Yagi-Uda Arrays
Yagi-Uda arrays are antennas that consist of a
driven element directly excited by a signal source (transmitter)
and one or more
parallel parasitic elements excited indirectly by radiation from
the driven element. The name comes from two Japanese engineers who invented
the antenna in the 1920s. In common usage today, the antenna is referred to
simply as a "yagi."
One research direction I am pursuing is the addition of
reactive components (inductors, capacitors, or transmission line stubs)
to the array elements to maximize the gain at multiple operating
frequencies while simultaneously
controlling the input impedance of the array.
Another area of investigation is the use of reactive components to control
the directions in which radiated or received energy is minimized (called
null directions). Null direction control can help to
limit interference to or from nearby wireless users.
A loop yagi array is a closely related antenna that
uses full-wave conducting loops for the elements, unlike the
standard yagi array, which uses half-wave dipole elements.
Circular and square loops are the most
widely used shapes. Conventional loop yagis radiate linearly polarized
electromagnetic waves,
which means that the electric field vector component of the wave always
points in the same direction. Many applications, including satellite
communication, make use of circularly polarization in which the
electric field vector rotates as the wave moves through space.
It turns out that a loop yagi antenna can be made to produce circular
polarization (CP) if the driven element is loaded with two inductors
(coils) located 1/8 and 5/8 of the way around the loop from the feed point.
The characterization and design of CP loop yagis has been a recent focus
of my research.
Contributions include (in chronological order):
- Applied the particle swarm optimization (PSO) method to determine the
inductor and capacitor values required to achieve target input impedances
at all of the operating frequencies of a multi-band dipole antenna.
This is a first step toward controlling the input impedance of a yagi
array.
- Applied the PSO method to determine the
inductor and capacitor values required to maximize the gain at
all operating frequencies of a multi-band yagi array.
- Investigated the extent to which reactive loading of array elements can
create nulls in desired directions without seriously compromising
gain and input impedance.
- Explored the use of folded dipole elements in place of standard dipole
elements to solve some of the mechanical problems associated with
adding reactive loads to yagi arrays.
- Explored the addition of inductive loads to the driven elements of
loop yagi arrays to generate circular polarization.
- Explored the addition of multiple reflector elements behind the
driven element of loop yagi arrays to help reduce the strength of the
cross-polarized back lobe.
- Explored the use of a pair of parallel plates with a feed point located
along a diagonal as the driven element for a circularly polarized
loop yagi array. The plates act much like a microstrip patch antenna
with the ground plane size reduced to that of the patch.
Bucknell Student Contributors
- Chunzhen (Tony) Wang (BSEE Spring '20)
- Hang Ha (BSEE Spring '18)
- Ryan Chaky (BSEE Spring '17)
- Evan Kerich (BSEE Spring '16)
- Evan Schlenker (BSEE Spring '16)
- Zachary Yu (BSEE Spring '16)
- Isaac Dost (BSEE Spring '14)
- Doug Bogan (Presidential Fellow, BSEE Fall '13)
- Tim Destan (Presidential Fellow, BSCS '08)
- Matt Mims (BSEE '04, MSEE '06)
Publications
- C. Wang and D. F. Kelley,
"A Circularly Polarized Loop Yagi Array with a Parallel-Plate Driven Element,"
2020 IEEE International Symposium on Antennas and Propagation,
Montreal, Quebec, Canada, July 2020 (virtual conference).
- R. J. Chaky and D. F. Kelley, "Reduction of Cross-Polarized Back Lobe
Radiation in Circularly Polarized Loop Yagi Arrays,"
2017 IEEE International Symposium on Antennas and
Propagation, San Diego, CA, July 2017.
- David F. Kelley,
"A Circularly Polarized Loop Yagi Array Using a Driven Element with
Two Reactive Loads,"
Proc. 2015 Antenna Applications Symposium, Monticello, IL., Sept. 2015,
pp. 33-50.
- D. M. Bogan and D. F. Kelley, "Discretized Reactive Loading Based on
Switched Stubs for Null Steering in Yagi-Uda Arrays,"
2014 IEEE International Symposium on Antennas and
Propagation, Memphis, TN, July 2014.
- David F. Kelley, "Yagi-Uda Arrays with Folded-Dipole Elements to Facilitate
Dynamic Reactive Loading Control," Paper No. 118.5,
USNC/URSI National Radio Science Meeting,
Toronto, Ontario, Canada, July 12, 2010.
- David F. Kelley, "A Tunable Yagi-Uda Array Using Dynamic Reactive Loading
Control," Proc. USNC/URSI National Radio Science Meeting,
Charleston, SC, June 2009.
- David F. Kelley and Timothy J. Destan,
"Investigation of the Null Steering Capability of Yagi-Uda Arrays with
Variable Reactive Loads,"
Proc. 2008 Antenna Applications Symposium, Monticello, IL., Sept. 2008,
pp. 306-325.
- Matthew E. Mims and David F. Kelley, "Application of Particle Swarm
Optimization to the Design of Multi-Band Antennas with Lumped Loads,"
Proc. IEEE Antennas and Propagation Society International Symposium,
vol. 4, Albuquerque, NM, July 2006, pp. 3547-3550.
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