HUFF et al.: DIRECTIONAL RECONFIGURABLE ANTENNAS ON LAPTOP COMPUTERS

3223

TABLE I

RESULTS FROM THE EVS

in (3) below), for which the electric

field polarization for these directions can be given as

(3)

IV.

The magnitude of steady state conduction current

on

generated by

density

can then be determined. Once

is known

is revisited on the set

for

residing on

.

of possible locations

Fig. 4. Fabricated model of laptop computer's internal shielding, showing

In the FDTD solution space, this is realized as the

, (for

1, 2, 3, and 4) for antenna integration.

candidate positions,

surface of the laptop with discritized spatial dimensions

confined by

[Fig. 3(e)]. For

V. ELECTROMAGNETIC ENVIRONMENT STUDY

3 [9] is used to perform

this study in particular, XFDTD

In order to fully evaluate the candidate positions for antenna

simulations, and

at 3.7

integration, it is important to take into consideration both the

GHz.

integration parameters around which the antenna will operate

V.

With the information generated in Guideline IV, the

with maximum performance, as well as the conditions that arise

conduction current density in the region(s) confined by

from operation in harsh, unfavorable, or changing electromag-

, (with

being the total number of cells

netic environments. To investigate the environmental effects

), can then be used to find the average

on the antenna as it assumes different positions on the laptop,

, over all incoming an-

conduction current density,

several test environments were created to mimic different

gles,  , and its standard deviation,

working situations. They include: 1) a dielectric surface [Lucite

]; 2) a conductive surface; 3) a dielectric surface with

scattering objects; and 4) a conductive surface with scattering

(4)

objects. These conditions are chosen to represent four basic

environmental conditions likely to be encountered by the laptop

computer. The scattering objects are an assortment of items

(5)

placed in the plane of the laptop (stacks of CDs, beverage

containers, etc.) that serves as one example of possible "real

world" environments.

VI.

Using (4) and (5), the areas of interest

can

be evaluated and ranked using the average steady state

VI. EXPERIMENTAL RESULTS

conduction current densities as well as the standard

.

deviation within the areas confined by

To experimentally verify the results from the EVS, the an-

For the generic laptop computer model used in this study,

tenna was conformally mounted onto the laptop chassis such

the candidate positions  can be seen in Fig. 4 and the results

plane of the antenna, was aligned with

that the H plane, or

from the EVS for these positions presented in Table I. For this

the azimuthal plane of the laptop chassis base unit. With the

example, a set of four candidate locations provides a sample

laptop sitting in the horizontal plane, the radiation character-

of nonoverlapping positions for comparison. Table I contains

configuration have linear polarization

istics from 1) the

the rankings of the four candidate locations from high to low

along the diagonal; 2) the

configuration is horizontally po-

visibility based on their respective local current densities and

configurations are vertically polarized.

larized; and 3) the

standard deviations. We hypothesize that positions with higher

For all positions and antenna configurations, input impedance,

and

levels of electromagnetic visibility (higher values of

2:1 VSWR bandwidth, and radiation patterns were measured.

lower values of ) will support antenna operation closer to that

The experimental setup used for this study, including the rel-

of free space.

ative antenna coordinate system on the laptop and the desired

free-space radiation of the reconfigured antenna configurations

3XFDTD

is a registered product of Remcom, 315 South Allen Street,

in their primary polarizations, is shown in Fig. 5. To provide

Suite 222, State College, PA 16801 USA.