US3039100A - Thin-wall radome utilizing irregularly spaced and curved conductive reinforcing ribs obviating side-lobe formation - Google Patents

Description

"June 12, 1962 CONDUCTIVE RIBS A. F. KAY

THIN-WALL RADOME UTILIZING IRREGULARLY SPACED AND CURVED CONDUCTIVE REINFORCING RIBS OBVIATING SIDE-LOBE FORMATION Filed D90. 5, 1958 2 Sheets-Sheet 1 IRREGULARLY CURVED AND SPACED RADIO WAVE TRANSPARENT INVENTOR.

June 12, 1962 A. F. KAY 3,039,100

THIN-WALL RADOME UTILIZING IRREGULARLY SPACED AND CURVEID CONDUCTIVE REINFORCING RIBS OBVIATING SIDE-LOBE FORMATION 2 Sheets-Sheet 2 Filed Dec. 3, 1958 INVENTOR. AM/v A Mr I BY MM Afivf/viff Pa -tented June 1 2, 1962 The present invention relates to radomes for the housing and protection of radar antennas and more particularly to radome structures having reinforcement members of a configuration which provides a maximum of structural strength with minimum interference with the desired electrical properties of the radome, and which members may be additionally or alternatively used as a radio frequency antenna.

Conventional radomes are usually designed on the basis of a compromise between desired electrical and structuralproperties. For ideal electrical performance the beam of the radar antenna should be entirely unaffected by the radome. No material in front of the radar antenna and hence no radome at all would be the most desirable electrical design. For structural reasons radomes are required both in airborne radar where the aerodynamic shape of the aircraft is of the utmost importance and also in ground based radar where the antenna must be protected against weather and wind loadmg.

Five common types of radomes in use today are (a) thin wall, (b) half-wave wall, multiple half-wave wall, (d) A-sandwich, and (2) multiple sandwich. (a), (b), and (0) above are homogeneous dielectric constructions. (d) and (e) above are non-homogeneous structures.

Of the above structures the thin wall (thin compared to a wavelength) is, in general, electrically the most desirable of the homogeneous walls. If the thin wall is not structurally adequate, a half-wave wall is the most desirable. If still further structural strength is required, a multiple half-wave wall (e.g. a full-wave wall, threehalves wavelength wall, or the like) may be used. If alternatively a sandwich type construction is to be employed the best electrical performance comes the A- sandwich comprising a three layered wall in which the middle layer is a foam 0r honeycomb of low relative dielectric constant (a value approximately equal to 1.2 forexample) which is covered on both sides by thin skins of higher dielectric constant (usually a fiber glass laminate). If the sandwich construction is desired, and if the A-sandwich is unsatisfactory structurally, a multiple sandwich may be used consisting of 5, 7 or more layers. Whether the homogeneous or the sandwich construction is employed, in general the more layers that are used the poorer the electrical performance'and the better the strength of the radome will be.

From the above description of the common practice in the-art of construction of radomes it will be realized that the practice is to form the radome from a wall of material either homogeneous'or non-homogeneous which is of suificient structural strength yet which provides a minimum ofinterference with the electrical propagation from the antenna.

On the other hand, the present invention utilizes a radome wall which is in itself of insufficient structural strength. In conjunction with this wall reinforcing elements are used which increase the structural strength of the radome to meet the specific requirements. Obviously for a given-structural requirement this procedure will enable the designer to utilize a thinner radome wall or a wall with a fewer number of layers and hence'to provide a wall with electrically superior characteristics. Although the reinforcing structure tends to degrade the performance of the unreinforced radome, the net result is an overall design that is a better compromise between structural and electrical requirements than could be realized without the use of reinforcement. Although the use of reinforcement in general is well known from a structural standpoint, such techniques have not been widely used in the radome art due to the fact that many deleterious electrical effects are produced by the inclusion of reinforcing structures and it has previously not been known how to overcome or avoid these effects in such a way that the added structural strength would not be outweighed by deterioration of the electrical properties of the radome.

This invention relates to the design of reinforcing members in a radome structure so as to minimize their undesired electrical effects and make possible radomes wherein the compromise of electrical and structural design is superior to that of radomes without these reinforcing members. Various radome structures are illustrated; however, it should be appreciated that radomes for different applications will have different structural and electrical requirements which will in a large measure determine the particular type'of structure according to the principles of the present invention which would be most suitable for a particular application. Structural and electrical requirements, the geometry of the antenna and of the radome, the wavelength or wavelengths at which the antenna is to be operated, the environmental conditions and various other factors will affect the design of the radome.

Two major effects of the radome reinforcing structure must be overcome in order to provide a practical radome structure. The first of these effects is attenuation or loss of gain of'the antenna radome combination due to the presence of the frame or reinforcing structure. In the present invention the design of the reinforcing structure is such that the loss of gain is limited substantially to the percentage of the total radome area blocked by the reinforcing structure. This may be accomplished by maintaining the hole size not less than approximately one wavelength. Since the maximum permissible loss of gain due to the presence of the reinforcing structuremay be of the order of ten to thirty percent, a structurally eflicient reinforcing structure may readily be constructed within the prescribed limits of area of obstruction by constructing a reinforcing structure consisting of a mesh wherein the holes or openings are large compared to the size of the reinforcing members.

A second problem in the use of reinforcing structure is that of directive scattering of energy incident upon the radome from either side. If the energy scattered by the reinforcing structure is scattered more or less uniformly in all directions then the only appreciable electrical effect is the loss of antenna gain. As previously: explained, a certain amount of loss of antenna gain is acceptable in view of the fact that the radome wall may be made much thinner and thereby compensate by improved characteristics for any loss due to the reinforcing structure. On the other hand, if the scattering from the reinforcing structure is directive in one or more directions in'space, that is, if the scattering from a substantial number of reinforcing elements adds up in space at some observation point distant from the reinforcing structure in'one particular direction or directions, then an error or aberration in the directivity' characteristics, generally in the form of a side lobe, will be created. If the radome structure causes a substantial side lobe to be created it will seriously diminish the utility of the antenna, rendering it useless for many applications.

The present invention provides an arrangement of the reinforcing structure which prevents directional scattering. This arrangement may be briefly described as an irregular, non-periodic, and. preferably non-linear arrangement of the members making up the mesh of the reinforcing structure. From the theory of linear arrays of radiators, it is well known that any set of scatterers which lie along a straight line in space add in phase in at least one direction in space if the spacing between neighboring elements exceeds a half wave-length. As previously explained, the fact that the radiation from a linear array of radiators adds in phase in one direction means that such an array in the radome reinforcing structure would produce a side lobe in a particular direction. The present invention provides an arrangement of the reinforcing structure which prevents this condition from arising and thus substantially eliminates the creation of any side lobes due to the presence of the radome reinforcing structure.

In addition to the above-described features and advantages of the present invention it is also an object of the present invention to provide a reinforcing structure for a radome which may be constructed of either a conductive material or a non-conductive material and is arranged in such a manner as to provide a maximum of structural strength in the radome and at the same time to provide a minimum of interference with the desired electrical characteristics of the radome.

It is another object of the present invention to provide a reinforcing structure for a radome which is arranged in such a fashion that the creation of unwanted side lobes in the antenna beam pattern is avoided.

It is a further object of the present invention to provide a mesh-like structure to be incorporated in a radome which may be formed of conductive material and insulated from the remainder of an aircraft body to provide an antenna for a propagation of radio frequency waves without interfering with the propagation of higher frequency radio waves through the radome structure.

Other objects and advantages will be apparent from a consideration of the following description in conjunction with the appended drawings, in which FIG. 1 is a perspective view of a teardrop-type radome structure showing the shape of a mesh-type reinforcing structure incorporated therewith;

FIG. 2 is a perspective view of a shell-type radome structure showing in dotted lines a reinforcing structure incorporated therewith;

FIG. 3 is a partially schematic cross sectional view of a cone-type radome having circumferential reinforcing elements presented to show the degree to which such elements obscure a beam of electromagnetic energy which is propagated in the direction of the axis of the cone;

FIG. 4 is a partially schematic perspective view of a conical radome including a reinforcing structure embodying principles of the present invention and which may me constructed of conductive material and utilized as a radio antenna; and

FIG. 5 is a perspective view of a spherical-type radome structure incorporating a reinforcing structure according to the present invention.

Referring now to the drawings and particularly to FIG. 1, a radome structure 11 is shown which is of the tear-drop type. That is, it is designed in a tear-drop shape suitable to be mounted on the surface of an aircraft where it will protrude therefrom and serve to house a radar antenna. The radome 11 comprises a wall 12 which may be formed of any homogeneous or nonhomogeneous material of suitable electrical and dielectric properties for the construction of a radome.

The wall 12 however is formed of a relatively thin material so that it does not have the required structural strength for a suitable radome structure. A reinforcing structure 16 is provided to give added structural strength to the radome 11. The reinforcing structure 16 includes a number of elements formed in the shape of rods, bars, strips or the like and shaped into a mesh to form reinforcing structure 16. A base 13 is provided surrounding the open end of the radome 11 and providing a rigid means for attachment such as to an aircraft frame.

As shown in FIG. 1, a first group of reinforcing elements 14 is provided which are generally but not exactly parallel, and a second group of reinforcing elements 15 is provided, these latter elements 15 being placed generally transverse to the first group of elements 14 over the surface of the radome 11. The elements 14 and 15 are spaced a substantially distance apart to form a meshlike structure having a number of relatively large openings 17 generally having four sides.

For clarity, the radome 11 in FIG. 1 is presented as though the reinforcing structure 16 were superimposed on the exterior of the wall 12 of the radome 11. In some cases this may be a desirable structure. However, in many cases the reinforcing structure 16 will be placed on the interior of the radome wall 12 to allow a smooth exterior surface to be presented to reduce air drag, particularly in the case of aircraft radomes. In other circumstances, it may be desired to place the reinforcing structure 16' between two or more radome walls 12, or to mold it into a radome wall. Combinations of the above arrangements could also be utilized if desired.

It should be noted in FIG. 1 that the arrangement of the reinforcing elements 14 and 15 can best be described as being irregular, the meaning of this term being made clearer below. As previously suggested, this irregular arrangement is intentional and provides a structure which eliminates substantially all side lobes in the antenna pattern which might otherwise result from the use of a reinforcing structure. The reinforcing elements 14 and 15 may be constructed of metal or some other conductive material, but in any case it is contemplated that the reinforcing elements 14 and 15 will be constructed of a material which is selected primarily for its structural characteristics, and will thus not provide optimum electrical transmission characteristics but will act as a scatterer for the electromagnetic radiation.

If the electromagnetic energy scattered by the reinforcing elements 14 and 15 is scattered more or less uniformly in all directions then the only appreciable electrical effect is the loss of antenna gain. Although this loss is not desirable, if the transverse dimension of the reinforcing elements 14 and 15 is relatively small compared to that of the opening 17, the percentage loss of antenna gain will remain within acceptable limits. If, however, the scattering of the reinforcing elements 14 and 15 is additive in one or more directions in space then appreciable side lobes will be produced in the antenna pattern due to the presence of the reinforcing structure 16. This effect is highly undesirable and must be avoided if a practical radome structure is to be provided.

The characteristics of the present arrangement of the reinforcing elements 14 and 15, which avoids the generation of antenna beam side lobes, may be understood from the following analysis of the scattering problem. The scattering from the reinforcing elements 14 land 15 will be directive if the scattered energy from a substantial number of reinforcing elements 14 or 15 is additive in I phase at observation points distant from the radome 11 in one or more particular directions from the radome 11. The reinforcing elements 14 and 15 may be considered as a set of scatterers of electromagnetic energy. Since they are relatively few in number and fairly well separated in space, the incident field at each scatterer is primarily the field of the original radar beam from the antenna. In other words, the effect of multiple scattering can be neglected. It may thus be assumed that the phase of the scattered field due to each individual scatterer is the same as the phase of the incident field at the scatterer or differs from the incident field by a constant value. The far field pattern of the scattered field is a sum of a number of terms each one representing the scattered field of'one of the reinforcing elements 14 or 15. If these terms add in phase in a particular direction in space, then a side lobe will occur in this direction.

From the theory of linear arrays of radiators it is known that any set of scatterers which lie along a straight line in space regardless of the orientation of this line must'necessarily add in phase in at least one direction in space provided that the spacing between neighboring elements exceeds a half wave-length. In the reinforcing structure 16 the spacing between elements 14 and 15 is preferred to be not less than approximately one wavelength. Therefore, the spacing between neighboring elements and the reinforcing structure 16 exceeds a half wave-length and thus any rectilinear arrangement of any one element or group of elements is to be avoided. A configuration of reinforcing elements 14 and 15 such as that shown in FIG. 1 best approaches the condition wherein there is no set of scatterers which lie along a straight line in space.

Several characteristics of the shaping and arrangement of reinforcing elements 14 and 15 are responsible for this desirable condition. In FIG. 1, and particularly in the case where reinforcing elements are many wavelengths long, these elements are not straight but are curved by a substantial amount along each portion of their length. Preferably the curvature of the reinforcing elements 14 and 15 is such that the curve cannot be contained in a single plane. That is, the curves should be skew, not plane curves. A more precise way of stating this characteristic of the reinforcing elements 14 and 15 is that they should be formed in a curve with torsion bounded away from zero, that is, differing widely from zero. Torsion is sometimes called the second curvature and is a measure of the curvature out of the osculating plane at any point of a non-planar curve.

' Each of the reinforcing elements 14 and 15 should be shaped in a curve which has a torsion substantially different from zero throughout the major portion of its length. This feature of the reinforcing structure 16 is not absolutely necessary for the practice of the invention, but provides an increased measure of effectiveness in that curves of the above description which differ substantially from plane curves are of such a nature that a set of such curves when placed together is not likely to form a set of scatterers which lie along a straight line in space. It will be understood that the term curve is usedherein in its general sense to include straight lines or series of straight line segments, or series of curved segments, whether smoothly or angularly joined.

Anothercharacteristic of reinforcing structures such as-16 which is important in eliminating the possibility of antenna beam side lobes is the characteristic of aperiodicity. In-other words, all periodic or regular meshes are to be avoided in the construction of the reinforcing structure 16. This is'necessary due to the fact that any regular mesh or set of'elements arranged in repetitive or periodic fashion tends to have one or more such sets of elements or portions of elements which are linearly arranged in space. It is inherent in the nature of propagation of scatterer elements that a regular or periodic array of such elements tends to produce scattering which is morepronounced and in phase in particular directions andthus to produce lobes in the radiation pattern.

From an examination of FIG. 1, it will be observed that the reinforcing structure 16 possesses in a high degree all of the above characteristics. The reinforcing elements 14 and 15 are not only curved but are formed in the shape of non-planar curves so that substantially every portion of each of the elements '14 and 15 is formed in acurve which has -a torsion bounded away from zero. It will further be noted, that although the holes 17 in the structure 16 are approximately of equal area (as is desirable for generally uniform reinforcing) the dimensions of these holes, and particularly the dimensions of adjacent holes, arenot similar. In fact, the dimensions of adjacent ones of the holes 17 or, in other words the spacing of adjacent scattering elements 14 and 15, is designed to be dissimilar, insofar as is consistent with the desirable feature of maintaining the hole '17 of approximately equal area. In addition to the apertures or holes 17 differing from one another it will be observed that the holes formed by the reinforcing elements 14 and 15 are individually formed generally in the shape of irregular rather than regular polygons and adjacent elements depart substantially from parallelism. Strictly speaking, the holes 17 are not polygons at all since they are bounded by curved lines.

Although the particular reinforcing structure 16, shown in FIG. 1, has all of the previously described desired characteristics in a high degree it will be appreciated that complete irregularity and nondinearity is difficult to obtain practically, and particularly when it is desired to produce the articles inexpensively and in relataively large numbers. It should be pointed out therefore that a certain amount of regularity in the reinforcing structure 16 is tolerable, but it should always be kept in mind that the regularity, periodicity and linearity of the structure 16 should be kept to a minimum.

In PEG. 2 an alternative shell-type form of radome structure 13 is shown. The radome structure 18 is formed generally in'the shape of a half cone. This'structure is relatively long and narrow and would derive substantial support from its adjacent structure along its point of attachment and the edges of the radorne structure 18. in this case, and in other circumstances, it may often be unnecessary to provide longitudinal reinforcing members in the radome structure. Radome structure 18 is therefore provided only with transverse reinforcing members 21. As in the case of FIG. 1, of course, a radiationtransparent wall 19 is provided which forms the body of the radome structure 18 where the reinforcing members Zilare attached or imbedded.

The reinforcing elements 21 generally have the characteristics of reinforcing elements 14 and 15 in FIG. 1 in that they are formed in the shape of non-planar curves. Since there are no longitudinal reinforcing elements there is no mesh as such in the embodiment of FIG. 2.. The spacing of elements in FIG. 2 is therefore defined by the average longitudinal spacing bet-ween the elements 21 rather than by the area of the holes 17 as was the case in FIG. 1. It will be noted in FIG. 2 that the spacing between elements 21 is not exactly equal but is generally of the same magnitude. It is apparent therefore that the radome structure 18 of FIG. 2 is a simplified form of the previously described structure 16 which is particularly adapted to situations where the radome is of a particular shape or in other special circumstances.

In certain radome applications the surface of the radome must necessarily form a relatively small angle with the direction of propagationo-f radio waves from the antenna. An example of such a situation is illustrated in FIG. 4 where a nose cone radome is shown such as might be utilized on supersonic airplanes or missiles. Where the surface of the radome cannot be made substantially perpendicular to the direction of propagation of the electromagnetic waves a problem arises which may he explained by reference to FIG. 3.

In FIG. 3 a fragmentary cross-section of a conical radome is shown wherein the direction of the propagation of'the electromagnetic energy is indicated by the arrow A. The angle between the axis and surface of the radome is indicated by the symbol 6 and is illustrated as 15 degrees. Assuming then, illustratively, that the reinforcing elements 20 are spaced three inches apart and are approximately three-eighths of one inch in diameter, it would appear that the ratio of opening size to element size, namely three inches to three-eighth inches, would provide a ratio of eight to one, and thus would produce very little attenuation of the signal. However, due to the fact that the direction of propagation of the electromagnetic energy is not substantially perpendicular to the radome waves but is at a relatively small angle degrees in this example) to the radome wall, the structure illustrated in FIG. 3 is, in fact, not suitable. This can be shown by taking the horizontal projection of the elements 2% on a transverse plane BB, where it will be seen that the center-to-center distance in this projection is only three-quarters of one inch. If the element diameter is assumed to be three-eighths of one inch the degree of obscuration due to the reinforcing elements 21 is increased to one-half for electromagnetic waves propagated in the direction of the radome axis as indicated by the arrow A.

The structure illustrated in FIG. 3 therefore brings out the fact that where a radome is used having a small angle between the radome surface and direction of propagation, the spacing of reinforcing elements along this direction must be greatly increased due to the increased obscuration of radiated energy of elements spaced along this direction. Fortunately, this increased spacing can be utilized without unduly weakening the reinforcing construction in most radome configurations.

In FIG. 4 for example, the conical radome requires relatively little reinforcing around its periphery and the greatest reinforcement is required longitudinally of the radome due to its long slender shape. In FIG. 4 a radome 22 of generally conical shape is shown incorporating a reinforcing structure which is generally similar in principle to the structure of FIGS. 1 and 2 but is adapted to the conical shape of the radome 22. A radome wall 23 is shown in phantom lines in FIG. 4 to reveal the details of the reinforcing structure 34). As in the case of the previous radome structure the wall 23 can be placed inside or outside the reinforcing structure 30, or

alternatively the reinforcing structure 30 can be built within the radome wall 23.

A number of generally longitudinal reinforcing elements 24 are provided which are curved so that they do not provide a linear array. Spaces 29 are formed between the elements 24, which are large compared with the size of the elements 24. Adjacent ones of the spaces 29 are preferably of unequal size. This further increases the irregularity of the reinforcing structure 3% and prevents the formation of side lobes in the antenna beam pattern. As Was the case with previous structures the spaces 29 are preferably approximately equal to one wave-length or greater. This spacing, together with the relatively large sizes of the spaces 29 compared to the elements 24, provides a structure wherein the degree of attenuation of the signal is kept to a small value.

Transverse reinforcing elements 25, 26 and 27 are provided to join the longitudinal elements 24 into a mesh-like reinforcing structure 30. As explained with reference to FIG. 3, it is desirable that the generally transverse reinforcing elements 25, 26 and 27 be spaced much further apart than are the longitudinal elements 24. The factor by which the elements 25, 26 and 27 must be increased depends upon the angle between the radome surface and the direction of wave propagation.

The transverse elements 25, 26 and 27 are also preferably formed in the shape of non-planar curves for maximum reduction of side lobe effect. As in the previous structures, however, it should be understood that the degree of reduction of side lobe depends on the overall design of the system and in many cases structures less than optimum from this standpoint can be utilized. In such a case a compromise for simplicity of construction can be made and the reinforcing elements 25, 26 and 27 can be made in the shape of simple circles.

The reinforcing structure at the radome nose 31 is not shown but it will be understood that the general configuration can be extended to a small conical tip at the end of the radome nose 31. In some cases, it may be desirable to reduce the number of longitudinally reinforcing elements 29 as the nose 31 of the radome is approached. This may readily be accomplished for example by eliminating alternate ones of the reinforcing elements 29 at the forward reinforcing element 25. A modification of the structure of FIG. 4 can be made wherein the number of longitudinal reinforcing elements 24 is also reduced in passing others of the transverse reinforcing elements such as 26 and 27.

In some cases, it may be unnecessary to carry the reinforcing structure 30 completely to the nose 31 of the radome so that the nose 31 of the radome may consist solely of the radome wall 23 without any reinforcing structure 39.

In addition to the function of reinforcements, or in place of this function, the structure 30 may be utilized as an antenna operating on a frequency lower than that of the radar antenna within the radome 22. Although the structure 3i) does not interfere with the radar propagation therefrom to any appreciable extent, it will form an antenna for somewhat lower frequency of propagation. A serious problem exists in the design of present day airplanes and missiles in providing a suitable communications antenna system without interfering with the aerodynamic integrity of the aircraft. The use of a structure such as shown in FIG. 4 provides an ideal solution to the problem in that the radome structure may be utilized as an antenna, for communications for example, thus eliminating the difiieult job of building such an antenna into the wing tip or other portion of the aircraft.

An arrangement for utilizing the structure 30 in FIG. 4 for a communications antenna is schematically illustrated. For this purpose the mounting ring 28 by which the radome 22 is secured to the aircraft body (shown in phantom lines at 32) should be formed of a non-conductive material, or alternatively should be provided with a non-conductive surface or otherwise arranged to insulate the frame of the aircraft body 32 from the radome reinforcing structure 30. It is thereafter a simple matter to connect a radio transmitter, shown in block form at 33, so that one terminal is connected to the reinforcing structure 30 by means of electrical lead 34 and terminal 35. The radio transmitter 33 would also be grounded by means of lead 36 to the frame of the aircraft body 32.

In some cases, it might be desirable to utilize a structure such as 30 for an antenna even though reinforcement of the radome 22 is not required. In such an arrangement it is possible to eliminate in part or substantially diminish the size of the elements 24, 25, 26 and 27, since they would no longer be reinforcing elements but would only be utilized as antenna elements.

The previous suggested applications for reinforced radomes has been for airborne applications. The application of reinforced radomes is by no means limited to these uses, however. FIG. 5 illustrates a ground-based radome which incorporates a reinforcing structure according to the present invention and particularly adapted to this type of radome structure. Ground-based radomes generally have a diameter of approximately 20 to 60 feet. For such structures, it is generally preferable to construct a radome at the radar site. In such cases particularly, there are obvious advantages to the use of generally linear reinforcing elements rather than to attempt to construct a radome reinforcing structure entirely of non-planar, curved elements. Although it is possible to construct a groundbased radome of non-planar curvilinear elements, a preferred ground-based radome reinforcing structure 46 is shown in FIG. 5 which utilizes primarily planar or linear elements and yet retains the major advantages of the previously illustrated structures.

The radome 42 will generally be in the shape of a portion of a sphere equal to, or somewhat greater than a hemisphere. The radome wall 42 will thus have a gen- 9 erally circular base 48. It is contemplated that the reinforcing structure 46 will therefore provide all, or nearly all, of the structural strength of the radome so that the radome wall 23 may be formed of cloth or film such as Dacron, nylon or the like and simply placed over and secured to the reinforcing structure 46. Such a structure will provide obvious advantages-over air-inflated radome structures or rigid fiberglass laminate'radome structures, particularly in the'case where it is necessary to remove the wall or-cover, as for portability; By theuse of the reinforced radome of FIG. the radome cover 43 may be replaced in temperate weather without any disruption of the radar system operation.

The reinforcing structure 46 is formed of approximately horizontal elements 44 and approximately. vertical elements 45. These elements are arranged to form a meshlike structure having openings 47. The openings 47 generally have the same characteristics as the openings of the previously described reinforcing structures. That is, the size of the opening is approximately equal to one wave-length or larger and the dimensions of adjacent openings 47 are preferably unequal to provide an irregularspacing of the elements 44 and45'.

In the radome 42 a compromise is provided with respect to the non-linear and non-planar characteristics of the reinforcing elements. Offsets 49 are formed at the junction of vertical and horizontal reinforcing elements and elsewhere in the structure so that virtually no reinforcing element 44 or 45 is linear for a distance greater than approximately one wave-length. This configuration retains the primary advantages .of'the previously described non-linear structures for the most part and provides a further practical advantage of allowing the use of linear elements in the construction of the radome 42.

As in the previous structures the size of the reinforcing elements 44 and 45 compared wtih the size of the openings 47 will be proportioned to obtain the desired compromise between structural strength and electrical properties. The transverse dimension of the reinforcing elements 44 and 45 will generally not exceed to 30% of element spacing. Since the surface of the radome 42 is generally transverse to the direction of propagation of Waves therefrom the problem of increasing spacing dis cussed in connection with FIGS. 3 and 4 does not arise From the foregoing explanation it will be observed that a radome structure has been provided which acquires a substantial portion of its structural strength from a re inforcing structure, which is of such a configuration that attenuation and side lobe effects due to the reinforcing structure will be within limits of toleration. Furthermore, such a structure, if formed of a conductive ma terial, can be utilized as an antenna structure in addition to, or instead of, a reinforcing structure.

Certain variations and modifications of the illustrated embodiments have been suggested in the foregoing description. However, many modifications can be made to the suggested embodiments by those skilled in the art without departing from the spirit of the present invention. The scope of the present invention is therefore not to be construed to be limited to the embodiments shown and suggested but is to be limited solely by the appended claims.

What is claimed is:

1. A combined radome and antenna structure comprising a radome wall, a network of elongated conductive elements of small cross section compared to their spacing united with said Wall, said elements being substantially aperiodically spaced with minimum spacing of not less than approximately one Wavelength at the minimum operating frequency of the radome, each of said elements being shaped so that no portion thereof of greater length than approximately one wavelength at the maximum operating frequency of the radome is in the form of a continuous planar curve, and means for electrically 1'0- connecting radio frequency electrical signal means to said conductive elements.

2. A combined radome and antenna structure comprising a radome wall, an arrangement of elongated conductive elements united with said wall, said elements being substantially aperiodically spaced withminimum spacing of not less than approximately one wavelength :at the minimum operating frequency of the radome, eachof said elements being'shaped so that no portion thereof of greater length than approximately one wavelength-at the maximum operating frequency of the radome is linear and continuous, and means for electrically connecting radio frequency electrical signal utilizationmeans to said conductive elements.

3. A combined radone and'antenna structure comprising a radome wall, an arrangement of elongated conductive elements united with said Wall, and means for electrically connecting radio frequency electrical signal utilization means to said conductive elements.

4. A radome reinforcing structure for a radome for radar or similar apparatus having a predetermined range of operating frequencies, said structure comprising a network of conductive elongated reinforcing elements spaced aperiodically to form interstices having a dimension ofat least approximately one wavelength at the minimumoperating frequency of said apparatus, said elements having a relatively small cross section compared to the aperture diameter of the antenna, each of said elements being formed in the shape of a curve with torsion unequal to zero at substantially all points along its length.

5. A combined radome and antenna structure comprising a radome wall, an arrangement of elongated conductive elements united with said wall, said elements being spaced with minimum spacing of not less than approximately one vvavelength at the minimum operating frequency of the radome, and means for electrically connecting a radio receiver or transmitter means to said conductive elements.

6. A radome reinforcing structure for a radome for radar or similar apparatus having a predetermined range of operating frequencies, said structure comprising an array of conductive elongated reinforcing elements formed of electromagnetic radiation-scattering material spaced at least approximately one wavelength apart at the minimum operating frequency of said apparatus, each of said elements having no portion which is linear and continuous for more than one Wavelength of the maximum operating frequency of said apparatus.

7. A radome reinforcing structure for a radome for radar or similar apparatus having a predetermined range of operating frequencies, said structure comprising a network of conductive elongated reinforcing elements spaced aperiodically to form interstices having a dimension of at least approximately one wavelengthat the minimum operating frequency of said apparatus.

8. A radome reinforcing structure for a radome for radar or similar apparatus having a predetermined range of operating frequencies, said structure comprising an array of conductive elongated reinforcing elements spaced aperiodically at least approximately one wavelength apart at the minimum operating frequency of said apparatus.

9. A combined radome and antenna structure comprisutilization ing a radome wall, an arrangement of elongated conductive elementsunited with said wall, each of said elements being shaped so that no portion thereof of greater length than approximately one wavelength at the maximum oeprating frequency of the radome is continuously linear, and means for electrically connecting radio frequency electrical signal utilization means to said conductive elements.

10. A radome reinforcing structure for a radome for radar or similar apparatus having a predetermined range of operating frequencies, said structure comprising an arrangement of elongated reinforcing elements, each of said 1 1 elements being formed of electromagnetic radiation-scattering material and shaped so that no portion thereof of greater length than approximately one wavelength at the maximum operating frequency of said apparatus is in the form of a continuous planar curve.

11. A radome reinforcing structure for a radome for radar or similar apparatus having a predetermined range of operating frequencies, said structure comprising an irregular arrangement of elongated reinforcing elements, each of said elements being formed of electromagnetic radiation-scattering material and having no portion which is linear and continuous for more than one wavelength of the maximum operating frequency of said apparatus.

12. A combined radome and antenna structure comprising a radome wall, an arrangement of elongated conductive elements united with said Wall, said elements being substantially aperiodically spaced, and means for electrically connecting radio frequency electrical signal utilization means to said conductive elements.

13. A radome reinforcing structure for a radome for radar or similar apparatus having a predetermined range of operating frequencies, said structure comprising an irregular arrangement of elongated reinforcing elements formed of electromagnetic radiation-scattering material with substantially aperiodic spacing, each of said elements having no portion which is linear and continuous for more than one wavelength of the maximum operating frequency of said apparatus.

14. A radome structure comprising an irregular arrangement of elongated reinforcing elements formed of electromagnetic radiation-scattering material with substantially aperiodic spacing, said elements defining a plurality of spaces of irregular form, whereby the scattering of radio frequency energy from said reinforcing elements will be sufliciently random to avoid the formation of side lobes in the pattern of a directional antenna associated with the radome.

15. A radome comprising an array of conductive elongated reinforcing elements spaced at least approximately one Wavelength apart at the minimum operating frequency of the radome, each of said elements having no portion which is linear and continuous for more than one wavelength of the maximum operating frequency of the radome and a radio frequency radiation transparent wall united with said array.

16. A radome comprising an array of conductive elongated reinforcing elements spaced aperiodically at least approximately one wavelength apart at the minimum operating frequency of the radome and a radio frequency radiation transparent wall united with said array.

References Cited in the file of this patent UNITED STATES PATENTS 2,160,047 Wiggins May 30, 1939 2,607,009 Atfel Aug. 12, 1952 2,712,604 Thomas et al July 5, 1955 OTHER REFERENCES IRE Convention Record, 1956, Part 1, vol. 4, page 237, March 22, 1956.

Analysis of the Electrical Characteristics of Structurally Supported Radomes, Dept. of Electrical Eng, Ohio State Univ. Research Foundation, Columbus 10, Ohio, Nov. 15, 1958, pp. 1-90 (only pp. 56, 62, 77, 78, and 89 relied on).

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