Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Reexamination Certificate
2002-10-18
2004-11-23
Ho, Tan (Department: 2821)
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
C343S853000
Reexamination Certificate
active
06822617
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is related to co-filed application Ser. No. 10/273,459 filed on an even date herewith entitled “A Method and Structure for Phased Array Antenna Interconnect” invented by John C. Mather, Christina M. Conway, and James B. West. The co-filed application is incorporated by reference herein in its entirety. All applications are assigned to the assignee of the present application.
BACKGROUND OF THE INVENTION
This invention relates to antennas, phased array antennas, and specifically to a construction approach for a phased array antenna.
Phased array antennas offer significant system level performance enhancement for advanced communications, data link, radar, and SATCOM systems. The ability to rapidly scan the radiation pattern of the array allows the realization of multi-mode operation, LPI/LPD (low probability of intercept and detection), and A/J (antijam) capabilities. One of the major challenges in phased array design is to provide a cost effective and environmentally robust interconnect and construction scheme for the phased array assembly.
It is well known within the art that the operation of a phased array is approximated to the first order as the product of the array factor and the radiation element pattern as shown in Equation 1 for a linear array
10
of FIG.
1
.
E
A
(
θ
)
≡
E
p
(
θ
,
φ
)
⏟
Radinition
Element
Pattern
[
exp
(
-
j
2
π
0
λ
)
r
o
]
⏟
Isotropic
Element
Pattern
·
∑
N
A
n
exp
[
-
j
2
π
λ
n
Δ
x
(
sin
θ
-
sin
θ
0
)
]
⏟
Array
Factor
Equation
1
Standard spherical coordinates are used in Equation 1 and &thgr; is the scan angle referenced to bore sight of the array
10
. Introducing phase shift at all radiating elements
15
within the array
10
changes the argument of the array factor exponential term in Equation 1, which in turns steers the main beam from its nominal position. Phase shifters are RF devices or circuits that provide the required variation in electrical phase. Array element spacing, &Dgr;x or &Dgr;y of
FIG. 1
, is related to the operating wavelength and it sets the scan performance of the array
10
. All radiating element patterns are assumed to be identical for the ideal case where mutual coupling between elements does not exist. The array factor describes the performance of an array
10
of isotropic radiators
15
arranged in a prescribed grid as shown in
FIG. 1
for a two-dimensional rectangular array grid
10
.
To prevent beam squinting as a function of frequency, broadband phased arrays utilize true time delay (TTD) devices rather than phase shifters to steer the antenna beam. Expressions similar to Equation 1 for the TTD beam steering case are readily available in the literature.
The isotropic radiation element
15
in
FIG. 1
has infinitesimal dimensions, as explained in subsequent paragraphs. The spacing of the isotropic radiators
15
determines the scan performance of the phased array
10
. The elements
15
must be spaced less than or equal to one half wavelength (&lgr;
o
/2) apart for the radiated pattern to be free from grating lobes. Grating lobes are false undesired beams having strength equal to the main beam. The wider the element spacing, &Dgr;x or &Dgr;y, the smaller the grating lobe-free scan volume is for the array
10
. Array factors are also available for 2-D and 3-D phased arrays having rectangular and hexagonal grid arrangements, but they are not discussed here for the sake of brevity.
The isotropic radiating element
15
is an infinitesimally small, nonphysical mathematical concept that is useful for array analysis purposes. However, all operational arrays utilize physical radiating elements
25
of finite size as shown in the array
20
of FIG.
2
. Radiating element size in the plane of a planar array, or along the array surface for a conformal array, is usually a large fraction of &lgr;
o
/2, as required for efficient radiation. Since the array spacing, &Dgr;x or &Dgr;y, sets the grating lobe-free scan volume of the array
20
, it also puts restrictions on the transverse size of the individual radiating elements
25
within the array
20
. The extremities of neighboring radiating elements
25
are frequently very close to one another and in some cases, the array spacing, &Dgr;x or &Dgr;y, prevents certain types of radiating elements
25
from being used.
A comparison of
FIGS. 1 and 2
illustrates how real, physical radiating elements
25
consume the majority of the surface area around the array grid intersection points. The array element spacing, &Dgr;x or &Dgr;y, and transverse size restrictions are further exacerbated in electronically scanned phased arrays. The most general two-dimensional, or three-dimensional (arbitrarily curved surface) electrically scanned phased array antennas require phase shifters at each radiating element
25
to electronically scan the main beam of the radiation pattern. A very space-efficient interconnect cable assembly is required to provide the proper control signals, bias and chassis ground to each individual radiating element
25
and the phase shifters (not shown). However, the physical size of the cabling assembly is often too large and cumbersome to effectively route around the array radiating elements
25
without perturbing the RF field of the radiating element
25
and/or the aggregate field of the sub-array or top-level array assemblies.
The referenced application effectively resolves the phased array interconnect problem by utilizing fine pitch, high-density circuitry in a thin self-shielding multi-layer printed wiring assembly. The new approach utilizes the thickness dimension of an array aperture wall (parallel to bore sight axis) to provide the surface area and volume required to implement all of the conductive traces for phase shifter bias, ground, and control lines. The thickness of the printed wiring assemblies
35
are now in the x-y plane (front view) of the radiating elements
25
in the phased array
30
as shown in FIG.
3
.
A packaging, interconnect, and construction approach is needed to create a cost-effective EMXT (electromagnetic crystal)-based phased array antennas having multiple active radiating elements in an X-by-Y configuration. EMXT devices are also known in the art as tunable photonic band gap (PBG) and tunable electromagnetic band gap (EBG) substrates. A detailed description of a waveguide section with tunable EBG phase shifter technologies is available in a paper by J. A. Higgins et al. “Characteristics of Ka Band Waveguide using Electromagnetic Crystal Sidewalls” 2002 IEEE MTT-S International Microwave Symposium, Seattle, Wash., June 2002. Each element is comprised of EMXT sidewalls and a conductive (metallic) floor and ceiling. Each EMXT device requires a bias voltage plus a ground connection in order to control the phase shift for each element of the antenna by modulating the sidewall impedance of the waveguide. By controlling phase shift performance of the elements, the beam of the antenna can be formed and steered. The maximum permitted distance between centerlines of adjacent apertures is &lgr;
o
/2 in both the X and Y directions and the total thickness of the EMXT plus mounting structure and interconnect must be minimized.
A design approach is needed that utilizes the interconnect scheme disclosed in the referenced application to construct a phased array antenna that can be assembled into a configuration with multiple radiating elements.
SUMMARY OF THE INVENTION
A phased array antenna for steering a radiated beam and having an egg crate-like array structure of array elements is disclosed. The phased array antenna is constructed from row slats formed from a metallic substrate. The row slats have a plurality of row slots. Column
Conway Christina M.
Lehtola Gary E
Mather John C.
West James B.
Wichgers Joel M.
Eppele Kyle
Ho Tan
Jensen Nathan O.
Rockwell Collins
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