Muntasir Sheikh

Sparse probability density function estimation using the minimum integrated square error

We develop a new sparse kernel density estimator using a forward constrained regression framework, within which the nonnegative and summing-to-unity constraints of the mixing weights can easily be satisfied. Our main contribution is to derive a recursive algorithm to select significant kernels one at time based on the minimum integrated square error (MISE) criterion for both the selection of kernels and the estimation of mixing weights. The proposed approach is simple to implement and the associated computational cost is very low. Specifically, the complexity of our algorithm is in the order of the number of training data N, which is much lower than the order of N2 offered by the best existing sparse kernel density estimators. Numerical examples are employed to demonstrate that the proposed approach is effective in constructing sparse kernel density estimators with comparable accuracy to those of the classical Parzen window estimate and other existing sparse kernel density estimators.

A radial basis function network classifier to maximise leave-one-out mutual information

We develop an orthogonal forward selection (OFS) approach to construct radial basis function (RBF) network classifiers for two-class problems. Our approach integrates several concepts in probabilistic modelling, including cross validation, mutual information and Bayesian hyperparameter fitting. At each stage of the OFS procedure, one model term is selected by maximising the leave-one-out mutual information (LOOMI) between the classifiers predicted class labels and the true class labels. We derive the formula of LOOMI within the OFS framework so that the LOOMI can be evaluated efficiently for model term selection. Furthermore, a Bayesian procedure of hyperparameter fitting is also integrated into the each stage of the OFS to infer the l^2-norm based local regularisation parameter from the data. Since each forward stage is effectively fitting of a one-variable model, this task is very fast. The classifier construction procedure is automatically terminated without the need of using additional stopping criterion to yield very sparse RBF classifiers with excellent classification generalisation performance, which is particular useful for the noisy data sets with highly overlapping class distribution. A number of benchmark examples are employed to demonstrate the effectiveness of our proposed approach.

Transmission Control of Electromagnetic Waves by Using Quarter-Wave Plate and Half-Wave Plate All-Dielectric Metasurfaces Based on Elliptic Dielectric Resonators

We present the design of all-dielectric Quarter-Wave Plate (QWP) and Half-Wave Plate (HWP) metasurfaces based on elliptic dielectric resonators (EDRs) for the transmission control of electromagnetic waves over the frequency band 20–30 GHz. First, an extensive numerical analysis was realized by studying the effect of the resonators geometry (thickness and ellipticity) on the transmission of both - and -polarized waves. Then, based on the numerical analysis, we have realized and characterized experimentally both QWP and HWP all-dielectric metasurfaces.

Microstrip line-fed monopole antenna on an epoxy-resin-reinforced woven-glass material for super wideband applications

Abstract A microstrip line-fed monopole antenna is proposed for super wideband (SWB) applications printed on an epoxy-resin-reinforced woven-glass material. The reported SWB antenna has been made of a rectangular partial ground plane with an L-type slit and a heart-shaped radiating patch. This antenna is connected precisely by a tapered feed line that provides SWB greater than ultra-wideband. The heart-shaped radiating patch and the partial ground plane containing a gap and an L-type slit on ground plane also play paramount roles to procure wide impedance bandwidth. It is determined from measurements that this antenna contains SWB characteristic [voltage standing wave ratio (VSWR) ≤2] spanning from 1.30 to 40 GHz (187.41%), with a bandwidth dimension ratio (BDR) of 5544.66 and a ratio bandwidth of 30.77:1. Simple construction, sharp surface current flow, much impedance bandwidth, nearly omnidirectional radiation patterns, stable peak gain (2.20–6.06 dBi), time domain performance, and considerable BDR (5544.66) make it a promising candidate for SWB applications.

Half-wave and quarter-wave plates metasurfaces with elliptic dielectric resonators for microwave applications

We present a simple design of Quarter-Wave Plate (QWP) and Half-Wave Plate (HWP) of an all-dielectric metasurfaces based on Elliptic Dielectric Resonators (EDRs) of minor radius 2.5 mm, ellipticity τ (τ1=1.4 or τ2=1.6), relative permittivity 10.2, loss tangent 0.003 and thickness 5.12 mm. The metasurfaces transmissions under x- and y-polarizations of the incident electric fields were studied over the microwave band 20-30 GHz. By optimizing the different design parameters such as the EDR ellipticity and orientation, we have realized both QWP and HWP metasurfaces with good performances.

Design of superdirective and compact antenna array

In this paper we propose the design of a superdirective and compact antenna array. This antenna system is based on a capacitively loaded loop (CLL) driven by an electrically small monopole antenna. This elementary antenna is then used in a two elements compact parasitic array, in order to achieve a higher directivity. The two elements of this array are identical, but only one of them is driven, the other one is used as a parasitic element. The design of the elementary antenna, its simulated radiation performance are reported, as well as those of the parasitic array. A 7.20 dB maximum total directivity is achieved for this antenna array.

Capacitively Loaded Loop-Based Antennas with Reconfigurable Radiation Patterns

A class of metamaterial-inspired antennas having reconfigurable radiation patterns is proposed. They consist of a driven monopole antenna with one- and two-capacitively loaded loop (CLL), near field resonant parasitic elements. Two configurations are studied by considering the state of these CLL elements as being either open or closed configurations. Simulation results explain the design features and demonstrate that the structure can change its beam direction simply by controlling the switched states. Two prototypes with one- and two-CLL elements were fabricated and tested. The measured impedance mismatch and radiation pattern results are presented and compared to the corresponding simulated values.