Umesh Navsariwala

Genetic algorithm optimization for small antenna design

Small antenna design is a complex balance of trade-offs imposed by geometry, volume, manufacturability, materials, and the operating environment. Experience and intuition are essential in the antenna design process, however, once design complexity reaches a certain level, the use of design optimization tools becomes extremely valuable if not a necessity. This paper demonstrates the use of genetic algorithm optimization applied to a proprietary field solver interfaced with a commercial CAD system.

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.

Accurate and efficient models of the human hand for the prediction of antenna efficiency in mobile devices

The antennas in a mobile device, like a cellular phone, are significantly impacted by the presence of the user, especially in the talk position. Traditionally, this impact has not been accurately modeled and, in many cases, it is completely ignored. This results in an inaccurate prediction of the antenna performance, especially the radiation efficiency, and can lead to poor antenna design. In this article, the modeling of the hand in greater detail is considered. Although many CAD tools have the capability to model the hand geometry in fine detail with multiple materials, there are associated issues dealing with the model complexity and constructing hand phantoms for measurements. Therefore, a balance needs to be reached between the details in the model geometry and materials and the needs of the simulation and measurement tools. In this paper, a homogeneous hand model is presented. The model represents the geometry of the hand in good detail and it can be adapted to form various hand grips. The effect of the material properties of this hand model on the radiation efficiency of a few typical antennas in mobile handsets is studied. These studies illustrate than an effective material property for a homogeneous hand model can be used for a reasonable accuracy in the radiation efficiency of the antennas. A two tissue model consisting of bone and muscle is also studied.

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.

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.

A reduced sized balanced antenna for 2.4 GHz WLAN

The proliferation of wireless LAN devices has placed a renewed focus on small, integrated antennas. Several classes of antennas have been investigated in prior literature including inverted-F antennas, patch antennas, etc. In this paper a novel antenna design, an inverted-C antenna, is described. The antenna is balanced and can be integrated into the main PCB of the device. Additionally, since the antenna is balanced, it is less sensitive to perturbations of the ground plane. The simulated performance of the antenna is shown to be satisfactory for WLAN applications. Impedance and radiation pattern measurements of several prototypes are presented to verify the antenna performance.

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.

Analyzing Commercial Mobile Phones by a Domain Decomposition Approach

This paper presents a domain decomposition method (DDM) to model commercial mobile phones in the vicinity of a human head. The DDM is employed in two ways: One is to facilitate a novel non-conformal coupling scheme between finite elements and boundary elements. Secondly, it is also used to obtain the numerical Greens function, which includes the effects of the surrounding environment. The method is applied to a sample example to demonstrate the potential applications of such an approach

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.