Mohammed Sobhy

Single and double layer planar multiband PIFAs

A compact multiband planar inverted-F antenna (PIFA) suitable for distributed radio-over-fiber repeater networks is modified into a planar structure. It is shown that the planar antenna performance is not degraded with respect to the original PIFA and further, a two layer design is demonstrated to offer improved feed matching. The European bands for GSM, DCS-1800, DECT, UMTS, Bluetooth and HiperLAN2 are all covered. A model of the antenna is introduced as a first stage to developing an equivalent circuit

Design and Analysis of a Reflectarray Using Slot Antenna Elements for Ka-band SatCom

This paper presents a folded reflectarray designed for Ka-band satellite communication applications. The array element is a dual-polarized slot antenna with multilayered PCB structure and is designed to operate at 29.5-30.8 GHz band for both transmitting and receiving with single linear polarization. Vias are employed to suppress the surface wave propagation and reduce the mutual coupling between adjacent array elements, for achieving a reflectarray with a wide scan angle range. An equivalent circuit model for the array element is developed and it agrees well with the EM simulation results. Several passive demonstrators consisting of 116 elements spaced by 0.5λ30GHz were fabricated and measured. The experimental results show that the presented reflectarray is capable of steering the beam up to ±60° in both Eand H-planes with low cross-polarization level.

Chaotic radar systems

The paper describes a radar system based on a chaotic microwave generator and an inverse system to reconstruct the radar pulse signal. Chaotic microwave communication systems offer the possibility of adopting spread spectrum techniques at microwave frequencies with greater noise immunity. Synchronised chaotic systems offer high security. The microwave generator used is based on a frequency multiplier chain and is designed to give any required frequency.

Compact UWB Wearable Antenna

This paper reports a novel UWB antenna suitable for wireless on body applications. The antenna is based on previous studies of wearable button antennas and uses the circular metal nail employed in some buttons to create the radiating element of the antenna. The visible part of the antenna was fabricated using PTFE, although other dielectric or plastic material could be used. The novel antenna is intended for textile jackets where the button structure can be easily camouflaged and disregarded as a plastic button. The antenna is fed by a microstrip line and denim was used as the substrate as well as the superstrate that hides the feeding. The antenna achieves the 3.1 GHz to 10.6 GHz bandwidth required for the ultra-wide-band technology. The radiation patterns are those of a planar circular monopole antenna with no significant deleterious effect of the dielectric structure on the far-field patterns.

Nonlinear system and subsystem modeling in time domain

Nonlinear models of microwave subsystems are identified from time domain measurements. Scattering functions in the form of nonlinear time domain functions are used to derive a system identification model instead of an equivalent circuit. The advantage being the simplicity of the measurement and the developed models and the speed and accuracy of the simulation of the entire system.

Compact Antenna for WLAN on body applications

A novel wearable antenna for WLAN applications is presented in this paper. The antenna is made up of a button shape cylindrical structure and a central metal disc connected to the metal ground plane. The structure and dimensions achieved are those of a standard metal button with greater deal of camouflage and rigidness than previous wearable antenna developments (Lukowicz, 2002), (Salonen, 2003). The proposed wearable antenna is designed for 2.4 GHz and 5 GHz with the omnidirectional pattern required for transmission with other wearable devices located across the body

Design of selective linear phase bandpass switched-capacitor filters with equiripple passband amplitude response

A novel approach is presented to the design and synthesis of switched-capacitor (SC) filters. An efficient iterative algorithm is described for the construction of a class of selective linear-phase bandpass filter with equiripple passband amplitude response. The solution is obtained in terms of digital linear phase bandpass polynomials. A novel SC implementation is performed using an approach based on the reflection filter concept. The synthesis of the SC filter follows the steps used in microwave filter synthesis. The resulting SC circuits are completely insensitive to parasitic capacitances. Design tables and an illustrative example are also given. >

Compact Smart Antenna With Electronic Beam-Switching and Reconfigurable Polarizations

This paper presents a compact-size, low-cost smart antenna with electronically switchable radiation patterns, and reconfigurable polarizations. This antenna can be dynamically switched to realize three different polarizations including two orthogonal linear polarizations and one diagonally linear polarization. By closely placing several electronically reconfigurable parasitic elements around the driven antenna, the beam switching can be achieved in any of the three polarization states. In this design, a polarization reconfigurable square patch antenna with a simple feeding network is used as the driven element. The parasitic element is composed of a printed dipole with a PIN diode. Using different combinations of PIN diode on/off states, the radiation pattern can be switched toward different directions to cover an angle range of 0° to 360° in the azimuth plane. The concept is confirmed by a series of measurements. This smart antenna has the advantages of compact size, low cost, low power consumption, reconfigurable polarizations, and beams.

A new multi-grid 3-D TLM algorithm for simulation of microwave FSS

This paper describes and demonstrates a new TLM multi-grid algorithm which allows arbitrary mesh dimension changes. Its use is demonstrated in the modelling of Frequency Selective Surfaces (FSS) used in microwave antenna systems where the mesh can be adjusted to describe arbitrary dimensions precisely. The algorithm demonstrates good numerical stability and has been applied to numerous Symmetric Condensed Node (SCN) TLM problems.

Dual Circularly Polarized Equilateral Triangular Patch Array

This paper presents a novel sequentially rotated patch array antenna with dual circular polarizations (CP). The present design has the advantages of compact size, simple feed networks, low cross polarization, and high isolation. The radiating elements are dual linearly polarized (LP) equilateral triangular patches with hybrid feeds. The vertical polarization (VP) of the patch antenna is obtained by using an aperture-coupled feed and the horizontal polarization (TIP) is obtained by using a proximity feed. These two feeds are orthogonally positioned and are printed on different PCB layers, which leads to the high isolation between these two ports and facilitates the design of the feed networks. The array antenna consists of six such dual-LP triangular patches sequentially rotated by 60° and fed by separated feed networks. Since LP antenna elements are used, the design of the feed network is much simplified. Through sequentially varying the feeding phase by ±60°, dual circular polarizations are obtained. The operation principle of the array antenna is also analytically explained in this paper. To verify the design concept, one dual LP equilateral triangular patch and one dual CP equilateral triangular patch array resonating at 10.5 GTIz are designed, fabricated, and tested. There is a good agreement between the simulation and measurement results, both of which show that the array antenna exhibits high port isolation and good circular polarizations with low cross polarization at different planes. The proposed design technique can be applied to the design of dual CP array antennas operating at other frequency bands.