandwidth problems of circular polarization are effectively improved. Then the 2 $ \times $ × 2 broadband CP antenna array is designed and fabricated. The measured results show that the −10 dB impedance bandwidth of 56.3% from 11.1 to 19.79 GHz, and the 3 dB axial ratio (AR) bandwidth of 32.1% from 11.72 to 16.20 GHz. The 3 dB gain bandwidth of 44.2% from 11.10 to 17.40 GHz, and the peak gain is 11.07 dBi. Owing to the above excellent performance, the proposed antenna array can be a candidate for satellite communications. [ABSTRACT FROM AUTHOR]

A novel compact printed broadband circularly polarized slot antenna is proposed in this paper. The antenna consists of an inverted L-shaped coplanar waveguide feed structure and a square ground plate loaded with three rectangular slots. The antenna achieves good impedance matching and circular polarization characteristics by adjusting the size of the L-shaped band and the rectangular slot. The simulation results show that the antenna has a 10-dB impedance bandwidth of 1360 MHz (690-2050 MHz) and a 3 dB axial ratio (AR) bandwidth of 490 MHz (770-1260 MHz). Additionally, the maximum gain reached 4.02 dBi. The antenna proposed in this paper can be applied to UHF RFID and GPS frequency bands. [ABSTRACT FROM AUTHOR]

This paper proposes a new dielectric resonator antenna (DRA) design that can generate circularly polarized (CP) triple-band signals. Atripleband CP DRA antenna fed by a probe feed system is achieved with metal strips structure on side of DRA structure. The design start with conventional rectangular DRA with F shaped metal strips on DRA structure alongside the feed. Then, the F metal strip is enhanced by extending the length of the metal strip to obtain wider impedance bandwidth. Further improvement on the antenna performance is observed by improvised the conventional DRA structure. The method of removing part of DRA bottom resulted to higher antenna gain with triple band CP. The primary features of the proposed DRA include wide impedance matching bandwidth (BW) and broadband circular polarization (CP). The primary features of the proposedDRAinclude wide impedance matching bandwidth (BW) and broadband circular polarization (CP). The CP BW values recorded by the proposed antenna were ~ 11.27% (3.3-3.65 GHz), 12.18% (4.17-4.69 GHz), and 1.74% (6.44-6.55 GHz) for impedance-matching BW values of 35.4% (3.3-4.69 GHz), 1.74% (5.36-5.44 GHz), and 1.85% (6.41-6.55 GHz) with peak gains of 6.8 dBic, 7.6 dBic, and 8.5 dBic, respectively, in the lower, central, and upper bands. The prototype of the proposed antenna geometry was fabricated and measured. A good agreement was noted between the simulated and the measured results. [ABSTRACT FROM AUTHOR]

This paper presents a conformal and biodegradable circularly polarized microwave sensor (CPMS) that can be utilized in several medical applications. The proposed textile sensor can be implemented in a Smart Bra system for breast cancer detection (BCD) and a wireless body area network (WBAN). The proposed sensor is composed of a wideband circularly polarized (CP) textile-based monopole antenna with an overall size of 33.5 × 33.5 mm2 (0.2 λo × 0.2 λo) and CPW feed line. The radiating element and ground are fabricated using silver conductive fabric and stitched to a cotton substrate of thickness 2 mm. In the proposed design, a slot is etched in the radiating element to extend bandwidth from 1.8 to 8 GHz at |S11| ≤ −10 dB. It realizes a circularly polarized output with AR ≤ 3 dB operation band from 1.8 to 4 GHz and an average gain of 6 dBi. The proposed CPMS's performance is studied both off-body (air) and on-body in proximity to breast models with and without tumors using near-field microwave imaging. Moreover, the axial ratio is recorded as a feature for a circularly polarized antenna and adds another degree of freedom for cancer detection and data analysis. It assists in detecting tumors in the breast by analyzing the magnitude of the electric field components in vertical and horizontal directions. Finally, the radiation properties are recorded, as well as the specific absorption rate (SAR), to ensure safe operation. The proposed CPMS covers a bandwidth of 1.8–8 GHz with SAR values following the 1 g and 10 g standards. The proposed work demonstrates the feasibility of using textile antennas in wearables, microwave sensing systems, and wireless body area networks (WBANs). [ABSTRACT FROM AUTHOR]

This paper presents and characterizes a novel antipodal linearly tapered slot antenna for generating the circularly polarized (CP) field. By introducing two symmetrical slots on the top and bottom layers of a rectangular WR-15 waveguide, we could obtain circular polarization with an axial ratio bandwidth of 34.1%. The waveguide was used to feed the proposed antenna with very wideband impedance matching. The antenna can achieve impedance bandwidth of 40% for S(1,1) <−15 dB from 50 to 75 GHz. The simulation and measurement results show that the antenna can produce very good radiation patterns, with stable gain of 9.8 dBi ± 1.24 dBi, low back radiation, and narrow beamwidth over the operating frequency range. The working principle of this CP antenna is explained, using theoretical equations and explicit current distributions. The proposed antenna is easy to manufacture and is a compact candidate for high performance CP millimeter-wave antenna. [ABSTRACT FROM PUBLISHER]

This paper presents a novel W-shaped parasitic strip to design the circularly polarized (CP) simultaneous transmit and receive antennas and reduce the mutual coupling (MC) between them. By disturbing the current fields and inducing the current distribution on the antenna patches, the CP radiation and MC reduction are achieved. The designed CP antennas have 30 MHz 10 dB impedance bandwidth, 16 MHz 3 dB axial ratio bandwidth, and approximate 5.08 dBic peak CP gain. This technique also reduces the MC from −7 to −50 dB when the antennas are placed with a $0.18\lambda _{0}$ center-to-center distance and a $0.033\lambda _{0}$ edge-to-edge distance, where $\lambda _{0}$ is the free-space wavelength. When achieving the MC reduction, the antenna radiation pattern restores to that of the isolated antenna. Furthermore, the antenna CP gain and efficiency are improved comparing those of the antenna without the parasitic strip or the classic corner cut CP antenna. [ABSTRACT FROM AUTHOR]

This paper proposes a novel coplanar waveguide (CPW) fed broadband circularly polarized (CP) monopole antenna, which applies to C-band and various wireless communication systems. The antenna consists of the double circular-shaped patch (DCSP) with square and L-shaped slots, and an improved asymmetric ground plane. The prototype of the designed antenna has been fabricated. The results of the measurement show that the 10-dB impedance bandwidth (ZBW) is 117.8% (2.2-8.5 GHz), the 3-dB axial ratio bandwidth (ARBW) is 62% (4.45-8.45 GHz). [ABSTRACT FROM AUTHOR]

In this paper, a narrow‐band circularly polarized (CP) microstrip leaky‐wave antenna (LWA) with open stopband suppressed is proposed. Coupled meandered slow‐wave lines are adopted to realize narrow‐band beam scanning. The asymmetric elements are employed as radiators to realize CP and zero‐crossing scanning. We modulated the antenna by loading the ground inductance and asymmetric capacitors on the meandered slow‐wave transmission line. The antenna consists of ten asymmetrical structural elements connected by coupling, the antenna size of L × W is 170 mm × 25 mm. In the operating band of 8.1 to 8.5 GHz, the measured scanning angel of the fabricated antenna is from −31°to +6°. The antenna axial ratios (ARs) are all below 3 dB at the corresponding beam directions. The gain is above 9.1 dBi and the relative bandwidth is only 4.8%. In the operating band, the radiation efficiency is above 60%. It has potential applications in radar detection and wireless communication systems for its simple and low‐profile structure with CP, beam‐scanning, and narrow‐band performance. [ABSTRACT FROM AUTHOR]

This paper presents a novel method of designing the compact dual-sense circularly polarized (CP) microstrip antenna/array with improved impedance bandwidth, axial ratio (AR) bandwidth, and interpolarization isolation. The lefthand and right-hand CP characteristics are achieved simultaneously by conceiving a vertically coupled resonant structure for the first time. Different from traditional methods, the antenna shows a compact size but exhibits the wide impedance and 3 dB AR bandwidths. For each input, two coupling paths are purposely designed to excite the TM10 and TM01-mode of the patch, respectively. By composing different coupling units in the two paths, an intrinsic ±90° phase difference over a broadband can be obtained, resulting in the broadband CP characteristics. In addition, a novel method of using the neutralization line between the two feeds is investigated to improve the isolation between the polarizations. Based on the dual-sense CP element, a 1 × 4 dual-sense CP array is composed to exemplify its potential applications in large arrays. Compared with traditional CP antennas, the proposed antennas have the advantages of compact size, simplified feed, broad impedance and 3 dB AR bandwidths, and improved isolation. Experimental results verify the predictions. [ABSTRACT FROM PUBLISHER]

A self-shielded antenna-in-package (AiP) covering IEEE 802.11a band is proposed in this paper, and the antenna is designed using quarter mode substrate integrated waveguide (QMSIW) subarray technology. Electromagnetic interference (EMI) in a system-in-package integrated with AiP is discussed firstly. Electric field distribution of the proposed AiP is simulated, and it shows that the metallic via-holes array in the QMSIW subarray approximates to the electric wall to isolate the electromagnetic field coupling and then to increase the EMI shielding. The operating principle of the proposed antenna is investigated through an isosceles right triangular waveguide. An antenna prototype is fabricated and measured. The measured results match with the simulated and analyzed results very well. It is demonstrated that the proposed QMSIW subarray with metallic via-holes array gives an attractive and promising way to design the AiP with self-shielded property. [ABSTRACT FROM PUBLISHER]

This paper describes a novel compact design of a planar circularly polarized (CP) tag antenna for use in a ultrahigh frequency (UHF) radio frequency identification (RFID) system. Introducing the meander strip into the right-arm of the square-ring structure enables the measured half-power bandwidth of the proposed CP tag antenna to exceed 100 MHz (860–960 MHz), which includes the entire operating bandwidth of the global UHF RFID system. A 3-dB axial-ratio bandwidth of approximately 36 MHz (902–938 MHz) can be obtained, which is suitable for American (902–928 MHz), European (918–926 MHz), and Taiwanese UHF RFID (922–928 MHz) applications. Since the overall antenna dimensions are only $54\times54$ mm2, the proposed tag antenna can be operated with a size that is 64% smaller than that of the tag antennas attached on the safety glass. With a bidirectional reading pattern, the measured reading distance is about 8.3 m. Favorable tag sensitivity is obtained across the desired frequency band. [ABSTRACT FROM PUBLISHER]

This paper presents a new wideband circularly polarized square slot antenna (CPS SA) with a coplanar waveguide (CPW) feed. The proposed antenna is composed of two arc-shaped and inverted-L grounded strips around opposite and mirror corners of the square slot. In this antenna the impedance bandwidth and the axial ratio bandwidth (ARBW) are increased compared to the previous CPSSA structures. For the optimized antenna prototype, the measured 3 dB axial ratio bandwidth is 76 % (3 GHz - 6.7 GHz) and the measured VSWR < 2 impedance bandwidth is as large as 108 % (3 GHz - 10.1 GHz). Throughout this paper, the improvement process of the axial ratio (AR) and S11 properties are presented and discussed in detail. [ABSTRACT FROM AUTHOR]

This paper presents a 2.45 GHz harmonic suppression rectangular patch antenna with circularly polarized for wireless power transfer applications. The miniaturized proximity-coupled antenna has the advantage of excellent higher harmonic suppression of up to −3 dB at harmonic frequency. This characteristic is achieved by introducing a U-slot and the symmetrical arm of inverted U-stub embedded on the transmission feed line. The overall size of the proposed antenna gives 36% reduction of substrate area as compared to conventional designs. The antenna is designed, optimized, and simulated on FR-4 substrate of dielectric constant 4.3, loss tangent 0.019, and height 1.6 mm offering moderate gain and good axial ratio of 1.48 dB. Details of the simulated and experimental characteristics of the antenna are presented and discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high-gain circularly polarized magnetoelectric dipole antenna array for millimeter-wave is proposed. • An antenna array design method of trade-off between high gain and low profile is proposed in this paper. • The 4 × 4 antenna array achieves 20.4 dBic peak right-handed circularly polarized gain. A high-gain circularly polarized (CP) magnetoelectric (ME) dipole antenna with metallic radiating structure is presented. The proposed CP antenna element consists of two pairs of metallic posts with a supporting metallic plate, a metallic air-filled elliptical cavity, and a feeding slot on the bottom substrate integrated waveguide (SIW). The two pairs of modified rectangular metallic posts combined with the gaps between them act as radiating ME-dipoles which are surrounded by a metallic air-filled elliptical cavity. The above-mentioned radiating structures are fed by a modified cross-shaped coupling slot etched on the bottom feeding SIW to generate CP radiation, where loading the elliptical metallic cavity significantly improve the CP performance of the antenna element. Then, a 4 × 4 antenna array with full-corporate feeding network is designed, fabricated, and measured, which has an impedance bandwidth of 18.9 % from 37.4 to 45.2 GHz and a 3-dB axial ratio (AR) bandwidth of 14.2 % from 36 to 41.5 GHz. Thanks to the all-metal radiating structures, a maximum measured gain of 20.4 dBic has been achieved. The measured and simulated results are in good agreement. [ABSTRACT FROM AUTHOR]

In this paper, a horizontally meandered strip (HMS) feed technique is proposed to achieve good impedance matching and symmetrical broadside radiation patterns for a single-fed broadband circularly polarized stacked patch antenna, which is suitable for universal ultrahigh frequency (UHF) RF identification (RFID) applications. The antenna is composed of two corner truncated patches and an HMS, all of which are printed on the upper side of the FR4 substrates. One end of the HMS is connected to the main patch by a probe, while the other end is connected to an SMA connector. Simulation results are compared with the measurements, and a good agreement is obtained. The measurements show that the antenna has an impedance bandwidth (VSWR<1.5) of about 25.8% (758–983 MHz), a 3-dB axial ratio (AR) bandwidth of about 13.5% (838–959 MHz), and a gain level of about 8.6 dBic or larger within the 3-dB AR bandwidth. Therefore, the proposed antenna can be a good candidate for universal UHF RFID readers operating at the UHF band of 840–955 MHz. In addition, a parametric study and a design guideline of the proposed antenna are presented to provide the engineers with information for designing, modifying, and optimizing such an antenna. At last, the proposed antenna is validated in RFID system applications. [ABSTRACT FROM AUTHOR]

This paper presents a small wideband circularly polarized patch antenna printed on the low-cost FR-4 material for radio-frequency-identification smart bookshelves in libraries. The antenna is composed of four top-loaded patches sequentially rotated with a phase difference of 90? and double shorted to the ground. It operates at a center frequency of 0.915 GHz. The impedance bandwidth (SWR < 2) is 26.8%, the axial-ratio (AR) bandwidth (measured AR < 3 dB) is 11.6%, and the 3-dB beamwidth is 115°. The antenna gain is about 4 dBi, and the overall dimension is reduced by ~60% in length, in comparison with that of the conventional sequential patch antenna. [ABSTRACT FROM AUTHOR]

ABSTRACT A compact circularly polarized (CP) antenna with fractal-geometry characteristics for dual-band applications is proposed in this paper. The antenna is fabricated on a 41 mm × 41 mm × 1.6 mm FR4 substrate with 10-dB impedance bandwidth of 2.19-3.7 GHz and 3-dB axial ratio (AR) bandwidth of 2.3 − 2.5 and 3.39-3.55 GHz. The antenna is designed based on fractal theory and the working mechanism is investigated. Due to its unique slot structure, left hand circular polarization radiation is achieved at the upper hemisphere. Simulated results and measured results are given and analyzed in detail. The dual-band CP performance demonstrates that the proposed antenna is well suited for the WLAN/WiMAX wireless applications. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:451-456, 2017 [ABSTRACT FROM AUTHOR]

This paper presents a compact 0.92/2.45-GHz dual-band directional circularly polarized (CP) microstrip antenna for handheld radio-frequency identification (RFID) reader applications. The proposed antenna comprises a wideband dual-feed network and two stacked concentric patches assembled by two orthogonally placed vertical probes. The dual-feed network feeds quadrature signals across the RFID bands between 0.92 and 2.45 GHz. The two stacked concentric patches provide resonance frequencies in fundamental mode for lower band and higher band, respectively. Additionally, the antenna features only one connection port and same sense CP radiation at two bands, beneficial to cost and complexity reductions of the dual-band front end of RFID readers. The measurement results show the performances of return loss (RL) > 10\;\textdB, 3-dB gain variation, and axial ratio (AR) < \text3\;\textdB are achieved on the bands 0.911–0.933 GHz and 2.40–2.57 GHz. The measured peak gains are 3.8 dBic at 0.926 GHz and 8.9 dBic at 2.48 GHz. In addition, the antenna provides symmetrical patterns with wide-angle half-power beamwidths and wide-angle 3-dB AR beamwidths. The size of the antenna \text110 \times \text110 \times \text6.6\;\textm\textm^\text3 is much smaller than reported dual-band one port RFID directional CP reader antennas. The antenna appropriates to both ultra-high frequency (UHF) and industrial scientific and medical (ISM) bands in handheld RFID reader applications. [ABSTRACT FROM PUBLISHER]

This paper presents a new high gain compact aperture-coupled circularly polarized antenna for WLAN applications. The proposed antenna comprises an asymmetric X-shaped slot etched on a circular patch and fed through the coupling between an annular slot and a microstrip line. The circular polarization is mainly due to the asymmetrical crossed-slots, respecting the angle of 450 between its two arms. The antenna with overall size of 60 × 60 × 5.83 mm3 has a measured 10-dB impedance bandwidth of 36%, a 3-dB axial ratio bandwidth of 3.47% (5.67-5.87 GHz) and 1-dB gain bandwidth of 19.5% (4.85-5.90 GHz) with a peak gain of 8.65 dBi. To validate the simulated results, a prototype was fabricated, and good agreement between simulations and measurements has been accomplished. [ABSTRACT FROM AUTHOR]

This paper proposes a nonuniform metasurface-based circularly polarized antenna utilizing characteristic mode analysis (CMA). The initial antenna is a corner-cut and slotted patch connected to the ground plane with a metal-via. By arranging 45° rotated slotted patches around it, CP radiation is achieved, forming a nonuniform metasurface. Through CMA, two satisfied CP modes are obtained by merging mode 1 and 4, as they exhibit similar far-field radiation patterns and surface current directions. Simulation results show that the proposed antenna has an S11 ranging from 4.1 to 5.7 GHz, a 3 dB AR bandwidth of 4.4–5.3 GHz, and an average 2 dB higher gain than the initial antenna with a maximum of 11.4dBic. The radiated mechanism is investigated to explain the bandwidth broadening caused by the arrangement of the 45° rotated slotted patches. It is found that the excitation of two orthogonal modes results in CP radiation and a wider bandwidth. Furthermore, a 2 × 2 array with sequential rotation is proposed to enhance the radiation properties. Simulated and measured results show that the antenna array achieves an S11 of 4–6.08 GHz, a 3 dB AR bandwidth ranging from 4.3 to 6.2 GHz, and a peak gain of 15.2 GHz, with a low profile of 0.08 λ 0. A LHCP antenna can also be achieved through slight adjustment, making the proposed antenna suitable for military and civilian communication, and point-to-point links. [ABSTRACT FROM AUTHOR]

A wideband differentially fed circularly polarized (CP) antenna featuring a slotted patch design with a large beamwidth is presented. The final design of the differentially fed CP antenna, aimed at achieving high gain and a wide axial ratio (AR) bandwidth, involves coupling a differential bending dipole antenna to the slotted patch in the same plane. The presented differentially fed CP antenna demonstrates characteristics of a large AR beamwidth, as verified by simulation and experiment. The measured AR beamwidths of 132.3° in the xoz plane (phi = 0°) and 116.2° in the yoz plane (phi = 90°) are realized at 5.5 GHz. The measured result exhibits broadband performance with a -10-dB impedance bandwidth of 78.8% (3.81-8.76 GHz), a 3-dB AR bandwidth of 36.7% (4.78-6.93 GHz), and a maximum gain of 10.2 dBic. [ABSTRACT FROM AUTHOR]

An improved mutual coupling compensation in circularly polarized (CP) multi-input multi-output (MIMO) dielectric resonator antenna (DRA) is presented in this paper. Using trimming approach, the mutual coupling (MC) between closely spaced DRA units at 0.3λ has been significantly reduced while axial ratio performance has been maintained. Mutual coupling reduction is obtained by trimming the DRA to ensure low mutual coupling below −20dB. The exclusive features of the proposed MIMO DRA include wide impedance matching bandwidth (BW), triple band circular polarization, and suppressed MC between the radiating elements. The impedance bandwidth matches perfectly with a triple band's 3 dB axial ratio (AR). It is designed with characteristic mode analysis with good agreement of the measurement that has been obtained. Using the probe feed method, the DRA and patch strip are coupled together to allow bandwidth widening of the pro-posed DRA. An impedance bandwidth of 34% at a lower frequency to around 2% at a higher frequency was achieved in all resonance frequencies. Thus, we refer to our newly designed DRA as a proposed method for effectively reducing the mutual coupling between DRAs. Additionally, the 3 dB AR bandwidth matched at 3.3 GHz, 4.6 GHz, and 6.3 GHz with a percentage of 11.66%, 3.04%, and 2.22% obtained at the three different frequencies. Note that the proposed DRA exhibits low mutual coupling (below −20 dB) at the targeted frequencies, which is suitable for better signal reception for MIMO applications. By computing, the metrics envelop correlation coefficient, diversity gain, channel capacity loss, and total active reflection coefficient, the MIMO performance of the proposed antenna is verified. The experiments show a close result between simulated and computed validation of the proposed DRA.

In this paper, a novel broadband CPW-fed circularly polarized (CP) monopole antenna is presented. The antenna is composed of a falcate-shaped patch and an improved ground plane. By adding an I-shaped stub in the ground plane, the impedance and axial-ratio (AR) bandwidths can be greatly enhanced. The antenna has been fabricated and measured. Good agreement is achieved between the simulation and measurement, which shows that the proposed antenna covers a 10-dB impedance bandwidth of 122% from 2.78 to 11.46 GHz, and a 3-dB AR bandwidth of 53.3% from 4.4 to 7.6 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a dual-band circularly polarized stacked annular-ring microstrip antenna which covers the bands of Galileo (E5a, E5b, E1, E2, L1), GPS (L1, L2, L5) and GLONASS (L1, L2, L3) is presented. The antenna is composed of two concentric annular-ring patches that are etched on a substrate to generate a dual-band response. Four H-shaped apertures are added to improve the coupling between the microstrip lines and rings. And a wide-band feeding network is used to broaden the axial-ratio bandwidth. Good agreement is achieved between the simulation and measurement, which shows that the return loss of the proposed antenna is less than −15 dB in the whole band and the 3-dB axial-ratio (AR) bandwidths for the lower and upper band are 12.5% and 20.8% respectively. The measured results confirm the validity of the designed antenna which is suitable for Global Navigation Satellite System. [ABSTRACT FROM AUTHOR]

In this paper, an effective approach for mitigating the near-field coupling between four-port circularly polarized (CP) antennas in a 30-GHz multiple-input, multiple-output (MIMO) system is suggested and investigated. This is obtained by incorporating a two-layer transmission-type frequency selective surface (FSS) superstrate based on planar crossed-dipole metal strips. This paper presents a comparison between the mutual coupling when the patches are radiating in free space and in the presence of the FSS layers. The simulated results, when the FSS layers are applied, show an average of 6-12-dB improvement in the isolation between four adjacent CP-MIMO antennas. In addition, an accurate study is carried out on the insignificant reflections produced by the FSS layers to redirect those and also prevent any interference. The proposed 2 x 2 CP-MIMO antenna along with the superstrate is implemented and tested to validate the simulation results. Experimental results of the coupling and reflection coefficients and axial ratio show an acceptable agreement with the corresponding simulated ones.

In this paper, a patch array antenna with wideband circular polarization and high gain is proposed by utilizing a hybrid metasurface (MS). A corner-cut slotted patch antenna was chosen as the source due to the possible generation of CP mode. The hybrid MS (HMS), consisting of a receiver MS (RMS) arranged in a 2 × 2 array of squared patches and a linear-to-circular polarization conversion (LCPC) MS surrounding it was then utilized as the superstrate driven by the source. The LCPC MS cell is a squared-corner-cut patch with a 45° oblique slot etched, which has the capability for wideband LCPC. The LCPC unit cell possesses wideband PC capabilities, as demonstrated by the surface current analysis and S-parameter simulations conducted using a Floquet–port setup. The LP EM wave radiated by the source antenna was initially received by the RMS, then converted to a CP wave as it passed through the LCPC MS, and ultimately propagated into space. To further enhance the LCPC properties, an improved HMS (IHMS) was then proposed with four cells cut at the corners, based on the original HMS design. To verify this design, both CMA and E-field were utilized to analyze the three MSs, indicating that the IHMS possessed a wideband LCPC capability compared to the other two MSs. The proposed antenna was then arranged in a 2 × 2 array with sequential rotation to further enhance its properties. As demonstrated by the measurements, the array antenna achieved an S11 bandwidth of 60.5%, a 3 dB AR bandwidth of 2.85 GHz, and a peak gain of 15.1 dBic, all while maintaining a low profile of only 0.09λ0.

A novel self-diplexing aperture-shared dual-band dual-sense circularly polarized (CP) antenna array is proposed for transmitting/receiving (Tx/Rx) applications in X-band satellite communication systems. The antenna is capable of receiving the left-handed CP (LHCP) signals in the low band while transmitting the right-handed CP (RHCP) signals in the high band. First, a dual-port cavity-fed linearly polarized (LP) patch antenna with high isolation is developed as the element of the array. The element is composed of a slotted patch, a U-slot loaded substrate integrated cavity (SIC), and two groups of split-ring resonators (SRRs). The LHCP and RHCP operations are achieved by employing two sequentially rotated feeding networks which are isolated by a ground plane. To reduce the mutual coupling between the radiators, narrow slots are etched out in the center of the patches. Importantly, the sharing of patches at different bands (i.e., common aperture) enables a compact footprint to be achieved for the array, which is beneficial for suppressing undesirable grating lobes due to the reduced interelement spacing. The measured results of a fabricated prototype agree well with the simulations, showing an impedance bandwidth of 7.2–7.75 GHz (7.85–8.4 GHz), 3 dB axial ratio (AR) bandwidth of 7.4–7.7 GHz (7.95–8.32 GHz), and gain of 14 dBic (14.2 dBic) at the low band (high band). The channel isolation is over 27 dB and the sidelobe levels are below −15 dB in both bands. The demonstrated low-profile dual-band, dual-sense CP antenna array can be a good candidate for satellite communication. [ABSTRACT FROM AUTHOR]

A novel millimeter-wave (MMW) endfire wideband circularly polarized (CP) antenna with simple structure is reported. By introducing two symmetrical septum blades filled in the widened rectangular waveguide, the proposed antenna can obtain a 40% bandwidth for both axial ratio (AR) < 2.5 dB and $S_{11} < -15$ dB. The CP operating mechanism of the antenna has been explained, using a three-port structure. The parametric studies for all of the antenna parameters are carried out to estimate their influences on antenna performance. The sharp corner in the AR plot is also explained by mode analysis. Its influences on the radiation pattern, gain, and reflection coefficient at this frequency point are evaluated. The proposed antenna has been fabricated and measured. The simulation results are in good agreement with the measurement results. Furthermore, this antenna is an appropriate choice for designing a MMW high-efficiency wideband antenna array. An $8 \times 8$ array with 64 equal amplitude and phase wave ports in HFSS has been designed to evaluate the array performance, which shows that the array can achieve 40% operating bandwidth without considering the bandwidth of feeding network. The simulated aperture efficiency of the array is above 85.34% from 50 to 75 GHz. [ABSTRACT FROM AUTHOR]

A dual-band, circularly polarized (CP) asymmetric dipole array antenna for Global Positioning System (GPS) applications with a wide beam is presented in this paper. The proposed antenna comprises two different-sized printed crossed dipoles with integrated baluns fed by an asymmetric feeding network to achieve dual-band functionality. Using two branch-line couplers with different dimensions in the feeding network performs Right-Hand Circular Polarization (RHCP) operation at GPS L1 and L2 bands. According to the experiments, the proposed antenna has wide impedance bandwidths of 24.82% (1139.5–1462.4 MHz) and 14.82% (1500.4–1740.5 MHz), and 3 dB Axial-Ratio (AR) bandwidth of 37.4% (1132.3–1653.2 MHz) to cover the GPS L1 and L2 bands. Furthermore, at 1227 MHz frequency, the antenna has a gain of 4.65 dBic, and a 3 dB AR beamwidth of 148.2° facing the sky. Also, at 1575 MHz frequency, a gain of 5.25 dBic and a 3 dB AR beamwidth of 139.3° are achieved. [ABSTRACT FROM AUTHOR]

Abstract A broadband circularly polarized (CP) printed monopole antenna which fed by coplanar waveguide (CPW) is proposed in the paper. The structure of the novel antenna includes a quarter circular disc radiating monopole, a coupled circular patch, and a bent L-shaped microstrip stub line. The L-shaped microstrip stub line is used to widen the impedance bandwidth and generate a horizontal component of the electromagnetic wave. The adoption of the asymmetric ground coplanar waveguide structure with the single-feed technology and the coupled circular patch, simultaneously achieve wide impedance bandwidth and wide axial ratio (AR) bandwidth. The structure parameters and the surface current of the designed antenna are analysed. The simulation and the measurement are conducted, showing good characterizations of the designed antenna. The 10-dB impedance bandwidth is 7.57 GHz, the fractional bandwidth from 6.05 to 13.62 GHz is 76.9%, the 3-dB axial ratio bandwidth is 3.01 GHz, and the fractional bandwidth from 6.05 to 9.06 GHz is 39.8%. The antenna can generate right/left hand circularly polarized waves in the direction of ± z axis. The designed antenna has wide applications in the fields of Internet of Things (IoT), broadband dual-CP communication systems and polarization diversity systems, wireless personal area network and other advanced communication systems.

A new approach to generate beam steering for the circularly polarized (CP) antenna array without phase shift circuits is proposed. The proposed approach is a low cost one compared with those with phase shifters. It is found that in spherical coordinate system ( $r$ , \theta $ , and \varphi $ ), for any constant r$ and \theta $ , as \varphi $ varies from 0 to 2\pi $ , the phase of the CP antenna’s copolarized far field will progress linearly by 2\pi $ , and the magnitude is constant. If a CP antenna is rotated around its own phase center by certain degrees, there is a phase difference between the copolarized electric far fields generated by the antenna before and after rotation. An N \times N , 45°, and 90°, the mainlobe can be scanned from −25° to +24°, −36° to +35°, and −24° to +25°, respectively. [ABSTRACT FROM PUBLISHER]

A novel method of achieving a single-feed circularly polarized (CP) microstrip antenna with both broad impedance bandwidth and axial ratio (AR) bandwidth is presented. The CP characteristics are generated by employing a resonator to excite the two orthogonal modes of the patch via two coupling paths and the required 90° phase difference is achieved by using the different orders of the two paths. The presented method, instead of conventional methods that power dividers and phase delay lines are usually required, not only significantly enhances the bandwidths of the antenna but also results in a compact feed, reduced loss and high gain. Based on this method, a dual-band shared-aperture CP array antenna is implemented for $C$ -/ $X$ -band satellite communications. The antenna aperture includes a $2 \times 2$ array at $C$ -band and a $4 \times 4$ array at $X$ -band. To accommodate the $C$ - $X$ -band elements into the same aperture while achieving a good isolation between them, the $C$ -band circular patches are etched at the four corners. The measured results agree well with the simulations, showing a wide impedance bandwidth of 21% and 21.2% at $C$ -band and $X$ -band, respectively. The $C$ -band and $X$ -band 3 dB AR bandwidths are 13.2% and 12.8%. The array also exhibits a high aperture efficiency of over 55%, low sidelobe ( $C$ -band: −12.5 dB and $X$ -band: −15 dB), and high gain ( $C$ -band: 14.5 dBic and $X$ -band: 17.5 dBic). [ABSTRACT FROM PUBLISHER]

A wideband single-fed circularly polarized (CP) stacked patch antenna with an L-shaped stub is presented. The CP antenna is made up of the bottom gradient microstrip transmission line, middle driven patch and top square radiation patch. The driven patch with an Lshaped stub and opening slot can achieve a wideband CP radiation which is different from a conventional patch. The presented CP stacked patch antenna maintains good directional radiation, while featuring wideband CP radiation. The final tested results indicate that the presented CP antenna has significant performance with a -10-dB impedance bandwidth of 42.1% (4.26-6.53 GHz), a 3- dB AR bandwidth of 26.0% (4.36-5.66 GHz) and broadside peak gain of 8.6 dBic. Moreover, the fifth-generation (5G) N79 band (4.4-5.0 GHz) and 5G wireless local area network (WLAN) band (5.15-5.35 GHz) can be covered by the operating bandwidth of the presented CP antenna. [ABSTRACT FROM AUTHOR]

This work introduces cost-effective solution for a millimeter-wave (mmW) antenna array development. We suggest an elliptical cavity-backed patch antenna array to achieve a wideband and high-gain circularly polarized (CP) at mmW frequencies. The whole array only uses two PCBs and a metallic fixture to build. We introduce a new configurable subarray with $2\times $ 1 radiating elements that are formed by two partially overlapped elliptical cavities to generate the radiation together with the driven patches of the subarray. The subarray can produce a wide impedance bandwidth of 37%, a wide 3 dB axial ratio (AR) bandwidth of 29.6%, and a maximum gain of 11.6 dBic. Based on the result from the subarray, we design a 32-element antenna array by a $4 \times $ 4 antenna array configuration. The power distribution is realized by a 1-to-16 full-corporate feed network. The measured results show that the proposed CP array obtains an impedance bandwidth of 31.5% and a 3 dB AR bandwidth of 24%. In addition, the gain of the array is from 19.1 to 21 dBic within the 3 dB AR bandwidth. With wide impedance and AR bandwidths, the proposed antenna array can find potential applications in long-range mmW communications. [ABSTRACT FROM AUTHOR]

This article presents 3-D printed metal-only dual-band millimeter-wave circularly polarized (CP) reflectarrays (RAs). The RAs’ unit cell (UC) is made of an anisotropic metal brick mounted on a full metal ground. In-plane rotating the metal brick introduces geometric Pancharatnam–Berry (PB) phase shifting, and vertically adjusting the position of the UC provides propagation phase shifting. The geometric PB and propagation phase shifting offer two different degrees of freedom, enabling independent wavefront shaping of CP wave over dual-band. Specifically, the low-band CP beam shaping solely depends on the propagation phase. In contrast, the high-band CP beam shaping depends on the geometric PB and the propagation phases. The coupling issue between dual-band is minimal because of the unique dual-band phase-shifting methods. In addition, 3-D printed dual-band left-hand CP (LHCP) horn antennas are designed, printed, and used as the feed. To demonstrate, two RA antennas with different dual-band CP beam directions are fabricated and measured. [ABSTRACT FROM AUTHOR]

In this paper, a broadband circularly polarized (CP) microstrip antenna array using simplified composite right/left-handed transmission lines (SCRLH-TLs) based sequential rotation (SR) feed network is presented. The characteristics of a SCRLH-TL are investigated initially. Then, a broadband low insertion loss 45° phase shifter is designed using the SCRLH-TL and the phase shifter is employed in constructing a SR feed network for CP antenna array. To validate the design method of the SR feed network, a 2x2 antenna array comprising sequentially rotated coupled stacked CP antenna elements is designed, fabricated and measured. Both the simulated and measured results indicate that the performances of the antenna element are further enhanced when the SR network is used. The antenna array exhibits the VSWR less than 1.8 from 4 GHz to 7 GHz and the axial ratio (AR) less than 3 dB from 4.4 GHz to 6.8 GHz. Also, high peak gain of 13.7 dBic is obtained. Besides, the normalized radiation patterns at the operating frequencies are symmetrical and the sidelobe levels are low at φ = 0° and φ = 90°. [ABSTRACT FROM AUTHOR]

The conventional short-range interferometric radar sensors usually employ two separate transmitting (TX) and receiving (RX) antennas for improved TX–RX isolation. However, they are subject to increased system size and misalignment of the TX/RX radiation patterns. In this article, a portable 5.8 GHz dual circularly polarized (CP) interferometric radar sensor is presented, which leverages the proposed dual CP common-aperture antenna that reduces the size of the entire radar system. The common-aperture nature gets rid of the radiation pattern misalignment and ensures that the object can be in the optimal boresight direction. Cross polarization, i.e., right-hand CP (RHCP) for TX and left-hand CP (LHCP) for RX or vice versa, was employed based on the sequentially rotated array (SRA), which not only improves the TX–RX isolation but also adapts with the polarization change in radar sensing. Moreover, a near-field cancellation technique was proposed to further increase the TX–RX isolation in the small form factor. A portable 5.8 GHz radar sensor integrated with the proposed dual CP antenna was custom-designed. Compared to the conventional two-antenna architecture, the proposed radar sensor is reduced in size by 140% but can still achieve a high TX–RX isolation of >60 dB at 5.8 GHz. Experiments were carried and the results illustrate that the proposed radar sensor has high micrometer accuracy in detecting the predefined displacement motions and is able to precisely track the human vital signs in the office environment. [ABSTRACT FROM AUTHOR]

This article presents a new type of beam-tilted circularly polarized (CP) radial line slot array (RLSA) antennas. When the conventional beam tilting method is applied to CP-RLSA antennas, the aperture efficiency of the antenna degrades significantly due to very sparse slots in some parts of the antenna. A new method is presented to prevent this, and hence a much higher gain and aperture efficiency are achieved from the same antenna area. The key to the new method is an aggressively biased truncation of the slot layout that leaves out sparse slots. Consequently, the feed point moves closer to an edge of the TEM waveguide. A reflecting wall is introduced to prevent leakage from this edge. It is shown that the gain of RLSAs with beams tilted to 25° and 45° (measured from normal direction) can be increased by 5.5 dB (from 20.5 to 26 dBic) using the new method as opposed to the conventional method. The new concept and predicted results are validated using a prototype antenna with the beam-tilted to an angle of 25°. The aperture diameter and overall thickness of the prototype are $12\lambda _{0}$ and $0.4\lambda _{0}$ , respectively, where $\lambda _{0}$ is the free-space wavelength at the operating frequency of 18 GHz. The measured results confirmed a higher gain of 26.2 dBic, an aperture efficiency of 30%, the overall efficiency of 93.2%, and sidelobe levels (SLLs) less than −25 dB at 18 GHz. The measured 10 dB return loss bandwidth of the antenna is greater than 63.7%, 3 dB axial-ratio bandwidth is 13.3%, and 3 dB gain bandwidth is 6.7%. [ABSTRACT FROM AUTHOR]

This paper presents a conformal and biodegradable circularly polarized microwave sensor (CPMS) that can be utilized in several medical applications. The proposed textile sensor can be implemented in a Smart Bra system for breast cancer detection (BCD) and a wireless body area network (WBAN). The proposed sensor is composed of a wideband circularly polarized (CP) textile-based monopole antenna with an overall size of 33.5 × 33.5 mm2 (0.2 λo × 0.2 λo) and CPW feed line. The radiating element and ground are fabricated using silver conductive fabric and stitched to a cotton substrate of thickness 2 mm. In the proposed design, a slot is etched in the radiating element to extend bandwidth from 1.8 to 8 GHz at |S11| ≤ −10 dB. It realizes a circularly polarized output with AR ≤ 3 dB operation band from 1.8 to 4 GHz and an average gain of 6 dBi. The proposed CPMS’s performance is studied both off-body (air) and on-body in proximity to breast models with and without tumors using near-field microwave imaging. Moreover, the axial ratio is recorded as a feature for a circularly polarized antenna and adds another degree of freedom for cancer detection and data analysis. It assists in detecting tumors in the breast by analyzing the magnitude of the electric field components in vertical and horizontal directions. Finally, the radiation properties are recorded, as well as the specific absorption rate (SAR), to ensure safe operation. The proposed CPMS covers a bandwidth of 1.8–8 GHz with SAR values following the 1 g and 10 g standards. The proposed work demonstrates the feasibility of using textile antennas in wearables, microwave sensing systems, and wireless body area networks (WBANs).

A high‐gain, low‐cost empty substrate integrated waveguide (ESIW)‐fed circularly polarized (CP) antenna array is demonstrated for millimetre‐wave 5G applications in this letter. The ESIW is formed by metallized FR4 printed circuit boards. By stacking the metallic aluminium z‐shaped radiating slots atop the ESIW feeding network, CP radiation is achieved. The proposed 1 × 8 antenna array offers a high measured gain of 17.8 dBic and high measured radiation efficiency of 89.1%. The measured impedance bandwidth for |S11| ≤ −10 dB and measured axial ratio (AR) bandwidth for AR ≤ 3 of the proposed 1 × 8 array are 11.4% (36.5–40.9 GHz) and 7.8% (37–40 GHz), respectively. [ABSTRACT FROM AUTHOR]

A continuous beam-steering solution for circularly polarized (CP) radial-line slot array (RLSA) antennas is presented and demonstrated with a fabricated prototype. The solution is based on the near-field meta-steering (NFMS) method, which is implemented through a pair of highly transmitting hybrid metasurfaces (HMs) that are placed above a high-gain CP RLSA antenna in the near-field region. Cells in HMs, unlike conventional metasurfaces (CMs), can provide exact or close to exact phase shift with transmission magnitude larger than −1 dB. This is achieved by combining the nonoverlapping phase ranges of two dramatically different phase-shifting cells. The RLSA is stationary, while the two HMs are rotated to steer the beam in a 2-D (azimuth and elevation) space. The measured results of the prototype demonstrate that the system can steer its beam to a maximum elevation angle of 40.6° with a maximum gain of 30.9 dBic. The axial ratio remained less than 3 dB in the 3 dB beamwidth even when the beam is steered. The height of the system is only 4.5 cm, which is much less than mechanically steered reflector antennas. Unlike electronically steered high-gain antenna arrays, this system requires only few watts of power only when rotating HMs and has zero power consumption when the beam is stationary. [ABSTRACT FROM AUTHOR]

A broadband circularly polarized patch antenna is proposed for universal ultra-high-frequency (UHF) RF identification (RFID) applications. The antenna is composed of two corner- truncated patches and a suspended microstrip line with open-circuited termination. The main patch is fed by four probes which are sequentially connected to the suspended microstrip feed line. The measurement shows that the antenna achieves a return loss of -15 dB, gain of 8.3 dBic, axial ratio (AR) of 3 dB, and 3-dB AR beamwidth of 75° over the UHF band of 818-964 MHz or 16.4%. Therefore, the proposed antenna is universal for UHF RFID applications worldwide at the UHF band of 840-960 MHz. In addition, a parametric study is conducted to facilitate the design and optimization processes for engineers. [ABSTRACT FROM AUTHOR]

In this article, a low-profile high-efficiency dual-band 0.915/2.45 GHz circularly polarized (CP) antenna and its array are designed for radio frequency identification (RFID) reader applications. First, a dual-band antenna element is introduced to achieve dual-sense CP radiation using two pairs of crossed-dipoles for the first time. The right-hand CP (RHCP) wave at lower band is mainly produced by the first-order mode on longer dipole, while the left-hand CP (LHCP) wave at upper band is generated by the combination of first-order mode on shorter dipole and third-order mode on longer dipole. An artificial magnetic conductor (AMC) is used to improve the antenna directivity with low profile and makes this antenna easy to integrate into RFID system. Then, a rotated sequential phase feed CP array is proposed, fabricated, and measured. Measured impedance bandwidth (IBW) for $\vert \text{S}_{11}\vert < -10$ dB is more than 40.0% at these two bands. Measured 3 dB axial ratio bandwidths (ARBWs) are 32.0% (0.77–1.06 GHz) and 27.8% (2.22–2.95 GHz). Compared with other dual-band CP reader antennas, which work in 0.915/2.45 GHz RFID systems, this new antenna array has a simpler configuration to achieve dual-band CP radiation. In addition, the 3 dB ARBWs are much wider than the previous antennas. Moreover, because the feeding network of this array is quite simple, the radiation efficiency is very high (>90%), and the peak gains are more than 9.0 and 15.0 dBic at corresponding bands. [ABSTRACT FROM AUTHOR]