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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 dual-feed circularly polarized (CP) antenna is presented for different axial ratio (AR) requirements. By analyzing the output characteristic of the feed network for the dual-feed CP antenna, an approximate function is obtained and utilized to calculate the variances of the output magnitude and phase of the feed network under a required AR. Based on the analysis, different branch-line couplers are used for achieving wide AR bandwidths of less than 3, 2, and 1 dB, respectively. Compared to the traditionally used 3 dB coupler, the presented feed method can have an AR peak with the expected value at the center frequency and two AR valleys beside the peak, while the traditional 3 dB coupler can only get an AR valley with narrower bandwidth. Therefore, much wider AR bandwidths for different AR requirements are obtained by using the presented method. The wideband dual-feed antenna fed by these different couplers was simulated, fabricated, and measured for the final performance verification. [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 wideband dual circularly polarized (DCP) antenna is presented for intelligent transport system (ITS) applications, which can be used to improve the receiver sensitivity and communication quality of ITS. The presented DCP antenna is composed of an orthogonal power divider (OPD) with two orthogonal input ports, four phase shifters for quadrature phase output, and four crossed dipoles for DCP radiation. Detailed equivalent circuit analysis shows that the OPD has two orthogonal inputs and four equal magnitude in-phase and out-of-phase outputs. To achieve two sets of orthogonal quadrature output signals for DCP radiation, the lumped element based differential right-hand transmission line unit cell and left-hand transmission line unit cell are elaborately introduced as the ±45° phase shifters, and incorporated into the OPD. Eventually, orthogonal quadrature signals are successfully obtained and fed to the crossed dipoles for DCP radiation. The proposed antenna was then designed, fabricated, and measured for ITS applications. The measured results show that the overlapped impedance bandwidth of both two input ports is 1.07–1.85 GHz (53.4%), and the isolation is higher than 15.2 dB. Moreover, low axial ratio (<1.7 dB) and symmetrical radiation patterns are achieved for unidirectional DCP radiation. [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 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]

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]

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]

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

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

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

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]