Nora Mohamed Mohamed-Hicho

A Novel Low-Profile High-Gain UHF Antenna Using High-Impedance Surfaces

A novel wideband low-profile planar antenna design based on the use of a high-impedance surface (HIS) is presented for digital television (DTV) reception in the UHF band. The proposed design is based on a wideband monopole antenna in close proximity to an artificial ground plane, composed of an array of square metal loops at the top, an air gap and a ground plane at the bottom, without grounded vias. Low-cost substrates are employed in the design: rigid PVC for the antenna and foamed PVC for the artificial ground plane. The advantages of the proposed design for DTV applications are high gain, low profile, light weight, low cost and large bandwidth. Details of the proposed antenna design are described, and measurements together with a comparison to a conventional antenna with PEC ground plane are presented.

Design Guidelines for the Excitation of Characteristic Modes in Slotted Planar Structures

This paper provides some design guidelines for the excitation of broadband slotted planar antennas, addressing key issues such as coupling, symmetries and multiple feeding. The theory of characteristic modes (CMs) is used to identify the collection of current modes that exists on these structures, dealing to a valuable understanding of the radiating mechanisms and allowing a more controlled design process. Modal analysis of a circular aperture cut on a finite square ground plane is presented in order to demonstrate that an optimum choice of the feeding mechanism can be made according to the current distribution of the desired modes. Based on the information yielded by this modal analysis, a capacitive-coupled dual-feed circular aperture antenna is presented. This antenna takes advantage of the symmetries of the characteristic currents by making use of multiple feeding, in order to excite only some particular modes. Usage of commonly-fed and differentially-fed configurations enables an increased control of the excitation of modes in the structure. CM analysis of the antenna including the feeding structures is presented, showing the influence of the feeding lines in the performance of this type of antennas. A prototype of the antenna has been fabricated and measured. Simulated and measured results are presented, being in good agreement.

Design of a compact low profile high-gain UHF antenna using High-Impedance Surfaces

A low-profile high-gain antenna for UHF applications is presented in this paper, which is based on the use of High-Impedance Surfaces (HIS). The proposed design is an improvement of the structure presented in [1]. This design is based on a wideband monopole antenna in close proximity to an artificial ground plane, composed of an array of square metal loops at the top and a ground plane at the bottom, without grounded vias. Low-cost substrates are employed in the design, rigid PVC for the antenna, and foamed PVC for the artificial ground plane. PVC substrate is ecologic, recyclable, long lasting and cheap, what makes it desirable for this application. The advantages of using a HIS structure as a reflecting surface are the reduction of back-radiation, the increase of the antenna gain, the broadening of bandwidth, and the mitigation of the effects of parasitic surface waves. Details of the proposed antenna design are described, and simulation results together with a comparison with the previous design [1] and with a conventional antenna with PEC ground plane are presented.

UWB planar monopole antenna with differential feed

This paper presents a differentially driven planar monopole antenna for UWB (Ultra-Wideband) applications. The dimensions of the antenna structure are first studied to achieve wideband characteristics with good impedance matching. The goal is to find dimensions which satisfy the UWB demands but also to show that antenna size can be miniaturized by using differential feeding. The −10 dB impedance matching of the presented antenna structure starts from 1.3 GHz and simulations are performed up to 12 GHz. Normalized surface current distributions are presented and 3D radiation patterns are compared to a reference monopole. The antenna structure shows more stable and omni-directional radiation patterns over the studied frequency range compared to a same sized single-fed reference monopole. The antenna structure is finally scaled to the UWB bandwidth.

Analysis of crossed dipole to obtain circular polarization applying Characteristic Modes techniques

The crossed dipole is a common type of antenna that is used to generate circularly polarized radiation in a wide frequency range. This antenna was originally developed in the 1930s and today is used in many wireless communication systems, including broadcast services, satellite communications, mobile communications, global navigation systems satellite system (GNSS), radio frequency identification (RFID), wireless local area networks (WLANs) and global interoperability for microwave access (WiMAX). This paper shows that it is possible to obtain circular polarization with two cross dipoles with different lengths and connected in parallel by applying the Theory of Characteristic Modes. The results obtained using this new approach is consistent with those obtained using the normal method of analysis of input admittances.

Comparison of wideband High-Impedance Surfaces for low-profile high-gain UHF antenna design

A comparison of wideband High-Impedance Surfaces (HIS) for The design of a compact low-profile high-gain UHF antenna is presented. In order to design the optimal HIS plane for the Digital Television (DTV) operating band, the separation between HIS layers is investigated in an effort to produce a low-profile and lightweight structure, and obtain a practical antenna. Low-density and low-cost substrates are employed in the design: rigid PVC for the antenna, and foamed PVC for the artificial ground plane. The final design consists of a microstrip-fed monopole placed over the proposed HIS. The artificial surface reflects effectively an in-phase field over a bandwidth of about 56%, and achieves around 10.25 dBi of peak gain (7 dB of increment with respect to the simple monopole). The overall structure is very compact (total height is 0.098λ). This paper describes the design procedure of the proposed antenna and shows simulated results.