Wideband microstrip‐fed tapered slot antennas and phased array

Two wideband tapered slot antennas are designed, fabricated, and tested. The first antenna, which is fabricated on a high dielectric constant substrate (?_r = 10.2), shows a measured return loss of better than 10 dB from 1.6 to 12.4 GHz (7.7:1 bandwidth), and an antenna gain varying from 3.6 to 7.8 dBi. The second antenna is built on a low dielectric constant substrate (?_r = 2.2), and demonstrates return loss of better than 10 dB from 1.8 to 15.2 GHz (8.4:1 bandwidth). The second antenna also has improved antenna gain, from 5 to 15.6 dBi, and is used to build a wideband 1 × 4 H‐plane phased array with a total gain of 9–17 dBi and a beam steering angle of ±15° from 3 to 12 GHz. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

A broadband slant polarized cavity backed microstrip‐fed wide‐slot antenna array

This article deals with the design of a broadband cavity‐backed microstrip‐fed wide‐slot antenna array for L‐band applications. For verification purpose, a sample 1 × 4‐element antenna array has been designed, manufactured and tested. Experimental results have shown satisfactory agreement with the simulation. The proposed antenna array exhibits a measured impedance bandwidth of 1.4 GHz (90%) with frequency of 0.85 to 2.25 GHz and the gain is higher than 11 dBi. The designed antenna has small size and low weight and can be fabricated using a low‐cost fabrication process for easy integration with RF circuits and microwave components. This work is useful for some radar applications and radio frequency identification systems.     

Planar UWB antenna with modified slotted ground plane

A compact coplanar waveguide‐fed (CPW) monopole antenna for ultra‐wideband wireless communication is presented. The proposed antenna comprises of a CPW‐fed beveled rectangular patch with a modified slotted ground. The overall size of the antenna is 30 mm × 27 mm × 1.6 mm. The lower edge of the band is attained by properly decoupling the resonant frequencies due to the extended ground plane and the beveled rectangular patch of the antenna. The upper edge of the radiating band is enhanced by beveling the ground plane corners near the feed point. Experimental results show that the designed antenna operates in the 2.7–12 GHz band, for S₁₁ ≤ ?10 dB with a gain of 2.7–5 dBi. Both the frequency domain and time domain characteristics of the antenna are investigated using antenna transfer function. It is observed that the antenna exhibits identical radiation patterns and reasonable transient characteristics over the entire operating band. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Wideband asymmetric microstrip‐fed circularly polarized antenna with monofilar spiral stub for WLAN application

A wideband circularly polarized printed antenna is proposed and fabricated, which employs monofilar spiral stubs and a slit in the asymmetrical ground plane which are fed by an inverted L‐shaped microstrip feedline. The CP operation is realized by embedding an inverted‐L shaped strip and modified ground plane and can be markedly improved by loading monofilar spiral stubs asymmetrically connected at the edge of the ground plane. After optimization, the measured results of the finally structure demonstrate that a 10‐dB bandwidth of 67.6% from 4.6 to 9.3 GHz and a 3‐dB axial‐ratio bandwidth (ARBW) for circular polarization (CP) of 60.1% from 5 to 9.3 GHz could be achieved which could completely cover the WLAN (5.725‐5.85 GHz) band. Therefore, the proposed antenna is suitable for circular polarization applications in C band. To explain the mechanism of broadband circular polarization operation, the analysis of magnetic fields distributions and a parametric study of the design are given. Compared to other recent works, a simpler structure, wider axial ratio and impedance bandwidths and a more compact size are the key features of the proposed antenna.     

Wideband circularly polarized hybrid dielectric resonator antenna with bi‐directional radiation characteristics for various wireless applications

In this article, a wideband circularly polarized (CP) dielectric resonator (DR) over an asymmetric‐slot radiator based hybrid‐DR antenna is proposed with bi‐directional radiation characteristics. Bi‐directional CP radiation of the dual sense is obtained using a rectangular‐DR over asymmetric‐rectangular‐slot radiator with L‐shaped feed line. The asymmetric‐slot radiator feed by L‐shaped stub with the coplanar waveguide is used for generating two orthogonal modes, namely TE ^x _δ11 and TE^y_1δ1 in the combined (rectangular‐DR and asymmetric‐slot radiator) hybrid‐DR antenna, which is verified by the distribution of electric field inside the rectangular DRA. The measured reflection coefficient bandwidth (S₁₁ < ?10 dB) and axial ratio (AR) bandwidth (AR < 3 dB) of the hybrid‐DR antenna are 80.5% (1.87‐4.39 GHz) and 43.8% (1.75‐2.73 GHz), respectively. The antenna radiation is in the broadside (θ = 0°, ? = 0°) direction as well as in the backside (θ = 180°, φ = 0°) direction with equal magnitudes in both the directions. Right‐handed and left‐handed CP waves are achieved respectively, in the boresight (+Z) and the backside (?Z) directions. The proposed CP hybrid‐DR antenna gives an average gain of 3.55 dBic and radiation efficiency of 95.0% in both directions. The proposed antenna covers various wireless useful bands such as ISM 2400 band, Wi‐Fi, Bluetooth, and Wi‐MAX (2.5‐2.7 GHz).     

A wearable flexible microstrip antenna based on the floating‐ground backplane

In the present study, a wearable coplanar waveguide fed flexible microstrip antenna is proposed, which is based on the floating‐ground backplane. When the antenna is placed on a high‐loss human body, the antenna maintains reasonable impedance matching and exhibits a peak gain of 5.6 dBi. Moreover, the performance of the antenna under different bending radii and crumpling conditions is also analyzed. The simulation and experimental results show that the bending and crumpling have little effect on the impedance bandwidth and radiation pattern of the proposed antenna. Accordingly, it is concluded that the proposed antenna has great robustness. Furthermore, it is found that the proposed floating‐ground backplane structure significantly reduces the backward radiation of the planar antenna and enables the antenna to obtain a very low specific absorption rate (SAR) and increase the antenna gain. It should be indicated that antennas with great robustness, very low SAR, and small size are ideal candidates for wearable applications.     

A low‐profile,dual‐polarized,and wideband square cavity‐backed antenna

A cavity‐backed antenna with low‐profile, dual‐polarization, and wide operating bandwidth characteristics is proposed. In this design, two orthogonally positioned triangular bowtie antennas printed on a low‐cost substrate are loaded onto a square cavity, so that two orthogonal linear polarizations can be excited. By further introducing four extended ground stubs from each side of the square cavity, the proposed antenna can also acquire low‐profile characteristic of approximately 0.1λ (15 mm). To achieve good impedance matching, additional circular slots are introduced into each bowtie design. The measured results show that the proposed antenna can cover a wide operating bandwidth of 62% (2.0–3.8 GHz) with a VSWR of 2:1. Besides exhibiting good isolation (>20 dB) between the two feeding ports, desirable realized gains (6.0–10.5 dBi) over the wide operation band are also demonstrated. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:724–730, 2016.     

Wideband mobile antenna design based on artificial neural network models

A compact wideband planar monopole antenna is designed and optimized based on artificial neural network (ANN) models. The antenna is suitable for DCS, PCS, DECT, PHS, IMT‐2000, UMTS, and WLAN in mobile communication. The design time decreases dramatically due to using the ANN models. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 316–320, 2003.     

Simulation‐based optimization for rigorous assessment of ground plane modifications in compact UWB antenna design

Introducing ground plane modifications is a popular approach in the design of compact UWB antennas. Yet, specific topological alterations are normally reported on case to case basis without thorough investigations concerning their general suitability for antenna miniaturization. In particular, detailed performance comparison of different ground plane modifications is lacking in the literature. In this article, the effect of selected ground plane modifications on achievable miniaturization rate is considered based on a set of four UWB antennas. EM‐driven optimization is carried out to minimize the antenna footprints while maintaining acceptable matching within the UWB frequency range. In each case, all geometry parameters of the respective structures are utilized in the design process. For the sake of fair comparison, all antennas are implemented on the same dielectric substrate. Our results indicate a clear performance pattern, here, an advantage of the elliptical ground plane slit below the feed line over the rectangular one (average size reduction ratio of 26% versus 19% across the benchmark set). Our conjectures are confirmed by physical measurements of the fabricated antenna prototypes.     

Wideband cavity‐backed log‐periodic‐slot end‐fire antenna with vertical polarization for conformal application

A 6–18 GHz wideband cavity‐backed log‐periodic‐slot end‐fire antenna with vertical polarization for conformal application is presented. The log‐periodic folded slots and parasitic slots with 10 slot elements are applied to cover 6–18 GHz frequency band and the log‐periodic metallic cavity is placed under each slot element to keep wideband performance and prevent the effects of large metallic carrier on radiation patterns. The ground plane etched with log‐periodic slots is reversed and touched directly to the backed cavity and a dielectric cover is added to the antenna, to further improve the antenna performance. Meanwhile, a broadband microstrip‐coplanar waveguide transition is inserted in the antenna for measurements. With these designs, the proposed antenna shows good impedance matching (|S₁₁|<27 dB) and end‐fire gain (>4 dBi) performances in 6–18 GHz. The proposed antenna also keeps low‐profile and easy flush‐mounted characteristic which is suitable for conformal applications of high speed moving carriers.     

A miniaturized ultra‐wideband planar monopole antenna with L‐shaped ground plane stubs

This article presents a miniaturized ultra‐wideband planar monopole antenna with an oval radiator. The proposed antenna is fed by a coplanar waveguide (CPW), and two L‐shaped stubs are extended from the ground plane of the CPW. This presented antenna is able to produce resonances in the lower frequency band and realize better impedance matching performance in the middle and higher frequency bands with the aid of the L‐shaped stubs. The antenna was built and tested. The total size of the proposed antenna is only 26 × 20 × 1.6 mm³. Its measured –10 dB impedance bandwidth is 10.1 GHz (3.1‐13.2 GHz). The measured far‐field radiation patterns are stable in the whole operating frequency band.     

Investigation on decoupling of wide band wearable multiple‐input multiple‐output antenna elements using microstrip neutralization line

An investigation to enhance the decoupling between the elements of a compact wide band multiple‐input multiple‐output (MIMO) antenna is presented in this communication. A microstrip neutralization line (NL) is designed on the top of antenna surface to enhance the port isolation. The geometry is embedded on a jeans material to be apposite for the on‐body wearable applications. The antenna covers the frequency spectra from 3.14 to 9.73 GHz (around 102.4%) and fulfills the bandwidth requirements of WiMAX (3.2‐3.8 GHz), WLAN (5.15‐5.35/5.72‐5.85 GHz), C band downlink‐uplink (3.7‐4.2/5.9‐6.425 GHz), downlink defense (7.2‐7.7 GHz), and ITU (8‐8.5 GHz) bands. The port isolation is found to be more than 32 dB over the whole application bands. The antenna is appraised in a rich scattering environment with very minimal envelope correlation coefficient (ECC < 0.12) and great amount of diversity gain (DG > 9.8). The proposed MIMO antenna system is able to achieve the channel capacity loss (CCL) of less than 0.2 BPS/Hz throughout the whole operating band. The proposed structure is etched on an area of 30 × 50 mm². The simulated and measured performances of the proposed antenna are in well‐matched state.     

Wideband circularly polarized dielectric resonator antenna loaded with partially reflective surface

A wideband circularly polarized (CP) dielectric resonator antenna (DRA) loaded with the partially reflective surface for gain enhancement is presented in this article. First, the DRA is excited by a microstrip line through modified stepped ring cross‐slot to generate the circular polarization. Four modified parasitic metallic plates are sequentially placed around the DRA for greatly widening the axial‐ratio bandwidth. Then, a partially reflective surface is introduced for enhancing the gain performance and further improving the CP bandwidth as well. Finally, an optimized prototype is fabricated to verify the design concept. The measured results show that the proposed DRA achieves 54.3% impedance bandwidth (VSWR<2) and 54.9% 3‐dB AR bandwidth. Besides, its average and peak gains are 10.7 dBic and 14.2 dBic, respectively. Wide CP band and high gains make the proposed DRA especially attractive for some broadband wireless applications such as satellite communication and remote sensing.     

Wideband omnidirectional circularly polarized antenna with offsetting slots and vertical strips

A wideband omnidirectional circularly polarized (CP) antenna is proposed in this paper. The antenna is comprised of two slotted square patches which are connected by four vertical metal strips at the edges and a simple feeding probe in the centre. Loop currents can be yielded on the patches when rotation‐symmetrically offsetting slots are cut. By combining the two orthogonal fields radiating from the loop and the feeding probe, omnidirectional circular polarization is obtained in the azimuth plane. One group of slots are cut to verify the CP performance and two groups of slots are cut to further broaden the operating bandwidth. Measured results show that the proposed antenna with a small size of 40 × 40 × 10 mm³ obtains an effective bandwidth of 22% (2.1–2.62 GHz) for |S₁₁| < ?10 dB and axial ratio < 3dB. © 2015 Wiley Periodicals, Inc. Int J RF and Microwave CAE 25:675–680, 2015.     

A wideband rectifier array on dual‐polarized differential‐feed fractal slotted ground antenna for RF energy harvesting

This article reports a novel wideband rectenna for RF energy harvesting applications. A wideband fractal slotted ground antenna (SGA) is adopted. The operating frequency bands of the antenna are GSM, UMTS, Wi‐Fi, and LTE2600/4G bands. The antenna is fed by a dual‐polarized and differential‐feed (DP‐DF) microstrip lines disposed with an angle of 90° each relative to the other. The feed lines are etched on the bottom side of the substrate and connected to an array of four wideband RF‐to‐DC rectifiers. A nonuniform transmission lines filter ensures wideband behavior for each rectifier. The rectenna performances are simulated and measured. The experiments show an output DC voltage of 1 V at a power density of 26.6 μW/cm² over the frequency band of operation with a peak efficiency of 50%. The proposed rectenna is suitable for energy harvesting applications in urban environments.     

Novel planar dual‐band balanced antipodal slot‐dipole composite antenna with reduced ground plane effect

A novel planar, dual‐band antenna composed of a symmetrical dipole and balanced antipodal slot radiator with low ground plane effect is proposed and investigated. Operation principle of the antenna is analyzed and design equations are drawn first. Then, the return loss, surface current distribution, radiation patterns, and gain are numerically and experimentally studied in detail. The impedance bandwidth of the antenna is from 2.36 to 2.56 and 5.13 to 12 GHz for return loss larger than 10 dB. The antenna has omnidirectional pattern at the lower band and quasi‐directional pattern at the higher band, and it has good immunity to a neighboring, large ground plane. The proposed antenna should be useful for dual‐band communication or identification systems. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.     

Compact microstrip‐via‐fed wideband circularly polarized antenna with monofilar spiral stub for C‐band applications

A wideband circularly polarized printed antenna is proposed and fabricated, which employs monofilar spiral stubs and a slit in the asymmetrical ground plane which is fed by an asymmetrical microstrip feedline using a via. The CP operation is realized by embedding an inverted‐L shaped strip and a modified ground plane and can be markedly improved by loading monofilar spiral stubs connected to the asymmetric feedline by means of a via. A parametric study of the key parameters is made and the mechanism for circular polarization is described. After optimization, the impedance bandwidth is approximately 3.6 GHz (4.4‐8 GHz) and the 3 dB axial ratio bandwidth is approximately 3.3 GHz (4.7‐8 GHz), which represent fractional bandwidths of approximately 58.1% and 52%, respectively. Therefore, the proposed antenna is suitable for circular polarization applications in C (4‐8 GHz) band. Compared with other recent works, the simpler structure, wider axial ratio, impedance bandwidths, and more compact size are the key features of the proposed antenna.     

Design of high gain/directional ultra‐wideband antenna for radar imaging systems

A compact size of 40 × 40 mm² ( λ₀ × λ₀ ) semi‐elliptical slotted ground structure (SESGS) directional ultra‐wideband (UWB) antenna is proposed for radar imaging applications. A vertical semi‐elliptical slot is inserted into ground and subsequently, an axis of semi‐ellipse is rotated diagonally (with 45°) in direction of the substrate. Axes of semi‐ellipse are optimized symmetrically around the circular patch to work antenna as a reflector. Furthermore, semi‐elliptical slot is rotated horizontally (with 90°) again to improve the impedance bandwidth. Proposed antenna achieves fractional bandwidth around 83% covering the UWB frequency range from 4.40 to 10.60 GHz (S₁₁ < ?10 dB) having 4.5/6/7/8/9.3/10.2 GHz resonant frequencies. Also, antenna is capable to send low‐distortion Gaussian pulses with fidelity factor more than 95% in time‐domain. Measured gain and half power beam width (HPBW) are 6.1‐9.1 dBi and 44°‐29° in 4.40‐10.60 GHz band, respectively, which show an improvement of 1‐3 dBi in gain and half power beam‐width is reduced by 5°‐10° when compared with previously designed antennas. Experimental results show good agreement with CST simulation.     

Broadband gap‐coupled half‐hexagonal microstrip antenna fed by microstrip‐line resonator

Half‐hexagonal microstrip antenna (H‐HMSA) is a compact version of HMSA, as it resonates at the same fundamental mode frequency. In this article, a compact configuration of a single layer, broadband gap‐coupled H‐HMSA has been proposed. Gap‐coupled H‐HMSA is fed indirectly by a λ/2 microstrip‐line resonator. Broad bandwidth (BW) is achieved with an effective use of resonance introduced by λ/2 resonator and gap‐coupled half‐hexagonal radiating patches. A peak gain of 7.07 dBi and measured BW (S₁₁ ≤ ?10 dB) of 11.5% at the center frequency of 5.2 GHz have been achieved, which occupies a small volume of 0.023 λ₀³ including the ground plane. The radiation patterns remain in the broadside direction throughout the return loss BW. Simulated results of the proposed antenna configuration are experimentally validated with good agreement.     

Dielectric‐loaded trapezoidal toothed log‐periodic antenna

In this article, dielectric‐loaded metal trapezoidal toothed log‐periodic antenna (TTLPA) is described. The dielectric material, Rogers RT/duroid 6010 (ε _r = 10.2, tan δ = 0.0023) of thickness = 5 mm and of same shape as TTLPA is placed on top of conventional metal TTLPA which provides enhanced bandwidth and/or miniaturizes its aperture size without degradation in gain. The dielectric loading increases the effective length of antenna, and therefore, extends its operating frequency towards lower frequency side which miniaturizes aperture cross‐section of antenna with slight increase in its thickness. The simulated input and radiation characteristics of TTLPA without and with dielectric loading are compared. The comparative studies show that the proposed antenna is 38.78% smaller in respect of aperture cross‐section as compared with conventional antenna having almost identical bandwidth of 8.6 GHz (2.2–10.8 GHz) and gain variation over the range 1.5–6.1 dBi. The proposed antenna of aperture size 48.9 × 48.9 mm² provides ?10 dB reflection coefficient bandwidth of 8.6 GHz (2.2–10.8 GHz) and gain variation in the range 1.3–5.7 dBi whereas the conventional antenna of same aperture size achieves somewhat reduced bandwidth of 7.6 GHz (3.2–10.8 GHz) and gain variation in the range 1.6–5.0 dBi over the operating frequency range.