The shaping of dispersion characteristics in a variant of discloaded circular waveguide was studied through electromagnetic analysis for assessing the structure for wideband coalescence of the beam- and waveguide-mode dispersion characteristics that entails the wideband gyrotravelling-wave tube (gyro-TWT) performance. In this variant of disc-loaded circular waveguide, the alternate disc-hole radii were varying, however, the structure was periodic. The structure periodicity coupled with Floquet's theorem and field-matching technique resulted into the dispersion relation of the infinitely long structure. A numerical code was developed to solve the dispersion relation, and the dispersion characteristics of the structure were analyzed for the azimuthally symmetric TE-modes. The effects of structure parameters were studied for getting a straight-line portion of the dispersion characteristics over a wide frequency range. The dispersion shaping was projected for typically chosen TE₀₁-mode. The results were validated against those obtained for the conventional and un-conventional known structures and those obtained using commercially available simulation tool. The variation of azimuthal electric field intensity over the radial coordinate was also studied to examine the control of structure parameter for maximaposition, where the gyrating electron beam would be positioned for optimum beam-wave interaction in a gyro-TWT.

This paper presents a six-port network over an ultra-wideband (UWB) of 2-8 GHz. Its key component is the six-port junction, which consists of a Wilkinson power divider and three 3-dB quadrature couplers, This six-port junction is accomplished in a low dielectric constant substrate (Rogers RT/duroid 5880). Multi-section impedance transformation is applied in the power divider, and the quadrature coupler is realized by using two 8.34 dB couplers in tandem. An ultra-wideband operation of the six-port junction is verified by full electromagnetic simulations and measurements. The results show that the designed devices exhibit good performance across 2-8 GHz band: the return losses at input ports are higher than 15 dB, the insertion losses from input ports to the remaining ports are 7.2 dB ± 1.7 dB, the isolation between two input ports is greater than 20.5 dB, and the maximum phase difference compared with the theoretical behavior between two test ports is 10°. For the manufactured six-port junction, a six-port phase measurement system and a calibration technique based on support vector regression (SVR) are introduced. Results show that the SVR model can achieve a mean phase error of 1.5274°.

An efficient numerical solution is presented for computing per-unit-length impedance of metallic rectangular transmission lines backed by semi-infinite lossy substrate. We formulate the problem into the set of integral equations, the kernel of which is analytically expressed in terms of special functions in the quasi-static regime. The method of moments is applied to find the current density distributions in the metal regions, where the discretization of cross sections is performed by using non-uniform grid arranged according to the skin effect. The practical numerical computations concern the influence of the substrate loss on the per-unit-length impedance for some types of parallel lines. We thereby show that the substrate loss cannot be neglected at high frequencies. The effectiveness of the proposed method is confirmed by showing that the computed values of resistance satisfy the law of energy conservation with acceptable accuracy.

This work presents a compact, high performance GaAs V-band bandpass filter (BPF) using a slow-wave coplanar waveguide transmission line (S-CPW TLine) and a CMRC (compact microstrip resonant cell). The slow-wave CPW Tlines have potential for the use in miniaturized low loss compact passive devices in the millimeter-wave frequency band. Owing to strong slow-wave effect, the longitudinal length of the S-CPW is shorter than that of a classical microstrip based on the same technology. The S-CPW TLines in the designed filter were realized with a reconfigurable defected ground structure (DGS). Adding the conventional inductively coupled resonator CMRC BPF allows the resonator to be miniaturized by the exploitation of the transversal dimensions of the CPW, while maintaining its performance as measured by insertion and return losses. However, the DGS cell allows reconfiguration of the structure from a low-band to a high-band BPF. The design of the filters with the DGS using filters that are designed for V-band applications is explained.

We study the Doppler features of electromagnetic scattering from a wind turbine with rotating blades in the presence of ground. Image theory in conjunction with a shooting-and-bouncing ray code, Ahilo, is used to carry out the dynamic signature simulation. The observed features in the simulation are corroborated with laboratory measurements. In addition, the Doppler features from a wind turbine in the presence of a moving ground is simulated and analyzed.

A CPW-fed slot antenna for achieving dual-band dual-sense circular polarization is introduced. The dual-band circularly polarized operations are generated by the slots loaded in the two opposite corners and the halberd-shaped strip connected at the end of the signal line of the CPW. The left-hand and right-hand circularly polarized performances can be achieved simultaneously for the lower and the upper band, respectively. The measured impedance bandwidth for 10-dB return loss at 2.5 and 3.5 GHz operating bands can be up to 1100 MHz and 260 MHz, respectively. The measured 3-dB axial ratio bandwidths are 30.8% for lower band (LHCP) and 3.1% for upper band (RHCP), which are completely inside their respective impedance bands. The designed antenna has a simple uniplanar structure and occupies a compact size of 40×40 mm², including the finite ground CPW feeding mechanism. Moreover, the antenna gain variations across the two operating bands are less than 1 dB.

A novel compact dual-band bandpass filter using spiral resonators and input/output (source-load) direct coupling structure has been presented. Two different transmission paths are utilized to realize independently controllable central frequencies and bandwidths for each passband. In addition, three transmission zeros has been introduced to improve the frequency selectivity. A dual-passband filter centered at 2.41 GHz and 4.22 GHz is designed, simulated, and fabricated to demonstrate the performance of the proposed filter structure. The measured results show good agreement with the simulated ones.

An interesting and original solution to the high channel noise sensibility problem of digital chaotic communications is proposed. The solution idea consist of avoiding disruption of the slave/receiver dynamics by injecting the driving signal. To realize experimentally this pertinent idea, an FPGA-based hardware architecture is developed, firstly to trigger the generation of the slave/receiver chaotic dynamics at each received data detection, and secondly to synchronize the driving signal with the slave generated chaotic signal for the demodulation operation. We have tested and validated the proposed solution through experimental realization of a wireless hyperchaotic communication system based on ZigBee communication protocol. Real-time results of experimental wireless communication tests are presented. The obtained results show the effectiveness and the robustness of the proposed solution against real channel noise in digital chaotic communications.

The design of resonators with degenerate magnetic and electric modes usually requires the ability to perturb one or both types of modes in order to induce alignment of magnetic and electric properties. In this paper perturbation theory is used to identify different types of inclusions that can be used to realize fundamental-mode degeneracy in a rectangular dielectric resonator and thus, can ultimately be used in the design of negative-index metamaterials. For reasons associated with fabrication in the infrared-frequency regime, rectangular resonator designs are of particular interest.

Our main objective in this article is to achieve minimum side lobe levels for a specific first null beam-width and also a minimum size of the circumference by an optimization-based design method for non-uniform, planar, and circular antenna arrays. Our approach is based on a new variant of Particle swarm Optimization technique. This new technique is a hybrid of Local Neighborhood based PSO with Hierarchical PSO Algorithms termed as Hierarchical Dynamic Local Neighborhood Based PSO (HDLPSO) Algorithm. Three difficult instances of the circular array design problem have been presented to illustrate the effectiveness of the proposed HDLPSO algorithm. The design results obtained with HDLPSO have been shown to comfortably beat the results obtained with other state-of-the-art meta-heuristics like Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Invasive Weed Optimization (IWO) and Differential Evolution (DE) in a statistically significant manner.

A novel compact monopole antenna with triple-band operation is proposed in this paper. The proposed antenna, fed by a 50-Ω microstrip line, consists of an inverted-L-shaped microstrip feed line loaded with a parasitic strip and a protrudent mirrored quasi-F-shaped strip on the ground plane, with a compact overall size of 20×25 mm². The protrudent mirrored quasi-F-shaped strip is aimed to excite a resonant mode at 2.4 GHz. Meanwhile, with the introduction of the parasitic strip to the inverted-L shaped strip, two adjacent resonant frequencies at 5.2/5.8 GHz are obtained. The numerical and experimental results exhibit the designed antenna operates over triple frequency ranges, satisfying the standards of wireless local area networks (WLAN) both in IEEE 802.11 b/a/g at 2.4-GHz, 5.2-GHz, and 5.8-GHz. Besides, the antenna is fabricated and measured, and the simulation and measurement results of the return loss, radiation patterns and peak antenna gains are studied showing that the presented antenna is in good performance.

This paper presents the design of a dual-band microstrip antenna with low wide-angle axial-ratio. The antenna is designed for global positioning satellite operations at 1227 MHz(L₂), 1575 MHz(L₁) and 1176 MHz(L₅, available after 2007). This antenna has another advantage of a much wider band in both VSWR and 3 dB axial-ratio compared with single-fed GPS antennas. Details of the design, simulated and experimental results of this GPS antenna are presented and discussed. The measured results confirm the validity of this design, which meet the requirement of GPS applications.

This paper presents a novel range-spread target detection algorithm for frequency stepped chirp radar (FSCR) which transmits a chirp-pulse train with frequency stepped carriers. FSCR achieves high range resolution by synthetic wide-band technique, and its process includes intra-pulse matched filtering and pulse-to-pulse inverse discrete Fourier transform (IDFT) or wavelet transform. For FSCR, the high resolution range profile (HRRP) of a target is obtained by target extraction from overlapping HRRPs which is caused by oversampling. During the target extraction (sometimes called de-correlation), some strong scattering points of target echo are discarded, as the result, the signal-to-clutter ratio (SCR) might be reduced and the target detection capability is degraded. To solve this problem for FSCR, a novel detection algorithm without target extraction is addressed. The new algorithm based on the power spectrum of radar echo uses not only the amplitude information, but also the phase information of overlapping HRRPs of a target to improve the SCR, therefore, has significant performance. Moreover, the test statistic and the false alarm probability of the detector are derived, and the implementation procedure and the flow chart of the detection algorithm are designed. Finally, the detection performance is assessed by Monte-Carlo simulation, and the results indicate that the proposed algorithm has about 3 dB detection improvement in SCR compared with the spatial scattering density generalized likelihood ratio test (SSD-GRLT) detector, and at the same condition, is superior to the integrator detector. In addition, the proposed algorithm is robust and easy to implement.

A novel design of planar dual and triple narrow-band bandstop filter is presented by adopting the proposed meandered slot defected microstrip structure (MS-DMS) and the simplified spiral microstrip resonator (SSMR). Through this design, the stopbands of the dual- and triple-band bandstop filters can be individually controlled and the improved spurious responses are achieved. First, the fundamental and the first spurious resonances of the MS-DMS and SSMR are analyzed to provide the design rules. Then, by utilizing the prominent stopband of the MS-DMS and the stopband produced by the SSMR coupled to main microstrip line, a dual narrow-band bandstop filter is constructed before its design procedure is outlined. Based on above investigations, a triple narrow-band bandstop filter is implemented by inserting extra SSMRs to another side of the main microstrip line of the dual-band filter to generate a new stopband. To verify the aforementioned design concepts, a dual and triple narrow-band bandstop filter are designed, simulated and tested. Both the simulation and measurement indicate that the fabricated filters exhibit good stopband/passband performance and improved first spurious resonance. Moreover, these filters are simple to design and quite compatible with planar fabrication technique, making them very attractive for practical applications.

Three dual band planar monopole antennas for wireless local area network (WLAN) application are proposed. The antennas have common configuration in the form of rectangular, rhombic and annular double rings. All the antennas use the self similarity property to exhibit dual band characteristics. The proposed antennas covers the frequency bands of the IEEE 802.11a/b/g (2.4-2.48 GHz, 5.15-5.35 GHz and 5.725-5.825 GHz), and have radiation patterns that are; almost omnidirectional in the H-plane, and like monopole pattern in the E-plane. The simulation results are analyzed and compared with measured results for verification.

In this paper, we present the chaotic verification for angular glint of complex radar target. Angular glint is a key factor in the generation loss probability in radar detections, and the intrinsic physical characteristic and suppression techniques of glint have been a hot topic in radar signal analysis. In this paper, the radar angular glint samples of a typical complex target are calculated by the Greco method based on Phase Gradient method. The simulated glint series fit the prerequisites of chaos for deterministic, nonlinear generation and no regularities in time domain, therefore the analysis the chaotic traits is required. We propose the design of chaotic verification flow, which is proved to be efficient and effective by the experiment of Lorenz Attractor signal model, and the details have been explained. The algorithm flow begins with the determination of optimum time lag and minimum embedding dimension, and is followed by the time-delay reconstruction in phase space. The results are presented with three qualitative verification results of attractor geometry, Poincare section and principal component analysis and two quantitative results of correlation dimension and largest Lyapunov exponent for the glint series. With comparison with results obtained by Lorenz attractor, the chaotic traits of angular glint data are verified. Therefore, the paper has proposed new possible reduction and prediction ideas to refrain angular glint in the digital processing unit of radar receiver in the future.

A novel dual-side mushroom ground plane (DMGP) structure is proposed for the noise suppression in high-speed multilayer printed circuit boards (PCBs). The proposed method is localized suppression technique where a dual-side mushroom structure is placed below the noise-sensitive device. In multilayer PCBs with DMGP, noise between two ports with large or small ports spacing can be minimized effectively, which is flexible for the layout of mixed-signal system. Wideband noise suppression is achieved for the fabricated boards even though the port spacing is only 3.5 mm.

A compact dual-band multiple-input-multiple-output (MIMO)/diversity antenna is proposed. This antenna is designed for 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX applications in portable mobile devices. It consists of two back-to-back monopole antennas connected with a T-shaped stub, where two rectangular slots are cut from the ground, which significantly reduces the mutual coupling between the two ports at the lower frequency band. The volume of this antenna is 40 mm * 30 mm * 1 mm including the ground plane. Measured results show the isolation is better than -20 dB at the lower frequency band from 2.39 to 3.75 GHz and -25 dB at the higher frequency band from 5.03 to 7 GHz, respectively. Moreover, acceptable radiation patterns, antenna gain, and envelope correlation coefficient are obtained. These characteristics indicate that the proposed antenna is suitable for some portable MIMO/diversity equipments.

The problem of localizing small scatterers (in terms of wavelength) by Time Reversal-MUSIC (TR-MUSIC) algorithm is addressed. In particular, we focus on uniqueness problems that might arise for certain far zone configurations when noise corrupts data. These lead to reconstructions affected by ghost targets from which it is difficult to discern actual targets. In order to remedy such a drawback, data obtained at multiple frequencies are employed. In detail, a new multi-frequency version of TR-MUSIC is introduced. It consists in mixing reconstructions obtained at different frequencies. Numerical analysis shows that this method outperforms classical TR-MUSIC as well as its multi-frequency implementation already present in literature.

Novel compact multiband microstrip transversal bandpass filters (BPF) using short-circuited or open-circuited stub-loaded half-wavelength resonators (SLR) are presented. The dual-band BPF consists of two SLRs and two T-shaped feedlines, and the tri-band BPF can be implemented by a simple reconfiguration of adding one resonator above the original circuit of the dual-band BPF. Multiple transmission zeroes are created to improve the selectivity of the filters. Furthermore, the high degree of design freedom is obtained for every passband of dual- or triple-band BPF is achieved by independent resonators and independent signal paths. To verify the proposed concept, two dual-band bandpass filters (filter I and II) and one tri-band bandpass filter (filter III) are designed and fabricated. Both theoretical and measured results are presented, with good agreements.