Showing papers on "Front-to-back ratio published in 2013"

Flexible and Compact AMC Based Antenna for Telemedicine Applications

Abstract: We present a flexible, compact antenna system intended for telemedicine applications. The design is based on an M-shaped printed monopole antenna operating in the Industrial, Scientific, and Medical (ISM) 2.45 GHz band integrated with a miniaturized slotted Jerusalem Cross (JC) Artificial Magnetic Conductor (AMC) ground plane. The AMC ground plane is utilized to isolate the user's body from undesired electromagnetic radiation in addition to minimizing the antenna's impedance mismatch caused by the proximity to human tissues. Specific Absorption Rate (SAR) is analyzed using a numerical human body model (HUGO) to assess the feasibility of the proposed design. The antenna expresses 18% impedance bandwidth; moreover, the inclusion of the AMC ground plane increases the front to back ratio by 8 dB, provides 3.7 dB increase in gain, in addition to 64% reduction in SAR. Experimental and numerical results show that the radiation characteristics, impedance matching, and SAR values of the proposed design are significantly improved compared to conventional monopole and dipole antennas. Furthermore, it offers a compact and flexible solution which makes it a good candidate for the wearable telemedicine application.

Dielectric Resonator Antenna for X band Microwave Application

Abstract: A simple Dielectric Resonator Antenna (DRA) for X band frequency operation is proposed in this paper. X band is a microwave band lies between frequency range 8 to 12 GHz. In proposed DRA reflector plane is used beneath the microstrip feed line with a small air gap, introduced between feed substrate and reflector plane to reduce the back lobe. Slot coupling is used to excite this DRA. Proposed DRA design gives dual band operation in X band and resonates at frequency 8.6 GHz and 10.3 GHz. Antenna design offers minimum return loss of -20.3 db and -24.5 db at 8.6 GHz and 10.3 GHz respectively. It also offers high front to back ratio (FBR) of 12.35db and 9.83 db at 8.65 GHz and 10.3 GHz respectively. Return loss impedance bandwidth of 390 MHz (4.5%) for Band I and 730MHz (7.3%) for band II is obtained. Simple DRA design with high FBR is proposed here for X band application that shows a total bandwidth of 11.8%. DRA is analysed using Ansoft HFSS based on finite element method. Radiation characteristics of this DRA are observed at resonating frequencies. This DRA is useful at microwave X band application such as satellite communication.

Development of a Low-Profile Circularly Polarized Cavity-Backed Antenna Using HMSIW Technique

Abstract: In this paper, two single fed low-profile cavity-backed planar slot antennas for circular polarization (CP) applications are first introduced by half mode substrate integrated waveguide (HMSIW) technique. One of the structures presents right handed CP (RHCP), while the other one offers left handed CP (LHCP). A single layer of low cost printed circuit board (PCB) is employed for both antennas providing low-cost, lightweight, and also easy integration with planar circuits. An inset microstrip line is used to excite two orthogonal quarter-wave length patch modes with required phase difference for generating CP wave. The new proposed antennas are successfully designed and fabricated. Measured results are in good agreement with those obtained by numerical investigation using HFSS. Results exhibit that both antennas present the advantages of conventional cavity backed antennas including high gain and high front to back ratio (FTBR).

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

Abstract: 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.

Small Director Array for Low-Profile Smart Antennas Achieving Higher Gain

Abstract: A small director array (SDA) is an antenna gain enhancing section of the low-profile smart antenna which can be used as a fixed array or reconfigurable array using switched parasitic elements. Gain improvements up to +10 dBi are achieved in the SDA through a Yagi-Uda configuration using parasitic elements with a large diameter. The array height is reduced by 50% comparing with the standard Yagi-Uda antenna. The reconfigurable SDA used an electronically steerable switched parasitic arrangement so that the beam can be steered from 0° to 360° in the horizontal plane. The height of the reconfigurable SDA is 0.2 λ. The measurements proved that the reconfigurable SDA can increase the antenna gain by 3 dB. The front to back ratio showed significant improvement. The proposed SDA also had the advantages of low cost and low power consumption, thus promising for applications in small satellites, unmanned aerial vehicles and mobile terminals.

Metasurface-loaded circularly-polarised slot antenna with high front-to-back ratio

Abstract: A new technique to achieve high front-to-back radiation ratios of slot antennas is presented. A 0.8 mm thin metasurface is loaded onto a circularly-polarised slot antenna and backed by a metallic reflector at close distances. The antenna has an overall height of ∼ 0.1 wavelengths. However, it exhibits wideband characteristics with a measured impedance bandwidth (voltage standing-wave ratio ≤ 2) of 73.3% and a 3 dB axial-ratio bandwidth of 29.1%. A broadside gain of 7 dBic with a front-to-back ratio of 23.7 dB is achieved at 2.7 GHz.

Bandwidth enhancement of substrate integrated waveguide cavity backed slot antenna by offset feeding technique

Abstract: In this paper, a novel technique to enhance the bandwidth of substrate integrated waveguide cavity backed slot antenna is demonstrated. The feeding technique to the cavity backed antenna has been modified by introducing offset feeding of microstrip line along with microstrip to grounded coplanar waveguide transition which helps to excite TE 120 mode in the cavity and also to get improvement in impedance matching to the slot antenna simultaneously. The proposed antenna is designed to resonate in X band (8–12 GHz) and shows a resonance at 10.2 GHz with a bandwidth of 4.2% and a gain of 5.6 dBi, 15.6 dB front to back ratio and −30 dB maximum cross polarization level.

4-Element Yagi array of microstrip quarter-wave patch antennas

Abstract: A new kind of Yagi array of microstrip quarter-wave patch antennas is presented. The antenna array has a low profile and provides a high gain and a vertical polarization at endfire. Compared with previous Yagi array of microstrip half-wave patch antennas, the Yagi array of quarter-wave patch antennas has a smaller size and does not suffer the constraint in dielectric constant in the substrate. Besides, the presented Yagi array generates a main beam pointing closer to endfire than the Yagi array of half-wave patch antennas. Measured results show that the presented Yagi array with 4 elements would generate a peak gain of about 9.7 dBi, an endfire gain of about 4.5 dBi, and a bandwidth of 11.3% for a profile of 0.026 wavelengths. The front-to-back ratio of the Yagi array is higher than 10 dB.

Design of Printed Yagi Antenna with Additional Driven Element for WLAN Applications

Abstract: A new conflguration of Yagi antenna is proposed, which can improve the forward/backward ratio (f/b) signiflcantly while maintaining a high gain. This conflguration involves the addition of one radiating element to the original Yagi array. This additional element may arrange on parallel (side-by-side) or collinear to a radiating dipole of the original Yagi antenna. It is shown here that the technique is most efiective for collinear conflguration (exhibits smaller mutual efiects) and that there then exists an optimum length and position for the added element. The amplitude of the excitation of the additional element determines the angular location of the back lobe reduction. To demonstrate the major beneflts, comparisons are made among the proposed and conventional Yagi conflgurations. Numerical and measured results of our design show more than 20dB front to back ratio at 2.4GHz. Moreover, the proposed array represents a simple and valuable alternative to the stack Yagi antennas as the obtainable radiation characteristics are satisfactory in terms of both forward and backward gain.

Effect of Partial Ground Plane Removal on the Radiation Characteristics of a Microstrip Antenna

Abstract: This study presents a new, simple method for reducing the back-lobe radiation of a microstrip antenna (MSA) by a partially removed ground plane of the antenna. The effect of the partial ground plane removal in different configurations on the radiation characteristics of a MSA are investigated numerically. The partial ground plane removal reduces the backlobe radiation of the MSA by suppressing the surface wave diffraction from the edges of the antenna ground plane. For further improving the front-to-back (F/B) ratio of the MSA, a new soft-surface configuration consisting of an array of stand-up split ring resonators (SRRs) are placed on a bare dielectric substrate near the two ground plane edges. Compared to the F/B ratio of a conventional MSA with a full ground plane of the same size, an improved F/B ratio of 9.7 dB has been achieved experimentally for our proposed MSA.

Compact, two-element array with high broadside directivity

Abstract: A combination of two high directivity, electrically small, slot-modified conducting disc-augmented Egyptian axe dipole (EAD) antennas is investigated to achieve interesting broadside radiation properties, including a high broadside directivity and front-to-back ratio. Their array arrangement is guided by a simple two-element dipole model. The parasitic conducting disc associated with each EAD antenna is modified only slightly from their original single-element dimensions to preserve nearly complete matching to their sources, to accommodate the coupling between the two elements and to maximise the array pattern characteristics. Parameter studies lead to a final design, whose simulation results demonstrate that the two-element array has outstanding performance characteristics, including a 9.98 dB broadside directivity, an 88.19% radiation efficiency, a 20.03 dB front-to-back-ratio, a - 22.42 dB mutual coupling level, more than a 30 dB level of polarisation purity, and good impedance matching to their respective 50 Ω sources, despite each antenna being electrically small, that is, ka <; 1, and the distance between the centre of each element being only slightly larger than a half wavelength.

Investigations of corrugation issues in SIW based Antipodal Linear Tapered Slot Antenna at 60 GHz

Abstract: In recent days, Substrate Integrated Waveguide (SIW) technology is attracting a lot of interest in the development of Millimeter-wave (MmW) based circuits due to its inherent advantages This paper focuses on the design of Antipodal Linear Tapered Slot Antenna (ALTSA) using SIW technique for Wireless Local Area Network (WLAN) and Wireless Personal Area Network (WPAN) applications The feeding is based on SIW structure which provides high Q-factors and allows planar printed circuit board fabrication process In this paper ALTSA at 60 GHz without corrugation and with inner and outer rectangular corrugation have been discussed and compared with traditional structure with the new corrugated structures It is noticed that, the proposed ALTSA designs are having better front to back ratio (F/B) and radiation patterns Though, such developments have been reported earlier in other frequency bands, rarely any literature have reported of such developments at 60 GHz band

An efficient, electrically small antenna with large impedance bandwidth simultaneously with high directivity and large front-to-back ratio

Abstract: Non-Foster element-augmented, electrically small electric and magnetic antennas have been designed, characterized numerically, fabricated and tested. Specifically tailored broad bandwidth inductive and capacitive devices were introduced into the near-field resonant parasitic (NFRP) components of their narrow bandwidth counter-parts. This internal non-Foster element approach led to nearly complete matching of the entire system to a 50 Ω source without any matching network and high radiation efficiencies over a 10dB fractional bandwidth that surpasses the fundamental passive bound. By including additional resonant parasitic elements, one can also enhance the directivity. Further augmentation of those parasitic elements with a non-Foster device leads to a large directivity bandwidth. A 300 MHz design with ka = 0.94 is reported which simultaneously achieves high radiation efficiencies (>81.63%), high directivity (> 6.25 dB) and large front-to-back-ratios (> 26.71 dB) over a 10.0% fractional bandwidth.

Novel EBG grounded PIFA for improved directivity in mobile communication bands

Abstract: A Novel EBG grounded PIFA has been designed for Universal Mobile Telecommunication System (UMTS) frequency band (2.1 GHz) with good directivity. In this paper a uniplanar compact Electromagnetic Band Gap (UC-EBG) structure is designed to use as ground for a Planar Inverted F Antenna (PIFA), to improve its radiation pattern and suppress the surface waves. The proposed EBG grounded PIFA has shown improvement over conventional PIFA in directivity, front to back ratio and radiation pattern. The front to back ratio has been improved from 8.75 dB to 15.80 dB.

Compact low profile antenna based on MSRR-AMC reflector

Abstract: This paper is dedicated to the study of volumetric MSRR-based AMC structure. The characteristics of a single MSRR unit cell are investigated; and a volumetric miniaturized AMC block is then designed. In order to validate the approach used to simulate an infinite periodic structure, a block of nine aligned layers is then simulated. The next step is to add a printed dipole antenna as an application to validate the performance of the AMC block. The results are very excellent and promising if compared with the simple dipole antenna as an enhancement of 5 dB is achieved considering the directivity. The front to back ratio is found to be about 20 dB.

Reflector with designed EBG cells for ultrawideband antenna performance improvement

Abstract: In this article, a frequency selective surface (FSS) cell is proposed. The band stop frequency performance is compared between the two and four layer FSS structure with the proposed cells. The four-layer structure has the same low frequency as the two-layer structure, but the four-layer structure has 3.6 GHz wider stop band in high frequency. Then, a reflector with the proposed EBG cells for ultrawideband antenna is developed. The performance for the reference antenna with and without the proposed reflector was compared, the average improvement of the front-to-back ratio of the UWB antenna with designed FSS reflector is 15 dB from 3.1 to 10.6 GHz and the peak even can get to 30 dB at 5 GHz. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2541–2544, 2013

Back Radiation Suppression in Modified Aperture Coupled Microstrip Antenna by using patches under the substrate

Abstract: A microstrip slot antenna for C Band has been proposed with compact structure and suppressed back radiation. In this paper, the feeding technique used is aperture coupling with a modification that patches and the feed line are positioned below the substrate and the slot is etched above the substrate. The position of the patches along the slot axis is kept at the negative peak of the standing wave distributions to generate the voltage null on the slot line so as to have a 180o phase shift in the centre of the patch hence achieving better front to back ratio. Also the gain of 6.774dB is achieved in this design. The results are validated by simulation measurements.

Volumetric MSRR-based AMC for low-profile antenna application

Abstract: This paper is dedicated to the study of volumetric MSRR-based AMC structure. The characteristics of a single MSRR unit cell are investigated; and a volumetric miniaturized AMC block is then designed. In order to validate the approach used to simulate an infinite periodic structure, a block of nine aligned layers is then simulated. The next step is to add a printed dipole antenna as an application to validate the performance of the AMC block. The results are very excellent and promising if compared with the simple dipole antenna as an enhancement of 5 dB is achieved considering the directivity. The front to back ratio is found to be about 20 dB.

Dielectric Resonator Antenna for X bandMicrowave Application

Abstract: A simple Dielectric Resonator Antenna (DRA) for X band frequency operation is proposed in this paper. X band is a microwave band lies between frequency range 8 to 12 GHz. In proposed DRA reflector plane is used beneath the microstrip feed line with a small air gap, introduced between feed substrate and reflector plane to reduce the back lobe. Slot coupling is used to excite this DRA. Proposed DRA design gives dual band operation in X band and resonates at frequency 8.6 GHz and 10.3 GHz. Antenna design offers minimum return loss of -20.3 db and -24.5 db at 8.6 GHz and 10.3 GHz respectively. It also offers high front to back ratio (FBR) of 12.35db and 9.83 db at 8.65 GHz and 10.3 GHz respectively. Return loss impedance bandwidth of 390 MHz (4.5%) for Band I and 730MHz (7.3%) for band II is obtained. Simple DRA design with high FBR is proposed here for X band application that shows a total bandwidth of 11.8%. DRA is analysed using Ansoft HFSS based on finite element method. Radiation characteristics of this DRA are observed at resonating frequencies. This DRA is useful at microwave X band application such as satellite communication.