A novel, compact wideband bandpass filter based on an improved quad-mode resonator is proposed in this paper. Due to the usage of a coupled-line section, the resonator has a quad-mode behavior. The resonant frequencies can be tuned by regulating not only the electrical lengths, but also the characteristic impedances. Owing to the symmetry of the construction, even- and odd-mode analysis is utilized to analyze the proposed resonator. Finally, a wideband bandpass filter with 88% (2.1 to 5.4 GHz) relative bandwidth is designed, fabricated, and measured. The measured results are in good agreement with the simulated ones, which demonstrates the feasibility of the design approach.

We have studied dynamics of a periodic X-band Gunn oscillator (GO) forced by microwave chaotic signals through numerical simulation and by hardware experiment. The chaos used as forcing signal is generated in a periodically driven non-oscillatory GO. Numerical simulation results indicate that the forced periodic GO becomes chaotic for a moderate strength of forcing chaos. The generated chaos in driven GO is found to become phase or general synchronized to the forcing chaos depending on strength of the latter one. Hardware experiments are performed in X-band of microwave frequency. It shows generation of chaos in driven GO due to forcing. Moreover, synchronization between forcing and generated chaos is indirectly verified.

A novel printed antenna with a slotted patch and a defected ground structure (DGS) for dual-band operation is presented. By inserting an I-shaped slot into the patch and defecting the ground plane, triple-mode resonance for achieving dual operation bands, especially an extremely wide bandwidth for the higher band, can be excited. The measured bandwidths are 100 MHz (2.38-2.49 GHz) and 2.94 GHz (3.4-6.34 GHz) for the lower and upper bands, respectively, which agree well with the simulation. The experimental average gains across the two operating bands are 1.0 and 3.9 dBi, respectively, with typical radiation patterns for a patch antenna having a defective ground. The proposed antenna with a compact size of only 22×25 mm² sufficiently covers performance requirement of the 2.4/5.2/5.8 GHz WLAN and the 3.5/5.5 GHz WiMAX operation systems.

A broadband rectifying circuit with high microwave-direct current (mw-dc) conversion efficiency is designed based on the voltage doubling circuit. The rectifying circuit consists of a broadband match network, a capacitance, a diode, a dc-pass filter formed by three fan-shaped stubs and a resistive load. The measured results show a maximum mw-dc conversion efficiency of 78.3% at 2.45 GHz centre frequency on a 900 Ω load. When the input power is 15 dBm, the bandwidth of efficiencies higher than 50% is about 57% (1.65 GHz-3.05 GHz). The simulated results agree with the measured ones. The rectifying circuit has the characteristics of simple structure and easy integration, which can be applied in the microwave power transmission systems.

A dual-band circularly-polarized microstrip antenna is proposed, and the antenna for GPS is designed. The radiation characteristics of the dual-band circular polarization are achieved by installing one pair of L-shaped slits at all edges of the square patch. The impedance matching in the dual band is tuned by an L-probe feed. The proposed antenna is effective and useful in the design for dual-band circularly-polarized operation.

This paper presents a broadband hexa-band dual-polarized loop antenna for mobile communications. Two orthogonal one-wavelength-perimeter modes of a rectangular loop are excited by two orthogonal feedings. One mode for vertical polarization is excited by a circular monopole, and the other mode for horizontal polarization is excited by a slot-coupled microstrip line. By optimizing the antenna structure and the orthogonal feedings, the orthogonal polarizations can be achieved in a wide bandwidth with high ports isolation. The overall size of the proposed antenna is only 58×53 mm² (0.43λ₀×0.39λ₀, λ₀ is the free-space wavelength at 2.2 GHz). A prototype of the proposed antenna is built and tested. The measured bandwidth with reflection coefficient less than -10 dB is 61.4% (1.65-3 GHz) for both orthogonal polarizations, covering the DCS, PCS, UMTS, WLAN, LTE 2300, and LTE 2500 operation. The measured ports isolation is better than 28 dB over the entire band. In addition, the radiation patterns, gains and diversity performance are also discussed.

This paper presents the design of an asymmetrical Doherty power amplifier (DPA) with improved linearity and efficiency performance. Resonator-type drain bias networks, providing high impedances at the carrier frequency and low impedances with small variation at the envelope frequency, are introduced to reduce the DPA's memory effects when transmitting wideband signals. The general criteria for DPA design are summarized, and the approach to obtain optimum fundamental and harmonic impedances is proposed to achieve back-off efficiency enhancement. For experimental validation, the asymmetrical DPA is designed and implemented using two identical GaN HEMTs. Measured with continuous wave (CW), the proposed DPA delivers a saturation power greater than 49.3 dBm from 3400 to 3600 MHz, along with high drain efficiency of over 62% and 48% at peak and 8-dB back-off power, respectively. Driven with 100-MHz LTE-advanced signals, the adjacent channel leakage ratio (ACLR) asymmetry of the DPA at 20-MHz offset is lower than 1-dB. After digital predistortion (DPD) linearization, the proposed DPA achieves an ACLR of better than -48 dBc at an average output power about 41 dBm and the drain efficiency over 45% across the frequency band.

We characterize the alpha power and chirped types of refractive index profile planar slab waveguide in terms of TE/TM mode study, waveguide dispersion study, mode profile properties, power confinement factor and universal b-V graph. Our own developed finite element method has been efficiently applied to analyze the symmetric planar slab waveguide having a complicated refractive index profile. There is a requirement for a high accuracy of numerical technique to analyze the arbitrary refractive index waveguide, as at some frequency the TE and TM modes are smeared on each other, and it is difficult to distinguish them while analyzing. This paper successfully demonstrates the different TE/TM modes supported by the waveguide with respect to alpha-power and linearly chirped types of refractive index profile. The main contribution of our work is to identify the TE/TM mode numerically for a complex refractive index planar slab waveguide and to characterize them in terms of their performance parameters. Then we apply the mode propagation concept to estimate the propagation phenomena in alpha-power and chirped types of refractive index profile waveguide. All the results presented in this paper are simulated in MATLAB only. Our study reveals that waveguide dispersion and number of allowed guided modes are small while for the case of triangular index profile followed by chirped profile and maximum for step index profile case. Hence triangular and chirped types of refractive index profile waveguide seem to be more efficient for long haul optical communication systems.

In this letter, a compact branch-line coupler using a new type of uniplanar composite right/left-handed transmission line (CRLH-TL) is proposed. The transmission line is obtained by etching spiral structure and series meandered capacitive gaps at both ends on the host line. With the aid of lumped element equivalent circuit model and dispersion relations, the CRLH property of the line is studied. By using the proposed structures, the 90-degree phase shift 35.35 ohm and 50 ohm transmission lines are designed for a compact branch-line coupler operating at 1 GHz. It's occupied size is only 32.5% of that of the conventional one. Its uniplanar prototype makes it very useful for wireless communication systems requiring high encapsulation quality.

In this work we present a new physics-based approach for formulating MoM problems based on the use of dipole moments (DMs) --- as opposed to the conventional Green's functions. The proposed technique is valid over the entire frequency range without any need for special treatments and is also free of singularities associated with the Green's function. The DM approach can be used equally well to both PEC and Dielectric objects. We also introduce certain refinements to the DM method to improve its computational efficiency like the use of higher-order basis functions, combining the DM with the Characteristic Basis Function Method (CBFM), the use of closed-form expressions for the calculation of interaction matrix elements and employing Fast Matrix Generation (FMG) for electrically large problems. We also demonstrate ways to incorporate lumped loads, capture sharp resonances even at low frequencies, calculate the input impedance of small antennas, calculate fields from irregular geometries; from faceted surfaces; from geometries with slot and slit; and also demonstrate the capability to model microstrip line type of geometries with fine features.

In order to reduce the higher harmonic component of the magnetic field in magnetically levitated permanent-magnet planar motors (PMPMs), a sinusoidal index for 2-dimensional (2D) wave is proposed and verified by calculating the average total harmonic distortion (THD) of the discrete waveform. Based on this, a novel optimal design method using THD for 2-dimensional wave (THD2D) and fundamental amplitude is proposed for PMPMs. The finite element analysis and experimental results show that the higher harmonic component of magnetic field is reduced with average fundamental amplitude invariant, and the back-EMF is better. So the optimal design method can improve the electromagnetic performance of magnetically levitated PMPMs.

To avoid the spatial variation of scattering characteristic effect, a three-dimensional synthetic aperture radar (3-D SAR) imaging based radar cross section (RCS) extraction technique with fixed transmitter is developed. The 3-D SAR image is used to extract targets' RCS, so it can spatially distinguish different parts of a complex object, or the targets' RCS from environment. With the abilities of outdoor measurement, it can greatly reduce the cost of measurement. Two simulations of three squares and a 3-D complex-shaped electric-large flight model demonstrate the accurate prediction of RCS.

Biomedical imaging has played an important role in identifying and monitoring the effectiveness of the current state of the art treatments for many diseases. The authors recently proposed a novel single-transmitter-multiple-receiver holographic microwave imaging (HMI) technique for imaging small inclusion embedded in a dielectric object which has potential application in medical diagnostics. HMI image quality depends highly on the antenna baseline difference, in order words, the antenna array configuration. Different antenna arrays produce different quality of dielectric images by using HMI imaging algorithm. This paper investigates the antenna array configurations effect on image quality by using HMI imaging approach. Three configurations including spiral, random and regularly spaced arrays are presented in this paper. Both simulated and experimental results are obtained and compared to fully demonstrate the effectiveness of antenna arrays to the HMI technique. The results show that the proposed spiral and random array configurations have an ability to produce high-resolution images at significantly lower costs than regularly spaced arrays.

In this paper, angular glint characteristics of a two-dimension (2-D) perfect electric conductor (PEC) target above a PEC rough surface are investigated. The induced surface currents on the target and on the rough surface are obtained by employing the method of moments com-bining UV matrix decomposition technique (MOM-UV). Based on electromagnetic (EM) theory and the phase-front distortion concept of angular glint, the formulae of angular glint for 2-D target are proposed, and angular glint is calculated precisely by using phase gradient method (PGM). The analysis of the result is implemented by means of numerical extraction of the coupling currents and relationship between the phase front and angular glint, thus revealing the effects of the coupling on the angular glint.

Advances in micro robots in non-invasive medicine have enabled physicians to perform diagnostic and therapeutic procedures with higher resolution and lower risk than before. However, navigation and precise localisation of such micro robots inside human body still remains a challenge. This is mostly due to the 1) lack of precise communication channel models, 2) inhomogeneity of the propagation medium and 3) non-geometric boundaries of the tissues morphometric parameters. In this study, we derive novel intra-body path loss channel models for wave propagation in wireless capsule endoscopy, i.e., propagation through the gastrointestinal tract and the abdominal wall. We formulate an adaptive attenuation parameter as a function of permittivity, conductivity and the thickness of various layers between the transmitter and the receiver. The standard deviation of modelling error of the path loss using our adaptive channel model is smaller than 50% of that of existing channel models. We further analyse the sensitivity of the path loss model to the variations of thickness of different abdominal wall layers. We finally show that the thickness of the fat layer has the greatest influence on the total attenuation parameter of the path loss model and therefore, we modify our adaptive model accordingly.

A right-angled waveguide bend using conformal transformation optics is proposed which guides the input electromagnetic wave smoothly through the waveguide, reduces the reflections and broadens the bandwidth of the device significantly. The isotropic material parameters are obtained through solving Laplace's equations with Dirichlet and Neumann boundary conditions. It is shown that the performance of the proposed bend is mainly determined by refractive indices lower than one. Utilizing this, the approximated resulting medium is implemented by drilling hole arrays in a dielectric background. In order to take advantage of planar technology, it can be implemented in a substrate integrated waveguide.

Active Magnetic Bearings (AMBs) are advantageous due to their active control on rotor position, but are disadvantageous due to their high initial as well running costs. The running cost of AMB can be reduced by improving design of electromagnet so that the same magnetic field can be generated with reduced supply of electric current. In the present paper, analyses of various arrangements of electromagnets using 2D finite element (FE) have been presented. To validate the results of magnetic flux density obtained from theoretical study, experiments were performed, and comparisons have been presented. The electromagnet using Halbach winding arrangement provides the best results.

Statistical Maxwell's Electromagnetic Theories have been developed over many years and applied to a wide range of practical problems in remote sensing of geographical media, imaging in biological media, medical optics, ultrasound imaging, and object detection and imaging and communications in clutter environment. This paper gives a review of recent advances, development and applications of statistical wave theory. Many important problems on imaging in geophysical and biological media have been treated often as separate problems. This paper attempts to present unified theoretical work and viewpoints under the statistical theories which may help further advance and understanding of theories and applications. The statistical electromagnetic theories encompass most advanced mathematical and theoretical work and most practical applications. This includes time-reversal imaging through multiple scattering media, super resolution, communication channel capacity in clutter, space-time vector radiative transfer, bio-electromagnetics and ultrasound in tissues, coherence in multiple scattering, memory effects, the use of transformation electromagnetics, seismic coda, and the fundamental multiple scattering theories. Statistical Electromagnetics Theories are one of the most challenging theoretical problems today involving many applications in geographical and biological media.

A novel miniaturized combined-element frequency selective surface (CEFSS) with simple design process is proposed for multiband applications. In this article, complementary meandered structures and complementary grid structures are combined to realize controllable tri-band characteristics, which allow the designed FSS to transmit different frequency signals at 3.3, 4.5 and 5.4 GHz while reflecting signals at 4.0 and 4.9 GHz. The miniaturized combined-element FSS in this paper has the advantage of smaller size comparing to traditional tri-band FSSs due to the use of meandered structures, which contributes to its independence of both angle and polarization. The associated equivalent circuit is provided to analyze its transmission characteristics. Furthermore, the performances of the proposed structure are evaluated by simulation and measurement, and they agree well.

A planar ultra-wideband (UWB) antenna with triple-notched bands based on square ring short stub loaded resonator (SRSSLR) is presented in this paper. By coupling a SRSSLR beside the microstrip feedline, band-rejected filtering properties around the C-band satellite communication band, 5.8 GHz WLAN band, and 6.8 GHz RFID band are generated. The notched frequencies can be adjusted according to specification by altering the SRSSLR. The results indicate that 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 that is suitable for UWB communications.