We characterize left-handed (LH) traveling-wave field effect transistors (TWFETs), which consist of two composite right- and left-handed (CRLH) transmission lines that are electromagnetically coupled by capacitances, inductances, and FET transconductances, for obtaining loss-free LH waves. In a device, two different propagation modes can support LH waves. We find that one of these modes gain wave amplitudes, while the other loses them. This amplitude gain can compensate wave attenuation resulting from electrode loss and substrate leakage. This study clarifies which mode gains amplitudes and the method of matched terminations, together with several experimental observations that validate the design criteria.
A small-sized, low-cost, and planar integrated Bluetooth and ultrawideband (UWB) monopole antenna with band-notched characteristics in the 3.5 GHz WiMAX and 5.2/5.8 GHz WLAN band is proposed. It is fed by a microstrip line and built on a FR-4 substrate with a whole size of 18*30 mm2. This proposed antenna consists of a slot on the edge of the radiation patch, which not only makes it achieve Bluetooth and UWB performance but also produces a high isolation between them. Additionally, two split rectangular ring resonators (SRRR) are placed close to the microstrip line to reject the WLAN band. Measured S11 is ≤-10 dB over 2.28-2.52, 3.66-5.02, and 6.05-12 GHz. The group delay characteristic indicates good transient response in the working band. The antenna shows acceptable gain flatness with stable omnidirectional radiation patterns across the integrated Bluetooth and UWB (3.1-10.6 GHz) band.
A compact triple-band monopole antenna with two different slots for WLAN and WiMAX applications is proposed and experimentally studied. The proposed antenna with a size of 30mm×25mm×1mm is excited by a 50Ω microstrip feed line. The designed antenna obtains three frequency bands through loading an inverted E-shaped slot and an inverted C-shaped slot which incise the surface current and change the path of the current on the rectangle patch. The obtained results show that the designed antenna has impedance bandwidths of 2.4 GHz, 5.8 GHz for WLAN and 3.5 GHz for WiMAX. The return loss, radiation patterns and peak antenna gains are presented using computer simulations and measurements.
This paper presents a novel tri-band unequal Wilkinson power divider. The proposed structure is derived from the conventional unequal Wilkinson power divider by replacing the quarter-wavelength branch lines and quarter-wavelength transformers with the extended T-shaped short stubs and three-section transformers respectively. The first and third operating frequencies of the proposed Wilkinson power divider can be flexibly controlled, while the second frequency is equal to the mean value of the other two frequencies. Both of the closed-form equations and design procedure are given. For verification, a tri-band unequal power divider with the power dividing ratio of 2:1 and operating frequencies of 1.3, 3.0 and 4.7 GHz is designed, fabricated and measured. The measurement results are in good agreement with the simulation ones. It is shown that the proposed power divider has simple topology and good performances in terms of insertion loss, port matching and isolation at all three operating frequency bands.
An infinitely flanged coaxial line is analytically solved with the mode-matching technique and Green's function to propose a precise yet fast-convergent scattering solution for complex permittivity measurement. Based on virtual current cancelation, we formulate the open half-space fields in terms of coaxial modes and related Green's functions and thus obtain the simultaneous equations with rapidly convergent integrals. Numerical computations were performed in terms of reflection coefficients and radiation patterns.
A compact zeroth order resonance (ZOR) antenna based on composite right left handed Transmission Line (CRLH TL) with complementary split ring resonators (CSRR) is presented in this paper. In the proposed antenna, CRLH TL is realized by the conventional mushroom type (CMT) of structure. The unit cell of proposed antenna comprises the CMT structure and CSRR where the CSRR is etched on the patch of the mushroom. Presence of CSRR introduces the lumped components in the shunt arm of the unit cell which results in the reduction of the shunt resonance frequency. The presented antenna consists of 4 unit cells and is excited by the quarter wavelength TL. The simulation and experimental results are in close agreement. The proposed structure has nearly 8.32% footprint area of the conventional half wavelength antenna.
We present new designs of waveguide components in photonic crystal structures used for routing light exhibiting high transmission. In particular, we focus on the design of a brick that will form the PhCs network, i.e., a double bends and Y-shaped splitter. Photonic crystals are considered a good way for realizing compact optical bends and splitters. The PhC consists of a triangular array of holes etched into InP/GaInAsP/InP heterostructure. Propagation characteristics of the proposed devices are analyzed utilizing two-dimensional finite difference time domain (FDTD) method. The FDTD simulations confirm their unprecedented efficiency and robustness with respect to wavelength and structural perturbations. The PhCs transmission properties are then presented and discussed. Numerical results show that a total transmission of about 75% at output ports is obtained.
In this paper, on the basis of proposing a novel complementary split-ring resonator (CSRR) using Koch fractal curve, a bandpass filter based on such a new structure is designed To validate the designing method. Transmission characteristics and reflection characteristics of the presented filter are given by both software simulation and experiment measurement. Consistent results have confirmed the design concept and excellent performance of the new structure and indicated that the proposed filter has a low insertion loss a high selectivity and small size.
In this letter, a novel compact quad-band microstrip circular slot antenna using edge-feeding is proposed to support the four wireless communication bands of GPS1.575 (1.525-1.625 GHz), WIMAX3.5 (3.3-3.6 GHz), WLAN2.45 (2.4-2.485 MHz)and WLAN5.2/5.8 (5.15-5.825 GHz). To expand the bandwidth of the GPS band and induce the WIMAX/WLAN band to support quad-band applications without affecting the compactness of the proposed antenna, a good method of implanting two T copper slices at the inner boundary of the two circular slots respectively is adopted. By adjusting the diameter of the two circular slots and the size of the T-shaped patch, resonant frequencies and bandwidth of the antenna are controlled and the multiple operating bands are achieved. In order to further reduce the size of the antenna that an edge-fed technology is used. This antenna has a simpler structure for realizing quad-band characteristics. Then, a prototype of the proposed antenna was successfully implemented, and good radiation performance is observed in all desired bands.
We simulate a 1D ternary photonic crystal (TPC) employed as a clad of a photonic crystal waveguide (PCW) which consists three different lossless dielectric layers as a unit-cell. Calculating input impedance at each layer interface and using a lossless reciprocal transmission line as a model, we can predict angle intervals in which reflection occurs due to photonic crystal effect. Comparing this method with transfer matrix method and bang structure shows perfect agreement.
A new microstrip structure for realization of wideband phase shifter has been designed and fabricated. The proposed design uses edge-coupled semi-elliptical structure and an elliptical defected ground plane to increase the coupling coefficient and operating bandwidth. Simulation performed using CST Microwave Studio and measured results confirm the good performance of the proposed design. The phase deviation is better than ±4º, insertion loss less than 0.6dB and return loss better than 10dB over a wide frequency range. The achievable bandwidth is more than 2.3 : 1.
A new design of a circularly polarized single-layer antenna which has a compact structure of 10mm×20mm×1mm is presented. The proposed antenna only consists of a feedline and a rectangular ground plane both printed on the same metallic layer. To compact the antenna size and overcome the high impedance problem, the circular polarization (CP) operation can be attained by locating the feedline at the left of the ground plane. Parameters such as substrate length and patch length are investigated and design results from parametric simulations are presented.
This letter presents a miniaturized dual-mode composite-right/left-handed line resonator with wide harmonic suppression. The pure right-handed microstrip transmission line adopt 36° electrical length instead of 90°, thus the size of the dual-mode filter can be reduced significantly meanwhile the spurious response suppression are improved effectively. A prototype filter is designed and implemented at 730 MHz, which not only has a size reduction of 92% against a conventional dual-mode filter, but also exhibits harmonic suppression characteristics over a decade bandwidth.
A novel method allowing the ultrafast scanning of an area thanks to an Ultra Wide Band (UWB) antenna array is proposed in this paper. This method is based on the use of asynchronous optical pulses trains with different repetition rates obtained in amplified regenerative cavities. By means of optoelectronic switching, providing short powerful electrical pulses trains to an UWB antenna array, it is possible to spatially scan a large area in less than 1 ms. The paper presents the principle of the transient beam steering and its potentialities to realize an ultrafast detection system.
The EM analysis of double-layered thick FSS structure with low-loss dielectric medium between the FSS layers has been carried out using MM-GSM technique. In this analysis, both evanescent and propagating modes are included that enhances the accuracy of the computation. This method provides less computational complexity in the formulation of FSS structures as compared to other numerical techniques. The cascaded FSS structure shows bandpass response (>95% transmission) over a frequency range from 8.84 GHz to 10.74 GHz. It is found that this FSS structure shows very good in-band transmission characteristics and excellent roll-off characteristics outside the band. Further, the dependence of transmission characteristics on the spacing between the FSS layers is also investigated. The optimum bandpass response is achieved for 0.3λ spacing between the layers. This FSS structure offers superior bandpass response and structural rigidity required for airborne radome applications.
A compact microstrip-line dual-band bandpass filter with controllable characteristics is presented using a stub-loaded resonator. The resonator is formed by loading one open circuit terminated stub in shunt to a simple uniform impedance line. The passband frequencies of the dual-band filter can be conveniently controlled by tuning the lengths of stub-loaded resonators. The bandwidth of the first passband can be controlled by tuning the parameters of center stub-loaded resonator, and the bandwidth of the second passband is determined by the coupling between the sideward stub-loaded resonators. To illustrate the concept, a second-order dual-band filter is designed, fabricated and measured. Simulated and measured results are found in good agreement with each other.
A new method for increasing the bandwidth (BW) of a class of cloaks is presented. Simulation results reveal that the bandwidth of this class of cloaks is increased by embedding the two-dimensional transmission networks in a medium whose refractive index is smaller than unity. The low refractive index medium is realized by embedding several thin wires in a host medium. The overall bandwidth of the proposed cloak for reflectance less than -25 dB is revealed to be increased by more than 17% compared to its conventional counterpart.
This paper develops a practical receiver suggested for cooperative systems using decode-and-forward transmission and compares it to the theoretical sub-optimum λ-MRC receiver model. The proposed receiver model adopts a channel blind λ-combiner and employs a practical estimation of the combiner's weight λ that changes adaptively for each received bit. The λ estimation process relies on a dynamic-blind calculation performed on the incoming bit stream using an approximate formula. The accuracy of the estimated values of λ against the numerical (optimum) values is verified by comparing their effects on the performance curves. Next, the performance of the proposed receiver is evaluated against the sub-optimum receiver using the closed-form performance equations then verified using an actual implementation of the decode-and-forward cooperative algorithm. The use of the proposed receiver is shown to have reliable performance under different channel assignments and provides adaptivity to channel variations without complexity or exaggerated signal processing.
The finite difference time domain (FDTD) method is widely used as a computational tool to simulate the electromagnetic wave propagation in biological tissues. When expressed in terms of Debye parameters, dispersive biological tissues dielectric properties can be efficiently incorporated into FDTD codes. In this paper, FDTD formulation with nonuniform grid is presented to simulate a dual medical implant communications service (MICS) (402-405 MHz) and industrial, scientific, and medical (ISM) (2.4--2.48\,GHz) band implantable antenna for continuous glucose-monitoring applications. In addition, we present computationally simpler two-pole Debye models that retain the high accuracy of the Cole-Cole Model for dry skin in MICS and ISM bands. The reflection coefficient simulation result with Debye dispersion is presented and compared with the published results. FDTD was also applied to analyze antenna's far-field.
In this paper, we introduce a new non-uniform memory access (NUMA) acceleration algorithm for parallel finite-difference time-domain (FDTD) method on NUMA architecture workstation. We compare the performance of parallel FDTD method with and without the NUMA acceleration technique. An ideal test case and an engineering example show that the NUMA acceleration technique can efficiently improve the computing performance of FDTD parallel applications.
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