Closely Spaced Orthogonal Dipole Array

Abstract

A broadband phased array antenna is shown wherein pairs of mutually orthogonal printed radiating elements, each one of such elements having a flared notch formed therein, are adapted to transmit or receive radio frequency energy having any one of a variety of polarizations.

Description

The invention herein described was made in the course of or under a contract or subcontract thereunder, with the Department of Defense.

DESCRIPTION OF THE INVENTION

This invention relates generally to phased array antennas and more particularly to such antennas wherein the radiating elements thereof are comprised of a conducting metal deposited or printed on a substrate. The invention also relates to phased array antennas of such nature which are adapted to transmit or receive radio frequency energy having any one of a variety of polarizations.

As is known in the art, it is frequently desirable to use a radiating element which may operate with one of a variety of polarizations (i.e. linear, circular, elliptical). One type of such a radiating element is sometimes referred to as a "double-ridged" horn. A radiating element of such type has a vertical feed and an independent horizontal feed, the phase centers associated with the feeds being coincident. In order to provide efficient matching to free space over a wide frequency variation or bandwidth, say in the order of 2:1, it is generally required that the width of the horn be larger than .lambda./2 (where .lambda. is the nominal operating frequency of the antenna) and sometimes even up to the order of one wavelength (.lambda.).

A phased array antenna is generally comprised of a plurality of radiating elements. To attain a relatively wide scan angle, say in the order of 120.degree., it is generally required that the phase centers of adjacent ones of the plurality of radiating elements be displaced by less than .lambda./2. It follows, therefore, that while a double-ridged horn is adapted to operate with radio frequency energy of one of a variety of polarizations, such a radiating element may not readily be used in a phased array antenna having a relatively wide bandwidth and relatively large scan angle.

As is also known in the art, radio frequency antennas are sometimes comprised of a radiating element formed from a conducting metal printed or deposited on a substrate. Such antennas have the advantage of lighter weight compared to waveguide antennas as a double-ridged horn. However, known antennas having printed radiating elements are not generally adapted to transmit or receive radio frequency energy having any one of a variety of polarizations.

SUMMARY OF THE INVENTION

With this background of the invention in mind, it is an object of this invention to provide an improved phased array antenna.

It is another object of the invention to provide an improved phased array antenna adapted to operate in one of a number of polarizations.

These and other objects of the invention are attained generally by providing a pair of mutually orthogonal printed radiating elements, each one of such elements having a flared notch formed therein.

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 drawing, the single FIGURE of which shows an exploded, perspective view of a phased array antenna according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the FIGURE, a phased array antenna 10 is shown to include a plurality, here five, of vertical radiating elements 12.sub.1 - 12.sub.5 arranged in a linear array, a pluraity, here five, of horizontal radiating elements 14.sub.1 - 14.sub.5 arranged in a linear array, and a back wall 15. Back wall 15 is comprised of a single planar substrate of dielectirc material having a conducting material, here copper, deposited or printed by any conventional method to make the face portion 17 thereof a conventional ground plane for the radiating elements.

Each one of the vertical radiating elements 12.sub.1 - 12.sub.5 (as shown most clearly in the exploded view of radiating element 12.sub.5) is identical in construction and includes a planar substrate 16.sub.1 - 16.sub.5 of dielectric material, a formed layer of conducting material, here copper, deposited or printed by any convenient method on a portion of one side of the planar substrate 16.sub.1 - 16.sub.5 and a feed line 18.sub.1 - 18.sub.5. The conducting material deposited on back wall 15 and the conducting material deposited on a portion of each one of the vertical radiating elements 12.sub.1 - 12.sub.5 are connected by a conventional solder joint (not numbered).

Considering in detail an exemplary one of the vertical radiating elements, say vertical radiating element 12.sub.5, it may be seen that the formed layer of conducting material is symmetrically printed about center line 20 to produce an upper portion 22 of the conducting material separated from a lower portion 24 of the conducting material by a notch 26. The notch 26 is flared from a narrow portion to a wide portion, here in one step. The narrow portion has a width a and the wide portion has a width b. A slot, not numbered, is formed within the substrate 26 along a portion of the center line 20, as shown, to permit alignment of the vertical radiating element 12.sub.5 with the horizontal radiating element 14.sub.5. The feed line 18.sub.5, here coaxial cable, is passed through back plate 15. One portion of such cable is orthogonal to the plane of back plate 15 and a second portion of such cable is parallel to such back plate. The former portion of the cable is displaced from the plane of the horizontal radiating elements by a dimension c and the second portion of such cable is displaced from the plane of back wall 15 by a dimension d.

Considering in detail an exemplary one of the feed lines 18.sub.1 - 18.sub.5, say 18.sub.5, such feed line is here a coaxial cable having its outer conductor connected by a conventional solder joint (not numbered) to the upper portion 22 of the conducting material and its inner conductor connected, again as by a conventional solder joint (not numbered) to the lower portion 24 of the conducting material. The dielectric sleeve, not numbered, of the coaxial cable 18.sub.5 insulates the inner conductor of the coaxial cable as such conductor passes across the narrow portion of notch 26.

Referring now to the horizontal radiating elements 14.sub.1 - 14.sub.5, it is first noted that the individual ones of such elements are similar in construction to the vertical radiating elements; here, however, the horizontal radiating elements 14.sub.1 - 14.sub.5 are formed on a single planar substrate 30 of dielectric material. Each one of such horizontal radiating elements 14.sub.1 - 14.sub.5 is made up of: a formed layer of conducting material, here copper, deposited or printed on a portion of one side of the planar substrate 30; and a feed line 32.sub.1 - 32.sub.5. The conducting material deposited on back wall 15 and the conducting material deposited on a portion of each one of the horizontal radiating elements are connected by a conventional solder joint (not numbered). When assembled, the phased array antenna 10 is a rigid unitary structure, the back wall 15 serving as an integral part of such antenna as a conventional ground plane for both the horizontal radiating elements and the vertical radiating elements.

Adjacent ones of the horizontal radiating elements, although physically joined together, may be considered to be separate identical units, divided from each other along dotted lines 34.sub.2 - 34.sub.5. An exemplary one of such units, say 14.sub.5, is shown in detail to have the layer of conducting material deposited thereon symmetrically about center line 20 on a portion of substrate 30. Aleft hand portion 36 of the conducting material is separated from a right hand portion 38 of the conducting material by a notch 40. The notch 40 is flared from a narrow portion to a wide portion here in one step. The narrow portion has a width e and the wide portion has a width f.

Feed lines 32.sub.1 - 32.sub.5 are here coaxial cables. Considering in detail an exemplary one thereof, say 32.sub.5, the outer conductor is soldered to the left hand portion 36 of the conducting material and the inner conductor of such cable is soldered to the right hand portion 38 of the conducting material. A sleeve, not numbered, of insulating material surrounds the inner conductor of such cable as such conductor passes across the narrow portion of the notch 40. Considering exemplary feed line 32.sub.1, such feed line has one portion thereof orthogonal to the plane of back wall 15 and a second portion parallel to the back wall. The former portion of the cable is displaced from the plane of the vertical radiating element disposed along its center line, here vertical radiating element 12.sub.1, by a dimension g and the second portion of such cable is displaced from the back wall 15 by a dimension h.

When the phased array antenna 10 is operating in either the transmit mode or the receive mode, radio frequency energy passes between free space and the wide portion of notches 26, 40 and such energy also passes between the narrow portion and the wide portion of such notches. The radio frequency energy passing through the narrow portion of such notch in the vicinity where the inner conductor of feed lines 32.sub.1 - 32.sub.5 and 18.sub.1 - 18.sub.5 passes across such narrow portion is associated with a potential difference developed between the inner conductor and the outer conductor of such feed lines. It is noted that when feed lines 18.sub.1 - 18.sub.5 are connected to a suitable bus, here represented by dotted line 28, the vertical radiating elements 12.sub.1 - 12.sub.5 act as a vertically polarized antenna and likewise, when feed lines 32.sub.1 - 32.sub.5 are connected to a suitable bus, here represented by dotted line 42, the horizontal radiating elements act as a horizontally polarized antenna. The relative phase shift of the radio frequency energy, between adjacent feed lines, defines the scan angle of the antenna in a conventional manner. Such phase shift may be provided by convential phase shifters (not shown). It is further noted that by having the center conductors of the coaxial cables passing across the narrow portion of each one of the notches substantially coincident electrically, the phase center associated with each one of the horizontal radiating elements 14.sub.1 - 14.sub.5 and each one of the vertical radiating elements 12.sub.1 - 12.sub.5 will be substantially disposed along a line in the plane of the substrate 30 and parallel to the plane of back wall 15. Such line is indicated by dotted line 46. It follows then that by properly adjusting the relative amplitude and phase between the radio frequency energy on the bus represented by dotted line 42 and the radio frequency energy on the bus represented by the dotted line 28, the phased array antenna 10 may transmit or receive radio frequency energy having any one of a variety of polarizations.

The phased array antenna 10 has been built and found effective to match radio frequency energy to free space over a 2:1 bandwidth and over a 120.degree. scan angle. The parameters used were:

Dimension a = 0.1 inches

Dimension b = 0.5 inches

Dimension c = 0.625 inches

Dimension d = 0.65 inches

Dimension e = 0.1 inches

Dimension f = 0.5 inches

Dimension g = 0.425 inches

Dimension h = 0.475 inches

Height of Vertical Radiating Element = 2.40 inches

Length of Horizontal and Vertical Radiating Elements = 1.35 inches

Separation Between Vertical Radiating Elements = 0.85 inches

Substrate Thickness = 0.032 inches

Length of Narrow Portion of Notch = 1.15 inches

Operating Wavelength = 4.5 - 9.0 inches

Having described a preferred embodiment of this invention, it is now evident that other embodiments incorporating its concepts may be used. For example, the feed lines may be of microstrip construction in place of coaxial cable. Also, the notch may be flared from a narrow portion to a wide portion in other than one step, for example it may flare in more than one step or it may flare according to a continuous function such as in linear function or in a parabolic function.

It is felt, therefore, that this invention should not be restricted to its disclosed embodiment but rather should be limited only by the spirit and scope of the appended claims.

Claims

What is claimed is:

1. An antenna element comprising: a pair of planar radiating elements, one thereof disposed in a plane orthogonal to the other one thereof, the phase center of one of such planar radiating elements being separated from the phase center of the other one of such planar radiating elements by less than .lambda./4 (where .lambda. is the operating wavelength of the antenna element), each one of such radiating elements including:

a. a radio frequency feed line; and,

b. a planar sheet of conducting material having a flared notch formed therein, the feed line being coupled across such flared notch.

2. The antenna element recited in claim 1 wherein each one of such radiating elements includes:

a planar substrate; and wherein the conducting material is deposited on a portion of such substrate, the flared notch formed therein having a narrow portion and a wide portion, the feed line being coupled across the narrow portion of such notch.

3. An antenna comprising: a linear array of antenna elements, each one thereof including: a pair of planar radiating elements, one of such pair of elements disposed in a plane orthogonal to the other one of such pair of elements, such pair of elements having phase centers coincident to less than .lambda./4 (where .lambda. is the operating wavelength of the antenna), each one of such radiating elements including:

a. a radio frequency feed line; and,

a planar sheet of conducting material having a flared notch formed therein, the feed line being connected across such flared notch.

4. The antenna recited in claim 3 wherein each one of the pair of planar radiating elements has one planar radiating element disposed in a common plane.

5. The antenna recited in claim 4 including additionally a ground plane element common to the antenna elements and disposed orthogonal to each one of the pair of planar radiating elements.

6. The antenna recited in claim 3 wherein each one of such planar radiating elements includes a planar substrate; and, wherein the conducting material is deposited on a portion of such substrate, the flared notch formed therein having a narrow portion and a wide portion, the feed line being coupled across the narrow portion of such notch.

7. The antenna recited in claim 6 wherein each one of the pair of planar radiating elements has one of the pair of substrates disposed in a common plane.

8. The antenna recited in claim 7 including additionally a ground plane element common to the antenna elements and disposed orthogonally to each one of the pair of substrates of the radiating elements.