Minimum Axial Ratio Research Articles

A dual band compact circularly polarized antenna for GPS applications

AbstractA novel dual band antenna with right‐hand circular polarization (RHCP) is fabricated. It consists of a T‐shaped parasitic element on the backside of T‐shaped patch (TSP) and a ground plane. The design comprises a rectangular and CPW fed clearance in the ground plane. The placing of a TSP and connecting rectangular stubs to the ground plane is used to achieve GPS L5 and L2 bands. Circular polarization in GPS L5 and L2 bands is produced by rectangular horizontal stubs and F‐shaped slots (FSS), respectively. The measured results show 34 MHz (1.160–1.194 GHz) and 57 MHz (1.207–1.260 GHz) –10 dB impedance bandwidth and 3‐dB axial ratio bandwidths are 10 MHz (1.174–1.184 GHz) and 10 MHz (1.223–1.233 GHz). It also displays a minimum axial ratio of 1.35 and 0.34 dB with broad beamwidth (>100°) essential for the GPS applications. The final design is verified in the experiment. The advantages of the proposed design are compact size, simple structure, and broad beamwidth.

A Modified-square Slot Antenna with Circular Polarization Characteristics for Military Band Applications

In this work, the design and performance of a circularly polarized (CP) antenna designed using characteristic modal analysis (CMA) for military band application is presented. The substrate used is single-sided glass-reinforced epoxy and the antenna dimensions are 37×37×1.6 mm 3 . The antenna is compact, low-profile, circular polarized having an ARBW of around 500 MHz (center frequency 4.6 GHz). A coplanar waveguide (CPW) fed monopole antenna is used for excitation of the modified-square slot antenna that incorporates quarter section of circular symmetrical patches on the four corners. A stub orthogonal to the CPW fed monopole capacitively tunes the low Q mode as identified by CMA technique to shift to a lower frequency to create degenerate modes in military band for circular polarization generation. The 3-dB AR bandwidth of the antenna is in the frequency range 4.43- 4.9 GHz and measured value of impedance bandwidth is 3.33 GHz. The fractional ARBW and impedance BW are 10.07 % and 61.6 % respectively. The peak antenna gain in the CP frequency band is 3.75 dBic. The proposed antenna exhibits good polarization purity, the minimum axial ratio is 1.38 at 4.6 GHz. The broad circular polarized antenna is suited for military applications covering the frequency range 4.43-4.9 GHz.

Seismic performance of squat UHPC shear walls subjected to high-compression shear combined cyclic load

Cyclic tests of five UHPC squat shear walls and one high-strength concrete counterpart were carried out in this study to investigate the seismic performance of UHPC shear walls with high design axial load ratio ranging from 0.5 to 0.6, and web distributed reinforcement ratio varying from 0.19% to 0.56%. The failure mode, crack pattern, force–displacement relationship, deformation mechanism, energy dissipation, the strength and stiffness degradation are comprehensively investigated. In addition, the stress development and shear contribution of horizontal rebar in the web is calculated and analyzed. Finally, design suggestions for UHPC squat shear walls are proposed in terms of minimum horizontal reinforcement ratio and axial load ratio. It is demonstrated by the test results that UHPC specimens showed an excellent crack control ability with narrow shear-related cracks distributed in a dense array. The shear capacity and ultimate deformation of UHPC specimen were significantly improved by almost 85% and 95% in comparison with high-strength concrete specimen. Noticeably, the UHPC specimen with the minimum amount of transverse rebars reached the highest ultimate drift ratio of 1.75%. The stress level of horizontal rebars in UHPC specimens can be reduced by at least 72%. The test results show the potential to reduce the horizontal reinforcement ratio to 0.19% for the UHPC squat shear walls under the high design axial load ratio of 0.5. A modified strut-and-tie model for predicting the shear strength of UHPC shear walls is proposed with an error of no more than 4%.

Low profile and broadband circularly polarized metasurface antenna based on nonuniform array

A broadband low-profile, circularly polarized metasurface antenna with a nonuniform aperture is proposed for L band satellite communications. By optimizing the nonuniform geometry, antenna size is minimized and bandwidth is expanded. Characteristic mode analysis (CMA) clearly reveals the dominant modes and stimulated modes for wideband operation. The feeding structure employs a quadrature phase quarter-power divider to excite a collection of orthogonal modes, generating stable circular polarization (CP) radiation and a phase center. Numerous feeds and crossing slots, in conjunction with the metasurface, produce multiple resonances and minimum axial ratio (AR) locations when excited, resulting in a broad impedance and AR response. The low profile nonuniform metasurface CP antenna achieves a 40% −10 dB impedance bandwidth, a 47% 3 dB AR bandwidth, and a peak gain of 8.7 dBic with a compact dimension of 0.67 × 0.67 × 0.06 λ3.

Compact Quad-Band CP Series-Fed Circular Slit Microstrip Array Antenna Using Machine Learning

This article presents the design and characterization of a dual-band, compact, and dual-circularly polarized (CP) traveling wave series-fed circular slit microstrip array (TWSCSMA) antenna operating in quad-band CP at 2.5/3.5/3.8 GHz WiMAX and 5.2 GHz WLAN applications. The radiating structure consists of an annular ring traveling wave series-fed circular slit array elements, rotates in sequence with seven circular quasi-lumped resonators contributes to two-impedance bandwidth (IBW) and quad CP bands. The four split-ring resonators with double-annular rings are introduced on the defected ground plane to improve the impedance matching, IBW, and axial ratio bandwidth (ARBW) effectively. The measured results show that the proposed dual-CP TWSCSMA antenna yields two <i>S</i>₁₁ &#x2264; &#x2013;10 dB IBW of 33.85% and 50.73% and four &#x003C; 3 dB ARBW of 16.26%, 12.52%, 8.22%, and 13.82% for port 1. Furthermore, modern machine learning regression techniques are used to improve the accuracy of the model performance requirements for the optimal design of the proposed antenna. The TWSCSMA antenna demonstrates a compact, low profile, wide impedance bandwidth, and minimum axial ratio which is making it a good candidate for WiMAX and WLAN applications.

A novel design of circularly polarized ring CDRA with wideband impedance bandwidth using slotted microstrip feed line for X-band applications

AbstractA circularly polarized ring cylindrical dielectric resonator antenna (ring-CDRA) of wideband impedance bandwidth is presented in this article. The proposed ring CDRA consist of an inverted rectangular (tilted rectangular) shaped aperture and inverted L-shaped slotted microstrip feed line. The tilted rectangular shaped aperture and inverted L-shaped microstrip feed line generate two-hybrid mode HEM11δ and HEM12δ while ring CDRA and slotted microstrip feed line are used for the enhancement of impedance bandwidth. The proposed ring CDRA is resonating between 6.08 and 12.2 GHz with 66.95% (6120 MHz) impedance bandwidth. The axial ratio (AR) bandwidth of 6.99% (780 MHz) is obtained between 10.76 and 11.54 GHz with a minimum AR value of 0.2 dB at a frequency of 11 GHz. The proposed geometry of ring CDRA has been validated with measurement performed by VNA and anechoic chamber. The operating range of the proposed radiator is useful for different applications in X-band.

Using the Starlight Polarization Efficiency Integral to Constrain Shapes and Porosities of Interstellar Grains

Abstract We have developed a new method for using the observed starlight polarization and polarized submillimeter emission to constrain the shapes and porosities of interstellar grains. We first present the modified picket-fence approximation and verify that it is sufficiently accurate for modeling starlight polarization. We then introduce the observed starlight polarization integral Πobs as a measure of the overall strength of the observed polarization of starlight, and the starlight polarization efficiency integral Φ to characterize the effectiveness of different grain types for producing polarization of starlight. The ratio Πobs/Φ determines the mass-weighted alignment 〈f align〉 of the grains. Approximating the aligned grains in the ISM as spheroids, we use Πobs/Φ to show that the observed starlight polarization constrains the grains to have a minimum degree of asphericity. For porosity  = 0 , the minimum axial ratio is ∼1.4 for oblate spheroids, or ∼1.8 for prolate spheroids. If the grains are porous, more extreme axial ratios are required. The same grains that produce the starlight polarization are able to provide the observed polarized emission at submillimeter wavelengths but with further limits on shape and porosity. Porosities  ≳ 0.75 are ruled out. If interstellar grains can be approximated by “astrodust” spheroids, we predict the ratio of 10 μm polarization to starlight polarization p V : p(10 μm)/p V = 0.219 ± 0.029. For Cyg OB2-12, we predict p(10 μm) = (2.1 ± 0.3)%, which should be observable.

Design of broadband circularly polarized THz antenna with stable radiation pattern for 6G communications

This paper presents a compact efficient and stable high gain broadside circularly polarized (CP) antenna using WR3 waveguide. Asymmetrical H-shaped slot arrays deployed on the broadside wall of the waveguide, suits the antenna for operating in the Sub THz range of frequencies. The designed antenna operates almost entire frequency range of WR3 waveguide from 227 GHz to 380 GHz with a return loss ≤ −10 dB roofing the WM834 band. The proposed antenna possesses a wide axial ratio bandwidth (ARBW) of 28.28 GHz spanning from 289.1 GHz to 317.38 GHz with persistent gain and exhibits a minimum axial ratio of 0.72 dB in the range of 296–309 GHz. Furthermore, the model attains a maximum directivity of 16.5 dBi and a peak gain of 16.1 dBi at 317 GHz with the first sidelobe level (SLL) of − 13.6 dB and radiation efficiency of 97.5% towards the broadside direction. Apart from the stable pattern in the CP band, beam scanning of the main lobe from 250 GHz to 340 GHz is also observed. The proposed antenna has been designed, simulated, and optimized using CST microwave studio and the results are validated using HFSS software.

Wideband Circularly Polarized Cylindrical Dielectric Resonator Antennas With Rectangular Curved Slots [Antenna Applications Corner

Wideband circularly polarized antennas with wide axial-ratio (AR) bandwidth and required gain are desired for point-to-multipoint communication and remote tracking applications. Two different designs of probe-fed rectangular curved slotted dielectric resonator antenna (SDRA) models are proposed in this article, one with an overall size of 50 × 50 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (SDRA-1) and the other a scaled-down version with 25 × 25 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (SDRA-2). Axially symmetric rectangular curved slots are introduced in cylindrical dielectric resonator antennas (CDRAs) to create asymmetry in the structure for circular polarization (CP). The proposed SDRA-1 offers a wide impedance bandwidth of 55% (4.14-7.31 GHz) and a 3-dB AR bandwidth of 38% (4.82-7.07 GHz) with a minimum AR value of 0.1 dB. The peak gain obtained for SDRA-1 is 6 dBi. A scaled-down version of the dielectric resonator antenna (DRA) provides an impedance bandwidth of 57.5% (7.34-12.94 GHz), a 3-dB AR bandwidth of 0.76 GHz, and a peak gain of 5.52 dBi. The proposed DRA models are suitable for IEEE wireless standard 802.11ac Wi-Fi (5 GHz), IEEE 802.11a (5.2 GHz), IEEE 802.16d worldwide interoperability for microwave access (WiMax) and x-band applications.

Compact wideband circularly‐polarized antenna for universal UHF RFID handheld reader

AbstractA compact wideband circularly‐polarized (CP) RF identification (RFID) handheld reader antenna based on inverted‐F antennas (IFAs) is proposed. The antenna consists of an upper layer of rotationally symmetric radiation structure and lower layer of feed network. Firstly, the feed network is verified by microwave circuit simulation software. Then the antenna is modeled and simulated with the aid of the full‐wave electromagnetic simulation software. Finally, a prototype is fabricated using FR4 plate and its performance of the proposed antenna is validated. The measured impedance bandwidth of 10 dB and the axial ratio (AR) bandwidth of 3 dB are wider than 13%. The peak gain is greater than 2.2 dBic, and the minimum AR is less than 1.1 dB, with the symmetrical and stable radiation patterns. The antenna has the compact size of 60 × 60 × 15 mm3. The proposed antenna can not only meet the requirements of RFID handheld reader applications in universal ultra‐high frequency (UHF) band (840‐960 MHz), but also has the advantages of wideband, small size, lightweight, low cost, and simple structure. Therefore, the design has a good application prospect in the field of Internet of Things.

Compact Dual-Band Circularly Polarized Antenna Using Double Cross Dipoles for RFID Handheld Readers

A miniaturized dual-band circularly polarized (CP) antenna that operates on 915 MHz and 2.45 GHz radio frequency identification bands (RFID) is proposed for handheld readers. The dimensions of the proposed antenna are 85.0 × 85.0 × 1.6 mm3, whereas broad impedance bandwidths are obtained (871–1297 MHz and 2.16–2.80 GHz). The antenna consists of two pairs of cross dipoles fed by concentric ring-delay lines. The first pair is thin strips terminated with an arrowhead-shaped trace, providing CP resonance at 915 MHz. The second pair is composed of rectangular patches, creating CP resonance at 2.45 GHz. The distinct feature of the proposed antenna is twofold. First, the double cross dipoles are arranged at a 45° angle. This leads to a simple and compact configuration, avoiding the use of complex feeding networks or power dividers. Second, the frequency of minimum axial ratio (AR) in each band is tunable by controlling the ratio between the lengths of the arrowhead-shaped trace and the length of the rectangular patches. Accordingly, the proposed antenna achieves 3 dB AR bandwidths of 882–936 MHz and 2.35–2.58 GHz. Meanwhile, the radiation pattern exhibits a half-power beamwidth (HPBW) of about 110°, facilitating the detection of tags abroad with arbitrary orientations.

Sub-THz Circularly Polarized Horn Antenna Using Wire Electrical Discharge Machining for 6G Wireless Communications

A novel compact high-efficient circularly polarized conical horn antenna is realized with Wire Electrical Discharge Machining (EDM) technique operating at 300 GHz for 6G wireless communications is presented. The proposed antenna structure consists of three main components; a waveguide feed, a circular polarizer disk, and a conical horn. The waveguide feed is a standard WR-03 rectangular waveguide which feeds the whole structure. The circular polarizer disk is comprised of a crossed slot with unequal lengths which are perpendicular to each other. By adjusting the lengths of both slots, two orthogonal modes are excited in the antenna to produce circular polarization. The conical horn is mounted on the circular polarizer disk. The proposed antenna was designed and optimized using CST Microwave Studio and is validated experimentally by an inexpensive direct Wire-cutting EDM technique over the WM-860 frequency band. The fabricated circularly polarized horn antenna achieved a wide impedance bandwidth of 20 % from 270 GHz to 330 GHz with a reflection coefficient ≤ -15 dB. The measured results show that the 3 dB axial ratio of the fabricated antenna prototype has a bandwidth of 7 GHz from 309 GHz to 316 GHz with a minimum axial ratio of 1.15 dB at 312 GHz. The measured normalized radiation patterns show good agreement with simulated results for different frequencies in both the elevation and azimuth planes at broadside direction with good symmetry in both planes.

Bandwidth Enhanced Circularly Polarized Fabry–Perot Cavity Antenna Using Metal Strips

This paper introduces a novel single feed wideband Tai Chi-shaped circularly polarized (CP) antenna that utilizes a Fabry-Perot cavity (FPC) with a 3D printed structure to increase the antenna gain and axial ratio (AR) bandwidth. Besides, a novel method is proposed for AR bandwidth enhancement. Some simple metal strips are introduced, which could adjust the phase of the particular electric field component. By placing the metal strips at an optimal position, the AR bandwidth of the antenna could be effectively broadened. Note that this method has little effect on the other antenna performance and it does not require additional structural changes. The proposed method to increase the axial ratio bandwidth is very simple and effective. The Tai Chi-shaped antenna consists of two separate small patches and two suspended metal rods. The two small patches are 180° out-of-phase excited which are centro-symmetrically placed to form a larger and complete circular patch. The two small patches and the total split patch generate two minimum AR points, which substantially broadens the AR bandwidth. Adding two layers of FR4 substrate to the antenna constitutes an FPC, and the antenna peak gain is increased from 9.42 dBic to 14.44 dBic. In addition, the AR bandwidth has been increased from 27.73% to 44.42%. In order to further increase the AR bandwidth of the CP antenna, some simple metal strips have been added to the FPC substrate. The AR bandwidth has been enhanced from 44.42% to 53.46% (4.07 - 7.04 GHz). Compared with other CP antennas with FPC, our proposed antenna shows advantages in terms of substantially broadened impedance and AR bandwidth, high gain, and low fabrication cost.

Optimum design of helical antennas by genetic algorithm

AbstractThe genetic algorithm is employed to obtain optimal designs for helical antennas that, over the frequency range of operation, provide considerably smaller axial ratio, higher gain, and an appreciably wider overall bandwidth than the conventional axial mode helices with the same size. Also, for nearly equal bandwidth and peak directivity, the new design provides a 2 to1 reduction in size. For these helical antennas the pitch angle and radius, which are constant in conventional helices, vary continuously along the length; pitch angle increases while radius decreases. Genetic algorithm is used to determine variations of these parameters such that maximum directivity and minimum axial ratio are simultaneously achieved over the largest frequency range. Radiation properties of optimized helices, including far‐field pattern, axial ratio, and directivity, are examined numerically over a wide range of frequencies. Empirical design equations are provided. A 12‐turn prototype optimized helix is constructed and measured. Comparison of measured and simulated radiation patterns shows excellent agreement.

A wideband circularly polarized slot antenna with antipodal strips for WLAN and C‐band applications

A single-fed circularly polarized square shaped wide slot antenna with modified ground plane and microstrip feed has been presented. The field in the slot is perturbed by introducing an antipodal strips section attached with a microstrip line to produce circular polarization in a wide band of frequencies. The antipodal strip section consists of a group of four strips of unequal length and separation. The presence of asymmetric perturbations in the slot is mainly responsible for exciting two orthogonal modes in the slot having equal magnitude and 90° phase difference which results in circular polarization. A wide bandwidth of 3.3 GHz (4.4 GHz-7.7 GHz) has been achieved for an axial ratio value AR < 3 dB with the minimum axial ratio value being 0.3 dB. The impedance bandwidth for |S11| < −10 dB ranges from 4.3 GHz to 8 GHz, and therefore covers most of the C-band communication systems. The antenna exhibits stable radiation patterns throughout the circular polarization bandwidth with a gain around 6 dBi in entire operational bandwidth. A prototype of antenna was fabricated and measured. The antenna has a planar size 0.40λ0 × 0.40λ0 and thickness of 0.02λ0 where λ0 is the wavelength in free space at the lowest frequency. With its compact size and low profile, the antenna is a favorable choice for WLAN (5.15-5.85 GHz) and a wide variety of C-band wireless applications.

Circularly polarized micro-strip antenna with fractal trees loaded ground plane

ABSTRACTNew designs of the circularly polarized micro-strip antennas (CPMSAs) based on tree fractal geometries are proposed, examined experimentally, and compared. The excellent circularly polarized (CP) radiation with minimum axial ratio (AR) of 0.26 dB is achieved by optimization of the key parameters (angle, length, and width) of the fractal trees etched on the ground plane. Parametric study revealed that the fractal tree defected ground structures (FTDGS) are responsible for satisfying the condition of CP operation. The micro-strip antennas with third iterative FTDGS and modified third iterative FTDGS are fabricated on FR4 substrate. The measured 10-dB return loss and 3-dB AR are 99 MHz (2.407–2.506 GHz) and 12 MHz (2.443–2.455 GHz), respectively, with stable gain of 4.52 dBic at 2.45 GHz, for third iterative FTDGS antenna. For modified third iterative FTDGS antenna, measured 10-dB return loss and 3-dB AR are 109 MHz (2.354–2.463 GHz) and 26 MHz (2.386–2.412 GHz), respectively, with gain about 4.62 dBic in the vicinity of center frequency 2.4 GHz. The proposed designs can be good candidates for the unlicensed 2.45 GHz industrial, scientific, and medical (ISM) band applications.

A broadband circularly polarized monopole antenna employing parasitic loops and defective ground plane

AbstractA simple printed monopole antenna using parasitic loops and defective ground plane is presented for broadband circular polarized (CP) radiation. For this purpose, two square open loops, which install air gaps at the corner and close to the monopole, are printed on both sides for achieving broadband CP radiation with three minimum axial ratio (AR) points. By using a defective ground plane with a vertical slot and a horizontal slot, additional AR points can be excited to further broaden the AR bandwidth. This design was fabricated, and the measured results show that the antenna with a simple structure achieves both wide impedance bandwidth of 87.2% (2.62‐6.67 GHz) and AR bandwidth of 83.9% (2.6‐6.36 GHz).

Pair of diagonal slots loaded low‐profile circularly polarised patch antenna with wide 3 dB axial ratio beamwidth

A low-profile circularly polarised (CP) antenna with wide 3 dB axial ratio beamwidth (ARBW) is proposed in this study. The possibilities of widening the 3 dB ARBW of single diagonal slot-loaded conventional CP antenna have been explored successfully by incorporating a pair of rectangular slots along the diagonal line of a square patch antenna. The design parameters and the symmetrical arrangement of this pair of slots across the centre of the patch are crucial to adjust and achieve the wide 3 dB ARBW with high CP purity. Coupling between the two diagonal slots provides nearly equal E θ and E φ radiation patterns over a large angular range, and hence the 3 dB ARBW has been enhanced by 85.71 and 55.4% for φ = 0° and φ = 90° planes, respectively, in comparison to the conventional slot-loaded CP antenna. The minimum 3 dB ARBW of 208° and a maximum of 230° have been achieved across different planes of radiation φ = 0°, 45°, 90°, and 135° with a minimum axial ratio of 0.20 dB only. The absolute planar antenna of size (0.29 × 0.29 × 0.013)λ0 3, where λ0 is the free-space wavelength corresponding to the CP frequency, has been fabricated and tested. The measured and simulated results show fair consistency to each other.

Dual‐band metasurface‐based CP low‐profile patch antenna with parasitic elements

A single-feed dual-band circularly polarised (CP) patch antenna is proposed. The antenna consists of a corner-truncated square patch antenna and a superstrate composed of a lattice of 2 × 2 metallic patches surrounded by parasitic elements. The driven patch generates one resonant mode. The metasurface with parasitic elements excites two additional resonant modes (TM10 and TM20). The combined resonances result in minimum axial ratio points, and a good dual-band CP operation is achieved. Simulations show that the antenna has a CP operating bandwidth of 40 MHz centred at 3.72 GHz (1.07%), and a CP operating bandwidth from 5.37 to 6.05 GHz (11.9%). The simulated gain is ∼7.05–7.1 dBic for the low-frequency band and 4.17–6.07 dBic for the high-frequency band, respectively. Measurements and simulations are in good agreement.

Application-Friendly Improved Designs of Single-Fed Circularly Polarized Microstrip Antenna [Antenna Applications Corner

Truncated-corner probe-fed (TCPF) patches are popular for their simple design that provides circularly polarized (CP) radiation with a very low axial ratio (AR). For a thin substrate (s 0.026lg), this antenna provides approximately 0.3% CP bandwidth (BW) (AR l 3 dB along with S11 l-10 dB). However, as the substrate thickness is increased for enhancing the matching BW, an offset among the frequencies featured with minimum AR and optimum S11 is observed. This degrades the effective BW, with an overlapping of both S11 l-10 dB and AR l 3 dB.