The complete design of 35 GHz, 200 kW gyrotron for various material processing and heating applications is presented in this article. The components of the device, such as Magnetron Injection Gun, interaction cavity, collector and RF window, are designed for the TE03 mode. Various in-house developed codes (GCOMS, MIGSYN and MIGANS) and commercially available codes (MAGIC, EGUN and CST-MS) are used for the design purpose. A thorough sensitivity analysis of the gyrotron components are also carried out. The designed device shows the capability to generate more than 200 kW of output power with more than 40% of efficiency.

A single feed compact rectangular microstrip antenna is presented in this paper. A triangular slot is introduced at the upper edge of the patch to reduce the resonant frequency. A small piece of triangular patch is grown within the triangular slot to improve the gain bandwidth performance of the antenna. The antenna size has been reduced by 46.2% when compared to a conventional square microstrip patch antenna with a maximum of 160 MHz bandwidth and -27.36 dB return loss. The characteristics of the designed structure are investigated by using MoM based electromagnetic solver, IE3D. An extensive analysis of the return loss, radiation pattern, gain and efficiency of the proposed antenna is presented. The simple configuration and low profile nature of the proposed antenna leads to easy fabrication and make it suitable for the applications in Wireless communication system. Mainly it is developed to operate in the WiMax frequency range of 3.2--3.8 GHz.

In this paper, the authors propose a method based on the combination of inverse fast Fourier transform (IFFT) and modified particle swarm optimization for side lobe reduction of a thinned mutually coupled linear array of parallel half-wave length dipole antennas with specified maximum return loss. The generated pattern is broadside (φ=90 degree) in the horizontal plane. Mutual coupling between the half-wave length parallel dipole antennas has been taken care of by induced emf method considering the current distribution on each dipole to be sinusoidal. Directivity, first null beamwidth (FNBW), return loss of the thinned array is also calculated and compared with a fully populated array. Two cases have been considered, one with symmetric excitation voltage distribution and the other with asymmetric one. The method uses the property that for a linear array with uniform element spacing, an inverse Fourier transform relationship exists between the array factor and the element excitations. Inverse Fast Fourier Transform is used to calculate the array factor, which in turn reduces the computation time significantly. The element pattern of half-wave length dipole antenna has been assumed omnidirectional in the horizontal plane. Two examples are presented to show the flexibility and effectiveness of the proposed approach.

A novel self-calibration scheme for rotating array antennas is proposed. It is based on the acquisition of some near field samples using a static probe providing information about the actual behavior of the antenna. If any error, fault or obstacle modifies the desired behavior, the weights applied to the feedings of the array elements are modified so that specifications are fulfilled again. Additionally, coupling between the elements of the arrays is also accounted for. Different disciplines such as near field to far field transformation, antenna modeling, adaptive filtering or automatic learning are involved in this system. Some significant results are also presented.

An accurate and efficient finite-difference time-domain (FDTD) method for characterizing transient waves interactions on axially symmetric structures is presented. The method achieves its accuracy and efficiency by employing localized and/or fast Fourier transform (FFT) accelerated exact absorbing conditions (EACs). The paper details the derivation of the EACs, discusses their implementation and discretization in an FDTD method, and proposes utilization of a blocked-FFT based algorithm for accelerating the computation of temporal convolutions present in nonlocal EACs. The proposed method allows transient analyses to be carried for long time intervals without any loss of accuracy and provides reliable numerical data pertinent to physical processes under resonant conditions. This renders the method highly useful in characterization of high-Q microwave radiators and energy compressors. Numerical results that demonstrate the accuracy and efficiency of the method are presented.

Scattering of electromagnetic (EM) waves by many small particles (bodies), embedded in a thin layer, is studied. Physical properties of the particles are described by their boundary impedances. The thin layer of depth of the order O(a), with many embedded small particles of characteristic size a, is described by a boundary condition on the surface of the layer. The limiting interface boundary condition is obtained for the effective EM field in the limiting medium, in the limit a→0, where the number M(a) of the particles tends to infinity at a suitable rate.

A complex image method is presented for the analysis of a subwavelength circular aperture in a perfectly conducting screen of infinitesimal thickness illuminated by a plane wave. The method is based on the Bethe-Bouwkamp quasi static model of the aperture field and uses the spectral domain formulation as the point of departure. Closed-form expressions are obtained for the electromagnetic fields valid for all observation points. Sample numerical results demonstrate the accuracy and efficiency of the method for both normal and oblique illuminations, including an evanescent wave. In the latter case, the results show a circulating power flux and enhanced field confinement near the aperture.

This work presents the analytical solution of vector wave equation in fractional space. General plane wave solution to the wave equation for fields in source-free and lossless media is obtained in fractional space. The obtained solution is a generalization of wave equation from integer dimensional space to a non-integer dimensional space. The classical results are recovered when integer-dimensional space is considered.

A microstrip-fed slot antenna is proposed for short-range UWB communication. First, the characteristics of a circular monopole UWB antenna, as a representative of a class of UWB antennas seen in the literature, are examined in time (pulse-shape) and frequency (reflection and transmission coefficients) domains. From these measurements, certain limitations of this class of antennas are brought out, which are not widely recognized. We then demonstrate that with proper optimization the traditional microstrip-fed slot antenna overcomes these defects and is an excellent candidate for UWB communication systems. This claim is justified with measurements in time domain and frequency domain.

Filter prototypes derived from Gegenbauer polynomials can represent a useful trade-off between amplitude and phase behavior. This paper discusses the main features of this prototype through a comparison with the more classical Chebyshev and Butterworth solutions; it shows, in the case of an X-band waveguide realization, how its intermediate characteristics, with respect to both amplitude and phase responses, can be very useful in satisfying particular filter performance requirements without increasing filter order.

The moment method technique has been improved to investigate the scattering properties of high Tc Superconducting circular antennas with anisotropic substrate in multi-layered configuration. In this method, the electric field integral equation for a current element on a grounded dielectric slab of infinite extent was developed by basis functions involving Chebyshev polynomials. An improved analytical model is presented taking into account anisotropic substrate, superconducting material for the circular patch and multilayered structure. To validate the theoretical results, an experimental study has been performed for a perfectly conducting circular patch on a single layer, with and without air gap. Good agreements were obtained between our theory and measurements. Effects of temperature and thickness of a superconducting film are also reported and discussed. The performances of high Tc superconducting circular antennas were improved by the use of uniaxial anisotropy substrate and multilayer configuration.

Novel circularly polarized antennas with a circular radiating aperture for broadband characteristics are presented in this paper. The vertical and horizontal components of the L-shaped probe are separated and placed at the front and back side of the substrate. The antennas are excited by a microstrip line which is connected to the vertical component of the L-shaped probe and electromagnetically couples the signal to the horizontal component of the L-shaped probe. A novel concept of placing stub in the slot of a planar antenna, by observing the electric field vector behaviour in the slot, is proposed to enhance the axial ratio (AR) bandwidth by around 10%. Unidirectional patterns can be obtained by having a cylindrical cavity of height λ_g/4 behind the antenna and is effective when no stubs are placed in the slot. A < 3 dB AR bandwidth of 39.5% with cavity and 41.18% without cavity but with stub in the slot is obtained in simulation and the results well match with the measurement.

Design and development of a low profile, compact, wide beam and wide band printed double layered exponentially tapered slot antenna (DTSA) with a coplanar waveguide (CPW) feed meant for wide scan active phased array antenna in X-band has been presented. DTSA satisfies the requirements on the maximum reflection coefficient of Γ ≤ -10 dB for ±60^o and ±45^o scan from broadside in H- and E-planes, respectively with a moderate gain of 4-7 dBi. Realized antenna has shown a symmetric pattern together with moderately high gain, low cross-polarization and 3 dB beam width better than ±60^o and ±45^o in H- and E-planes, respectively. The designed structure is expected to find applications in mounting platforms with limited RF real estate available to it like in military aircrafts, owing to its easy integration with the uni-planar monolithic millimeter-wave integrated circuits.

This paper deals with the design of a reconfigurable antenna that resembles a monolithic UWB bow-tie antenna for Ground Penetrating Radar (GPR) applications. In particular, the attention is focussed on the design of the balun system able to work in the frequency band 0.3--1 GHz; the effectiveness of the design is shown by examining the behaviour of the scattering parameters S11 for both the reference monolithic antenna and the designed reconfigurable antenna. Also, an analysis of the radiation pattern of both the monolithic and reconfigurable antennas is presented and confirms the effectiveness of the designed balun system.

A methodology for electromagnetic simulation of initially charged structure with a discharge source (ICSWDS) has been investigated. The ICSWDS can be applied to a lot of areas such as high power electromagnetic (HPEM) radiators. As a method of electromagnetically simulating the ICSWDS, converting initially charged structures into equivalent transient structures and modeling discharge sources by using step voltage sources have been found. A Blumlein pulse forming line (PFL) has been simulated, manufactured and tested to validate this approach. A measured waveform from the test has a good agreement with a simulated waveform.

This paper presents various applications where wide-band signals are the dominant factor. The approaches applied here are based on the present knowledge in the field of white light theory (the THz band), the particle theory of light, and the wave theory of light. White light theory is used to investigate wide-band applications of non-coherent electromagnetic waves in the GHz range represented by noise. In addition, the theoretical approaches to the field of white light are confirmed by various experiments with noise fields applied in the GHz range. These experiments show clear advantages of measurements performed by means of noise fields. The most important feature of these fields is the absence of interference effects.

In this paper, we report experimental results on detecting and analyzing the Brillouin precursor through vegetation at frequencies from 100MHz to 3GHz. An experimental method to collect data is reported. The outcomes in terms of energy and time-spreading are presented using modulated rectangular and Gaussian pulses, as well as a sequence of rectangular pulses. Using field-collected data, this study shows the estimated dynamical evolution of the Brillouin precursor fields for wideband wireless systems, such as those represented by IEEE 802.16. The advantages of Brillouin precursors in terms of power spectrum density and bit energy are discussed. Complex relative permittivity is extracted from the experimental data and is used in theoretical formulation to analyze dispersive propagation for any kind of input waveform. Finally, a near-optimal pulse is proposed to achieve maximum propagation distance and/or signal-to-noise ratio for the transmission of bit stream sequences through vegetation.

Novel formulas are presented that allow the rapid estimation of the number of terms L that needs to be taken into account in the translation operator of the vectorial Nondirective Stable Plane Wave Multilevel Fast Multipole Algorithm (NSPWMLFMA). This is especially important for low frequencies, since the L needed for error-controllability can be substantially higher than the L required in the scalar case. Although these formulas were originally derived for use in the NSPWMLFMA, they are equally useful in at least three other fast matrix multiplication methods.

A circular waveguide loaded with dielectric and metal discs was chosen to evaluate its dispersion characteristics and dispersion shaping with change of structure parameters for wideband coalescence of beam- and waveguide-mode dispersion characteristics for wideband gyro-TWT performance. The azimuthally symmetric TE-mode analysis of the structure was carried out in field matching technique by considering the propagating wave in cylindrical free-space region having radius equal to the hole-radius of metal disc, and the stationary waves in free-space and dielectric regions between two consecutive metal discs. The dispersion relation and, in accordance, a computer code were developed. Further, the roots of the dispersion relation for various sets of the structure parameters were obtained using the developed computer code; the dispersion characteristics were plotted; and the dispersion shaping was projected for typically chosen TE₀₁-, TE₀₂- and TE₀₃-modes. The analytical results were validated against those obtained for the conventional and earlier published structures, and also those obtained using commercially available simulation tool. Finally, a study on azimuthal electric field available over the radial coordinate was carried out to show the control of structure parameter on the gyrating electron beam position for the chosen operating mode of a dielectric and metal discs loaded gyro-TWT.

The total scattering cross section (TSCS) of various targets is computed in this letter from a numerical method in a reverberation chamber (RC). Theoretically TSCS measurements need both a free-space environment (for instance anechoic chamber modeled numerically by absorbing boundary conditions) and various plane waves' stimulations. The method developed allows predicting the TSCS from few simulations in a RC. The foundations and numerical results presented demonstrate the ability of the technique to straightforward compute the TSCS with the finite difference in time domain (FDTD) method. The agreement from these TSCS treatments in RC is finally obtained considering the expected results in free-space.