Kathleen L. Virga

Low-profile enhanced-bandwidth PIFA antennas for wireless communications packaging

The development of small integrated antennas plays a significant role in the progress of the rapidly expanding military and commercial communications applications. The recent advances in RF and microwave high-density circuit packaging technologies in multifunction wireless communications systems have called for the parallel development of compact and efficient antennas that can be used over a wide frequency range. This paper addresses the development and characterization of several low-profile and integrated antennas with enhanced bandwidth for wireless communications systems. The new radiators are developed by adding parasitic elements or tuning devices to a familiar integrated antenna-the planar inverted F antenna (PIFA). Simulations based upon the finite-difference time-domain (FDTD) method and method of moments (MoM) are used to model the performance of the antennas. Comparisons with measured results on fabricated antenna structures are provided for simulations validation.

Performance characteristics of the dual exponentially tapered slot antenna (DETSA) for wireless communications applications

The dual exponentially tapered slot antenna (DETSA) is a low-profile slot line radiator that is a modified form of a Vivaldi radiator. The DETSA is created by taking a Vivaldi radiator and tapering the outside edge of the slot line conductors. The shape of the outside edge of the slot line conductors adds additional antenna design degrees of freedom. This paper describes how the different shape parameters of the DETSA impact antenna performance.

Efficient wide-band evaluation of mobile communications antennas using [Z] or [Y] matrix interpolation with the method of moments

The development of novel antennas for mobile communications often relies on performance simulations. The evaluation of the antenna surface currents for many frequencies using the method of moments (MoM) can take a long time since the impedance matrix must be computed for each new frequency. This paper investigates and compares two efficient methods for the computation of the broad-band performance of mobile communications antennas using frequency interpolation of either the MoM impedance matrix [Z] or admittance matrix [Y]. In either method, the elements of only a few matrices at relatively large frequency intervals are directly computed. These matrices are then used to interpolate the elements of the respective [Z] or [Y] matrices at the intermediate frequencies. Both methods reduce the time it takes to compute the antenna performance over a wide frequency band. The implementation of each method to evaluate the performance of several different antennas used for mobile communications is discussed. Examples with both frequency-domain and time-domain results are presented and both near-field and far-field quantities are considered. The accuracy, the simulation run times, and the computational requirements of direct MoM, [Z] matrix interpolation, and [Y] matrix interpolation are compared.

Improved global rational approximation macromodeling algorithm for networks characterized by frequency-sampled data

Recently, the demand for high-performance wireless designs has been increasing while simultaneously the speed of high-end digital designs have crossed over the gigahertz range. New simulation tools which accurately characterize high-frequency interconnects are needed. This paper presents improvements to a new macromodeling algorithm. The algorithm employs curve-fitting techniques to achieve a pole-residue approximation of the frequency-sampled network. The frequency sampled S-parameters or Y-parameters can be obtained from measurement or full-wave simulation to characterize the frequency-dependent interconnects behavior. The improvements extend the approach to lossless structures, increase its accuracy with pole-clustering, and ensure its validity with a passivity test. This paper addresses some of the special considerations that must be made to the method so it can efficiently and accurately be applied to lossless circuits and structures. The resulting algorithm is now capable of accurately extracting a wide-band frequency domain macromodel from frequency-sampled data for either LC circuit (lossless) or RLC circuits (lossy). The frequency-domain macromodel can be linked to a SPICE circuit simulator for mixed signal circuit analysis using RF, analog, and digital circuits. The circuit can be simulated in the time domain using recursive convolution.

Pole-residue formulation for transient simulation of high-frequency interconnects using householder LS curve-fitting techniques

As digital circuits approach the GHz range, and as the need for high performance wireless devices increases, new simulation tools which accurately characterize high frequency interconnects are needed. In this paper, a new macromodeling algorithm for time domain simulation of interconnects is presented. The algorithm incorporates Householder LS curve-fitting techniques. The approach generates a universal macromodeling tool that enables simulation of interconnects in a modified version of simulation program with integrated circuit emphasis (SPICE). This results in a method that conveniently incorporates accurate EM models of interconnects or experimental data into a circuit simulator. The time domain simulation results using this new tool are compared with results from other simulators.

Dielectric constant and loss tangent measurement using a stripline fixture

An approach to dielectric material characterization with a vector network analyzer is presented. As the characteristic impedance (Z/sub 0/) of a stripline transmission line can be accurately determined by measuring the two-port scattering parameters in the frequency range of interest, the dielectric constant of the insulation material that consists of part of the stripline configuration is then obtained by relationship to the characteristic impedance. The dielectric loss (or loss tangent) can be determined by measuring the return loss and the insertion loss of the stripline. The validity of the technique is demonstrated for well-characterized dielectric materials such as Teflon-based and other composite laminates. The technique is then applied to IC molding compounds as processed.A new approach to dielectric material characterization with a vector network analyzer is presented. As the characteristic impedance (Z0) of a stripline transmission line can be accurately determined by measuring the two-port scattering parameters in the frequency range of interest, the dielectric constant of the insulation material that consists as part of the stripline configuration is then obtained by a relationship to the characteristic impedance. The dielectric loss (or loss tangent) can be determined by measuring the return loss and the insertion loss of the stripline. The validity of the technique is demonstrated for well-characterized dielectric materials such as Teflon-based and other composite laminates. The technique is then applied to integrated circuit (IC) molding compounds as-processed.

Methods to reduce radiation from split ground planes in RF and mixed signal packaging structures

Split ground planes are sometimes used in RF and mixed signal packages in order to isolate the RF and analog circuits from the digital circuits. Undesired radiation in a packaging environment may occur when a signal trace is routed over a slot in the ground plane. This paper examines and investigates ways to eliminate signal coupling into split ground plane structures and assesses the impact of this reduced coupling on signal integrity in a packaging environment. Suggested methods to reduce coupling of energy into the slot are to alter the shape of the slot with RF chokes or corrugations.

Measured characteristics of 30-GHz indoor propagation channels with low-profile directional antennas

The millimeter-wave frequency band is emerging as an interesting choice for high data-rate indoor wireless communications. The features of large bandwidth, small antenna size and high indoor path loss to isolate separate channels offer many advantages. This paper reports on the experimental setup, the experimental results, and statistical characteristics of line-of-sight (LOS) indoor wireless propagation channels using a low-profile directional antenna for both transmit and receive functions at 30 GHz. The path loss and small-scale fading characteristics are explored. The measured results are used to determine the coefficients used in Rician and Nakagami distribution models at 30 GHz.

Characterization and design methodology for the dual exponentially tapered slot antenna

Tapered slot antennas are simple planar structures with broadband characteristics that are typically used in arrays for radar applications, mobile satellite communications and phased arrays. Most published work has been limited to the linearly tapered slot and Vivaldi antennas. Very little has been published on the dual exponentially tapered slot antenna (DETSA), originally referred to as a wideband bunny-ear element. In this paper a performance characterization for the DETSA is presented. It has been found that careful design of the DETSA can give improved directivity and half power beamwidth (HPBW) performance over the Vivaldi antenna. Also presented is a method for defining the DETSA dimensions in terms of ratios, so design features of different DETSAs can be quantified and their performance compared.

Wide-band evaluation of communications antennas using [Z] matrix interpolation with the method of moments

An important task associated with the evaluation and comparison of broadband antennas for communications applications involves performing simulations to predict the antenna performance over a wide range of frequencies. The method of moments (MoM) is one popular simulation methodology. Since the MoM impedance matrix must be computed at each frequency, the computation over a wide frequency range can take a long time. In the paper, a method proposed by Newman [1988] is revisited and applied to complex antenna structures being considered for modern personal communications applications. With this method, the impedance [Z] matrices for several relatively widely spaced frequencies are directly computed and stored. The elements of the impedance matrix at an intermediate frequency are computed by interpolating the elements of the stored [Z] matrices. This method is particularly well-suited for the analysis of antennas for personal wireless applications. Such antennas are either small and low-profile or consist of thin wires. The paper presents the results of the [Z] matrix interpolation method applied to both type of antennas; a planar inverted F antenna (PIFA) and a helix.