A perturbation method based on the decoupling of propagation and diffusion phenomenons is proposed in order to calculate losses in microwave structures. Starting from the first problem in which the conducting regions are not described, a perturbation is calculated by solving a second problem restricted to the vicinity of the conductors; iterations between these problems can be performed when the perturbed solution is not sufficiently accurate. The perturbation approach is however more accurate than a method based on a surface impedance model, without introducing the huge calculations that appear when both conducting region and external medium are described in a single problem. 2D examples are presented using the finite element method and the integral equation method.

This paper presents an effective Polar Format Algorithm (PFA) for spotlight bistatic synthetic aperture radar (SAR) with arbitrary geometry configuration. Nonuniform interpolation and resampling are adopted when converting raw data from polar coordinates to Cartesian coordinates according to the characteristics of raw data samples in spatial frequency space. Thus, the proposed algorithm avoids both rotation transformation and the calculation of azimuth compensation factor and thereby avoids the corresponding approximate error appeared in the conventional PFA. Meanwhile, the proposed algorithm inherits the character of decomposing 2-D interpolation to two 1-D interpolations from conventional PFA algorithm applied in monostatic SAR imaging. Therefore, the processing flow, computation efficiency and performance of the proposed algorithm are the same as those of conventional PFA for monostatic spotlight SAR. Point target simulations are provided to validate the proposed algorithm.

With the emergence of UWB systems and, in particular, the pulsed modulations, the modeling of antennas as Linear Time Invariant (LTI) systems has been studied in the last years extensively. This approach offers the advantage of modeling the antennas in frequency domain as well as in time domain. Further, the performance in terms of dispersion is taken into account implicitly in the modeling. This paper presents and compares methods in order to model antennas as LTI systems. The models are analyzed and discussed: physical interpretations are specified; differences between the models are highlighted; alternatives are proposed; advantages and drawbacks of approaches are emphasized.

This paper is an overview of important concepts and formulas involved in the application of coupling coefficients of microwave resonators for the design of bandpass filters with a particular emphasis on the frequency dispersion of coupling coefficients. The presumptions and formulas are classified into accurate, approximate, and erroneous ones.

In this paper, a small modified circle-like slot antenna with modified radiating patch, for UWB applications is proposed. The proposed antenna consists of a modified radiating patch with novel notch and a semi-circle-like with a slope which provides a wide usable fractional bandwidth of more than 135% (3.07-16.26 GHz). By optimizing the notched radiating patch, the total bandwidth of the antenna is greatly improved. The designed antenna has a small size of 27.5×27.5 mm².

This article presents a theoretical characterization of the regular polygonal waveguide (RPW) having n-sides. Based on the symmetrical circular symmetry of the RPW and the circular waveguide (CW), the analogy between the electromagnetic (EM) behaviors of these to waveguide (WG) is established. After a brief recall about the state of the art concerning the WG engineering and its application, we introduce a basic theory of the WG presenting a regular polygonal cross-section with n-sides. By considering, the fundamental mode TE₁₁, we develop the main mathematical formulas summarizing the different characteristics (cut-off frequency, f_c, propagating constant, k₁₁ and S-parameters) appropriated to any RPW in function of its physical parameters (number of sides, n, diameter, D and height, h). In order to verify the validation of the developed analytical expressions, comparisons between the HFSS simulated and theoretical dispersion diagrams of regular pentagonal (n=5), hexagonal (n=6), heptagonal (n=5) metallic (copper) WG with for example, 50 mm outer diameter are presented. So, it was demonstrated that very good correlation between the theoretical predictions (f_c(n), k₁₁(n)) is found with a relative error less than 1%. As application of the present study in terms of EM wave shielding, simulation of metallic wall with hexagonal aperture is also performed. Finally, discussion about the future work is drawn in conclusion.

The approximate distribution of the current density induced on the tape surface by guided electromagnetic waves supported by an infinite open tape helix is estimated from an exact solution of a homogenous boundary value problem for Maxwell's equations. It is shown that the magnitude of the surface current density component perpendicular to the winding direction is at least three orders of magnitude smaller than that of the surface current density component parallel to the winding direction everywhere on the tape surface. Also, the magnitude and phase distribution for the surface current density components parallel and perpendicular to the winding direction are seen to be nearly uniform at all frequencies corresponding to real values of the propagation constant.

A low profile dual-band mobile phone antenna with a very small volume of 0.768 cm³ (40 × 4 × 4.8 mm³) is presented. The antenna is formed by a monopole and an open-end slot embedded therein. The impedance bandwidths for the lower and upper bands with a definition of 3:1 VSWR (6 dB return loss) reach 215 MHz (815-1030 MHz) and 515 MHz (1660-2175 MHz) respectively. Furthermore, small excited surface current distributions on the ground plane of the antenna are achieved, and the ground plane length has smaller effect on the achievable bandwidths of the antenna compared with the conventional internal patch antennas for mobile phones, which make the antenna very attractive to be applied to the mobile phones with various possible ground plane lengths. Good radiation characteristics over the operating bands are obtained.

Unlike ellipsometry using light, ellipsometry using microwaves can be subject to significant standing wave effects resulting from reflection of the received wave back to the source. This paper examines these effects on the apparent homogeneity of circular polarization. These effects are examined experimentally using an ellipsometer with no sample and compared with calculated results for a single order of reflection. Good agreement is obtained. That the peak-to-peak variations in the observed irradiance are on the order of four times the amplitude reflectance is observed. The angular dependencies of these effects are path length dependent.

This paper presents compact on-chip finite ground coplanar waveguide (FGCPW) lowpass filter (LPF) and bandpass filter (BPF) for V-band multi gigabit per second (Gbps) wireless personal area network (WPAN) applications. The equivalent lumped-element circuit of the proposed filters can be represented by an ABCD matrix which is obtained by consecutively multiplied ABCD matrixes of one T-network impedance and two shunt admittances. The full-wave EM simulators, Ansoft^TM HFSS and Agilent^TM Momentum, were used to fine tune the desired frequency response. The FGCPW LPF and BPF were implemented in WIN^TM semiconductor 0.15 μm pHEMT process. The obtained insertion losses are smaller than 0.5 dB and 1.5 dB with return losses of better than 20 dB and 13 dB, respectively. The 1-dB bandwidths of the LPF and BPF are 70 GHz (0-70 GHz) and 11 GHz (55-66 GHz), respectively. The stopband rejections are better than 20 dB from 95 to 120 GHz in the LPF, and from 0 to 42 GHz and 82 to 120 GHz in the BPF. The measured frequency responses show good agreements with the simulations. The chip size is very compact of 0.43×0.45 mm².

This paper presents a flexible and generic broadband RF predistortion linearizer designed using backward reflection topology that can correct for the dualinflection point type compression characteristics usually encountered in the gain profile of metal semiconductor field effect transistor (MESFET) based power amplifiers. It employs circuit configuration of two parallel Schottky diodes with one p-intrinsic-n (PIN) diode in parallel, connected at two ports of a 90°hybrid coupler. The Schottky diodes are coupled via a quarter wave transmission line segment which generates dual inflection points in the gain characteristics of the linearizer. The incorporation of a PIN diode helps in improving the achievable range in the gain and phase characteristics of the linearizer. Overall, the linearizer is capable of linearizing various types of power amplifiers owing to the flexible control on the linearizer's parameters and eventually the gain and phase characteristics of the linearizer. The proposed linearizer can be employed in the frequency range of 1.4-2.8 GHz and can simultaneously improve the third- and fifth-order intermodulation distortions. The measurements carried out on a commercial ZHL-4240 gallium arsenide field effect transistor (GaAs FET) based power amplifier demonstrates the broadband functionality of the proposed linearizer.

The Moment Method is used to estimate the error induced by a compact measuring probe in the near-field. A crossed-dipole is used as a compact near-field measuring probe of a waveguide radiator in an infinite ground plane, since it measures both co-pole and cross-pole components simultaneously. However, due to multiple reflections between radiator and probe, in addition, mutual coupling effects between the poles, near-field values are changed. The relative sampled electric field pattern (without the probe) is compared to the relative sampled co-pole voltage pattern in the scan plane and the induced error is computed. The radiating waveguide's reflection coefficient is altered with respect to the reflection coefficient when there is no probe in the near-field. The numerical results concerning the reflection coefficient without the probe are compared to the measured values, and good agreement is observed.

Application of multi-dimensional Cauchy approximation and coarse-discretization electromagnetic (EM) models to surrogate-based optimization of microwave structures is discussed. Space mapping is used as an optimization engine with the surrogate model constructed as a Cauchy approximation of the coarsely discretized device EM model. The proposed approach allows us to perform computationally efficient optimization of microwave structures without using circuit-equivalent coarse models traditionally exploited by space mapping algorithms. We demonstrate our technique through design of a range of microwave devices, including filters, antennas, and transitions. Comprehensive numerical verification of the proposed methodology is carried out with satisfactory designs obtained --- for all considered devices --- at a computational cost corresponding to a few fullwave simulations.

The spectral switch phenomenon of light induced by scattering from a collection of particles is, to the best of our knowledge, reported for the first time. It is shown that when a spatially coherent light wave with a spectrum of Gaussian distribution is scattered from a collection of particles, the rapidly transition of the spectrum of the scattered field from red shift to blue shift (i.e., spectral switch) can be observed. It is also found that the spectrum of the scattered field will experience several spectral switches with the increase of the scattering angle.

We apply the linear embedding via Green's operators (LEGO) method to the scattering by large finite dielectric bodies which contain metallic or penetrable inclusions. After modelling the body by means of LEGO bricks, we formulate the problem via an integral equation for the total incident currents over the boundaries of the bricks. This equation is turned into a weak form by means of the Method of Moments (MoM) and sub-domain basis functions. Then, to handle possibly large MoM matrices, we employ an order-reduction strategy based on: i) compression of the off-diagonal sub-blocks of the system matrix by the adaptive cross approximation algorithm and ii) subsequent compression of the whole matrix by using a basis of orthonormal entire-domain functions generated through the Arnoldi iteration algorithm. The latter leads to a comparatively small upper Hessenberg matrix easily inverted by direct solvers. We validate our approach and discuss the properties of the Arnoldi basis functions through selected numerical examples.

This paper presents a closed-form analysis of composite right/left handed transmission lines. The ladder network structure of the transmission line allows to obtain a rational form of any twoport network representation. As a consequence of the rational form of the transfer functions, poles and residues are easily computed and the dominant ones selected leading to an efficient time-domain macromodel. The numerical results confirm the robustness and the accuracy of the proposed method in capturing the physics of composite right/left handed transmission lines.

A modified microstrip combline array antenna (MMCA) is designed to obtain wide beamwidth (≈90°) in E-Plane radiation pattern and therefore the better coverage for using in the radio controller systems for avionic application. Beside wide beamwidth, wide bandwidth can be obtained by designing of MMCA in travelling wave mode. Moreover, as will be seen in the paper, to achieve a better performance we need the low sidelobe level and tilted radiation pattern, which can be obtained by suitable tapering the amplitudes of array elements and adjustment the phase difference between them, respectively.

In this paper, a frequency reconfigurable active array antenna (RAA) system, which can be reconfigurable at three different frequency bands, is proposed. The proposed RAA system is designed with a novel frequency reconfigurable front-end amplifiers (RFA) designed with the simple reconfigurable impedance matching circuits (RMC) with the MEMS switches. With the MEMS switch, the RFA is realized without any performance sacrifice especially linear characteristic. The proposed RMC is composed of a series transmission line and a shunt capacitor, and an arbitrary impedance can be transformed to any other impedance value with single switch control for a desired frequency band. The proposed RAA antenna system is composed of the RMC, RFA with the RMC, 2×2 array of reconfigurable antenna elements (RAE), as well as a reconfiguration control board (RCB) for MEMS switch control, and the validity of the proposed RMC, RFA, as well as RAA system, which is presented with the experimental results.

Generalized band structure equation for photonic crystals which containing dielectric rods in metals medium was derived by using the plane wave expansion method. From the band structure, we can study band gap of photonic crystals in both E and H polarizations. Since metals are frequency-dependant materials, modification needs to be done on the plane wave expansion equation to calculate the metallic photonic crystals containing dielectric constant rods. To ease the calculation, simple Drude model for metals are used. In this model, the equation is without damping constant. We have plotted the band structure for photonic crystals in metals medium. Then, we studied the ffective plasma frequency of the structure from the band graph in E polarization mode (TM). We found that effective plasma frequency can be tailored as we want. Detailed results are presented with different sizes of radius. Comparison is made for different background materials.

Guided-wave propagation in chiral H-guides is analyzed, using a building-block approach. In a first stage, a 2D chiral parallel-plate waveguide is studied using a frequency dispersion model for the optically active medium, where the constitutive chiral parameter is assumed to be dependent on the gyrotropic parameter. In the second stage, the mode matching technique and the transverse resonance method are used to characterize the 3D structure. A full parametric study is presented for a fixed frequency. The operational and dispersion diagrams for the chiral H-guide are presented. By replacing the common isotropic slab with a chiral slab, chirality provides an extra degree of freedom in the design of new devices.