Phased Array Antennas
Phased arrays consist of multiple antennas arranged in a
geometrical pattern and operated cooperatively in such a way that they can
concentrate their radiated energy (transmission mode) or increase their
sensitivity (reception mode) in one or more directions.
Arrays are sometimes designed specifically to limit radiation in other directions
as well.
The physical process that makes this possible is the constructive and destructive
interference of waves.
The individual antennas in the array are called elements,
all of which usually have the same physical shape and orientation.
The array elements are connected directly to individual signal
transmitters and receivers (an active array), or only one element is connected
to a signal source
and the other elements contribute via reflection and electromagnetic interaction
(a parasitic array). Electromagnetic interaction, usually called
mutual coupling, occurs in both active and
parasitic arrays, but it is usually seen as a detrimental effect in the former
and a beneficial (and, in fact, necessary) effect in the latter.
I am investigating methods of accounting for mutual coupling effects in both the
analysis and design of phased array antennas. This is an area that is sometimes
thought to be well understood, but in fact many important details are neglected
in much of the literature. Significantly, many investigators miss opportunities
for increasing the speed of "what-if" analyses when designing certain kinds of
array antennas.
There is a common misconception that, in the absence of mutual coupling, the gain
of an N-element array is close to N times that of a single element
regardless of the element spacing.
One of my interests is dispelling this myth in a way that avoids highly complex
math and concepts that are familiar only to antenna engineers.
Contributions in this area include:
- Described a relationship between the mutual impedances of
phased array antenna elements and the array's embedded element patterns
(the radiation
patterns that result when one element is excited by a source and the others'
feed points are short-circuited or open-circuited).
This has led to the development of a new method for determining mutual
impedances from the radiation pattern data obtained when single elements
are driven in turn by signal sources and the others are connected to known
standard impedances.
- Extended the mutual impedance-embedded element pattern relationship to
include embedded element patterns obtained by connecting the elements'
feed points to arbitrary impedances.
My earliest work in this area constituted the primary portion of the
research for my MSEE degree at
Virginia Tech.
The principal contributions of my masters research were:
- Investigated the effects of electromagnetic interactions
between phased array elements on
the radiation patterns of array antennas.
- Clarified the conditions under which various types of embedded element
patterns (called active element patterns at the time) can be used in
weighted sums to calculate the total radiation patterns of phased
arrays.
- Raised awareness that the embedded element patterns associated with the
elements near the edges of small arrays need to be accounted for in
radiation pattern calculations.
This led to the development of the Hybrid Active Element Pattern Method
for determining the total radiation pattern of an array.
Journal Papers
- David Buck, Karl F. Warnick, Rob Maaskant, David B. Davidson, and
David F. Kelley,
"Measuring Array Mutual Impedances Using Embedded Element Patterns,"
IEEE Transactions on Antennas and Propagation, vol. 71, no. 1,
pp. 606-611, January 2023.
- David F. Kelley and Warren L. Stutzman, "Array Antenna Pattern
Modeling Methods that Include Mutual Coupling Effects," IEEE
Transactions on Antennas and Propagation, vol. 41, no. 12,
pp. 1625-1632, December 1993.
Conference Papers
- David F. Kelley,
"Relationship Between Phased Array Gain and Element Radiation
Resistance in the Absence of Mutual Coupling,"
accepted for presentation at the 2023 Antenna Applications Symposium,
Monticello, IL, Sept. 2023.
- Karl Warnick, David Buck, Rob Maaskant, David Kelley, David Davidson,
"Array Mutual Impedances Can Be Determined From Antenna Range Pattern
Measurements,"
2023 IEEE Antennas and Propagation Society International Symposium,
Portland, OR, July 2023.
- David F. Kelley, "Embedded Element Patterns and Mutual Impedance
Matrices in the Terminated Phased Array Environment," Proc.
IEEE Antennas and Propagation Society International Symposium,
vol. 3A, Washington, DC, July 2005, pp. 659-662.
- David F. Kelley, "Relationships between Active Element Patterns
and Mutual Impedance Matrices in Phased Array Antennas," Proc.
IEEE Antennas and Propagation Society International
Symposium, vol. 1, San Antonio, TX, June 2002, pp. 524-527.
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