Unidirectional Antenna Research Articles

U‐shaped bow‐tie magneto‐electric dipole antenna with a modified horned reflector for ultra‐wideband applications

A novel U-shaped bow-tie magneto-electric dipole unidirectional antenna with a dual-layer horned reflector for ultra-wideband (UWB) applications is proposed. To broaden impedance bandwidth, a U-shaped bow-tie electric dipole structure with two notch slots is presented. In addition, to reduce the size of the antenna and improve impedance matching, a new feeding structure designed with perforation and tapered line is introduced. Finally, a double-layer horned reflector, instead of a ground plane, is employed to improve radiation patterns and gains for high-rate data transmission. The prototype antenna can achieve a stable gain of 10 ± 1.2 dBi and an impedance bandwidth of 118% for standing wave ratio ≤ 2 from 2.81 to 10.92 GHz. To the best of the authors knowledge, it is the first U-shaped bow-tie magneto-electric dipole unidirectional antenna for UWB applications. The proposed antenna, which possesses the advantages of UWB antenna and magneto-electric dipole antenna simultaneously, can be easily fabricated with low cost. With these features, it is a practicable candidate for UWB communications.

Isolation enhancement between tightly spaced compact unidirectional patch-antennas on multilayer EBG surfaces

In this article, ultracompact unidirectional patch antennas are used in different two-antenna systems for biomedical applications at 5.2 GHz. Multilayer mushroom type electromagnetic bandgap (EBG) structures are designed as slow-wave medium to reduce the size of the individual patch antennas to 0.1λ0 by 0.18λ0. Various techniques are investigated herein to improve antenna isolation for an enhanced Multiple-Input Multiple-Output (MIMO) performance. First, the coupling between 0.3λ0-spaced antennas is verified to occur dominantly through radiation and near-field coupling between the patches rather than through substrate-bound modes. Second, various configurations are proposed to suppress antenna coupling. These approaches include reorientation of the antennas and employment of parasitic radiators between the patches. A novel design is presented in which a unidirectional parasitic slot radiator on an EBG reflector is inserted between the antennas to decouple them. Measurement results confirm efficacy of these approaches in mitigating antenna coupling by more than 11 dB in the operating bandwidth of the antennas. The compact patch antennas maintain efficiency values of higher than 70%. © 2014 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:30–38, 2015.

Dual-Band Loop-Dipole Composite Unidirectional Antenna for Broadband Wireless Communications

The design of a novel dual-band loop-dipole composite unidirectional antenna for broadband wireless applications is proposed. First, design guidelines of the antenna are presented, and then, a step-by-step derivation of the antenna geometry is drawn. The antenna's operation principle is analyzed by carrying out parametric studies of surface current distribution, impedance and radiation patterns. The reflection coefficient, radiation patterns and gain of the antenna are numerically and experimentally studied to verify the operation principle and the design approach. It is demonstrated that two pass-bands, from 1.54 to 3.24 and from 4.88 to 6.80 GHz, of reflection coefficient smaller than -10 dB are obtained. The antenna has stable and unidirectional radiation pattern with low cross polarization within its pass-bands. The average gain of the antenna is 6.7 dBi at low frequency band and 6.5 dBi at high frequency band.

A Low-Profile High-Gain Substrate-Integrated Waveguide Slot Antenna Enabled by an Ultrathin Anisotropic Zero-Index Metamaterial Coating

A low-profile high-gain unidirectional antenna is proposed and demonstrated using both metamaterial (MM) and substrate-integrated waveguide (SIW) technologies. First, the leaky modes supported by a grounded anisotropic slab are studied. These investigations reveal that a grounded slab consisting of an anisotropic zero/low index material can provide an extremely low value for the real part of the propagation constant of the leaky mode, thereby facilitating stable unidirectional broadside radiation over a wide frequency range. The truncation effect of the slab is then investigated through full-wave simulations, which is found to be beneficial for a practical implementation of dispersive metamaterials. Finally, to validate the proposed concept, a subwavelength end-loaded dipole array is designed to realize the required anisotropic zero-index property and is applied to a SIW fed longitudinal slot antenna for the 5.8 GHz wireless local area network (WLAN) band. Measurements of the fabricated antenna prototype are shown to be in strong agreement with simulation results, thus confirming the proposed antenna design. The resulting antenna is only 0.12 λ thick, all while accomplishing a broadside gain of more than 10 dBi and a front-to-back ratio larger than 26 dB, which is ~ 7 dB and ~ 10 dB higher than that of the SIW fed slot alone, respectively. The -10 dB impedance bandwidth is more than 9% both with and without the presence of the MM coating. The proposed technique offers a means for realizing low-cost and low-profile unidirectional antennas with moderate bandwidth.

Design and analysis of bidirectional deployable parabolic cylindrical antenna

A bidirectional deployable parabolic cylindrical reflector for an L-band synthetic aperture radar is presented in this study, in which a self-deployed antenna with low weight was designed. The antenna consists of four curved surfaces formed from thin sheets of composite materials connected by hinges along the edges, and the reflective surface is provided by the front surface. The edge profiles of connecting lines were obtained through geometric analysis. A scaled model, including design and manufacture, was demonstrated to validate the process from the folded state to the fully deployed state. The non-contact synchronous vision measuring method was used to test the basic frequency of the scaled model, and the test results gave the verification of the analyses. Compared with the existing unidirectional deployable antenna, this new type of bidirectional deployable antenna can be applied to larger-size antennas and has better performance because the glass-woven tape connections were substituted with more reliable hinges. Static, modal, harmonic response, and transient response analyses of the full-sized reflector structure were modeled with the commercial finite element (FE) package ABAQUS. The modeling techniques were developed to predict the structural dynamic behavior of the reflector and the results showed that the first natural frequency was 0.865 Hz, and the reflector structure had good stiffness in three directions. This proposed structure has very high stiffness-to-mass ratio because of its hollow solid construction. A preliminary simulation of radiation properties of the parabolic cylindrical antenna, fed by an off-set linear feed horn array, was conducted to obtain the radiation pattern of the feed and the reflector.

Distributed Wireless Sensor Network Localization Algorithm using Space Standard Normal Vector (SSNV)

—In this paper a low cost but effective localization algorithm for wireless sensor networks (WSNs) is introduced. From the proposed scheme unknown nodes only have to listen to three anchor nodes and establish a space standard normal vector (SSNV) to estimate the coordinates of them. Many localization algorithms for WSNs require the exits of extra components, such as a GPS, ultrasonic transceiver, and unidirectional antenna on sensor nodes. Conversely the proposed localization scheme is range-free which means there is no demanding of any extra devices for the sensors. In this scheme, by collecting information from the three nearest anchors a geometric plane surface is built whose standard normal vector is also obtained correspondingly. The estimated location of each unknown sensor is adjusted according to its relative normal vector in the space which belongs to the built plane surface. This paper compares the proposed scheme with the well-known DV-Hop mechanism, Centroid method and the OSSDL algorithm that we proposed before. Simulation results show that the proposed scheme outperforms the other three in localization accuracy, communication cost, and computational complexity. Analysis about the effects of different length of normal vector is also made.

WIDEBAND UNIDIRECTIONAL BOWTIE ANTENNA WITH PATTERN IMPROVEMENT

A wideband unidirectional bowtie antenna with stable radiation patterns is proposed and investigated. It is fed by a wideband microstrip balun, using a coupling triangular structure to induce more balanced currents. Particularly, the corners of the conventional triangular bowtie dipole are rounded to achieve an impedance BW of 106.9% for jS11j • i10dB ranging from 1.97GHz to 6.49GHz. Additionally, a special small circular re∞ector between the ground plane and the bowtie dipole is used to stabilize the radiation patterns. The antenna achieves a stable gain of around 9.5dBi with a little variation of 1.4dBi and unidirectional radiation patterns over the whole operating band.

WIDEBAND PATCH ANTENNA WITH STABLE HIGH GAIN AND LOW CROSS-POLARIZATION CHARACTERISTICS

A wideband unidirectional patch antenna with two meandering strips and a i-shaped feeding structure is designed. The investigation shows that the antenna achieves an impedance bandwidth of 54.2% for VSWR • 2 and a stable gain of around 9dBi. The far fleld radiation patterns with low cross polarization which levels are less than i27dB, low back radiation and symmetrical E- and H-plane patterns are obtained over the whole operating frequency range.

Slot-Loaded Folded Dipole Antenna With Wideband and Unidirectional Performance for L-Band Applications

Wideband antennas operating at L-band are rapidly finding their applications in various microwave-based medical diagnostic systems. To increase signal penetration while working in a limited space, these systems require compact unidirectional antennas. To meet these requirements, a three-dimensional folded dipole antenna is presented. It is composed of a slot-loaded coaxially fed printed slab and a U-shaped copper structure that completes the folded dipole loop. An appropriate slot loading enables achieving significant improvements of the proposed design in terms of bandwidth, gain, and front-to-back ratio compared to the conventional folded dipole antenna. A parametric analysis is performed for a deep understanding of the antenna's mechanism. A fabricated prototype demonstrates 57% fractional bandwidth, centered at 1.44 GHz with an average gain of 3.7 dBi over that band. The antenna has a directional radiation pattern with around 9 dBi front-to-back ratio and -10-dB cross-polarization levels along the boresight direction. The overall volume of the antenna is 0.24 × 0.10 × 0.05 λ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , where λ is the wavelength of the lowest operating frequency.

A Broadband Dual-Element Folded Dipole Antenna With a Reflector

A wideband dual-element planar folded dipole antenna is proposed in this letter. It is composed of a pair of asymmetric coplanar strip folded dipoles. The dual-element folded dipole antenna is fed by a microstrip feedline. With suitable design of the asymmetric coplanar strip folded dipole and the microstrip feedline, a 10-dB return-loss operating bandwidth of 107% (1.23 ~ 4.07 GHz) is achieved. By adding a metal plate, a wideband unidirectional antenna can be obtained with a measured impedance bandwidth of 113% (1.15 ~ 4.07 GHz) with better than 10 dB return loss. Its fabricated prototype is also measured with stable unidirectional radiation patterns in working band 1.13 ~ 3.3 GHz with a gain in + z-direction higher than 8.2 dBi and a front-to-back ratio better than 11.5 dB.

WIDEBAND VERTICAL PLANAR PRINTED UNIDIRECTIONAL ANTENNA

A new wideband vertical planar printed unidirectional antenna is presented. The proposed antenna is composed of a bowtie electric dipole, a loop antenna and a microstrip-to-coplanar stripline balun. All of them are printed in the same plane perpendicular to the ground. The antenna has a wide impedance bandwidth of 88.9% for SWR • 2 from 3.3 to 8.58GHz and a stable gain of 7:3 § 1:5dBi over the operating frequencies. Moreover, stable unidirectional radiation pattern with low back-lobe radiation, low cross polarization and nearly identical E- and H-plane patterns is also demonstrated over the frequency of interest. A prototype is fabricated and measured. The measured results indicate that the antenna is suitable for wideband wireless communication system.

Triple-Band Unidirectional Circularly Polarized Hexagonal Slot Antenna With Multiple L-Shaped Slits

The design of a triple-band circularly polarized hexagonal slot antenna with L-shaped slits is presented in this study. By adding three L-shaped slit arms to the hexagonal slot, circularly polarized radiation is achieved at three different frequencies. The proposed slot antenna is excited by a simple tapered microstrip feeding line. A conducting reflector is also used to enhance the antenna gain. The measured -10 dB reflection bandwidths are 33.16% (3.22-4.5 GHz) and 22.72% (4.76-5.98 GHz). The measured 3 dB axial ratio bandwidths for the triple bands are 1.7%, 3.86%, and 5.23%, respectively. The measured peak gains within the 3 dB axial ratio bands are 5.5 dBic, 4.63 dBic, and 6.77 dBic.

Single-element based ultra-wideband antenna array concepts for wireless high-precision 2-D local positioning

Abstract. We generally categorize the approaches for ultra-wideband antenna array design, and consequently propose simplified concepts for antenna arrays for a high-precision, ultra-wideband FMCW radar 2-D local positioning system to obtain robustness against multi path interference, perform angle of arrival analysis, as well as instantaneous heading estimation. We focus on low-cost and mechanical robust, industrial-application ready antennas. The antenna arrays are optimized for operation in the 5 GHz to 8 GHz frequency range and are designed towards supporting full omnidirectional 360° as well as partial half-plane direction of arrival estimation. Two different concepts for vehicle- as well as wall-mounted antenna array systems are proposed and discussed. We propose a wideband unidirectional bow-tie antenna array element having 97% impedance and 37% pattern bandwidth and a robust vehicle mounted omnidirectional antenna element having more than 85% impedance and pattern bandwidth.

Unidirectional wideband circularly polarised aperture antennas backed with artificial magnetic conductor reflectors

The reflection coefficient phase is studied for four different artificial magnetic conductors (AMCs) having canonical frequency selective surface (FSS)-type two-dimensional periodic structures to be used as back reflectors for an aperture antenna. The bidirectional circularly polarised (CP) radiation of the octagonal-shaped aperture (OSA) antenna is made unidirectional using these AMC surfaces as ground planes. The antenna height measured from the upper surface of AMC reflector to the OSA radiator is chosen to be small to realise low-profile antenna: 0.0825λ o at the lowest analysis frequency of 4.5 GHz. Different antenna parameters like voltage standing wave ratio (VSWR) of 2, 3-dB axial ratio (AR) bandwidth, gain, and front-to-back ratio are studied and compared for these four AMCs and the conventionally used perfect electric conductor (PEC) ground plane as back reflectors. Four different aperture shapes with fixed aperture perimeter are designed to integrate with the square-loop AMC as back reflector to realise a low-profile unidirectional wideband CP aperture antenna. Hexagonal-shaped aperture antenna over the square-loop AMC shows the largest measured 3-dB AR bandwidth of 23.33% (5.65-7.05 GHz), VSWR of 2 bandwidth of 36.67% (5.16-7.36 GHz), and the gain of around 7 dBic over the band for overall antenna volume of 0.72λ o × 0.60λ o × 0.19λ o at 6.0 GHz.

Vertical Planar Printed Unidirectional Antenna

A novel printed vertically oriented unidirectional antenna is proposed. The proposed antenna is composed of a bowtie-shaped electric dipole, a loop antenna that works as a magnetic dipole, and a microstrip-to-stripline transition balun. All of them are printed in the same plane perpendicular to the ground. With a single vertical planar structure as well as large beamwidth, the proposed antenna would find itself suitable for improving the H-plane maximum steering angle when involved in an array application. The antenna operates at 2.6 GHz with an impedance bandwidth of 17.1% for SWR ≤ 2, stable unidirectional radiation pattern with low cross polarization, low back radiation, nearly identical E- and H-plane patterns, and stable gain of around 6.5 dBi over the operating frequencies. The antenna also fulfills the requirement for outdoor applications as it is direct current (dc) grounded.

Range-Free Localization Scheme in Wireless Sensor Networks Based on Bilateration

A low-cost yet effective localization scheme for wireless sensor networks (WSNs) is presented in this study. The proposed scheme uses only two anchor nodes and uses bilateration to estimate the coordinates of unknown nodes. Many localization algorithms for WSNs require the installation of extra components, such as a GPS, ultrasonic transceiver, and unidirectional antenna, to sensors. The proposed localization scheme is range-free (i.e., not demanding any extra devices for the sensors). In this scheme, two anchor nodes are installed at the bottom-left corner (Sink X) and the bottom-right corner (Sink Y) of a square monitored region of the WSN. Sensors are identified with the same minimum hop counts pair to Sink X and Sink Y to form a zone, and the estimated location of each unknown sensor is adjusted according to its relative position in the zone. This study compares the proposed scheme with the well-known DV-Hop method. Simulation results show that the proposed scheme outperforms the DV-Hop method in localization accuracy, communication cost, and computational complexity.

Design of Multiplate Back-Reflector for a Wideband Slot Antenna

A novel multiplate back-reflector wide-bandwidth unidirectional slot antenna is presented in this letter. The proposed structure not only maintains the wideband nature of slot structure, but also exhibits stable antenna gain and better front-to-back (F/B) ratio over the frequency band of interest. A slot antenna consisting of a pair of matching disc patches and a microstrip feeding line is employed to demonstrate the advantages of the new reflector structure. Four smaller metallic plates in different distances are used. Initial parameter measurement of the new slot antenna is conducted. The result shows an impedance bandwidth can exceed the original slot antenna bandwidth for <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$S_{11}\leq-10~$</tex></formula> dB in the range 1.56–3.14 GHz, stable gain more than 8.5 dB, and F/B ratio higher than 17 dB, with unidirectional radiation patterns and low cross polarization over the whole operating band. Those performances are exceeding the performance that a conventional back-reflector slot antenna can obtain.

Unidirectional Dual-Band CPW-Fed Antenna Loaded with an AMC Reflector

A unidirectional dual-band coplanar waveguide fed antenna (DB-CPWFA) loaded with a reflector is presented in this paper. The reflector is made of an electric ground plane, a dielectric substrate, and artificial magnetic conductor (AMC) which shows an effective dual operational bandwidth. Then, the closely spaced AMC reflector is employed under the DB-DPWFA for performance improvement including unidirectional radiation, low profile, gain enhancement, and higher front-to-back (F/B) ratio. The final antenna design exhibits an 8% and 13% impedance bandwidths for 2.45 GHz and 5.8 GHz frequency regions, respectively. The overall gain enhancement of about 4 dB is achieved. The F/B ratio is approximate to 20 dB with a 16 dB improvement. The measured results are inconsistent with the numerical values. The presented design is a suitable candidate for radio frequency identification (RFID) reader application.

A Wideband Printed Quadruple-Element Antenna With Integrated Balun

A printed ultrawideband (UWB) unidirectional quadruple element antenna is presented. The antenna is composed of four radiating elements with corrugated boundaries and a microstrip-to-double-sided parallel-strip line transition. The antenna size is 0.285λL × 0.285λL × 0.174λL at the lower operating frequency. Experimental results reveal that it can achieve an impedance bandwidth of 83.7% for VSWR <; 2 and a stable unidirectional radiation pattern with measured gain around 6.7 dB. Simulated and measured results are given, and they agree well with each other.

A Dual-Wideband Double-Layer Magnetoelectric Dipole Antenna with a Modified Horned Reflector for 2G/3G/LTE Applications

A novel dual-wideband double-layer magnetoelectric dipole unidirectional antenna with a modified horned reflector for 2G/3G/LTE applications is proposed. Firstly, a double-layer electric dipole structure is presented to provide a dualwideband, whose folded lower layer mainly serves the lower frequency band while the inclined upper layer works for the upper frequency band. In addition, to reduce the size of the antenna and improve impedance matching, a new feeding structure designed with inverted U-shaped and tapered line is introduced. Finally, a modified horn-shaped reflector, instead of a ground plane, is employed to achieve stable and high gains. The antenna prototype can achieve a bandwidth of 24.4% (790 MHz–1010 MHz) with a stable gain of 7.2 ± 0.6 dBi for the lower band, and a bandwidth of 67.3% (1.38 GHz–2.78 GHz) with a gain of 7.5 ± 0.8 dBi for the upper band covering all the frequency bands for 2G/3G/LTE systems. To the best of our knowledge, it is the first double-layer magnetoelectric dipole antenna proposed. Compared with the existing ME dipole antennas, the proposed antenna, which is completely made of copper, can be easily fabricated at low cost and thus is practicable for 2G/3G/LTE applications.