Proposed Circularly Polarized Antenna Research Articles

Circularly polarized metalens antenna design for 5G NR sub-6 GHz communication systems

5G NR (new radio) FR1 range refers to as Sub-6 GHz band (410–7125 MHz and 3.4–6 GHz). In this paper, the frequency range of interest is from 3.4 to 6 GHz, as many cellular companies are focusing on this Sub-6 GHz band. A wideband circularly polarized (CP) antenna radiator is designed with diamond shape patches, fed by a microstrip line at the bottom through a rectangular shape wide slot on a ground plane. The proposed CP antenna covering a −10 dB bandwidth of 21.52 % (5.0–6.3 GHz) with 3-dB axial ratio (AR) bandwidth of 12.48 % (5.1–5.8 GHz). Furthermore, a metasurface-based lens (metalens) is designed for gain enhancement and fed by 3 × 1 array of the proposed CP antennas for multibeam operation. The lightweight dual-layer metasurface structure consisting of circular shape unit cell elements are used to implement the lens. For the proof-of-concept, the array of radiating elements is implemented and experimentally validated, which gives a ±18° beam scanning range with a maximum gain of 13dBic at 5.6 GHz.

Axial ratio beamwidth enhancement of a low-profile circularly polarized antenna using defected ground structures

AbstractThis article explores the possibilities of incorporating a defected ground structure (DGS) for widening the 3 dB axial ratio beamwidth (ARBW) of a simple low-profile planar circularly polarized (CP) antenna. Two pairs of DGSs are etched symmetrically along the diagonals of the ground plane to overcome the limited 3 dB ARBW performance of a crossed-slotted circular-shaped planar CP antenna. Here, one pair of DGSs is orthogonal to another pair of DGSs. The distance between the pairs of DGSs plays a key role in enhancing the 3 dB ARBW by 40.62%. A gap of 0.18λ0 is considered between the DGSs to maintain the symmetrical electric field distribution in the substrate. It also helps to reduce orthogonal current components and provides uniformly distributed patch surface currents. These phenomena collectively help the proposed CP antenna to exhibit right-handed circular polarization radiation with the 3 dB ARBW of 186° and 188° in the E-plane and H-plane, respectively. The measured results yield impedance bandwidth (S11 ≤ −10 dB) of 2.6% (2.283–2.342 GHz), CP bandwidth of 0.9% (2.294–2.315 GHz), gain higher than 4.8 dBic, and total antenna efficiency more than 64% across the entire CP band.

Four-Port Orthogonal Circularly Polarized Dual-Band MIMO Antenna With Polarization and Spatial Diversity Using a Dual-Band Linear-to-Circular Polarization Converter

A dual-band circularly polarized (CP) four-port multiple-input-multiple-output (MIMO) antenna for K/Ka-bands fixed-satellite service is proposed in this communication. The single element of MIMO is composed of a cascade of two dipoles of different lengths resonating at around 20 and 30 GHz. An array of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7 \times 7$ </tex-math></inline-formula> elements of the unit cell of the dual-band linear-to-circular polarization converter is placed at a distance of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{o}$ </tex-math></inline-formula> /4 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{o}$ </tex-math></inline-formula> is calculated with respect to 19.51 GHz) in the endfire direction of MIMO antenna to obtain an orthogonal CP wave at the two frequency bands. The proposed CP antenna shows good MIMO performance with a correlation coefficient (CC) of less than 0.19 and diversity gain (DG) of better than 0.99 at both the frequency bands. The proposed MIMO also agrees with polarization and spatial diversity, and the CP nature at lower and upper frequency bands can be interchanged by exciting the orthogonal ports. A prototype of the MIMO antenna is fabricated, and the measured CP bandwidths of 11.51% and 3.69% are obtained in the lower (19.65–22.05 GHz) and upper (29.25–30.35 GHz) frequency bands, respectively. The proposed antenna can be used for the Ka-band: 29.5–30.0 and 19.7–20.2 GHz fixed satellite service as uplink and downlink frequencies, respectively.

Gain-Enhanced Wideband Circularly Polarized Antenna with a Non-Uniform Metamaterial Reflector

In this paper, a gain-enhanced wideband circularly polarized (CP) antenna with a non-uniform metamaterial (NUM) reflector is presented, which is composed of a modified wide S-shaped slot antenna and a NUM reflector. To achieve a wideband CP operation, a modified S-shaped slot is fed by an L-shaped microstrip feedline that ends with a triangular patch to improve axial ratio (AR) bandwidth and impedance bandwidth. A NUM reflector composed of rectangular metal units with different sizes is employed and its units are unevenly distributed. The proposed CP antenna is designed, fabricated, and measured. The measured results show that the impedance bandwidth covers 3.0-6.0 GHz (66.7%) and a 3-dB AR bandwidth covers 3.1-5.6 GHz (57.4%). A peak gain of 6.0 dBi is obtained at 3.8 GHz by using the reflector. The advantages of the proposed antenna are the simple structure, high gain, and broad CP bandwidth.

Wideband Bidirectional Same Sense Endfire Circularly Polarized Antenna

In this paper, a wideband bidirectional endfire circularly polarized (CP) antenna is proposed by combining two endfire CP antennas with a single coaxial probe feed. The wideband characteristics are achieved with the help of a two-layered substrate separated by an air gap, and the excitation of CP waves in the endfire directions is yielded by the wideband magnetic dipoles and tapered electric dipoles. The proposed CP antenna has shown wide 10-dB impedance bandwidth (IBW) and 3-dB axial ratio bandwidth (ARBW) of 20.76% (5.05 - 6.22 GHz) and 16.10% (5.14 - 6.04 GHz), respectively. Besides showing an overall size of 0.733&#x03BB;_L &#x00D7; 0.863&#x03BB;_L&#x00D7; 0.058&#x03BB;_L (&#x03BB;_L is the wavelength corresponding to the lowest operating frequency) with wide operational bandwidth, the proposed CP antenna has also demonstrated a desirable peak gain of 4.45 dBic.

A new periodic fractal parasitic structure to design the circularly polarized microstrip antenna for the satellite navigation system

This study presents a novel approach to design the single-feed circularly polarized (CP) microstrip antenna by the periodic fractal parasitic structure (PFPS). By adding the PFPS along the radiated patch, a new independent orthogonal mode is generated. When the magnitudes of these two modes are the same and the time-phase difference between them is 90°, the antenna can realise CP radiation. Parameter studies of the PFPS show how to design the CP microstrip antenna. The proposed CP microstrip antenna, designed for the satellite navigation system, has a 30 MHz 10-dB impedance bandwidth and an 8 MHz 3-dB axial ratio bandwidth in the centre frequency of 1.575 GHz. The advantage of this presented CP antenna is that these two modes for realising the CP radiation are independent of each other. This makes it more convenient to simplify the designing and debugging of the proposed CP antenna.

Smart antenna with circular polarization for high accuracy indoor localization system

This article presents a new switched beam antenna (SBA) for indoor localization applications. The SBA consists of seven circularly polarized (CP) element antennas using a novel feeding network. The attractive characteristics of the proposed CP antenna are high gain, wide bandwidth (BW) with the BW of 36.2% at the reflection coefficient less than −10 dB (4.6–6.7 GHz), the 3 dB axial ratio (AR) BW of 22.4% (5.4–6.7 GHz), wide 3 dB AR beamwidth as about 60 degrees, and maximum gain of 9 dBi within the total bandwidth. Experimental results show good agreement with simulated ones in terms of radiation pattern, AR, and reflection coefficient. We proposed a low-cost and simple RF-based indoor localization system based on a single anchor node equipped with this SBA. The system is demonstrated through experimental validations in a 6 m × 6.5 m × 3.5 m office room with a mean localization error of 0.72 m.

Wideband circularly polarized antenna with metallic walls for L-band applications

PurposeTo achieve right-hand circular polarization (RHCP), a 3-dB Wilkinson power divider with a λ/4 phase shifter is used. The crossed-dipoles are placed at almost λ/4 elevation on the ground plane and connected to two coaxial cables. Experiments show that the impedance bandwidth of 49.40% (913.7–1,513.1 MHz) and axial ratio bandwidth (ARBW) of 22.88% (1,145.8–1,441.8 MHz) are achieved.Design/methodology/approachIn this study, a wideband crossed-dipole antenna with circularly polarized (CP) radiation for L-band satellite and radar applications is presented. The proposed CP antenna comprises two orthogonally placed printed dipoles, a quadrature coupler and a box-shaped ground plane.FindingsFurthermore, by fixing the box-shaped ground plane under the radiators, 5.13 dBic RHCP peak gain at 1,300 MHz and maximum half-power beamwidth (HPBW) of 84.5° at 1,170 MHz are realized for the antenna.Originality/valueEight metallic walls are connected to four corners of the substrate to stabilize the radiation properties in this study. Results show that the ARBW and front-to-back ratio are improved and the maximum HPBW around 127° across the operating frequency band is achieved. The proposed CP antenna is a good candidate for Global Positioning System (GPS) L2 (1.227 GHz), GPS L5 (1.176 GHz) and air route surveillance radar system at 1,215–1,390 MHz frequency band.

A broadband circularly polarized magneto-electric dipole array antenna for 5G millimeter-wave applications

A millimeter-wave (mm-wave) broadband circularly polarized (CP) magneto-electric (ME) dipole array antenna is proposed. The antenna element consists of a ME dipole, a direct T-shaped probe, and a pair of shorted parasitic elements. The shorted parasitic elements are employed to ensure a considerable expansion of the 3 dB axial ratio (AR) bandwidth to lower frequencies. As a result, the ME dipole antenna element achieves a wide overlapped AR/impedance bandwidth of 56.89% (22.45–40.3 GHz). Based on the proposed CP antenna element, a 2 × 2 CP array antenna that incorporates an improved X-shaped power divider network is developed. A prototype of the 2 × 2 CP array antenna is fabricated and experimentally verified. The measured results indicate that a −10 dB impedance bandwidth of 50.39% (23.9–40 GHz) and a 3 dB AR bandwidth of 50% (24–40 GHz) are achieved, forming a broad overlapped AR/impedance bandwidth of 24–40 GHz, which covers most of the current mm-wave 5G bands. Moreover, a peak gain of 14.88 dBic is also observed. Thus, the demonstrated antenna with broadband CP operation and good radiation performance can be an excellent candidate for 5G mm-wave applications.

Wideband circularly polarized triangular monopole antenna for high-speed internet access

In this report, a miniaturized low profile circularly polarized (CP) monopole antenna with broad 3 dB axial ratio (AR) bandwidth is investigated. The proposed antenna comprises an equilateral triangular monopole radiator, an inverted L-shaped element (ILSE) protruded from the finite ground plane to perturb the current distribution on the finite ground plane and an inverted L-shaped strip (ILSS). The CP radiation characteristics can be achieved by protruding an ILSE from the finite ground plane and connecting ILSS with the triangular patch. The proposed CP antenna has a dB impedance bandwidth along with the 3 dB AR bandwidth of 127.3% in the frequency band of 2−9 GHz. The antenna occupies the overall footprint of and is ideally propitious for broadband wireless communication systems which permit users to access high-speed internet. Furthermore, the proposed antenna has stable bidirectional radiation properties with a measured peak gain of 6.3 dBi.

Miniaturized Circularly Polarized Periodically Structured Surface Antenna for RFID Application Inspired by SRR

This article presents a novel miniaturized circularly polarized (CP) antenna based on periodically structured surfaces inspired by the vertical split-ring resonator (VSRR). The VSRR is considered as a magnetic dipole placed above the ground, which could excite strong boresight radiation with a reduced size. To enhance the aperture gain, multicapacitors and inductors (Multi-C&L) are loaded on the loop, which replace the single capacitive gap of the conventional split-ring resonator (SRR). Here an SRR-inspired periodic structure with a relatively uniform field distribution is achieved. The stepped impedance resonator (SIR) structure, as the unit cell of the SRR-inspired surface, is analyzed and investigated using the circuit models derived from the SRR. By cascading multiple high-value capacitors, a larger aperture with a uniform field distribution is obtained. Linearly polarized (LP) and CP antennas are studied. The proposed CP antenna is made of thin substrates and metallic screws, resulting in a negligible dielectric loss. It offers attractive features including a compact size, 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">$0.191\lambda _{0} \times 0.191\lambda _{0} \times 0.032\lambda _{0}$ </tex-math></inline-formula> ), good radiation efficiency, novel working principle, flexible performance control, and a bandwidth well covering the 902–928 MHz UHF band, which is well situated for radio frequency identification (RFID) application.

S-Band Full-Metal Circularly Polarized Cavity-Backed Slot Antenna With Wide Bandwidth and Wide Beamwidth

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 3-D-Printed Wideband Circularly Polarized Dielectric Reflectarray of Cross-Shaped Element

A novel wideband circularly polarized (CP) dielectric reflectarray operating at Ka -band is proposed. Each element consists of a cross-shaped dielectric block and a metal ground. The two arms of the cross element are arranged along the diagonal of the square metal floor. For ease of the design, the dimensional scaling factor is used to obtain the reflection phase. The dielectric reflectarray of the size 15 × 15 and dielectric constant 9.8 is designed. Genetic algorithm (GA) is applied to optimize the element size. It is found that the maximum gain is 24.2 dBi, and 1 dB gain bandwidth is 10.7%, respectively. A broad 3 dB axial ratio (AR) bandwidth of 19.3% can also be obtained. The proposed CP antenna is fabricated using the high-precision 3-D printing technology. Relatively good agreement between the simulated and measured results is achieved.

Design Approach of a Single Circularly Polarized Patch Antenna With Enhanced AR-Bandwidth Under Triple-Mode Resonance

A novel design concept to widen axial-ratio (AR)-bandwidth of a single circularly polarized (CP) patch antenna is presented by resonating its TM $_{1/2,0}$ , TM $_{1/2,1}$ , and TM $_{3/2,0}$ modes. First, a set of shorting pins is loaded around the edge of the patch with decreased width, aiming to suppress undesired nonbroadside modes. Second, the far-zone radiated fields of the antenna are theoretically studied by using equivalent magnetic currents (EMCs). The results demonstrate that its broadside $\vert {E}_{\theta }\vert $ , $\vert {E}_{\varphi }\vert $ , and $-\vert {E} _{\theta }\vert $ components of xo z plane radiation patterns could be orthogonally generated under TM $_{1/2,0}$ , TM $_{1/2,1}$ , and TM $_{3/2,0}$ modes, respectively. Most importantly, these three broadside EMCs must be sequentially rotated. Third, the resonant frequencies of these triple radiative modes ( ${f}_{1/2,0}$ , ${f}_{1/2,1}$ , and ${f}_{3/2,0}$ ) are extensively analyzed and reallocated by loading the shorting pins. It proves that the ${f}_{1/2,0}$ and ${f}_{1/2,1}$ could be progressively pushed up to around the ${f}_{3/2,0}$ , resulting in generating the CP radiation as expected. With these arrangements, the AR-bandwidth of the proposed CP antenna is significantly widened under triple-mode resonance. In final, the proposed antenna is fabricated and measured. Simulated and measured results are in good agreement with each other. The measured results depict that the CP antenna has acquired an enhanced AR-bandwidth with two minima poles, covering a fractional bandwidth of about 5% from 3.25 to 3.41 GHz, which is about 3.3 times wider than the traditional counterpart (1.5%). Besides, its profile is kept only about 0.03 free-space wavelength. Particularly, the single-layer, single-fed, single-radiator, and high-efficiency properties are simultaneously maintained for the CP antenna without needing to rely on any extra feeding networks, patches, or resisters.

A miniaturized circularly polarized multi‐dipole antenna with wide axial‐ratio beamwidth via loading loop resonators

A miniaturized, loop resonators (LRs)-loaded, circularly polarized (CP) multi-dipole antenna with wide axial-ratio (AR) beamwidth is proposed and demonstrated in this article. The radiator of this CP antenna consists of two pairs of parallel dipoles loaded with four LRs at their corners. By increasing the length of the LR, or decreasing the coupling space between the dipole and the LR, the effective length of the dipole can be lengthened significantly and thus the working frequency can be reduced without increasing the whole aperture size. As a result, a miniaturized radiator structure is completed. A feeding network consisting of a T-shaped coupling feeding structure and four coplanar striplines having different lengths are specially designed to feed these dipoles with approximately the same magnitude and 90° phase quadrature. What is more, a cavity reflector is employed to achieve a unidirectional radiation with wide axial-ratio beamwidth. The radiator of the proposed CP antenna has a small aperture size of only 0.34λ0 × 0.34λ0, where λ0 is the free space wavelength at the working frequency. Measured results are in a good agreement with the corresponding simulated counterparts. Especially, the experimental results show that the antenna has achieved a wide AR beamwidth of 182° and 174° at the center frequency in the xoz and yoz planes, respectively.

A Wideband Series-Fed Circularly Polarized Differential Antenna by Using Crossed Open Slot-Pairs

A novel method of designing a wideband series-fed circularly polarized (CP) differential antenna by using crossed open slot pairs is presented in this article. The near-field distributions and input impedance analyses show that the closely spaced open slot-pairs can radiate as the crossed dipoles and have stable radiating resistance with a compact radiator size. Besides, a wideband half-power phase shifter using open slot is proposed and utilized to realize CP radiation. The proposed CP antenna is composed of a wide slot-pair and a narrow slot-pair. In the antenna design, the narrow slot-pair is not only excited as a radiator, but also elaborately loaded to provide wideband half-power output and quadrature phase excitation to the wide slot-pair. Both the proposed half-power phase shifter and CP antenna are illustrated by the corresponding equivalent circuits. Based on these analyses, the proposed antenna is designed, fabricated, and measured. Compared with the simulated traditionally designed counterpart, 2.1 times wider axial ratio (AR) bandwidth is achieved for the proposed antenna. The measured overlapped bandwidth for AR 10 dB is 1.95–3.45 GHz (55.6%). Also, the antenna gain and radiation patterns are measured, which agree well with the simulated results.

The New C-Shaped Parasitic Strip for the Single-Feed Circularly Polarized (CP) Microstrip Antenna Design

A new single-feed circularly polarized (CP) microstrip antenna with the C-shaped parasitic strip is proposed in this paper. The proposed CP antenna is designed for the transmitting terminal in the Global Navigation Satellite System (GNSS). The square patch is surrounded by a C-shaped parasitic strip. By adjusting the parasitic strip dimension, the antenna CP operation is achieved. The main advantage of this method is that those two resonant modes for achieving the CP operation are independent from each other, which is liable to design and debug the proposed CP microstrip antenna. The designed CP microstrip antenna has the good impedance matching, the good CP radiation pattern, and the stable CP gain across the 3 dB AR (axial ratio) bandwidth.

W-Band LTCC Circularly Polarized Antenna Array With Mixed U-Type Substrate Integrated Waveguide and Ridge Gap Waveguide Feeding Networks

In this letter, a low-temperature co-fired ceramic (LTCC) substrate integrated 8 × 8 circularly polarized (CP) antenna array is proposed for the wideband and high-gain W-band antenna-in-package application. By introducing the planar L-probe together with the original coupling probe, the E-fields in the substrate-integrated-waveguide (SIW) cavity are changed, and additional E-field components with a 90° phase difference are produced. Then, a CP antenna array is obtained. To reduce the losses in the feeding network, the gap waveguide technology is utilized with the SIW technology, as a mixed feeding network. To validate the proposed CP antenna array design, an 8 × 8 CP antenna array is fabricated by the LTCC technology and measured. Measured results show that the LTCC CP antenna array obtains a gain of 22.3 dBi, and its axial-ratio (AR) bandwidth is from 89 to 98.5 GHz for AR <; 3 dB. Besides, good agreements of the radiation patterns between the simulations and measurements are achieved within the operational frequency range.

A corner expanded slot antenna loaded with copper strips for dual‐band circular polarization characteristics

AbstractIn this article, the design and implementation of a dual‐band circularly polarized (CP) microstrip line fed square slot antenna with compact size is proposed. The proposed CP antenna consists of a square slot antenna with a pair of symmetric rectangular extensions on opposite corners and loaded with an array of inclined and truncated rectangular copper strips. The square slot with diagonal extensions resonates at 2.24 to 2.62 GHz with a 3 dB axial ratio (AR) bandwidth of 15.7%. Besides, loading it with an array of inclined and truncated rectangular copper strips helps produce a resonance at higher band with CP. The higher band operates between 3.26 and 5.18 GHz and centered at 4.52 GHz, with a 3 dB AR bandwidth of 45.5%. The polarization sense and resonant frequency of the proposed antenna can be independently tuned depending on the position and dimensions of the slot and strips, respectively. The proposed antenna is fabricated and measured in terms of impedance bandwidth, axial ratio bandwidth, peak gain, and radiation efficiency. Good agreement between the simulations and measurements of the prototype is obtained.

Miniaturized Low-Profile Circularly Polarized Metasurface Antenna Using Capacitive Loading

A miniaturized circularly polarized (CP) metasurface (MS) antenna using capacitive loading is investigated. First, one novel miniaturized MS unit cell is proposed. By introducing a pair of capacitive-loading strips inserted along the diagonal of a corner-truncated patch, 56% size reduction is achieved for this miniaturized unit cell. Accordingly, a compact CP MS antenna of a $4\,\,\times \,\,4$ array composed by the miniaturized unit cells is designed and fed by a slot structure. Compared with the conventional CP MS antenna without capacitive-loading strips, 63% overall size reduction can be achieved. Furthermore, the CP radiation mechanism of the CP MS antenna is revealed and explained clearly using the characteristic mode analysis (CMA). For demonstration, a prototype of the proposed CP antenna was fabricated and measured. The measured 3 dB axial ratio (AR) band is from 3.33 to 3.63 GHz, and the 10 dB impedance band is from 3.02 to 3.82 GHz, while 6.5 dBi gain is realized within the CP operating band.