Showing papers on "Front-to-back ratio published in 2010"

Circularly Polarized Stacked Annular-Ring Microstrip Antenna With Integrated Feeding Network for UHF RFID Readers

Abstract: A novel circularly polarized (CP) annular-ring microstrip antenna (ARMSA) is proposed for American ultrahigh frequency (UHF) radio frequency identification (RFID) readers. The annular ring is fed by an equal-split power divider with 90° phase difference. For the compactness of the entire antenna, the divider with the shape of Archimedes gradual-change lines is designed at the inside of the annular ring. A circular parasitic patch is suspended above the ring to improve the impedance matching and bandwidth. It also enhances the performances of axial ratio (AR). The impedance bandwidth for S11 <; -10 dB and 3-dB AR bandwidth are 870-967 MHz (10.6% at 915 MHz) and 893-948 MHz (6%), respectively. The CP gain is 8.9 dBi at 915 MHz with the front-to-back ratio (F/B) of 16.5 dB. The proposed antenna is low profile as the total height is 0.043 λ0 (λ0 is the free-space wavelength).

Frequency Selective Surfaces for Extended Bandwidth Backing Reflector Functions

Abstract: This paper deals with the use of frequency selective surfaces (FSS) to increase the efficiency X bandwidth product in wideband antenna arrays, whose efficiency is limited by the front-to-back ratio. If the backing reflector for the antenna is realized through a single metal plane solution, its location will be suitable only on a relatively limited frequency range especially if wide angle scanning is required. In order to extend the frequency range of usability, an FSS can be sandwiched between the antenna and the ground plane, providing an additional reflecting plane for an higher frequency band. The possibility to integrate in the antenna different functionalities, otherwise performed by several antennas, is also discussed in the paper. The proposed backing structure composed by the FSS and the ground plane has been designed to be used in conjunction with a wideband antenna consisting of an array of connected dipoles. A hardware demonstrator of the backing structure has also been manufactured and tested.

Frequency reconfigurable quasi-Yagi dipole antenna

Abstract: A frequency reconfigurable quasi-Yagi dipole antenna is presented in this paper. Simulation results show that a 35% continuously tuning impedance bandwidth, from 1.85 to 2.5GHz, is obtained. Loaded with varactor diodes, the effective electrical lengths of the driver and director dipoles are varied by changing the biasing voltages. The length adjustable director allows the endfire pattern with relatively high gain being maintained over each tuning sub-band. Across the tuning bandwidth, the predicted gain variation is from 5.8dBi to 7.9dBi. The H-plane cross-polarization level is below −17dB while this value is below −32dB in the E-plane. The front-to-back ratio is better than 12dB.

Miniaturized yagi class of antennas for GSM, WLAN, and WiMax applications

Abstract: This paper presents a miniaturized broadband Yagi antenna design for GSM, WLAN, and WiMax applications. This antenna is comprised of an inverted-F and two inverted-L shaped wires as active and parasitic elements in the array configuration. The realizable gain of the antenna is over 4 dBi and the front to back ratio of the radiation is over 6 dB. The measured return loss of the antenna shows the good broadband characteristics. The radiation patterns of the antenna are close to the omni-directional characteristics in the half-hemi sphere.

Performance Analysis of a Dual Cycle Engine with Considerations of Pressure Ratio and Cut-Off Ratio

Abstract: of the cycle are obtained. The results show that if compression ratio is smaller than certain value, the increase of pressure ratio and the decrease of cut-o ratio make the power output bigger. While if compression ratio exceeds certain value, the power output first increases and then starts to decline as pressure ratio and cut-o ratio are increased. With further increase in compression ratio, the power output decreases with increasing pressure ratio and decreasing cut-o ratio. The eects of pressure and cut-o ratios on the variation of the thermal eciency with compression ratio are similar to those for the power output. The results obtained in this work can provide significant guidance for the performance evaluation and improvement of modern high speed compression ignition engines.

A novel wide beam UWB antenna design for Through-the-Wall radar

Abstract: This paper presents a novel wide beam UWB antennae design for Impulse Radio-Ultra Wide Band (IR-UWB) Through-the-Wall detection radar. The design is based on a typical bowtie slot antenna structure with an added reflector in order to achieve unidirectionality and wide beam. The effects of different parameters of the added reflector on the impedance and radiation characteristics are analyzed. The different structural parameters of antenna are optimized by numerical simulations. Simulated and measured results show that the front-to-back ratio is great than 10dB and the beam width is approximately 120° ~145 ° within operation band for |S11|<-10dB (0.8GHz~2.3GHz).

A New Low-Profile and Cost SPA-PIFA for Mobile 2.4 GHz ISM Applications

Abstract: A new low cost switched-beam antenna array suitable for 2.4 GHz ISM applications is presented in this paper. The proposed structure consists of four planar inverted-F antennas (PIFA), sharing the same ground plane, in a configuration designed for symmetrical coverage of the horizontal plane (Quad-PIFA). A custom Genetic Algorithm (GA) is used in order to optimize the array parameters regarding resonation frequency and radiation pattern orientation angle and beamwidth. The optimized Quad-PIFA exhibits low profile (size equal to 8 cm × 8 cm), high front to back ratio (15.6 dB), and satisfactory directivity (3.6 dB) over an operational bandwidth of over 200 MHz. Simulation and measurement results are presented indicating consistency between design and implementation and demonstrating the performance of the array.

Triangular Lattice Dielectric EBG Antenna

Abstract: A novel electromagnetic band-gap (EBG) antenna based on a triangular lattice of dielectric rods is presented and analyzed using an in-house developed finite-difference-time-domain software simulator. The design steps and the simulations results are presented, focusing on the design of antenna structures with high directivity patterns on the H-plane. Finally, the measurement results of a set of experiments carried out on a prototype designed and built to operate in the X-band are presented and discussed, showing very good agreement with simulations: 31% fractional bandwidth and an average gain of 11.5 dBi are achieved within the bandwidth with 27 dB front-to-back-ratio in the azimuthal plane.

A directional dogbone flextensional transducer

Abstract: Sonar flextensional transducers, in order to transmit energy in one direction, are combined into arrays of elements that are spaced one-quarter of a wavelength apart. The directionality (front to back ratio) is a modest 6 dB, caused by diffraction effects of the size of the projectors. Here a projector that is one-third of a wavelength in size capable of developing unidirectional beams with a front to back ratio greater than 20 dB is described. The directional class VII dogbone flextensional is a modified version of a class IV flextensional having a concave shell rather than a convex one. The piezoelectric ceramic stack is a trilaminar bar with two active sections separated by an inactive center section. Driving both sections of the stack in-phase, the shell is driven into an omnidirectional pattern. Driving each stack section180 deg out of phase causes a bending mode, resulting in a dipole pattern. Driving both sections using complex coefficients determined from the omnidirectional and dipole patterns, a cardioid directional pattern is developed with a front-back pressure ratio of 50 dB that is over an octave bandwidth wide. COMSOL acoustics module FEA code is used to predict in water electroacoustic performance and compared with experimental data.

Pattern optimization in an uwb spiral array antenna

Abstract: We have proposed a new architecture for an array in which the elements are placed on a spiral curve in order to obtain an ultra wideband (UWB) radiation pattern. In addition, array factor and bandwidth of the proposed spiral array are calculated. Simulated results obtained by SuperNEC and CST software have shown good agreement with the analytic calculations. Although the proposed antenna array is wideband in nature, it lacks desirable e-ciency, due to poor front to back ratio (FBR) and sidelobe level (SLL). In this paper, we have chosen three difierent approaches in order to improve the e-ciency of proposed array. First, the efiect of length and thickness tapering of elements has been studied. Second, we have used Genetic Algorithm (GA) to optimized pattern shape. Finally, the in∞uence of metamaterial cover on array performance has been investigated. Although the flrst and second methods improve the radiation pattern, the array bandwidth is reduced. It is shown that the third method improves array directivity and FBR by 5{7dB and 15{17dB respectively within the frequency band of operation.

Slot-wedge multiple-element antennas

Abstract: The slot antenna at its second resonance (also call anti-resonance) is a wide band antenna [1]-[2]. A centrally fed, open slot provides direct match to 50Ω over a bandwidth of about 25% at its second resonance [2]. The wide bandwidth is insensitive to groundplane details, such as its size and shape, as long as the groundplane size is large enough to support the current distribution for the second mode.