US2465416A - Resonant circuit and radiator - Google Patents

Description

March 29, 1949. N. w. ARAM RESONANT cmcun AND RADIATOR 5 Sheets'-Shet 1 Filed Oct. 2, 1945 NUUDOQ INVENTOR. NATHAN W ARAM HIS ATTORNEY March 29, 1949. N, ARA 2,465,416

' RESONANT CIRCUIT AND RADIATOR Filed Oct. 2, 1945 5 Sheets-Sheet 2 SOURCE OF P Tf/VT/fl BEAT FREQUENCY UTILIZATION CIRCUIT FIG. 8

INVENTOR. NATHAN W ARAM HIS ATTORNEY March 29, 1949.

Filed 001;. 2, 1945 N. w. ARAM RESONANT CIRCUIT AND RADIATOR 5 Sheets-Sheet 3 FIG. l2

FIG. ll

INVENTOR NATHAN w. ARAM HIS ATTORNEY March 29, 1949. N. w. ARA 2,465,416

I RESONANT CIRCUIT AND RADIATOR Filed 001:. 2, 1945 5 Sheets-Sheet 4 INVENTOR NATHAN -w. ARAM SOURCE QF W'M' @2561; HIS ATTORNEY March 29, 1949. N. w. ARAM 2,465,416

RESONANT CIRCUIT AND RADI ATOR I Filed Oct. 2, 1945 5 Sheets-Sheet 5 FIG. 15

INVENTOR NATHAN W. ARAM WMQ h w HIS ATTORNEY Patented Mar. 29 1949 UNITED STATS ATENT OFFlCE Nathan W. Aram, Chicago, Ill., assignor to Zenith Radio Corporation, a corporation of Illinois Application October 2, 1943, Serial No. 504,717

6 Claims. 1

This invention relates to electric translating systems and more particularly to such systems which include a resonant cavity.

High frequency radio signals, Whose wave length is of the order of five meters or less, may be conveniently translated through resonant cavities. Any suitable cavity havin conductive boundaries is space resonant. Such cavities are usually made cylindrical. toroidal or rectangular and are usually resonantin complex modes and at many frequencies.

It is an object of my invention to provide a new and improved electric translating system comprising a cavity resonant in a simple mode, that is, one in which resonance of a single type is established in a harmonic series of frequencies. In this type of cavity, the resonant frequency is a linear function of wavelength. the larger the cavity, the greater is the wavelength.

It is also an object of my invention to provide a new and improved electric translating system which is space resonant in such a way that a reenforcement of energy substantially at a focal. point within the space is produced,

It is a corollary object of my invention to plO- vide such a new and improved electric translating system in which external circuits may be coupled to the system at such a focal point.

Still another object of my invention is to provide such a new and improved energy radiator which radiates energy into space in desired directions.

It is a further object of my invention to provide a new and improved resonant cavity electric translating device which may be readily designed with simple parameters so that, upon construction. it is resonant at a predetermined frequency, and its resonance is substantially of a single type in a harmonic series of frequencies.

It is an additional object of my invention to provide a new and improved space resonant translating device especially suitable for excitation by a wide variety of exciting means.

It is still another object of my invention to provide a new and improved form of spaceresonant cavity having an input and an output and one capable of providing highly efficient filtering action between such input and output.

The features of my invention which I believe to be novel, are set forth with particularity in the appended claims. My invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

Figure 1 illustrates one embodiment of my in vention;

Figure 2 illustrates schematically a principle of operation of my invention;

Figures 3 through 9 illustrate alternative embodiments of my invention;

Figure 10 illustrates schematically a principle of operation of the embodiment of Figure 9;

Figures 11 through 15 illustrate still other embodiments of my invention; and

Figure 16 illustrates certain characteristics of an embodiment of Figure 15.

In Fig. 1 a space-resonant cavity is formed by a pair of conductive confocal paraboloidal shells l3 and H with their concave sides facing each other. The two shells l0 and H are clamped together at their edges by rings l2 and is held together by bolts i l. The depth of each of the paraboloidal shells ill and H, measured from a plane passing between the two shells perpendicular to their common axis to the deepest point of each shell, is equal to the focal distance of the paraboloid defining the shell. That is, the focus of each one of the paraboloidal shells H) and H coincides with the focus of the other shell.

Energy is transferred from a suitable source into the cavity bounded by the paraboloidal shells to and it through a coaxial transmission line includin an inner conductor and an outer cylindrical concentric conductor 16, the terminals of the source [5 being connected to the inner and outer conductors. The coaxial line including the inner conductor and outer conductor 56 is terminated by a small loop H at the common focus of the two paraboloidal shells H] and H, said inner and outer conductors each being connected to opposite terminals of loop l1.

Energy may be abstracted from the space bounded by the shells to and l l, through a second coaxial transmission line including an inner conductor l8 and an outer conductor l9, terminated at any point within the shell by a small loop 20.

In Fig. 2 there is illustrated graphically the manner in which space resonance in a simple mode is produced between the two paraboloidal shells H3 and H, these shells being identical With those illustrated in Figure l and being given like reference characters. The point 2 l, which is the confocal point at which the loop ll of Figure 1 is placed, is the focus for each of the parabolas H3 and i i. It is a property of a parabola that a line drawn from its focus to any point along the parabola intersects the parabola at the same angle as the parabola is cut at the same point by another line parallel to the axis of the parabola.

A ray 22 of energy is illustrated in Figure 2 proceeding from the focal point 2! to impinge upon parabola H0 at a point 23. By Well known laws of reflection this ray 22 is reflected at the point 23 from parabola ill in a direction illustrated by line 24 parallel to the axis of parabola ill; the angle 25 of incidence and the angle 26 of reflection 'being equal.

The two axes of the two parabolas l0 and I I, as

pointed out previously in connection with the paraboloidal shells i8 and i l of Figure 1, are common to each other so that the ray 24 is parallel not only to the axis of the parabola it but also to the axis of the parabola ll. Since the axes and focal points 2i of the parabolas It and II coincide, the ray 24, when it strikes parabola l I, is reflected as a ray 2'5 toward the focal point 2|, the angle 23 of incidence and angle 29 of reflection being equal.

This process of double reflection and return to the focus takes place for any energy ray emitted from the focus H. A ray 3% emitted from the focus 2| in a different direction from the ray 22 is reflected from parabola it as a ray 3% parallel to the axes of the parabolas it and H and is reflected from parabola H as a ray 32, which passes through the focus 2!. No matter in what direction a ray is emitted from the focus 2 5, after being reflected from each of the parabolas l G and H in succession, it returns to the focus 2 i.

The length of path traveled by a ray of energy emitted in any direction from the focus 2i is always the same when it first returns to the focus 2|. That is, the length of path traveled by a ray of energy following lines 22, 2d and El in a single circuit from the focus 2! and back to the focus 2! is the same as the length of path traveled by a ray of energy in a single circuit along the lines 30, 3| and 32.

It may be proved mathematically that such paths, from focus 2! through a reflection from each of the p'arabolas Id and i I back to the focus 2|, are always of the same length. If it be assumed that the parabola iii be defined by the equation:

y =4ax (1) then the focus 2i is at a distance a from the point on parabola Ill at which it is cut by its axis. The perpendicular distance from any oint :2, y, on parabola iii to a line through focus 2i perpendicular to the axis of the parabola id is or, expressed in terms of y,

The distance from focus 2! to the point x, y (the coordinates of point 2! being a, is

or expressed in terms of y:

t o-e The sum of these two distances expressed by Equations 3 and 5, from the point a, 0 to point 3:, y, and from point :r, y to a line through a, 0, perpendicular to the axis of parabola Ill is:

the axis of parabola It may be simplified, and is then found to be:

This mathematical analysis indicates that the distance along path 22 and half of the length of line 24 is equal to 2a, or that the distance along paths 22, 24 and 27 is equal to 4a. In other words, a ray of energy emitted from focus 2| in any direction travels away from focus 2|, is reflected once from each of the parabolas Ill and il, and returns to focus 2| in phase after having traveled a distance equal to twice the distance between the parabolas i9 and H measured along their common axis. Therefore, all rays travel from focus 2! and are reflected once from parabola H3 and once from parabola H, and return to focus 2| in phase.

The small loop I! is effective in transferring energy between the end of transmission line I6 and the space surrounding loop ll through the magnetic component of electromagnetic radiation in the vicinity of loop IT. A dipole may be substituted for loop I! so that energy is transferred through the electric component of the radiation near the dipole.

For any particular size of parabolas I0 and II and with loop IT or with the substituted dipole, resonance occurs at a harmonic series of frequencies uniquely determined by the reflection path length. When such a resonant condition exists, it is called resonance of a single type.

The loop I! is made as small as possible with respect to the dimensions of the cavity enclosed by shells l0 and N. This is preferable in order that energy radiated from loop ll shall appear to come as nearly from a point source as is possible. Since the loop i"! must necessarily have finite size, energy of frequencies within a finite band of frequencies centered about a mean fre-- quency determined by the ideal point source resonator produces resonance within the space bounded by shells iii and H. This finite band of frequencies has a width measured in frequency which width is a function of the size of loop i! with respect to the size of the space bounded by shells It and ii. That is, as loop I? is made smaller, the finite band of frequencies within which resonance occurs is smaller.

In order to make the relative size of loop H small, so as to obtain a cavity bounded by shells It and H resonant at a very narrow range of frequency, it may be desirable to make that space fundamentally resonant at a much lower frequency which frequency is a sub-harmonic of the desired frequency. It may be desirable to make line 96 an integral number of half waves in length, in order that impedance of the line I 6 shall not substantially affect the resonant frequency of the space bounded by shells it and H,

The phenomenon of space resonance by alternate concentration and dispersion of oscillatory energy from a focal point in a space may be utilined in several very useful ways. In Fig. 3 a pair of paraboloidal shells at and ii have their concave sides facing each other and are spaced apart with their deepest points, measured along their common axis, at a distance apart equal to twice the focal distance of either one of the paraboloidal shells 41s or :3 l The two shells are identical and their focal distances are correspondingly identical. These two shells it and H are identical with shells i9 and i l of Fig. 3. except that they do not meet at their rims, so that a 32 is left open all of the way around the two shells it and i i. Proper spacing between the two shells it and 31 is maintained by supporting members :23, which are preferably formed of such material and so spaced that they provide minimum interference with energy radiated from within the shells it] and 45 to external space.

Radiation of such energy from within the shellsdi! and ll to external space is M d M indicated by ar rows an a.

Oscillatory energy at a frequency such that space resonance is produced within the shells 46 and M is transferred from a generator, not shown, to the common focus of the shells Gil and 4! through a coaxial transmission line including an external cylindrical conductor l5, and a concentric inner conductor M. This transmission line comprising conductors 46 and El is terminated at the focus of the shells ill and H in a short dipole d8, of which one arm is connected to inner conductor ll and the other arm to the outer conductor 46. The length of the arms of dipole 48 may, but need not, be an integral fractional part or multiple of the wave length of the energy radiated into shells 50 and 4!.

Space resonance is produced between the shells 40 and ll by reason of the fact that energy radiated from dipole 48 in directions intercepting either of the shells ii) and M is reflected once from each of the shells ail and Ill and returned to dipole =28. Radiation from between the shells All and 4! passes out through the gap 22, not only by reason of radiation of energy directly from the dipole 48 but also by reason of energy reflected back to dipole .8 from shells it and M, such reflected energy being thereafter radiated by the dipole 48 through gap 42.

Energy thus radiated from the gap (l2 between the shells i-ll and ll is concentrated in directions from the dipole 58 through the gap 12. If the gap 42 be mad quite small, this concentration of energy can be made great. With the structure shown, in which the gap 12 extends completely around the shells 45 and ll, energy is radiated substantially in a plane. If one of the shells (ill or H be cut off more than the other shell, so that the gap 62 faces up or down, energy is correspondingly radiated in such upward or downward direction.

Paraboloidal shells, such as shells Hi and ii in Figure l, or shells 45 and ii in Figure 3, are separated by twice their focal distance measured along their common axis, since they must have a common focus, and, as explained above, this separation bears a direct relation to the resonant frequency of the space enclosed by the shells, so that the configuration of the paraboloidal shells, which is related to their focal distance, bears a definite relationship to the resonant frequency of the space enclosed thereby. It has been found in practice, however, that it is not difficult to shape such paraboloidal shells and space them apart a proper distance so as to be resonant at a desired frequency.

The necessary dimensional accuracy to which shells if} and H must conform is greater as the resonant frequency approaches more closely a single desired frequency as distinct from a band of frequencies. Some mechanical distortion of of one or both shells it and H may be effected to alter over a narrow range the resonant frequency of the space bounded by those shells.

Th dipole 48 shown in Figure 3 should have an overall length which is a very small part of a Wave length in order that it shall appear substantially as a point source of radiant energy within the space bounded by shells ill and ll. The mechanism of such radiation is similar to that explained in connection with the loop ii in Figure 1.

It is desirable that the surge impedance of the transmission line comprising conductors it and 4'! be substantially matched to the impedance of dipole 43 coupled to the space bounded by shells 40 and 41.

As with the loop H, the smaller the dipole 48" with the devices of Figures 1 and 3. The edges ofshells 5ft and 5% are joined at all points except for a small opening 52 at one point along the perimeter. Oscillatory energy represented by arrow 53 escapes in substantially a single direction through this opening 52. The device in this form ierefore affords transmission of oscillatory en-- orgy in a highly concentrated beam.

Two truncated cones 55 and 55 provide excitation for the space within shells 53 and 5|. Both cones are truncated near their apices, and have the truncated portions facing each other with the base portions centrally affixed respectively in shells 5b and 59. The common axis of the two cones 5t and 55 coincides with the common axis of the shells 5ft and 5E. The cone 55 may desirably be made hollow, but is entirely closed Within th shell 56. The cone 55 is hollow and the truncated end affords an opening 56 adjacent the closed truncated end of the cone 5 3.

Shells 50 and 5 I, as well as cones 54 and 55, are made of reflecting material so that they bound the space which is enclosed by them. They may, for example, be made of conducting material, such as metal, or of material having a high dielectric constant. A wave guide or conductive pipe 5'! is connected with the base portion of the cone 55, where it is joined to the shell 5|, and oscillatory energy within the wave guide 51 is transferred through the cone 55 and out through opening 56 into the space enclosed by shells 50 and 5d. The radiator, or cone 55, which narrows down to the small opening 55, provides that oscillatory energy from the wave guide 51 is radiated within the space enclosed by shells 50 and 51 substantially only at the common focus of the shells 55 and 5E.

The size of the opening 55 is, as stated, small with respect to the size of shells 59 and 5!, but it is also sufliciently large with respect to the wave length of the wave passing therethrough so that undesirably large attenuation does not occur. Similarly, the size of the wave guide or pipe 57 is sufficiently large with respect to the wave length of the wave transmitted therethrough that attenuation of the wave in passing through the pipe is not intolerably large.

When energy is transferred between pipe 51 and the space bounded by shells 50 and 5|, resonance of a single type occurs, as previously explained in connection with the previous forms of the invention.

In Figure 5 certain parts of the arrangement are similar to parts of the arrangement shown in Figure 4, and have like reference numerals. A somewhat different form of excitation is provided, the structure in Figure 4 being excited through a wave guide while the structure in Figure 5 is excited from a spark or are gap. In Figure 5 the spark or arc gap is formed by a pair of cones 60 and t l, whose apices are rounded, the cones being placed with their rounded apices adjacent so that, upon the application of suitably high potentials between the cones B0 and 6!, sparks or arcs pass therebetween. Any space current flow may be induced between cones 60 and BI so long as there are high frequency com- 1 ponents of that current of frequency comparable tothe fundamental frequency of the resonant cavity formed by shells i! and 55.

The cones 69 and 6! are preferably formed of a metal, such as copper, aluminum or silver, having low resistance to the flow of heat. Each cone is preferably solid and is integrally formed with a conductor of substantial cross-section. Conductor 62 is joined with cone 5t and conductor 63 is joined with cone 5 8. The conductors 52 and 63 each have a set of flanges or fins numbered respectively 64 and st, for the better dissipation of heat flowing from the cone out through the conductor.

Each cone is insulated from the conductive shells 50 and 5! by an insulating support. That is, cone 6!) is fastened to a hollow truncated conical section 65 by a truncated conical insulating portion 51, the conical section 66 being joined at its base to the shell 59. Similarly, the cone BI is joined to a conical section as by a conical piece of insulation 6%, the conical section 68 being joined to the shell 5i at its base.

Since the insulating sections t'l and ts isolate the shells 50 and 5! from the cones 8t and 6 l, the shells may be grounded and suitable high potentials may be applied to conductors t2 and 63 for the formation of sparks or arcs between cones 60 and 6|. When sparks or arcs containing energy of certain wavelengths are so formed, such high frequency energy is radiated from between the two cones 60 and ti into the space bounded by the shells 50 and 5|, so that energy of those certain wavelengths comparable to the physical size and configuration of the shells 5t and ti is selectively radiated through the hole 52, as illustrated by the arrow 53.

All forms of the invention illustrated in Figures 1 through 5 have been constructed of that conic section termed a parabola, and are formed of circular paraboloi-dal surfaces. Other conic sections may be utilized to form surfaces of revolution bounding a space which is resonant in a manner useful in practicing my invention. In fact, other conicoids or second degree tridimensional surfaces may be used, such as confocal hollow conicoids.

'In Figure 6, a hollow sphere it, with a small loop H at its center fed by a coaxial transmission line including outer conductor l2 and inner conductor 13 encloses a space resonant in a single mode when excited by energy of a certain frequency transmitted through the line into that space. Energy transmitted through the line to the loop "H and radiated within the sphere i0 is reflected from the surface of the sphere 10 directly back to the loop H.

If it be desired that the hollow spheroid to, loop H, and transmission line including conductors 12 and 13 act as a two-terminal resonant net-work of Very sharp resonance, the loop H should be as small as possible in comparison with the dimensions of the sphere iii in order that the loop shall appear as a point source. On the other hand, if it be desired that the spheroid 10, loop H, and the line act as a two-terminal band pass filter, the loop H may be made larger to obtain the desired band pass characteristics or the shell in be made a distorted spheroid. In fact, in all modifications of my invention, the exciting source within the resonant space may be made of such dimension with respect to the dimensions of that space so as to cause the space to act as a band pass filter of desired band pass characteristics.

'If desired energy may be extracted from the space bounded by shell lit by providing a loop ex tending into that space as shown for example by loop 28 in Fig. 1.

If it be desired, a dipole may be substituted for the loop H. The dipole is connected to its line in the same manner as dipole 48 in Fig. 3 is connected to lines 46, ii.

In Fig. 7 another method of excitation is shown for a structure similar in certain respects to the structures illustrated in Figures 1 through 5. A pair of:v paraboloidal conducting shells 8d and M are arranged with their concavities facing each other and with common focal points. shells 8D and 8| are completely reflecting except in two opposite directions where openings are left for the egress of radiation. These openings are sealed hermetically respectively by covers 62 and 83, which are made of a material substantially transparent to the desired radiation and which may be formed in such a lens shape that radiation tends to pass from the space bounded by the shells 8B and Si in substantially parallel lines, as indicated by the dotted lines tit and 85.

Means is provided at the common focal point of the two shells and for creating corona of high intensity in the region of that common focal point. As illustrated, two conducting members tit and 87 are placed close to the common focal point on either side of it with a gap 88 therebetween within which the corona may be formed when suitable ionizing potential is impressed between the conducting members 36 and 87. Means including a suitable source of potention 89 and conductors 90, passing respectively to the two conducting members 86 and 6? through a shield 91, are provided for the purpose of impressing suitable ionizing potential between the members 36 and 31. The shield s: is so arranged internally as to provide a hermetic seal through which the conductors 9t pass, so that the space bounded by the shells at and iii is sealed hermetically.

An atmosphere is provided in the space between the shells 8B and 35 of such nature and at such pressure that the potential supplied from source 89 between arms 86 and 3? produces corona of a desired intensity in the gap 88. The formation of corona is attended by the production of high frequency potentials of substantial intensity. Such high frequency corona potentials existing between the members 86 and iii are accompanied by radiation of energy over a wide band of frequencies in the space bounded by shells 3d and 8!, which radiation includes a particular frequency, of which the corresponding wavelength is comparable as has been heretofore explained in connection with the structures illustrated in Figs. 1 through 5 to the dimensions of the space bounded between shells 8i and iii. Energy of such fre-- quency by direct paths and reflected paths passes out through lenses 8?. and 83 as beams. By suitable choice of the character of the gaseous atmosphere filling the space between shells 8t and 3| and by suitable correlation of the pressure of that atmosphere with the potential supplied from source 89, the intensit of the potential supplied from source 89, the intensity of the radiation coming through lenses Bland 83 may be made maximum.

The physical size of the discharge produced in the gap'88 and the overall length of the members 86 and 81 of the corona producing means influences the band width of frequencies which may be emitted. general, the larger the sizes the greater the bandwidth of frequencies emitted-and These two the smaller is the selectivity produced by the composite shells 80 and SI. That is, when it is desired to make the space broadly resonant, so that the band width is relatively large, the members 85 and 3'! may be made like a dipole, as illustrated, but the members 86 and 87 are made as small as possible when sharp resonance or high selectivity is desired.

In Fig. 8 a modified form of space resonant device, bounded by surfaces of revolution formed of conic sections, is shown. This device is fundamentally resonant at substantially two different frequencies. Energy is transferred into the device through a coaxial transmission line Iilfl, terminated by a small loop ILI. Space on one side of a plane passing through the center of the loop iill is bounded by a pair of paraboloidal shells H32 and IE3, the two shells having their concave sides facing each other and having a common focal point at the center of the loop IilI. Space on the other side of the plane passing through loop illI is bounded by two additional paraboloidal shells I84 and I05 having their concave sides facing each other, having a common focal point at the center of the loop Ill! coinciding with the common focal point of the shells I02 and H33, and each having a major axis of different length from the major axes of shells I02 and Hi3. The pair of shells I94, I 05 and similarly, the pair of shells I82, I93 are similar to halves of shells 5D and 5! in Figure 5. If desired, the space between the edges of shells IE2 and I03 and the edges of shells HM. and H25 may be closed b a suitably shaped strip I66 lying in the previously mentioned plane passing through loop IOI.

Energy transferred through the coaxial line Hill and to the loop IilI is radiated into the space bounded by the doubly resonant chamber comprising shells I92 and I133. The chamber comprising shells IBZ and I93 is resonant at certain frequencies corresponding to the dimensions of that space, in a manner explained in connection with the structures of Figs. 1 through 5. Similarly, due to the shape of the chamber comprising shells H34 and I05, en-

ergy of a wavelength comparable with the shell size, such energy being transferred through line I08 and radiated from loop MM, is selectively reenforced, the wavelength and the corresponding frequency of that energy being determined by the dimensions of the space bounded by shells IM and I05. Space resonance is therefore produced in the space bounded by shells I52, I93, I94 and I65 at substantially two discrete fundamental frequencies, and the impedance appearing between the two conductors of the coaxial line I06 is correspondingly affected at these two discrete frequencies.

Energy may be abstracted from the space bounded by shells I82 and IE3 through a small loop IIQ connected to a coaxial transmission line IIl'I. Such energy abstracted through the loop Iiil and line It? is predominantly of the frequency determined by the space resonance of the space bounded by shells I92 and IE3.

Similarly, energy of a frequency determined by the dimensions of a space bounded by shells I94 and I85 may be abstracted from that space by a small loop I68 and a connected coaxial transmission line Hi9.

When a loop and connected line such as the loops Hi3 and led and lines It)? and I09 are utilized, the structure may be used as a filter, resonant at two discrete frequencies, for separating out energy at one of those frequencies. A1-

it) ternatively,-energy may be fed into lines Ill! and m9 at respectively different frequencies and such energy transferred through the space bounded by shells Iili, I83, iil l, and I to line IElIl, where, for example, the energy of two different frequencies may be mixed by heterodyne action.

Such heterodyne action takes place when line set is connected across a crystal detector I33 in series with a condenser i3 3. Condenser I34 has low reactance at the frequencies of energy in lines iiil and 5% and high reactance at their beat frequency. Beat frequency voltage appearing across condenser I3 may be utilized in device I35.

In Fig. 9 there is shown another structure in which still another conic section is utilized to form a surface of revolution bounding a space which is resonant at a single predetermined frequency. In this case the conic section is an ellipse rotated about its major to form the desired surface of revolution. That is, the space is bounded by the shell of a prolate spheroid. The shell ii s is formed of a reflecting material in the shape of the resulting surface of revolution. Excitation of the space bounded by shell I I9 may be provided through. a small loop III at one of the foci of the ellipse determining the shape of shell IE9 and through another small loop H2 at the other focus. The small loop III terminates a coaxial transmission line II3, of which the outer conductor is connected to the shell H9 and the inner conductor is connected to one terminal of the secondary winding of a high frequency transformer l M. The small loop I I2 terminates another coaxial transmission line II5, of which the outer conductor is connected to shell I It and the inner conductor is connected to the other terminal of the secondary winding of transformer Ill. The anodes H6 and Ill of a high freonency electron discharge device H8 are connected in push-pull relation to respective terminals of the primary winding of transformer II l.

Ultra gh frequency energy of a wavelength comparable to that determined by the dimens ons of ell se H9, is generated in the device H8 or amplified through it, and is then transferred through transformer IM to the small loops III and M52 in bush-pull, or balanced, relation, that is in opposite phase. The size of shell I I9 is such that energy of the frequency of the wave from device H8, radiated from loop HI and traveling by refl ction f o t e shell I69 to the loop H2, reaches the loop I I2 in such phase as to establish a r wual resonance between the two foci. This resonance is of a single type at a fundamental frequency or harmonic.

In Fig. 10 there is a graphical illustration of the path taken by such radiated and reflected energy. The shell II9 is represented by an ellipse I28 and a single ray of radiation I2I is represented as traveling from the focal point I'M occupied by loop Ill in Fig.9 It is a wellknown proposition (see Coordinate Geometry by Fine and Thompson, published by The McMillan Company in New York in 1937, on page 84) that the tangent at any point of an ellipse makes equal angles with the lines joining the points to the foci of the ellipse. According to this proposition, therefore, the ray I2 I, after reflection from the ellipse I223, takes the path E22 to the other focus E23 of the ellipse.

It is also a known property of an ellipse that the sum of the lengths of the paths III and I22 between the first focus IM and the second focus 23 is 'a constant, no matter in what "direction thepath I 2I is oriented.

It follows from the above-mentioned geometrical properties of the ellipse I20 that all energy radiated from focus I2 l, as along the representative path I25, must arrive at focus I23 after one reflection from the ellipse I29 in'predetermined phase relation.

If the path. I22 be extended through focus I22,'as illustrated by path I25, so as to impinge again upon the ellipse I22, energy is reflected from the ellipse I25} along a path I26 passing through the first focus I24, the sum of the lengths of paths I25 and I 26 being equal to the sum of the length of paths I2! and I22. Similarly path I26 may be extended through focus I2-t as math I21, and after reflection from the ellipse I20 as path I28, energy traveling along those paths passes back through the second focus I23 again. Extension of the path I28 through focus I 23, as path 129 results in still another reflection from the ellipse I2Il, as illustrated by path I311, which extends again back to the original focus I2 3.

Following the energy paths I2I, I22, I25, I25, I21, I28, I29 and I36 in order, it is evident that energy radiated from either focus passes through the other focus and then. alternately through the first focus and the other focus many times, and, after each reflection, approaches more and more nearly a path directly through the two'foci'l23 and I24. It is therefore evident that energy'radiated from the foci 523 and I2 tends to become concentrated along the major-axis of the ellipse. Since the prolate spheroidal shell I I9 in Fig.9 is formed by revolution of the ellipse i293 about its major axis, the same action as illustrated in Fig. 10 takes place in any plane passing through the major axis.

Because of the peculiar property of an ellipsoid, formed by revolution of an ellipse about its major axis, in reflecting radiation. inside so that it ultimately is concentrated along the major axis, such an ellipsoid arranged as a space resonant cavity is useful in radiating a narrow concentrated beam of energy. The ellipsoidal shell H9 in Fig. 9 has a hole I3I at oneendin. line with the major axis and in line with the two small loops .III and H2. Direct and concentrated radiation energy from the loops I II and H2. is radiated as a narrow con-- centrated beam of energy through the hole I3I, the beambeingrepresented by an -arrow I32.

.'In Fig. 11 an ellipsoidal shell I4; encloses a space into which energy is radiated from a dipole IM, energy being abstracted from the spacethrough a dipole I42. The dipole MI is energized througha coaxial cable M3, of which the inner-conductor is connected to one arm of the dipole I4! and the outer conductor of the.

line I43 to the other arm. The dipole M2 is similarly connected to a coaxial cable I44 through which energy within the space bounded by the shell I40 isabstracted.

.A representative path for energy traveling from .the:.dipole IM to. the=dipole 142 is ;illus tratedras aline I45 from the dipole MI to a representative .point onthe'shell Mill, and another line-I 45, representing the path taken by reflection of the ray traveling the path I i-5 and striking the representative point, the ray It's passing --eventually .to the dipole I422. The ray I46, easit 'passesthe dipole I42, proceeds in a path I4I.to.strikeanotherpoint of the shell I48 and be reflected along a'fourth path 143 back to the dipole i ii.

In Fig. 12 a shell Mil has'a small loop IF-Il at one focus and another small loop 'I5I at the other focus, those two small loops being .connected respectively, as are the dipoles M5 and M2 in ll, to the coaxial transmission lines Hi3 and Hi l. In operation, the structure shown in Fig. 12 is similar to the operation described for the structure of Fig. 11. That is, energy radiated into the shell I m from loop lfi is abstracted by loop E52.

The structures of Figs. 11 and 12 may be used as filters for selecting from a wave having harmonics, desired ones of the harmonics. In that case, the physical dimensions of the dipoles I ll and I i-2 and loops Hit and 556 as related to th'e size of shells determine the band pass characteristics of the filter. When employed as a filter, energy in a band of frequencies'related to the size of the components of the resonant cavity is radiated from dipole MI or-loop I fiil and then selectively transferred to the other dipole or loop Iti.

In 13 there is illustrated a conicoid, par ticularly an ellipsoid, which is not a surface of revolution and in which the three dimensions are all different. For clearness, the shell I82 is illustrated viewed from three diiferent'directions, the relation between those directions being indicated respectively by dotted lines 56!, N32, and iiiil. That is, the dotted lines lEI illustrate that the length of shell 'Ifili viewed from the top and from the front elevation is the same, lines H32 illustrate that the height of the shell viewed from the front elevation or from one end is the and lines I53 illustrate that the thickness of shell i533 viewed from the top 'or from the end is the same.

A small loop the is placed substantially at one focus of the shell its and a second small loop I555 is placed substantially at the other focus. It is to be understood that shell l te does not have true foci but the dimensions transverse to the long dimension do not diiler too greatly, the loci of sections of shell 5% taken through that long dimension nearly coincide and may fall Within the compass of loops 56 i and Such a condition is tolerable in a band pass filter. These two loops Hit and I65 are connected respectively to a source of high frequency wave and a load (not shown).

Any plane passing through the two foci, at which the loops I64 and I65 are located, cuts the shell its in an ellipse. Consequently radiation from one of the loops I65 or I65 in that plane is resonant at a frequency corresponding to the size of the ellipse cut by such plane. Another plane cutting the shell I63 at a different angle and passing through the loops I54 and H35 cuts the shell Itll in an ellipse of a different size in which resonance of a different frequency is produced.

:As illustrated in Figure 13, a vertical plane through the loops i6 3 and I65 cuts'the largest ellipse possible from the shell I (it! and a horizontal plane through the-loops I84 and I55 cuts the-smallest ellipse in which resonance maybe produced. These two sections correspond'respectively to the lowest and the highest frequency at which resonance is produced .in the space bounded by the shell I60, and resonance is produced at all intermediate frequenciesibyintermediate sections cut by planes passing :through the loops I64 and I65. This structure1istherer fore a band-pass filter in which the cut-off frequencies correspond respectively to the highest and lowest frequencies described, corresponding respectively to the smallest and the largest. ellipses in which space resonance is produced.

In general any conicoid may be excited in accordance with my invention so that in at least a single plane, space resonance is produced. That is, so that in at least that one plane energy returns from all directions in predetermined fixed phase relation.

In Fig. 14 a radiator I10, similar to the radiator illustrated in Fig. 3, except that the shells 40 and II are closed for a major part of their circumference, is energized through a concentric transmission line I'II from a source I11 of pulsed wave energy at a suitable frequency and radiates pulsed short bursts of high frequency electromagnetic energy represented by arrows I12 upward in a mountain pass encompassed between two mountain sides E13 and I14.

A plane, or other object, I 15, passing above the mountain pass between mountains I13 and I14, intercepts the pulsed rediation I12 and reflects it back towards the radiator I10, as indicated by arrow I15. The reflection detector I11, of known form, deflects such reflected pulsed radiation and, if desired, measures the time elapsed between its transmission from radiator I and'its later reception thereby after reflection, thereby indicating not only the presence of plane I15 but its altitude or distance from radiator I10.

In Fig. 15 there is illustrated still another resonant cavity bounded by surfaces of revolution formed by conic sections rotated about their axes. A hyperboloidal shell I80 is placed with its concave side facing an ellipsoidal shell I 8|, with a respective .foci coincident at the position of a small loop I82 connected to a concentric transmission line I83 arranged to transmit energy into the space bounded by the shells I80 and I8I. Energy radiated from the loop I82 toward the shell I99 is reflected from shell I80 as though it were radiant from the conjugate focus of the hyperbola defining shell I80. perbola has a focus at the loop I82, and it has also a conjugate focus behind the shell I80 from which such energy after reflection from the shell I80 appears to be radiant. That radiant reflected energy from shell I80, upon impinging upon shell ISI and reflection therefrom is directed back toward the loop I82.

Energy so reflected successively once from shell I so and once from shell IBI and so returning to loop traverses a circuit which is the same length for energy radiated from loop I82 in all directions. Hence, such energy returns to loop I82 in the same phase and resonance is established at a harmonic series of frequencies determined by the path length.

In Fig. 16 a graphic illustration is used to demonstrate why energy radiated in any direction from loop IE2 is, after one reflection from each of shells I80 and I0: of Fig. 15, returned to loop I82 in predetermined phase relation. In this figure the X axis is represented by a line I99 and the Y axis by a line IIII, and a hyperbole, symmetrical about both axes, is illustrated as having two arms I92 and I93. Revolution of arm I92 about axis I9I is effective to define the shell I80 of Fig. 15. The hyperbola having the two arms I92 and I99 has respective focal points I94 and I95. A line I98 drawn from the focus I94 to a representative point I91 along the arm of I92 of That is, the hythe hyperbole represents a ray of energy radiant from loop I82 in Fig. 15.

An ellipse having any desired eccentricity is constructed about the two foci I99 and I95, and a portion I of this ellipse, forming with a part of the arm I92 of the hyperbola a closed space containing the line I99, is illustrated.

It is a known property of an hyperbola that the tangent at any point thereof bisects the angle included by the lines extending from each focus to that point (see page 198 of the previously identified text on Coordinate Geometry). The tangent I99 at point I91 on the arm I92 of the hypcrbola in Fig. 16 therefore bisects the angle A between the line I99 and the line 200 joining the focus I with the point I91. Extension of the line 299 throughpoint I91 to a point 20I on the ellipse I93 forms an angle B between this extension 292 and the tangent I99, such angle being equal to the angle C between line 200 and the lower part of the tangent I99, which in turn is half the angle A between the line 200 and the line I96. In consequence, the angle D between line I95 and the tangent I99 is equal to the angle B between the line and the tangent I99. The line 292 therefore represents also the path of a ray which traveled toward the arm I92 along the path I99 and which was reflected from the arm I92 of the hyperbola at point I91.

It has been previously explained in connection with Fig. 16 thatlines 200-292 and 293, joining the foci I95 and I99 respectively to point 2!, form equal angles with the tangent to the ellipse I99 at point ZI'iI, because the points I94 and I95 at the ends of those lines are the foci of the ellipse. Consequently, the path 299 is the path of a ray reflected from a point 2% of ellipse I98 after traveling along path 202 to the ellipse. Therefore, a ray emitted from focus I94 in any direction along a representative path I99 is reflected from the arm I92 of the hyperbola along path 202 and is then reflected from the ellipse I93 along path back to the focus I 99. Conversely. a ray radiated from the point I94 along a representative path 293 takes the opposite circuit.

It is also demonstrated below that the total length of the path from focus I94 along the line I99 and then along lines 202 and 203 back to the focus I99 is always the same, no matter in what angular direction the rays first leave the point I9 2. It may be shown that the distances of any point along an arm of a hyperbola from the foci differ by a constant distance (see page 104 of the text on Coordinate Geometry cited previously). Futhermore, as explained in connection with the ellipse illustrated in Fig. 16, the sum of the distances from any point along an ellipse to its foci is a constant distance. Therefore (the numbers placed within brackets representing the length of the designated lines in Fig. 16 for convenience in forming equations) expressing well known properties of an ellipse and an hyperbola:

(200) minus (196)=k1 (200) plus (202) plus (203) =k2 Subtracting the first of these equations from the second:

(196) plus (202) plus (203) =kz-k1 It is therefore demonstrated that the paths I96, 202 and 203 in Fig. 16 represent the true re flection path of a ray radiated from focus We in any direction and the total length of the three reflection paths is always the same no matter in what direction the ray be originally radiated.

Therefore, energy radiated from loop 92 in. Fig. 15 returns in phase to the loop after one complete circuit, having started from loop in any direction, so that the space hounded. I. theshells i539 and 101 of Fig. 15 is space r onant in the same fashion as is the case with structures previously described.

It is evident from inspection of the various structures which I have illustrated that o con'icoids or second degree tridin" I may be utilized as surfaces noun spaces which resonance of a single type is established. Such resonators are useful for many purposes besides those I have described, and they are in general useiul at ultra high frequencies for the same purposes for which lumped tuned circuits are useful at lower frequencies.

While I have shown and described the particular embodiments of my invention, will be ohvious to those skilled in the art that changes and. modifications may he made Without departing from my invention in its broader aspects, and I, therefore, aim in the appended claim to cove all such changes and modifications as l wit e true spirit and scope of my invention.

I claim:

1. A high quality singly resonant cavity comprising a pair of substantially identical circular paraboloidal reflecting shells having a common focus, the concavities of said shells being juxtaposed in continuous relation to each other, thereby defining a substantially continuous inner space, and means for radiating energy within said space at said common focus whereby radiated energy after reflection from each of said shells returns to said focus in predetermined phase relation.

A high quality singly resonant cavity comprising a pair of substantially identical curved conductive surfaces having a common focus, each of said surfaces being defined by revolution of a parabola about its major axis, said surfaces being substantially coaxially disposed with the concavities thereof juxtaposed in contiguous relation to each other, and means for radiating ergy at said common focus whereby radiated energy after reflection from each of said surfaces returns to said focus in predetermined phase relation.

3. A high quality singly resonant cavity comprising a pair of substantially identical confocal paraboloidal reflecting shells having their concavities juxtaposed in contiguous relation to other, an opening in said cavity communicating with outer space, and means for radiating energy in said cavity at a point such that the radiant energy after reflection from each of said shells returns to said point in predetermined phase relation and energy is radiated through said opening into said outer space.

lien a 4. In combination, a pair of substantially identical circular paraboloidal reflecting shells having a common focus, said shells being disposed with the concave sides facing each other, and corona discharge means for radiating energy at said common focus, whereby radiant energy after reflection from each of said shells returns to said focus in predetermined phase relation.

5. In combination, a pair or substantially identical curved conductive surfaces having a common focus, each of said surfaces being defined by revolution of a parabola about its major axis, said surfaces being substantially coaxially disposed with the concavities thereof juxtaposed in contiguous relation to each other, and corona discharge means for radiating energy at said common focus, whereby radiant energy after reflection from each of said surfaces returns to said common focus in predetermined phase relation.

6. In combination, a pair of substantially identical confocal circular paraboloidal reflecting shells, the concave sides of said shells loeing juio taposed in coaxial and contiguous relation to each other thereby defining a reflecting cavity, an opening said cavity communicating with an outer space, a cover hermetically sealing said opening, and corona discharge means for radiating energy within said cavity at a point such that the radiant energy after reflection from each of said shells returns to said point in predetermined phase relation, said cover being substantially transparent to said radiant energy, whereby energy is radiated through said cover into outer space in a predetermined direction.

NATHAN W. ARAM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 775,840 Bose Mar. 29, 1904 781,606 Hewitt Jan. 31, 1905 1,278,026 Salto Sept. 3, 1918 1,304,868 Franklin May 27', 1919 1,735,377 Caughlan Oct. 19, 1927 2,118,419 Scharlau Sept. 15, 1932 2,044,413 Weyrioh June 16, 1936 2,106,770 Southworth et a]. Feb. 1, 1938 2,129,713 Southworth Sept. 13, 1938 2,241,119 Dallenbach May 6, 1941 2,245,669 I-Iollmann June 17, 1941 2,250,934 0111 July 29, 1941 2,265,796 Boersch Dec. 9, 1941 2,281,274 Dallenbach et a1. Apr. 28, 1942 2,281,550 Barrow May 5, 1942 2,354,658 Barber Aug. 1, 1944 2,445,784 Lehmann July 27, 1948

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