Electronically switchable microwave filters are attracting more attention for research and development because of their importance in increasing the capability of wireless communication and cognitive radios. In this paper, novel switchable microwave band-stop to all pass filters are designed by using stepped impedance resonator. Commercially available Pin diodes are used in order to allow the fastest switching between band-stop and all pass responses. The theoretical analysis is presented in this paper, and its feasibility has been experimentally verified with a micro-strip prototype. The design was also characterized by measuring the filter performance with increasing power levels of 20, 15, 10, 5, and 0 dBm. The results have shown that the switchable filter is immune to power saturation effects. Nonlinear measurements at higher power levels are also performed and the switchable filter produced low power inter-modulation product. The main advantage of this filter is its capability to switch between band-stop and all pass mode of operation. Other advantages include being small in size, and low in cost.

Efficient and compact wireless power transfer (WPT) systems are proposed and designed for recharging small implantable medical devices. They use the magnetic resonance coupling scheme to transfer power over a relatively large distance. The receiver resonator coil and the load loop are designed in correspondence to size restriction of implantable devices. The dimensions of the coils are optimized and effective values of the lumped capacitors are investigated and fine-tuned for efficiency enhancement. Three design configurations of the WPT system, each consisting of two coils at the transmitter and two coils at the receiver, are designed and fabricated. The transfer efficiency is measured over different transmission distances and with different orientation angles of the receiver coils. The measurement results show good agreements with the simulations and illustrate that the proposed WPT systems exhibit nearly omnidirectional radiation performance. Furthermore, the receiver coils are implanted inside of a biological object to show the power can be transferred effectively.

A co-designed compact dual-band filter-antenna suitable to be embedded inside a wireless access point (AP) in the 2.45/5.2-GHz wireless local area network (WLAN) bands is presented. The proposed filter-antenna comprises a loop-loaded dual-band monopole radiator and a microstrip dual-band pseudo-interdigital bandpass filter. The monopole consists of a uniform width monopole, two identical capacitively loaded magnetic resonators and a top loaded loop. The two magnetic resonators are loaded at the center of the monopole for dual-band operation and the rectangular loop loaded at the top is involved for miniaturization. Instead of using the traditional 50Ω interfaces, the impedance between the filter and antenna is optimized to improve the performance. The filter-antenna and the system circuit board of an AP share the same substrate and ground plane. In this case the design can fully integrate the circuit board of the AP into an internal filter-antenna solution. The proposed filter-antenna provides good selectivity and rejection in out of band regions and omni-directional radiation patterns within the two desired bands. The measured results show good agreement with the simulated ones.

Time-reversal (TR) invariance of the wave equation in lossless transmission line (TL) is here introduced as an improvement for fault-detection techniques in wire networks. This new approach is applied to reflectometry in wire diagnosis. To test the efficiency of this method, the reverse time algorithm simulated with FDTD (Finite Difference Time Domain) is developed in a one dimension space. It uses a new signal processing and an adapted signal to the wire under test for diagnosing the fault in the wire. In addition the interest of the convolution product between the incident signal and the output signal from this reverse time method will be also shown and applied in this paper. Through numerical simulations and experimental results measured on coaxial cable, the benefits of this method have been illustrated.

Guided-Mode Resonance (GMR) effects in transparent periodic gratings possess a number of remarkable phenomena. GMRs exhibit strong features in the optical spectrum, i.e. dips, peaks, cusps, and may attain extremely high Q-factors. In some cases resonant reflection with the efficiency equal to unity can be observed. We demonstrate that the introduction of small losses in the structure can drastically modify its optical response by causing strong absorption resonances. Unity reflection in loss-free structures can be almost completely converted into unity absorption peaks as soon as very small losses are introduced. Even thin absorbing films in the structure (or in its vicinity) can lead to such strong resonant absorption effects. The resonances may exhibit a negligible spectral shift, but a significant variation in the magnitude when losses are slightly altered, which is highly attractive for sensor and switch applications. Absorption peaks experience a resonant behavior with respect to both frequency and material losses. We show that the width of the absorption peaks decreases and approaches the width of the reflection peaks, as losses decrease. Thus, high-Q resonances can be observed. The absorption resonances also possess strong angular dependence; they may split and significantly increase in magnitude for a slightly inclined incidence. We elucidate the resonant reflection/absorption effects theoretically and provide numerical examples.

This paper proposes a compact zeroth-order resonant (ZOR) antenna with improved gain and efficiency. The proposed CRLH unit cell is based on the coplanar waveguide (CPW) structure. The proposed ZOR antenna is designed for a 2.45 GHz frequency band, and it has the characteristic of monopolar radiation. Shunt inductance is implemented by microstrip short-circuit stubs, and a metal-isolator-metal (MIM) capacitator provides series capacitance, where a large capacitance can be achieved in a small footprint. The proposed antenna comprises two interleaving composite right-/left-handed CRLH unit cells, where the size of one unit cell is measured at only 0.12λ₀ x 0.098λ₀. Because the field is loosely confined within the CPW-based unit cell, a good antenna peak gain of 2.03 dBi, and a radiation efficiency of over 68% is achieved when fabricated on a thin substrate. The proposed antenna did not require an additional matching network, reducing the total antenna footprint. This paper presents antenna parameters such as the return loss, radiation pattern, antenna gain, and radiation efficiency to validate the proposed design, which achieved good simulation results.

A broadband circularly polarized (CP) cylindrical dielectric resonator antenna (DRA) is presented. The DRA is excited by an L-shaped microstrip feed line through the coupling of an annular slot in the ground plane. The broadband CP radiation is achieved by using two CP radiators, DRA and annular slot. Broadband impedance match is obtained by introducing an impedance transformer. The optimal configuration offers a 3-dB axial ratio bandwidth of 15.9%, from 6.22 to 7.28 GHz, and a 10-dB impedance bandwidth of 21.3%, from 5.78 to 7.16 GHz. The measured results for the constructed prototype are also exhibited and discussed.

The goal of this paper is to present a semi analytical method which makes it possible the calculation of the dynamic iron losses in a three phase induction machine taking the slotting effect into account. The particularity of this method is that it allows the distinction of the stator and the rotor slot openings contribution in the dynamic and, consequently, in the total iron losses. This analytical study shows that a convenient choice of the stator and the rotor slot openings leads to an iron loss reduction, due to the cancellation of particular flux density slotting harmonics. Theoretical results are confirmed numerically.

A compact and planar dual band antenna for wireless communication is presented. The impedance bandwidth of the proposed antenna can cover Bluetooth (2.4-2.484 GHz) and ultrawideband (UWB: 3.1-10.6 GHz) bands. It is composed of a semi-bevelled-rectangle patch and a bended L-shaped strip and fed by a microstrip line. The antenna is built on a FR4 substrate with only 21×35 mm surface area included the ground plane. Details of the antenna design and the measured results included voltage standing wave ratio, radiation patters, peak gain, etc. are presented and discussed.

The time delay, space shift and widening of wave packet transmitted and reflected by structures with Bragg mirrors have been investigated. The specific structures such as Bragg mirrors, resonators, and structures with chirp variation of thickness of the ``period'' have been considered. The calculation has been carried out under the conditions that carrier frequency, and incidence angle is in the vicinity of the Bragg resonance. Integral (mass center) and differential (group) estimates of the delay time and space shift have been compared. The conditions for the appearance of anomalous (negative) mass center delay or mass center shift (Goos-Hänchen shift) of the reflected wave packet have been determined. The shape transformations of the wave packet illuminating periodic and quasiperiodic apodized Bragg reflectors have been under consideration. Spatial apodization of permittivity contrast yields much smaller shape deformation of the transmitted wave packet upon incidence at angles and carrier frequency near the edges of reflection band, as well in Bragg reflection band, in comparison with phenomena in similar periodic structures. The values of group delay for layered structures with a small chirp variation of optical (electrical) thickness of the period along longitudinal coordinates have been experimentally obtained in microwave range.

Guided-mode resonance filters (GMRFs) are highly compact structures that can produce a strong frequency response from a single thin layer of dielectric. When a GMRF is formed onto a curved surface, the local angle of incidence varies over the aperture of the device and the overall performance significantly degrades. In the present work, we spatially varied the grating period of a curved GMRF to perfectly compensate for the local angle of incidence. The performance of the curved device actually surpassed that of a flat device because it also compensated for the spherical wave front from the source. This paper summarizes our design process and experimental results obtained around 25 GHz.

A Substrate Integrated Waveguide (SIW) planar array is presented using a right handed circularly polarized (RHCP) element with four crossed tilted radiating slots. In addition, a pair of metallic tuning vias is included to really improve the reflection of longest slots. A corporate feeding network over SIW has been designed for distributing the input signal to 128 radiating elements, divided into 8 progressive wave linear arrays of 16 elements each. The designed planar array has been manufactured and measured to verify the antenna performance. 25.5 dB gain, 2.33 dB axial ratio, as well as 85% radiation efficiency values have been experimentally achieved at 17 GHz. A 3% usable bandwidth (16.75-17.25 GHz) is obtained due to the typical frequency main beam tilt dispersion in the elevation plane of the progressive wave arrays.

Maxwell equations can be used to formulate an analytical full time-domain theory of skin effect phenomena in circular cylindrical conductors without any detour into the frequency domain. The paper shows how this can be done and concomitantly provides the means to determine the time-varying per unit length voltage drop along the conductor from a given time-varying conductor current. The developed relationship between voltage and current is not very complicated and led the authors to examine the reasons why it has never been utilized in transient analysis, nor given special emphasis in the literature. Those reasons are thoroughly examined and the conclusion is that the conditions required for the application of a purely time-domain skin effect theory are very restrictive.

This paper presents a new approach to calculate the accurate fourth-order Doppler parameters for Geosynchronous Synthetic Aperture Radar (Geo-SAR). To get exact calculation results, the Earth is modeled as an ellipsoid and the relative motion between the sensor in an elliptical orbit and the rotating Earth is analyzed. The J₂, J₃ and J₄ orbital perturbation items and attitude steering are analyzed. Ignoring the perturbation force would produce errors of the Doppler parameters for spaceborne SAR because it can influence the six orbital elements. Since the Doppler parameters are related to the antenna beam pointing directions and influenced by attitude of SAR platform, the calculation results before and after attitude steering are shown. Furthermore, the Doppler parameter properties during the whole orbital periods of Geo-SAR are compared with those of Low-Earth-Orbital SAR (Leo-SAR). Finally, the effects on Doppler parameters stemmed from the radar beam pointing accuracy are analyzed.

Based on the observation that sparsity assumption is well satisfied in the synthetic aperture radar (SAR) imaging applications, there is increasing interest in utilizing compressive sensing (CS) in SAR imaging. However, there are still several problems which should be concerned in CS-based imaging approaches. Firstly, inevitable noise and clutter challenge the performance of CS algorithms. Secondly, the super-resolving ability of CS algorithms is not sufficiently exploited in most cases. Thirdly, nonideal characteristics of mutual coherence affect the performance of CS algorithms in complex scenes. In this paper, a novel CS imaging framework is proposed for the purpose of improving the imaging performance of stepped frequency SAR. Meanwhile, a super-resolving imaging algorithm is proposed based on the nonquadratic optimization technique. Simulated and rail SAR measured data are applied to demonstrate the effectiveness of the novel framework with the proposed super-resolving algorithm. Experimental results validate the superiority of this method over previous approaches in terms of robustness in low SNR, better super-resolving ability and improved imaging performance in complex scenes.

Linear array synthetic aperture radar (LASAR) is a promising radar 3-D imaging technique. In this paper, we address the problem of sparse recovery of LASAR image from under-sampled and phase errors interrupted echo data. It is shown that the unknown LASAR image and the nuisance phase errors can be constructed as a bilinear measurement model, and then the under-sampled LASAR imaging with phase errors can be mathematically transferred into sparse signal recovery by solving an ill-conditioned constant modulus linear program (ICCMLP) problem. Exploiting the prior sparse spatial feature of the observed targets, a new super-resolution sparse autofocus recovery algorithm is proposed for under-sampled LASAR 3-D imaging. The algorithm is an iterative minimize estimation procedure, wherein it converts the ICCMLP into two independent convex optimal problems, and joints l₁-norm reweights least square regularization and semi-definite relax to find the optimal solutions. Simulated and experimental results confirm that the proposed method outperforms the classical autofocus techniques in under-sampled LASAR imaging.

This paper presents that the extra passband with two transmission zeros can be obtained by adding shunt open stubs to the asymmetric half-wavelength resonators structure. By using this method, a fourth or even higher passband with good selectivity and compact size can be obtained. Dual-band, tri-band and quad-band bandpass filters are demonstrated by using this method. The measured bandwidth is 80/180 MHz for the dual-band, 60/180/180 MHz for the tri-band and 130/360/170/70MHz for the quad-band filter, respectively. The measured insertion loss for the dual-band, tri-band and quad-band filter is less than 2.7 dB, 2.5 dB and 2.9 dB at the center frequency. All the simulated results and the measured results agree well.

Cognitive radio technology proposes the utilisation of under-utilised spectrum resources which may include time, frequency, geographical location, direction, polarisation et cetera. Frequency is the conventional spectrum resource, considered to be exploited for cognitive radio, especially in the field of antenna design. We address the unconventional directional resource for cognitive radio, from antenna design perspective. The design concept of a multi-band compact array, capable of providing separate and simultaneous access to frequency and directional resources, is presented. The initial explorations are carried out for three frequency resources (bands) and three directional resources, providing nine degrees-of-freedom altogether. Laboratory version of the proposed antenna system is then used to gain proof-of-principle through line-of-sight measurements in an over-the-air test-bed, followed by static outdoor measurements in a multipath scenario. At the end, simulations are performed for arbitrary arrays in heterogeneous propagation scenarios to study the influence of antenna radiation pattern on the availability of directional opportunity. Recommendations are made for possible antenna design based on the simulation results.

A design and analysis of a novel proximity-fed printed slot antenna with 3.5/5.5 GHz dual band-notched characteristics are presented. To obtain an ultra-wideband (UWB) response, a circular patch with a rectangular conjunction arm is etched concentrically inside a ground plane aperture. The antenna is proximity-fed by a microstrip line with an open shunt stub on the other side of the substrate. The designed antenna satisfies a -10 dB return loss requirement in the frequency band from 2.7 to 17 GHz. In order to obtain dual band-notched properties at 3.5 and 5.5 GHz, an open ring slot is etched off the circular patch and a π-shaped slot is etched off the microstrip feeding line, respectively. A curve fitting formulation is obtained to describe the influences of the notched resonators on the corresponding notched frequencies. The proposed antenna is designed, simulated and fabricated. The measured data show a good agreement with the simulated results and the equivalent circuit results through the use of a modified Vector Fitting technique for a rational function approximation. The proposed antenna provides almost omnidirectional radiation patterns, relatively flat gain and high radiation efficiency over the entire UWB frequency excluding the two rejected bands.

This paper introduces a method for canceling the parasitic capacitance of integrated common mode (CM) filter by optimizing the layout of ground winding. Firstly, the CM filter with positive or negative coupling between the ground and inductor winding is researched, respectively. Then, the two coupling polarizes are combined to form the bi-directional coupling, simulation and measured results show bi-directional coupling ground can effectively improve the high frequency (HF) filtering performance. The equivalent circuits are given to demonstrate the cancellation mechanism, and modelling is derived for the design of ground winding. To further validate the application of proposed technique, CM noise and input/output signals for PFC (Power Factor Correction) converter with bi-directional coupling ground CM filter is simulated. The noise spectrums show conductive interference at high frequencies is effectively suppressed and meets the required electromagnetic interference (EMI) standard.