Michael T. Chryssomallis

Design, fabrication, and measurements of an RF-MEMS-based self-similar reconfigurable antenna

Reconfigurability in an antenna system is a desired characteristic that has been the focus of much research in recent years. In this work, ohmic contact cantilever RF-MEMS switches are integrated with self-similar planar antennas to provide a reconfigurable antenna system that radiates similar patterns over a wide range of frequencies. The different issues encountered during the integration of the MEMS switches and the overall system design procedure are described herein. The final model radiates at three widely separated frequencies with very similar radiation patterns. The proposed concept can be extended to reconfigurable linear antenna arrays or to more complex antenna structures with large improvements in antenna performance.

Planar Monopole Antenna With Attached Sleeves

The analysis of a new printed antenna is presented and discussed. This antenna consists of a printed monopole, with one or two sleeves on each side, fed by a coplanar waveguide (CPW) line. Switches are used to control the length of the monopole and the sleeves and to tune the resonant frequencies of the antenna. In the case of the double-sleeved antenna, the switch is used to connect or disconnect a second sleeve in the cactus antenna. Measurement results show that the cactus antenna maintains the dipole-like radiation patterns for all the different resonant frequencies

Reconfigurable UWB Antenna With RF-MEMS for On-Demand WLAN Rejection

A MEMS reconfigurable ultra-wideband (UWB) antenna that rejects on-demand all WLAN signals in the entire 5.15 to 5.825 GHz range (675 MHz bandwidth) is presented. The antenna design, miniaturization procedure, and monolithic integration with the MEMS and biasing network on SiO2 Quartz substrate are described. The integration challenges are addressed and the work is presented in a way that is useful for antenna engineers. A method to vary the rejection bandwidth is also provided. The fabricated prototype is conformal and single-sided. The antenna is measured using a custom-built platform at a university laboratory. Results indicate a successful integration and minimal interference of the MEMS and biasing circuitry with the antenna, paving the road for more integrated reconfigurable antennas on SiO2 using MEMS technology. Such antennas can improve UWB, WLAN and cognitive radio communication links.

Azimuth and elevation angles estimation using 2-D MUSIC algorithm with an L-shape antenna

A noise subspace process, based on the eigenvalue decomposition of an array correlation matrix, which uses an implementation of MUSIC algorithm in two dimensional (2-D) direction of arrival estimation (DOA) problems is proposed. Simulation results are presented, that illustrate the success of the process to determine the correct azimuth and elevation angles of signal wavefronts impinging on a special L-shape antenna array, consisting of two array branches placed on x and y axes.

Silicon-etched re-configurable self-similar antenna with RF-MEMS switches

Self-similar antennas have been well known for their multiband characteristics. The use of series ohmic contact cantilever RF MEMS switches in coordination with a simple self-similar antenna is exploited. The compatibility of the designs and the fractal nature of the antenna can lead to large increases in antenna performance, since not only a wider selection of frequencies, but also several different radiation patterns can be radiated with a single antenna. In this paper, the design and the compatibility of the switches and simulated results are presented.

Simulation of mobile fading channels

Many aspects of a mobile radio system are basically determined by the propagation characteristics of the channel. Therefore, an understanding and good knowledge of mobile radio channels is essential for the analysis, design, and operation of wireless systems. It allows the successful development, evaluation, and testing of any current or future communication system, whether it is for cellular mobile telephony, for radio paging, or for mobile satellite systems. This article tries to present a simple and efficient way to simulate mobile channels for development and testing of mobile wireless systems, using some of the commercial circuit-analysis and simulation programs. So, in parallel with an overview of fading-channel propagation mechanisms and aspects, compact simulation models are given that can effectively be used for further analysis and understanding of the operation of mobile fading channels.

Evaluation of the Quality Factor, Q, of Electrically Small Microstrip-Patch Antennas [Wireless Corner]

The quality factor, Q, for a number of configurations of a microstrip antenna is evaluated using exact and approximate quality-factor formulas found in the literature. A number of slits parallel to the radiating edges are used to miniaturize the microstrip antennas size. The microstrip antenna in use is considered to be electrically small according to Wheelers electrically small antenna definition. The Q for each configuration is numerically evaluated using the given expressions, for simulated and measured data, and is compared to the Chu lower bound. There is good agreement between the results, while the Q lower fundamental limitation is not violated. Despite the size reduction, satisfying radiation efficiency is achieved, and the radiation pattern remains unchanged.

Improved multiband performance with self-similar fractal antennas

Fractal antennas have the characteristic of radiating in multiple frequencies, usually in a logarithmic pattern, through the property of self-similarity that fractal shapes possess. By connecting fractal shaped antennas, wideband coverage can be achieved. The analysis, design principles and several examples are shown to demonstrate this concept.

Transmission line model design formula for microstrip antennas with slots

A technique, based on the transmission line model, for the analysis of a rectangular microstrip antenna, in which more than one slot have been embedded in its non-radiating edges, is presented. Using this method, the number and the dimensions of the slots in a microstrip antenna can be calculated, in order to get a desired lower resonant frequency from a much smaller patch than the initial rectangular one.

Re-configurable Sierpinski gasket antenna using RF-MEMS switches

Fractal antennas are well known for their multiband characteristics. A new approach to multi-frequency re-configurable antennas using RF-MEMS switches is presented. Fractal antenna elements can be connected together using RF-MEMS switches in order to achieve a larger number of resonances. The RF-MEMS switches permit a controlled connectivity of sections of the antennas conductive parts. This conductive coupling between the triangular elements of a Sierpinski structure provides clear multiple frequency operation with a single fractal antenna. The analysis and design principles are discussed and presented.