High Cross-polarization Discrimination Research Articles

Dual Linearly Polarized 2-bit Programmable Metasurface With High Cross-Polarization Discrimination

Dual Linearly Polarized 2-bit Programmable Metasurface With High Cross-Polarization Discrimination

A Compact 1:3 Power Divider Incorporating 180° Shifted Path for Polarization Purity Enhanced Base Station Subarray

This paper presents a compact 1:3 power divider and a base station subarray antenna with enhanced polarization purity exhibiting high cross-polarization discrimination (XPD) and high input port isolation. The compact 1:3 power divider incorporating a 180° shifted path is proposed to achieve both polarization purity and the wideband characteristics of the subarray antenna, which is difficult to implement using the conventional dual-feed method in limited areas. Using the proposed power divider, a dual-polarized quadruple Π-probe feed stacked patch antenna array is designed, which achieves a wide bandwidth of over 30% (< -13 dB) from 1.68 GHz to 2.25 GHz. The XPD is increased by approximately 8 dB and 5 dB at 1.71 GHz and 2.11 GHz, respectively, to attain an increase in the isolation bandwidth (< -20 dB) from 14% to 43%. Furthermore, the measurement results of a 4 × 3 antenna array confirm the effectiveness of the proposed design in terms of XPD and isolation while maintaining the bandwidth and beam performance. This study demonstrates a relatively wide bandwidth between patch antennas, despite the use of multiple subarrays. The comparative results also show a relatively better frontto-back ratio and isolation of the proposed design.

Millimeter-Wave Wideband ±45° Dual-Polarized Phased Array Antenna Based on Compact Wideband Widebeam Dipole Element Antenna

To meet the requirements of a millimeter-wave (mmWave) communication system prototype complying with 5G (24.25-29.5GHz) and B5G/6G (30-33GHz) standards, this letter presents a compact wideband widebeam ±45° dual-polarized dipole element antenna to form a wideband phased array antenna (PAA) covering the entire 24-33GHz (∼31.6%) band. First, by placing two orthogonal coupling feeding baluns over a dual-polarized dipole to excite the dipole's two pairs of orthogonal arms and employing four parasitic patches, a ±45° dual-polarized dipole element antenna is developed, showing a compact size (0.34λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ×0.34λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> @24GHz), wide -14-dB impedance bandwidth (24-33GHz, 31.6%), wide 3-dB beamwidth (>100°), high polarization isolation (>25dB), and high cross-polarization discrimination (XPD) (>25dB) within the -14-dB impedance bandwidth. Then, based on the element antenna, a 4×4-element ±45° dual-polarized PAA is designed, fabricated using the LTCC process, and measured. The measurements show that, within the entire 24-33GHz band, the broadside scanning gain of the PAA is up to 14dBi, and the 3-dB gain variation scanning range is >±41° with a peak up to ±60º.

A Survey of Five Generations of MIMO Multiband Base Station Antennas

AbstractAs telecommunication systems evolve, there is an increasing demand for multi‐band MIMO base‐station antennas. Antenna arrays are generally used to support multiple frequencies with multiple ports in a compact size. However, this can result in significant degradation in scattering patterns and return loss/port isolation due to the close proximity of the radiation from the array. Various techniques have been proposed in the literature to address these issues. This paper presents an overview of the challenges faced by base station antennas (BSAs) over time and their general solutions. With the technological advancements of communication systems, accompanied by high data rates, high‐frequency antenna designs and MIMO operations have been introduced at the base station level. Base station antennas encountered design challenges, including broad bandwidth, high isolation levels, stable half‐power beam width, beam squint reduction, high cross polarization discrimination (XPD), gain improvement, beam steering, compact size, and cost reduction. This survey provides information on the solutions adopted by researchers over time for each design challenge, with citations. Additionally, the authors discuss techniques developed to overcome these challenges, demonstrating the evolution of BSAs from the first to the fifth generation of telecommunication systems.

Structural and Radio Frequency Co-Design and Optimization of Large Deployable Reflectarrays for Space Missions

The structural and Radio-Frequency (RF) design and optimization of a large deployable faceted reflectarray (RA) generating double polarization contour beam are presented in this work. The issue addressed is the thermoelastic stability of large RAs and the impact of the thermoelastic deformation (TED) under transverse thermal gradient on the RA performances. Finite elements TED analysis are conducted on a deployable RA with self-standing structures, demonstrating the detrimental effects of the in-orbit TED impact on the RA performances, estimated to be above 3 dB losses. To this extent, a novel structural solution is proposed, based on the employ of reliable mechanical support capable to mitigate the TED. The mechanical design reorientation is contingent on the RF design reformulation. The proposed novel mechanical and RF co-design concept and methodology allows the conception of a low profile, thermo-structurally stable RA with compliant radiation patterns and high cross-polarization discrimination in the worst-case thermal load. This methodology is based on a direct optimization of nine panels faceted RA composed of advanced high-order Phoenix cells directly optimized to fulfill the contoured beam requirements and by respecting the local periodicity requirements of the layout.

Very Compact Waveguide Orthomode Transducer in the K-Band for Broadband Communication Satellite Array Antennas

A very compact waveguide orthomode transducer (OMT) is described in this paper. The design is characterized with a twofold rotationally symmetric cross-section in the probing area, adapted from a side-coupling OMT design, simultaneously enabling low port-to-port coupling and high cross-polarization discrimination (XPD) over a fractional bandwidth of about 15-20%. Compared to previously reported compact waveguide OMTs, the proposed design is simpler, thus facilitating its manufacture at millimeter-wave frequencies. The concept is demonstrated with a design in the K-band for a broadband communication satellite downlink over the frequency band of 17.3-20.2 GHz. For test purposes, transitions to standard waveguide WR42 are included, and the OMT is assembled with a conical horn antenna. The measured reflection and coupling coefficients are below -19.5 dB and -22.9 dB, respectively, over the nominal bandwidth, and they are in good agreement with the simulation's results. The on-axis XPD, measured in an anechoic chamber, is better than 30 dB over the nominal bandwidth, which is also in line with simulations. The proposed waveguide OMT may be designed to fit in a lattice below one wavelength at the highest operating frequency, which is desirable for dual-polarized closely spaced array antennas in low and medium Earth orbit communication satellite systems. The simple mechanical design of the proposed OMT makes it particularly appealing for additive manufacturing techniques, as demonstrated with a variant of the design having folded single-mode waveguides, which preserves the RF properties of the original design.

Wideband and High Cross-Polarization Discrimination 45° Linearly Polarized Slot Array Antenna Without Cavity-Backed Layer

This letter presents a wideband and high cross-polarization discrimination (XPD) 8×8-slot full corporate- feed 45° linearly polarized slot array antenna. A new vertical 1-to-4 power divider consisting of one H-plane T-junction and two E-plane T-junctions is employed to replace the 1-to-4 cavity-backed power divider in the conventional designs, which balances the amplitude and phase distributions among the output ports. By further bending the output ports of the 1-to-4 power dividers upward 90° along the diagonal plane, the TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> mode in the signal path is smoothly shifted along the intended E- and H- planes and directly excites the 45° tilted radiation slots. Combined these features, the grating lobe suppression and XPD improvement over a wide frequency band can be achieved without introducing additional metal structures. For demonstration, a prototype covering 24–33 GHz is implemented. The experimental results are in good agreement with the simulation ones, which verifies the design concept.

Wideband Dual-Polarized Hollow-Waveguide Slot Array Antenna

A wideband dual-polarized slot array antenna based on hollow waveguide (HW) is presented in this article. Its wide bandwidth and high performance are enabled by two separate feeding networks, from the side and the bottom, using square coaxial line and ridge waveguide structures, respectively. The full-corporate-feed networks excite the radiation slots in a one-to-one fashion without using backed cavities. Tight element spacing is made possible, suppressing the grating lobe and maintaining high cross-polarization discrimination (XPD) across the wideband. This resolves a usual tradeoff between bandwidth and grating lobe. A double-ridge rectangular waveguide cavity is devised as an orthogonal mode splitter for isolation enhancement. Several design features are used to minimize the signal path length and facilitate routing. An <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8\times8$ </tex-math></inline-formula> element prototype in K-band is designed, fabricated, and measured. Experimental results show that the antenna has a wide bandwidth of 23.4% (from 17 to 21.5 GHz) free from grating lobes. More than 25.5 dBi peak gain higher than 51.2 dB isolation and over 43.6 dB XPD are also obtained for the dual polarizations.

Differentially Fed Dual-Polarized 2-D Multibeam Dielectric Resonator Antenna Array Based on Printed Ridge Gap Waveguide

In this article, a differentially fed dual-polarized dielectric resonator antenna (DRA) subarray excited by a substrate integrated waveguide (SIW) cavity is proposed. A #-shaped slot etched on the top wall of the SIW cavity is used to achieve the differential excitation due to the intrinsic field distribution of TE120 mode in the SIW. Based on the proposed antenna subarray, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times $ </tex-math></inline-formula> 2 dual-polarized 2-D multibeam DRA antenna array with simple structure is designed, fabricated, and measured, which can achieve high cross-polarization discrimination (XPD) in the direction of maximum radiation. To reduce substrate loss, the printed ridge gap waveguide (PRGW) technology is used to feed the SIW cavity. Two orthogonal PRGW Butler matrices are placed at different layers so as to realize 2-D beamforming scanning with dual-polarization. The SIW cavity is placed in the air gap of PRWG, which can increase the stability of the antenna structure. By cleverly combining the SIW cavity and PRGW structure, the proposed multibeam antenna array has the advantages of high XPD and high radiation efficiency. Measured results show that an impedance bandwidth of 10% (28.5–31.5 GHz) and a peak gain of 11.8 dBi are obtained. Also, the measured XPDs are 28.3 dB at the center frequency and larger than 19.2 dB over the band of operation. Besides, the measured radiation efficiency of 67% is achieved for both the polarizations at 30 GHz.

Wideband Antenna for High-Frequency 5G Wireless Communication

In this study, a wideband patch array antenna for high-frequency 5G wireless communication is proposed. The wideband high-frequency 5G antenna is needed to handle the increase in 5G data traffic. The proposed antenna, a 2 × 16 element array with gap-coupled parasitic elements and a multi-section or stepped transformer feeding network with feed cover to prevent unwanted feed radiation, can cover 5G new radio (NR) n257 (26.5–29.5 GHz), n258 (24.25–27.5 GHz), and n261 (27.5–28.35 GHz) bands. Using parasitic elements with a single substrate instead of cavity and stacked structures, a wide impedance bandwidth (dB magnitude of S&lt;sub&gt;11&lt;/sub&gt; &lt; –10) of 24.2% (23.75–32 GHz) is achieved. A high cross-polarization discrimination (XPD &gt; 25.2 dB) is achieved using orthogonal dual polarization. The peak gain obtained is 18.69 dB.

Planar dual‐polarized differentially fed multibeam patch antenna array

A design of planar dual-polarized differentially fed multibeam patch antenna array (DFMPAA) is presented in this article. The dual-polarized DFMPAA is composed of two circular 4 × 4 butler matrixs (BMs) and a 1 × 4 dual-polarized patch antenna array. The two BMs are designed in the top and bottom layer as the feeding network of horizontal polarization (HP) and vertical polarization (VP), respectively. The patch is designed as the radiation element of the dual-polarized DFMPAA, which is fed by the slot and aperture coupling to generate the HP and VP wave, respectively. To achieve high cross-polarization discrimination (XPD), the antenna element is fed differentially. A prototype working at 5.5 GHz is fabricated and measured in order to validate the performance of the proposed dual-polarized DFMPAA. The dimension of the dual-polarized DFMPAA is 3.8 λ0 × 1.7 λ0. Measured results show that when the beam scan to the maximal pointing angle, the XPD of the dual-polarized DFMPAA in HP and VP are higher than 27 and 29 dB, respectively. Additionally, the beams of the dual-polarized DFMPAA can cover the range of ±42° in horizontal plane.

Use of Narrower Reflection-Canceling Slots to Design Linearly Polarized Radial Line Slot Arrays With Improved Radiation Performance

In linearly polarized (LP) radial line slot arrays (RLSAs), reflection canceling slots (RCSs) are used in addition to the radiating slots (RSs) to reduce the return loss. The densely populated slotted RLSA apertures present the challenge of avoiding physical overlap between the RCSs and RSs. A solution to displace RCSs from their optimal position complicates the design and makes it less predictable. A design presented here addresses this issue using narrower RCSs on the same current-flow lines as their corresponding RSs. A high-gain LP RLSA antenna with diameter 12 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\lambda _0$</tex-math></inline-formula> was designed, fabricated, and tested using the proposed strategy. The measured prototype demonstrated a wide matching bandwidth of 74.3%. The antenna achieved a maximum gain of 28.3 dBi at the operating frequency of 17 GHz, and a 3 dB gain bandwidth of 6.3%. At this frequency, it has an aperture efficiency of 51%, a total efficiency of 95.3% along with high cross-polar discrimination, which is more than 70 dB in the direction of the beam peak.

Dual‐polarized stacked microstrip antenna with trident‐shaped baluns for MIMO array development

Owing to the high cross-polarization discrimination (XPD) and high isolation characteristics, differential excitation is often employed in dual-polarized microstrip antennas. However, the number of excitation ports will be doubled, and the power dividers in the differential circuit will introduce additional loss, the differential excitation scheme is thus not suitable for dual-polarized large-scale MIMO antenna arrays. In this work, a novel dual-polarized stacked microstrip antenna with trident-shaped baluns is proposed for base station MIMO array development. The trident-shaped balun is proposed to replace the traditional differential excitation structures, while keeping the merits of high XPD and high isolation. The proposed antenna operates in the frequency band of 3.3-3.8 GHz. The profile height of the antenna is only 0.09λ0 (λ0 is the free-space wavelength at the central frequency), which is much lower than traditional base station antennas (0.25λ0) in the sub-6 GHz band. Moreover, a defective ground structure is implemented in a 2 × 2 MIMO antenna array to efficiently suppress the mutual coupling among antenna elements. Both simulated and measured results validate the design. Owing to its low-profile height and low mutual coupling characteristic, the proposed design is a good candidate for sub-6 GHz band base station MIMO array developments.

Millimeter-Wave 45° Linearly Polarized Corporate-Fed Slot Array Antenna With Low Profile and Reduced Complexity

A millimeter-wave 45° linearly polarized corporate-fed slot array antenna is presented in this communication. A key feature is the much reduced number of metallic layers and, therefore, the complexity of the array, as compared with other competitive designs. With the reduced antenna profile, high cross-polarization discrimination (XPD) and low sidelobe level (SLL) are still achieved by a combination of techniques. The back cavity of the 2 ×2 slot subarray is optimized to confine the H-field along the direction of the radiation slots, enhancing its XPD. Stubs are loaded in the same cavity to compensate for the phase imbalance, suppressing both cross-polarization and grating lobes without introducing additional metallic layers. Combining these features, the proposed array antenna demonstrates high performance with only three essential metallic layers. A prototype with 8 ×8 radiation slots at the Ka-band is implemented for demonstration. Experimental results show that the grating lobes are suppressed to below -30.5 dB, and the first SLL (FSLL) of less than -26.2 dB. XPD of more than 31.3 dB is achieved over the frequency range of 26.5-32 GHz. The peak gain of better than 25 dBi and antenna efficiency of over 71.7% are also obtained over the same frequency range.

A Low-Profile Hybrid-Fed Dual-Polarized Antenna with High Isolation and High Cross-Polar Discrimination

This work presents a wideband hybrid-fed ±45o linear dual-polarized patch antenna design for sub- 6 GHz 5G base stations. Two polarizations are created by a slot-coupling with rectangular H-slot (+45) and a capacitive coupling with modified L-probe (−45). Antenna exhibits wideband −10 dB impedance bandwidths of 40.7% and 35.6% for slot-fed and probe-fed ports, respectively. Due to the special design of suspended stacked patches with hybrid-fed excitations, high port isolation ( 38 dB) are achieved. Symmetric and directional radiation patterns with stable gain are obtained in E and H planes for each polarization. Compared to its bandwidth, antenna is low-profile (10.6 mm) with front-to-back ratio greater than 22 dB. Simulations and experimental results are reported and discussed.

Design of Wideband Linearly Polarized 3-Bit Transmit-Array Antenna With Polarization Rotation Unit Cell

The millimeter-wave (mm-wave) band is expected to be the optimal solution for future wireless communication systems as it provides a wide bandwidth, which enhancing data transmission rate. Therefore, high-directive antennas, principal elements for mm-wave wireless communications, are used at the mm-wave band as they can overcome the negative effect of high path losses. A transmit-array antenna (TA) operates at the mm-wave band (around 28 GHz) with high aperture efficiency, high gain, wide bandwidth, and low-profile TA surface has been designed. Basically, the aperture efficiency of the TA depends on the unit cell (UC) characteristics, and feed antenna radiation pattern. Therefore, the UC elements designed based on capacitive differential feeding and true time delay techniques, as a result the designed UC has a wide bandwidth with a stable broadside radiation pattern, high cross-polarization discrimination and a full phase range (0-360°) and a maximum element loss of 0.5 dB. Moreover, the designed UC rotates the polarization of linearly polarized electromagnetic (EM) wave to its orthogonal direction with high efficiency, a polarization conversion ratio higher than 0.9 is achieved within the operating frequency band. The used techniques to design the proposed UC have a significant effect on TA antenna performance, in terms of gain and bandwidth. The TA antenna surface and the feeding antenna have been designed and fabricated. The maximum gain is 31.15 dBi. The 1 dB gain bandwidth is 12.7% while the 3 dB gain bandwidth is 21% around 28 GHz. The aperture efficiency is better than 50% and the cross-polarization level is less than -37 dB, on the frequency range from 25 to 31.5 GHz.

Millimeter-Wave Dual-Polarized Differentially Fed 2-D Multibeam Patch Antenna Array

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.

A Dual-Polarized Planar Antenna Array Differentially-Fed by Orthomode Transducer

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 |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -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.

Cavity-Backed Slot-Coupled Patch Antenna Array With Dual Slant Polarization for Millimeter-Wave Base Station Applications

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 × 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.

An OAM-Mode Reconfigurable Array Antenna With Polarization Agility

An Orbital angular momentum (OAM) antenna with both mode reconfigurability and polarization agility is proposed in this paper. The proposed antenna is designed based on a four-element uniform circular array with a phase-shifting reconfigurable feed network. To reduce its dimensions and complexity, the feed work is constructed with two stages of single-pole double-throw switches and a stage of 90° phase-shifting power dividers, partially of which can be shared among the chosen operating states. Moreover, the use of a small amount of p-i-n diodes as binary switches allows low insertion loss and low component cost. By varying the ON/OFF status of the diodes strategically, the resultant array can be reconfigured to horizontal polarization (HP) or vertical polarization (VP), along with OAM mode $l = -1$ or +1 achieved for each polarization. The antenna performance is evaluated in terms of reflection coefficients, near-field distributions and far field radiation patterns. According to the measured results, the antenna exhibits an overlapped frequency band ranging from 2.29 to 2.59 GHz among the different operating states. Meanwhile, stable radiation patterns as well as high cross-polarization discrimination can be obtained. Benefiting from the above features, the antenna could help to improve the signal quality and increase the channel capacity in wireless communications.