Vol. 55

A simple end-fire high-gain antenna with side-lobe level suppression is proposed for 60 GHz technology in this paper. The antenna has a tapered slot radiation patch which is obtained by subtracting a quarter of ellipse from a bigger quarter. Two reflecting circle units (RCU) are located at both sides of radiant patch to suppress side-lobe level of radiation patterns. The antenna has a simple two-layered planar structure with on via and is fabricated on a Rogers 4350 substrate with a compact size of 15 mm × 15 mm. Simulated and measured results match well, and both show makes it fit 60 GHz wireless communication systems.

In this letter, a novel sleeve antenna with wideband characteristic is presented for wireless communication applications. By employing a sleeve structure, impedance bandwidth of the antenna is improved through exciting a new resonant point. To obtain an impedance bandwidth enhancement further, four symmetrical ridges are introduced between the sleeve and the main radiator. An excellent wideband impedance bandwidth for VSWR≤2 of 148.45% is achieved, covering the frequency range from 1.04 to 7.03 GHz, and good monopole-like radiation patterns are obtained where the un-roundness in the H-plane is less than 1.49 dB. It is very suitable for recent wireless communication services such as DCS, PCS1900, UMTS, IMT2000, WLAN, WiMAX2350/3500, WiBro, etc.

In this paper, a novel frequency reconfigurable U-slot microstrip antenna with T- shaped feed line for Software Defined Radio applications is proposed. The proposed antenna, indexed as A-I in this paper, operates at three different frequencies: 1.85 GHz, 1.9 GHz and 2.4 GHz depending on the switching states of PIN diodes. Furthermore, to strengthen the proposed design concept and strategy another improved antenna (A-II) is designed and tested. In comparison to antenna A-I, the improved antenna design (A-II) utilizes four slots/PIN diodes in order to increase the number of reconfigurable frequency states. Depending on the switch states of four PIN diodes, antenna A-II operates on five different reconfigurable frequency bands centered at: 1.5 GHz, 1.6 GHz, 1.8 GHz, 1.9 GHz and 2.24 GHz. The measured results show a return loss better than 22dB, maximum gain of 2.5 dB and maximum efficiency of 78%. Moreover, radiation pattern for the proposed antennas is stable at all operating frequencies.

In this paper, an ultra-wideband (UWB) conformal monopole antenna integrated with a narrow-band (NB) rectangular slot antenna is designed and fabricated. The proposed structure consists of a circular disc monopole antenna printed on a cylindrical surface, and fed by a coplanar waveguide line (CPW). A rectangular slot antenna that is excited by a microstrip line, is integrated in the front of the UWB antenna. The simulations are performed using the CST Microwave Studio software. To validate the proposed antenna concept, an experimental prototype is fabricated and measured. The measured results show that the monopole antenna covers an ultra wideband from 2 GHz to 12 GHz with S₁₁ < -10 dB and provides a very good isolation with a transmission coefficient below -20 dB across the operating band. Compared to planar integrated antennas, the proposed conformed structure possesses an important wideband, which can be used in many wearable electronic applications and communication systems.

In this paper, a planar microstrip branch-line coupler is designed to have dual-band operation. A Pi-typed structure is used in place of the conventional quarter wavelength transmission line for dual-band application. This structure consists of a pair of coupled line in which one has two ends while the other has open stubs attached to its two ends, and its circuit parameters are determined by the transmission line theory. Explicit design equations are derived using ABCD-matrix. For verification, a 3-dB branch line coupler with operating frequencies of 900 MHz and 3.5 GHz is fabricated and measured on an FR-4 printed circuit board (PCB). The simulated and measured results are in good agreement with each other.

In this paper, a pattern diversity antenna, capable of radiating broad side as well as conical radiation patterns using quarter mode substrate integrated waveguide sub-array, has been presented. The pattern diversity is achieved by in-phase and out-of-phase excitation of the sub-array using a rat-race coupler feed network. The overall profile height of the proposed antenna is 3.17 mm. The measured performance of the antenna, in terms of return loss, isolation, gain and diversity performance in the -10 dB impedance bandwidth, is in agreement with the simulated results. The proposed sub-array occupies 25% less area than the conventional microstrip antenna.

In this paper, a novel dual-band antenna with coupled line and different impedance extension lines is presented and analyzed. This simple antenna is composed of three antenna radiations with symmetric coupled lines, and it occupies a compact space of 80 × 30 × 1 mm³. The achieved 10-dB bandwidths of the dual-band operation in free-space condition are 200 MHz and 100 MHz, respectively, which support the 1.8/2.6 GHz Long Term Evolution (LTE) operating bands. Furthermore, various parameters are investigated to examine the effects of the antenna parameters on return loss as well as the gain of the proposed antenna.

A new balanced bandpass filter (BPF) with tunable bandwidth using tri-mode stub-loaded resonators is proposed. To tune the differential-mode bandwidth, the two even-mode resonance frequencies and two transmission zeros (TZs) are tuned while the odd-mode resonance frequency keeps unchanged. To realize high selectivity for differential mode, another two TZs are created by the source-load coupling and coupling sections. Furthermore, wideband common-mode (CM) suppression is achieved. The fabricated filter has 3-dB fractional bandwidth ranging from 20.0% to 26.0% centered at 1.71 GHz and wideband suppression (17 dB from 2 to 4.4 GHz) for the differential mode, as well as common-mode suppression better than 20 dB from 0 to 4.5 GHz.

A compact 4-port asymmetric coplanar strip (ACS)-fed MIMO antenna working in the ultra-wideband (UWB) frequency band with two shared radiators is presented in this paper. The proposed antenna is composed of two radiators, and each radiator is shared by two antenna elements in order to achieve a very compact size of 36×36 mm². By etching two I-shaped slots in the radiators and attaching a rectangular patch on the back, the operating band width is broadened, and the isolation between any two antenna elements is enhanced. The stub of the ground also has great effect on the return loss and isolation. The working frequency band of the MIMO antenna covers 3.1-10.6 GHz with isolation over 15 dB between any two antenna elements. Furthermore, the proposed antenna with a simple feeding structure and compact size makes it possible to be used in portable devices.

A tri-band multiple-input-multiple-output (MIMO) antenna that covers all frequency bands required for WLAN and WiMAX applications is presented. Three resonant bands are achieved by a folded monopole with a compact size of 11.5×15.6 mm². The MIMO system consists of two symmetrically placed monopoles. A stepped slot ended with an ellipse on the ground plane is etched to reduce the mutual coupling between the two monopoles. The overall dimension of this MIMO system is 50×50 mm². The prototype of the antenna is fabricated and measured. Measured results show that the antenna's impedance bandwidth is 450 (18%), 350 (10%), 1200 (21.8%) MHz at the three resonant frequency points (2.5 GHz, 3.5 GHz, 5.5 GHz) with mutual coupling between the antenna elements less than -18 dB in whole frequency band, making this antenna a good candidate for portable application.

In this paper, we propose an enhancement of the Equivalent Circuit Method (ECM) for analysis of frequency selective surface (FSS) with square loop geometry of the unit cell. For this, genetic algorithms and rational algebraic models are used to obtain a more accurate value of the effective electrical permittivity (ε_eff). We use simulated data obtained with a commercial software to adjust some parameters. So, genetic algorithm is used to obtain a better value of an exponent that calculates ε_eff minimizing the rational algebraic models. In this paper, this is done for the square loop geometry, but the methodology can be extended to any geometry. Finally, prototypes are built and the technique is validated.

A novel polarization independent RFID tag employing multiple resonators is proposed. The prototype of the tag is fabricated on a low-cost substrate of dielectric constant 4.4 and loss tangent 0.02. Designing a reader for chipless RFID is a hard task since both the polarization and operating frequency agility have to be implemented. The new tag design proposed in this paper is polarization independent, making the design of the reader easier. A prototype of a 3 bit data encoded tag is demonstrated using single structure which can be extended to any order by cascading. This new design is experimentally validated in the frequency domain using monostatic measurement with magnitude response to decode the information.

A three-step molding softlithographic process has been developed for the construction of a sharp Y-junction structure formation in a 1x2 Y-branch plastic optical fiber (POF) coupler design. The 1x2 Y-branch POF coupler is based on a Y-junction splitter which requires that the splitting part is constructed with sharp infinitesimal junction. The softlithographic process enables a PDMS mold to be constructed which then allows mass replication of the polymer-based POF coupler. A standard master mold based on PMMA material is fabricated using CNC milling. A secondary or auxiliary-mold process step is then introduced in order to produce a sharp Y-junction structure which is then transferred to the final PDMS stamp prior to device replication. This step utilizes a free flowing, low viscosity casting-based resin, which after curing and hardening provide the auxiliary mold for PDMS mold fabrication. The result shows that a very fine and sharp Y-junction structure can be produced easily which cannot be produced via standard two step molding softlithographic process. Models for the Y-branch POF coupler produced with and without an auxiliary mold process are constructed which show that a 16% increased in optical performance with the device replicated with the auxiliary mold process.

A planar ultra-wideband (UWB) antenna with triple-notched bands using triple-mode stepped impedance resonator (SIR) is presented in this paper. By coupling the novel triple-mode SIR beside the microstrip feedline, band-rejected filtering properties around the C-band satellite communication band, the 5.8 GHz WLAN band, and the X-band satellite communication band are generated. The notched frequencies can be adjusted according to specification by altering the triple-mode SIR. The results indicate that the proposed planar antenna not only retains an ultra wide bandwidth but also owns triple band-rejections capability. The UWB antenna demonstrates omnidirectional radiation patterns across nearly whole operating bandwidth, which is suitable for UWB communications.

In this paper, three omnidirectional microstrip array antennas are optimized, fabricated and measured. The proposed planar antennas are composed from series of microstrip line sections with inverted top and bottom conductors at each section. The antenna design parameters are optimized to design three different antennas: wide bandwidth, high-gain and dual-band antennas. In the wideband antenna, a good impedance matching is obtained for relative bandwidth of 31% that covers the frequency range of WLAN. The dualband omnidirectional antenna operates at 2.45 GHz and 5.25 GHz with gain of 6.69 dBi and 7.71 dBi, respectively. Also, the optimized high-gain antenna achieves 9.3 dBi gain. The three optimized antennas are fabricated and tested. The measurement results show a very good agreement with the simulation ones. The optimization results verify the ability and capability of the antenna to achieve the desired specifications.

This paper presents two dual-band bandpass filters with controllable passband frequencies and bandwidths. The filters are realized utilizing a novel quad-mode stub-loaded ring resonator. All the four mode equivalent circuits of the resonator are quarter-wavelength resonators, and their fundamental resonance frequencies are used to form the passbands. So the designed filters have a compact circuit size and relatively wide upper stopband. For validation, two experimental filters operating at 1.5/2.4 GHz and 1.5/3.5 GHz are designed. In the design of the second filter, hook-shape feed-lines and source-load coupling are applied to generate more transmission zeros, which greatly improve the selectivity of the filter. Finally, the filters are fabricated, and measured. The measured results have good agreement with the simulated ones.

In this paper, we present the design of a low-profile antenna consisting of two orthogonal parasitic meandered monopoles excited by the near-filed coupling with a feeding bow-tie. The two parasitic radiators and the driven element are placed on two different faces of the same dielectric substrate and a coaxial probe excites the bow-tie through a metallic ground plane. In this way, the antenna has compact dimensions of 21×10.5×1.6 mm³(λ₀/6×λ₀/12×λ₀/75, excluding the ground plane) and exhibits a good impedance matching in the 2.4-2.485 GHz Wi-Fi band with an overall efficiency around 50%.

Sparse representation is the fundamental technology of compressive sensing, sparse three-dimensional (3-D) imaging, and dictionary-based parameter estimation. Typical sparse representation models of radar signal work in the frequency domain, which may encounter high dimension and large data amount of dictionary. This paper presents a time-domain (TD) representation model for multi-aspect SAR data. We generate the multi-aspect two-dimensional (2-D) TD responses of the 3-D scattering center model. Then we cut off the low-energy area of the 2-D TD response and use cutoff responses to construct the dictionary of sparse representation. Such a TD dictionary is a sparse matrix. Moreover, we build and solve the sparse representation model based on the TD dictionary. Compared with the frequency-domain (FD) sparse representation model, the data size of our TD dictionary is remarkably lower, and the solving of TD sparse representation problem is in higher efficiency. We utilize the TD sparse representation to reconstruct 3-D images from multi-aspect SAR data. Experimental results demonstrate the effectiveness and efficiency of the TD sparse representation model.

A theoretical analysis of numerical dispersion in the high-order finite-difference time-domain (FDTD) method with weighted Laguerre polynomials (WLPs) is proposed in this paper. According to the numerical dispersion relation for the two-dimensional (2-D) case, the numerical phase velocities relevant to the direction of wave propagation, grid discretization and time-scale factor are obtained. For a fixed relative error of the numerical phase velocity, the suitable sampling point density and time-scale factor can be determined. Compared with the low-order WLP-FDTD, the high-order one shows its good dispersion characteristics while a low sampling density is used. Three numerical examples are included to validate the effectiveness of the high-order scheme.

A compact coplanar waveguide-fed tri-band monopole antenna for WLAN/WiMAX applications is proposed. By employing a pair of inverted-L slots etched on the ground plane and a split-ring resonator (SRR) and further carefully adjusting the lengths and positions of these structures, two notched bands can be obtained. Measured results show that a tri-band of 280 MHz (2.28-2.56 GHz), 920 MHz (3.29-4.21 GHz), and 860 MHz (5.05-5.91 GHz) with reflection coefficient less than -10 dB is obtained covering all the 2.4/5.2/5.8 GHz WLAN bands and 3.5/5.5 GHz WiMAX bands. In addition, good dipole-like radiation characteristics over the required bands is achieved in both E- and H-planes.