Ajay Chakraborty

Phase-Only and Amplitude-Phase Only Synthesis of Dual-Beam Pattern Linear Antenna Arrays Using Floating-Point Genetic Algorithms

In this paper, we present a comparison study between phase-only and amplitude-phase synthesis of symmetrical dual-pattern linear antenna arrays using floating-point or real-valued genetic algorithms (GA). Examples include a sum pattern and a sector beam pattern. In the former, phase is only optimized with predetermined Gaussian amplitude distribution of fixed dynamic range ratio (|amax/amin|) and in the latter, both are optimized with less dynamic range ratio than the former and yet share a common amplitude distribution.

SYNTHESIS OF THINNED PLANAR CIRCULAR ARRAY ANTENNAS USING MODIFIED PARTICLE SWARM OPTIMIZATION

In this paper, the authors present an optimization method based on modifled Particle Swarm Optimization (PSO) algorithm for thinning large multiple concentric circular ring arrays of uniformly excited isotropic antennas that will generate a pencil beam in the vertical plane with minimum relative side lobe level (SLL). Two difierent cases have been studied, one with flxed uniform inter-element spacing and another with optimum uniform inter-element spacing. In both the cases, the number of switched ofi elements is made equal to 220 or more. The half- power beam width of the synthesized pattern is attempted to make equal to that of a fully populated array with uniform spacing of 0:5‚. Simulation results of the proposed thinned arrays are compared with a fully populated array to illustrate the efiectiveness of our proposed method.

Design of Phase-Differentiated Reconfigurable Array Antennas With Minimum Dynamic Range Ratio

In this letter, we propose a real-coded genetic algorithm (GA) for optimal design of reconfigurable dual-beam linear array antennas with phase only control. The problem is to find a common amplitude distribution with minimum dynamic range ratio (DRR) that will generate a pencil beam with zero phases and a flat-top beam with continuously controllable phases of an analog phase shifter. Results are also shown for the same design without minimizing dynamic range ratio (amax /amin) of excitation amplitude

Augmentation of Anti-Jam GPS System Using Smart Antenna with a Simple DOA Estimation Algorithm

Smart Antenna system analysis presented with multipath and null constraint for reducing interference and efficient use of spectrum with the help of LMS algorithm for GPS (Global Positioning System) System. A new simple DOA (Direction of Arrival) estimation method by rotation of antenna plane proposed. Simulated Result obtained using MATLABTM.

Design of Fully Digital Controlled Reconfigurable Array Antennas with Fixed Dynamic Range Ratio

In this paper, we propose an optimization method based on Genetic Algorithm (GA) for design of reconfigurable dual-beam linear isotropic antenna arrays with phase only control of digital phase shifters. The problem is to find a fixed amplitude distribution using four-bit digital attenuator that will generate two broadsided symmetrical beams in vertical plane: a pencil beam with zero phases and a flat-top beam with discrete phases of a five-bit digital phase shifter, with or without pre-fixing the dynamic range ratio (I max /I min) of excitation amplitude distribution to a value equal to or less than seven.

A NOVEL MODELING TECHNIQUE TO SOLVE A CLASS OF RECTANGULAR WAVEGUIDE BASED CIRCUITS AND RADIATORS

A new methodology has been developed, based on moment method; for analyzing a class of rectangular waveguide based circuits and radiators. The methodology involves in modeling the given structure using tetragonal bricks or cavities and then replacing all the apertures and discontinuities with equivalent magnetic current densities so that the given structure can be analyzed using only the Magnetic Field Integral Equation (MFIE). As it is necessary to use a number of such cavities in order to study these complicated waveguide structures, the present method is named as Multiple Cavity Modeling Technique (MCMT). The major advantage for using the MCMT in rectangular waveguide based structures is the fact that since only the magnetic currents present in the apertures are considered the methodology involves only solving simple magnetic field integral equations rather the coupled integral equation involving both the electric and magnetic currents. Further it is possible to consider both co and cross polarization and also the thickness of the waveguide discontinuities like diaphragm thickness or window thickness in the analysis. Due to this, it is possible to get highly accurate result. It is also possible to extend the method to any number of resonators, cavities or irises regardless of the polarization. To demonstrate, the methodology has been applied to analyze an open end of a waveguide with dielectric plug, both in transmitting and receiving mode, and a waveguide step discontinuity. Even mode and odd mode admittances of interacting identical inductive diaphragms have also been calculated using this methodology. Data obtained using this technique has been compared with measured, CST microwave studio simulation and literature available data. The theory has been validated by the reasonable agreement obtained between experimental data, simulated data and literature available data with numerical data.

LOADED WIRE ANTENNA AS EMI SENSOR

This paper describes the performance of different loaded wire antennas (e.g., inverted L, T, I and C-shaped antennas) as electromagnetic interference (EMI) sensors. Loaded wire antennas in transmitting mode are widely used for low frequency communication. However, while using these antennas as EMI sensors, the extra loading is likely to introduce the reception of cross-polarized component of incident electric field and investigation on this has not yet been performed. This paper highlights the results of the initial investigation on the performance of these loaded antennas as EMI sensors in terms of the Antenna Factor for the desired and cross-polarized component of incident electric field. The Method of Moments with Pulse basis function and Point-matching technique has been used to evaluate the current distribution on the antenna surface and hence the Antenna Factor.

Electromagnetic Interference Shielding Effectiveness of Hybrid Conductive Polymer Composite

Electromagnetic interference (EMI) shielding characteristics of ethylene vinyl acetate (EVA) and ethylene propylene diene (EPDM) and their 50: 50 blend filled with conductive carbon black and short carbon fibre (SCF) have been studied. The measurements of shielding effectiveness (SE) were carried out in two different frequency ranges 100-2000 MHz and 8-12 GHz (X-band range). The return loss and the loss due to absorption were also measured as a function of frequency in the X-band range and microwave region. It is observed that the SE of the composites is frequency dependent, especially at higher frequency range, and it increases with increasing frequency. The SE also increases with the increase in filler loading. It was found that electromagnetic waves interact with the material via the impurities, inclusions and voids existing in the bulk composites. The SCF-filled composites show higher SE compared to that of conductive carbon black. The correlation between SE and conductivity of the various composites is also discussed. The results suggest that the fibre-filled (20 phr) composites can be used for the EMI shielding, as well as for some microwave applications.

CHARACTERISTICS OF AN OFFSET LONGITUDINAL/TRANSVERSE SLOT COUPLED CROSSED WAVEGUIDE JUNCTION USING MULTIPLE CAVITY MODELING TECHNIQUE CONSIDERING THE TE00 MODE AT THE SLOT APERTURE

A moment method analysis of a broad wall slot coupled crossed rectangular waveguide junction has been presented in this paper. The coupling slot is longitudinal/transverse and offset from the centre lines of the guides. The integral equations, governing the characteristics of the device, have been obtained using Multiple Cavity Modeling Technique, taking into account of the finite wall thickness and the TE00 mode at the slot apertures and have been solved using Moment Method to obtain the aperture distribution. The normalized resonant lengths/complex S-parameters have been calculated from this field distribution for different guide height/slot offsets/slot widths/slot thickness of the longitudinal/transverse slot over the frequency band. Numerical data, thus obtained, have been compared with measured/literature available/CST Microwave Studio Simulated data. The theory has been validated by the reasonable agreement obtained between them. It has been shown that, neglecting the TE00 mode at the slot apertures can adversely effect the estimation of the resonant frequency and equivalent network parameters.

RECTANGULAR WAVEGUIDE-FED HEMISPHERICAL DIELECTRIC RESONATOR ANTENNA

Hemispherical dielectric resonator (HDR) antenna excited with a thick slot at the short circuited end of waveguide is analyzed theoretically and verified experimentally. The problems are formulated using the Green’s function approach; with unknown slot currents solved using the method of moments (MOM). The HDR is modeled using exact magnetic field Green’s function due to the equivalent magnetic current in the slot. The field inside the waveguide is expressed in terms of model vectors and modal functions. Thickness of the slot is analyzed using cavity approach. For the analysis of HDR antenna part, the modal series is represented as a sum of particular and homogeneous solutions. The particular solution is computed efficiently using spectral domain approach. In order to determine the effects of varying design parameters on bandwidth and matching, sensitivity analysis is carried out using the code developed. Measurements were carried out to verify the theory, and reasonable agreement between them is obtained.