A flush mounting, cavity-backed, dual orthogonal slot antenna for aircraft and space vehicles is described. Improved radiation pattern characteristics are obtained by making the spiral slot pattern elliptical in the aperture plane. A cavity and a flanged aperture plate are configured such that one slot pair is orthogonal with respect to another slot pair within the aperture plate. Coaxial split-tube baluns are used to drive the junctions between corresponding slot pairs. An optional cavity dielectric is provided and a drive coupling arrangement includes a four port comparator hybrid having sum and difference ports respectively, for alternate excitation to produce a single lobe or a double lobe pattern with null. Switching apparatus is provided to connect a common terminal to either of the ports

Ellis, H., Jr.

English

NASA Technical Reports Server

United States Patent ~ 1 9 1  - 
-- Ellis, Jr. 
[54] SPIRAL SIB7TED PHASED ANTENNA 
[7h] Inventor: Robert A. Frosch, Administrator of 
ARRAY 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Haynes Ellis, Jr., Chino, 
Calif. 
[21] Appl. No.: 172,099 
[22] Filed: Jul. 25, 1980 
[ 5  I ]  
[ 5 2 ]  
1581 
1561 References Cited 
Int. Cl.? ............................................... HOlQ 1/36 
U.S. CI, ..................................... 343/895; 343/?89 
Field of Search ............... 343/895, 854, 789, 769, 
343/767 
U.S. PATENT DOCUMENTS 
2,863,145 12/1958 Turner ................................ 343/895 
3,344,425 9/1967 Shelton, Jr. ......................... 343/895 
Primary Examiner-David K. Moore 
[1!1 4,315,266 
14-51 Feb. 9, 1982 
Alfornc-v, Ageril, or Firm-Edward K. Fein; John R 
Manning; Marvin F. Matthews 
w1 ABSTRACT 
A flush mounting, cavity-backed, dual orthogonal slot 
antenna in which improved radiation pattern character- 
istics are obtained by making the spiral slot pattern 
elliptical ir, thc aperture plane. A cavity (11) and a 
flanged aperture plate (lla) are shown i n  which one slot 
pair (12 and f3) is orthogonal with respect to another 
slot pair (14 and 15) within the aperture plate (110). 
Coaxial split-tube baluns (12a and 14a) $re used to drive 
the junctions between corresponding slat pairs. Op- 
tional cavity dielectric (18) is provided and a drive 
coupling arrangement includes a four port comparator 
hybrid (30) having S and A ports (17 and 15) respec- 
tively, for alternate excitation to produce a single lobe 
or Y double lobe pattern with null. Switching apparatus 
is provided to connect a common terminal (26) to either 
of the ports (17 or 16). 
10 Claims, 8 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19820019682 2020-03-21T17:13:19+00:00Z
U.S. Patent Feb. 9, 1982 Sheet 1 of 3 4,3 15,266 
FIG. 
//a 
U.S. Patent Feb. 9, 1982 Sheet 2 of 3 4,3 15,266 
FIG, 
FIG. 5 
U.S. Patent Feb. 9,1982 Sheet 3 of 3 4,3 15,266 
4,315,266 
1 
SPIRAI. SI'OTTED PHASED ANTENNA ARRAY 
DESCRIPTION 
ORIGIN OF T H E  INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA Contract and is sub- 
jcct to the provisions of Section 305 of The National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(72 Stat. 435; U.S.C. 2457). 
TECHNfCAL FIELD 
My invention relates generally to electromagnetic 
antennas and more specifically to flush mounted anten- 
nas for aircraft and space vehicles for such functions as 
communications and the like, most particularly for op- 
eration in the microwave bands. 
In high performance aircraft and reentry spacecraft 
the problems of aerodynamic load and friction heating 
preclude the employment of any antenna system which 
wholly or partly protrudes beyond the skin surface of 
such high performance airhpace vehicles. 
The usual frequencies of operation are very high and 
therefore compact structures are possible, even where 
speciat radiation patterns are required. The so-called 
cavity-hacking concept has been used in the prior art 
and is also used in the invention because of the opportu- 
nity for effecting radiation reenforcement due to cavity 
resonance. 
BACKGROUND A R T  
In the prior art, various approaches have been taken 
for the implementation of flush-mounted antennas for 
various end uses. Some of these are adapted for flush 
mounting in airhpace vehicles, even though deficient in 
certain important aspects, vis-a-vis the invention herein 
disclosed and described. 
Cavity-backed antennas for the airhpace vehicle 
application are particularly attractive because they 
readily afford flush mounting, consequently the perti- 
nent prior art comprises cavity-backed configurations. 
Moreover, spiral antennas per se are known to have 
relatively broad beam characteristics normal to the 
plane of the spiral. Cavity backing of a spiral antenna is 
known to provide increased directional sensitivity and a 
favorable electrical combination otherwise, since the 
spiral elements are, in a sense folded, thereby permitting 
them to be electrically relatively long within a corre- 
spondingly small aperture. 
Arrays of spiral antennas each with resonant cavity 
backing have been used for direction finding. Those 
spirals are spaced about the points of a compass and lie 
in vertical planes. Frequently no particular effort to  
compact such arrays is required, however, in U.S. Pat. 
No. 4,143,380 an arrangement is described in which the 
spirals are disposed about a cylindrical surface and 
share a common resonant chamber of annular cross-sec- 
2 
well covered by a radome, is subject t o  damage from air 
friction heating. 
A retro-directive. cavity-backcd assembly of spiral 
radiators is shown in U.S. Pat. No. 3,508,269. Tunnel 
5 diodes are connected to provide discontinuities in the 
associated transmission line to cause reflection of signal 
energy toward the feed assembly. Etched circuit tech- 
niques are employed to produce the spiral elements 
from copper clad dielectric sheets. Essentially the same 
10 vulnerabiiity to air friction heating as noted in connec- 
tion with U.S. Pat. No. 4,032,921 can be attributed to 
this cunfigutatinn. 
U S .  Pat. No. 3,568,206 discloses a square filamentary 
sprial antenna within a square cavity. Significance is 
1 5  attached to a slot formed by the clearance between the 
c-avity sidewalls and the perimeter of the spiral. Again 
the same vulnerability to air friction heating attaches to 
this device as aforementioned. 
U.S. Pat. No. 4,015,264 depicts a cavity-backed spiral 
20 antenna, in which a piurality of resistively loaded 
monopoles are disposed within the cavity for broad- 
banding purposes, without oversft size increase. Yet 
again, the filamentary spirai of this antenna would be in 
a plane parallel and close to the plane of the vehicle skin 
25 surface, with the result that it too would be very subject 
to air friction heating. Such heating produces very high 
localized temperatures and filamentary elements of any 
kind can thereby be subject to severe damage or even 
destruction. 
The known prior art, including the teachings of the 
aforementioned U 3 .  patents d o  not provide truly ad- 
vantageous structures for the purpose of the present 
invention. 
DISCLOSURE OF THE INVENTiON 
In consideration of the state of the prior art and the 
limitations thereof, it  may be said to have been the gen- 
eral object of the invention to provide an inexpensive 
thermal load resistant, flush mounting, cavity-backed 
40 compact antenna for aidspace vehicle use, it wiis also 
desired to provide circular polarization and alternative 
radiation patterns as a function of excitation control. 
The details of such an excitation control for the purpose 
of radiation pattern selection will be evident as this 
The radiating elements comprise a pair of collocated 
center-fed, interleaved, spiral slots in the aperture plane. 
The centers of the two slots are adjacent, one on either 
side of the center of the cavity. The slots are cut 
50 through a conductive aperture plate, the latter forming 
the external face of the cavity, At the center feed point 
of each slot, a balanced feed assembly is presented and 
each of these center points i s  fed from a split-tube coax- 
ial balun. Both coaxial baluns extend through the cavity 
55 and through a second side thereof parallel to the afore- 
mentioned aperture plate. Beyond this second side, a 
comparator hybrid is instrumented in stripline medium, 
for example, although not necessarily in that medium. 
The four port comparator hybrid, a known device per 
30 
35 
45 description proceeds. 
tion within the cyiindrical surface. The combination of 50 se, has two outpu; ports (sum and difference pork). 
the aforementioned Pal. No. 4,143,380 is of interest Switching means are included so that the sum fH) or 
because of its teachings in respect to compaction of difference (A) port of the comparator hybrid may be 
cavity-backed spiral antennas, but obviously it is not selectively excited to choose a sum or difference radia- 
applicable for flush mounting, at the skin surface of an tion pattern. The hybrid output ports each feed one of 
airt'space vehicle. 
U.S. Pat. No. 4,032,921 describes a cavity-backed The spiralled slots cover a pattern in the aperture 
spiral antenna which would readily be flush mounted, plate which is elliptical, the reason for this being the 
however the spiral is filamentary in nature and, even if control of the radiation pattern. 
65 the slot centers through the corresponding balun. 

4.3 15.266 
5 
b c d h  bo) 
p(h) = 
lvn'tb + fb , /a ,  ~ 0 5 4 ) ~  
where: 
Ao is the ellipse major axis (initially) 
bo is the ellipse minor axis (initially) 
a is the coefficient of spiraling (pitch) 
is the angular distance around antenna 
then 
aperture plate constituting one face thereof, said cavity 
being of substantially uniform depth measured normal 
to said aperture plate; first and second radiator slot pairs 
CUI through the thickness of said aperture plate, the 
5 slots of said pairs spiralling in the same rotation sense 
from corresponding first and second slot center points 
adjacent on either side of the center of said aperture 
plate; and slot feed means for separately feeding said 
first and second slot center points to effect electrically 
2. Apparatus according to claim 1 in which said spi- 
ralled slots are radially substantially uniformty spaced 
throughout their spiral trajectories and form an ellipti- 
cal pattern in said aperture plate. 
3. Apparatus according to claim 1 in which said slot 
where 6bw= desired beamwidth. feed means comprises first and second coaxial split-tube 
It should be noted that the quarter wave cavity depth baluns connected respectively to said first and second 
referred to is a near free space number whereas the slot center points. said baluns extending through said 
quarter wave balun slot to depth 20 is somewhat short- cavity and the wall thereof opposite said aperture plate. 
ened quarter wave due to the nature of the coaxiat 20 4. Apparatus according to claim 3 including a four 
medium of the baluns. port comparator hybrid including two branch ports, 
The cavity backing the slot radiation structure may one connected to each of said baluns at their ends exter- 
be filled with a low-loss dielectric material 18 if the nal to said cavity, said hybrid also including B and A 
device is to be operated at substantial power and/or ports which, when selectively energized, provide dis- 
high altitude. In that event, the volume of the cavity can 25 crete sum and difference patterns selectively. 
be reduced by a factor 1/= where a is the dielectric 5. Apparatus according to claim 1 in which said cav- 
constant of 18. ity is dielectric filled. 
The spiral slot arrangement of FIG. 1 may be re- 6. Apparatus according to  claim 3 in which said cav- 
ferred to as "arrayed cross-slot radiators" which will ity is dielectric filled, said. dieiectric surrounding said 
radiate circularly polarized R.F. energy in the beam 30 baiuns, the latter extending substantiaily normal to said 
patterns described. aperture plate from said slot center points. 
The entire apparatus is, of course, reciprocal and 7. Apparatus according to claim 4 in which said hy- 
accordingly, R.F. terminal 25 can provide received brid is instrumented in stripline medium, said hybrid 
signals as well as accept transmitable energy. being enclosed in a compartment attached to said cavity 
stripline instrumentation of the hybrid employed can be 8. Apparatus according to claim 1 in which a dielec- 
replaced by coaxial, waveguide, or some other micro- tric cover plate is affixed over the external face of said 
wave medium. The particular instrumentation of the aperture plate to provide a radome. 
hybrid is not per se a part of the invention, although the 9. Apparatus according to claim 7 in which switching 
hybrid is an element of the fully operative confirmation. 40 means are provided whereby said hybrid Z and A ports 
The foregoing and other advantages are obvious to may be selectively energized to selectively connect said 
those skilled in the art of antennas. P and A ports to common input/output port. 
What is claimed is: 10. Apparatus according to claim 1 in which said slots 
1. A cavity-backed, Rush-mountable antenna corn- of each slot pair are a multiple of one wavelength from 
10 mutuafly orthogonal operation of said slot pairs. 
I5 
It will be realized by those of skill in this art that 35 wall opposite said aperture plate. 
prising: a conductive-walled cavity of generally ellipti- 45 said slot center points spirally outward. 
cal cross-section and having a substantially elliptical * * * * *  
55 
60 
65 


Spiral slotted phased antenna array

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