Lale Alatan

Analytical evaluation of the MoM matrix elements

Derivation of the closed-form Greens functions has eliminated the computationally expensive evaluation of the Sommerfeld integrals to obtain the Greens functions in the spatial domain. Therefore, using the closed-form Greens functions in conjunction with the method of moments (MoM) has improved the computational efficiency of the technique significantly. Further improvement can be achieved on the calculation of the matrix elements involved in the MoM, usually double integrals for planar geometries, by eliminating the numerical integration. The contribution of this paper is to present the analytical evaluation of the matrix elements when the closed-form Greens functions are used, and to demonstrate the amount of improvement in computation time.

Design of dual-frequency probe-fed microstrip antennas with genetic optimization algorithm

Dual-frequency operation of antennas has become a necessity for many applications in recent wireless communication systems, such as GPS, GSM services operating at two different frequency bands, and services of PCS and IMT-2000 applications. Although there are various techniques to achieve dual-band operation from various types of microstrip antennas, there is no efficient design tool that has been incorporated with a suitable optimization algorithm. In this paper, the cavity-model based simulation tool along with the genetic optimization algorithm is presented for the design of dual-band microstrip antennas, using multiple slots in the patch or multiple shorting strips between the patch and the ground plane. Since this approach is based on the cavity model, the multiport approach is efficiently employed to analyze the effects of the slots and shorting strips on the input impedance. Then, the optimization of the positions of slots and shorting strips is performed via a genetic optimization algorithm, to achieve an acceptable antenna operation over the desired frequency bands. The antennas designed by this efficient design procedure were realized experimentally, and the results are compared. In addition, these results are also compared to the results obtained by the commercial electromagnetic simulation tool, the FEM-based software HFSS by ANSOFT.

Use of computationally efficient method of moments in the optimization of printed antennas

Derivation of the closed-form Greens functions and analytical evaluation of the method of moments (MOM) matrix entries have improved the computational efficiency significantly in the analysis of printed geometries. With this background in mind, an extension of this efficient numerical technique is to incorporate an optimization algorithm and to assess its potential as a computer-aided design (CAD) tool. Therefore, we have employed the gradient search and genetic algorithms, in conjunction with the electromagnetic (EM) simulation technique, to a number of representative examples of interest.

Equipotential shells for efficient inductance extraction

To make three-dimensional (3-D) on-chip interconnect inductance extraction tractable, it is necessary to ignore parasitic couplings without compromising critical properties of the interconnect system. It is demonstrated that simply discarding faraway mutual inductance couplings can lead to an unstable approximate inductance matrix. In this paper, we describe an equipotential shell methodology, which generates a partial inductance matrix that is sparse yet stable and symmetric. We prove the positive definiteness of the resulting approximate inductance matrix when the equipotential shells are properly defined. Importantly, the equipotential shell approach also provably preserves the inductance of loops if they are enclosed entirely within the shells of their segments. Methods for sizing the shells to control the accuracy are presented. To demonstrate the overall efficacy for on-chip extraction, ellipsoid shells, which are a special case of the general equipotential shell approach, are presented and demonstrated for both on-chip and system-level extraction examples.

Use of Asymptotic Waveform Evaluation Technique in the Analysis of Multilayer Structures With Doubly Periodic Dielectric Gratings

The reflection and dispersion characteristics of multilayer structures that involve periodically implanted material blocks are obtained by using the MoM solution of the volume integral equation. The asymptotic waveform evaluation (AWE) technique is utilized to obtain a Pade approximation of the solution in terms of a parameter such as frequency or incident angle. The use of AWE technique enables a fast sweep with respect to the approximation parameter. Moreover, a robust method for extracting the dispersion characteristics of periodic structures via Pade approximation is proposed. The AWE procedure requires the calculation of high order derivatives of the complicated kernel function that consists of Greens functions for stratified medium. These derivatives are calculated by employing the automatic differentiation theory. The reflection coefficient, propagation constant and band diagram of the structure are obtained both via point-by-point simulations and through the use of AWE technique. It is observed that AWE technique increases the computational efficiency without losing accuracy.

Design of triple-band reconfigurable microstrip antenna employing RF-MEMS switches

A triple-band inset-fed reconfigurable microstrip antenna is designed. The switching between the three different frequency bands is achieved through the use of RF-MEMS switches placed along the inset and along the slot placed on the radiating patch.

Equipotential shells for efficient partial inductance extraction

The shift-truncate potential method was introduced as an approach to sparsify the partial inductance matrix while maintaining the stability and symmetry. This was accomplished with the use of spherical return shells around point-like current segments. In this paper we propose the use of filament current distributions for the same purpose. Ellipsoidal shells are introduced to model the equipotential surfaces for filament currents. Importantly, we prove that the positive definiteness of the resulting sparse partial inductance matrix is preserved for this and all other potential-shell models when the compensating currents are placed on equipotential surfaces of the original current distribution. The utility and efficiency of this ellipsoidal shell partial inductance approximation are demonstrated for both on-chip and system-level extraction examples.

A compact corporate probe fed antenna array

This paper presents a linear antenna array system with a compact corporate feed network. The antenna elements are probe fed circularly polarized microstrip patch antennas. By using probe feed topology, it is possible to combine all the antenna elements on the backside of the array. Besides, the overall size of the feed network is reduced with the proposed special corporate feed topology. An 8 times 1 linear array is designed and produced as the building block of a larger 2D array. The antenna arrays return loss, radiation pattern and polarization characteristics give good agreement with the numerical calculations.

An Efficient Numerical Solution Method for Reflectarrays of Varying Element Sizes

A novel method is developed for the efficient solution of reflectarrays of variable size elements. The method relies on using characteristic modes (CM) as macro basis functions and reusing the dominant CM of the resonant element for all elements in the reflectarray. This utilization leads to obtaining a reduced matrix system where the number of unknowns is drastically decreased. As far as the far field is concerned, accurate results are achieved even with a single CM. The accuracy is attained owing to preservation of mutual coupling information via the original method of moments (MoM) impedance matrix. The solution is further accelerated by tabulating the entries of the reduced matrix as a function of interacting patch sizes and their relative displacements. It is observed that for sufficiently separated patches, the reduced matrix entry is almost a separable function of the two-dimensional (2-D) displacement between patches and patch sizes associated with the matrix entry. Tabulation is efficiently performed by exploiting this fact. Achieved acceleration is sufficient to use this analysis method in the design of reflectarrays. For a 1000-element array, the tabulation process takes 28 min on a platform with 3.3 GHz CPU clock speed. With the lookup table at hand, the solution time is 0.38 s which is important for the design iterations.

Design and Implementation of a Triple-Band Re-Configurable Microstrip Antenna

A hybrid combination of RF MEMS and microstrip patch triple band inset-fed reconfigurable antenna is presented. A rectangular slot is placed on the antenna to obtain a dual frequency antenna. Furthermore, MEMS switches are placed on the slot to change the electrical length of the slot and obtain a third resonance frequency. Similarly, MEMS switches are used in the inset to match the antenna input impedance at different frequencies. All of the parts are manufactured and the hybrid structure will be built