US 3599220 A
Description (OCR text may contain errors)
United States Patent lm enmr Richard C. Dempsey Chatsworth. Calif Appl No 770.340
Filed Oct. 24. 1963 Patented Aug-10.1971
Assrgnee International Telephone and Telegraph Corporation New York, NY.
CONICAL SPIRAL LOOP ANTENNA 8 Claims, 5 Drawing Figs.
343/863. 343/895 Int. Cl... H0lg 1/36 Field olSearch 343/895,
 References Cited UNlTED STATES PATENTS 3.246.245 4/1966 Turner 343/895 3,375,525 3/1968 Fisk etal. 343/863 3.381.297 4/l968 Zisleretal. 343/895 FOREIGN PATENTS 1.135.532 8/1962 Germany 343/895 Primary- E.rami'ner Eli Lieberman Attorneys-C. Cornell Remsen. Jr. Walter J. Baum, Paul W. Hemminger, Percy P. Lantzy and Thomas E. Kristofferson PATENTED m 1 0 Ian SHEET 1 BF 2 0 m .e X m m C A m M P Y CONICAL SPIRAL LOOP'ANTENNA The invention relates in general to conical spiral loop antennas, and, more particularly to a compact antenna for transmitting and receiving circularly polarized waves.
BACKGROUND OF THE INVENTION With the advent of navigation systems utilizing satellites, it has been found necessary to-provide antennaswhich are compact, while simultaneously havinggood impedance matching characteristics at the frequencies of interest. Moreover, such antennas must have low back lobe suppression and when circularly polarized waves are utilized, they must have-high selectivity in the selected polarized sense.
Conventional antennas suchv as conical logarithmic spiral antennas which normally can be used for receiving circularly polarized navigational frequencies become unusually large for such frequencies, and thus, shipboard mounting of such antennas becomes a problem. For example, the United States Navy Navigational Satellite System. transmits signals at ISO-MHZ. and 4.00 MHz. At such frequencies, a conventional conical logarithmic spiral antenna'would have to be approximately 8 .feet high with a base diameter of 3% feet to provide good pat terns of efficiency. Further,.since signals-are to be received at two frequencies, the use ofa single-antenna for both frequencies requires that undesirablenulls' and peaks in the antenna radiation pattern caused by undesirable phasing be eliminated.
In order to overcome the.attendantdisadvantages .of prior art antennas, the antenna of .the-present-invention provides a compact structure which may. be .used- .on receiving stations such as ships where a minimum size-antenna is necessary. Moreover, the antenna provideshigh selectivity in a selected sense for circularly polarized waves.'-Further, excellent impedance match is. provided at the frequenciesof-interest while,
simultaneously, back lobes are adequately suppressed. Moreover, for the lower frequency of operation an improved elipticityv ratio is obtained for signals emanating from the horizon. I
SUMMARY OF THE INVENTION accompanying drawings;=in which- .like=reference numerals designate like parts throughout the figures.
BRIEF DESCRIPTION OFTI-IE DRAWINGS FIG. 1 depicts a perspective view of a preferred embodiment of the antenna in-accordancewith the invention.
FIG. 2. is an exploded side view, partly. in section, of one of the arms of the antennawhichcontains acoaxial-feed line-at its junctionwith the base of the antenna taken along the lines 2-2 of FIG. 1.
FIG. 31s atop view, partiallybrokenaway, of the antenna of FIG..1 show-ingonly the top portionof the antenna.
FIG. .4 is anex-ploded view-of the top portionofthe -antenna within .line4 .ofFIG.13.
FIG. 5 is-a sideview in section of. the top portion of the antenna .takenalong the. lines-5-5 of F IG. 3.
2 DESCRIPTION oarne PREFERRED EMBODIMENT Referring now to the drawings, there is shown in FIG. 1, a preferred embodiment of the antenna 10 in accordance with the invention. The antenna 10 comprises a first pair of hollow spiral radiating arms l2, l4 and a second pair of hollow spiral radiating arms 16, 18. Each of the arms 12, I4, 16 and 18 are secured at one end to a base member 22 and at the other end to a disc member 24. The base member 22.is generally flat and formed ofa top surface area 26, and a sidewall 32.
Referring now to FIG. 2, the base member is shown in greater detail. The top area 26has discs'34, attached thereto by means ofa nut 36 and bolt'38 arrangement at the junction of each of the'hollow arms l2, l4, l6 and 18. The arms are normally brazed to the discs 34. The arms 14 and l8 each have a coaxial cable 42, 44, respectively, passing therethrough and through a rubber grommet 46 which is inserted in an opening in the top area 26 and disc 34. The coaxial cables 42 and 44 pass through the base member 22 into a cylindrical casing 48 which contains auxiliary equipment and is mounted on the center of the top area 26 and secured thereto by means of mounting'ilanges 49,50.
Referring now to FIGS. 3 and'S, the disc member 24 comprises a top cover member 52 and a bottom cover member 54 which are made of Fiberglas and are secured together by means of bolts 56 to form a cylindrical disc having a hollowed center 58. An O-ring $9 prevents moisture from entering the .center 58. Cylindrical metal plate members 60 are secured to the bottom side of the bottom cover member and each forms toptermination for the hollow arms 12, 14, I6 and ISJRubber grommets-61. pass through openings in the plate member" 60 and bottom-cover member'54 to allow the coaxial cables 42, 44 in arms I4 and 18, respectively, to enter the" hollowed center 58.
Mounted within the hollow center 58 are four substantially pie-shaped metal members'62, 64, 66 and 68 .whichare associated with each of the hollow members. Each of the mem bers 62, 64, 66 and 68 are connected to the plate member 60 associated with its respective hollow member 12, l4, l6, and 18 by means ofa nut72 and bolt 74 arrangement.
The pie-shaped members '64 and 68 each contain an opening through which a grommet 76 is inserted and the coaxial cables 42,44, respectively, pass therethroughThe braided outer conductor of each of the coaxiaLcables 42, 44 terminate. .in receptacle members 78, 82, having lug members .84, 86 secured thereto and to the members 64, 68, respectively. The pie-shaped members'62 and 66 .each have lugs94;'96, respectively secured thereto. 1
An inner "conductor 98 of coaxial line 42 is. connected through a pair of parallelcapacitors 102, 104 to the lug94 of pie-shaped member 62. Further, an inner conductor..lt06 of coaxial cable 44 is connected through a pair of parallel connected capacitors 108, 1112 to .the lug 96 of pie-shaped member 66JAn inductor 114 is connected between the lug 84 of pie-shaped member 64 to the lug 94 of pie-shapedmember 62, and an inductor 116 is connected between the lug 86' of pie-shaped member 68 and the lug 96 of pie-shaped member 66.
Referring once againto FIG, 1, a pair of parasitic, ground planes for the high frequency signal comprises a first cylindrical shaped-plate 122 which is secured to a second cylindrical shaped-plate 124 by means of metallic rods l'26whichare fastened to the plates 122 and 124 by means of bolts 128. The plates'l22 and 124 are mounted in aplane parallel to the plane of the base member 22 and the disc member 24. Further, the plate 124 has secured thereto, ahollow metal cylindrical skirt 132 which extends downwardly from the plate 124 towards the base member 22. A plurality of support rods 133 are fastened at one-end by means of-bolts- 134 to theplate 124 and the cylindrical skirt 132, andat its other end-are secured to feet 136 mounted on the base member 22.
The. loop antenna thus far described has less than one full turn in its spiral length, the antenna depicted in the drawings hen mg approximately a 2 turn m its length Normally. asingle loop antenna hating less than one full turn in its spiral length would have a poor SWR and p larization sense and a high-hack radiation To overcome these drawbacks while simultaneously protiding an antenna of manageable size, the antenna depicted adds a second loop l6. [8 to the first loop formed by the arms l2. 14.
In the transmitting mode. the signal is divided into the two coaxial feed lines 42, 44 by a 90 phase shift hybrid network located In the casing 48. Each of the feed lines is matched to the antenna arms l2, l4. l6 and 18 by means ofthe matching network located within the disc member 24. This matching network is composed of the inductive and capacitive network within the disc together with the pie-shaped members 62. 64, 66 and 68. The transmitted signals propagate down the arms pairs toward the base 22 in phase quadrature until they reach a region on the arms where the cone diameter is approximately one'third of a wavelength at the frequency of operation at which the radiation into space occurs. This radiating energy propagates back to ,the disc member 24 with a polarization sense opposite to that conductively propagated down the arms as is conventional of backward wave radiators. The radiated energy which propagates in the direction of the base member 22 is reflected by the ground planes formed by the base member 22 at the low frequency of operation. At the high frequency of operation, the energy is reflected by the ground planes formed by the plates 122 and 124. This reflected energy returns in the proper phase to reinforce the energy traveling in the direction ofdisc member 24.
Two plate members I22 124 were chosen instead ofone for the high frequency of operation since it was determined that the radiation which occurs at discrete concentric belts on the spiral loops l2. l4. l6 and 18 would produce undesirable phasing should only one plate be used. By utilizing the plate members 122, 124 which are scaled to be resonant at the upper frequency of operation, and nonresonant at the lower frequency of operation the higher frequency of operation is essentially decoupled from the base member 22. Further, the vertical skirt 132 improves the vertical component of the signal at the higher frequencies thus improving polarization ellipticity near the equatorial plane.
For an antenna as depicted, for transmission and reception at both 150 MHz. and 400 MHz. the following design criteria was utilized:
XIII ltliini nlllll'll mine ofinductors 1H, [16
I. An antenna comprising a pair of spiral radiating arms. said spiral radiating arms being wound in the shape of a cone and terminating at one end in a truncated portion of said cone, and having a base, a feed line mounted in insulating relationship with one of the arms, and impedance matching means connecting said feed line to said radiating arms at said one end.
2. An antenna in accordance with claim 1 wherein said am tenna comprises a plurality of pairs of arms, each of said pairs of arms being diagonally opposed and equally spaced in the planes perpendicular to said cone 3. An antenna in accordance with claim 2 and comprising feed means associated with each pair of said radiating arms.
4. An antenna in accordance with claim I wherein the base of said cone forms a ground plane for said antenna and wherein the other ends of said arms are secured to said base 5. An antenna in accordance with claim 1 wherein said an tcnna is designed to operate at either a first predetermined frequency or a second predetermined frequency, the base of the antenna forming the ground plane for the lower of said frequencies, and a first platform extending in a plane parallel to said base intermediate said one end of said arms and said base and connected to said base, said platform forming the ground plane for the higher of said frequencies.
6. An antenna in accordance with claim 5 and further com-- prising a second platform associated with said first platform, said first and second platform being resonant at said higher frequency and nonresonant at said lower frequency.
7. An antenna in accordance with claim 1 wherein said antenna is designed to transmit and receive circularly polarized waves.
8. An antenna in accordance with claim 1 wherein said impedance matching means comprises a substantially pie shaped member associated with each radiating arm.