Nicholas E. Buris

Impact of a user on the performance of MIMO antenna systems in small wireless devices

The antenna of a single antenna mobile device is impacted by the presence of the user. Advances have been made in characterizing this effect. However, in multiple input multiple output (MIMO) antenna systems, this loading effect is even more complicated. This paper presents a study of a MIMO antenna system and the impact of the user on MIMO performance. The MIMO performance of the antenna systems is assessed using tools that combine the active E-field radiation patterns of the antennas with appropriate channel models. The studies properly treat the effect of the user on the antenna system via an electromagnetics exact formulation. It is shown that MIMO antennas in wireless devices provide a degree of system robustness under a variety of simulated usage conditions.

A switched polarization dual loop antenna for 2.4 GHz ISM band applications

A dual loop antenna has been designed for a 2.4 GHz ISM band application. The design uses a diode switch to alter the configuration of a single feed, two-loop antenna. One loop is always driven while the other acts as a counterpoise. It is an open or closed loop, depending on the state of the switch, and is simply connected to the ground lead of the antenna port. The pattern of the antenna switches between two significantly different states providing the required directional and polarization diversity. The impedance of the antenna also changes significantly and matching is addressed via a switched network. After the antenna simulations, electromagnetic and circuit simulations were used to model the matching and bias networks and their layout. Results are presented showing a complete design with acceptable performance. The simulation results were verified by comparison to measurements. This work linked several different electromagnetic simulation tools, with coupling of the results generated from them to construct accurate prototypes.

Reciprocity calibration of TDD smart antenna systems

Calibration of the rf branches of the arrays at the two sides of the link is a necessary procedure for the channel estimation algorithms of smart antenna based wireless communication systems. Reciprocity calibration is a procedure adopted by Time Domain Duplex (TDD) systems such as WiMAX [1]. This paper discusses the reciprocity calibration of an MxN TDD wireless system and uses a termination based formulation to identify a new design constraint.

A dual band feed structure for slot and notch antennas

The design of a multi-band microstrip to slot line junction structure was described in this article. The structure uses multiple crossings of the microstrip line over the slot line. Each crossing excites a resonant frequency of the slot or notch antenna, thus enabling multi-band operation of the slot or notch antenna. The design was applied to a 3 antenna system that operates in the 2.4 GHz and 5.2/5.8 GHz bands for IEEE 802.11a/b/g/n.

An antenna-channel-antenna modeling methodology for estimating MIMO system performance

Link budget analysis of SISO communication systems involves the usual parameters of antenna gains and path loss through the channel. For MIMO systems, however, the traditional metrics (including mean effective gain) are insufficient for predicting link performance. For SISO systems, it is practical to isolate the antennas and channel as separate blocks. For MIMO systems, it is necessary to consider the complete antenna-channel-antenna interface in order to accurately predict link performance. This paper offers a precise formulation of the ant-channel-ant interface and demonstrates its usefulness by simple example.

Solving Maxwell's equations by edge element time domain methods

The finite difference time domain (FDTD) algorithm has been used widely in solving the transient responses of electromagnetic problems. However, in its original form, it is difficult to model complex EM problems with curved surfaces using the FDTD method. Many variants have been proposed in the past with the aim to circumvent this difficulty with varying degrees success. Almost all of these approaches are based upon, one form or the other, the use of finite difference approximation in both spatial and temporal domains. This paper shows a finite element time domain formulation, the Whitney (1954) element time domain (WETD) method, which uses Whitney l-forms in the spatial domain and the finite difference in the time domain, respectively, for solving Maxwells equations. In this way, the proposed WETD method can be used on a tetrahedral finite element mesh and consequently, it imposes no geometric limitations. We also generalize the formulation by the /spl Theta/ method to three WETD methods depending on the choice of /spl Theta/. In particular, both the WETD1 and WETD3 methods are unconditionally stable. Therefore, the time step used in the computation can always be chosen with compatible resolution with its spatial counterparts.

Performance evaluation of an IEEE 802.11n Access Point antenna system

Multiple external antennas are typically used on Access Points (APs) to combat and, indeed, exploit multipath via the spatial diversity they provide. However, external antennas are not aesthetically pleasing and are prone to reliability failures. This paper presents a study of a MIMO internal antenna system and compares its performance to that of a traditional external dipole array. The MIMO performance of the two antenna systems considered is assessed using tools that combine the active E-field radiation patterns with appropriate channel models. The studies properly treat the effect of the product box on the antenna system via an electromagnetics exact formulation. It is shown that the proposed internal antenna system performs comparably to the external dipoles.

Design and implementation of a low cost portable material analyzer

Site-specific wave propagation simulators used for wireless channel characterization have shown promising results in the last decade. However, accuracy of predicted results by such tools relies on their input data about the environment (i.e. geometry and material properties). A low cost and portable/handheld device capable of estimating the material properties of the objects could provide valuable data about the environment for a site-specific simulator. One such device is described in [1]. The idea is to monitor the change in the reflection coefficient of an antenna when holding it against the object of interest and to transfer the measured data to a laptop for post processing and estimation of the objectpsilas material (epsivr, sigma) and thickness, as appropriate. When such data is combined with a building database, the geometry can be analyzed to produce a site-specific wireless channel model. Toward this vision, this paper presents the magnitude and phase measurement capability achieved by a system of directional couplers, an IC capable of measuring gain and phase and a ZigBee radio for wireless data transfers between portable material analyzer and a laptop. Its accuracy is verified with a commercial Vector Network Analyzer (VNA).

A sensitivity study of ray-tracing based wireless channel simulators using field measurements

Toward the goal of achieving robust ray tracing based channel models this paper compares simulation results using a 3D ray-tracing tool [F. Aryanfar and S. Safavi-Naeini, 1998] vs. field measurements in different environments. The tool has been validated for many outdoor and indoor scenes at different frequency bands and is capable of accurate prediction of wireless channel parameters. To test model robustness, we also examine the sensitivity of the predicted results on inputs such as angular resolution, material properties and detail of geometry.

Correction of antenna phase center offsets in outdoor range measurements

Radiation pattern measurements of antennas mounted on vehicles present difficulties in centering the AUT with respect to the axes of rotation of the measurement system. Gain corrections dependent on the measurement system geometry have been implemented to correct the variation in the measurements introduced by the AUT offset. An outdoor antenna range is described, measurement repeatability is established, expressions for the corrections are given, and examples of corrected measurement results are presented.