Dual polarization antenna array with radiating slots and notch dipole elements sharing a common aperture

Disclosed is a common aperture dual polarization antenna array (30). This common aperture dual polarization antenna array (30) includes an antenna aperture (36) and a plurality of centered slot arrays (32) positioned within the antenna aperture (36). A plurality of notch dipole arrays (34) are positioned within the antenna aperture (36) and positioned substantially orthogonal to the plurality of centered slot arrays (32). A first feed guide (46) is coupled to the plurality of centered slot arrays (32) and a second feed guide (56) is coupled to the plurality of notch dipole arrays (34).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an antenna array and, more particularly, 
to a dual polarization antenna array having radiating slots and notch 
dipole elements sharing a common antenna aperture. 
2. Description of Related Art 
Radar and communication systems commonly use dual polarized antennas which 
are capable of achieving significant performance advantages over single 
polarization antenna arrangements. Current trends in radar and 
communication antenna designs emphasize the reduction of cost and volume 
of the dual polarization antenna, while achieving high performance. The 
dual polarization antenna is particularly useful with energy waves such as 
those employed in the radio frequency spectrum having two orthogonal 
components which are orthogonally polarized with respect to each other. 
The first orthogonal component is conventionally known as the vertical or 
principle polarization component, while the second component is generally 
known as the horizontal or cross polarization component. The orthogonal 
polarization of the energy waves allows for the possibility of 
broadcasting two different signals at the same operating frequency. In 
doing so, one signal is derived from the principle polarization component 
and the second signal is derived from the cross polarization component. 
The more basic conventional antenna systems are capable of employing the 
orthogonally polarized signal components to double the information sent at 
the same frequency by using two separate antennas. One type of 
conventional dual polarization antenna utilizes a reflector antenna with 
dual polarization feed elements. This reflector antenna consumes a large 
volume and is therefore bulky by today's standards. In addition, the 
conventional reflector arrangement can exhibit a relatively poor 
efficiency as compared to other types of antennas and often experiences 
poor isolation between the two polarizations. The conventional dual 
polarization reflector antenna is also limited in its ability to offer low 
sidelobe radiation pattern performance. 
Another type of dual polarization antenna includes an array of dual 
polarized patches typically made up of conductive patches fabricated on a 
dielectric substrate. The dual polarized patch antenna can be manufactured 
at a low cost and provides for a low profile antenna configuration. 
However, the bandwidth of each element of the dual polarized patch antenna 
is typically quite narrow and therefore it is very difficult to achieve a 
high antenna performance with the patch antenna. Also, the efficiency of 
the dual polarized patch array antenna can be quite low due to the 
presence of undesirable dielectric losses. 
Another antenna includes a dual polarization rectangular waveguide array 
10, as shown in FIG. 1, which consists of a stack up of rectangular 
waveguide fed offset longitudinal slot arrays 12 and waveguide fed tilted 
edge slot arrays 14. The offset slots 16 on the longitudinal slot arrays 
12 excites both the desirable TEM mode and the undesirable TM.sub.01 odd 
mode in the parallel plate region formed by the edge slot arrays 14 (see 
FIG. 1). This undesirable TM.sub.01 odd mode exhibits poor performance. 
The excited TM.sub.01 odd mode also causes high sidelobes and RF loss. A 
further limitation in performance of this type of antenna results from the 
coupling between arrays 12 and 14 caused by the tilted edge slots 18 of 
the edge slot arrays 14 containing a cross polarization component. 
A further approach includes arched notch dipole card arrays 20, as shown in 
FIG. 2, erected over a rectangular waveguide fed offset longitudinal slot 
arrays 22. The arched notch dipole card arrays 20 have arches 24 provided 
to improve the performance of the principal-polarization slot arrays 22 
and minimize interactions between the two arrays 20 and 22. However, this 
type of antenna is difficult to design due to the lack: of a convenient 
method to account for the presence of the arched dipole arrays 20 in the 
design of the slot arrays 22. Also, the requirement to maximize the 
spacing between the face of the slot arrays 22 and the arch arrays 20 to 
reduce interaction conflicts with the desire to place the notch radiators 
26 one-quarter wavelength above the slot array surface for optimal image 
current formation. Moreover, this limitation becomes especially severe at 
higher frequencies of operation. 
It is therefore desirable to provide for a compact low cost dual 
polarization antenna array which achieves high performance. More 
particularly, it is desirable to provide for a dual polarization antenna 
array which shares a common aperture of radiating slots and notch dipole 
elements at a low cost and yet exhibits high antenna performance. 
SUMMARY OF THE INVENTION 
In accordance with the teachings of the present invention, a common 
aperture dual polarization antenna array is provided for achieving high 
antenna performance at a low cost and in a compact structure. The common 
aperture dual polarization antenna array provides high gain and low 
sidelobe performance for both the principle polarization and cross 
polarization of the antenna array. 
In one preferred embodiment, the common aperture dual polarization antenna 
array includes an antenna aperture and a plurality of centered slot arrays 
positioned within the antenna aperture. A plurality of notch dipole arrays 
are positioned within the antenna aperture and positioned substantially 
orthogonal to the plurality of centered slot arrays. A first feed guide is 
coupled to the plurality of centered slot arrays and a second feed guide 
is coupled to the plurality of notch dipole arrays. 
In another preferred embodiment, the common aperture dual polarization 
antenna array includes a principle polarization array having a plurality 
of principle polarized radiators which are operable to radiate principle 
polarized energy. A cross polarization array having a plurality of cross 
polarized radiators is operable to radiate cross polarized energy. A 
polarization selective ground plane is operable to simultaneously reflect 
substantially all of the cross polarized energy radiated from the 
plurality of cross polarized radiators and simultaneously pass 
substantially all of the principle polarized energy radiated from the 
plurality of principle polarized radiators. 
Use of the present invention prides a common aperture dual polarization 
antenna array which provides high gain and low sidelobe performance for 
both polarizations. As a result, the aforementioned disadvantages 
associated with current dual polarization antenna arrays have been 
substantially eliminated.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A dual polarization antenna array 30 according to the teachings of the 
preferred embodiment of the present invention is shown in FIG. 3 generally 
made up of a combination of radiating slots and notch dipole elements 
provided in one common aperture. This invention provides a low cost, low 
profile and high performance dual polarization antenna array 30 that is 
particularly useful in electrically medium to large size array 
applications. The dual polarization antenna array 30 as described herein 
has potential applications suitable where high efficiency, low sidelobes 
and high isolation are required in a dual polarized antenna array at low 
to moderate costs and is particularly attractive for use in high 
performance missile seeker applications. However, it should be appreciated 
that various other modifications and applications of the dual polarization 
antenna array 30 are conceivable. 
The dual polarization antenna array 30 includes a plurality of rectangular 
waveguide fed centered shunt slot arrays 32 each positioned parallel to 
one another and a plurality of stripline fed notch dipole arrays 34 each 
positioned perpendicular between adjoining centered shunt slot arrays 32. 
The main or principle (vertical polarization) array is achieved with the 
plurality of centered shunt slot arrays 32 and the cross (horizontal 
polarization) array is achieved with the plurality of notch dipole arrays 
34. The fully populated main or principle polarization array formed by the 
centered shunt slot arrays 32 and the fully populated cross polarization 
array formed by the notch dipole arrays 34 each share a common aperture 36 
defined by the outer periphery of the combination of the arrays 32 and 34. 
Each centered shunt slot array 32 includes a rectangular waveguide 38 
having a plurality of principle polarized radiators or longitudinally 
centered shunt slots 40 disposed on a broad wall 42 of the rectangular 
waveguide 38. Each longitudinally centered shunt slot 40 is fed by 
corresponding offset ridge resonant irises 44 which are disposed within 
the rectangular waveguide 38 and centered under each centered shunt slot 
40, further discussed herein. The centered shunt slots 40 may also be 
excited by "L"-shaped resonant irises or other suitable means. Usable RF 
bandwidth of each centered shunt slot array 32 is inversely proportional 
to module size or the number of centered shunt slots 40 in a single 
standing wave rectangular waveguide 38. Each rectangular waveguide 38, is 
preferably fed by a rectangular slot array feed guide 46, or other 
appropriate feed arrangement. 
Each notch dipole array 34 is secured perpendicular between adjacent 
rectangular waveguides 38 by the use of a pair of vertical retaining walls 
48. The parallel plates formed by each of the notch dipole arrays 34 are 
each positioned at about one-half to three-quarters of a wavelength 
(0.50.lambda. to 0.75.lambda.) apart in free space, identified by 
reference numeral 50. The cross polarized radiators of the notch dipole 
arrays 34 consist of constant width notch radiators 52 arranged along the 
edge of the vertically disposed notch dipole arrays 34 and embedded 
dipoles 54. The notch radiators 52 are excited by the embedded dipole or 
balun elements 54, further discussed herein. Each notch dipole array 34 is 
fed by a rectangular dipole array feed guide 56, via a probe coupling 
element 58. Each probe coupling element 58 is located between and at the 
end corners of the centered shunt slot arrays 32, such that the probe 
element 58 can penetrate into the dipole array feed guide 56 without 
interrupting the main (vertical-polarization) array formed by the 
plurality of centered shunt slot arrays 32. 
Positioned substantially parallel with the shunt slot arrays 32 and 
substantially perpendicular to the notch dipole arrays 34 is polarization 
selective ground plane 60. The polarization selective ground plane 60 
includes a series of parallel conductive or metal strips 62 each arranged 
along the radiating dipole direction. The metal strips 62 simultaneously 
reflect substantially all of the cross polarized energy radiated from the 
notch dipole arrays 34 but simultaneously passes substantially all of the 
principle polarized energy radiated from the centered shunt slot arrays 
32. This enables both sets of arrays 32 and 34 to radiate simultaneously 
without any substantial coupling between the arrays 32 and 34. In other 
words, the parallel strips 62 act as a ground plane for the notched dipole 
arrays 34 but are substantially invisible or transparent to the centered 
shunt slot arrays 32, thereby further enhancing the isolation between the 
two orthogonal polarized arrays. The polarization selective ground plane 
60 is preferably located one-quarter wavelength (1/4.lambda.) below the 
top of the notch dipole arrays 34, identified by reference numeral 64, 
thereby providing image currents which add in phase near broadside in the 
far field radiation pattern. It should further be noted that each notch 
dipole array 34 has a height that is much larger than one-quarter free 
space wavelength (1/4.lambda.) to accommodate for the stripline feed 
circuitry of each notch dipole array 34 which enables improved bandwidth. 
Turning to FIGS. 4 and 5, a notch dipole array 34 and the rectangular 
dipole array feed guide 56 are shown in detail. The notch dipole array 34 
is made of a bonded assembly of two (2) 15 mils thick duroid boards with a 
conductive stripline feed circuitry 66 positioned therebetween, and shown 
here in solid lines. The notch radiators 52 are formed on the outside of 
the bonded assembly by etching the notch radiators 52 out of two (2) solid 
ground planes 68 which are also bonded to the outside of the duroid 
boards. Each notch dipole array 34, shown in FIG. 4, includes a plurality 
of notch radiators 52 etched within the ground plane 68 and six (6) 
radiating dipoles or baluns 54 which form a portion of the conductive 
stripline circuitry 66. Each dipole 54 is located orthogonal to every 
other notch radiator 52. Each dipole 54 is fed from the probe element 58 
through a conductive stripline feed 70 and separate stripline transformers 
72. It should be noted that the notch dipole array 34, shown in FIG. 4, 
includes the six (6) radiating dipoles 54 while the arrays 34, shown in 
FIG. 3, only show a portion or section of the arrays 34. Moreover, the 
dual polarization antenna array 30, shown in FIG. 3, is shown with four 
(4) notch dipole arrays 34 and five (5) centered shunt slot arrays 32 for 
merely exemplary purposes and may include more or less arrays 32 and 34. 
The width of each transformer 72 controls the amount of excitation or 
impedance. The notches 74 and tabs 76 on the transformers 72 are used to 
compensate for junction reactance and radiation phase errors. The purpose 
of the notches 72 and tabs 76 is to make each antenna radiator equivalent 
circuit element look purely shunt to the main stripline feed circuitry 66. 
Desired sidelobe levels for antenna 30 require a preferable conductance 
range of about 3.5 to 1 for the transformers 72. This implies that over 
this conductance range, the radiation phase and the insertion phase need 
to be constant. The amount of excitation or the impedance can also be 
adjusted by adjusting the stripline 70 and dipole 54 geometries, using 
known techniques. The bandwidth is controlled by subdividing each notch 
dipole array 34 into modules through the use of known equal or unequal 
power dividers which may be embedded within each notch dipole array 34. 
Packaging space for the conductive strip line feed circuitry 66 is 
available because of the use of the polarization selective ground plane 60 
positioned above the principle polarization array face of the centered 
shunt slot arrays 32 and one-quarter wavelength (1/4.lambda.) below the 
notch dipole arrays 34. The notch radiators 52 intercept almost none of 
the currents flowing in the walls of the notch dipole arrays 34 due to the 
principle polarization array TEM parallel plate mode which subsequently 
leads to extremely low coupling between the two polarizations or arrays 32 
and 34. 
The probe coupling from the probe element 58 is located at the end of the 
notch dipole array 34 and at the ends of the centered shunt slot arrays 32 
so that a minimal interference with the principle polarization array from 
the centered shunt slot arrays 32 occurs. The probe coupling approach 
requires only a small diameter hole to be positioned between adjacent 
rectangular waveguides 38 so that the probe element 58 can be passed down 
into the dipole array feed guide 56, shown in detail in FIG. 5. The probe 
element 58 has a natural reactance to it so that the use of inductive 
tuning or an inductive iris 80 along the feed guide 56 sidewalls 82 are 
used to cancel this reactance. Conductance can then be determined as a 
function of the iris 80 width or the amount of penetration of the iris 80 
into the center of the feed guide 56 and the probe 58 penetration depth 
into the feed guide 56. There will generally be an insertion phase delay 
as a function of conductance, but this phase delay is preferably 
compensated by adjusting the length of the stripline feed 70 in each array 
34 to provide a conductance range of about 2.5 to 1. 
Turning now to FIG. 6, a detailed perspective view of a portion of the 
centered shunt slot array 32 is shown along with the slot array feed guide 
46. As shown in FIG. 6, the rectangular waveguide 38 includes the centered 
longitudinal shunt slot 40 positioned on the broadwall 42 of the 
rectangular waveguide 38. Positioned substantially perpendicular to the 
waveguide 38, is the slot array feed guide 46 which includes a centered 
transverse feed slot 84 passing through both the feed guide 46 and the 
waveguide 38 in order to feed the waveguide 38. Positioned within the 
waveguide 38, as well as within the feed guide 46 are offset ridge 
resonant irises 44 which are disposed centrally under each longitudinal 
shunt slot 40, as well as the transverse slots 84. Each offset ridge 
resonant iris 44 is comprised of a first portion 44a that is disposed 
within the waveguide 38 on an opposite internal broadwall 86 of the 
waveguide 38 relative to the centered longitudinal shunt slot 40. The 
first portion 44a of the offset ridge resonant iris 44 has a length that 
is a predetermined portion of the width of the waveguide 38. Each offset 
ridge resonant iris 44 also has a second portion 44b that is disposed on 
an internal lateral sidewall 88 of the waveguide 38 relative to the slot 
40. Each offset ridge resonant iris 44 has a finite thickness, typically 
or the order of about 16 to 25 mils when used to radiate energy in the Ka 
frequency band. A more detailed description of the resonant offset ridge 
iris 44 is described in a commonly assigned Application Ser. No. 
09/058,112, entitled "Centered Longitudinal Shunt Slot Fed By a Resonant 
Offset Ridge Iris", naming as inventors Pyong K. Park and Sang H. Kim 
(Hughes Docket No. PD-96233), filed on Apr. 9, 1998, which is hereby 
incorporated by reference. 
Returning now to FIG. 3, an illustration of the intended performance 
exhibited by the dual polarization antenna array 30 will be discussed. The 
centered longitudinal shunt slots 40 of the shunt slot arrays 32 excite 
only the desirable TEM even mode, as shown in FIG. 1, within the parallel 
plate region of the notch dipole arrays 34. The centered shunt slots 40 do 
not excite the undesirable TM.sub.01 odd mode, also shown in FIG. 1, which 
is caused by of the offset slots 16. The TM.sub.01 odd mode excitation is 
a waste of energy and constitutes undesirable radiation because the 
TM.sub.01 odd mode is not used for main beam radiation. The use of the 
centered longitudinal shunt slots 40 completely eliminates the TM.sub.01 
odd mode excitation compared with various prior art antennas which have 
prior restrictions of high side lobes and significant RF loss. 
Significant system performance advantages can be achieved in radar and 
communication systems by use of the dual polarization antenna array 30. 
The dual polarization antenna array 30 provides the common aperture 36 
fully populated with elements for both polarizations and also provide high 
gain and low sidelobe performance for both polarizations. Both arrays in 
this dual polarization antenna array 30 utilize the entire aperture 36 to 
maximize its antenna performance to realize both the principle 
polarization and the cross polarization arrays in efficient standing wave 
configurations. The high RF performance achieved by the dual polarization 
antenna array 30 provides low sidelobes, low RF loss and exceptional 
isolation between both arrays of the principle polarization and cross 
polarization below about -50 dB that may be applied to frequencies up to 
at least the Ka band or higher. 
The foregoing discussion discloses and describes merely exemplary 
embodiments of the present invention. One skilled in the art would readily 
realize from such a discussion and from the accompanying drawings and 
claims, that various changes, modifications and variations can be made 
therein within departing from the spirit and scope of the invention as 
defined by the following claims: