Loop Radiator Research Articles

Conformal cylindrical microstrip loop radiator input impedance calculation

Problem statement. Antennas that fully or partially repeat the shape of the object on which they are placed are called conformal. The main areas of application of conformal antennas are aviation, rocketry, and vehicles. Despite the presence of a large number of publications devoted to conformal antennas in our country and abroad, issues related to the formation of the radiation characteristics of conformal microstrip antennas, as well as the influence of the overall dimensions and geometry of the emitter on the radiation characteristics, have still not been sufficiently studied. Goal. The purpose of this work was to obtain an approximate formula for calculating the input impedance of a conformal cylindrical microstrip loop radiator. Results. In this article, an integral equation is obtained for the unknown current density distribution function on the surface of a conformal cylindrical microstrip loop radiator; as a result of its solution, an approximate formula for this function is obtained. An approximate formula for calculating the input impedance is obtained. The dependences of the input impedance of a conformal cylindrical microstrip loop radiator on its length normalized to the wavelength are calculated. Practical significance. The proposed method for calculating the input impedance of a conformal cylindrical microstrip loop radiator makes it possible to effectively calculate and study the dependence of the input impedance on the geometric dimensions of the emitter, as well as the dimensions and electrodynamic parameters of the substrate. This technique can be generalized to emitters located on substrates made of other materials, for example, chiral metamaterials.

Analysis and Experimental Study of Puncture Leakage Characteristics of Pump-driven Fluid Loop Radiator

Abstract The radiator is a key component of the pump-driven fluid loop in the thermal management system of spacecraft, and it has a high probability of being penetrated by Micro-Meteoroid and Orbital Debris (MMOD). Therefore, for long-life manned spacecraft such as space stations, the study of the leakage characteristics of radiators after breakdown is an important work that needs to be solved urgently. In this paper, the leakage state characteristics of the emitter after leaking are analyzed, and a mathematical model is established to calculate the relationship between the aperture and the leakage volume rate. Finally, the accuracy of the mathematical model is verified by experiments.

A monopole antenna with cotton fabric material for wearable applications

A monopole antenna operated at 2.45 GHz and embedded with artificial magnetic conductor (AMC) for wearable communication systems is investigated in this article. The proposed antenna is composed of a metalized loop radiator with a coplanar waveguide microstrip feedline which is affixed on a cotton fabric material substrate. As well, a cotton-based AMC surface is utilized to eliminate the body’s absorbed radiation and enhance the gain of the antenna. It is composed of 5 × 5 array unit cells etched with I-shaped slots. Using this configuration, simulations show that the specific absorption rate (SAR) level was significantly reduced. Considering flat and rounded body parts, it was found that the SAR values averaged over 10 g at a distance of 1 mm away from the tissues model were only 0.18 W/kg and 0.371 W/kg, respectively. Additionally, the antenna gain was improved up to 7.2 dBi with an average radiation efficiency of 72%. Detailed analysis with experimental measurements of the cotton-based antenna for different operation scenarios is introduced. The measured data show a good correlation with the electromagnetic simulation results.

Optimization of novel flat serial single-phase radiators for spacecraft thermal control

Space thermal radiators play a significant role in the thermal management of spacecraft. With the increase in heat dissipation requirement, the heat pipe radiators are being replaced by mechanically pumped fluid loop radiators. In recent years, authors proved that optimum serpentine serial radiators are advantageous over conventional optimum parallel radiators in terms of the mass and pressure drop. The spiral radiators, inspired by spiral plate heat exchangers, are proposed and analyzed as a replacement for the serpentine serial radiators. Performance analysis of radiators is carried out using conjugate heat transfer analysis. Conjugate heat transfer results are validated with the experimental results obtained from the literature. The performance analysis indicated that the circular spiral radiator performs better than the other two types due to their lower mass and pressure drop. Optimization of radiators is carried out using Taguchi Signal to Noise ratio analysis. Analysis of Variance is conducted to determine the percentage contribution of each variable to the performance of the radiator. When lower pressure drop requirement is prominent, the contribution of the diameter of the tube is 79.3%, whereas the contribution of fin thickness and pitch of the tubes are only 6.1% and 8.2%, respectively. The contribution of the fin thickness is 57.39%, the diameter of the tube is 37.71%, and the pitch of the tubes is 1.89% when the lower mass of the radiator is the prime requirement. The high-performance spiral radiators may find their application in the thermal management of human space flights and high-power GEO satellites.

A Planar Bidirectional Circularly Polarized Antenna Using Orthogonal Magnetic Dipoles Without Extra Phase Shift Line

A planar bidirectional circularly polarized (CP) antenna using orthogonal magnetic dipoles (OMDs) without an extra phase shift line is proposed in this work. It consists of a rectangular microstrip magnetic dipole antenna (MMDA) and a loop radiator with two arms directly connected to the open edge of MMDA. The working principle is revealed by the equivalent sources model to provide a clear physical insight at first. The theoretical investigations imply that by controlling the width and the feed locations of the loop antenna on the aperture, the phase and magnitude for CP radiation can be realized in both endfire and backfire directions without introducing an additional phase shift line structure. For demonstration, one antenna prototype is designed and fabricated. The experimental results indicate that an overlapping bandwidth of 5.91% from 2.30 to 2.44 GHz is attained. Compared with the counterpart using OMDs, the proposed antenna exhibits a low design complexity and improved gains of 3.56/1.83 dBic in the endfire/backfire directions.

Directive Multiband Antenna Based on Rectangular Loop Array and Dumbbell-Shaped Slot Radiator.

In this article, a combination of rectangular loop array and slot radiator for multiband applications is presented. The antenna is configured by arranging, concentrically, a set of rectangular loop radiators excited by electromagnetic coupling provided by a dumbbell slot. The size of the loops is calculated to obtain the desired resonant frequencies, which are almost independent of the adjacent rings. The exciting slot is designed to operate in a wideband frequency range to cover the upper desired resonance. In addition, to obtain directive radiation patterns, a reflector shaped like a box is introduced, giving a stable gain, radiation pattern shape, and port matching at the selected frequencies. The configuration presents great results, since to the authors’ knowledge, even a similar configuration given in the open literature presents some disadvantages compared to this one; moreover, not just any structure can be employed as the resonating elements, obtaining multiband behavior at the same time.

Heat-transfer optimization of fluid loop radiator based on entransy analysis

Heat-transfer optimization of fluid loop radiator based on entransy analysis

Dual-Band Dual-Polarized Base Station Antenna With a Notch Band for 2/3/4/5G Communication Systems

This letter proposes a new design of a dual-band dual-polarized base station antenna with a notch band for second-generation (2G), 3G, 4G, and the sub-6 GHz 5G systems. The antenna is composed of a four-leaf loop radiator, two-layer parasitic annular disk and a pair of crossed Y-shaped baluns. By introducing mouse-ear shaped arm to the edge of each radiator, a dual-band operating characteristic and a notch band from 2.9–3.2 GHz are realized. The annular disks and gradient strips are beneficial for bandwidth enhancement. The measured results show that the proposed antenna offers two broad bands with the fractional bandwidth of 55.8% (1.55–2.75 GHz), and 14% (3.3–3.8 GHz) for voltage standing -wave ratio (VSWR) 30 dB. This design achieves stable gain of 7.1 ± 0.5 dB and half power beam width of 68 ± 5° during the working bands. These attractive features make the antenna an ideal candidate for 2G, 3G, 4G, and the sub-6 GHz 5G base station applications.

A broadband multiple-input multiple-output loop antenna array for 5G cellular communications

In this study, we propose a multiple-input/multiple-output (MIMO) antenna array for fifth-generation (5G) mobile-phone applications. Its configuration is composed of eight planar loop antenna elements located at different edges of the mobile-phone mainboard with 75 × 150 × 0.8 mm3 FR-4 dielectric. In order to easily integrate with phone circuits, the ground-plane and antenna resonators have been etched on the same side of the substrate. By addling modified arrow-shaped strips among the adjacent loop antennas, the operation bandwidth and isolation level of the closely spaced radiators have been improved. The presented MIMO antenna is designed to cover the spectrum of commercial sub 6 GHz 5G network with the bandwidth of 3.2–4 GHz. Due to the compact size and placements of the loop radiators, the presented MIMO antenna array occupies a small part of the board. In addition, the proposed array provides not only full radiation coverage covering different sides of the PCB but also the diversity function to support both vertical and horizontal polarization. The MIMO performance and radiation behavior of the proposed antenna design in the presence of the user-hand/user-head phantoms are also discussed. Moreover, a new and compact phased array millimeter-wave (MM-Wave) antenna with broad bandwidth and end-fire radiation is introduced to be easily integrated into the smartphone antenna system.

Near-Field HF-RFID and CMA-Based Circularly Polarized Far-Field UHF-RFID Integrated Tag Antenna

This research proposes an integrated high-frequency (HF) and ultrahigh-frequency (UHF) passive radio frequency identification (RFID) tag antenna for near-field (13.56 MHz) and far-field (920–925 MHz) communication. This tag antenna is advantageous for the applications with lossy material in the near-field communication and mitigates polarization loss in the far-field communications. The HF-RFID tag antenna is of square spiral structure, and the circularly polarized UHF-RFID structure consists of a square loop radiator with cascading loop feeding and shorted stub. The structure of HF-RFID tag antenna situated inside the circularly polarized UHF-RFID tag can avoid the significant effect of the near-field magnetic coupling from the square loop. The UHF-RFID tag antenna is realized by using characteristic mode analysis for wideband circular polarization. The HF-RFID structure is conjugate-matched with NXP NT3H2111 chip, and the UHF-RFID structure is conjugate-matched with NXP G2X chip. Simulations were carried out, and an antenna prototype was fabricated. The experimental results reveal that the radiation pattern of UHF-RFID tag antenna is bidirectional with a gain of 0.31 dBic. The impedance bandwidth covers the frequency range of 903–944 MHz, and the axial ratio in boresight direction at 922.5 MHz is 1.67 dB, with the axial ratio bandwidth over 863–938 MHz. The maximum near-field and far-field reading ranges are 4.9 cm and 8.7 m. The proposed integrated dual-band passive tag antenna is operationally ideal for HF-RFID and UHF-RFID applications.

Tilted bi‐sense circularly‐polarized antenna and its application for radio frequency identification system

A tilted bi-sense circularly polarized (CP) antenna and its application for UHF radio frequency identification (RFID) system is proposed. A planar concial monopole working as the electric dipole is designed at first. When a shorting pin is added, a loop radiator would be generated, and thus a pair of orthogonally oriented complementary dipoles is realized. In this way, both right-handed circularly polarized (RHCP) and left-handed circularly polarized waves (LHCP) are generated simultaneously in tilted directions within one hemisphere. Then, closed-form formulas are derived to reveal the tunability mechanism of bi-sense property and provide a design guideline for system application. It is demonstrated that flare angle of conical monopole has a linear relationship and sine function to CP beam direction and 3-dB axial ratio (AR) beamwidth, respectively. Finally, antenna prototypes are fabricated and tested for validation. It is also demonstrated that at the tilted direction of θ = ± 45°, a 3-dB AR bandwidth of 4.9%, and gain up to 5 dB are realized. Comparing with conventional microstrip patch antenna, an enhanced reading range over 5 m can be obtained in the tilted range from 40° to 75° and − 75° to −40° in UHF RFID sytem application.

Compact, High Directivity, Omnidirectional Circularly Polarized Antenna Array

A compact omnidirectional circularly polarized (OCP) antenna system is reported, which achieves high directivity and operates with the 2.4 GHz WLAN band. It is formed by cascading several stages of electric (metallic strips) and magnetic (loops) radiators into a highly compact array. Two OCP antenna array designs are developed to demonstrate the approach and their resulting high directivities. First, a four-stage OCP antenna array is presented. It consists of three electric radiators (E-radiators) and four magnetic radiators (M-radiators) arranged in collinear formation. A prototype was realized by mechanically fabricating the folded copper loops. Measurements confirm that this compact cost-effective design generates OCP fields that have a 5.1 dBic peak LHCP realized gain in its horizontal plane. The overlapped impedance and AR bandwidth cover 130 MHz from 2.34 to 2.47 GHz. Second, a six-stage OCP antenna array with helical loops is implemented to further increase the directivity. Its prototype was realized with all-metal 3-D printing technology. Six stages of bar and helical loop radiators form five E-radiators and six M-radiators. This highly compact OCP array achieves a measured maximum realized gain of 7.1 dBic with a 110 MHz operational bandwidth that covers 2.37-2.48 GHz.

A Dual Layered Loop Array Antenna for Base Stations With Enhanced Cross-Polarization Discrimination

This paper presents a novel dual-loop array antenna targeted at current and future base station applications. The antenna has four rectangular loops and four trapezoidal loops printed on the front and back sides, respectively, of a substrate placed above a flat square reflector. All eight loop radiators are excited simultaneously with properly designed feed networks to achieve its ±45° polarization states. The trapezoidal loops act like folded (electric) dipoles; the rectangular loops act primarily as magnetic dipoles. The combination of these two loop arrays leads to a type of magnetoelectric loop antenna that has stable directivity patterns with high cross-polarization discrimination (XPD) values across a 45.5% operational fractional bandwidth from 1.7 to 2.7 GHz. A fabricated and measured prototype confirms the simulation results and demonstrates that the half-power beamwidths in the horizontal plane vary between 63° and 70°, the XPD values are >20 dB in the boresight direction, and are >10 dB within the entire cellular coverage angular range: $-60^\circ \leq \theta \leq 60^\circ $ .

Multi‐mode broadband antenna for 2G/3G/LTE/5G wireless communication

A broadband dual-polarised antenna for 2G/3G/LTE/5G wireless communication is proposed. A new resonant mode is induced with parasitic resonator loaded inside the loop radiator. Wide impedance bandwidth of 72.2% for VSWR<;2 (1.69-3.6 GHz) is achieved with three controllable resonant modes. Stable gain and radiation patterns are obtained over the whole band.

A Broadband ±45° Dual-Polarized Multidipole Antenna Fed by Capacitive Coupling

A broadband ±45° dual-polarized multidipole antenna is proposed in this communication. A pair of big dipoles and a pair of small ones are printed on a square substrate. The large dipoles mainly dominate the low operating frequency of the antenna, while the small dipoles work at the high one. A pair of H-shaped coupler is introduced to feed the antenna through capacitive coupling with loop radiator dipoles, and a rectangular box-shaped reflector is used for keeping the radiation patterns over the operating frequency. The antenna achieved a wide impedance bandwidth of about 56.6% for 8.1 dBi is achieved for both ports. A stable radiation pattern with 3 dB beamwidth 62°±6° at E-plane and 75°±3° at H-plane for port 1 and 60° ±4° at E-plane and 71° ±5° at H-plane for port 2 is obtained. The antenna is manufactured and tested. The measured results of the antenna are in well agreement with the simulation ones. Design details of the proposed antenna are presented and discussed.

Balanced circularly polarized square loop antenna under even-mode resonance

Design approach to a novel balanced, circularly polarized (CP) square loop antenna under even-mode resonance is proposed in this paper. The loop antenna is diagonally fed by a fork-like dipole launcher. By matching the respective natural boundary condition of the loop radiator and the dipole launcher, the resonant even-mode with inherent CP radiation characteristic can be sufficiently excited. Both the bi- and uni-directional cases are designed and investigated. A bi-directional CP loop antenna with a 3-dB ratio axial ratio (AR) bandwidth of 6.6% is designed at first. A uni-directional antenna having a planar metallic reflector is further designed. The uni-directional loop antenna exhibits excellent uni-directional CP performance with a high front-to-back ratio of 40dB and a 3-dB AR bandwidth of 7.6% in both theory and experiment.

Compact, Printed, Tri-Band Loop Antenna With Capacitively-Driven Feed and End-Loaded Inductor for Notebook Computer Applications

The shorted monopoles and the planar inverted-F antennas have been utilized for wireless local area network (WLAN) notebook applications for years. This paper presents an alternative and yet promising antenna type with a compact and smaller size of 5 mm $\times20$ mm to operate in the 2.4 GHz (2400–2484 MHz), 5.2 GHz (5150–5350 MHz), and 5.8 GHz (5725–5825 MHz) WLAN bands. The loop antenna, formed on a 0.4-mm-thick FR4 substrate, was adopted in this study. The loop radiator comprised a capacitively-driven feed and an end-loaded inductor. The capacitively-driven feed allowed the antenna to generate the quarter-wavelength loop resonance for possible lowest resonant mode excitation in addition to the loop’s half-wavelength mode. By loading an inductor at the loop end to be connected to the small antenna ground, the operating frequencies of the quarter- and half-wavelength resonances were further decreased to cover the 2.4 and 5.2/5.8 GHz bands with good input impedance therein.

Design of a bandwidth enhanced hybrid slot loop antenna for GSM/UWB standards

PurposeThis paper aims to presents the bandwidth enhancement of a hybrid slot–loop antenna using a modified feed structure.Design/methodology/approachThe conventional monopole feed of the hybrid slot–loop radiator is loaded with a flat microstrip patch to excite higher-order modes. The proposed antenna combines the resonant modes of the slot antenna, the loop antenna and the patch loading.FindingsThe antenna exhibits a dual-band response suitable for GSM 1800/1900 and ultrawideband (UWB) standards. The impedance bandwidth extends from 1.65 to 1.95 GHz (11.42 per cent) and 3 to 11.1 GHz (114.9 per cent). The proposed antenna has the smallest footprint with a peak gain of 5.07 dBi at 1.8 GHz and 4.97 dBi at 6 GHz. The prototype antenna is fabricated and the simulation results are validated using experimental measurements. The performance of the bandwidth-enhanced hybrid slot–loop antenna is compared with that of other slot antennas.Originality/valueThus, a hybrid slot–loop antenna with an enhanced bandwidth has been reported in this study. The conventional monopole feed of the antenna is replaced with a monopole ending with a microstrip patch load. The antenna covers the operating bands of GSM 1800/1900 and UWB. The proposed antenna has a smaller footprint compared with other wide-slot antennas reported in the literature.

Compact 3D‐loop antenna with bandwidth enhancement for WWAN/LTE mobile‐phones applications

This study presents a 3D-loop antenna for wireless-wide-area network/long-term evolution (WWAN/LTE) operation. The size is compact and low profile and so the antenna is suitable for mobile-phone applications. The loop itself generates four resonant modes. Three parasitic elements are placed closely to the 3D-meandered loop radiator to generate three more resonant modes. These resonant modes form a dual-band, a lower band and a wide upper band, to cover many current mobile standards. The antenna performance, in terms of impedance bandwidth, efficiency, peak gain and radiation pattern, is studied using simulation. The antenna is also fabricated and the prototyped antenna is measured using the Satimo StarLab system. The measured results of the antenna inside a phone case on a phantom hand and phantom head in the data mode and talk mode, respectively, (defined by the Cellular Telephone Industries Association) are also presented. The measured efficiencies are subsequently used to estimate the total-radiated powers (TRPs). Results show that the TRPs in all covered standards meet the strictest over-the-air testing requirement of Vodafone.

A Hybrid Integrated High-Gain Antenna With an On-Chip Radiator Backed by Off-Chip Ground for System-on-Chip Applications

This paper presents the design of a V-band hybrid integrated high-gain antenna. This antenna is designed to meet the system-on-chip applications in a quad flat no-lead (QFN) package. The antenna consists of an on-chip loop radiator, a dielectric resonator (DR), and an off-chip ground plane. The on-chip radiator is fabricated to excite the DR using the standard 0.18- $\mu \text{m}$ CMOS technology with a high-resistivity (HR) silicon substrate. The off-chip ground is realized by a simplified QFN die pad. Several advantages of this off-chip ground structure are discussed in this paper. The impact of the off-chip ground on the performance of the proposed DR antenna is investigated by both simulations and measurements. The DR, the off-chip ground structure, and the HR silicon substrate are simultaneously introduced in this design to augment the gain of the antenna. A measured gain of 7.8 dBi is achieved at 67 GHz with a simulated radiation efficiency of 96.7% and chip size of only $0.7 \times 1.25$ mm2.