US3383444A - Method of constructing radome - Google Patents

Description

15 m Z BESS fifizfiimima; aux mm y 1968 D. L. LOYET- 3,383,444

METHOD OF CONSTRUCTING RADOME Filed Sept. 15, 1965 2 Sheets-Sheet 1 INVENTOR. DONALD L. LOYET y 14, 1968 D. L. LOYET 3,381.3;444

METHOD OF CONSTRUCTING RADOME Filed Sept. 15, 1965 2 Sheets-Sheet 2 Fig. .9

INVENTOR. DONALD L. LOYET Fig. 7 BY CCCMZEWAGENT r0 NEY United States Patent Gfice 3,383,444 METHOD OF CONSTRUC'HNG RADOME Donald L. Loyet, Palos V'erdes Peninsula, Califl, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Sept. '15, 1965, Ser. No. 487,642

r 2 Claims. (Cl. 264-87) ABSTRACT OF THE DISCLOSURE A high-strength low-weight radome of high radar transparency and method of making same, which method includes filling a radome-shaped mold with slip material, applying pressure to the mold contents, and then removing excess slip material to leave a thin-wall hollow core in the form of a radome. By repeating the process with slip material of different electrical characteristics, the microwave attenuation characteristics of the radome may be varied.

This invention relates to the method of constructing dielectric walls for the transmission of microwave or centimetric electromagnetic radiation. It is particularly directed to radomes for guided missiles and the like.

The many interrelated factors which make up a satisfactory radome construction require a balanced design which is adapted to the environment and the type of signal to be transmitted. Thus an airborne radome must be strong, light, vibration resistant, corrosion resistant, smoothly contoured, resistant to thermal shock, resistant to rain, weathertight and must be fabricated by a process which is simple, does not require grinding or other ma-- chining operations and permits great reproducibility time after time within acceptable dimensional limits. Of course in addition it must permit maximum transmission of radiated waves therethrough with minimum distortion and degradation. 1

Heretofore many diiferent types and shapes of micro= wave transparent wall constructions have been proposed. When used on missiles these may be provided various shapes such as ogival, conical, the Von Kar-man and Newtonian, all of which have their advantages.

When a radome is formed of ceramic material it has been customary in the past to use a thin-wall radome or a one-half wavelength thick radome as the basis of the ra dome design. However, recently much effort has been given to the construction of ceramic sandwich radomes which transmit electromagnetic radiation of greater electrical bandwidth and are of less weight. Furthermore, diamond grinding of radome surfaces is avoided.

Of course, airborne radomes must not only protect the contents of the missile head, but must be weatherproof and of sufiicient strength to resist missile vibration and bending moments, the latter being greatest at the joint where the radome is secured to the missile body. In some constructions a middle layer of a foam or a honeycomb of plastic material is located betwen two outer walls of thin skins of higher dielectric constant, however this meth= d of gaining physical strength usually results in loss of desired electrical characteristics.

Accordingly it is one object of the present invention to provide a method of constructing a radome which alfords a minimum interference to the transmittal of high frequency signals but has sufiicient strength to resist normal vibrations, bending moments and the impact of rain.

A further object is to provide a method of constructing radomes which is simple, quick, inexpensive and practical and wherein successive parts made thereby are uniform in dimension and in microwave transmission characteris= tics.

3,383,444 Patented May 14, 1968 Additional objects and many of the attendant advantages of this invention will be readily apparent as the same becomes better understood by the reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a vertical sectional view through a mold construction for manufacturing the device of the present invention;

FIG. 2 is a view similar to FIG. 1 showing the step of applying fluid pressure to the mold contents;

FIG. 3 shows the mold tilted to permit excess slip to be poured therefrom leaving a thin coating on the mold faces;

FIG. 4 discloses an additional step wherein a small amount of slip is reinserted into the mold to form a solid radome tip;

FIG. 5 is a vertical section through a radome constructed in accordance with .the process illustrated in FIGS. 1-4;

FIG. 6 is a view similar to FIG. 5 showing a sealing ring closing the space between radome shell walls;

FIG. 7 isan enlarged vertical cross-sectional view taken on a line substantially corresponding to line 7-7 of FIG. 6;

FIG. 8 is a view similar to FIG. 7 showing one means for securing a radome in place; and

FIG. 9 is a view showing an alternate form of radome wherein several layers of material are built up.

Referring now to the drawings wherein like reference characters designate like or corresponding parts throughout the several views, there are illustrated in FIGS. 1 through 4 the steps employed to form a radome embodying the characteristics of the present invention. Throughout this description the steps will be discussed as performed to mold a double thin-wall'radome of the general shape illustrated in FIG. 5. It will be apparent however, that the ultimate radome shape depends upon many design considerations and that other shapes within the spirit of the present invention may readily be molded bythis method. I

As shown in FIG. 1 there is provided a lower mold half 10 and an upper mold half 11 which may be formed from any suitable absorbent material such as plaster of Paris. These mold members when fitted together provide a space therebetween of the desired shape and characteristics. In making the molds, due allowance is made for shrink so that molded parts are properly dimensioned upon completion aril no further grinding or machining is required.

As shown, there may be provided an inlet 12 at the upper left hand corner of the mold through which a suitable liquid called slip may be introduced intojt he mold interior. This slip may be in the form of a vehicle having finely dispersed ceramic particles throughout. The mold is filled until liquid slip emerges from the mold through port 13.

A portion of the liquid vehicle of the slip thereof is absorbed into the plaster of paris leaving the finely dispersed ceramic material in a layer along both surfaces of the mold.

The next step is shown in FIG. 2 where the exit 13 is shown obstructed by a plug 14 and at this step pressure is applied to the mold contents preferably through inlet 12. After the parts have been permitted to set so as to allow a build up of the desired wall thickness on bothmold surfaces the pressure is released, exit 13 is unblocked and When the tip has set the upper mold half 11 can be removed so that the cast radome may be lifted out of the lower mold half. The result is a radome of the character illustrated in FIG. wherein an inner wall 15 and a Spaced outer wall 16 are interconnected at their tips by a slug 17 of solidified casting material. This slip serves not only to provide strength at the critical tip area of the radome but also, being of the same homogeneous material as the inner and outer walls 15 and 16, provides minimum interference with the high frequency radiations being transmitted therethrough.

The composition of the slip or slurry may vary from radome to radome and also from one sandwich layer to another. Examples of suitable slip material are ceramic based materials, plastic and alumina. When desired small beads of plastic or microspheres may be added to the slip material. This addition has been found to improve resistance to the effect of rain drops on the radome.

In order to complete the radome an annular spacer of ceramic material 18 may be placed between the open ends of walls 15 and 16 of the radome. This spacer ring may be cemented in place by a portion of the slip material from which the radome is made and materially strengthens this critical area. In FIG. 7 there is provided a greatly enlarged view of the after portion 20 of a radome with the collar in place and in FIG. 8 there is shown the manner in which the rear edge 21 of the radome may be received in a ledge 22 formed in the mating forward end 24 of the missile body.

In the foregoing there has been described the manner of manufacturing a double thin-wall radome having a homogeneous tip portion for added strength. It will readily be apparent however that the present process can also be applied to other forms of radome construction. For example, to produce a sandwich type wall the initial step may be repeated twice, each time with different material and perhaps a different upper mold half 11 and, if desired, the remaining central space may be filled with other material. By this means a sandwich type radome wall corresponding to that illustrated in FIG. 9 is provided. There the two outer thin-wall halfwave sections A are reinforced by inwardly located additional thin walls B and a central core C of suitable material will complete the sandwich layers.

Numerous variations of this technique may be employed whereby a ceramic radome with a homogeneous tip may be constructed and, by variations in the material being used, desired electrical characteristics may be selected. If desired, suitable apertures, not shown, may be provided in the wall of the radome to equalize pressures between the inside and outside surfaces. It will be apparent that a radome produced by the above described process has a number of desirable characteristics. It is relatively light in weight, has low interference with electrical transmission therethrough, has a reinforced nose portion for strength against rain and ice, has a reinforced missile contacting skirt which provides maximum resistance to bending moment, and yet allows differential expansion at this point of contact with the missile. Furthermore the radome is made of materials which are readily available and can readily be fabricated in the manner described to provide good reproducibility item after item, thus uniformity of product is assured. It is furthermore low in cost and the resulting radome does not require machining, grinding or other working prior to use.

As is understood in the art, strength may be provided by a solid radome wall and a sandwich type construction thereof has greater resistance to thermoshock. However, the double thin walls illustrated provide the best transmission of electrical characteristics, and, when formed of homogeneous material and strengthened in the manner described provide an excellent radome for hypersonic missiles. This is particularly true when frequencies above the X-band and approaching the K-band are involved.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described,

1 claim.

1. The method of forming a strong, light-weight radome with low attenuation effects on microwave energy passed therethrough comprising;

(a) filling upper and lower mold portions which define a desired radome shape with a castable slip mate rial;

(b) applying pressure to the contents of said mold;

( c) removing excess slip material to leave a thin Wall adjacent each mold surface; and

(d) repeating steps (a), (b) and (c) with slip material of different electrical characteristics to form additional thin walls of differing electrical characteristics.

2. The method of claim 1 including the final step of applying a central core of such slip material to form a sandwich type radome.

References Cited UNITED STATES PATENTS 1,693,429 11/1928 Austin 26487 X 1,733,729 10/1929 Gouverneur et a1, ....H 264-86 3,195,138 7/1965 Beck 343 -872 3,292,544 12/1966 Caldwell et a].

OTHER REFERENCES Ceramic Age, Fused Silica for Missile Components, August 1960, vol. 76, No. 2, pp. 3238.

Ceramic Age. Fused Silica for Missile Components, September 1960. vol. 76, No. 3, pp. 23-28.

ROBERT F. WHITE, Primary Exatmflterv 'i. H. SILBAUGH, Assistant Examiner.

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