Sajjad Ur Rehman

Compact bandstop filter using defected ground structure (DGS)

This paper presents a new structure to implement compact bandstop filters by employing coupled DGS resonators etched in the ground plane. The proposed bandstop filter consists of symmetrical DGS resonators with a microstrip excitation to obtain a bandstop filter response. By adjusting space S between the two DGS coupled resonators, the bandwith of the bandstop filter can be easily controlled. A bandstop filter is designed, analyzed and implemented on FR4 dielectric substrate to operate at 2GHz. The measured results are in good agreement with simulations.

Design and System Characterization of Ultra-Wideband Antennas With Multiple Band-Rejection

This paper presents system modelling and characterization of multiple-band notched ultra-wideband (UWB) antennas using the singularity expansion method (SEM). Multiple-band notches in a classical UWB coplanar disc monopole antenna are achieved by introducing systematic defection slots in the coplanar ground structure solely. The antenna uses two dual-band meander ground-defects to create quadruple band notches to avoid possible interference with pre-existing standard services. The SEM with an improved pole-residue extraction scheme is developed to precisely characterize the band-notched antenna in the time and frequency domains. The improved matrix pencil method is applied to the bore sight impulse response of the proposed notched-band UWB antenna to precisely recognize the band-notches and extract the complex poles and residues at the operating bands between the reject-bands. This procedure is validated by reconstructing the impulse response of the antenna from the extracted poles and residues. The obtained simulation and measurement results are in a very good agreement and demonstrate the reliability of the proposed antenna model and characterization method.

Effects on RCS of a perfect electromagnetic conductor sphere in the presence of anisotropic plasma layer

Abstract Effects on RCS of perfect electromagnetic conductor (PEMC) sphere by coating with anisotropic plasma layer are studied in this paper. The incident, scattered and transmitted electromagnetic fields are expanded in term of spherical vector wave functions using extended classical theory of scattering. Co and cross-polarized scattered field coefficients are obtained at the interface of free space-anisotropic plasma and at anisotropic plasma-PEMC sphere core by scattering matrices method. The presented analytical expressions are general for any perfect conducting sphere (PMC, PEC, or PEMC) with general anisotropic/isotropic material coatings that include plasma and metamaterials. The behavior of the forward and backscattered radar cross section of PEMC sphere with the variation of the magnetic field strength, incident frequency, plasma density, and effective collision frequency for the co-polarized and the cross polarized fields are investigated. It is also observed from the obtained results that anisotropic layer on PEMC sphere shows reciprocal behavior as compared to isotopic plasma layer on PEMC sphere. The comparisons of the numerical results of the presented analytical expressions with available results of some special cases show the correctness of the analysis.

Characterization of Ultra-wide band diamond shaped monopole using singularity expansion method

This paper presents characterization of Ultra-wide band diamond shaped patch monopole (DSM) antenna based on the singularity expansion method (SEM) model. The diamond shaped patch is designed to provide Ultra-wide bandwidth (UWB) of 12 GHz (3 to 15 GHz). To extract the complex poles in the SEM based model, Matrix Pencil method (MP) is used to provide the accurate complex poles and residues for the studied diamond shaped monopole. MP is directly applied to the impulse response of the proposed DSM antenna. A numerical code is developed in order to apply the MP method. The results show that all the complex poles and their corresponding residues are located within the operating UWB of antenna. To validate the results for the DSM antenna, the impulse response of the antenna is reconstructed using SEM and compared to the original response.

Scattering from isotropic plasma coated nihility sphere

In this study, it is observed that when an isotropic collisional plasma coating layer is produced on a nihility sphere, its back scattering efficiency becomes non-zero. Field equations, at each interface, are expanded in terms of spherical wave vector functions (SWVFs) by enforcing the extended classical wave scattering theory. Electromagnetic boundary conditions are applied at both interfaces, i.e., free space-plasma and plasma layer-nihility sphere core to obtain the scattering coefficients. The obtained scattering coefficients are used to calculate the forward scattering, back scattering, and extinction efficiencies. The obtained computational results show that an increase in collisional frequency causes a decrease in both forward and backscattered efficiencies and an increase in extinction efficiency. Furthermore, the numerical results indicate that an increase in plasma density causes an increase in both forward and backscattered efficiencies and a decrease in extinction efficiency.

Time to Frequency Domain Analysis of Narrow Band Antennas

This paper presents system modeling of three different single band antennas using the singularity expansion method (SEM). To acquire the accurate physical complex poles and the corresponding residues of the narrow band antenna model, an enhanced Matrix Pencil (MP) method has been applied to the impulse response of the antennas. A delayed time parameter is introduced to enhance the performance of the MP method to extract the actual physical poles and eliminate the nonphysical poles caused by the early time response of the narrow band antennas. The poles extracted by the enhanced MP method are located precisely within the single operating band of each antenna. The one set of the developed parameters is used to accurately characterize narrow band antennas in both time and frequency domains. The far field impulse response of a fabricated single band microstrip antenna has been measured in the laboratory and then reconstructed precisely using the SEM based model with the proposed MP scheme.

Reconfigurable bandstop filter using Defected Ground Structure (DGS)

The paper presents a new compact reconfigurable bandstop filter using Defected Ground Structure (DGS). The proposed reconfigurable bandstop filter is constructed by employing coupled DGS resonators etched in the ground plane. The bandstop filter consists of symmetrical DGS resonators with a microstrip excitation to obtain a bandstop filter response. The reconfigurability is achieved by short circuiting part of the slots etched in the ground plane. A reconfigurable bandstop filter is designed, analyzed, and implemented on Duroid dielectric substrate with 2.2 dielectric constant and 0.78mm thickness. The filter is designed to switch between the two center frequencies 1.40 and 2.25 GHz with approximately 50MHz rejection bandwidth under the condition of 15dB, rejection. The measured results are in good agreement with the simulations.