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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 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]

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 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]

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 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]

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]