Khalil H. Sayidmarie

BANDWIDTH CONSIDERATIONS FOR A MICROSTRIP REFLECTARRAY

The paper describes a theoretical investigation into a limited bandwidth operation of a microstrip reflectarray. Two main factors limiting the bandwidth are considered. One is related to the requirement of phase compensation to convert a spherical wavefront launched by a feed into a planar wavefront. The other one is linked to the limited phasing range of microstrip antenna elements. The two factors contribute to the reflectarray phasing errors that in turn reduce its gain as a function of frequency. Simple formulas for an upper bound of gain bandwidth are derived, assuming the phase compensation by the elements is independent of frequency changes and verified against the results produced by other researchers. It is shown that the phase errors incurred in the path equalization to obtain conversion from spherical to planar wavefronts have a more profound effect on the reduction of operational bandwidth of the reflectarray than the phase truncation implemented on the required phase from each element.

Aperture-Coupled Asymmetric Dielectric Resonators Antenna for Wideband Applications

A compact dielectric resonator antenna (DRA) for wideband applications is proposed. Two cylindrical dielectric resonators that are asymmetrically located with respect to the center of a rectangular coupling aperture are fed through this aperture. By optimizing the design parameters, an impedance bandwidth of about 29%, covering the frequency range from 9.62 to 12.9 GHz, and a gain of 8 dBi are obtained. Design details of the proposed antenna and the results of both simulation and experiment are presented and discussed.

A PLANAR SELF-COMPLEMENTARY BOW-TIE ANTENNA FOR UWB APPLICATIONS

A new planar bow-tie antenna is proposed here for UWB applications. The self-complementary principle has been applied to a planar triangular monopole antenna along with bending the microstrip feed line. The antenna has a wider frequency band compared to the traditional bow-tie antenna, complies with the UWB requirements and it is directly matched to the (SMA) connector via 50› microstrip feed line. This antenna has a simple shape which overcomes the complicated matching techniques using baluns or impedance matching sections that are commonly used in bow-tie antennas for widening their limited bandwidths. Another improvement on this new bow- tie antenna is achieved through fractal self-similarity repetition of the triangular shape on each of the patch and its complimentary slot. The simulation results obtained from the CST and HFSS software packages are verifled by experimental measurements.

Investigations into phasing characteristics of printed single and double cross elements for use in a single layer microstrip reflectarray

In this paper, we focus our considerations on a single layer microstrip reflectarray because it is easy to manufacture. By selecting suitable phasing elements we aim to overcome the main problem faced in many single-layer microstrip reflectarray designs, which are reduced phase range and a large phase gradient. The reduced phase range and the sharp slope contribute to the phasing errors of the reflectarray that in turn degrade its directivity. We turn our attention to multi-resonant variable size planar antenna elements, for which we have shown in that they can offer an extended phase range when used in a unit cell of a single-layer reflectarray. Here we choose printed double cross elements to form a reflectarray unit cell with an extended phase range and a lower slope. In the presented investigations, we show that a unit cell containing a single resonant cross still faces similar phase range and slope problems as a unit cell with single dipoles or patches. By using a double cross element on the same substrate we demonstrate that the phase range can be doubled. Next, to reduce the slope and still keep the phase range more than 360deg, we use a thick composite material including a thin laminate and a thick layer of foam to support the double cross. Such substrate combination offers phase responses of reduced slopes over an acceptable phase range. We compare the obtained results with those for double stacked patches developed on similar thickness foam.

Design aspects of UWB printed elliptical monopole antenna with impedance matching

Printed elliptical monopole antenna PEMA has been designed to cover the UWB frequency range. The design procedure of this antenna is accomplished by two stages; Firstly, the PEMA has been designed according to some suggested and known formulas. Secondly, two impedance matching (IM) techniques are suggested to improve the designed antenna by moving the locus of the input impedance towards the center of the Smith chart. Simulation results showed that this orientation of the impedance locus leads to very wide operating frequency range 2.83~13.7 GHz, which exceeds the UWB requirements, as well as good gain and efficiency.

COMPACT DUAL-BAND DUAL-RING PRINTED MONOPOLE ANTENNAS FOR WLAN APPLICATIONS

Three dual band planar monopole antennas for wireless local area network (WLAN) application are proposed. The antennas have common conflguration in the form of rectangular, rhombic and annular double rings. All the antennas use the self similarity property to exhibit dual band characteristics. The proposed antennas cover the frequency bands of the IEEE 802.11a/b/g (2.4{2.48GHz, 5.15{ 5.35GHz and 5.725{5.825GHz), and have radiation patterns that are; almost omnidirectional in the H-plane, and like monopole pattern in the E-plane. The simulation results are analyzed and compared with measured results for veriflcation. During the last decade, enormous advancements in designing wireless systems have been achieved. The portable devices in the market are ofiering many advantages like the small size, low cost and the support of many applications like Bluetooth, internet service, making calls and GPS services. Variety of applications, which are working on designated frequency bands, need antennas operating on these bands to be mounted in the same device. The use of more than one antenna in the same device is not a practical solution, because of the limited size in the new wireless devices. Therefore, various antennas working on dual or multi bands have been developed by the researchers over the years. Taking the beneflts of utilizing the self similarity property of fractal shapes a dual band fractal monopole was proposed by (1,2). The use of slot structures to achieve multi-band characteristics was proposed in (3{5). The use of ring shaped antenna to operate on dual

PHASING OF A MICROSTRIP REFLECTARRAY USING MULTI-DIMENSIONAL SCALING OF ITS ELEMENTS

The paper reports on investigations into new schemes for dimensional scaling of the elements of a microstrip reflectarray to obtain a slower slope of the reflected wave phase characteristic. First, the phase response as a function of various shape elements is investigated when only one of their dimensions is varied. Next investigations concern the case when two dimensions or features of the element are scaled in a certain manner simultaneously. In the latter case, it is shown that phase responses of lower slopes with a minimal range reduction can be obtained. The feasibility of this concept is illustrated for dipoles, rectangular patches, and square and circular rings. Comparisons of the obtained results show that two- dimensionally scaled square and circular rings offer much better phase responses than those observed for dipoles and patches.

SELF-COMPLEMENTARY CIRCULAR DISK ANTENNA FOR UWB APPLICATIONS

In this paper, the self-complementary principle has been applied to develop the traditional planar monopole antenna into a dipole antenna whose frequency range exceeds UWB requirements. The proposed design has compact, planar, and simple shape arranged in self-complementary manner connected to the (SMA) connector via rectangular microstrip line. The self-complementary structure ofiers better reduction of the imaginary part of antenna impedance, which allows matching on a wider band of frequencies. The proposed antenna showed i10dB return loss bandwidth extending from 1.86GHz up to 17.7GHz. Moreover, this antenna has a simple shape as compared with complicated and irregular shapes with curves, slots or parasitic elements. The proposed design is validated by experimental measurements. The phase of the return loss is investigated for more insight into antenna matching.

Multi-Ring Unit Cells for Increased Phasing Range in Single-Layer Microstrip Reflectarrays

In this paper, we investigate planar antenna elements in the form of multi-rings of square and circular shapes, and explain the concept behind their increased phase range in a unit cell of a single layer microstrip printed reflectarray. It has been shown that the extended phase range can be obtained by utilizing similar in shape, but different in size, resonant elements. Using this principle it has been shown that two resonant elements forming a unit cell can double while three elements can almost triple the phasing range of a single resonant element unit cell, while the slope of the phase response remains almost unchanged. The issue of bandwidth improvement has not been considered. However, this can be achieved using thicker substrates similarly, as in the multi-layer approach.

Sidelobe Cancellation for Uniformly Excited Planar Array Antennas by Controlling the Side Elements

A sidelobe cancellation over a wide angular range for the uniformly excited planar array is proposed. The approach is to readjust the amplitude and phase excitations of the boundary elements only, while keeping the rest of elements unchanged. Simple expressions for computing the required amplitude and phase excitations of these boundary elements are given. The technique simplifies the feed network as it requires only one attenuator and two phase shifters. Simulation results show that cancellation of sidelobes across a wide angle can be obtained.