Compact Clock-Shaped Broadband Circularly Polarized Antenna Based on Characteristic Mode Analysis

This paper proposes a low-profile, coplanar waveguide (CPW)-fed non-uniform metasurface (MS)-based antenna with wideband circular polarization (CP) and compact geometry. The design integrates rotationally asymmetric slots in the CPW ground plane and spatially truncated non-uniform MS elements on a single-layer Rogers 5880 substrate (55 × 55 × 3.5 mm3). Through systematic characteristic mode analysis (CMA), orthogonal degenerate modes are excited by structural asymmetry, achieving balanced amplitude and a 90° phase difference. Simulations reveal a −10 dB impedance bandwidth of 5.2–6.8 GHz (24.6% fractional bandwidth) and a 3 dB axial ratio (AR) bandwidth of 5.2–5.96 GHz. Experimental validation demonstrates a measured impedance bandwidth of 5.2–6.8 GHz and an AR bandwidth of 5.2–5.92 GHz, alongside a peak gain of 6.9 dBic, cross-polarization suppression below −30 dB, and stable broadside radiation patterns. The truncated outer MS elements suppress higher-order modes, enabling a low-profile configuration (0.04λ0 at 5.5 GHz) while outperforming prior works in bandwidth and polarization purity. This work establishes a CMA-driven framework for merging structural asymmetry with modal orthogonality, offering a robust solution for satellite communications and 5G systems requiring wideband CP radiation.

This article presents a miniaturized reconfigurable tri-polarization metantenna with compact size of 0.58 λ 0 × 0.58 λ 0 × 0.04 λ 0 ( λ 0 is the free space wavelength referring to the antenna center frequency). Metantenna means the metasurface is directly used as the antenna radiator aperture instead of an accessory. The metantenna is formed by miniaturized windmill like units, which is evolved from square patch units based on characteristic mode analysis, and 46% size reduction is achieved. Two PIN diodes are introduced into the feeding microstrip for switching among tri-polarization. The measured −10 dB impedance bandwidths are 24.6% (3.24–4.15 GHz) and 24.1% (3.26–4.05 GHz) for circular polarization (CP) and linear polarization (LP), respectively. The measured overlapped 3 dB axial ratio (AR) bandwidth is 15% (3.4–3.95 GHz). The measured peak gains are 5.15 dBi, 5.21 dBic, and 5.25 dBic for LP, left hand (LH) CP and right hand (RH) CP, respectively. The aperture efficiency is 77.3%, 78.5%, and 79.1% for LP, LHCP, and RHCP, respectively. The measured AR beamwidth (BW) of LHCP in XZ-plane and YZ-plane is 192° and 174°, respectively, the measured ARBW of RHCP in XZ-plane and YZ-plane is 201° and 166°, respectively. The developed metantenna has the following advantages: broadband 3 dB AR bandwidth, wide ARBW > 166°, least PIN number (tri-polarization with 2 PIN), and high-aperture efficiency.

A new broadband circularly polarized (CP) metasurface (MS) antenna based on characteristic mode analysis (CMA) is proposed. The antenna consists of 4×4 truncated Γ-shaped unit cells and is fed by an improved slot coupling structure. The characteristic modes required to achieve CP are analyzed by CMA, and the CP performance is improved by changing the characteristic currents distribution. By introducing a stepped slot structure on the slot floor, the bandwidth of the antenna has been further broadened. By loading the microstrip line to feed the MS, left-handed circular polarization (LHCP) can be realized. In addition, the equivalent circuit method is used to explain how the designed MS antenna achieves CP. The overall size of the designed and fabricated MS antenna is 0.72 λ 0 ×0.72 λ 0 ×0.08 λ 0 at 6.2 GHz. The measured −10 dB impedance bandwidth of the antenna is 25.17% (5.21 GHz-6.71 GHz) and the measured 3 dB axial ratio bandwidth is 17.42% (5.87 GHz-6.99 GHz). Moreover, the highest gain in the working frequency band is 7.52 dBic. The proposed CP MS antenna has good application prospects in C-band satellite communications.

A low-profile and broadband metasurface antenna is proposed for circular polarization radiation. The metasurface is an array of subwavelength square patches. The modal behaviors of the proposed metasurface are investigated by using the characteristic mode theory. Two characteristic modes with the same resonant frequencies and orthogonal current distributions are chosen as operation modes. Furthermore, a hybrid feed system consisting of a cross-slot and a microstrip line is employed to excite the two orthogonal modes having a 90° phase difference to obtain circular polarization radiation. Based on these concepts, an antenna with low profile of 0.07λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at an operation frequency of 5.5GHz) is designed. The measurement results show that the proposed antenna has -10 dB impedance bandwidth of 4.8-6.35 GHz and 3 dB axial-ratio bandwidth of 4.85-6 GHz. Moreover, the antenna gain is 6.8-9.7 dBic in the whole axial-ratio bandwidth.

This article studies a quad-port multi-input-multi-output (MIMO) circularly polarized antenna with good isolation properties. Using characteristic mode analysis (CMA), the first six distinct modes of the asymmetric square slot with an inverted L-strip are analyzed. In this study, modal parameter extraction is carried out for circular polarization (CP) radiation. A simple annular ring microstrip feed is excited to obtain broadband CP based on CMA. The single-unit feeding structure is replicated orthogonally four times to achieve a CP MIMO antenna. This antenna provides port isolation of more than 21 dB without the use of an additional decoupling element. The quad-port CP-MIMO antenna is simulated with a total dimension of 50 × 50 mm2. The antenna attains impedance matching (S11 < −10 dB) from 5.37 GHz to beyond 11 GHz with an axial ratio bandwidth (ARBW) of 4.65 GHz (5.61 GHz to 10.26 GHz). The peak realized gain of the MIMO antenna is measured at 5.69 dBi at 8.4 GHz. Additionally, the diversity performance parameters of the MIMO structure are computed. The advantages of the proposed structure have been evaluated by comparing it to previously reported MIMO structures. A prototype of the MIMO structure measurements was found to match the simulation results.

In this communication, an S-band wide-bandwidth and wide-beamwidth full-metal circularly polarized (CP) cavity-backed slot antenna is proposed. A pair of triangular prisms placed at the corners of the cavity is introduced to produce TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">101</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">011</sub> modes with orthogonal electric fields. These two modes are used to achieve the CP radiation and radiate the energy through a single-circular slot. By simultaneously varying the prisms' size and slot radius, the axial ratio (AR) bandwidth (ARBW) improves. The ARBW is further improved by replacing the circular slot with an elliptical slot. As a result, the ARBW increases from 1.0% to 10.3% without complicating the antenna structure and without enlarging the antenna size. Besides, the antenna still operates at two degenerate modes to introduce stable radiation gain and pattern. In addition, the proposed CP slot antenna features a wide ARBW. The final measurement shows that the proposed CP antenna can achieve a 9.5% bandwidth, a stable gain of 7.65 dBic ± 0.15 dBic, and higher than 140° ARBWs in a wide frequency range. The peak total radiation efficiency and aperture efficiency are about 97% and 91%, respectively.

A circularly polarized (CP) metasurface (MS) antenna with wide operating band and low-profile is proposed. To reveals the working mechanism of the broadband MS CP antenna, characteristic mode analysis (CMA) which can provide physical insight is introduced. The desired modes are selected to construct CP radiation and then excited by a L-shaped slot while the undesired modes are shifted towards higher frequencies. After modulating the higher order mode, the in-band boresight gain is improved. After full-wave simulation, the results show the impedance matching bandwidth and the axial ratio (AR) bandwidth are 24% and 32.1% respectively. Besides, the radiation patterns are greatly improved comparing with the reference antennas.

Characteristic mode (CM) analysis of multi-scale and complex targets has attracted much attention in computational electromagnetics. However, it is hard to calculate the multi-scale problems in terms of desired accuracy and stability by using conventional methods. What is more, it is a challenging work to generate a good quality mesh for the multi-scale structures including very fine features. In this paper, we present Discontinuous Galerkin (DG) surface integral equations-based theory to analyze the CMs. The multi-scale objects are firstly divided into several subdomains, and we generate the meshes of every parts independently. HRWG basis functions are adopted in our work and the characteristic currents are expanded by HRWG basis functions. In many applications, only characteristic currents with small eigenvalues are desired because they are corresponding to the modes that radiate efficiently and have large modal coefficients. Special singularity extraction schemes are chosen to treat the infinite term in the resulting integral equations since HRWG basis functions are not divergence-conforming and there is divergence operator in electric field integral equation (EFIF) and magnetic field integral equation (MFIE). In DG method, they are no requirements for normal continuity of currents across the contour of between every two subdomains, hence, the proposed method can handle both non-conformal mesh and conformal mesh. Numerical results are presented to validate the propose formulation. This work may offer great flexibility to CM analysis of multi-scale and complex structures.

A compact broadband circularly polarized antenna with novel tilt fences for GNSS applications is proposed in this paper. The proposed antenna consists of Y-shaped feedlines with vacant-quarter rings, parasitic patches, ground, and novel tilt fences. Good impedance matching as well as circular polarization (CP) characteristics are achieved with novel tilt fences. New resonance modes and CP modes are introduced at low frequencies through novel tilt fences, which is equivalent to antenna miniaturization. The proposed antenna with four CP modes is fabricated using simple PCB technology and has a compact dimension of 0.29λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> *0.29λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> *0.18λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength of the center frequency). Based on the measured results, a wide impedance bandwidth (IBW) and axial ratio bandwidth (ARBW) are achieved. The -15 dB IBW can cover 1.07-1.98 GHz, and the 3-dB ARBW is 61.5% from 1.07-2.02 GHz. In addition, the antenna has a wide overlap bandwidth of 1.07-1.98 GHz (59.7%). This simple and compact CP antenna has good potential in GNSS applications.

In this work a multi wideband circularly polarized (CP) compact antenna is designed. CP is achieved by loading stubs and slots in the ground plane. It provides wide impedance bandwidth (IBW) and axial ratio bandwidth (3-dB ARBW). Coplanar waveguide feeding techniques has been used to achieve significant gain and stable radiation pattern. It provides peak gain about 5dB. Rigorous simulation is done using CST MWS for design optimization and result computation. This antenna design provides a 3dB ARBW (4-9.2 GHz) and (11.9-15.04 GHz) while the IBW are (3.6-9.11GHz) and (10-13.5 GHz) for lower and upper bands respectively. The overall floor area of proposed antenna is 20 × 20 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> .

This paper proposes a novel method for enhancing the half-power beamwidth (HPBW) of an end-fire circularly polarized (CP) terminal antenna, whereby the end-fire CP antenna is designed for 6 G satellite communication. First, the CP property is realized by allocating the resonances of both In-phase mode (IM) and out-of-phase mode (OM) based on the theory of characteristic mode (TCM). The HPBW of OM and IM is enhanced by layering the radiator, which introduces interlayer currents for OM and substrate thickness for IM. Besides, by using the stepped ground edge to regulate field distribution in the radiator, the HPBW is further broadened. The proposed wide HPBW CP antenna is manufactured and measured to validate the novel design concept. The measured results show that −6 dB impedance bandwidth is 2.45 ~ 2.56 GHz, and 3 dB axial ratio (AR) bandwidth is 2.48 ~ 2.50 GHz. The measured HPBW in the xoy and yoz planes are 76° and 94°, respectively. The high normalized comprehensive coefficient (NCC), considering AR bandwidth, Gain, HPBW, and antenna size, proves that the proposed antenna is especially suitable for 6 G terminal satellite communication.

This article presents an innovative design for a low-profile, high-gain circularly polarized (CP) antenna using a single-layer metasurface (MTS). The proposed design incorporates an MTS layer, comprising a 4 × 4 array of hexagonal-shaped patches, printed on the top layer of the substrate. The bottom layer features a coplanar waveguide-fed slotted ground. Circular polarization and broadside radiation are achieved through the application of characteristic mode analysis (CMA). CMA is employed to simultaneously excite desired modes, aiming for wideband circular polarization and gain enhancement. Experimental results validate the effectiveness of the design, with compact dimensions of 0.67λ0 × 0.67λ0 × 0.04λ0. The measurements demonstrate an impressive impedance bandwidth of 84.3% within the 3.7–9.1 GHz. Additionally, a 3-dB axial ratio bandwidth of 18.6% is observed between 4.96 and 5.98 GHz and 3.74% between 8.38 and 8.7 GHz. The antenna exhibits excellent radiation pattern characteristics, featuring a maximum gain of 10.08 dBi at 7.1 GHz. The radiation pattern is symmetrical with broadside directionality, making the antenna well-suited for sensing applications.

This study introduces a simple, compact broadband dual‐band circularly polarised slot antenna suitable for the use in the compact universal ultra‐high frequency (UHF) radio‐frequency identification (RFID) reader devices and Global Positioning System (GPS) applications. The proposed antenna is fed using an open‐end coplanar waveguide with an inverted ‘L’ structure. To realise a broadband circular polarisation and good impedance matching, an inverted L‐shaped strip line is inserted adequately into a square slot at the right centre of the slot toward the slot centre. The experimental results demonstrate that the proposed antenna exhibits a 10 dB return loss bandwidth of 552 MHz (716–1268 MHz) and 3‐dB axial ratio (AR) bandwidth of 564 MHz (824–1388 MHz). Additionally, the antenna gains are 3.8 and 4.29 dBi throughout UHF RFID band and GPS band, respectively. The proposed antenna has a wide AR bandwidth, a compact size, and a simple structure. Furthermore, the proposed antenna is printed on one substrate layer with an overall size of 112 × 112 × 1.6 mm3, which makes it more practical for universal UHF RFID handheld readers and GPS applications.

Characteristic mode (CM) analysis and a waveport modeling method is combined for analyzing antenna radiation and scattering. Base on the mode matching method, a MoM waveports modeling method is presented for general metallic-dielectric structures. To analyze waveguide port fed antenna with characteristic modes analysis, a suitable weighted matrix is established based on energy relationship and the CMs can be obtained by solving the new eigenvalue problem. Once the CMs are found, modal weighted coefficients of CMs, equivalent electric and magnetic currents on the antenna can readily be obtained. Numerical results of a microstrip antenna with coaxial cable line feeding is given to validate the proposed method.

Rydberg atomic sensors (RASs) have garnered significant attention as a novel type of electric field sensor with high sensitivity. While the integration of electric field enhancement structure (EFES) and RASs has been proven to improve the sensitivity and the minimal detectable electric field of RAS, there are concerns regarding their omnidirectional and polarization performance. However, most existing RASs or RASs loaded with EFES operate with linear polarization, which reduces the sensitivity to circularly polarized (CP) microwave reception. It is a challenging method to change the property of the lasers to modify the RAS’s CP property, while it is simpler to use EFES to change RASs’ polarization indirectly. Meanwhile, current EFES research mainly focuses on the response of electric field enhancement at a fixed incident angle, limiting extension to 3-D CP patterns and lacking clear physical insights to guide. To address this, we propose an RAS with CP EFES to achieve CP reception capability. The EFES converts spatial CP electric field into local linearly polarized (LP) electric field, adjusting the RAS characteristics accordingly. We use characteristics mode (CM) methods, dividing the problem into modal current, governing the modal patterns, and external CP excitation sources, determining the coefficients of each modal pattern. This method reduces the complexity of the pattern analysis and improves the efficiency of optimization design. To validate the proposed method’s efficiency, we fabricate a prototype to measure reception pattern and further study the CP performance using an atomic heterodyne approach. The results indicate that the RAS with EFES achieves the right-hand CP (RHCP) omnidirectional reception capability, and the sensitivity is improved by 19.2 dB at 2.195 GHz. The cross-polarized level can be further improved to 24.5 dB using an atomic heterodyne approach.