Planar-type Spiral Antenna

Abstract

A planar-type spiral antenna assembly capable of handling higher input powers than prior art planar antennas and enabling greater ranges of a radiated beam of electromagnetic wave energy. This is accomplished by recessing the spiral convolutions of conductive material forming the antenna into corresponding spiral slots formed in a dielectric disc having a high-dielectric strength, the disc being formed from a material such as quartz or alumina. The spiral convolutions of conductive material, recessed within the aforesaid slots, are preferably covered with a dielectric material such as silicon monoxide or silicon dioxide to further increase the dielectric constant in the space between adjacent conductors.

Description

BACKGROUND OF THE INVENTION

As is known, a planar-type spiral antenna is a dipole, or more accurately a modified dipole. The length of a dipole antenna is related to the frequency of the electromagnetic energy it can radiate. That is, as the frequency decreases and wavelength increases, the length of the dipole, which is approximately one-half wavelength of the radiated energy, must increase also. At the lower frequencies, therefore, the length of a dipole antenna, if it is to extend along a straight line, can become prohibitive. Designers, therefore, have wound the two halves of a dipole antenna intended for use at low frequencies into two interleaved spiral convolutions. This enables the antenna to be fabricated in a compact, circular configuration; but since the spiral convolutions are closely adjacent each other, problems arise due to corona discharge between oppositely polarized conductors when attempts are made to radiate high powers from such an antenna.

In the past, spiral planar antennas of the type described above have usually been fabricated by forming interleaved spiral convolutions of conductive strips on a fiberglass board using printed circuit techniques. A coating of high dielectric strength material is then placed over the conductive strips. Antennas of this type, however, cannot radiate high powers due to the fact that arcing will occur between adjacent spiral convolutions. The arcing problem is most severe at the centers of the spiral convolutions where the waveforms on the respective halves of the dipole are 180.degree. out of phase with respect to each other, meaning that the potential difference is greatest at this point.

In prior art spiral antennas deposited on fiberglass boards, for example, the arc-over at the center of the antenna would sometimes cause the fiberglass board to burn or disintegrate; and there could also be considerably arcing at points radially spaced from the center of the antenna. The heat generated at the center was also sufficient to cause melting of the solder at the joints between the feed lines and antenna. As a result, such antennas have normally been limited to relatively low powers and ranges, notwithstanding the fact that they are ideally suited for airborne applications because of their planar nature, enabling them to fit into the skin of an aircraft without any projecting elements.

SUMMARY OF THE INVENTION

In accordance with the present invention, a planar-type spiral antenna structure is provided which includes, as a starting material, a disc of material of high dielectric strength. This material is preferably quartz but may also comprise materials such as alumina, beryllia or even certain types of glass.

Cut into one face of the disc, preferably by ultrasonic impact grinding techniques, is a pair of channels forming interleaved spirals having an essentially common center point. By "common center point" it is meant that radially innermost ends of the spiral channels terminate closely adjacent each other but, of course, do not touch so as to be electrically insulated from each other. Holes are then drilled through the disc from the backside so as to communicate with the radially innermost ends of the channels. The channels and drilled holes thus formed are subsequently filled with a metallizing material, such as a silver or gold paint, which is cured to form a ribbon of electrically conductive material in each channel. This electrically conductive material, after curing, is also applied to the walls of the holes extending through the disc and communicating with the radially innermost ends of the channels.

Thereafter, electrical leads, adapted for connection to a coaxial transmission line or the like, are brazed into the holes so as to make electrical connection with the electrical conducting material in the respective channels. The assembly is completed by applying a coating of silicon dioxide, silicon monoxide, or some other material of high dielectric strength over the entire face of the disc which contains the channels having ribbons of conducting material therein.

With this configuration, the ribbons of conducting material forming the interleaved spirals are recessed beneath the surface of the disc and separated from each other by a substantial thickness of quartz or other high dielectric material. The oxide deposited over the surface of the disc further increases the dielectric strength of the space between adjacent conductors. With this configuration, therefore, substantially higher powers can be transmitted from the antenna without corona discharge effects; and the range of the antenna can be materially increased. The rise in temperature, due to dielectric and conductor losses, will not affect the hard brazed connection as it would a soft solder joint.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is a schematic diagram showing the antenna of the invention and the manner in which it is connected to a waveguide;

FIG. 2 is a top or plan view of the central portion of the antenna of FIG. 1 showing the manner in which interleaved spiral convolutions are formed therein;

FIG. 3 is a cross-sectional view taken substantially along line III--III of FIG. 2 showing how the electrically conducting ribbons of the respective spirals shown in FIG. 2 are electrically insulated from each other; and

FIG. 4 is a cross-sectional view taken substantially along line IV--IV of FIG. 3 showing the manner in which electrical leads are connected to the respective interleaved spiral conducting ribbons forming the antenna.

With reference now to the drawings, and particularly to FIG. 1, the antenna shown is identified generally by the reference numeral 10 and comprises a disc 12 of electrical insulating material having on one face thereof a pair of interleaved spiral grooves 14 and 16 containing ribbons of electrical conducting material. The inner ends of the respective spiral ribbons of electrical conducting material in grooves 14 and 16 are connected through the disc 12 to a pair of leads 18 and 20 which are connected through an impedance matching transformer arrangement 22 to the grounded, outer conductor 24 of a coaxial transmission line and the inner conductor 26 thereof, respectively.

The two interleaved spiral ribbons of conducting material on the face of disc 12 form the two elements of a dipole antenna and are arranged in the spiral grooves 14 and 16 as explained above in order to facilitate transmission of relatively low-frequency signals while at the same time minimizing the size of the antenna. The radiated beam is identified by the reference numeral 28 in FIG. 1 and comprises circularly polarized wave energy. An antenna of the type shown in FIG. 1 will transmit and receive only circularly polarized wave energy which is polarized in one direction. Thus, the device is ideal for eliminating the possibility of receiving false echos or interference signals.

The details of the two interleaved spiral grooves 14 and 16 are shown in FIG. 2. The groove 14, for example, starts with a center termination 30. Similarly, the groove 16 starts with a center termination 32. In FIG. 3, four convolutions of the spiral 14 are shown in cross section and identified as 14A-14D. Similarly, four convolutions of the spiral configuration 16 are shown and identified as 16A-16D.

In accordance with the present invention, the convolutions 14 and 16 are formed by initially grinding spiral slots in the face of the disc 12 which may comprise quartz, beryllia, alumina, 7056 glass or some other similar material of high dielectric strength. The convolutions 14 and 16 are preferably formed by means of ultrasonic impact grinding techniques. In this process, a die, having spiral protrusions thereon corresponding to the spiral groove configurations 14 and 16, is brought into close adjacent relationship with one surface of the disc 10 and connected to an ultrasonic transducer. By bathing the surface of the disc with a slurry containing a highly abrasive grinding material, this grinding material, vibrating at an ultrasonic frequency, will penetrate into and form the spiral grooves 14 and 16.

After the grooves 14 and 16 are thus formed, holes 34 and 36 are drilled through the quartz plate 12 such that they communicate with the central terminations 30 and 32. These holes, as will be seen, serve as a means to connect the electrical leads 18 and 20 to the centers of the electrical conducting material deposited in the spiral grooves 14 and 16.

With the spiral grooves 14 and 16 formed in the face of the disc 12 and the holes 34 and 36 drilled, the face containing the grooves is swabbed with a metallizing material, such as a silver or gold paint. The interior walls of holes 36 and 34 are also coated with this metallizing material. The excess paint is then wiped from the face of the disc 12 containing the grooves 14 and 16 and the disc fired in order that the binder for the metallic paint will burn off, leaving layers of electrical conducting material at the bottom of each groove, these layers of electrical conducting material being identified in FIG. 3 by the reference numerals 38 and 40, respectively. During firing, any paint on the sides of the grooves will flow downwardly to the bottoms of the grooves, forming the essentially flat ribbons shown. The antenna assembly is completed by applying over the surface of the disc 12 containing the grooves 14 and 16 a layer of silicon monoxide, silicon dioxide or some other suitable insulating material of high dielectric strength.

With reference to FIG. 4, once the holes 34 and 36 are drilled into the disc 12 and the metallic paint applied and cured, a layer of electrical conducting material 42 will surround each hole 34 or 36, this electrical conducting material being in contact with, and contiguous with, the metallic ribbons 38 and 40 at the bottoms of the respective grooves 14 and 16. Received within the holes 34 and 36, after the metallic coatings 42 are applied thereto, are tubular members 44, also formed from electrically conducting material and fastened to the metallic coating by brazing. These tubular members, then, receive the ends of the conductors 18 and 20 shown in FIGS. 1 and 3 to connect the antenna to a wave guide or other type of wave transmitting device. In a typical embodiment of the invention, the thickness of the quartz disc 12 is about 0.125 inch while the thickness and width of each of the grooves 14 and 16 are about 0.02 inch. Similarly, the respective adjacent grooves shown in FIG. 3 are separated by about 0.02 inch. As long as the ratio of the thickness of each groove to the spacing between the grooves is maintained at about 1:1, a constant impedance to the impedance-matching device 22 is presented.

With the arrangement shown in FIGS. 2 and 3, it can be seen that because of the quartz material separating the two conducting ribbons 38 and 40, as well as the silicon dioxide or silicon monoxide, covering the ribbons, the material filling the discharge path between adjacent ribbons 38 and 34 has an extremely high dielectric strength. As a result, the size of the antenna may be kept extremely small while maximizing the power delivered from the antenna.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

Claims

We claim as our invention:

1. A planar-type spiral antenna comprising a slab of material of high dielectric strength having formed on one face thereof a pair of separated grooves defining interleaved spirals, electrically conductive material deposited in said grooves to form two metallic ribbons of spiral configuration, said two ribbons forming the two radiating elements of the antenna, and holes extending through said slab and communicating with the radially innermost ends of the respective grooves to facilitate electrical connection to said innermost ends to a wave energy transmission line.

2. The planar-type spiral antenna of claim 1 wherein said material of high dielectric strength is selected from the group consisting of alumina, beryllia, quartz and glass.

3. The planar-type spiral antenna of claim 1 including a layer of electrical insulating material deposited over the face of said slab containing said grooves and extending down into said grooves.

4. The planar-type spiral antenna of claim 3 wherein said insulating material is selected from the group consisting of silicon monoxide and silicon dioxide.

5. The planar-type spiral antenna of claim 1 wherein the ratio of the thickness of each groove to the spacing between grooves is about one to one.

6. The planar-type spiral antenna of claim 1 including a layer of electrical conducting material on the wall of each of said holes, said layers being electrically connected to and contiguous with the innermost ends of said metallic ribbons.

7. The planar-type spiral antenna of claim 6 including tubular elements of electrical conducting material inserted into said holes and brazed to said layers of electrical conducting material.