Cross-polar Radiation Patterns Research Articles

Parasitic Loaded Shorting Pin Based Compact Multi-slot LoRa Antenna for Military Application

In this paper, work on a compact multi-slot patch antenna with a parasitic load and shorting-pin has been presented for its use in long range (LoRa) defense applications. Initially the antenna is designed and simulated using HFSS and a parametric study has been carried out for achieving an optimized antenna configuration. This is followed by the fabrication of antenna prototype based on the optimal performances obtained from the simulated results. Further, the return loss along with free space co-polar and cross-polar radiation pattern measurements has been carried out for the fabricated antenna. The experimental results show a good comparison with that of the simulated one. The proposed antenna resonates at an operating frequency of 866 MHz, providing a -10 dB bandwidth from 856 MHz-877 MHz, which covers the wireless standard used for LoRa technology. Finally, a comparative analysis of the proposed antenna with the recently reported works is presented.

Development of a metasurface-based slot antenna for 5G MIMO applications with minimized cross-polarization and stable radiation patterns through mode manipulation

This paper presents an approach for designing metasurface antennas using the characteristic mode analysis method for 5G mm-wave multiple input–multiple output (MIMO) systems. The proposed metasurface antenna consists of a 3 × 3 array of modified patches with additional slits and stubs, which are fed by a coupling slot. This configuration reshapes surface currents and improves the radiation performance across a broad frequency range. The design offers significant advantages such as reduced antenna size, minimized influence of higher-order modes, and maintained low cross-polarization (XP) level. Experimental results demonstrate that the proposed metasurface-based slot antenna provides a bandwidth of 29.6% (23–31 GHz) with a return loss better than 10 dB. It achieves a peak gain of 9.43 dB and exhibits an XP level below − 26 dB and − 48 dB at φ=0∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varphi = 0^{ \\circ }$$\\end{document} and φ=90∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varphi = 90^{ \\circ }$$\\end{document} planes, respectively. The physical dimensions of the antenna are 0.9λ0 × 0.9λ0 × 0.08λ0, where λ0 is the free space wavelength at 27 GHz, resulting in an approximately 41% reduction compared to the conventional metasurface patch antenna. Moreover, the design proves to be well-suited for MIMO systems, enabling close placement of antenna elements without degrading their radiation patterns. The experimental results in 1 × 2 and 2 × 2 MIMO configurations represent that the isolation between antenna elements are better than 18 dB and 21 dB, respectively. The performance of the antennas remains stable in both configurations, effectively addressing concerns such as beam squint and eliminating the common issue of beam splitting observed in conventional metasurface MIMO antennas. Moreover, the envelope correlation coefficient value in both MIMO configurations is lower than 0.003. This significant advancement offers a promising solution for compact 5G mm-wave massive MIMO applications.

Design and investigation of pocket shaped fractal antenna using circular ring elements for UWB technology with stub loaded DGS

ABSTRACT Stub loaded pocket-shaped fractal antenna (PSFA) with defected ground structure of volumetric dimensions 32 × 36 × 1.6 mm3 for UWB technology has been presented in this manuscript. Proposed structure exhibits improved impedance bandwidth in juxtaposition to other geometries like antenna with partial ground plane and ground plane with defects. Ground plane of proposed antenna has been modified for attaining the improved results. Finally, the structure of antenna with modified ground plane reveals the wider impedance bandwidth of 11.80 GHz (149.36%) and 5.33 GHz (30.75%) in the frequency range from 2.0 to 13.80 GHz and 14.67 to 20.0 GHz, respectively. The peak gain of antenna is also computed and divulged as 7.02 dB at 9.7 GHz frequency band. The co- and cross-polarisation radiation patterns in E- and H-plane of proposed antenna are measured and presented at frequency points 3.0, 4.9, 7.3, 8.8, 10.2, 13.0, 16.6 and 19.4 GHz. Proposed antenna has been simulated and its performance is also being investigated using HFSS V13 simulator. Further, optimised antenna geometry is fabricated, and fair comparison between simulated and measured results has been drawn and divulged in reasonable agreement with each other. The proposed antenna has reported the wider bandwidth which made it a suitable candidate for distinct wireless applications in the UWB frequency range.

Four-Arm Sinuous Antenna With Low Input Impedance for Wide Gain Bandwidth

An improved method of reducing the input impedance of a four-arm sinuous antenna is demonstrated for a wide gain bandwidth. The proposed antenna has a dual-linear polarized response for electronic support measures (ESM) systems and is designed with a planar substrate. The structure for reducing the input impedance is developed based on the transmission and coupled line theory and is shown to be in excellent agreement with theoretical predictions. The proposed antenna achieves an impedance bandwidth in the range of 0.45–6 GHz with a reference impedance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$100 ~\Omega $ </tex-math></inline-formula> . Simulations for comparison according to the difference in input impedance of designed antennas with feeding structures are also presented. Finally, the performance of the fabricated antenna with wideband balun is verified by measuring co- and cross-polarization radiation patterns. As a result, the proposed antenna achieves a wide gain bandwidth (>2.5 dBi) and a cross-polarization isolation (>−13 dB) of more than 12:1 in the frequency range over 0.6 GHz, which can be used in ESM systems.

Backfire suppressed low profile aperture coupled stacked patch antenna backed by a high impedance surface (HIS) reflector for UHF RFID reader applications

In this paper, a backfire suppressed aperture coupled circularly polarized (CP) stacked patch antenna for universal ultra-high frequency (UHF) radio frequency identification applications is presented. Cross-polarized backfire radiation patterns were successfully suppressed by a planar high impedance surface (HIS) reflector. The size of the fabricated antenna is 250 × 250 × 26.9 mm3 (0.71λ0 × 0.71λ0 × 0.076λ0) and its peak gain value of 7.1 dBi is measured. The distance between the antenna and the HIS reflector is only 4.8 mm (0.014 λ0). The HIS reflector suppressed cross-pol backfire radiations by about 10 dB. Detailed antenna and HIS reflector design are discussed thoroughly in this paper. The presented backfire suppression technique using the HIS reflector is scalable to other applications and frequency bands. This paper demonstrates the feasibility of the HIS structure at UHF band.

A Multiband antenna using plus‐shaped fractal‐like elements and stepped ground plane

A multiband planar symmetrical plus-shaped fractal monopole antenna with stepped ground plane is presented in this study. Measured results show that the proposed antenna operates with 10 dB return loss bandwidths from 1.630 to 1.88 GHz and from 4.5 to 8.5 GHz covering The Global System for Mobile Communications (GSM) 1800 MHz 2G spectrum band, 4400 to 4900 MHz 5G spectrum band adopted by Japan and China for future 5G communication in sub-6 GHz band, 5.15 to 5.925 GHz LTE band 46, WLAN IEEE 802.11 y/a/h/j/n/P bands, and 5.8 to 7.707 GHz military band. The antenna gain varies between 1.73 and 1.97 dB in lower band and 3.6 to 5.05 dBi in upper band with radiation efficiencies more than 90% in lower band and more than 80% in upper band. The antenna has more than 64 and 28 dB isolations between the copolar and cross-polar radiation patterns in the lower and upper bands, respectively.

Mutual Coupling Reduction of ±45° Dual-Polarized Closely Spaced MIMO Antenna by Topology Optimization

A hybrid topology optimization (HTO) method is adopted to reduce the mutual coupling of a ±45° dual-polarized closely spaced MIMO antenna. In order to shorten the optimization time, only the isolation structure region of the two-element MIMO antenna is selected for optimization. More importantly, by exploiting the symmetry of both the MIMO antenna and the isolation structure, only a quarter of the isolation structure needs to be optimized to achieve good antenna performance. In this way, not only the optimization variables, but also the optimization sub-objectives are greatly reduced, and the optimization time is further diminished. The performance of the dual-polarized MIMO antenna with the optimized isolation structure (OIS) is validated by both simulation and measurement. The OIS resonates in both polarizations, thus lowering the mutual coupling between co-polarization ports ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{31}\vert $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{42}\vert$ </tex-math></inline-formula> ) and between cross-polarization ports ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{41}\vert $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{32}\vert$ </tex-math></inline-formula> ) simultaneously. With the center distance of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.35\lambda _{0}$ </tex-math></inline-formula> , the measured mutual coupling between different ports are reduced by 6~11 dB within the 10-dB impedance bandwidth (Reflection coefficients < −10 dB) by adding the OIS, and the highest mutual coupling between different ports is reduced from −15 to −21 dB. Besides, the antenna maintains a low profile ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.026\lambda _{0}$ </tex-math></inline-formula> ), low cross-polarization and excellent radiation pattern performance.

Developer Design of Hybrid Plasmonic Nano Patch Antenna with Metal Insulator Metal Multilayer Construction

Hybrid plasmonic nanopatch antenna with metal-insulator-metal (HMIM) multilayer has been investigated for operation at the frequency of 125–250 THz using the finite element method (FEM) implemented in Ansoft High Frequency Structure Simulator (HFSS). The proposed antenna exhibits a wide bandwidth of 49.5 THz (151.5 THz–201 THz) for the slots thicknesses Wg = 50 nm and Ws = 100 nm and dual bandwidth for Ws = 20 nm. The obtained results show the input impedance of 50.3 Ω input resistance (real part) and 2.3 Ω reactance (imaginary part) occurring at (near) the operation frequency. The maximum gain of 23.98 dB has been observed for resonant frequencies of 176 THz, and the maximum directivity remains above 6.73 dB and 7.46 dB at resonant frequencies of 170 THz and 190 THz, respectively. Our proposed antenna performance is compared to previously reported designs. The copolar and cross-polar radiation patterns are simulated at different resonant frequencies of 160 THz and 197 THz for planes Φ=90° and Φ=0°. The arrays of a proposed antenna are designed in one and two dimensions in order to appropriate high-gain applications.

Vertically‐integrated differential filtering patch antenna excited by a balun bandpass filter

This study develops a differential-fed filtering patch antenna, which features superior frequency selectivity, compact size, low cross-polarisation, and symmetrical radiation patterns. The proposed antenna consists of a rectangular patch on the top layer, which is differentially fed by a balun bandpass filter on the bottom layer. A pair of rectangular coupling slots were etched on the middle layer for energy coupling. The patch antenna performs not only as the radiator but also as the last resonator of the whole filter circuit for compactness. A prototype of the proposed filtering antenna operating at 2.45 GHz was fabricated and tested. The measured in-band peak gain is 5.9 dBi with steep roll-off at band edges, and the out-of-band gain is less than - 25 dBi. Moreover, symmetrical radiation patterns and low cross-polarisation levels of - 22 dB are also realised for the proposed filtering antenna.

Theoretical Analysis of 3-D Channel Spatial Correlation and Capacity

An approximate closed-form expression for 3-D channel spatial correlation (SC) is derived, given cross-polarized rectangular arrays and standards-based antenna radiation patterns. Furthermore, we evaluate the impact of 3-D SC on system performance and derive the capacity relationship between 2-D and 3-D channels. As expected, the 3-D channel is characterized by lower SC and higher channel capacity than its 2-D counterpart by taking the advantage of the additional degrees of freedom in the elevation domain, where the 3-D antenna arrays and the 3-D channel propagation are considered.

Antenna Cross-Polar Requirements for 3-PolD Weather Radar Measurements

The analysis and correction of the bias occurring in weather radar polarimetric measurements is a challenging problem. Polarization coupling due to the cross-polar radiation pattern of the radar’s antenna is known to be responsible for errors in the estimation of the polarimetric covariance matrix, and consequently in the hydrometeor classification and quantification, either when using the ATSR or the SHV method. An alternative method for Doppler and polarimetric measurements based on transmitting three different polarizations (3-PolD) has been proven to provide accurate polarimetric covariance matrix estimates without making any hypothesis about the target polarimetric response or its Doppler spectrum. This method does not reduce the Doppler capabilities or the unambiguous range of the radar despite alternately transmitting 3-PolD. These characteristics have encouraged evaluating the polarimetric parameter biases due to cross-polar radiation when this method is used. Biases are calculated considering reflector antenna systems as well as phased-array antenna systems. The results show that this method may guarantee a tolerable bias level even with a poor co- to cross-polar antenna pattern ratio.

Modified star‐star fractal (MSSF) super‐wideband antenna

ABSTRACTA microstrip line fed star‐star fractal antenna with notch loaded semi‐elliptical ground plane is presented for super wideband applications. An impedance bandwidth of 4.6–52 GHz, i.e., a bandwidth ratio of 11.31:1 is achieved for VSWR &lt; 2. The antenna structure has advantages of compact dimensions and wider bandwidth over previously reported SWB structures. Radiation characteristics, i.e., co and cross polar radiation patterns, peak gain, and efficiency has been presented and discussed. The simulated and experimental results are found to be good agreement. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:624–630, 2017

Investigation of spherical and cylindrical Luneburg lens antennas by the Green's function method

Luneburg lens antenna radiation fields are calculated with Green's functions of spherical and cylindrical layered structures. Electric field components of spherical and cylindrical Luneburg lenses excited by linear and circular polarized incident field are analysed. Dipole, slot and aperture antennas are described by electric and magnetic extraneous currents. Radiation patterns of cylindrical and spherical Luneburg lens are analysed. Co-polarized and cross-polarized field radiation patterns are shown. The proposed method significantly reduces the computing time for multi-layered lenses in comparison with the most commonly used in antenna design. The first step antenna structure optimization may be performed for a shorter time. The results may be used as the first approximation for Ansys HFSS and other software.

Low Side-Lobe Substrate-Integrated-Waveguide Antenna Array Using Broadband Unequal Feeding Network for Millimeter-Wave Handset Device

A low side-lobe substrate-integrated-waveguide (SIW) antenna array is presented at the 28-GHz band using broadband unequal feeding network for millimeter-wave (mm-wave) handset devices. The ground-plane size of the proposed antenna is fixed to half of the size of the Samsung Galaxy Note 4. The antenna array has been implemented with a multilayer structure created by stacking three substrates and a copper plate. An 8-way SIW feeding network with broadband 4-stage T-junction dividers and a cavity-backed antenna are investigated to obtain broadband performance. The proposed unequal T-junction dividers with phase compensation are introduced and designed for various output ratios. Applying Taylor beam-pattern synthesis in the 8-way SIW feeding network, low side-lobe performance is achieved. The measured result of the fabricated antenna has 2.3 GHz bandwidth within $\text{S}_11\,{ . The fabricated antenna can be performed with a gain up to 13.97 dBi with a low cross-polarization and symmetrical fan beam radiation patterns with low side-lobe levels. Most of the measured results are validated with the simulated results. The proposed antenna array provides low cost, broadband performance, and good radiation performances with low side-lobe levels for mm-wave handset devices.

Full‐polarisation three‐dimensional pattern synthesis for conformal conical arrays with dynamic range ratio constraint by using the initialisations based on equivalence theorem

To design three-dimensional (3D) conformal conical arrays with desired 3D co-polarisation and cross-polarisation radiation patterns, a pattern synthesis method based on equivalent principle and trust region method is presented. Dynamic range ratio (DRR) of element excitations is taken into consideration. An analytical function is utilised to constrain DRR and avoid discontinuity of objective function. Owing to the optimisation is based on very good initial currents distribution, the optimisation procedure is very fast. The analytical gradient and Hessian matrix expressions of the objective function are derived. This also improves the optimisation efficiency compared with using the finite difference methods to solve gradient and Hessian matrix. To demonstrate the effectiveness of this proposed method, a conformal conical array with 454 elements has been designed. The amplitude and phase excitations were optimised by using the proposed method.

Comparison of Theoretical Biases in Estimating Polarimetric Properties of Precipitation With Weather Radar Using Parabolic Reflector, or Planar and Cylindrical Arrays

Planar or cylindrical phased arrays are two candidate antennas for future polarimetric weather radar. These two candidate antennas have distinctly different attributes when used to make quantitative measurements of the polarimetric properties of precipitation. Of critical concern is meeting the required polarimetric performance for all directions of the electronically steered beam. The copolar and cross-polar radiation patterns and polarimetric parameter estimation performances of these two phased array antennas are studied and compared with that obtained using a dual-polarized parabolic reflector antenna. Results obtained from simulation show that the planar polarimetric phased array radar has unacceptable polarimetric parameter biases that require beam to beam correction, whereas biases obtained with the cylindrical polarimetric phased array radar are much lower and comparable to that obtained using the parabolic reflector antenna.

Radiation Pattern Measurement of a Low-Profile Wearable Antenna Using an Optical Fibre and a Solid Anthropomorphic Phantom

This paper presents a study into radiation pattern measurements of an electrically small dielectric resonator antenna (DRA) operating between 2.4 and 2.5 GHz in the industrial, scientific and medical (ISM) radio band for body-centric wireless communication applications. To eliminate the distortion of the radiation pattern associated with the unwanted radiation from a metallic coaxial cable feeding the antenna we have replaced it with a fibre optic feed and an electro-optical (EO) transducer. The optical signal is then converted back to RF using an Opto-Electric Field Sensor (OEFS) system. To ensure traceable measurements of the radiation pattern performance of the wearable antenna a generic head and torso solid anthropomorphic phantom model has been employed. Furthermore, to illustrate the benefits of the method, numerical simulations of the co-polar and cross-polar H-plane radiation patterns at 2.4, 2.45, and 2.5 GHz are compared with the measured results obtained using: (i) an optical fibre; and (ii) a metallic coaxial cable.

An Efficient and Versatile Technique for the Synthesis of 3D Copolar and Crosspolar Patterns of Phase-Only Reconfigurable Conformal Arrays With DRR and Near-Field Control

An accurate and flexible iterative algorithm of power synthesis for reconfigurable arrays is proposed. The algorithm is based on an alternating projection approach, and is suitable for arrays of arbitrary geometry, thus including conformal and sparse arrays. It allows to generate a number of copolar and crosspolar radiation patterns satisfying assigned requirements, switching each pattern into any of the others by phase-only control of the excitation applied to each array element. Moreover, the algorithm allows to reduce the dynamic range ratio (DRR) of the excitations and the maximum electric field amplitude in a region close to the antenna. A modified version of this algorithm including the previous one as a particular case, is then proposed, which introduces, as an additional capability, the reduction of the power radiated in the side lobe region, in presence of the above constraints, and the squared amplitude of the electric field in an assigned region close to the antenna. This allows to significantly improve the final results. Numerical examples, including a comparison with existing literature, show the effectiveness of the proposed algorithm.

Compact Fractal Left-Handed Structures for Improved Cross-Polarization Radiation Pattern

A set of two-dimensional (2-D) left handed (LH) transmission line (TL) structures are proposed based on the single-layered and double-layered fractal-perturbed mushrooms. The effects of the Koch Island on the LH characteristics have been investigated physically by examining the dispersion diagram of the LH structure with and without fractal perturbations, showing that the parasitic transverse electric mode has been considerably suppressed without any deteriorative penalty on the dominant transverse magnetic mode. Therefore, the interaction of the degenerated parasitic mode with the operation modes has been considerably weakened. The concept has been employed to suppress the cross-polarization (XP) radiation of a microstrip antenna which incorporates a 2 × 2 array of the LH structure into a conventional microstrip patch. Numerical and experimental results indicate that the XP radiation (<; -30dB) has been notably reduced at three working frequencies (f-1 = 1.5, f0 = 2.96 and f+1 = 3.7 GHz) while the antenna performances such as gain, co-polarization radiation and impedance matching are without any deterioration.

Direct Optimization of Printed Reflectarrays for Contoured Beam Satellite Antenna Applications

An accurate and efficient direct optimization technique for the design of contoured beam reflectarrays is presented. It is based on the spectral domain method of moments assuming local periodicity and minimax optimization. Contrary to the conventional phase-only optimization techniques, the geometrical parameters of the array elements are directly optimized to fulfill the contoured beam requirements, thus maintaining a direct relation between optimization goals and optimization variables, and hence resulting in more optimal designs. Both co- and cross-polar radiation patterns of the reflectarray can be optimized for multiple frequencies, polarizations, and feed illuminations. Several contoured beam reflectarrays, that radiate a high-gain beam on a European coverage, have been designed and compared to similar designs obtained using the phase-only optimization technique. The comparisons show that the designs obtained using the proposed direct optimization technique are superior in performance, both for multi-frequency and dual-polarization designs. A reflectarray breadboard has been manufactured and measured at the DTU-ESA Spherical Near-Field Antenna Test Facility to validate the proposed technique. An excellent agreement of the simulated and measured patterns is obtained.