Mark A. Schamberger

Parameter extraction and correction for transmission lines and discontinuities using the finite-difference time-domain method

The finite-difference time-domain (FDTD) method is useful for performing broadband characterization of uniform transmission lines and discontinuities. Modeling a geometry often requires the implementation of an absorbing boundary condition (ABC). When this is the case, numerical reflections from the ABCs will add significant error to the calculated transmission line or scattering (S) parameters. This paper introduces a simple post-processing algorithm for extracting these parameters and correcting for numerical reflection error. Furthermore, this method is shown to have a unique relationship to Pronys method. Practical application and limitations of this technique are also discussed. Finally, the impedance and propagation constant of a microstrip line are calculated using this method.

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.

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.

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.