Title:
Microwave power accumulation structures comprising a plurality of stacked elliptical cavities
United States Patent 3873935
Abstract:
A plurality of stacked microwave cavities each shaped substantially in the form of a right elliptical cylinder, with each cavity being adapted to receive microwave energy at one focus hereof and to deliver amplified microwave energy to the other focus thereof; means are provided for delivering microwave energy in proper phase relationship to each of said cavities and for extracting amplified microwave energy, in proper phase relationship, from said plurality of stacked microwave cavities.


Inventors:
OLTMAN JR HENRY G
Application Number:
05/469578
Publication Date:
03/25/1975
Filing Date:
05/13/1974
Assignee:
Hughes Aircraft Company (Culver City, CA)
Primary Class:
Other Classes:
330/61A, 331/117D, 333/230
International Classes:
H01P7/06; H03F3/10; (IPC1-7): H03F3/60
Field of Search:
330/61R,34,56 331
View Patent Images:
Primary Examiner:
Kaufman, Nathan
Attorney, Agent or Firm:
Macallister Jr. V, Link Lawrence W. H.
Claims:
What is claimed is

1. A power accumulation device adapted for responding to applied input signals to provide amplified signals at an output terminal therof, said power accumulation device comprising:

2. The power accumulation device in accordance with claim 1 wherein said signal coupling means includes a first coaxial line disposed to pass through the first focus of each of said stacked elliptical cavities so that the applied signal processes from a first end of the stacked structure and wherein a portion of the inner conductor of said first coaxial line is exposed within each of said elliptical cavities; a second coaxial line disposed to pass through the second focus of each of said elliptical cavity structures so that the output signal, comprised of the accumulation of the amplified signals extracted from each of the cavities, is applied to the output terminal disposed at the other end of the stacked elliptical cavities and wherein a portion of the inner conductor of said second coaxial line is exposed within each of said elliptical cavities.

3. The power accumulation device of claim 2 wherein the size of the portion of the inner conductor of said first coaxial cable which is exposed within each of said elliptical cavities is different for each of the cavities, with the relative size of the exposed areas being selected to provide the same amount of applied signal to each of the cavities.

4. The power accumulation device of claim 2 in which said signal amplifying devices comprise a plurality of amplifiers, positioned on the periphery of each of said cavity structures to receive energy from said first focus of said cavity structure and to deliver amplified energy to said second focus of said cavity structure.

5. The power accumulation device of claim 4 in which said amplifiers are diode amplifiers.

6. The power accumulation device of claim 2 in which said signal amplifying devices comprise a plurality of microwave oscillators positioned on the periphery of each of said cavity structures, phase locked with signals received from said first focus and adapted to deliver signals to said second focus, whereby signals from said plurality of oscillators arrive at said second focus in phase and large amounts of microwave power may be extracted from said cavity structure at said second focus.

7. The power accumulation device of claim 6 in which said oscillators are diode oscillators.

8. A power accumulation device adapted for responding to applied input signals to provide amplified signals at an output terminal thereof, said power accumulation device comprising:

9. The power accumulation device in accordance with claim 8 wherein said signal coupling means includes a first coaxial line disposed to pass through the first focus of each of said plurality of stacked elliptical cavities so that the signal from the second focus of said additional cavity structure processes from a first end of the stacked structure and wherein a portion of the inner conductor of said first coaxial line is exposed within each of said elliptical cavities; a second coaxial line disposed to pass through the second focus of each of said elliptical cavity structures so that the output signal, comprised of the accumulation of the amplified signals extracted from each of the cavities, is applied to the output terminal disposed at the other end of the stacked elliptical cavities and wherein a portion of the inner conductor of said second coaxial line is exposed within each of said elliptical cavities.

10. The power accumulation device of claim 2 wherein the size of the portion of the inner conduction of said first coaxial cable which is exposed within each of said elliptical cavities is different for each of the cavities, with the relative size of the exposed areas being selected to provide the same amount of applied signal to each of the cavities.

11. A power accumulation device adapted for responding to applied input signals to provide amplified signals at an output terminal thereof, said power accumulation device comprising:

12. The power accumulation device of claim 11 further comprising a first impedance element coupled to the other focus of one of said stacked cavity structures and a second impedance element coupled to the other focus of the other said stacked cavity structures, and wherein the value of said first and second impedance elements is equal to the characteristic impedance of the associated focus.

Description:
CROSS-REFERENCES TO RELATED PATENTS AND APPLICATIONS

A portion of the subject matter disclosed herein is related to that of U.S. Pat. No. 3,733,560, for Elliptical Structure for Combining the Power of Many Microwave Sources, by Henry G. Oltman, Jr. and Hans A. Maurer; U.S. Pat. No. 3,783,401; for Means and Method for Suppressing Microwave Resonance in Elliptical Cavities, by Henry G. Oltman; and an application entitled, Devices for Coupling Microwave Diode Oscillators and Amplifiers to Power Accumulation Structures, by Henry G. Oltman, Jr. and Richard J. Wagner; filed concurrently herewith.

BACKGROUND OF THE INVENTION

This invention relates to microwave power accumulation structures which comprise a plurality of stacked elliptical cavities.

U.S. Pat. No. 3,733,560 discloses an elliptical structure which comprises coupling means for introducing energy at a first focus thereof, signal amplifying devices disposed on the periphery of the cavity for producing signals of greater amplitude than received at the periphery from the first focus and means positioned at the second focus of the cavity for removing energy therefrom. In accordance with this just cited patent although in theory any desired power gain can be achieved by increasing the number of amplifying devices, and hence the diameter of the cavity so as to accommodate them; there is a practical limit to the diameter which is permissible for any given application.

SUMMARY OF THE INVENTION

A significant aspect of the subject invention relates to the recognition of the fact that more efficient use of space can be achieved if a number of elliptical cavities of the type described in U.S. Pat. No. 3,733,560 are stacked, one on top of another; and of providing the means for exciting each of the elliptical cavities and for removing the amplified power therefrom in the proper phase relationship.

In accordance with the subject invention, a plurality of such elliptical cavities are stacked and intercoupled such that greater input-output isolation is provided along with a reduction in the volume and weight required for a device having a given amount of power gain capability. For example, in one embodiment of the invention two elliptical cavities are stacked one on top of the other with a coupling between the two elliptical cavities provided by diode cavities at the periphery of the ellipse. In this embodiment, the two elliptical cavities are substantially identical, anmd the foci of the two cavities are substantially coaxial. A signal introduced at the first focus of a first cavity, radiates along a radial path from that focus to the periphery of the first cavity where it enters the diode amplifier cavities. The diodes within the diode cavities amplify the signal and return it to the second focus of the second cavity. To minimize unwanted signals, terminals at the second focus of the first cavity and the first focus of the second cavity are preferably terminated with their characteristic impedance.

In a second embodiment of the invention, a plurality of elliptical cavities are stacked and a simple coaxial cable delivers energy into the stacked cavities at a first focus thereof so as to introduce microwave energy consecutively into the stacked cavities. The microwave energy in each of the stacked cavities radiates radially outward from its input focus to amplifiers or phase-locked oscillators on the periphery of that elliptical cavity. A second coaxial cable receives energy consecutively from the second focus of each of the elliptical cavities. Since energy is introduced into the cavities in sequence and it is removed from the cavities in the same sequence, the time delay between receipt of energy by the sequentially excited elliptical cavities and the time delay between delivery of energy by corresponding elliptical cavities is the same, whereby the power outputs of the individual cavities add.

In still another embodiment of the invention, at least one additional elliptical cavity is used as a preamplifier for the microwave input signal to a plurality of cavities.

It is therefore an object of this invention to provide an improved device for microwave signal amplification.

Another object of the invention is to provide the apparatus and method for producing high microwave signals.

Yet another object of the invention is to allow for the stacking of elliptical power amplifying cavity structures so as to provide, for a given gain capability, microwave amplifers of reduced weight and volume.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features which are characteristic of the invention both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which like characters refer to like parts and in which:

FIG. 1 is an outside view of an elliptical cavity, which view is useful for explaining the operation and functions of cavities of the general type as those which are combined and intercoupled to form structures in accordance with the subject invention;

FIG. 2 is a sectional view, taken at 2--2 in FIG. 1;

FIG. 3 is a sectional view, taken at 3--3 in FIG. 1;

FIG. 4 is a fragmentary view, partly in section, of a portion of the apparatus of FIG. 1 with the top cover partly removed to show a typical embodiment of a coupling mechanism for coupling diode cavities to the elliptical cavity of the apparatus;

FIG. 5 is a fragmentary view, partly in section, of a portion of the apparatus of FIG. 1 with the top cover partly removed to show a second typical embodiment of a coupling mechanism for coupling diode cavities to the elliptical cavity;

FIG. 6 is a view, partly in section, taken at 6--6 in FIG. 5;

FIG. 7 is an outside view of a plurality of stacked elliptical cavities with the peripheral diode cavities positioned with their axes directed outward;

FIG. 8 is a sectional view taken at 8--8 of FIG. 7;

FIG. 9 is a sectional view taken in a plane of the major axes of the cavities of FIG. 7;

FIG. 10 is a sectional view, taken in the plane of the major axes of a plurality of elliptical cavities stacked and fed in accordance with one embodiment of this invention;

FIG. 11 is a sectional view of a pair of stacked elliptical cavities showing an alternative structure for coupling the cavities;

FIG. 12 is a sectional view taken at 12--12 in FIG. 11;

FIG. 13 is a sectional view taken at 13--13 in FIG. 12;

FIG. 14 is a sectional view of the periphery of a pair of stacked elliptical cavities showing another structure for coupling the cavities; and

FIG. 15 is a sectional view of the periphery of a pair of stacked elliptical cavities showing yet another structure for coupling the cavities.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference is first directed to FIGS. 1-4 for the purpose of explaining the operation and function of the individual elliptical cavities which are combined in various modified configurations to form structures in accordance with the subject invention. The devices of FIGS. 1-4 are described in U.S. Pat. No. 3,733,560 and that description is included herein for completeness. Referring to those figures, a substantially right, substantially elliptical, substantially cylindrical microwave cavity 10 is defined by a pair of substantially elliptical top and bottom plates 12, 14 and an up-standing side wall 16 electrically contacting the top and bottom walls 12 and 14. Around the periphery of the cavity 10 are formed a plurality of smaller cavities 20a, b, c . . . , as shown particularly in FIG. 4, for receiving microwave energy from the coaxial cable 22 which is positioned substantially at one focus of the elliptical cavity. In the embodiments shown in the figures, only eight such cavities are indicated on each side of the major axis of the elliptical cavity. In practice, the cavities may be more closely spaced and a larger number of cavities, as desired, may be used. The cavity 10 is mentioned hereinafter as an "elliptical cavity."

Referring to FIG. 3, probes 24a, b, c . . . extend upward from the cavities 20a, b, c . . . into the elliptical cavity 10. The cavities 20a, b, c . . . are shown, typically, bored out of a ring 28 which depends from the side wall 16. Within each cavity 20a, b, c . . . is an amplifying diode 30a, b, c . . . , each being connected through a radio frequency choke 32a, b, c . . . to a pigtail 34a, b, c . . . to which a source of DC bias voltage (not shown) may be attached to cause the diode 30a, b, c . . . to operate in the proper range. Another mode of operation is to use a pulsed D.C. voltage to provide energy to the diodes.

Within each of the cavities 20a, b, c . . . is a tuning screw 36a, b, c . . . for adjusting the cavity 20a, b, c, . . . to the frequency band of the incoming and transmitted radiation. The coupling of the cavities 20a, b, c . . . to the elliptical cavity 10 is adjusted by adjusting the position of the screws 38a, b, c . . . and 40a, b, c . . . between the up-standing probes 24a, b, c . . . . Between the cavities 20a, b, c . . . , septums 42a, b, c . . . may, optionally be structured to minimize cross talk between the cavities 20a, b, c . . . . The septums 42a, b, c . . . are preferably conductive plates extending outward from the wall 16 into the cavity 10 far enough that the tuning screws 38a, b, c . . . and 40a, b, c . . . control the amount of coupling or energy delivered to and received from each of the cavities 20a, b, c . . . .

Incoming microwave energy is amplified by the diodes 30a, b, c . . . and retransmitted into the cavity 10 to the focus of the elliptical cavity where a coaxial cable 50 removes the power. It is understood that the coaxial cables 22 and 50 are representative only and that other known means for coupling microwave power into and out of the cavity 10 may be used.

When the cavities 20a, b, c . . . are operated as generators or oscillators, the incoming microwave energy phase-locks the generators so that the cumulative signal at the terminal 50, from each of the generators, arrives in phase.

It is important that resonances within the cavity 10 is suppressed. One means for absorbing or suppressing the resonant modes is to place an absorbing material 52, 54 and 56 along the major axis of the elliptical cavity.

Microwave power is introduced through coaxial cable 22 into the cavity 10. The power radiates radially from the axis of the coaxial cable 22 toward the cavities 20a, b, c . . . . The incident fields are amplified by the diodes 30a, b, c . . . and transmitted back to the coaxial cable 50 at the other focus of the elliptical cavity 10. All signals travel from the focus associated with the coaxial cable 22 to the focus associated with the coaxial cable 50 via the elliptical boundary of the cavity 10 along equal length paths, whereby all signals received at the coaxial cable 50 are in phase and can be removed by the coaxial cable 50.

Alternatively, the diodes 30a, b, c . . . may be operated in an oscillatory mode, that is in an unstable condition to produce signals which, in general, would be out of phase. A small amplitude incident signal from the coaxial cable 22 injection phase-locks the sources causing them to deliver in phase signals to the coaxial cable 50.

Although the apparatus operates without absorbers 52, 54 and 56, it operates better with the resonant modes suppressed. the absorbers 52, 54 and 56 are representative of the resonance suppressors which are described and claimed in U.S. Pat. No. 3,733,560; by Henry G. Oltman, Jr.; for "Means and Method for Suppressing Microwave Resonance in Elliptical Cavities."

FIG. 5 illustrates a second structure for coupling the diode cavities 20a, b, c, . . . to an elliptical cavity 10. Instead of using coupling screws such as 40a, b, c, of FIGS. 2, 3 and 4, the coupling technique of FIGS. 5 and 6 uses a plurality of orifices, 70a, b, c in a conductive wall or septum 72. The size of the orifices 70a, b, c are predetermined to produce the desired amount of coupling. In all other respects, the apparatus of FIGS. 5 and 6 is substantially the same as the apparatus of FIGS. 3 and 4.

When, as in accordance with the subject invention, a plurality of elliptical cavities, such as cavities 80, 82 and 84 (FIG. 7), are stacked, it may be necessary, and/or desirable, that the diode cavities such as diode cavities (modules) 74a, b, c, . . . 76a . . . 78a . . . , be positioned perpendicular to the sidewalls of the elliptical cavities 80, 82 and 84. A typical structure for illustrating such an arrangement is presented in FIG. 7. It is noted that to maintain the clarity of FIG. 7 only a sufficient number of diode modules are shown as are necessary to indicate the pattern of their disposition about the periphery of elliptical cavities 80, 82 and 84. It will be understood, for example, that diode modules are spaced completely around elliptical cavity 80 in accordance with the pattern exhibited by modules 74a, b and c; and that the disposition of diode modules around elliptical cavities 82 and 84 is similar to that described for cavity 80.

Diode modules 74a are shown in greater detail in FIG. 8 to which reference is now directed. As there shown, a loop 90a provides the coupling between the diode cavity and the fields of elliptical cavity 80, and the degree of coupling may be adjusted by rotating the loop. Frequency adjustment and support of coaxial center conductor (probe) 24a is provided by a dielectric cylindrical slug 92a which is adapted for movement into or out of the high electrical field region of the cavity. Freguency tuning is provided by means of a screw 94a which is disposed in the high field region.

In the embodiment of FIGS. 7 and 9 elliptical cavities 80, 82 and 84 are stacked and single coaxial cable 22', whose outer conductor is split within the space of each cavity, delivers energy into the stacked cavities at a first focus thereof so as to introduce energy consecutively into the stacked cavities. The microwave energy in each of the stacked cavities radiates radially outward from its input focus to the amplifying modules, such as 74a, b, c . . . , on the periphery of each elliptical cavity. Coaxial cable 50' receives energy consecutively from the second focus of each of the elliptical cavities 80, 82 and 84. Since the energy is introduced into the cavities in sequence and it is removed in sequence, the time delay between receipt of energy by the sequentially excited elliptical cavities and the time delay between delivery of energy by corresponding elliptical cavities is the same, whereby the power outputs of each of the cavities 80, 82 and 84 add.

For the structure of FIGS. 7 and 9, an equal part of the incident signal would be fed to each unit. However, for application in which it may be desirable to stack structures of different diameters having different numbers of diodes modules, the fractional power coupling to each elliptical cavity would be varied according to its respective size and/or maximum power output. As noted above, although each elliptical cavity is excited in successively later phase relationships, the phase lag is corrected by collecting the amplified signals with the opposite phase relationship. This is accomplished by arranging the input and output couplings on opposite sides of the elliptical structure. As a result, the transit time of any fractional part of the signal through the structure is the same as any other part of the signal.

As previously mentioned, for the embodiment of FIGS. 7 and 9 the relative coupling along coaxial lines 22' and 50' generally would be adjusted so that equal amounts of power are removed (or added) from the lines. However, the lines have either a reducing or increasing power level. That is, the power level on the input line is decreased after passing each input port, 96, 98 and 100, and the output power is similarly increased after passing each output port 102, 104 and 106. Therefore, on input line 22', a successively larger fraction of the available power must be extracted from the line in order to achieve power equality in each ELLPAC. This requirement dictates a change in physical dimensions for each coupling port.

It is noted that the diameters of the elliptical structures are completely independent even though they have equal foci separation as shown. The separation of the foci is determined by the relative lengths of the major and minor axes of the ellipses -- not by the absolute length of the major axis.

FIG. 10 depicts a second embodiment of the subject invention wherein elliptical cavity 83 is used as a preamplification stage for the signal driving the amplifying structure comprising parallel coupled cavities 80', 82' and 84'. In this manner an input signal applied on line 23, which is too low to be split up to drive the four output structures, can be amplified to the required power level.

In accordance with a third embodiment of the invention, a plurality of elliptical cavities are stacked and intercoupled such that greater input-output isolation is provided along with a reduction in the volume and weight required for a device having given amount of power gain capability. As shown in FIGS. 11 through 13, two elliptical cavities 110 and 112, which have a common wall 13, are stacked one on top of the other with the coupling between the two elliptical cavities provided by the diode cavities (modules) at the periphery of the ellipse. One such diode module, designated 114, is illustrated in FIGS. 12 and 13. The direction of signal flow is indicated by an arrow 113 in FIG. 12. Input and output coupling is primarily determined by the size of irises 115 and 117, with a small amount of coupling variation being provided by coupling screws 119 and 121. The diode module 114 is offset from the symmetry line of elliptical cavities 110 and 112 in order to create both the small iris 115 and the larger iris 117. In this manner the amplifier is made nominally unidirectional.

In the embodiment of FIG. 11 the two elliptical cavities are substantially identical, and the foci of the two cavities are substantially coaxial. Energy introduced on coaxial line 116 at the focus of cavity 110 radiates along a radial path from that focus to the periphery where it enters the diode modules, such as 114 of FIG. 12. The diodes within the various modules amplify the signal and return it to focus 118 of cavity 112. To minimize unwanted signals, terminals at focus 120 of cavity 110 and focus 122 of cavity 112 are terminated with their characteristic impedance. Hence the diode modules operate as two-part amplifiers having a relatively weak coupling to input cavity 110 and a relatively strong coupling to output cavity 112. Thus, the largest fraction of the amplified signal is coupled to the output coaxial lead 124. Usually, that fraction of the input signal coupled back to the input would be adjusted to be less than the input signal power. However, this particular adjustment limits the overall gain and hence can be undesirable. The embodiment of FIGS. 11 and 12 allows isolation and stability without this last mentioned adjustment and the accompanying deleterious results.

One of the advantages of the embodiment of FIGS. 11 and 12 is that greater output-to-input isolation is provided. Because of the weak-strong diode module coupling, signals that are traveling in the reverse direction and are incident on output terminal 124 will be amplified but only weakly coupled to input terminal 116. Most of the amplified power will be absorbed in the load at the second focus 122 of output cavity 112. The advantage of this increase isolation is a reduced tendency of the amplifier to oscillate.

A second advantage of this embodiment is better impedance match to both input transmission line 116 and output transmission line 124. This advantage results because all signals reflected by the diode modules on either the input or output side are propagated to the respective foci on which a matched load is attached. The signals are not reflected back towards the input or output terminals. With this arrangement, only the mismatch of the transducers at the input and output ports affect the impedance match of the amplifier.

A third advantage is greater latitude in diode module dimensional tolerances. This advantage is a result of the two loaded second foci as discussed above. Because reflected signals are absorbed, greater dimensional tolerances, which would result in greater mismatches, can be permitted.

Also, greater latitude of input and output coupling is provided by the embodiment of FIGS. 11 and 12. This advantage also results from the loaded foci. For a two-port diode module amplifier, this advantage permits stronger input coupling which results in greater gain, but eliminates the stronger return signal. This return signal is composed of a signal reflected from the coupling iris combined with a signal amplified by the diode module and recoupled into input cavity 110. The load on the second focus 120 of input cavity 110 absorbs both parts of this return signal. A further advantage is the elimination of direct coupling between input transducer and output transducer which is possible in structures having input and output terminals in the same cavity. Any signal directly coupled between terminals will beat with that signal propagating to the elliptical perimeter before being collected at the output terminal. This effect will reduce the bandwidth. Absorber can be used in a single cavity configuration of FIG. 1 to reduce the direct coupling, but here, it is completely eliminated.

It is also noted that additional signal gain and input-output impedance isolation for the overall amplifying structure may be readily realized by stacking any number of the structures shown in FIG. 11, one on top of each other. For example, line 116 may be inserted into the output port of a similar elliptical structure (not shown) and the signal to be amplified would be applied to the input line of this additional structure. Although the impedance loading (elements 103 and 107) of foci 121 and 122 are shown as external to the elliptical cavities for clarity of the illustration, it is understood that these loads may be implemented internal to the structure so as not to interfere with their stacking. Also, either of the foci of a particular cavity may be selected for loading so as to simplify the stacking implementation. For example, referring to the structure of FIG. 11, the focus 101 could be "loaded" in its characteristic impedance and the input signal applied to the line 105, i.e. load 103 would be connected to line 116.

The structure of FIGS. 12 and 13 provides for coupling the amplifier module, such as 114, to the elliptical structure so as to create an overall structure which is flat. FIG. 14 illustrates a method of coupling two elliptical cavities in which the amplifier diodes cavity is arranged similarly to that of FIGS. 3-6. When combined with elliptical cavities such as 110 and 112 of FIG. 11 the coupling of FIG. 14 results in a two-port amplifier module which provides the advantages discussed above relative to FIG. 11. In accordance with the embodiment of FIG. 14, the input signal is fed into the upper elliptical cavity 110 which couples the signal to each of the diode amplifiers, such as 130, arranged around the perimeter, through slot 132 located in septum or wall 13 which separates cavities 110 and 112. The size of slot 132 and hence the amount of coupling can be varied by means of slideably mounted plate 134. Tuning screw 136 is disposed to capacitively load the center of coupling 132. The output coupling is adjustable by means of screw 138 and is normally greater than the input coupling. In this manner the signal reflected back to input cavity 110 is minimized.

FIG. 15 shows another means for coupling the input signal into the diode amplifiers located in elliptical cavity 112. In this embodiment coaxial center conductor 140 is extended through septum 13 which seperates the two cavities. The degree of coupling is determined primarily by capacitive by-pass 142 and secondarily by coupling adjustment screws 144 and 146. The larger the by-pass capacity, the smaller the coupling and the by-pass capacitor may be viewed as a leaky end wall of the coaxial cavity in lower elliptical cavity 112. Screw 148 provides tuning adjustment.

Thus there has been described improved devices for microwave signal amplification by the accumulation of power produced within a plurality of stacked elliptical cavity structures.