Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, March 2007. / Thesis Advisor(s): Andrés Larraza, Bruce C. Denardo. "March 2007." Includes bibliographical references (p. 63-64). Also available in print.

Antennas design procedure, especially in portable devices, has been influenced by the growing demand for development of modern wireless communications. Hence, antennas that are wideband, compact, low profile, low cost, and easy to integrate into printed circuits are required. The research described in this dissertation focuses on optimally design and analysis of compact, low profile, and planar wideband patch antennas for modern wireless communications, namely, an open slot wideband planar antenna, a dielectric loaded wideband antenna, a planar antenna with ultra-wideband performance, and an E-shaped patch antenna. A novel very compact planar antenna with wideband performance is proposed and investigated. The proposed antenna has a size of only 9.2 mm x 9.8 mm x 1.52 mm. The size miniaturization is achieved by inserting an open slot in the ground plane to reduce the phase velocity. The antenna has achieved an impedance bandwidth of 52.16% and a stable radiation patterns over a wider bandwidth with a size reduction about 88%. Optimization of a dielectric loaded antenna by using Covariance Matrix Adaptation Evolutionary Strategy (CMA-ES) technique to achieve wideband and ii symmetrical broadside radiation performance is presented. Simulation is used to investigate the frequency-domain performance, regarding return loss, gain, and radiation pattern. Experimental measurements have also been performed to validate the performance of the proposed antenna. The obtained results show that the proposed dielectric loaded antenna achieves a good impedance matching and radiation characteristics in the entire band of WLAN IEEE 802.11a. A new ultra-wideband low profile microstrip antenna is presented for wireless applications. The proposed antenna has a compact size of 20x16 mm2 and an impedance bandwidth of 134.88% (3.5 GHz to 18 GHz). With the compact, ultra-wideband, and low profile, the proposed antenna can be a very good candidate for a wide range of communication applications. Spider Monkey Optimization (SMO) method is introduced for the first time for solving electromagnetic problems. The SMO is a new swarm intelligence technique which models the foraging behavior of spider monkeys. To show the efficiency of the SMO, different examples are presented and the results are compared with the results obtained using other popular optimization techniques. The optimization procedure is used to synthesis the array factor of a linear antenna array and to optimally design a rectangular and an E-shaped patch antenna for wireless applications. By comparing to traditional optimization techniques that reported in the literature, it is evident that SMO is efficient in reaching the optimum solutions with less number of experiments. The performance results obtained from study of these antennas show that these antennas can be an excellent choice for a wide range of wireless communication applications.

This work deals with the principles on which they are based multiband antennas, especially for GSM (900/1800). It then focuses on different ways you can implement these multi-band antennas, mainly deals with structures that can be easily realized using planar technology. These antennas was designed and optimized in electromagnetic simulation software. Selected antenna was practically realized.

The design of antenna arrays involves, amongst others, the selection of the array elements and geometry, as well as the element excitations. The feeding network to obtain the desired excitations can become quite complex, and hence expensive. One possible alternative would be to make use of micros trip wire-grid antenna arrays. These arrays are composed of staggered interconnected rectangular loops of dimensions a half¬wavelength by a wavelength (in the presence of the dielectric). It is because the short sides are considered to be discrete elements fed via micros trip transmission lines, that these antennas are viewed as arrays. While considerable success has been achieved in the design of these antennas, published work has been either of an entirely experimental nature or based on approximate (albeit clever) network models which do not allow for fine control of the array element excitations or off-centre-frequency computations generally. It is the purpose of this thesis to perform an almost rigorous numerical analysis of these arrays in order to accurately predict their element excitations. Models used to study microstrip antennas range from simplified ones, such as transmission-line models up to more sophisticated and accurate integral-equation models. The mixed-potential integral equation formulation is one of these accurate models which allows for the analysis of arbitrarily shaped microstrip antennas with any combination of frequency and dielectric thickness. The model treats the antenna as a single entity so that physical effects such as radiation, surface waves, mutual coupling and losses are automatically included. According to this formulation, the microstrip antenna is modelled by an integral equation which is solved using the method of moments. By far the most demanding part of the integral equation analysis is its actual numerical implementation. For this reason a complete description of the numerical implementation of the formulation is given in this thesis. To verify the accuracy of the implementation, rectangular microstrip patch antennas were analysed and surface current distributions were shown to compare favourably with published results. The formulation is then applied to the analysis of micros trip wire-grid antenna arrays which makes it possible to accurately predict surface current distributions on these arrays. Radiation patterns are determined directly from computed current distributions in the presence of the dielectric substrate and groundplane, and are essentially exact except for finite groundplane effects. To verify theoretically predicted results for wire-grid antenna arrays, several arrays were fabricated and actual radiation patterns were measured. Good correspondence between measured and predicted co-polar radiation patterns was found, while the overall cross¬polarization behaviour in cases with large groundplanes could also be predicted. The fact that numerical experimentation can be performed on wire-grid antenna arrays to examine element excitations, means that it is now possible to carefully design for some desired aperture distribution. / Dissertation (MEng)--University of Pretoria, 2010. / Electrical, Electronic and Computer Engineering / unrestricted

In this work, Paper-based inkjet-printed Ultra-wide band (UWB) fractal antennas are presented. Three new designs, a combined UWB fractal monopole based on the fourth order Koch Snowflake fractal which utilizes a Sierpinski Gasket fractal for ink reduction, a Cantor-based fractal antenna which performs a larger bandwidth compared to previously published UWB Cantor fractal monopole antenna, and a 3D loop fractal antenna which attains miniaturization, impedance matching and multiband characteristics. It is shown that fractals prove to be a successful method of reducing fabrication cost in inkjet printed antennas while retaining or enhancing printed antenna performance.

No description available.

This master's thesis deals with a design of a planar parabolic reflector antenna. The thesis is divided into several parts. The first section is dedicated to the theory of the parabolic antenna design and a basic introduction of the SIW technology which is used for the realization of an antenna prototype. The second chapter deals with the design of individual parts of the antenna (i. e. a primary and secondary reflector and an antenna feeder excited by a waveguide) for particular assignment. The third part is focused on modeling the designed antenna using ANSYS HFSS. Other parts of the thesis include a conversion of the proposed antenna to the SIW technology and a design of a transition between the antenna and a feeding waveguide WR15. The last part of the thesis deals with measuring of the reflection coefficient and the radiation pattern of the fabricated antenna prototype.

No / Radiation efficiency of antennas is shown to be measurable by a modified radiometric technique where the antenna's physical temperature is varied, rather than the noise temperature of its surroundings. The method is accurate, flexible and much more convenient for routine use. A means of avoiding errors caused by temperature-dependent antenna impedance is described. The accuracy of the method is verified by measuring the radiation efficiency of a horn antenna with a 3 dB attenuator to simulate a 50% efficient antenna, and by using microstrip patch antennas, whose measured efficiencies compared well with values computed from a transmission-line model.

No / A loop feed meander-line Antenna (LFMLA) RFID tag on a relatively low dielectric constant substrate operates on the European UHF band 865-868 MHz is presented. The tag modeling is analyzed using two different electromagnetic simulator HFSS and CST. A prototype tag antenna is constructed and measured for validation. The input impedance of the proposed antenna is verified against the simulated data results, the measured and simulated results are found to be in good agreement. The compact size tag antenna shows excellent impedance matching to the typical input impedance of a RFID integrated circuit chip and a significant improvement in reading range up to 5 meters.

Yes / A tunable band-notch printed monopole antenna is presented, exhibiting a wide impedance bandwidth from 1.5 to 5.5 GHz with good impedance matching (VSWR ≤ 2) and a tunable rejected frequency band from 2.38 to 3.87 GHz. The band-notching is achieved by adding an inner chorded crescent element within a driven element of a similar shape. By varying the value of the varactor which is placed between the inner and outer arcs, the desired variable rejected can be obtained. Simulated and measured results show wide impedance bandwidth with a tunable band notch, stable radiation patterns, and consistent nearly constant gain. The antenna is suitable for mobile and portable applications.