Circular Radiation Research Articles

A compact multilayer wide-band and high-gain circularly polarized antenna

In this paper, we present a high-gain wide-band circularly polarized antenna that uses double circular radiation patches and a double Y-shaped slot fed by microstrip line. The antenna consists of four layers stacked on top of each other and spaced by air gaps. In proposed antenna a copper layer is used as a reflector for directing radiation patterns, increasing front to back ratio (FBR) and gain. Three other layers include radiation patches with the same dimensions. Second layer includes a microstrip feed line on one side and a double Y-shaped slot on its other side. Third and fourth layer include circular radiation patches for controlling the polarization and bandwidth of the proposed antenna. Right-hand circular polarization {is obtained by optimizing} the dimensions of the circular patches. {Measured frequency bandwidth ranges from 3.35 GHz to 6.45 GHz, with} an S11 less than -10 dB. {Moreover, axial ratio and gain} are less than 3 dB and more than 7.5 dBi, respectively.

Generalized design approach to compact wideband multi-resonant patch antennas

In this work, a generalized design approach to compact, wideband multi-resonant microstrip patch antenna is proposed. Theoretical criterion of the length of the prototype dipole is laid down based on the simplest dipole model and the associated eigenmodes at first. Then, the criterion is employed to reveal the general relationship between the prototype dipole length, operational modes, sizes, and radiation behaviors of the resultant multi-resonant circular sector patch antennas. Next, a compact wideband, dual-resonant circular sector patch antenna is designed accordingly. It is operating at the TM3/4,1 and TM9/4,1 modes within a 240° circular sector patch radiator with its radii short circuited. The antenna fabricated on a single-layered air substrate exhibits an available radiation bandwidth of 25.0%, with a profile as small as 0.043 guided wavelength at the center frequency. It is evidently verified that the approach can be employed to realize compact, dual-resonant wideband microstrip patch antennas without increasing antenna profile, inquiring multiple radiators or employing reactance compensation techniques. In addition, it may lead to a series of novel wideband patch antenna designs with diverse performances.

Applying Neuro-Fuzzy Soft Computing Techniques to the Circular Loop Antenna Radiation Problem

Analytical methods used to solve the circular loop antenna radiation problem are effective and accurate, but also time-consuming, due to the complex mathematical background. However, soft computing techniques do not require complex mathematical procedures and are more straightforward and fast. In order to solve the circular loop antenna radiation problem, we examine two methods based on artificial intelligence and fuzzy logic. Different neural network learning algorithms are examined, and the fuzzy inference system parameters are identified. Extensive numerical tests show that the predicted values are consistent with those calculated from the analytical techniques. High accuracy and fast convergence make the proposed methods ideal for the prediction of the circular loop antenna characteristics.

Modified circular common element four-port multiple-input-multiple-output antenna using diagonal parasitic element

A four-port multiple input multiple-output (MIMO) antenna with common radiating element is proposed for 2.4 GHz Wi-Fi applications. It comprises a modified circular radiator fed by four identical modified feedlines, partial ground planes, and a diagonal parasitic element (DPE). The parasitic element is used to enhance the interport isolation. The antenna has a 2:1 Voltage standing wave ratio (VSWR) impedance band 2.34-2.56 GHz and nearly omnidirectional radiation patterns. The radiation efficiency is more than 79% and gain is 2 dBi at resonant 2.43 GHz. The isolation in the given frequency band is 10 dB. At the 2.43 GHz, the isolation between adjacent ports (1, 2 and 1, 4) is 14 dB and between opposite ports (1, 3) is 12 dB. The mean effective gain (MEG) ≤ −2.7 dB and envelope correlation coefficient is <0.01. The −10 dB total active reflection coefficient bandwidth is 202 MHz. The antenna is designed for a Wi-Fi device and the effectiveness of antenna has been checked for distance of ½ feet from the human head. The specific absorption rate (SAR) is found to be ≤0.17 W/Kg by CST simulation tool.

Circular geodesic radiation in Schwarzschild spacetime: A semiclassical approach

Extreme curvature settings and nontrivial causal structure of curved spacetimes may have interesting theoretical and practical implications for quantum field theories. Radiation emission in black hole spacetimes is one such scenario in which the semiclassical approach, i.e. quantum fields propagating in a nondynamical background spacetime, adds a very simple conceptual point of view and allows us to compute the emitted power in a straightforward way. Within this context, we reexamine sources in circular orbit around a Schwarzschild black hole, investigating the emission of scalar, electromagnetic and gravitational radiations. The analysis of the differences and similarities between these cases provide an excellent overview of the powerful conceptual and computational tool that is quantum field theory in curved spacetime.

Circular-polarization-sensitive absorption in refractory metamaterials composed of molybdenum zigzag arrays.

Circularly polarized light (CPL) is utilized in various fields, including optical communication and biological imaging. To overcome the lack of circular-polarization-sensitive absorbers working at high temperature, a refractory and circular-polarization-sensitive absorber comprised of molybdenum zigzag arrays is proposed. At certain resonant wavelengths, one component of circular polarization is absorbed by confining electromagnetic field in the dielectric layer, while the other component is backscattered. The circular-polarization-sensitive absorber could be applied as a CPL thermal radiator as well as a reflective linear-to-circular polarizer. As a CPL thermal radiator, left-handed circular radiation and right-handed circular radiation are dominant at different temperatures, respectively. As a linear-to-circular polarizer, both perfect left-handed circularly polarized light and nearly perfect right-handed circularly polarized light are obtained.

Four port MIMO integrated antenna system with DRA for cognitive radio platforms

An integrated four-port multi input multi output (MIMO) system with Cylindrical Dielectric Resonator Antenna (CDRA) for Cognitive Radio (CR) application is investigated. In this study the proposed design performs dual state operation i.e ultrawideband (UWB) and narrowband (NB) functionality with modified feeding mechanism, where the feeding line of UWB antenna is made orthogonal to NB CDRA. In UWB state the proposed integrated antenna consisting of two port circular radiators, excited by micro-strip transmission line. In NB state two CDRAs are integrated on the UWB radiators where the current density is effectively low. The DRAs are excited by aperture coupled orthogonal T feed micro-strip transmission line to perform the triband operation at targeted bands. The proposed integrated MIMO system occupies a compact total area of 0.18λ02(λ0 is the highest operating wavelength) with isolation less than −15 dB among all ports. The design approach is verified by fabricating the antenna prototype and the performances are experimentally evaluated in terms of S parameter, radiation pattern and gain. Moreover, the MIMO performance metrics in terms of Envelope correlation coefficient (ECC), diversity gain (DG) and mean effective gain (MEG) are also evaluated for satisfactory diversity performance.

Investigations on Convective Heat Transfer Enhancement in Circular Tube Radiator Using Al2O3 and CuO Nanofluids

In this study, forced convective heat transfer inside a circular tube automobile radiator is experimentally and numerically investigated. The investigation is carried out using Al2O3 and CuO nanofluids with water as their base fluid. A single radiator circular tube with the same dimensions is numerically modeled. Numerical model is validated using the experimental study results. In the experimental study, Al2O3 and CuO nanofluids of 0.05% volume concentrations (ϕ) were recirculated through the radiator for the Reynolds number (Re) between 260 and 1560. The numerical investigation is conducted for the nanoparticle volume concentration from 0% to 6.0% and 260 &lt; Re &lt; 1560. The investigation shows an enhancement of convective heat transfer coefficient (h) with the increase in nanoparticle volume concentration and with the Reynolds number. A maximum enhancement of 38% and 33% were found for Al2O3 and CuO nanofluids of ϕ = 1% and Re = 1560. For the same cooling load of the radiator, the pumping power can be reduced by 8% and 10%, when Al2O3 and CuO nanofluids (ϕ = 0.8%) were used. Enhancement in convective heat transfer can be utilized to reduce the radiator surface area required. However, the addition of nanofluid results in an enhancement of density (ρ) and viscosity (μ) along with a reduction in specific heat capacity (Cp). Hence, the selection of nanoparticle volume concentration should consider its effect on the thermophysical properties mentioned earlier. It is found that the preferred concentration is between 0.4% and 0.8% for both Al2O3 and CuO nanofluids. In our investigations, it is observed that the convective heat transfer performance of Al2O3 nanofluid is better than the CuO nanofluid.

Wave radiation and diffraction by a circular cylinder submerged below an ice sheet with a crack

Wave radiation and diffraction by a circular cylinder submerged below an ice sheet with a crack are considered based on the linearized velocity potential theory together with multipole expansion. The solution starts from the potential due to a single source, or the Green function satisfying both the ice sheet condition and the crack condition, as well as all other conditions apart from that on the body surface. This is obtained in an integral form through Fourier transform, in contrast to what has been obtained previously in which the Green function is in the series form based on the method of matched eigenfunction expansion in each domain on both sides of the crack. The multipole expansion is then constructed through direct differentiation of the Green function with respect to the source position, rather than treating each multipole as a separate problem. The use of the Green function enables the problem of wave diffraction by the crack in the absence of the body to be solved directly. For the circular cylinder, wave radiation and diffraction problems are solved by applying the body surface boundary condition to the multipole expansion, through which the unknown coefficients are obtained. Extensive results are provided for the added mass and damping coefficient as well as the exciting force. When the cylinder is away from the crack, a wide spacing approximation method is used, which is found to provide accurate results apart from when the cylinder is quite close to the crack.

Pin‐loaded circularly‐polarised patch antenna with sharpened gain roll‐off rate and widened 3‐dB axial ratio beamwidth

A circularly-polarised patch antenna with the loading of shorting pins is proposed in this study to sharpen the gain roll-off shape and widen the 3-dB axial ratio beamwidth (ARBW). First of all, it is theoretically revealed that when the electrical size of a circular patch radiator is appropriately constituted, the radiation gain at the horizon can be significantly suppressed and the axial ratio can be maintained below 3 dB over a wide angular range. By introducing a set of metallic pins, which short the patch in a circular contour, the resonant frequency of the antenna will be increased. In this way, the patch radius with respect to wavelength can be freely chosen, so that sharp gain roll-off rate and wide ARBW can be simultaneously achieved. After the extensive analysis is executed, two circular patch antennas with and without loading of shorting pins are designed, fabricated and tested for comparison. Simulated and measured results show that the gain roll-off is enhanced up to near 20 dB and 3-dB ARBW is extended to around 140° so as to effectively reduce the undesired multipath interference as highly demanded in the application of global navigation satellite system.

A Patch-Slot Antenna Array With Compound Reconfiguration

This letter presents the design of a novel compound reconfigurable antenna array for WiMAX and WLAN application. The proposed array consists of a unit-cell antenna composed of a truncated circular radiator, C-shaped parasitic elements, and perturbed rhombic slot element. A compound reconfigurable unit-cell antenna element loaded with p-i-n diodes is investigated, and using the inference made, a 1 × 2 array is designed to increase the gain and efficiency of the dynamic antenna. In the first case, slot antenna alone gets excited with the feedlines of 0° and 90° phase difference to achieve pattern and polarization reconfiguration for WiMAX applications. In the other case, the patch is excited at the WLAN band and, with the help of parasitic elements, pattern tilting at 0° and ±30° is obtained. The proposed antenna array is fabricated, and the simulation results are verified using experimental measurements.

Electrically Small, Low-Profile, Huygens Circularly Polarized Antenna

The design, simulation studies, and experimental verification of an electrically small, low-profile, broadside-radiating Huygens circularly polarized (HCP) antenna are reported. To realize its unique circular polarization cardioid-shaped radiation characteristics in a compact structure, two pairs of the metamaterial-inspired near-field resonant parasitic elements, the Egyptian axe dipole (EAD) and the capacitively loaded loop (CLL), are integrated into a crossed-dipole configuration. The EAD (CLL) elements act as the orthogonal electric dipole (magnetic dipole) radiators. Balanced broadside-radiated electric and magnetic field amplitudes with the requisite 90° phase difference between them are realized by exciting these two pairs of electric and magnetic dipoles with a specially designed, unbalanced crossed-dipole structure. The electrically small (ka = 0.73) design operates at 1575 MHz. It is low profile $0.04\lambda _{\mathbf {0}}$ , and its entire volume is only $0.0018\lambda _{\mathbf {0}}^{\mathbf {3}}$ . A prototype of this optimized HCP antenna system was fabricated, assembled, and tested. The measured results are in good agreement with their simulated values. They demonstrate that the prototype HCP antenna resonates at 1584 MHz with a 0.6 dB axial ratio, and produces the predicted Huygens cardioid-shaped radiation patterns. The measured peak realized LHCP gain was 2.7 dBic, and the associated front-to-back ratio was 17.7 dB.

An Arrow-shaped, Dual-Polarized Antenna and Its Three-Beam Splitting Array

In this paper, an arrow-shaped, dual-polarized antenna is demonstrated. It mainly contains five parts: the arrow-shaped dipoles, feed substrates, circular radiator, bedframe, and reflector. Both of the two dipoles of the proposed antenna participate the synthetic process, which is quite different from the working mode of the conventional crossed dipole antenna. A circular radiator is then suspended above the dipoles to further broaden the bandwidth. The proposed antenna element can provide a measured bandwidth of 34% ( $\vert S_{11}\vert dB or VSWR $4\times4$ array is presented and verified in simulation. By assigning each antenna element with different amplitude and phase, the antenna array could provide 10~14° downtilt in V-plane and three-beam radiation in H-plane. Thus, the antenna array could precisely control the coverage area and substantially improve the communication capacity. All the results reveal that the antenna is suitable for the hot spots communication which needs high speed and high capacity.

Shared Circular Radiator for UWB-MIMO Applications

Shared Circular Radiator for UWB-MIMO Applications

Design Approach to a Novel Dual-Mode Wideband Circular Sector Patch Antenna

A design approach to a novel wideband circular sector patch antenna is proposed. Design guidelines are laid down based on an approximate 1.5-wavelength, multimode magnetic dipole, and the cavity model. Then, the flared angle of the circular sector patch and the corresponding usable resonant modes for wideband radiation are determined. It is demonstrated that the resonant TM4/3,1 and the TM8/3,1 modes within a 270° circular sector patch radiator can be simultaneously excited, perturbed, and employed to form a wideband unidirectional radiation characteristic with two resonances. Prototype antennas are designed and fabricated to experimentally validate the dual-resonant wideband property on a single-layered substrate. It is further demonstrated that the antenna designed on a 5-mm-thick air substrate exhibits an available radiation bandwidth (ARB) of 14.5%, while the printed one designed on a 2-mm-thick modified Teflon substrate exhibits an ARB of 6.5%. It is evidently validated that the proposed approach can be employed to effectively enhance the operational bandwidth of microstrip patch antennas without increasing antenna profile, inquiring multiple radiators or employing reactance compensation techniques.

Bandwidth and Gain Enhancement of MIMO Antenna by Using Ring and Circular Parasitic with Air-Gap Microstrip Structure

This research was proposed a circular patch MIMO antenna by using a ring and circular parasitic radiator structure. As a novelty, in order to enhance bandwidth and gain of circular patch MIMO antenna, a conventional circular patch MIMO antenna will be added a ring and a circular parasitic. Therefore, this research was investigated a conventional MIMO antenna (C-MA), ring parasitic MIMO antenna (RP-MA), and circular parasitic MIMO antenna (CP-MA) as Model 1, Model 2, and Model 3, respectively. This MIMO antenna was designed on FR4 microstrip substrate with r= 4.4, thickness h=1.6 mm, and tan = 0.0265. This MIMO antenna has center frequency 2.35 GHz which is a frequency band for LTE application in Indonesia. An Advance Design System (ADS) software was used to determine the antenna parameters. The MIMO antenna C-MA / RP-MA/ CP-MA achieves 2.36GHz/ 2.38GHz/ 2.38 GHz, 70 MHz/ 100 MHz/ 120 MHz, 1.625 dBi/ 4.066 dBi/ 4.117 dBi, 6.414 dBi/ 7.26 dBi/ 7.153 dBi, 33.9 %/ 47.8 %/ 49.70 %, -12.35 dB/ -22.21 dB/ -23.66 dB, and -30.924 dB/ -28.46 dB/ -27.59 dB for center frequency, bandwidth, gain, directivity, efficiency, reflection coefficient, and mutual coupling, respectively. Compared to C-MA (Model1) performances, The result showed that proposed antenna has wider-bandwidth/ higher-gain with 42.8%/ 150.2 %, and 71.4%/ 163.3% for RP-MA (Model 2) and CP-MA (Model 3), respectively. The proposed antenna has size of 50 mm x 130 mm x 23.2 mm. Measured results are in a good agreement with the simulated results.

Dual-layered polarization and frequency reconfigurable microstrip antenna by rotating breach-truncated circular radiator

In this study, a dual-layered polarization and frequency reconfigurable microstrip antenna is proposed based on sequential mechanical axial rotation of the circular metal radiator. The antenna can be reconfigured among three different polarized modes, including the linear polarization (LP), left-handed circular polarization and right-handed circular polarization in the band from 4.68 to 4.80 GHz (2.53%). The resonance frequency of the proposed antenna with the same LP mode could also be tuned in the range from 4.70 to 5.03 GHz by mechanical rotation of the breach-truncated circular metal radiator as well as the circular substrate. Furthermore, the polarization characteristic and frequency can be reconfigured, respectively, as the circular radiator is taken an axial rotation with an angle of 360°. The presented antenna in the four different states has been numerically simulated and fabricated for the experimental measurement, the investigated characteristics includes the port reflection coefficient, axial ratio, radiation pattern, gain, and the radiation efficiency. The simulated and test results agreed well with each other. This antenna enriches the novel mechanical reconfigurable method except for the popular electrical approach.

Reduced size elliptic UWB antenna with inscribed third iteration sierpinski triangle for on‐body applications

ABSTRACTIn this article, a combination of an elliptical UWB monopole with a series of Sierpinski triangle iterations inscribed in the planarized radiator is used to develop a highly‐impedance stability UWB antenna, performing from 700 MHz to 9 GHz. The fractal iteration is introduced in order to obtain a radiator size reduction and to improve the current distribution stability. With this implementation, a 31% radiator area reduction is obtained compared to a conventional circular or elliptical radiator. The antenna impedance matching is maintained over the entire bandwidth, even when an external lossy dielectric body is around or even in contact to the radiator. The antenna presents quasi‐omnidirectional radiation patterns and a gain around 0 dBi and group delay variations lower than 2 ns, making it suitable for short‐pulse communications systems and on‐body communications applications. © 2017 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:635–641, 2017

A Compact Four Concentric Rectangular Rings Slot Antenna for Mobile Handset Applications

A novel compact four concentric rectangular rings slot broadband microstrip antenna is proposed for mobile handsets in the paper. The antenna has a circular radiator with four concentric rectangular rings slot structure. The antenna can cover more than ten mobile applications with -10dB bandwidth of 88.7% (1.6-4.15GH) for DCS1800(1710-1880MHz), TD-SCDMA(1880-2025MHz, 2300-2400MHz), WCDMA(1920-2170MHz, 1755-1880MHz), LTE33-41/42/43 (1900-2690MHz, 3400-3800MHz), Bluetooth, GPS, COMPASS, GLONSS, GALILEO, WLAN (802.11b/g/n:2.4-2.48GHz), and WiMAX(3.3-3.8GHz) wireless applications. The proposed antenna is fabricated on a 1.6 mm-thick FR4 substrate with dielectric constant of 4.4, and the size is 50*40mm2. The good agreement between the measurement results and the simulation validates the proposed design approach and meets the requirements for mobile handset applications.

Planar Quasi-Isotropic Magnetic Dipole Antenna Using Fractional-Order Circular Sector Cavity Resonant Mode

The radiation behavior of the fractional-order, resonant mode within a circular sector cavity radiator is revealed at first, and then, it is employed to design a novel, planar quasi-isotropic magnetic dipole antenna. A set of closed-form formulas is derived and employed to determine the key parameters of the proposed antenna. The resultant circular sector magnetic dipole antenna operates at its dominant TM(2/3), 1 mode. It is numerically verified and experimentally validated at the 2.45-GHz band. It is seen that the antenna exhibits a good non-uniformity of less than 5.7 dB within the three principal planes, and an average radiation efficiency up to 82% within its impedance bandwidth from 2.4 to 2.5 GHz (for reflection coefficient smaller than −10 dB). Good agreement between the theoretical, simulated, and measured results has evidently verified the proposed antenna design approach.