Recent Publications:
Application of Spatial Bandwidth
Concepts to MAS Pole Location for Dielectric Cylinders
J. Richie, IEEE Transactions on Antennas and Propagation,
Vol. 59, No. 12, pp. 4861 - 4864, Dec. 2011.
Abstract
The concept of effective spatial bandwidth (EBW) is extended from the
case of an MAS solution for perfectly conducting (PEC) cylinders to
dielectric cylinders. It is shown that the ideas and results for the
con- ducting cylinder apply in a straightforward manner to the
dielectric case. For the dielectric case, there are two auxiliary
surfaces. Because the EBW calculations are independent of the
scatterer material, the auxiliary sur- face for the scattered field
will follow the same guidelines for both the PEC and dielectric
cases. The guidelines for the second auxiliary surface are de- scribed
and verified here. Guidelines for both a plane wave incident field and
a monopole line source incident field are provided.
MAS Pole Location and Effective Spatial Bandwidth of the
Scattered Field
J. Richie, IEEE Transactions on Antennas and Propagation, Vol. 58, No. 11, pp. 3610 - 3615, Nov. 2010.
Abstract
In this work, the concept of effective spatial bandwidth (EBW) is
introduced for periodic domains. The EBW is applied to the incident
and scattered fields along the boundary of an infinite circular
cylinder. The scattered field is formulated using the Method of
Auxiliary Sources (MAS). In MAS, monopoles on an auxiliary surface
(AS) are used to model the scattered field. It is shown that the EBW
of the incident field can provide some insight regarding the placement
of poles for the MAS scattered field model. Example simulations are
provided to demonstrate the usefulness of EBW with respect to monopole
placement rules in MAS.
UHF Propagation in the Magnetic Resonance Bore
J. A. Black, and J. Richie, IEEE Antennas and Wave Propagation Letters,
Vol. 8, pp. 869-871, 2009
Abstract
The magnetic resonance (MR) bore's structure, loading
parameters, and material make-up greatly influence the ability of a
frequency-specific signal to propagate. The relative path loss
behavior of the MR bore has been determined experimentally at ultra
high frequencies. An experiment is conducted to determine signal
attenuation when the bore is empty (air-filled) or dielectrically
loaded (patient-filled). This information is especially important to
the wireless network designer who is implementing an in-bore
physiological monitoring network. Experimental results show that the
MR bore exhibits impressive path loss performance at 434 MHz, with
greatest signal strength arriving at the receiver when the bore is
dielectrically loaded.
A Top-Mounted, Two-Loop Antenna Configuration
with Nearly Omnidirectional Radiation Characteristics
J. Richie, B. Koch, IEEE AP-S International Symposium Digest,
Albuquerque NM, July 2006.
The Use of Side-Mounted Loop Antennas on
Platforms to Obtain Nearly Omnidirectional Radiation
J. Richie, and B. Koch, IEEE Transactions on Antennas and Propagation,
Dec. 2005.
Abstract
Antennas mounted to vehicles at VHF frequencies are limited to whip and
loop antennas. Often, mechanical constraints force antenna placement
to be less than optimal. In this work, we investigate the use of
side-mounted loops on rectangular conducting platforms. It will be
shown that tall thin platforms radiate simlar to a dipole. In
addition, as the thickness increases, the loop antennas can radiate in
a nearly omnidirectional fashion if the antenna-mounted sides of the
platform are not too wide. In effect, a narrow platform width implies
return currents for a loop antenna that remain mostly vertical.
HF Antennas for NVIS Applications Mounted to
Helicopters with Tandem Main Rotor Blades
J. Richie, and T. Joda, IEEE Transactions on
Electromagnetic Compatibility, May 2003.
Abstract
Antennas mounted to helicopters for HF Near Vertical Incidence Skywave
(NVIS) communication suffer from severe rotor modulation at
frequencies where the blades are nearly resonant. Helicopters with
tandem main rotors such as the US Army Chinook cargo helicopter are
considered. It is determined that there are two effects contributing
to rotor modulation: the parasitic radiation from the rotor blades,
and the induced current on the hubs. It is shown here that two towel
bar (loop) antennas, one on each side of the airframe and centered
with respect to the hubs, can be used to reduce the severe drop in
gain due to hub currents. However, the variation in gain due to
parasitic radiation from the blades remains.
VHF Helicopter Antennas the Incorporate the Airframe
and Reduce Rotor Modulation
J. Richie, and T. Barrett,
IEEE Transactions on Electromagnetic Compatibility, August 2000.
Abstract
Antennas at VHF frequencies mounted to small (with respect to
wavelength) helicopter platforms are usually limited to whip and loop
antennas. Antenna placement and rotor position can drastically change
antenna performance due to induced currents on the platform. This
work illustrates deliberate antenna-platform interactions that cause
induced currents to reinforce and improve the radiating system
performance. Additionally, rotor modulation effects can be
simultaneously limited. This is accomplished by using oppositely
placed loop antennas at a location on the airframe that is nominally
one wavelength in circumference. The resulting broadcast pattern
admits low cross-polarization radiation and low copolarized rotor
modulation, but is not uniform. The dipole moment of the loops
dictates this nonuniformity. Double-loop antennas are used to create
a more uniform broadcast pattern without sacrificing the desired low
cross-polarized radiation and low copolarized rotor modulation.