GB1561442A - Cavity resonator assembly having linear frequency tuning and circuitry incorporating the assembly - Google Patents

Description

PATENT SPECIFICATION

( 21) Application No 51515176 ( 22) Filed 9 Dec 1976 ( 44) Complete Specification published 20 Feb 1980 ( 51) INT CL 3 HOIP 7104 ( 52) Index at acceptance H 1 W 1 2 3 B 1 GA ( 72) Inventors IMRE TORMA, SANDOR FOLDES, ERNONE TEMESI and JOZSEF DOROGI ( 11) 1561442 ( 19) ( 54) CAVITY RESONATOR ASSEMBLY HAVING LINEAR FREQUENCY TUNING AND CIRCUITRY INCORPORATING THE ASSEMBLY ( 71} We, TAVKOZLESI KUTATO INTEZET, of 1026 Budapest, Glbor Aron ut 65, Hungary, a body corporate organized under the laws of Hungary, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following

statement: -

The invention relates to a cavity resonator assembly having substantially linear frequency tuning One or more such assemblies may be used in circuits especially signal generators, measuring oscillators, and frequency meter and measuring-receiving microwave-circuits.

A cavity resonator assembly usually consists of a cavity, a tuning unit and wellknown complementary elements, for instance a coupling loop, an iris, a reflex-klystron, a semi-conductor as well as units for signal feeding and control.

In tunable cavity resonators and circuits with cavity resonators (for example circuits such as resonant frequency meters, measuring oscillators tuned by a cavity resonator, signal generators and receivers) the following known techniques are used for tuning:In case of a non-linear tuning tuning the resonant frequency takes place by using a driving structural element having non-linear displacement, so that reading frequency is performed indirectly, by using a calibration diagram, or by a non-linear calibrated frequency scale In circuits having several cavity resonators, using this type of tuning, either there is a separate driving element for each single resonator, which must be adjusted individually, or a common drive is used for each resonator and suitable constructions are applied for compensating the differences between the characteristics of the single resonators.

In one prevalent solution, linear frequency tuning is achieved by using a cam The tuning element of the cavity resonator is actuated by an eccentric construction in which the cam radius changes in accordance with the non-linear tuning rule of the cavity; an adjustable embodiment of the cam arrangement is also well-known.

In a helical tuning method, which can be considered as a more developed variant of tuning using the cam, the cam is replaced by a spiral with non-linear pitch, fixed to the outside of the cavity.

Realization of linear frequency tuning is well known using a construction having a rod-mechanism approximating the nonlinear tuning characteristics of the cavity resonator by a circular arc.

Approximate linear tuning may be achieved electrically by the simultaneous tuning of several spaces shaped within the cavity resonator.

Frequency-meters are known, in which the displacement of the inner conductor of the cavity causes a change in both the TEM and the TM-components of the electromagnetic field of the cavity.

With respect to the thermocompensation, that is to the reduction in resonant frequency-change due to the change in temperature, the following solutions are wellknown:In cavity resonators and circuits, respectively, where the relative frequency accuracy does not surpass 10-3, steps are not taken to reduce thermosensitivity.

Where the frequency accuracy surpasses ', the cavity resonator, and in some cases the tuning element, are made of materials with a low temperature factor, for example invar (Registered Trade Mark), or the cavity resonator and the tuning element are made of materials having different coefficients of thermal expansion.

Disadvantages of known ways of achieving 1,561,442 linear tuning can be summarized, as follows:Among the methods employing non-linear tuning the variant having indirect reading is considered out moded, since its operation in wearisome Arrangements providing direct reading either require individual calibration involving high expense or manufacturing inaccuracies in cavity resonators and the circuit-elements located therein or coupled thereto, cannot be subsequently corrected, thus deteriorating from the accuracy of calibration.

In circuits containing several resonators, adjustment of the separate tuning elements is difficult, whereas those labour-intensive constructions serving to provide compensation are produced only with difficulty.

Linear tuning of the cam system is simple with respect to construction, but producing the cam requires a special technology, which, besides being expensive, is less accurate, than other technologies requiring simple rotating or progressive movements Calibration errors due to inaccuracies in dimensions occurring during production again cannot be corrected.

Solutions employing an adjustable cam and spirals allow subsequent correction but at the expense of a more complicated, consequently more expensive structural form.

In order to achieve accuracy, labour-intensive adjustment at several points is imperative and in course of adjustment material deformation occurs, reducing the stability of the adjustment.

By using the tuning method employing a rod-mechanism, an approximate linearisation may be achieved, but errors cannot be reduced to below the value corresponding to the difference between the circular characteristics realized by the tuning rule of the cavity resonator and the rod mechanism.

Simultaneous tuning at several frequencies necessitates a form of the cavity resonator which is disadvantageous in respect of quality factor, consequently the attainable accuracy of linear tuning will be restricted too and the theoretically approximate nature of the tuning realized is a further restriction of accuracy.

Disadvantages of the techniques used for the reduction of temperature-errors are, as follows: Where materials with a low temperature-factor are used, these special materials (invar, superinvar Registered Trake Mark) are expensive, processing costs are also very high, and their temperature coefficient is not equal to zero Also significant inaccuracies result in manufacturing.

The drawback of known thermocompensating solutions lies in that compensation takes place only at one single point in the tuning range of the cavity and the circuit, respectively, and effectiveness is restricted 65 to a rather small frequency range.

The aim of our invention has been to produce a cavity resonator assembly in which in manufacture limits of accuracy and labourintensivity can be significantly reduced 70 According to the present invention there is provided a cavity resonator assembly comprising a cavity containing at least one tuning element fixed to a guide member, the tuning element and the guide member being 75 constrained to move along a first straightline path, a structural element pivoted about an axis perpendicular to the said path and defining a second straight-line path relative to the structural element, means for con 80 straining the guide member to move along the second straight-line path, and frequencycontrol means for controlling the angular position of the structural element about the said axis, the frequency-control means in 85 cluding a displaceable control member and being so constructed and/or arranged that displacement of the control member is linearly related to movement of the guide member along the first straight-line path 90 Cavity resonator assemblies according to the invention can be arranged to have the following advantages: A reduced modification of characteristics resulting from inaccuracies in manufactur 95 ing the cavity and any coupled circuitelements to an extent, where few adjusting elements are required.

Instead of linear tuning having an approximate character, a linearisation strictly based 100 on the operational field strength distribution within the cavity resonator can be achieved.

This distribution plays a significant role in forming the tuning characteristics of the cavity resonator 105 The frequency control means may comprise a further guide member and means for constraining the further guide member to move also along a third straight-line path at an angle other than 1800 to the first straight 110 line path, displacement of the control member so causing movement of the further guide means along the third straight-line path that the structural element rotates about the said axis 115 In a cavity resonator assembly according to the invention, the said axis of pivoting the structural element, the axis of rotation of a roller forming the guide member fixed to the tuning element and the axis of rotation 120 of a roller of the further guide member lie in a straight line, parallel to the second straight line path.

The direction of movement of the further guide member forming part of the frequency 125 control means may be at right angles to (or an angle smaller than a right angle to) the direction of movement of the tuning element.

Preferably the axis of rotation of the 1,561,442 roller fixed to the tuning element, is so formed that its position relative to the tuning element can be adjusted.

Where the said axis is defined by a pivot for the structural member, the position of the pivot is preferably adiustable relative to the cavity in a plane defined by the first and third straight-line paths.

In addition the position of the further guide means in the third straight-line path is preferably adjustable without displacement of the control member.

Any deviation in dimensions of the cavity resonator and the tuning element, occurring in a manufacturing process, can then be so compensated that the position of the tuning element and the third guide member of the frequency-control means in relation to the first straight-line path, is adjustable, as is the position of the axis of rotation of the structural element in relation to the cavity Using the three adjustments mentioned above the zero frequency-error can be adjusted at three different points of the frequency-characteristics As a consequence of the exact linear transformation, in the case of such an adjustment, the frequencyerror due to the transformation will be equal to zero over the whole operational frequency band of the cavity resonator.

A linearly tuned measuring oscillator or a signal generator can be formed by connecting a negative resistance semi-conductor, for example a Gunn-diode, an IMPATTdiode, or a Baritt-diode, between the outer and inner conductor of the cavity resonator according to the invention constructed to operate in the TEM mode In this case the range of the adjusting elements has to be increased to an extent, which allows compensation for the effect of the reactance of the semi-conductor exerted on the frequencycharacteristic of the generator Instead of a semi-conductor an electronic tube for example a refiex-klystron, can be used in constructing a measuring oscillator or signalgenerator.

Parts for cavity resonator assemblies according to the invention for TEM, TE or TM modes can be easily and accurately prepared and technological difficulties occurring in preparing structural elements having special shapes, use in the previously described prior art cavity resonators do not occur.

Owing to its exact linear properties with respect to the fundamental mode, accuracy of frequency is not restricted by a theoretical approximation-error.

Errors are produced mainly by additional reactances, for example the reactance of the semi-conductors or electronic valves, built into the cavity resonator or coupled to the same However, the adjustments provided for the compensating errors in manufacturing, also serve to compensate for the above mentioned additional reactances.

Thus in compensating manufacturing errors, as well as the optimal approximation of the said additional reactances, if any, 70 only a few adjusting elements are needed and, as a consequence, the labour-intensity of adjusting tuning characteristics is reduced.

If a change of the active-element (semi 75 conductor or electronic valve) is required in the cavity resonator, readjustment of the frequency-characteristic can be performed with the original accuracy and without needing much skilled effort 80 Thermal compensation of the cavity resonator assembly according to the invention may include ensuring that when a rise in temperature occurs, within the working temperature range of the assembly, the resultant 85 thermal expansion of the perpendicular distance between the pivotal axis of the structural element and the end of the cavity opposite the tuning element equals the resultant thermal expansion of the distance 90 between the guide member which is fixed to the tuning element and the face of the tuning element which is opposite the said end of the cavity.

Where the assembly comprises the further 95 guide member mentioned above and if the further guide member is constrained to move along the second straight line path when the control member is displaced, sthen preferably, the coefficient of thermal expansion 100 of the components defining the movement of the further guide means equals the sum of the resultant coefficients of thermal expansion of the components defining the perpendicular distance between the straight 105 line path of the guide member which is fixed to the tuning element and the pivotal axis of the structural element, and of the components defining the perpendicular distance between the third straight-line path 110 and the pivotal axis of the structural element.

As an alternative the further guide member is fixed to the structural element remote from the said axis and displacement of the 115 control member changes the length of that portion of the structural element between the said axis and the further guide member so causing the structural element to rotate about the axis In providing thermal com 120 pensation the coefficient of thermal expansion of the components defining the perpendicular distance between the pivotal axis of the structural element and the straight line path followed by the guide member 125 fixed to the tuning element In addition the resultant coefficient of thermal expansion of components defining the distance between element may be made equal to the coefficient of thermal expansion of the cavity and may 130 1,561,442 be made equal to the resultant coefficient of thermal expansion of the components defining the perpendicular distance between the third straight line path and a line through the pivotal axis of the structural element at right angles to the first straight line path.

A further advantage of the invention lies in that beside linear frequency control, thermo-compensation independent of frequency, is also possible, contrasting with other known techniques, where thermocompensation takes place at one single frequency only.

Certain embodiments of the invention are now described by way of example with reference to the accompanying drawings in which:Figure 1 is a cross-section of a cavity resonator assembly for the TEM mode according to the invention, Figure 2 is a cross-section of a cavity resonator assembly for the TE or TM mode according to the invention, and Figure 3 is a cross-section of an oscillator employing a cavity resonator assembly according to the invention.

In Figure 1 a cavity 1 contains an inner conductor 2 and a tuning element, expediently formed as a non contacting piston 3.

A spacer, consisting of rods 4 and 7 and a holder 8, connecting the same, is fixed to the piston 3 Displacement of the piston 3 is forced into a path parallel to the longitudinal axis of the cavity 1, by a straight path 9 formed by the holder 8 Displacement of the tuning piston 3 on this path is caused by the arrangement shown, in which a roller 10 fixed to the rod 7 contacts a structural element 16, and rolls along a guide-path 15, formed in a plane perpendicular to the plane of the drawing At the same time a roller 11 fixed to a rod 12 also rolls along the guide-path 15 The forced coupling between the rollers 10, 11 and the guide-path 15 is expediently ensured by springs 23 and 29 In this way the moment, resulting from the tension exerted by the spring 23 and applied about the axis of rotation 26 of the element 16 (this axis being perpendicular to the plane of the drawing) is always greater, than the moment of opposite sense, resulting from tension in the spanner spring 29.

The roller 11 and the rod 12 connected thereto move along a straihtt path defined by a bush 13 and a threaded sleeve 19, the roller 11 being in a forced coupling with the guide-path 15 of the structural element 16.

The straight path of the rod 12 expediently is at an angle of inclination of 90 to the path of the tuning element (but any angular value differing from N X 180 is acceptable, where N = a real number) The angular displacement of the threaded sleeve 19, and that of a rotatable knob 20 having a scale 21 is directly proportional (owing to the forced coupling between a threaded spindle 18 formed on the rod 12 and the threaded sleeve 19) to the displacement of the rod 12 70 along the path Furthermore, due to the forced coupling described above, the said angular displacement is directly proportional to the change in the resonance-frequency of the cavity resonator, caused by the displace 75 ment of the tuning piston 3 As a consequence of this direct proportionality, the scale 21 may be prepared with a linear frequency graduation, and for reading the scale an index 22 may be used The factor 80 of the proportionality is defined by the mode-index of the cavity resonator (i e the quotient of the length of the cavity and the resonant wavelength), by the velocity of light, the pitch of the threaded spindle 18, 85 the length of the arc of the scale 21, and the product of the distances, measured from the axis of rotation 26 of the structural element 16 to the axes of rotation of the rollers and 11, respectively A holder 25 serves 90 for the adjustment of these rollers and is shaped as a bearing for the axis of rotation 26, which is able to move along the path 24 formed in the holder 27 and fixable in the same Positioning the tuning piston 3 in 95 relation to the axis of rotation of the roller is carried out by displacing the rod 7 in the holder 5 in the direction of the longitudinal axis of the cavity, whereby the final position is fixed by a screw 6 By turn 100 ing the scale 21 on the threaded sleeve 19 and fixing the same, the relative position of the axis of rotation of the roller 11 and the scale 21 can be adjusted By the aid of the three adjusting elements mentioned 105 above, the resonance frequency of the cavity resonator can be adiusted to the prescribed value at three different points, and thus the error of frequency, resulting from the manufacturing tolerances of the tuning 110 structural elements can be eliminated In cavity resonators operating with in the pure TEM mode, the adjustments described above yield a theoretical frequency-error equaling to zero over the entire tuning range, and 115 also an exact linear connection may be achieved between the resonant frequency and the position of the rod 12 and the scale 21, respectively.

A holder 14 serves to the structural ele 120 ments to the cavity resonator, as well as for defining the straight path of the rod 12 A coupling loop 28 serves to couple electromagnetic signals to and from the cavity resonator, but instead of the loop, one or 125 more coupling elements employing an iris or a probe may be used Instead of the frequency-scale formed on the knob 20, a scale with a digital reading, with a number indicating disc, driven from the axis of the 130 1,561,442 knob through a geared transmission can expediently be used.

In Figure 2 a cavity resonator 11 according to the invention, for operating in a TE or TM mode, is shown in a longitudinal section A spacer, consisting of the rods 41 and 71 is connected to a tuning piston 31 The displacement of the tuning piston 31 is forced into a straight path, parallel with the longitudinal axis of the cavity, by the straight path 9 ' formed by a holder 8 '.

The displacement of the tuning piston 3 ' along the path is determined by an arrangement in which a roller 101, fixed onto the rod 7 ', rolls along a guide-path 151 formed on a rod 12 ', while a structural element 161 together with the rod 121 rotates about an axis 261, which is perpendicular to the plane of the drawing The rod 12 is able to move in the direction of the longitudinal axis of the structural element 16 ' Movement of the rod 121 is controlled by the rolling movement of a roller 111 along any other straight guide-path 171, perpendicular to the axis of the cavity resonator and formed on a holder 141 The rollers 111 is fixed, expediently by the aid of the spacer 441, onto the operating rod.

The roller 101 is constrained towards the guide-path 15 ', and the roller 111 is constrained towards the second path 17 ' by a spanner spring 29 '.

In the embodiment of Figure 2, the guidepath 15 ' is formed not directly on the structural element 161 itself, but on the rod 12 ', a path formed on the structural element itself would yield the same quality of tuning, since the structural element and the rod rotate together around the axis of rotation 261 The displacement of the rod 12 ' in relation to the structural element 16 is achieved by the use of a threaded spindle 181, rotatably arranged in a threaded sleeve 191, a rotatable knob 201 being fixed to the spindle 18 '.

In the said embodiment of Figure 2 the threaded sleeve 19 ' is formed on the rod 12 ' instead of the structural element connected to the turn knob, consequently the threaded spindle 18 ' is formed on the structural element connected to the turn knob instead of the rod 121; of course the linear frequency tuning according to the invention can also be realized with an opposite arrangement of the spindle and the threaded nuts.

The axes of the rollers 101 and 11 ', and also the axis of rotation 261 are arranged in a plane perpendicular to the plane of the drawing In this case the displacement of the rod 121 in relation to the structural element 161 and consequently the angular displacement of the knob 201 is directly proportional to the resonance-frequency of the cavity resonator Thus the knob may be provided with a frequency-linear scale 211 which can be read with the aid of an index 221 A lug 321, moving in a notch and formed in the structural element 161 prevents the rod 121 becoming detached from the structural element 161 when the knob 201 is 70 turned.

A condition for linear frequency tuning is that the distance between the axis of rotation 261 of the structural resonator is equal to the product of the half-wavelength 75 of the mode of oscillation, i e the waveform in the cavity resonator and the mode-index with respect to the longitudinal axis of the cavity (i e the number half periods in the field strength occurring along the longitu 80 dinal axis) Furthermore the projection of the distance between the axis of rotation 261 and the axis of rotation of the roller 101 onto the longitudinal axis of the cavity resonator should be equal to the electric 85 length of the cavity, i e to the distance between the end plate 451 of the cavity and the piston To ensure these conditions, the holder 251 is so shaped that that its position may be adjusted in relation to the axis of 90 the cavity The position selected is fixed with the aid of the screw 301 The rod 71 may also be shifted in the rod 41 and its position fixed by a bolt 61 The factor of proportionality of the linear displacement 95 of the rod 121 in relation to frequency is defined by the cut-off wavelength of the operative waveform of the cavity resonator, the velocity of light and the distance between the plane of the guide-path 171 and 100 the plane passing through the axis of rotation 261 and perpendicular to the axis of the cavity The latter can be adjusted by the displacement of the holder 141 parallel to the longitudinal axles of the cavity, the posi 105 tion of the holder 141 being fixed by a screw 311 In addition to the above mentioned factors, when determining the factor of proportionality of the scale-division, the pitch of the spindle 181 and the scale 110 arclength of the turn knob is also calculated.

By positioning the rod 71, the axle of rotation 261 the holoder 141, and the scale on the knob 20, the resonant frequency of the cavity resonator can be adjusted to a 115 perscribed value at least at three different points in the operative range of the cavity resonator, thus eliminating frequency errors resulting from manufacturing tolerances in the cavity resonator and the tuning struc 120 tural elements.

By performing the adjustment described above in cavity resonators o Derating with a pure TE or pure TM waveform, not only can a theoretically frequency-error equal to 125 zero be achieved over the entire tuning range, but also an exact linear relation between the position of the rod 121, i e the scale 211, and frequency can be attained.

An iris 35, connecting the cavity to the 130 1,561,442 interior 331 of a waveguide joined to an end plate 341 of the cavity, and a coupling loop 281 serve to couple electromagnetic signals in and out, respectively, of the cavity resonator Of course, instead of these input and output units one or more other known coupling elements may be used.

Instead of the simple arrangement illustrated in Figure 2, that is a scale arranged on the rotatable knob, a frequency-scale with digital reading, driven expediently from the axis of the knob by gears, can be used for reading the resonant frequency.

Figure 3 shows a longitudinal section of an oscillator comprising a reflex-klystron as the active circuit element which excites oscillation in the mode In the description of Figure 3, only the details which differ from the arrangement illustrated in Figure 1 are described.

In the inside of the inner conductor of the cavity 1 a bore is provided, partly to enable the electrical connection of one of the cavity grids 38 of a reflex-klystron 36 to the end of the inner conductor 2, and partly to allow the connection of a supply voltage to the reflector-electrode-connection 39 of the reflex-glystron.

The other cavity grid 37 of the reflexklystron 36 is electrically connected to the external conductor of the cavity The voltage for the reflector of the reflex-klystron, the accelerating voltage for the unit 40, the voltage for the electrode (grid or Wehneltcylinder) of the beam-current controller 41, as well as the heating voltage for the unit 42 are supplied by supply-units 43.

As it is well-known, the frequency of oscillation of an oscillator tuned by a cavity resonator is fundamentally defined by the resonant frequency of the cavity; the characteristics of the active circuit element in this case the reflex-klystron exerting a relatively small effect Thus the tuning characteristics of the oscillator illustrated in Figure 3 is similar to that of the cavity resonator shown in Figure 1, i e it is linear with a good approximation; deviation from linearity being due to the contributory effect of the active element The deviation can be adjusted to zero at three different frequencies of the tuning range, using the same adjusting element, which serve for the elimination of the errors resulting from manufacturing tolerances in the cavity resonator and the tuning structural elements.

In the oscillator according to Figure 3, positioning of the holder 25, the rod 7 and additionally the scale 21, besides playing a role that is identical with the function of the corresponding adjusting elements of the cavity resonator according to Figure 1, simultaneously serve to approximate at three zero-points the contributory effect of the active circuit element.

A signal generator using a cavity resonator according to the invention, operating with a TEM-waveform and tuned by the cavity resonator, differs from the oscillator illustrated in Figure 3 in the level-measuring, controlling and dividing circuits of the coupling circuits Since such circuits arewell known, description in detail has been omitted.

In the oscillator according to Figure 3 active circuit elements, semi-conductors (f i.

Gunn-diodes, IMPATT-diodes, Barittdiodes, transistors, etc) may be used instead of the reflex-klystron, furthermore instead of the supply and modulator units illustrated in Figure 3, supply and modulator units, serving to operate the semiconductor circuit element, are used, thus producing an oscillator and signal generator, respectively, having the same properties in respect of linear frequency tuning, as described in connection with Figure 3.

Claims (19)

WHAT WE CLAIM IS:-

1 A cavity resonator assembly compris 90 ing a cavity containing at least one tuning element fixed to a guide member, the tuning element and the guide member being constrained to move along a first straight-line path, a structural element pivoted about an 95 axis perpendicular to the said path and defining a second straight-line path relative to the structural element, means for constraining the guide member to move along the second straight-line path, and frequency 100 control means for controlling the angular position of the structural element about the said axis, the frequency-control means including a displaceable control member and being so constructed and/or arranged that 105 displacement of the control member is linearly related to movement of the guide member along the first straight-line path.

2 A cavity resonator assembly according to claim 1 wherein the frequency control 110 means comprises a further guide member and means for constraining the further guide member to move also along a third straightline path at an angle other than 1800 to the first straight-line path, displacement of the 115 control member so causing movement of the further guide means along the third straight-line path that the structural element rotates about the said axis.

3 A cavity resonator assembly accord 120 ing to Claim 2 wherein the further guide member is also constrained to move along the second straight-line path when the control member is displaced.

4 A cavity resonator assembly accord 125 ing to Claim 2 wherein the further guide member is fixed to the structural element remote from the said axis and displacement of the control member changes the length of that portion of the structural element be 130 1,561,442 tween the said axis and the further guide member so causing the structural element to rotate about the axis.

A cavity resonator assembly according to any preceding claim wherein at least one of the straight-line paths is defined by a surface and the guide member which is constrained to move along that straight-line path comprises a roller or slider constrained to roll or slide in contact with the surface.

6 A cavity resonator assembly according to Claim 5 wherein the tuning element comprises a piston in the cavity, the guide member which is fixed to the tuning element comprises a roller or slider external to the cavity and fixed by way of a structural member to the piston, and the guide member which moves along the second straight-line path is constrained to do so by resilient means urging the roller or slider into contact with a surface of the structural element which defines the second straight-line path.

7 A cavity resonator assembly according to Claim 6 insofar as dependent upon Claim 3 wherein the further guide member comprises a roller or slider which is urged into contact with the said surface of the structural element by further resilient means.

8 A cavity resonator assembly according to Claim 6 insofar as dependent upon Claim 4 wherein the third straight-line path is defined by a surface fixed in relation to the cavity, and the further guide member comprises a roller or slider resiliently urged into contact with the surface.

9 A cavity resonator assembly according to Claim 7 or 8 wherein the guide members comprise rollers, and the said axis and the axes of the rollers lie in a straight line parallel to the second straight-line path.

A cavity resonator assembly according to any of Claims 2 to 9 wherein the angle between the first and third straight line paths is equal to, or less than, 90 .

11 A cavity resonator assembly according to any of Claims 2 to 10 wherein the frequency-control means comprises a threaded sleeve in engagement with a threaded spindle, one of which is fixed relative to the pivotal axis of the structural element, the other being fixed relative to the control member and the further guide means.

12 A cavity resonator assembly according to any preceding claim wherein the position of that guide member which is fixed to the tuning element is adjustable along the first straight line path in relation to the tuning element.

13 A cavity resonator assembly according to any preceding claim wherein the pivotal axis of the structural element is defined by a pivot and the position of the pivot is adjustable relative to the cavity in a plane defined by the first and third straight 65 line paths.

14 A cavity resonator assembly according to Claim 2 or any of Claims 3 to 13 insofar as dependent on Claim 2, wherein the position of the further guide means in 70 the third straight-line path is adjustable without displacement of the control member to allow setting up adjustment of the assembly.

A cavity resonator assembly accord 75 ing to any preceding claim wherein, when a rise in temperature occurs, within the working temperature range of the assembly, the resultant thermal expansion of the perpendicular distance between the pivotal axis of 80 the structural element and the end of the cavity opposite the tuning element equals the resultant thermal expansion of the distance between the guide member which is fixed to the tuning element and the face of 85 the tuning element which is opposite the said end of the cavity.

16 A cavity resonator assembly according to Claim 3 or any of Claims 4 to 15 insofar as dependent on Claim 3 wherein 90 the coefficient of thermal expansion of the components defining the movement of the further guide means equals the sum of the resultant coefficients of thermal exnansion of the components defining the perpendicular 95 distance between the straight-line path of the guide member which is fixed to the tuning element and the pivotal axis of the structural element, and of the components defining the perpendicular distance between 100 the third straight-line path and the pivotal axis of the structural element.

17 A cavity resonator assembly according to Claim 4 or any of Claims 5 to 15 insofar as dependent on Claim 4, wherein 105 the coefficient of thermal expansion of the cavity equals the resultant coefficient of thermal expansion of the components defining the perpendicular distance between the pivotal axis of the structural element 110 and the straight-line path followed by the guide member fixed to the tuning element.

18 A cavity resonator assembly according to Claim 4, or any of Claims 5 to 15 insofar as dependent on Claim 4, or Claim 115 17, wherein the resultant coefficient of thermal expansion of components defining the distance between the further guide means and the pivotal axis of the structural element equals the coefficient of thermal expansion 120 of the cavity and equals the resultant coefficient of thermal expansion of the components defining the perpendicular distance between the third straight line path and a line through the pivotal axis of the struc 125 tural element at right angles to the first straight line path.

19 A cavity resonator assembly substantially as hereinbefore described with 1,561,442 reference to, and as shown in, Figure 1 or Figure 2 of the accompanying drawings.

A microwave circuit substantially as hereinbefore described with reference to, and as shown in, Figure 3 of the accompanying drawings.

T Z GOLD & COMPANY, Chartered Patent Agents, European Patent Attorneys, 9 Staple Inn, London, WC 1 V 7 QH.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon), Ltd -I 980.

Published at The Patent Office, 25 Southampton Buildings, London, WC 2 A IAY from which copies may be obtained.