US2593183A - Tunable wave signal device - Google Patents

Description

April 15, 1952 J, RADQ 2,593,183

TUNABLE WAVE SIGNAL DEVICE Filed March 30, '1946 INVENTOR.

JOHN A. RADO,

A TORNEY.

This invention relates Patented Apr. 15, 1952 TUNABLE WAVE SIGNAL DEVICE John A. Bade, Nutley, N. .L, assignor to Hazeltine Research, Inc., Chicago, 111., a corporation of I Illinois Application March 30, 1946, Serial No. 658,405

"1 Claims.

irequency range, and particularly to such a device including a. resonant wave-guiding structure of adjustable electrical length.

As used. broadly in this specification and in the appended claims, the term wave-guiding structure applies to a system of conductive surfaces which act as the boundaries of an electric wave and have the ability of directing the propagation of such a wave, much as the rigid walls o'f a speaking-tube guide sound by preventing the sound from spreading freely into space. Wave-guiding structures are well known in the art and may take the form of two or more. separated conductors in open space, such as a power line or a telephone line. Such structures may be called transmission lines of the open-wire line type. Another type of wave-guiding structure comprises simply a single hollow conductor capable of propagating the wave through its interior; this type may be called a hollow guide.

7 Still other types include one or more conductors enclosedwithin but electrically insulated from another conductor, as in the conventional coaxial transmission line. While certain details the types mentioned and refers also to the relatively short structures often designated as cavity resonators. l i l The electrical length of a wave-guiding structure may be determined by establishing a shortcircuit thereacross, and the structure may be excited by the introduction of energy adaptable to *the generation of electromagnetic waves. The

waves travel along the guide, and reflections occasioned when the waves encounter the short, circuit result in the setting up of standing waves in the cavity, which isthen said to be in a resonant condition. In such a resonant condition, the alternating magnetic field in the guiding-structure has a maximumintensity at the short-circuit, and a pointof maximum intensity -'0f the electric field is established .farther along, the structure, measured in the direction from which the waveapproaches the short circuit.

The distance between'these points of. maximum magnetic and electric field intensities isicqual to one-quarter of the instant operating ,wave length of the structure. l/Vh'ere-the active portion of the resonant structure has a length greater than one-quarter of the operatingwave length,

generally to an improved tunable wave-signal device adj ustableover a giventhe points of maximum magnetic and electric field intensities recur cyclically, each field varying sinusoidally between its maximum and minimum points but shifted 90 degrees in phase with respect to the other.

With a wave-guiding structure operating in such a resonant manner, the resonant frequency maydepend on the method of excitation and on the nature and disposition of the materials within the wave-propa .gatingv space. In any case the resonant frequency is determined by the eifective electrical-length of the structure. If an arrangement is provided for changing the effective length, the structure becomes a tunable wavesignal device since its resonant frequency may be changed at will. At the higher radio frequencies, such tunable devices have found considerable use because of their accuracy of tuning, efiiciency, and convenient dimensions.

Aprior tunable wave-guiding structure includes a movable short-.circuiting member adjustably placed .near one end portion of the structure. Various forms have been proposed for this shortcircuiting member, perhaps the simplest, being merely a shortingbar or end cap. The portion of an end .cap in contact with the conductive surfaces of the structure often is slit or otherwise divided into transverse segments, which press against the conductive surfaces by spring action to maintain adequate contact. Such a shorting device serves to delimit an active portion oi th e guiding structure, and adjustment of the device therealong changes the active physical length of the structure, causing a corresponding .change in its effective electrical length, andthus accomplishing tuning.

The high magnitude of the alternating currents flowing in such asimple shorting member has prompted the addition of conductive surfaces connected to the end bar or cap and disposed in parallel relation to the surfaces of the wave-guiding structure proper. With these additional surfaces the short-circuiting member "takes the form of a piston or cup slidable-along the .structure the short-circuiting being efiected by the closed end of the cup. The cup is usually proportioned so thatit extends parallel to the wave-guiding structure for a distance equal to one q-uarter wave length at the mean operating wavelength. This permits electrical connection from. the shorting member to the guiding struccture to be-qmade ,eftfectivelyina region of high 1 or maximum, electric field intensit air ,inithe structure have low or minimum Values.

magneticifielcl intensity and the currents .efiects on the magnetic and electric fields.

With such a tuning piston, effective electrical connection may be made at radio frequencies by A. C coupling, eliminating the use of contact segments or fingers employing spring pressures.

The use of a short-circuiting member adjustable along a portion of the guiding structure has necessitated in some cases, in order to tune over the desired range, a distance of travel of that member equal to a substantial fraction of the over-all length of the structure. This lengthy adjustment not only makes tuning cumbersome, but also increases the mechanical complexity of the device and may be undesirable when space and Weight are at a premium. since a given adjustment may produce an un-' desirably small tuning efiect, the sensitivity of adjustment available with this tuning arrangement may be too small.

Another prior tunable wave-guiding structure utilizes a loading element movable along the structure in the wave-propagating space. With this arrangement the tuning varies with the position of the loading element, while active:

physical length of the structure remains the same for all tuning adjustments. The loading element changes the nature and disposition of the materials in the wave-propagating space,

causing a change in the magnetic or electric fields, or in both fields, in the loaded section of the structure, that is, in the vicinity of the loading element. The change may be thought of as a phase shift brought about by thediscontinuity resulting from the abrupt change in characteristic impedance caused by the loading element. The change also often may be thought "considered as having a value of inductance or capacitance equal to the apparent inductance or capacitance of a difierent length of the structure without the loading and its resulting phase shift. Accordingly, the changes in the fields within the wave-propagatingspace, due to the loading element, have the efiect of altering the electrical length of the wave-propagating struc- "ture, but without altering its active physical length. 7

Tuning of this prior wave-guiding structure is accomplished by moving the loading element axially along the structure. This causes the element to move relative to the points of maximum magnetic and electric field intensities, so that it enters a region where both fields have modified values. In other Words, the ratio of magnetic to electric field intensities in the vicinity of the loading element changes as the element is moved along the resonant wave-guiding structure. Now, a given loading element may be made of materials having markedly difierent For instance, the element may have a strong efiect on an electric field but practically no efiect on a magnetic field. Hence, moving the element along the guiding structure into a region where the magnetic and electric field intensities have modified values and are in a different ratio changes the effect of the element on the fields so In other words, A

4 as to alter the effective electrical length of the guiding structure.

As with tuning by adjusting a short-circuiting member, however, instances have arisen in which it is desired to tune over such a wide range that excessive movement of a loading element, or a loading element of such a large size as to impair operation of the tuning device, would be required. In some installations the mechanical requirements of an adjustable loading element may prove bothersome. It may even prove impossible in some instances to tune over the entire desired range with any adjustable loading arrangement. The sensitivity of tuning adjustments with a loading element thus may be too small.

The described prior arrangements for tuning a resonant wave-guiding structure also may lack the nicety of adjustment desirable in certain types of equipment, particularly measuring and testing equipments. For such equipments it is often desirable to make a substantial adjustment of a tuning element or member when tuning over a relatively narrow range. In this instance the sensitivity of adjustment practically available with the known tuning arrangements, may be greater than that desired.

Accordingly, it is an object of this invention to provide a tunable wave-signal device which substantially avoids one or more of the abovementioned limitations of prior arrangements.

It is also an object of this invention to provide a tunable wave-signal device having improved means for adjusting the device over a given frequency range.

It is a further object of the invention to provide a tunable wave-signal device including a tuning arrangement having a desired sensitivity characteristic and effective to tune the device over a given range of frequencies.

In accordance with the invention a tunable wave-signal device adjustable over a given frequency range comprises a wave-guiding structure including a plurality of longitudinally extending conductive surfaces defining a propagating space for electromagnetic waves. The device also comprises a short-circuiting member adjustable in a path extending longitudinally of the propagating space to effect tuning of the device over the frequency range, and efiective to determine in accordance with its position the location of points of maximum intensity of the electric and magnetic fields Withinthat space. The device further comprises a loading element of such cross-sectional shape and of such material as to provide in the Wave-guiding structure a substantial coefiicient of wave reflection, theelement being positioned in a region of the propagating space subject to approximately the greatest longitudinal shifting of said fields during the tuning of the device. The tuning device further includes at least one support for the aforesaid element having a length substantially equal to one-quarter of the mean operating wave length of the device and affixed to the waveguiding structure at a point outside of the path of adjustment of the short-circuiting member.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Fig. l is an axial section through a tunable wave-signal device of the coportions iI, i2 defining a propagating space I3v for, electromagnetic waves. The longitudinally "extending conductive portion I I is a hollow cylindrical outer conductor, while the conductive surface or portion i2 is a coaxially aligned inner conductor, providing therebetween the propagating space I3. The outer conductor II and inner conductor Hare aligned andspaced by means of an end plate is, which may be of either conductive or insulating material. The remote end of the structure is terminated in an end plate I5,

which may be of a dielectric or a conductive material, depending on whether the structure has an effective electrical length of an odd or an even number of quarter waves, 'a dielectric end plate being illustrated. The structure maybe excited by oscillatory means (not shown), and connections to suitable oscillatory circuits may be made at points it and IT in circuit with outer conductor 1 i and inner conductor I2, respectively.

In order to effect tuning of the device over a given frequency range, there is provided a pistontype short-circuiting member it] which includes two coaxially aligned hollow cylindrical conductors, an outer conductor 2I and an inner conductor 22, forming piston walls parallel to conductors ii and I2. The piston 20 is closed atone end by a short-circuitin ring 23, which aligns the conductors 2! and 22 and maintains them in positions adjacen to the longitudinally extending conductors I l and I2, respectively. The piston is open at the opposite end so that it embraces a portion of propagating space i3. Conductors 2i and 22 are chosen of such a length that the piston to has an eiiective electrical length substantially equal to an odd integral multiple of one-quarter of the mean operating wave length of the device. A convenient length for the piston is usually approximately one-quarter of the mean operating'wave length.

Piston 25 is adjustable longitudinally ofpropagating space I3 by means of rods 25, 2B, fastened to the ba'clr oi ring 23. These rods pass through appropriate holes in end plate I4, and are joined outsideof the wave-guiding structure to -a' driv-V ing rod 2?. As indicated by arrow '23, any suitable driving mechanism may be applied to driving'rod ii to effect displacement of piston20. V

' f The tunable wave-signal device further comprises a toroidal loading element 30. In the illustrated embodiment, the loading element is made of a conductive material, but a loading element of the same shape also may be made of nonconductive dielectric or magnetic material, inaccordanee with principles disc'ussed hereinafter. Element 36 is supported for movement relative 'to piston so during the tuning of the device by at least one support, which'may be of dielectric or conductive material, conductive supports being indicated for convenience in Fig.1. This embodi "ment utilizes two radiallythinsupportsor straps 31, 32 for supporting theelement/and spacing it ing of the device.

6 from the closed end of the piston in the direction of the open end. The straps (H, 32 may be movably or fixedly connected to one of the conductors of the wave-guiding structure in such a manner that longitudinal adjustment of piston Zilproduces relative movement of the loading element with respect to the piston; for convenience of illustration the straps are shown fastened to outer conductor II at points 33, 34, which are outside of the longitudinally extending path'of adjustment of the piston.

Operation of the tunable wave-signal device of Fig. l will be described first neglecting the effects due to loading element 30. This discussion as sumes the wave-guiding structure to be considerably longer than one-quarter wave length, for instance oneand one-quarter wave lengths, but the same principles apply to shorter structures. oscillatory energy is introduced at the fixed dielectric end plate I5 through terminals I6 andII so that Wave energy propagates down the structure and. is reflected from short-circuiting ring 23, bringing about a resonant condition as described above. When excited in this manner, the active propagating space of the structure has an effective length equal to an, odd integral multiple of one-quarter wave length, and alternatepoints of maximum electric and magnetic field intensities appear along the propagating space and at each end thereof, these points being spaced oneuuarter wave length apart. If piston 20 is moved longitudinally of the wave-guiding structure, the position of short-circuiting ring Ail-with relation to the remote end I5.oi the structure is changed. This causes a change in the physical length of the active portion of the structure and a like change in its effective electrical length. If properly excited, the structure remains in a resonant condition, but the quarter wave-length distance corresponding to the separation of succeeding points of maximum magnetic and electric field intensities is changed.

When piston 20 is moved, the point of maximum magnetic field intensity located at ring 23 necessarily moves with it. However, the point of maximum electric field intensity occurring atthe remote end I5 of the structure is fixed and does not move. Therefore, displacement of the tuning piston, which alters the operating frequency, causes a redistribution of both the magnetic and electric fields within thev wave-propagating space of the guide, shifting all points of maximum field intensity except that at end I5. It may be shown that the most pronounced longitudinal shifting of the fields takes place in the regions of the propagating space nearest to the tuning piston. Thus, it is seen that displacement of the piston 20 varies the effective electrical length of the structure to effect tuning. Further, it becomes apparent that the location of points of ment 30 on the described tuning process, it will 7 be assumed that thejelement is located in its preferred position 'notvery far from the shortcircuiting ring, so as to be positioned in a region of propagating space I3 which is subject to the greatest longitudinal'rmovement or shifting of the magnetic and electric *ficlds during the tun- As shown in Fig. 1, the element is positioned at thetun'ing,adjustmentillustrated in a region'of-the space I3 wholly between the coaxial walls of- 'the' piston. I With-the extreme tuning adjustment which givesthe greatest active physical length, however, one end portion ofthe element may protrude somewhat from the open end of the piston.

Since the loading element, as shown, is stationary during a tuning adjustment, the fields shift with reference to it during tuning and hence, place it in a region where the magnetic and electric field intensities have a ratio difierent from that resulting from the previous setting of piston 20. As pointed out above, this alteration in the field intensities changes the efiect of the loading element on the fields, so asto alter the effective electrical length of the active portion of the guide structure. This alteration in effective electrical length is, in addition to that already described, due solely to adjustment of piston 20. Whether the tuning effects occasioned by the adjustment of the piston and by the presence of the loading element are additive, so that a more sensitive tuning arrangement is provided, or subtractive, so that a less sensitive tuning arrangement is provided, depends on the nature of the loading element and also on its position along the active part or" the guiding structure.

Three types of loading elements may be mentioned. The element may be conductive, it may be of nonconductive material whose predominant characteristic is a high dielectric constant, or it may be a composition of low conductivity, the predominant characteristic of which is .a high magnetic permeability. In general, the action of a conductive loading element is to decrease the effective electrical length when placed in a region of high magnetic field intensity and to increase the effective electrical length when placed in a region of high electric field intensity. A di= electric element has little efiect in a region of high magnetic field intensity, but tends to increase the effective length if located in a region of high electric field intensity. A magnetic element having high permeability usually also has a rather high dielectric constant, so thatitaffects both magnetic and electric fields. The effect of a magnetic composition used in accordance with thepresent invention depends in part on the resistivity of the composition and, in part on the proportions of magnetic material and binding material ordinarily used to hold together the particles of magnetic material. Neglecting the action of dielectric or conductive materials in a so-called magnetic element, it tends to increase the effective length when positioned in a region of high magnetic field-intensity.

To continue with the detailed operation of the Fig. 1 embodiment, let it be assumed that loading element 30 is of a conductive material and is positioned for the initial adjustment of piston it half way between the point of high magnetic field intensity at the shorting ring 23 and the nearest point of maximum electric field? intensity. In this position the element. islocatedwithin the quarter-wave region nearest the closed end of the piston. Adjustment of the piston toward the loading element shortens the active physical length of the structure; Simultaneously, theintensity of themagnetic-field in the immediate neighborhood of the loading'element increases. As mentioned above, this tends further toshorten the efi'ectiye electrical length of the structure. Consequently, the described relative movement of the pistonand theloading element produces additive effects and --tends greatly to shorten the j ,tioncf the fixed end plate l5.

tensities.

efiective electrical length of the structure. Simllarly, if the active physical length is increased by the opposite adjustment of piston 20, away fromelement 30, the element finds itself in a region of higher electric field intensity but lower magnetic field intensity, where it tends further to increase the effective length of the structure. Again, the two effects are additive. The net result is a more sensitive arrangement for tuning, since a smaller adjustment accomplishes the same .result as would a larger adjustment of a loading element without a movable short-circu'iting member, or of a movable short-circuiting {member in the absence of a loading element.

. If, however,.the conductive loading element is located farther along the structure, so that its mean position is about one-quarter wave length farther removed from the shorting ring, its effect the element in the direction of the adjustable shorting ring 23, while a point of maximum magnetic field intensity exists near it in the direc- Its orientation with respect to the fields, thus is the reverse of the case previously considered where the element was positioned quite near the shorting ring. In the case now under consideration, a physifcal shortening of the propagating space brings the conductive memberinto a region of higher electric and lower magnetic field intensities, where it tends to increase the effective length. Thus, the two efiects oppose each other, and the sensitivity of adjustment is smaller than would be obtained without the loading element.

An analysis of the operation in the case of a dielectric loading element shows its action to be similar to that of a conductive element. Similarly positioned dielectric and conductive elements produce similar effects on sensitivity of tuning, the dielectric element being responsive to the variations in the electric field alone rather than to variations in a combined field condition, such as ratio of electric to magnetic field in- A predominantly magnetic loading element, on the other hand, can be shown to have opposite effects. on sensitivity of tuning. Thus, a dielectric element placed within a quarter- -wave tuning piston increases the sensitivity, while a predominantly magnetic element in the same position decreases the sensitivity. Various combinations of element positioning, materials, and effects will be apparent to those skilled in the art.

The shape and dimensions of the loading element, as well as the material of which it is constructed, contribute to determine its effect on .tuning. Within the limitations presently to be ments are used, the effects of the two end portions may cancel each other, and further lengthening of the-element until an effective length of one-half wave length is reached causes the operating wave length of the device.

tuning effect of the element to become negligible.

Accordingly, the greatest tuning effect ordinarily is obtained with quarter-wave elements.

treme tuning adjustment .the entire element occupies a region in which the magnetic field predominates. A conductive element so positioned has a large tuning effect during initial adjustment if it has a major axial dimension substantially equal to one-eighth of the mean the tuning adjustments may be large enough to change the position of the element until it is centered on that point of maximum electric field intensity which exists one-quarter wave length distant from the. short-circuiting ring. When in the latter position, theelement is far enough removed from the shorting ring so that However,

its length should be approximately equal to one-.

quarter wave length to produce optimum tuning effect during subsequent small adjustments. For optimum tuning effect overthe tuning range mentioned, a conductive element supported in the vicinity of the short-circuiting member, and having a length of between one-eighth and three-sixteenths of the mean operating wave length, for instance one-sixth wave length, is

desirable. V v

In a specific embodiment of the invention using a quarter-wave tuningpiston two and width to provide the required strength andof a polystyrene material having low dielectric loss properties. Without the loading element and its support-s, one and seven-eighths inches of travel of the piston were required to tune over the desired band. With the struoture of the invention, however, only seven-eighths inch of travel accomplished tuning over the same range. The presence of the loading element also substantially decreased the over-all dimensions of the device. In such an embodiment,the material of the support itself serves as an additional loading element, thus increasing the effectiveness ofthe toroidal element.

The support or supports employed to position the loading element in the propagating space advantageously may have a length substantially equal to one-quarter of the mean operating wave length of the device, especially when conductive supports are used. A support so proportioned has a resonant length permitting the establishment of a standing wave therealong, with the attendant differences in voltage and current between the two ends which are separated by a distance equal to one-quarter wave length.

Thus, voltages and currents induced on the loading element, at its points of support, may be maintained in spite of the different electrical values existing on the wave-guiding conductors where the other ends of the supports are fastened.

Figs. 2, 3., and 4 illustrate embodiments of the ever, portions of the. outerand inner conductors H and Rare shown, as are the ends of rods 25, 26 for eiiecting longitudinal adjustments of the short-circuiting member.

Fig. 2 illustrates an embodiment of the inventionin whichthe disposition of the short-sir cuiting member and of the supports for the loading element differs from the embodiment of Fig. 1. A piston-type short-circuiting member 40 includes conductive portions 4! and 42 adjacent the outer and inner conductors I! and I2, re spectively. The piston 48 is open at one end but closed in a convergingly tapered section-at the opposite end. This tapered section includes an extension of outer conductive portion 4| in the formiof a truncated cone 43 converging toward inner conductor 12, and also includes an extension of inner conductive portion 42 in the form of an oppositely converging truncated cone it.

The outer cone 43 and inner cone 44 are trun cated by a short-circuiting ring 45 having a small radial Width; 1

A loading element snof generally toroidal shape is supported in fixed relation to the waveguiding structure so as to be positioned in a region of the propagating space in the vicinity of the tapered section #3, it, butspacedfrom the closed end r45. 'Iwo radially extending supports 5| and 52 pass through slots 53 and 55 in the conductive portions t! and 42, respectively, and support the element 55 The slots permit longitudinal adjustment of the piston 4t! in spite of the presence of the radial supports El, 52.

In connection with the operation of the em} bodirnent of Fig. 2, it has been pointed out above that positioning of the loading element in the vicinity of the short-circuiting member is advantageous because of the large shifting of the fields in that vicinity during tuning. Positioning of the element between the walls of. a pistontype short-circuiting member is advantageous also because the relative nearness of the walls of the piston increases the efiectiveness of the loading element. With the element in the vicinity of a tapering section of the piston, effectiveness of the loading element is further increased due to the approach of the cones t3, 44 during the adjustment to shorten the active physical length of the device. A particular advantage of supports 5|, 52 may all be of conductive material,

but an element of dielectric material also is effective to alter the sensitivity of tuning. In Fig. 8 there is illustrated an embodiment'oi the invention similar to that shown in Fig. 1, but with a loading element of a different form. As in Fig. l, the'piston 2a includes the conductors 2| and 22 adjacent the outer and inner conductors H and lzrrespectively, of the wave-guiding structura'and the piston is closed by the ring 23. A loading element St! is provided within the piston. Element 68 is considerably shorter longitudinally of the wave-guiding structure than loading elements of the other embodiments illustrated. In order to make this short load-' ing element efiective, it is desirable to have it extend as far as possibly radially within the portion of the wave-guiding space inside the terminating cup. Thus, element 60 is shown with a central hole only slightly larger in diameter than the diameter of the inner conductor 22 of the piston, and with an outer radius only silghtly smaller than the radius of the outer conductor 2| of the piston. The element 60 i supported by rods GI, 62 fastened to the outer conductor H of the structure.

The loading element 60 advantageously may be of a dielectric material having low dielectric loss properties, and as described, fits rather snugly within the terminating cup. When high voltages may appear, however, it of course is necessary to provide adequate spacing as a precaution against arc-over. Operation of the embodiment of Fig. 3 is similar to that of the apparatu of Fig. 1.

Referring now toFig. 4, conductors or conductive surfaces I I and I2 define the propagating space I3, as in Fig. 1, and a short-circuiting member 63 is disposed within the propagating space and made longitudinally adjustable by means of the rods 25, 26. To efiect the necessary electrical contact with the wave-guiding structure proper, the member 63 is slit radially at its edges 64 and 65 where it makes contact with outer conductor II and inner conductor I2, respectively. These radial slits separate both outer and inner peripheries of member 63 into flexible segments which bear against conductors II and I2 as member 63 undergoes longitudinal adjustment. As with a piston-type short-circuiting member, adjustment of member 63 results in substantial longitudinal shifting of the fields along propagating space I3.

Positioned within space I3 is a conductive loading element I supported by and conductively connected to inner conductor I2. This conductive element may be considered a raised portion of conductor I2, in efiect establishing a short length of the wave-guiding structure having a characteristic impedance diiferent from that of the remainder of the structure. Operation of this embodiment also is similar to that of the embodiments discussed above.

In the embodiment of Fig. 5, the tunable wavesignal device comprises a longitudinally extending hollow conductive structure defining a propagating space H3. The conductive structure includes a conductive surface comprising at least two portions HI and H2 forming a hollow conductive structure. This structure constitutes a hollow guide, which may have any suitable cross-sectional configuration. An end plate H4 is provided in the end portion of the hollow guide illustrated.

The device also comprises a piston-type shortcircuiting member I20 of similar cross-sectional con iguration, including conductive portions I2I and I22 adjacent to the conductive portions III and H2, respectively, of the hollow structure. Piston I20 is open at one end and closed at the opposite end by a plate I23, which also supports and aligns the conductive portions I2I, I22 of the piston. A driving rod I2'I, fastened to the back of plate I23, passes through a hole in end plate H4. As indicated by the arrow I28, any suitable tunin drive may be applied to driving rod I2'I to provide adjustment of the piston longitudinally of propagating space I I3 and thus eifect tuning of the device. Piston I20, by virtue of the conductive portions adjacent the hollow structure III, H2, is electrically coupled to the hollow structure and provides an end portion of the active propagating space. The piston ad.-

vantageously has an effective electrical length of substantially one-quarter of the mean operating wave length of the device.

A loading element I30 is supported by means of a radial support I3I for movement relative to the piston I20 during the tuning of the device. Support I3I passes through a slot I33 in conductive portion I2I of the piston. The loading element is thus illustrated as positioned within the piston I20 and spaced from the closed end I23 in the direction of the open end and, of course, is positioned in a region of propagating space H3 subject to substantial longitudinal shifting of the fields during the tuning of the device. Although the design and manner of use of the hollow guide involve detailed electrical phenomena differing from the phenomena associated with a transmission-line structure, as is well understood by those skilled in the art, the general principles governing operation of the embodiment of the invention illustrated in Fig. 5 are the same as those which govern the other embodiments illustrated.

A While-there have been described what are at present considered to be thepreferred embodi ments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A tunable wave-signal device adjustable over a given frequency range comprising, a waveguiding structure including a plurality of longitudinally extending conductive surfaces defining a propagating space for electromagnetic waves, a short-circuiting member adjustable longitudi nally of said propagating space to eiiect tuning of said device over said range, and a loading element of such cross-sectional shape and of such material as to provide in said wave-guiding structure a substantial coefficient of wave refiection, said element being supported in the vicinity of said short-circuiting member for movement relative to said member during the tuning of said device, said loading element having a major axial dimension of between one-eighth and one-quarter of the mean operating wave length of said device.

2. A tunable wave-signal device adjustable over a given frequency range comprising, a Waveguiding structure including a plurality of longitudinally extending conductive surfaces defining a propagating space for electromagnetic waves, a short-circuiting member adjustable in a path extending longitudinally of said propagating space to effect tuning of said device over said range and efiective to determine in accordance with its position the location of points of maximum intensity of the electric and magnetic fields within said space, a loading element of such cross-sectional shape and of such material as to provide in said wave-guiding structure a substantial coefficient of wave reflection, said element being positioned in a region of said propagating space subject to approximately the greatest longitudinal shifting of said fields during the tunin of said device, and at least one support for said element having a length substantially equal to one-quarter of the mean operating wave length of said device and aflixed to said waveof adjustment of said short-circuiting member.

over a given frequency range comprising, a hollow cylindrical outerv conductor and a coaxially aligned inner conductor providing therebetween a propagating space for electromagnetic waves, a piston-type short-circuitin member including two coaxially aligned hollow cylindrical conductors short-circuited at one end but open at the opposite end adjustable longitudinally of said propagating space to effect tunin of said device and effective to determine in accordance with its position the location of points of maximum intensity of the electric and magnetic fields within said space, and a loading ele-- ment of such cross-sectional shape and of such material as to provide in said wave-guiding structure a substantial coeflicient of wave reflection, said element being supported for longitudinal movement relative to said short-circuiting member during the tuning of said device, spaced from said closed end of said member in the direction of said open end thereof, and positioned in a region of said propagating space subject to approximately the greatest longitudinal shifting of said fields during said tuning.

4. A tunable wave-signal device adjustable over a given frequency range comprising, a waveguiding structure including at least one longitudinally extending conductive surface, said structure defining a propagating space for electromagnetic waves, a short cup-shaped piston having an effective electrical length substantially equal to an odd integral multiple of one-quarter of the mean operating wave length of said device and being adjustable longitudinally of said propagating space to effect tuning of said device over said range, and a loading element supported within said piston for movement relative thereto during tuning of said device and positioned in a region of said propagating space subject to substantial longitudinal shifting of said fields during said tuning,

5. A tunable wave-signal device adjustable over a given frequency range comprising, a hollow cylindrical outer conductor and a coaxially aligned inner conductor providing therebetween a propagating space for electromagnetic waves, a coaxial-line tuner adjustable longitudinally of said propagating space to effect tuning of said device and efiective to determine in accordance with its position the location of points of maximum intensity of the electric and magnetic fields within said space, and a ring-shaped member surrounding said inner conductor in spaced relation to both said conductors and of such material as to provide in said wave-guiding structure a substantial coeificient of wave reflection, said ring-shaped member being supported for longitudinal movement relative to said tuner during the tuning of said device and being positioned in a region of said propagating space subject to substantial longitudinal shifting of said fields during said tuning.

6. A tunable wave-signal device adjustable over a given frequency range comprising, a hollow cylindrical outer conductor and a coaxially aligned inner conductor providing therebetween a propagating space for electromagnetic waves, a coaxial line tuner adjustable longitudinally of said propagating space to efiect tuning of said I device and effective to determine in accordance with its position the location of points of maximum intensity of the electric and magnetic fields within said space, and a ring-shaped conductive member surrounding said inner conductor in spaced relation to both said conductors to provide in said wave guiding structure a substantial coeificient of wave reflection, said ringshaped member being supported for longitudinal movement relative to said tuner during the tuning of said device and being positioned in a region of said propagating space subject to substantial longitudinal shifting of said fields during said tuning.

'7. A tunable wave-signal device adjustable over a given frequency range comprising, a hollow cylindrical outer conductor and a coaxially aligned inner conductor providing therebetween a propagating space for electromagnetic waves, a coaxial-line tuner adjustable longitudinally of said propagating space to eifect tuning of said device and effective to determine in accordance with its position the location of points of maximum intensity of the electric and magnetic fields within said space, and a sleeve of conductive material surrounding said inner conductor in spaced relation to both said conductors to provide in said wave-guiding structure a substantial coefficient of wave reflection, said sleeve being supported for longitudinal movement relative to said tuner during the tuning of said device and being positioned in a region of said propagating space subject to substantial longitudinal shifting of said fields during said tuning.

JOHN A. RADO.

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

Roberts June 27, 1950

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