Corporate-network Printed Antenna System

Abstract

A corporate-network printed antenna system is described wherein the feed lines are located in coplanar relationship with and in the field of the antenna.

Description

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

This invention relates to antenna systems and more particularly to an array of printed antennas energized from a corporate feed network.

Microwave antenna array systems which are lightweight, rugged, low-cost and compact find wide use in both military and commercial applications. Printed antenna systems which are generally made of a plurality of dipoles formed on the surface of a low dielectric circuit board provide these desirable features. The feed for the plurality of dipoles is either provided by a plurality of feed lines on both sides of the insulating board or in a different plane from that of the dipoles. The dipoles are usually arranged in rows with the dipoles in each row spaced approximately one-half wavelength apart with the feed lines and dipoles arranged in transposed relation so that the dipoles are fed in equal phase. This type of system is inherently narrow in bandwidth.

It is therefore an object of the present invention to provide an improved printed antenna system which is broadband.

Briefly, this and other objects of the present invention are provided by an improved, lightweight, compact printed antenna system wherein a plurality of dipoles arranged in adjacent pairs are secured to the broad planar surfaces of a sheet of insulative material. Pairs of adjacent dipoles are connected in parallel through feeder lines disposed on the insulating material. The center point of the feeder lines is connected by another feeder line to another double group. Likewise, this is repeated whereby all of the dipoles are fed with feeder lines of equal length.

Additional features and objects of the invention will be more clearly apparent as the invention is described in connection with the drawing in which:

FIG. 1 illustrates the general layout of an antenna system in accordance with an embodiment of the present invention,

FIG. 2 illustrates one broad surface of the sheet of insulative material having a portion of the feed line and dipoles thereon,

FIG. 3 illustrates the opposite broad surface of the sheet of insulative material having a portion of the feed lines and dipoles thereon,

FIG. 4 is a cross-sectional view of a portion of the antenna in accordance with an embodiment of the present invention,

FIG. 5 is a cross-sectional view of feed points to the antenna system, and

FIG. 6 is a circuit diagram illustrating the impedance matching network.

Referring to FIGS. 1, 2 and 3, there is shown the general layout of the fanlike center fed dipoles 11 and feed line 13 of a printed circuit panel antenna system 10 in accordance with a preferred embodiment of the present invention. The fanlike dipoles 11 and the feed lines 13 are placed on insulative sheet 15 of a one thirty-second inch thick, low dielectric material such as low loss polyolifin dielectric having a dielectric constant of 2.32. A half-portion 12 of each dipole element 11 is on one surface of the sheet 15, and the remaining half-portion 14 of each dipole element 11 is on the opposite surface of the sheet 15. That side of the sheet 15 having half-portions 14 thereon is shown in FIG. 1, with the half-portions 12 on the opposite side of sheet 15 not visible in FIG. 1 shown as dotted lines. As shown in FIGS. 2 and 3, the feed lines 13 are made up of a transmission line of the character having one conductor 17 on one surface and a second conductor 19 on the opposite surface. Conductors 17 on one surface, illustrated in FIG. 2, are coupled to the half-portion 12 of each dipole element 11 on that one surface, and conductors 19 on the opposite surface, illustrated in FIG. 3, are coupled to the half-portion 14 of each dipole 11 on the opposite surface.

The slight offset due to the thickness of the insulative sheet between the two halves of each of the dipoles is electrically insignificant and eliminates the need for pass-through connections which would be required if both halves of the dipoles were on the same side of the sheet.

For purposes of description, FIG. 1 is described in detail, bearing in mind however, that in actual practice there are feed lines on both sides of the dielectric sheet 15 with the feed line on one surface coupled to the half-portion of the dipole element on that one surface and the feed line on the opposite surface of the insulative sheets coupled to the half-portion of the dipole element on the opposite surface. If unidirectivity is desired, this printed circuit panel antenna system 10 having half of the dipole on one side and half of the dipole on the opposite side may be foam supported in a shallow metal pan with the metal pan acting as a reflector for the dipoles. FIG. 4 shows a cross-sectional view of a portion of such an arrangement. The transmission line conductors 17 and 19 on either side of a dielectric sheet 15 are spaced from a reflector 23 by means of foam section 21. To provide weather proofing and mechanical protection of the printed circuit panel network, another layer of foam 25 and a second dielectric sheet 27 may be provided on the opposite surface of sheet 15.

As shown in FIG. 5, a coaxial line 28 may be coupled near the center of the printed circuit panel antenna system 10. The outer conductor 29 of the coaxial line 28 is coupled to conductor 59 at the one or bottom surface of the printed circuit dielectric sheet panel 15 at points 35 and 36 and is also coupled to the shallow metal pan or ground plane reflector 23. The center conductor 31 of the coaxial line 28 is fed through the insulative sheet 15 to the conductor 57 of the feed lines at the upper surface of the insulative sheet at point 31 as shown in FIGS. 2 and 5. At point B conductor 57 is connected to conductor 17 and conductor 59 is connected to conductor 19. The individual dipole radiators 11 are made in the form of fans having a flare angle of 90.degree. in order to provide greater impedance bandwidth.

The dipoles are fed from a corporate network of balanced transmission line sections branching out from points 37 and 39 in FIG. 1. The conductors 17, 19 which make up the feed lines from points 37 and 39 to the dipoles on opposite sides of the insulative sheet are of equal width to provide balanced lines from points 37,39 to the dipoles 11. The width of the conductor 17 from point B to point 37, and from point B to point 39 on the surface of the insulative sheet 15 changes so that a 50 ohm balanced impedance at the points 37,39 is transformed to 100 ohm unbalanced impedance at point B (see FIG. 2). The width of the line on the opposite surface of the panel 15 does not change from point B to points 37 or 39 (see FIG. 3). The two halves of the complete array, when joined together, as in the example, give a 50 ohm impedance. The impedance of the line at the point of the coaxial input connection across points 31 and 35,36 is also 50 ohms to match the coaxial line impedance.

The impedance in the line from point B to point 31 is matched by a section of microstrip line where, as shown in FIGS. 2 and 3, the conductor 57 shown in FIG. 2 is considerably narrower than that of 59 illustrated in FIG. 3 to make a microstrip transmission line. A vernier impedance matching device 58 is formed by a small chip of dielectric material with a conductor such as copper on the upper surface. By changing the length of the chip 58 and its position along the microstrip line, an impedance match between the coaxial line 28 across points 31 and 35, 36 and point 35,36 is provided with low VSWR at the given frequency. Once the optimum chip position is located, one may simply glue the chip to the surface of the conductor 57.

From points 37 or 39 on the feed lines to the dipoles 11, the feed lines on the opposite ends of the array are identical and follow from a basic building block as described further in connection with FIG. 6. Referring now to FIG. 6, each of four antenna dipole elements 11 has a load impedance Z.sub.A, for example. Lines 43 and 44 each represent that section of line in the array directly connected to a dipole 11. Thus, it is to be understood that line 43 terminates at a dipole 11 including half-portions 12 and 14. Likewise, line 44 terminates at a second dipole 11 including half-portions 12 and 14. Again, it is to be remembered that each line 43,44 represents a conductor on one side of the sheet 15 and a matching conductor on the opposite side thereof. The configuration of lines 43 and 44 are each arranged to provide a characteristic impedance of Z.sub.1, for example. The lines 43 and 44 are identical with both being one-half wavelength long. The impedance at the junction point 45 is Z.sub.A/2 independent of the value of the characteristic impedance Z.sub.1 of lines 43 and 44. A line 47 having a configuration such as to provide a characteristic impedance of Z.sub.2, for example, is coupled perpendicular to the lines 43 and 44 at point 45 to form a T with the lines and extends a length one-quarter wavelength long (.lambda./4) at approximately the mean operating frequency of the antenna system. The impedance at point 49 is equal to (Z.sub.2).sup.2 /(Z.sub.A/2 ) or 2(Z.sub.2).sup. 2 /Z.sub.A. A second line 51 one-quarter wavelength long at approximately the mean operating frequency of the antenna system connected to the free end of line 47 at point 49 will give an impedance at point 53 (.lambda./4 wavelength from point 49) of Z.sub.3 .sup.2 (Z.sub.3 being the characteristic impedance of line 51) divided by the impedance at point 49 resulting in (Z.sub.A Z.sub.3 .sup.2) (2Z.sub.2 .sup.2). Since the lower half 54 of the circuit is identical to that of the upper half 41, the impedance at the junction 53 is halved and is equal to (Z.sub.A Z.sub.3 .sup.2)/(4Z .sub.2 .sup.2). Now if the characteristic impedance Z.sub.3 of the line 51 is equal to twice that of the characteristic impedance or Z.sub.2 of line 47, then the impedance of point 53 is equal to that of Z.sub.A or the load. Thus if there is no coupling between the antenna elements, the input impedance to the corporate network feed is equal to the individual antenna load impedance. The characteristic impedance Z.sub.1 or Z.sub. 2 may have any chosen value. The only requirement is that Z.sub.3 be twice Z.sub.2. In practice, it is desirable to choose the values of Z.sub.) and Z.sub.2 to minimize the standing waves throughout the network.

Referring now to FIG. 1, the four element array of FIG. 6 may be any one of the four element arrays such as the four element array 61 in FIG. 1. The antenna loads provided by dipoles 11 are, for example, 50 ohms. The feed line section 62 between the dipoles 11 and the common point 63 of the array, is for example, half a wavelength long with the characteristic impedance Z.sub.1 of the line being 50 ohms. The characteristic impedance Z.sub.2 of the line 66 between the junction at point 63 and point 64 is 50 ohms. The length of the line 66 between point 63 and point 64 is one-quarter of a wavelength. Following with the arrangement described in FIG. 6, the length of the line 67 between point 64 and common point 65 which is the junction point with the lower half of the circuit is likewise one-quarter wavelength long. The width of the conductor 67 is narrower than that of line 66, so as to provide a characteristic impedance of 100 ohms. Considering the four element array 61 in FIG. 1 and FIG. 6 as one load, the dipole array 61 is joined with a similar corporate network to three other similar four element arrays, 71, 72 and 73 to give a 16 dipole array which 16 dipole array has a total input impedance of (in this example) 50 ohms. Impedance match is provided by the .lambda./4 stub at the junction and the 2 to 1 ratio in the 2 impedance of the two line section. In the present application, this process is repeated once more, where four 16 dipole arrays 75, 76, 77 and 78 are combined resulting in a 64 dipole array fed at point 37 of FIG. 2. Hence if the antenna impedance is 50 ohms, the impedance at point 37 is also 50 ohms and the greatest theoretical VSWR throughout the system is about two-to-one. Repeating the structure described at point 39 on the other end of the printed circuit array provides an array when combined at point B, of 128 dipole elements impedance-matched at points 37 or 39 at 50 ohms. The result is also feed lines of equal length to all of the dipoles.

The corporate network in the present array is located in the same plane as that of the dipole array. One-quarter wavelength notches 81 as shown in FIG. 1 are cut at the T-junctions where horizontal lines branch into vertical lines. This notch effectively breaks the currents which may be induced on the two conductor lines by the radiating dipoles and which are equal in magnitude and flow in the same direction. By breaking this current flow in the same direction, the push-push mode which would result in undesired transmission line radiation is prevented. The notch width is made relatively small compared to the line width, so that the characteristic impedance of the line operating in the push-pull mode would not be greatly changed.

Claims

What I claim is:

1. An antenna system comprising:

a broad sheet of dielectric material,

a plurality of planar dipole elements with a first half portion of each dipole element fixed to one of the broad surfaces of said sheet and with the second half portion of each dipole element fixed to the opposite broad surface of said sheet,

feed means including two narrow conductive strips fixed in opposed relation on said broad surfaces of said dielectric sheet and extending from a common feed point to said plurality of dipole elements with a length between the common feed point and one of said dipole elements being the same as that from the common feed point to any of the other dipole elements, said dipole elements being arranged on said sheet so that said feed means extends horizontally and vertically from said common feed point to said elements, said horizontally extending feed means at the junction with said vertically extending feed means having a notch located thereat in a manner so that currents will not be introduced into the feed means which are equal in magnitude and flow in the same direction.

2. An antenna system comprising:

a broad sheet of dielectric material,

a plurality of planar dipole elements with a first half portion of each dipole element fixed to one of the broad surfaces of said sheet and with the second half portion of each dipole element fixed to the opposite broad surface of said sheet,

feed means including two narrow conductive strips fixed in opposed relation on said broad surfaces of said dielectric sheet and extending from a common feed point to said plurality of dipole elements with the length between the common feed point and one of said dipole elements being the same as that from the common feed point to any of the other dipole elements, said feed means being unbalanced for a given length from said common feed point and balanced from the end of said given length remote from said common feed point to said dipole elements.

3. The combination as claimed in claim 2, wherein one of said conductive strips forming said given length of said feed means is of constant width and the second conductive strip forming said given length of said feed means is tapered in width to provide said unbalance, the common feed point being located at the narrowest end of said given length.