Corner-cut Square Research Articles

A new wideband CP antenna with a single-layer metasurface

ABSTRACT In this paper, a new wideband circularly polarized (CP) antenna with a single-layer metasurface (MT) is developed. The single-layer MT consists of 4 × 4 truncated corner square patch cells with corner-cut square slots. Compared to the single truncated corner square patch, introducing corner-cut square slot can increase the design flexibility by changing the slot size for a wider CP operating bandwidth. A slit-shaped aperture coupling structure and a microstrip fed structure are placed together to provide coupling energy to the MT. Note that such MT and slot antenna share the same reference ground plane, and there is no air gap among the overall CP antenna structure. This design could easily make the profile low and the structure compact. The tested results reveal that the presented antenna features a broad 3-dB axial ratio bandwidth (18.2%, 5.25 ~ 6.3 GHz) and a wide −10-dB impedance bandwidth (19%, 5.25 ~ 6.35 GHz), which is very suitable for wireless communication systems with low-profile and wideband requirements.

Wideband circularly polarized array antenna based on sequential phase feeding metasurfaces for 5G (sub-6G) applications

In this paper, a broadband circularly polarized array antenna is presented, which consists of four loop slot antennas based on metasurfaces. The antenna element is a loop slot antenna fed by a microstrip line. Cross slots are added to the loop slot to improve the antenna bandwidth, and four corner-cut square metasurfaces are loaded above it, thus generating circularly polarized radiation. The antenna adopts a sequential phase (SP) feed network to realize broadband characteristics. The antenna has been fabricated and experimented. The overall size of the antenna is 78 × 78 × 10.1 mm3 (approximately 1.22 λ0 × 1.22 λ0 × 0.15 λ0), the antenna array has a measured |S11| < −10 dB bandwidth of 3.6–6.2 GHz (53.1%) and a 3-dB axial ratio bandwidth of 3.7–4.8 GHz (28.32%). Furthermore, the antenna also has radiation with a peak gain of 5.5 dBi.

A novel Fabry–Pérot (FP) antenna with high gain, low radar-cross-section (RCS), and wideband circular polarization

AbstractWe propose a novel Fabry–Pérot (FP) antenna consisting of a checkered polarization-conversion metasurface (PCM), corner-cut square patch antennas, and sandwiched compounds. The proposed antenna achieves low radar-cross-section (RCS), high gain, and wideband circular polarization (CP). The corner-cut square patch antennas facilitate high reflectivity, satisfactory transmission magnitude, and the desired phase difference. An embedded metal between two rings of substrate contributes to reducing cross-polarization, improving transmission efficiency, enhancing bandwidth, and reducing RCS. Following simulations, we fabricated a prototype of the proposed antenna and tested its performance. Measurements from the simulation and prototype tests were similar within a reasonable margin of error. Compared with alternative antennas, our proposed FP antenna offers high gain, wideband CP, low cost, a low RCS, and a lower profile.

A low‐cost, wideband, dual‐circularly polarized traveling wave antenna array

This article presents a low-profile dual-circularly polarized array based on the series feed and sequential rotation techniques. The basic radiation element is the microstrip based corner-cut square patch that could achieve dual-circularly polarized radiations. By rotating four basic elements in sequence to constitute a 2 × 2 subarray and series feeding with a phase difference of 90°, the axial ratio bandwidth can be greatly enhanced. Further, by symmetrically positioning four of such 2 × 2 subarrays coupled with out-of-phase feeding of the four subarrays, the beam deflection against frequency is corrected. To validate the proposed design, an 8 × 8 dual-circularly polarized array operating at 6.0 GHz was developed and examined experimentally. Measurements and simulations confirm the design well.

A novel composite transmission metasurface with dual functions and its application in microstrip antenna

Generally, a double corner-cut square structure transmission linear to circular polarization conversion metasurface (DCS-PCM) is difficult to realize circularly polarized radiation when it is applied to a linearly polarized microstrip antenna as electromagnetic surfaces superstrate. A novel composite transmission metasurface (NCTM) with dual functions of linear to circular polarization conversion and polarization selection is proposed and verified. For a y-polarized incident wave, transmission linear to right-hand circular polarization conversion can be realized from 8.43 GHz to 9.50 GHz, and for an x-polarized incident wave, co-polarized total reflection can be realized. Different from the DCS-PCM, the unit cell of the NCTM is made up of a corner-cut square, a substrate, and a polarization gate. Thanks to the novel design of polarization gates, the proposed NCTM is easier to realize circularly polarized radiation when it is applied to a linearly polarized source antenna. The realized gain of the antenna with NCTM can be improved because of the Fabry–Pérot resonant cavity, and the maximum amplitude of the gain improvement is 6.8 dBi. The results of simulation and experiment show that the linearly polarized microstrip antenna with NCTM can realize circularly polarized radiation with an axial ratio less than 3 dB and a significant gain improvement simultaneously.

Microstrip array antenna in-band RCS reduction using polarization reconfigurable elements

ABSTRACTAn efficient approach for in-band radar cross section (RCS) reduction of microstrip patch array antenna without employing extra-low RCS artificial materials is proposed and analysed. The element of the array has a simple structure, consisting of a corner-cut square patch and two tiny perturbation elements. By controlling two independently biased PIN diodes, it can produce linear polarization (LP), left- and right-handed circular polarization (LHCP/RHCP) radiation waves. The backscattering RCS reduction of the array can be achieved by changing the polarization status of array elements. For verification, the performance of a polarization reconfigurable microstrip array with different polarization modes is designed, compared and analysed. From the simulation and measurement results, the peak RCS of the array can be reduced by more than 7 dB without affecting its radiation performance.

A miniaturized circularly polarized coaxial fed superstrate slot antenna for L‐band application

A miniaturized circularly polarized superstrate antenna is presented in this letter. The antenna consists of a corner cut square radiating patch in which 4 arrow type slots are etched out, a superstrate placed exactly above the radiating patch and a coaxial feed. Circular polarization in the design is accomplished by the corner cuts in the radiating patch and placing the feed point below origin (0, 0, 0) along x‐axis. The slot miniaturization technique results in about 73.7% and 79.8% reduction in volume and active patch area of the designed antenna. The antenna has a compact dimension of about 0.11λ0 × 0.11λ0 × 0.02λ0 at a frequency of 1.21 GHz with S11 &lt; − 10 dB bandwidth of about 3.03% (1.30–1.34 GHz). Axial ratio &lt; 3, good impedance matching, acceptable gain, radiation efficiency greater than 90%, and stable radiation characteristics are observed across the operational bandwidth of the designed antenna.

Analytical synthesis of coupling matrix for a dual mode dual band filter

ABSTRACTIn this article, a simple approach for synthesis of coupling matrix of dual mode dual band filters is presented. Odd and even modes of dual mode cavities are used as basis of this coupling matrix. Each mode of cavities is coupled to the same mode of the adjacent cavity independent from the other mode and hence, two separate paths, odd path and even path, are provided from source to load. Therefore, the sensitivity of filter with respect to the fabrication tolerance is reduced. For validation of this approach, the coupling matrix of two‐cavity dual mode dual band filter is calculated and also, a dual mode dual band SIW filter by using corner cut square SIW cavities is designed and realized. Filter prototype is fabricated on a single layer substrate using PCB technology and the measured results are in a good agreement with the simulated results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:80–83, 2017

Polarization conversion of metasurface for the application of wide band low-profile circular polarization slot antenna

In this letter, based on a corner-cut square metasurface, a planar polarization conversion structure is presented and the application for wide band low-profile circular polarization (CP) slot antenna is proposed. The mechanisms for achieving the CP state from a linearly polarized incident wave and for broadening the working bandwidth of conventional slot antenna are analyzed theoretically. The wide band low-profile CP slot antenna is achieved with numerical optimizations and parameter studies. Both simulations and measurements are performed to demonstrate the proposed antenna, and good agreements are obtained. Such results will open the path for polarization conversion metasurfaces used in the CP antenna area.

Metamaterial Based Electronically-Scanned Circularly-Polarized LWA

An electronically-scanned circularly-polarized leaky-wave antenna (LWA) designed for ETC system is proposed in this paper. Based on the theory of composite right/left-handed (CRLH) transmission line (TL), the proposed antenna can fulfill the beam-scan from -6° to -21° in the half plane continuously at the fixed frequency of 5.8 GHz by tuning the bias voltage of varactors loaded on the CRLH TL. By loading corner-cut square patches, a circularly-polarized radiation is obtained at the main beam, and the maximum gain in the main beam direction keeps above 11 dB.

Analysis of quadruple corner-cut ridged square waveguide using a scaled boundary finite element method

This paper describes the development of an efficient semi-analytical method, namely scaled boundary finite-element method (SBFEM) for a quadruple corner-cut ridged square waveguide. Thinking about its symmetry, only a quarter of its cross-section needs to be considered and divided into a few sub-domains. Only the boundaries of the sub-domains are discretized with line elements leading to great flexibility in mesh generation. The singularities in the re-entrant corners are represented analytically by locating the scaling center in those points. Variational principle approach is presented to formulate the basis SBFE equations for the sub-domains. Then, an equation of the ‘stiffness matrix’ on the discretized boundary is established. Finally, by using the continued-fraction solution and introducing auxiliary variables, a generalized eigenvalue equation with respect to the cutoff wave number is obtained without introducing an internal mesh. Numerical results are presented to verify the accuracy and efficiency of the present technique. Variations of the cutoff wave numbers of the dominant and higher-order modes for both TE and TM cases with the corner-cut ridge dimensions are investigated in details. Simple approximate equations are found to accurately predict the cutoff wave number of TE20U, TE22, TM11 and TM13L modes. The single mode bandwidth of the waveguide is also calculated.

Novel circularly-polarized ceramic dielectric resonator antenna excited by a corner-cut square patch

A ceramic dielectric resonator antenna excited by a corner-cut square patch for the circularly-polarized operation is introduced. The effect of patch size and cut size is investigated, showing that the resonant frequency of the antenna can be changed by simply changing the patch size. The reflection, axial ratio, and radiation characteristics of the antenna are found. Measurements were carried out to verify the design. The antenna is compact in structure, which is attractive in the application as the satellite communication terminals.

Scaled boundary finite element approach for waveguide eigenvalue problem

The scaled boundary finite element method (SBFEM) is developed for the solution of waveguide eigenvalue problems, which combines the advantages of the finite element method and the boundary element method. A new variational principle formulation to derive the SBFEM equations for waveguide is developed. An equation of the dynamic stiffness matrix for waveguide representing the relationship between the ‘flux’ and the longitudinal field components at the discretised boundary is established. A continued fraction solution in terms of eigenvalue is obtained. By using the continued fraction solution and introducing auxiliary variables, the flux–longitudinal field relationship is formulated as a system of linear equations in eigenvalue then a generalised eigenvalue equation is obtained. The eigenvalues of rectangular, L-shaped, vaned rectangular and quadruple corner-cut ridged square waveguides are calculated and compared with analytical solution and other numerical methods. The results show that the present method yields excellent results, high precision and less computational time and rapid convergence is observed.

An ultra-narrow band eight-pole dual-mode HTS patch filter

An ultra-narrow band eight-pole dual-mode HTS patch filter was designed and fabricated. The filter is constructed by four corner-cut square patches, each of which has two resonating modes. The influence of the change of the corner-cut position on the filter response was investigated by simulations. Four small rectangle patches were added in the topology of the filter as tuning tools. By employing this unique tuning structure, the simulated filter responses and current density distributions on the patches have been greatly improved. The filter was fabricated using double sided YBCO films on a 3 in. LaAlO 3 substrate. The measured results showed satisfactory performance with center frequency 2.494 GHz, fractional bandwidth 0.2%, return loss in passband better than 16 dB, and out-of-band rejection of the filter better than 90 dB at 15 MHz away from its center frequency.

Whispering gallery modes in micron-sized SrS:Eu octahedrons

Optical whispering gallery modes were observed in micron-sized SrS:Eu2+ octahedrons. Cathodoluminescence in a scanning electron microscope was used to evaluate the emission characteristics of individual octahedrons with various sizes. The resonance modes superposed on the orange Eu2+ broadband emission were explained by a plane wave model, taking the wavelength dispersion of the refractive index into account. The resonance modes occur in the three equatorial planes in the octahedrons, which were approximated by corner-cut square disks.

Fabrication and characterization of optimized corner-cut square microresonators

In this paper we report the fabrication and characterization of waveguide coupled square resonators with modified corners, in particular the corner-cut square resonator. We employ rigorous FDTD analysis to identify an optimal corner-cut length and compare this with our experimental findings. Two- and three dimensional FDTD analysis is also used to optimize the coupling gap and the width of the coupling waveguide. Fabrication of the square microresonators on silicon-on-insulators by conventional E-beam lithography and dry etching techniques will be discussed in detail. The characterization of these corner-cut square microresonators shows good performance and excellent agreement with the rigorous electromagnetic simulations.

Planar corner-cut square microcavities: ray optics and FDTD analysis

We analyze corner-cut square microcavities as alternative planar microcavities. Ray tracing shows open-ray orbits that are 90-degree-rotated can oscillate between each other upon reflections at the 45-degree corner-cut facets, and have the same sense of circulation. Our two-dimensional finite-difference time-domain simulations suggest that a waveguide-coupled corner-cut square microcavity with an optimum cut size supports traveling-wave resonances with desirable add-drop filter responses. The mode-field pattern evolutions confirm the concept of modal oscillations. By applying Fourier transform on the mode-field patterns, we analyze the modal composition in k-space. The add-drop filter responses can be optimized by fine-tuning the waveguide width.