Radio Frequency Slot Antenna

Abstract

A stripline slotted array antenna is disclosed wherein the radiating efficiency and bandwidth are improved by including in each radiating element a pair of adjacent radiating slots. The antenna includes center conductor circuitry separated from a pair of ground plane elements, one of which is the radiating face of the antenna and one of which is the back plate of the antenna. The pair of slots is formed in the radiating face of the antenna. The pair of radiating slots is disposed adjacent to an end portion of the center conductor circuitry, one being coupled to an electric field existing between the end of such circuitry and the back plate and the other one of such pair of radiating slots being coupled to an electric field existing between the center conductor circuitry and the radiating face of the antenna.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to radio frequency antennas and more particularly to stripline slotted array antennas.

As is known in the art, stripline antennas are sometimes used in place of waveguide antennas because of their relatively lighter weight and compactness. Such stripline antennas generally include center conductor circuitry separated from a pair of ground plane elements (one the radiating face of the antenna and the other the back plate of the antenna) by a dielectric material. The radiating face of such an antenna generally includes an array of radiating slots. The radiating slots are coupled to the electric field existing between end portions of the center conductor circuitry of the stripline and the ground plane elements. One such stripline antenna is described in U.S. Pat. No. 3,701,158, issued to Robert H. Johnson, Oct. 24, 1972.

In the vicinity of each one of the radiating slots of known stripline antennas the electric field existing between the center conductor circuitry and the radiating face is not balanced with the electric field existing between the center conductor circuitry and the back plate. Such unbalance causes energy to be reflected within the stripline, thereby reducing the radiating efficiency of the antenna by about 50 percent. One technique used to reduce reflections and thereby improve the radiating efficiency has been to electrically enclose the radiating slot within a high Q resonant cavity. Such a cavity may be formed by using known mode suppression posts, or pins, of conducting material adjacent to each radiating slot. A high Q resonant cavity of such nature, while improving the radiating efficiency of the antenna, reduces the operating bandwidth of the antenna so that, generally, only a 5-15 percent variation in operating frequency may be attained.

SUMMARY OF THE INVENTION

With this background of the invention in mind, it is an object of this invention to provide a stripline slotted array antenna having improved radiating efficiency and bandwidth.

The foregoing and other objects of the invention are attained generally by providing, in a stripline slotted array antenna (including center conductor circuitry separated from a pair of ground plate elements, one of which is the radiating face of the antenna and one of which is the back plate of the antenna), an array of radiating elements, each one thereof terminating an end portion of the center conductor circuitry and including a pair of adjacent radiating slots formed in the radiating face, one thereof being adjacent to the end of the center conductor circuitry and coupled to an electric field existing between such circuitry and the back plate and the other one being coupled to an electric field existing between the center conductor circuitry and the radiating face.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of this invention, as well as the invention itself, may be more fully understood from the following detailed description read together with the accompanying drawings, in which:

FIG. 1 is a plane frontal view of a radio frequency antenna according to the invention; and

FIG. 2 is a cross-sectional view of one of the radiating elements of the antenna of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1 and 2, a stripline antenna 10 is shown to include center conductor circuitry 11 separated from a pair of ground plane elements 12, 14 by a dielectric material 16. Ground plane elements 12, 14 are herein sometimes referred to as the radiating face of the antenna and the back plate of the antenna, respectively. In particular, such antenna 10 is here fabricated from two slabs of dielectric material, one having plated or deposited thereon a conducting material, here copper, to form the back plate 14 of the antenna and the other one having plated or deposited on portions of such side thereof a conducting material, here copper, to form the radiating face of the antenna 10 and center conductor circuitry 11. The two slabs are secured together by any suitable conventional means, such as epoxy, not shown.

Antenna 10 includes an array of radiating elements 18.sub.1 -18.sub.28. Each one of the radiating elements is identical in construction and each terminates an end portion of center conductor circuitry 11 (only the end portion 19, which terminates radiating element 18.sub.1, being numbered). An exemplary one of such radiating elements, here 18.sub.1, includes a pair of radiating slots 20, 22, here formed in the radiating face 12 by conventional etching of portions of the conducting material making up such face. The pair of radiating slots 20, 22 is surrounded by mode suppression pins 24. Such mode suppression pins 24 are formed by drilling holes through the radiating face 12 and dielectric material 16 to the back plate 14, and by filling such holes with a conducting material, here copper. The mode suppression pins 24 are secured to the radiating face and to the back plate by any suitable means, here solder, not shown. However, such mode suppression pins 24 may be formed by providing holes through the antenna 10 and by electroplating the walls of such holes. The mode suppression pins 24 form a relatively low Q resonant cavity around the radiating slots 20, 22. Because such a cavity forms no part of the present invention, the mode suppression pins 24 may be omitted. Included intermediate the pair of radiating slots 20, 22 is a pair of additional pins, 26, 28. Also included is an additional pin 29. Such pins 26, 28, 29 are formed by drilling holes through the radiating face 12 and the dielectric material 16 of the upper dielectric slab to the center conductor circuitry 11 and by filling such holes with a conducting material, here copper, as shown in FIG. 2 or by the electroplating process mentioned above in connection with pins 24.

The radiating elements 18.sub.1 - 18.sub.28 are here arranged in four sectors, or quadrants A, B, C, D, to configure antenna 10 as a monopulse antenna. The four quadrants are separated along dotted lines 30, as shown.

Each one of the four sectors includes seven radiating elements. Here quadrants A-D include radiating elements 18.sub.1 -18.sub.7, 18.sub.8 -18.sub.14, 18.sub.15 -18.sub.21, and 18.sub.22 -18.sub.28, respectively. Considering any one of the quadrants, say exemplary quadrant A, center conductor circuitry 11 may be seen to be connected with a terminal 32A, with seven branch lines (not numbered), the end portion of each one of such branches being adjacent to, and terminated by, a different one of radiating elements as shown. It follows, therefore, that each radiating element in quadrant A is coupled to terminal 32A. Thus, when antenna 10 is used as a receiving antenna, radio frequency energy from an external source (not shown) irradiating the radiating elements 18.sub.1 -18.sub.7 in quadrant A is passed to terminal 32A. The equivalent is true for quadrants B-D and terminals 32B - 32D respectively. It follows then that by coupling terminals 32A - 32D to a conventional monopulse arithmetic unit (not shown), the conventional sum and difference channels of a monopulse antenna may be obtained.

Referring again to FIG. 2, now in more detail, it may be observed that an electric field may exist between the center conductor circuitry 11 and the radiating face 12 (as indicated by arrows 34), and also an electric field may exist between such circuitry and the back plate 14 (as indicated by arrows 36). It may further be observed that radiating slot 20 is coupled to the electrical field existing between the radiating face 12 and the center conductor circuitry 11 and radiating slot 22 is coupled to the electric field existing between center conductor circuitry 11 and back plate 14. To put it another way, pin 26 and portions of center conductor circuitry 11 and radiating face 12 may be viewed as being a feed for radiating slot 20 whereas pins 28, 29, back wall 14 and the end of center conductor circuitry 11 may be viewed as being a feed for radiating slot 22. Therefore, the electric fields in the pair of dielectric slabs are balanced. Reflections within the antenna, which normally result without such radiating slot 22, are reduced. By separating the radiating slots 20, 22 by an integral multiple (half wavelength) .lambda./2 (where .lambda. is the nominal operating wavelength of the antenna 10 in the dielectric material 16) radio frequency energy fed to such slots will be "in phase." On the other hand, by separating such slots by a distance equal to an integral multiple of .lambda. in the dielectric material 16, such energy will be 180.degree. "out of phase" along the boresight axis of the antenna.

Having described a preferred embodiment of this invention, it is now evident that other embodiments incorporating the concepts may be used. For example, in reference to FIG. 1, the shape of radiating slots 20, 22 may take other forms to provide proper impedance matching. For example, the shape of such slots as herein shown provides a capacitive impedance matching. Further, while a monopulse antenna has been shown it is understood that other antenna configurations, as a beacon antenna, may use the inventive concepts herein described. Further, the separation between the pair of radiating slots 20, 22 may be selected to provide for one of a variety of desired radiation patterns. It is felt, therefore, that this invention should not be restricted to its disclosed embodiments but rather should be limited only by the spirit and scope of the appended claims.

Claims

What is claimed is:

1. In a stripline slotted array antenna including center conductor circuitry separated from a pair of ground plane elements, one of which is the radiating face of the antenna and one of which is the back plate of the antenna, an array of radiating elements, each one thereof terminating an end portion of the center conductor circuitry and comprising:

a. a first radiating slot, formed in the radiating face, disposed adjacent to the end of the center conductor circuitry and coupled to an electric field existing between such circuitry and the back plate of the antenna; and

b. a second radiating slot, formed in the radiating face, disposed adjacent to, and totally separated from, the first slot by a portion of the radiating face, such second radiating slot being coupled to an electric field existing between the center conductor circuitry and the radiating face of the antenna.

2. The radiating element recited in claim 1 including conducting material disposed intermediate the first and second radiating slots and extending from the radiating face to the center conducting circuitry.

3. The radiating element recited in claim 2 including an additional conducting material disposed outside the first radiating slot and extending from the radiating face to the back plate of the antenna.

4. The radiating element recited in claim 1 including:

a. a first conducting material disposed intermediate the first and second radiating slots and extending from the radiating face to the center conductor circuitry, such first conducting material, center conductor circuitry and radiating face being arranged to form a feed for the second radiating slot; and

b. a second conducting material disposed outside both the first radiating slot and the end of the center conductor circuitry and extending from the radiating face to the back plate, such second conducting material, center conductor circuitry, first conducting material, and back plate being arranged to form a feed for the first radiating slot.

5. The radiating element recited in claim 1 wherein the first radiating slot and the second radiating slot are separated by an integral number of .lambda./2 where .lambda. is the operating wavelength of the antenna.

6. In a stripline slotted array antenna including center conductor circuitry separated from a pair of ground plane elements, one of which is the radiating face of the antenna and one of which is the back plate of the antenna, an array of radiating elements, each one thereof terminating an end portion of the center conductor circuitry and comprising:

a. a first radiating slot, formed in the radiating face, disposed adjacent to the end of the center conductor circuitry and coupled to an electric field existing between such circuitry and the back plate of the antenna;

b. a second radiating slot, formed in the radiating face, disposed adjacent to the first slot and coupled to an electric field existing between the center conductor circuitry and the radiating face of the antenna; and,

c. a conducting material disposed outside the first radiating slot and extending from the radiating face to the back plate of the antenna.

7. The radiating element recited in claim 6 including:

a. a first conducting material disposed intermediate the first and second radiating slots and extending from the radiating face to the center conductor circuitry, such first conducting material, center conductor circuitry and radiating face being arranged to form a feed for the second radiating slot; and

b. a second conducting material disposed outside both the first radiating slot and the end of the center conductor circuitry and extending from the radiating face to the back plate, such second conducting material, center conductor circuitry, first conducting material, and back plate being arranged to form a feed for the first radiating slot.

8. In a stripline slotted array antenna including center conductor circuitry separated from a pair of ground plane elements, one of which is the radiating face of the antenna and one of which is the back plate of the antenna, an array of radiating elements, each one thereof terminating an end portion of the center conductor circuitry and comprising:

a. a first radiating slot, formed in the radiating face, disposed adjacent to the end of the center conductor circuitry and coupled to an electric field existing between such circuitry and the back plate of the antenna; and

b. a second radiating slot, formed in the radiating face, disposed an integral multiple of .lambda./2, where .lambda. is the operating wavelength of the antenna, from the first slot and coupled to an electric field existing between the center conductor circuitry and the radiating face of the antenna.

9. The radiating element recited in claim 8 including conducting material disposed intermediate the first and second radiating slots and extending from the radiating face to the center conducting circuitry.

10. The radiating element recited in claim 9 including an additional conducting material disposed outside the first radiating slot and extending from the radiating face to the back plate of the antenna.

11. The radiating element recited in claim 8 including:

a. a first conducting material disposed intermediate the first and second radiating slots and extending from the radiating face to the center conductor circuitry, such first conducting material, center conductor circuitry and radiating face being arranged to form a feed for the second radiating slot; and

b. a second conducting material disposed outside both the first radiating slot and the end of the center conductor circuitry and extending from the radiating face to the back plate, such second conducting material, center conductor circuitry, first conducting material, and back plate being arranged to form a feed for the first radiating slot.