High Frequency Design
THROUGH-WALL COUPLER
Figure 5 · Normalized output power of the receiving 2.4 GHz coupler com-
municating through a 25 cm concrete wall.
Figure 6 · Electromagnetic fields of
a vertical cut near center; 2.4 GHz
couplers on a 51 cm concrete wall.
side wall. In this system, the panel
the FDTD algorithm is not without
antenna attached to the outside cou-
errors. Warnik [5] gives an approxi-
pler (Fig. 2) can be turned as far as
mation of error accumulation with
References
±90º off the normal, directing it into
time step size and time. Guidelines
1. P. Bhartia, et al, Millimeter-
the strongest transmission. In other
for FDTD simulation setup can be
wave Microstrip and Printed Circuit
installations, there may be cable loss-
found in this other references, or pro-
Antennas, Artech House, Inc., 1991.
es and other unpredictable losses. For
vided by FDTD software vendors.
2. K. S. Kunz and R. J. Luebbers,
example, at 2.4 GHz a 10-inch wall of
Conclusion
The Finite Difference Time Domain
moist concrete has a loss of 24 dB,
These couplers provide quick,
Method for Electromagnetics, CRC
increasing to 50 dB when wet. In con-
flexible, cable-free installation of
Press, 1993.
trast, a dry concrete wall of 20 inches
WiFi house antennas, avoiding build-
3. G. Knapp, US Patent No.
(51 cm) shows a loss of 24.5 dB (Fig.
ing restrictions and lightning
6,963,305 B2, Nov. 8, 2005.
6). The ground plane of the coupler
arrestors.
4. J. D. Kraus, Antennas,
helps keep the concrete underneath
The wall coupler is a new device
McGraw-Hill Book Company, Inc.,
dry, in addition to aiding the
that could not have been built with-
1950, p. 553.
microwave beam concentration.
out an electromagnetic simulation
5. K. F. Warnik, "An intuitive error
The bandwidth of the coupler is
program such as the FDTD algo-
analysis for FDTD and comparison to
material and frequency dependent. A
rithm, because of the difficulty in
MoM,"
IEEE
Antennas
and
single patch antenna (without a
achieving confinement and concen-
Propagation Magazine, Vol. 47, No. 6,
housing [3]) has a 3% bandwidth,
tration of RF with sub-wavelength
December 2005, pp. 111-115.
which increases for concrete to 7% at
reflector dimensions, and a path
2.4 GHz (Fig. 5) and increases to 11%
Author Information
through materials with frequency
at 5.3 GHz when operating as a cou-
Guenther Knapp is an indepen-
dependent dielectrics and losses.
pler pair.
dent consultant. He received the
Field confinement is important for
At this time no attempt was made
Dipl. Ing. degree in Electrical
secure LANs, both wired or infrared
to increase the bandwidth further.
Engineering from the Berlin Gauss
(IR). The wall coupler's stray radia-
There are many solutions available
College of Engineering. He is a Senior
tion becomes unreadable outside an
in the literature for wide bandwidth
Member of the IEEE with 14 techni-
office area when used with approxi-
microstrip patches suitable as cou-
cal publications and four US Patents.
mately 60 dBm or less power (power
pler parts. Reduction of coupler loss-
He is licensing his patents. He can be
level adjustment to a minimum for a
es is the subject of ongoing R&D.
reached at wbridge@localnet.com.
given wall).
Finally, readers should note that
62
High Frequency Electronics