Planar Dipole Array Mounted On Dielectric Substrate

Abstract

An improved microwave antenna system employs a flat or planar array of radiating elements and, behind it, a distribution network of feeding circuit portions. The radiating elements and distribution network are physically separated by two wire connections and each feeding circuit portion terminates in a balun aligned with an associated dipole pair. The assembly includes a mounting frame and is of sandwich form incorporating frame portions therein so that the whole is an integral and rigid assembly. The antenna array is provided with a protective cover sheet arrangement and the frame circumscribes and covers the edges of the sandwich assembly.

Description

BACKGROUND OF THE INVENTION

In conventional microwave antennas, a substantial depth is occupied by the antenna horns and such depth increases as the aperture of the system is increased. By utilizing a flat or planar array of radiators, it would be possible somewhat to decrease the depth required for any particular aperture, but the usual microwave feeding or distribution arrangement for such an array still occupies substantial depth. Moreover, the problem of making the necessary electrical connections may become quite complex and may necessitate resort to unusual and difficult techniques for making them.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a microwave antenna system which has very little depth with respect to its aperture and which also provides an excellent mounting base upon which the associated electronics may be attached.

The system employs a flat or planar array of radiating elements in association with a distribution circuit which also is of planar form. The distribution circuit incorporates an array of baluns aligned with the radiators and two wire connectors extend between these baluns and the associated radiators. The entire assembly provides a very thin antenna of large aperture.

The antenna array is amenable to contouring or shaping to a given surface and is readily fabricated by photo-etching. In this way, automated manufacture and consequent low production cost is possible. Also, the feeding or distribution circuit may be fabricated by photo-etching. The entire assembly lends itself to fabrication and assembly by sandwich technique, uses a minimum of materials and is of very lightweight construction.

The large number of individual radiators with separate feed to each allows easy tailoring of the beam shape and sidelobe levels; the amplitude taper is very flexible and can be specified separately for the E and H planes. Further, the large number of radiators provide large redundancy for the formation of the antenna beam and, in consequence, high reliability and tolerance to damage is provided. Individual radiator elements can be shunted, destroyed or eliminated with negligible effect on overall gain, input VSWR, or antenna pattern.

The assembly makes maximum use of low cost dielectric materials, preferably polystyrenes, and easily allows for maximum protection against weather and environmental conditions. An aluminum housing or frame may be employed and the edges of the antenna and distribution circuit arrays may be sealed and protected within the frame. As well, the front face of the antenna array may be covered by a protective layer or sheet of polystyrene material.

The photo-etched antenna array with feed or distribution circuits behind it permits full use of the antenna area for radiation without encroachment upon the frontal area by such feed or distribution circuit, and the back or rear surface of the antenna-distribution system provides a convenient mounting space for the associated electronics package, thereby providing trouble-free assembly and avoidance of any need for external microwave coaxial lines or waveguides. In the present invention an improved feeding or distributing circuit is disclosed, embodying and array or network of stripline circuits each terminating in a balun.

The feeding network array is physically oriented and registered with the antenna dipole array such that the baluns are positioned in a particular manner with respect to the inner ends of the dipoles with which they are associated. Each balun is of C-shape and points thereon which are separated by a distance of one-half wavelength (mean frequency) are connected by conductor pairs to the associated dipoles. The two wire connections between the two arrays provide not only means by which the arrays may be separated physically but they also provide a degree of freedom, by length variation, for adjusting antenna impedance to fit the requirements of a particular design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of the antenna array;

FIG. 2 is a plan view of the feed circuits;

FIG. 3 is an exploded perspective of the sandwiched antenna-distribution system;

FIG. 4 is an enlarged plan view of a portion of the feed circuit;

FIG. 5 is a sectional view showing a portion of a preferred form of the invention; and

FIG. 6 is a diagrammatic view illustrating the relation between the baluns and the dipoles.

DETAILED DESCRIPTION OF THE INVENTION

With reference now more particularly to FIG. 1, the antenna dipole array is illustrated therein and will be seen to consist of a substrate of low loss dielectric material 10 having pairs of dipole elements 12 and 14 thereon. The array will be seen to consist of vertical columns and horizontal rows of these dipole element pairs with the exception of the blank spaces in the portions indicated by the reference characters 16, 18, 20 and 22 wherein in such space, a dipole pair is missing, the purpose of which will be presently apparent.

As is shown in greater detail in FIG. 6, each element 12 and 14 is of trapozoidal configuration and the inner edges 24 and 26 of these elements are spaced apart by a distance as indicated in FIG. 6 which is substantially less than one-half wavelength of the microwave energy radiated or received, it being understood that the mean frequency or center frequency is intended. The total length of each dipole pair on the array is in the order of one-half to a full wavelength, as indicated. It will be understood that the specific dimensions of the dipole elements will be in accord with conventional design practices having reference to the particular frequency involved and other considerations, particularly antenna impedance, normally accommodated for in microwave antenna design.

As previously stated, the array of antenna dipoles is on a substrate 10 of low loss dielectric material and, for this purpose, it is preferred to use polystyrene sheet material which initially is copper cladded at least on that surface thereof upon which the antenna array is formed. The antenna array is then formed by photo-etching processes which are well known so as accurately to produce the dipoles in proper positions and of proper dimensions as may be accomplished, for example, by progressive reduction from a master drawing of enlarged size wherein the array is laid out with great accuracy.

Disposed beneath or behind the antenna dipole array is the distribution or feeding circuitry shown in FIG. 2 and, as illustrated, a substrate 30 is provided upon which the array of feeding circuit portions are formed, substantially as is shown. The circuitry of FIG. 2 is a strip transmission line which is a microwave transmission line consisting of thin, narrow rectangular strips or strip portions forming the network and, as will hereinafter be seen, the assembly is mounted between two wide ground-plane conductors. Again, the material of the sheet 30 is of low loss dielectric material, preferably polystyrene and the network of FIG. 2 again is preferably formed by photo-etching techniques. For purposes of description herein, the strip transmission line network will be referred to as a stripline system.

In the particular embodiment shown in FIG. 2, there are in actuality two feeding or distributing systems, each having an input section 32 or 34 leading from input connection points 36 and 38 although it will be understood that a single input connection point for the entire array may be provided or, alternatively, four separate input points may be provided, one for each quadrant of the antenna system, as will be well understood by those in the art.

As will be seen from the specific embodiment shown in FIG. 2, having reference to the input section 32, same is connected to a power splitter portion 40 through a one-fourth wavelength portion 42, and the power is split equally to the two branch line portions 44 and 46. From these principal branch line portions 44 and 46, further power splitting is effecting as at 48 which again is an equal power splitter to the branch input sections 50 and 52 leading to the unequal power splitter sections 54 and 56 whereby a greater proportion of the power is transmitted to the branch section 58 and a lesser amount to the branch section 60 and these portions are again split as by the unequal power splitter 62 to provide greater power to the input section 64 and less power to the section 66 with, for both sections 64 and 66, there being further power splitting portions as at 68, which are of unequal power distribution ultimately leading to the equal power splitter portions 70 and 72. As will be recognized by those skilled in the art, the power splitting will be carried out in accordance with the pattern desired for a particular antenna, it being appreciated that the greatest amount of power is radiated from the central portion of the antenna array as will hereinafter appear.

The transmission line branch portions ultimately lead to an array of terminal portions which are in the form of C-shaped baluns. As used herein, it will be understood that the term balun is meant to refer to a device used for matching an unbalanced coaxial or similar transmission line or system to a balanced two-wire line or system. In FIG. 2, four of these baluns are indicated by reference characters 74, 76, 78 and 80 and, as will hereinafter appear, it is to be understood that these baluns are registered or aligned with the inner ends of the dipole element pairs in a particular fashion as will be described in conjunction with FIG. 6 hereinafter. However, for the purpose of more accurately defining the feeding circuitry configuration as it relates to an individual balun, reference to FIG. 4 is now had.

In FIG. 4, certain basic constructional relationships which are followed throughout the entire matrix or network of the distributing system, will be seen. For example, a branch line input section is indicated in FIG. 4 by the reference character 82 and an unequal power splitter is indicated by the reference character 84. For the purpose of impedance matching between the input section 82 and the power splitter 84, a one-fourth wavelength impedance matching section 86 is utilized. The power is split unequally to the relatively narrow branch output section of the power splitter as indicated by the reference character 88 as compared with the relatively wide output section 90. With respect to the power being split to the right in FIG. 4, an input section is indicated by the reference character 92 which is coupled to the power splitter 94 by means of the one-fourth wavelength impedance matching section 96 providing the transmission line output section 98 which leads to the balun indicated by the reference character 100. The power splitter section 94, as is the case with all of the power splitters therein, will be seen to include a 45.degree. miter section 102 and the balun, as shown, will be seen to be of C-shaped configuration having two points 104 and 106 thereon which are spaced apart along the medium line 108 by a one-half wavelength. The dimensions of the balun 100 in each case are such as to place the points 104 and 106 substantially in registry or alignment with connection openings 108 and 110 of an associated dipole pair as is shown in FIG. 6. And, as will be presently described, a two-wire connection is made between the imaginary points 104 and 106 in each case and the dipole element pairs at the points 108 and 110 thereof. It will be understood that suitable coaxial lines provide the inputs to the points 36 and 38 in FIG. 2 from the associated electronics package associated with the antenna system.

An antenna sandwich system is shown in FIG. 3 wherein it will be noted that the stripline sandwich is composed of the previously mentioned low loss dielectric substrate 30 which, on the left-hand side in FIG. 3 has the dsitributing system array thereon and has, on the right-hand side thereof a full layer of copper cladding as indicated by the reference character 120. The stripline sandwich is completed by the low loss dielectric sheet 122 which is bare on the side indicated by the reference character 124 and is provided with a full copper cladding on the opposite or left-hand side as indicated by the reference character 126. The copper sheets or claddings 120 and 126 define the ground-planes and for rigidity and protection as well as assembly purposes as will hereinafter appear, forward and aft ground-plane aluminum sheets 128 and 130 are provided. The sandwich assembly which is comprised of all of the sheets 130, 30, 122 and 128 are drilled and properly threaded in the plate 128 to receive fasteners such as those indicated by the reference characters 132 and 134 which serve to rigidly sandwich the components together, it being preferred that two such fasteners 132 and 134 be associated with each balun as indicated in phantom lines by the reference character 100 in FIG. 3. The openings in the several sheets receiving the fastener 132 are indicated by the reference characters 136, 138, 140 and 142, the bore 142 being internally threaded as shown and those for receiving the fastener 134 are indicated by reference characters 144, 146, 148 and 150, the latter of which is internally threaded. In addition to these openings, the sheet 122 is provided with a pair of bores 152 and 154 which are accurately drilled and are in alignment with the aforementioned points 108 and 110 of a corresponding dipole element pair and with the imaginary points 104 and 106 on the associated balun 100. A relatively large opening 160 is provided in the forward ground-plane sheet 128 in registry with the openings 152 and 154 and this opening receives the reduced shoulder portion 162 of a shielding sleeve indicated generally by the reference character 164. The forward end of the shielding sleeve as indicated by the reference character 166 is of enlarged diameter and serves to bear against the left-hand or forward side of the ground-plane plate 128 and against the right-hand or aft surface of the antenna sheet 10 to space the plate 128 from the sheet 10 in accord with the axial length or extent of the portion 166 of the shielding sleeve 164. The shield sleeve 164 is provided with a throughbore 168 which snuggly receives a core member 170 of low loss dielectric material and which is provided with throughbores 172 and 174 which align with the respective bores 152 and 154 and also, at their forward ends, with bores 176 and 178 provided in the antenna sheet 10.

A two-wire connection is made between each balun 100 and the associated dipole element pairs 12 and 14 as previously described in conjunction with FIG. 6 and this two-wire pair in each case comprises two headed copper wire connectors, one of which is shown in FIG. 3 and is indicated by the reference character 180. The headed end portion 182 of each of these connectors bears against the aft-bare side surface 124 of the stripline sandwich sheet 122 so that when the stripline assembly is in properly sandwiched condition, the wire connector in each case engages a balun 100 at one of the two imaginary points 104 or 106 thereon. The connectors in each case projects through the bores 152, 172 and 176 on the one hand or the bores 154, 174 and 178 on the other hand so that their forward extremities as indicated by the reference character 184 engage against or through the respective dipole elements 12 or 14 and are electrically connected thereto as by soldering or the like.

A low loss dielectric sheet 186 may be provided on the forward face of the antenna array for protective and closure purposes and the stripline sandwich assembly preferably is circumscribed by a copper foil strip for protective purposes and for interconnecting the ground-planes. Further, it will be understood that suitable synthetic resinous material may be utilized for sealing in circumscribing relationship to the stripline sandwich and, as well, to the entire antenna system as will be apparent more particularly hereinafter.

In a preferred embodiment of the invention as shown in FIG. 5, the forward ground-plane aluminum sheet 128' may form an integral part of a frame assembly indicated generally by the reference character 200. In this case also, the shielding sleeve 154 may be dispensed with and may be formed, instead, directly as an integral portion of the frame 200 as bosses 164' on the forward ground plane sheet portion 128'. Otherwise, the assembly is essentially as is described in conjunction with FIG. 3. The frame has forward and aft flange portions 202 and 204 presenting shoulders at 206 and 208 against the peripheral edges of the antenna array portion on the one hand and the stripline sandwich assembly on the other hand bear and suitable gasketing material such as is indicated by reference characters 210 and 212 may be provided for weather sealing purposes.

Claims

What is claimed is:

1. In a microwave antenna system for transmitting and/or receiving at a selected microwave wavelength, the combination of:

a planar array of antenna dipoles, each dipole comprising a pair of elements having inner ends spaced apart by an amount substantially less than one-half of said selected wavelength;

a distribution network of stripline feeding circuits disposed in a plane spaced from the plane of said dipoles, each feeding circuit terminating in a balun disposed in registry with an associated dipole; and

two wire connector means extending between said inner ends of each dipole and selected points of an associated balun for conveying RF energy therebetween, said selected points being axially spaced on each balun by a distance equal to one-half of said selected wavelength;

each balun being C-shaped and said connector means connecting two points on each balun to an associated dipole, said points being spaced apart along the balun by one-half wavelength.

2. In a microwave antanna system as defined in claim 1 wherein each dipole comprises a pair of trapezoidal elements having their short sides spaced apart by a distance substantially less than one-half wavelength.

3. In a microwave antenna system for transmitting and/or receiving at a selected microwave wavelength, the combination of:

a planar array of antenna dipoles, each dipole comprising a pair of elements having inner ends spaced apart by an amount substantially less than one-half of said selected wavelength;

a distribution network of stripline feeding circuits disposed in a plane spaced from the plane of said dipoles, each feeding circuit terminating in a balun disposed in registry with an associated dipole; and

two wire connector means extending between said inner ends of each dipole and selected points of an associated balun for conveying RF energy therebetween, said selected points being axially spaced on each balun by a distance equal to one-half of said selected wavelength;

said distribution network comprising a body of low loss dielectric material having said stripline feeding circuits therein, and ground plates sandwiching said dielectric material therebetween;

each balun being C-shaped and said connector means connecting two points on each balun to an associated dipole, said points being spaced apart along the balun by one-half wavelength.

4. In a microwave antenna system as defined in claim 3 wherein each dipole comprises a pair of trapezoidal elements having their short sides spaced apart by a distance substantially less than one-half wavelength.