In this paper, a Frequency-Dependent Forward-Backward Time-Stepping (FD-FBTS) inverse scattering technique is used for reconstruction of homogeneous dispersive object. The aim of the technique is to reconstruct the relative permittivity at infinite frequency, static relative permittivity and static conductivity of the homogeneous dispersive object simultaneously. The technique utilizes iterative finite-difference time-domain (FDTD) method for solving inverse scattering problem in time domain. The minimization of the cost functional is carried out utilizing Dai-Yuan nonlinear conjugate-gradient algorithm. The Fréchet derivatives of the augmented cost functional are derived analytically with respect to scatterer properties. Numerical results for reconstruction of two-dimensional homogeneous dispersive illustrate the performance of the proposed technique.

Transmission zero behavior of two coupled sections - interdigital and combline - is investigated. It is shown that the shifting of transmission zero of any coupled-section of a particular length depends on the width of various parts and the orientation of coupled-section. Mathematical formulation has been performed to show the effect of stepped discontinuity on the transmission zero. Further, this transmission zero allocation property is used in suppression of harmonics. The idea is implemented in two types of resonators - first in parallel-coupled resonators and second in open-loop resonators. Two parallel coupled resonator based bandpass filters (BPFs) with second harmonic suppression - one of second-order and the other of fourth-order - using different coupled-sections have been fabricated, and suppression up to -30 dB and -54 dB respectively has been achieved. A fourth-order open-loop resonators based BPF with suppression of undesired passbands up to 6.3f_o has been fabricated. Further, the above property is also used to design a dual-band BPF with wide stopband without increasing the size of the filter.

Wireless power transfer system to capsule endoscope at sub-gigahertz (GHz) frequency is presented. Compact self-resonant antennas are designed to realize the transcutaneous power transfer. Experiment shows that at a distance of 5 cm, the designed system operating at 433.9 MHz can realize 1.21% power transfer efficiency (PTE) through duck intestine and porcine multilayered tissues, that is, 47.55 mW power delivered to load (PDL) at the specific absorption rate (SAR) occupational exposure limitation.

This paper proposes a fully integrated broadband power amplifier for LTE-A application using GaAs HBT process. To improve the linearity and broadband performance, RC feedback structures and dynamic bias circuits are employed and designed through optimization. With careful design of the broadband matching networks in the proposed 3-stage power amplifier topology, a power gain above 21.6 dB is achieved from 1.8 GHz to 2.8 GHz. Driven by an 80 MHz wideband LTE-A signal with PAPR of 7.5 dB, the designed RF power amplifier achieves an average output power about 22 dBm at ACLR=-30 dBc over the entire 1 GHz frequency band. Considering the broad bandwidth of the driven signal and wide frequency coverage bandwidth, the performance merits of the proposed design compare favorably with the state-of-the-art.

ƒA novel compact circularly polarized microstrip antenna (CPMA) with bandwidth enhancement is proposed and studied. By employing capacitive loading and inductive loading, the size miniaturization is achieved. The cross-shaped aperture in the ground plane is able to excite two orthogonal modes. The near-equal amplitudes and 90° phase difference between these two modes are realized by properly designing the feed network, i.e., a 0°-90° hybrid comprising a 3-dB Wilkinson power divider cascaded with a 90° phase shifter. The proposed antenna exhibits a global bandwidth of 11.5% ranging from 1.88 GHz to 2.11 GHz with an overall size 50 mm × 50 mm × 6.8 mm (0.33λ₀ × 0.33λ₀ × 0.045λ₀). The global bandwidth is defined where return loss is larger than 10 dB, broadside axial ratio (AR) smaller than 3 dB, and gain above 0 dBic.

In this paper, a coplanar waveguide (CPW)-fed dual-band slot antenna with circular polarization (CP) is presented. In order to achieve CP characteristic, an asymmetric slot and F-shaped end patch are introduced to a conventional rectangular slot antenna. Moreover, by cutting a T-shaped notch on the ground plane, the axial ratio (AR) bandwidth (ARBW) can be extended. The antenna shows left-hand CP (LHCP) radiation in the boresight direction (i.e. +Z direction) at both ARBWs. The proposed antenna is fabricated and measured. The measured results have a good agreement with the simulated ones. The measured impedance bandwidths (|S₁₁| < -10 dB) are 1.08 GHz (2.02 to 3.10 GHz, 40% at 2.70 GHz) and 2.31 GHz (4.57 to 6.88 GHz, 39.8% at 5.8 GHz). The two measured ARBWs are 600 MHz (2.60 to 3.20 GHz, 22.2% at 2.70 GHz) and at least 1.15 GHz (4.85 to 6.0 GHz, 19.8% at 5.8 GHz) at the lower and upper bands, respectively.

The Adaptive Cross Approximation (ACA) algorithm has been used to compress the rank-deficient sub-blocks of the matrices that arise in the numerical solution of integral equations (IEs) with the Method of Moments. In the context of the linear embedding via Green's operator (LEGO) method - a domain decomposition technique based on IEs - an electromagnetic problem is modelled by combining ``bricks'' in turn described by scattering operators which, in many situations, are singular. As a result, macro basis functions defined on the boundary of a brick can be generated by applying the ACA to a scattering operator. Said functions allow compressing the weak form of the LEGO functional equations which then use up less computer memory and are faster to invert.

Previously reported staggered double vane (SDV) slow wave structure (SWS) traveling wave tube (TWT) gave electron efficiency as low as 3.4% at 220 GHz, which needs to be improved. One easy method to improve the electron efficiency and the output power is to reuse the spent electron beam energy, by resynchronizing electron velocity to the phase velocity of the terahertz (THz) signal at the second section of the TWT. In this article, we have modified the pitch of the SWS to realize the tapered phase velocity, which is for the first time to our knowledge applied to the SDV SWS at 220 GHz. By varying the geometry configuration, an optimized structure of tapered pitch SWS has been successfully developed. The results reported in this paper show a significant improvement of the output power, gain and electron efficiency. At 220 GHz, the output power has increased by about 65% with respect to the previous reported value reaching 111 W, and the electron efficiency has improved from 3.4% to 5.6%. In order to simplify the microfabrication process, an input/output coupler with E-plane bending has been designed, which can be fabricated by using only one mask UV-LIGA process.

This paper presents an ultra-compact filtering integrated antenna for GPS (1.57 GHz) and LTE (2.65 GHz) applications. The antenna comprises integration between dual composite right/left-handed antenna and band stop filter in one platform. The whole integrated antenna size is only 30×28.5 mm². Compared to conventional antenna with the same dimensions, the proposed antenna is only 6.5% at GPS band and 16.5% at LTE band. The deign procedures of individual antennas, bandstop filter and the filtering integrated antennas are explained in details. The full wave simulations supporting the design procedures and experimental measurements for all introduced components are introduced with good agreement. Finally, as a consequence of the proposed antenna ultra small size and its filtering capability, the antenna is a good candidate for implanted antenna applications.

In this paper, a magnetically tunable metamaterial is proposed and studied. The metamaterial is based on the combination of ferrite sheets and dielectric rods. The tunable property is originated from the ferromagnetic resonance and electric response of dielectric rods. The retrieved electromagnetic parameters and transmission characteristic showed that by simultaneously inspiring the ferromagnetic resonance and electric resonance, composite metamaterial can possess double-negative band in the resonant state. Moreover, this band was tunable by adjusting applied magnetic fields. The simulations and experiments verified that the composite metamaterial clearly displayed a tunable feature. The proposed method is simple in designing tunable metamaterials.

Polarization converters based on metamaterial have broad application in imaging, sensing and communication from microwave to optical frequency. However, its performance is limited by single function and narrowband. In this paper, a new type of polarization converter based on square loop shaped metamaterial has been presented. It works in the reflection mode to achieve broadband polarization conversion for both circular and x/y linear polarization waves. The incident linearly polarized wave will be converted to its cross-polarized state with a polarization conversion ratio (PCR) lager than 0.9 in two distinct broad frequency ranges; on the other hand, circularly polarized wave will be reflected to its co-polarized state efficiently in the same spectrum regimes. Good agreements have been observed for both simulation and measurement results. This work offers a further step in developing high performance multi-function microwave or optical devices.

Two single-layer X/Ku dual-band dual-polarization reflectarray antennas of different sizes with double parallel dipole elements are presented. Elements of the two bands are set to two orthogonal linear polarizations and placed in interlaced grid. The proposed reflectarrays operate in two frequency-bands within X-band centered at 10 GHz and Ku-band centered at 13.58 GHz. The smaller size reflectarray with elements arranged in a 13×13 grid for X-band and in a 12×12 grid for Ku-band is designed and simulated first. Based on the excellent dual-band performance of the small size reflectarray, then a larger size prototype has been designed, manufactured and measured. Measured results demonstrate the maximum gain of 28.54 dB with 50.93% radiation efficiency at 10 GHz and 31.06 dB with 51.34% radiation efficiency at 13.58 GHz, which show desirable dual-band dual-polarization radiation performance.

An unequal power divider which features quasi-arbitrary output phase difference is proposed in this paper. The circuit consists of four microstrip lines and a resister. By the even- and odd-mode analysis technique, the closed-form design equations of this structure are derived. The characteristic impedances, electrical length and bandwidth variations with power division ratio and phase difference are analyzed. For proving its validity, a prototype with this proposed structure is designed and implemented at 1 GHz. The results of simulation and measurement show that the pro-posed power divider can effectively produce two outputs with controllable power division and phase difference.

In this work, a novel family of Finite Airy array beams have been produced by an optical Airy transform system illuminated by Gaussian Array beams. Based on the generalized Huygens- Fresnel integral, an analytical expression is developed to describe the pattern properties of the beam generated at the output plan of the optical system. The well-known Finite Airy beam generated from the fundamental Gaussian beam using an optical Airy transform system is deduced, here, as a particular case of the main result of the actual study. Numerical calculations are performed to show the possibility to create a multitude of Finite Airy array beams with controllable parameters depending on the number of beamlets, the distance between the adjacent modules and the positions and orientations of the beamlets.

Security detection is becoming extremely important with the growing threat of terrorism in recent years. An effective millimeter-wave (mmw) holographic imaging system is presented in this paper, which can be applied in nondestructive detection such as security detection in airport or other public locations. The imaging algorithm is an extension of the work before as it takes the decay of the amplitude with range into account. The experiment result of an imaging system working at 28-33 GHz frequencies indicates good quality of the algorithm.

In earlier time, we proposed a flat LHM-based hyperthermia scheme for conformal hyperthermia of a large superficial tumor. It is demonstrated that in this scheme by de-ploying multiple microwave sources in a specific array to shape the heating zone and properly setting the source-to-lens distance or phases of sources to adjust the inclination of heating zone, a heating zone better fit to large superficial tumor can be generated. In this paper, we propose a new hyperthermia scheme based on a cylindrical LHM lens which would be more maneuverable for tumors located in tissues with curved surface. It is shown that the same way adopted in the flat LHM-based scheme can be used in this new scheme to acquire desired heating zone for better fitting to tumor region. And larger critical source intervals defined in this new applicator greatly relax the restriction to the size of practical antennas applied in this scheme.

In this paper, a compact filtering power divider (PD) based on half mode substrate integrated waveguide (HMSIW) is presented. The proposed structure is realized by etching slots on the top layer of the HMSIW PD. Accordingly, two resonators are embedded in each patch, as a second order filter. The slots dimensions are obtained by the relationship between them and the extracted external quality factor and coupling coefficient. A good agreement between the simulated and measured results is reported. The measured 3 dB fractional bandwidth is 25% (6.3-8.1 GHz). The maximum insertion loss is 0.9 dB, and the return loss is above 20 dB in the passband. This design has the advantages of low insertion loss, improved out-of-band rejection, compact size, controllable bandwidth, and high selectivity.

In this study, we present an implementation of Ultra wide band (UWB) Koch Snowflake antenna for Radio Frequency Identification (RFID) applications. The compact antenna, based on the Koch Snowflake shape, is fed by coplanar waveguide (CPW) and microstrip line with an overall size of 31x27x1.6 mm³. The simulation analysis is performed by CST Microwave Studio and compared with HFSS software. The antenna design exhibits a very wide operating bandwidth of 13 GHz (3.4-16.4 GHz) and 11 GHz (3.5-14.577 GHz) with return loss better than 10 dB for microstrip line antenna and CPW antenna respectively. A prototype of CPW and microstrip antenna was fabricated on an FR4 substrate and measured. Simulated and measured results are in close agreement. The small size of the antenna and the obtained results show that the proposed antenna is an excellent candidate for UWB-RFID localization system applications.

The improvement of Terahertz (THz) antenna requires efficient (nano)materials to operate within the millimeter wave and THz spectrum. In this paper, doped graphene is used to improve the performance of two types of patch antennas, a rectangular and an elliptical antenna. The surface conductivity of conventional (non-doped) graphene is first modeled prior to the design and simulation of the two graphene based antennas in an electromagnetic solver. Next, different graphene models and their corresponding surface conductivities are computed based on different bias voltages or chemical doping. These configurations are then benchmarked against a similar antenna based on conventional metallic (copper) conductor to quantify their levels of performance improvement. The graphene based antennas showed significant improvements for most parameters of antenna than that of the conventional antenna. Besides that, the higher chemical potentials resulting from higher biasing voltages also resulted in this trend. Finally, the elliptical patch graphene antenna indicated better reflection performance, radiation efficiency and gain than a rectangular patch operating at the same resonant frequency.

A novel family of fractal curves is proposed which provides the designer a systematic way of miniaturizing the microwave components with the freedom of choosing among form factor, design complexity and achieved miniaturization. The proposed fractal curve is characterized by two integer values m and n. The m value determines the form factor of the fractal while n value governs the iteration number. The equations governing the geometry of fractals are also presented. The proposed fractal is characterized for miniaturization by designing a printed monopole antenna for various values of m and n. The results from the full wave simulations and experiments are analysed and explained. The effect of fractal on reducing the resonant frequency is quantified by an equation based on its physical interpretation. Based on this analysis, saturation point for miniaturization is established. The curves being symmetric around a straight line, distortionless radiation patterns are seen.