US3597691A

US3597691A - Radio transmitter antennae comprising a plurality of open-ended coaxial cavities and means for exiting them with pulsed electron beams

Info

Publication number: US3597691A
Application number: US738335A
Authority: US
Inventors: Harold Kilner Robin; Francis Michael Russell
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-06-19
Filing date: 1968-06-19
Publication date: 1971-08-03
Anticipated expiration: 1988-08-03
Also published as: GB1223845A; FR1588821A; DE1766587A1; NL6808630A; CH509702A

Abstract

A radio antenna suitable for the transmission of high-power signals in the medium and high radiofrequency ranges, includes at least one electromagnetically resonant cavity, each cavity being excited by at least one pulsed electron beam which interacts with the cavity and generates radiofrequency oscillations within it. A radiator element is mounted on and directly connected to the cavity. Embodiments comprising two cavities and modulation apparatus, for modulating the signals transmitted by controlling the relative phases of the electron beam pulses, are described.

Description

United States Patent Inventors Harold Kilner Robin 17 Broadwater Down, Tunbridge Wells,

Kent; Francis Michael Russell.

130 Oxford Road. Abingdon.

Berkshire, both of England 738,335

June 19, 1968 Aug. 3, 1971 June 19, 1967 Great Britain Appl. No. Filed Patented Priority RADIO TRANSMITTER ANTENNAE COMPRISING A PLURALITY OF OPEN-ENDED COAXIAL CAVITIES AND MEANS FOR EXI'IING THEM WITH PULSED ELECTRON BEAMS 13 Claims, 5 Drawing 1 1;.

1-1. c1 1104b 1/04 Field of Search 325/120,

[56] Reierencm Cited UNITED STATES PATENTS 2,406,370 8/ I 946 Hansen et al. 325/120 3,080,523 3/1963 Miller 325/120 3,098,980 7/1963 Doclington... 325/120 3,119,965 1/1964 Phillips 325/120 3,292,033 12/1966 Kenmoku.... 325/120 3,473,125 10/1969 Babillon 325/120 Primary Examiner- Robert L. Griffin Assistant Examiner-Albert J. Mayer AltorneyCameron, Kerkam & Sutton FROM 55 1 5011 53 59 57 07 7| 7p 66 S6 S8 aee'nsu-zn TELEMETRY TELEMETRY v RECHFIER 1 I "men ramsm'r-rea rnmsmrren MV FILTER l I l BEAM BEAM CONTROL umr CONTROL UNIT (RECEIVER a (RECEIVER a 130 POWER AMP) POWER AMP) SUBSIDIARY SUBSIDIARY COLLECTOR (consume) 7 ELECTRODE ELECTRODE 8 [1? iii D a 8c:

SUPPLY PATENTEUAUG sum 3,597,691

sum 1 0F 5 w d W 2 PATENTEU-Aus 3|97l 3 597,591

I sum 2 BF 5 PATENTED ms 31% SHEET 0F 5 FIG.

PATENTEU IIuI; 3 IHYI I SHEET 5 UF 5 I I FROMSS FROM 54 I 5,9 511 67 7| 7;) 66 ls gg I RECTIFIER V L TELEMETRY TELEMETRY' v RECTIFIER I I &F|LTER *Mv TRANSMITTER TRANSMITTER Mv 8.F|LTER I III 1' BEAM BEAM flab CONTROL UNIT CONTROL UNIT (RECEIVER & (RECEIVER &

POWER AMP) POWER AMP) SUBSIDIARY SUBSIDIARY CQLLECTOR COLLECTOR 7 ELECTRODE ELECTRODE 8 i -I- I I! I I Q51 "v' E.H.T.

SUPPLY FIGS The present invention relates to radio antennae of a kind particularly suitable for the transmission of large quantities of power in the medium and high radiofrequency ranges. The inefficiencies of known methods of generating radiofrequency power, of coupling it to an antenna and radiating it as an electromagnetic wave are the fundamental causes of most of the difficulties and costs encountered in the transmission of highpower radiofrequency signals. These inefficiencies are not only wasteful but troublesome, since they tend to cause the generation of considerable quantities of heat at places where heat is not wanted, and where overheating must be avoided.

It is known from the work of Haeff and Nergaard published in the Proceedings of the IRE, Mar. I940, pp. l26l30, that the interaction ofa pulsed electron beam with an electromagnetically resonant cavity may afford an efficient means for transforming direct-current power into radiofrequency power.

According to the present invention, a radio transmitter antenna includes an electromagnetically resonant cavity, a radiator element mounted on and directly connected to the cavity, and excitation means for providing at least one pulsed electron beam to interact with the cavity and generate radiofrequency oscillations therein. The cavity may be a quarter-wave coaxial cavity, and the radiator element may be an extension of the center conductor of the coaxial cavity. The excitation means may include one or more electron beam accelerator-decelerator tubes connected between the inner and outer conductors of the coaxial cavity.

By making the antenna in the form of a resonant cavity and exciting the cavity directly with one or more pulsed electron beams, the usual need for the transmission of the output radiofrequency power from a transmitter through transmission lines and coupling devices is avoided. In effect, the final stage of the transmitter is mounted within the antenna, and the antenna provides the tuned load for the final transmitter stage. This reduces the number of components required to carry high radiofrequency power and thereby increases the efficiency of the arrangement, reducing both the capital costs and the running costs involved.

The energy supplied to a single-cavity arrangement may be modulated by controlling the amplitude or the duration (or both) of the beam pulses. This is satisfactory for on/off code transmissions such as telegraphy and frequency-shift-keyed transmissions. While modulation by an analogue signal is possible in a system of this kind, it is comparatively inefficien't unless the high acceleration voltage can be modulated as well, which would introduce additional difficulties and complications.

To provide a convenient and efficient arrangement for the amplitude modulation of the radiofrequency power output according to an analogue signal, the antenna may include a plurality of electromagnetically resonant cavities, each having a radiator element mounted on and connected to it and each having separately controllable excitation means for providing at least one pulsed electron beam to interact with the cavity and generate radiofrequency oscillations therein. The cavities may be quarter-wave coaxial cavities with their radiator elements close to each other. The radiator elements may be extensions of the center conductors of the cavities. The excitation means may include one or more electron beam accelerator-decelerator tubes in each cavity, connected between the inner and outer conductors of the cavity. The electron beams ofthe accelerator-decelerator tubes are controllable by applying voltage pulses to grid or modulator electrodes. Stabilizing means may be provided for stabilizing the amplitude of the oscillations, and may include a feed back arrangement responsive to the induced radiofrequency voltage and controlling the duration of the beam pulses.

To generate and transmit radiofrequency power, the electron beams are pulsed under the control of signals applied'to the modulator electrodes. The beam pulses are arranged to have a recurrence frequency equal to the frequency of the radio wave which is to be generated, and the cavities are tuned to resonate at this frequency. In each cavity the electron beams induce radiofrequency oscillations which are synchronized with and will interact with the beam pulses. The radiofrequency voltage induced in the cavity decelerates the electrons and power is transferred from the beam to the radiofrequency electromagnetic field; this power is derived from a direct voltage power supply which is provided to accelerate the electron beams before they enter the cavity.

The electron beam pulses occur once in each cycle of the radio frequency, and have a duty cycle of less than or not much more than six percent. Hence, they will extend for a time which corresponds to a phase angle of not more than I 1 degrees on each side of the occurrence of peak radiofrequency voltage across the deceleration section of the tubes.

To provide a modulated radiofrequency output, the timing of the beam pulses may be controlled to induce radiofrequency signals of stabilized amplitude in different cavities which are out of phase with each other by variable but controlled amounts. The waves radiated from the cavities then combine vectorially to produce a resultant whose amplitude depends on the relative phase displacements between the signals; its amplitude can be modulated by varying the relative phase displacement of the pulses in different cavities. For example, there may be two cavities supplied with push-pull pulse-position-modulating signals.

The axes of the coaxial cavities may be parallel to each other, and their open ends and radiator elements may be covered by a radome. The radome may incorporate or support a plurality of conductive annuli arranged in planes normal to the axes of the cavities. This ensures that the waves radiated will be polarized in a direction parallel to the axes of the cavities.

An embodiment of the invention will not be described, by way of example only, with reference to the accompanying drawing, of which:

FIGS. 1 and 2 are sectional elevations of two alternative high-power transmitting aerial assemblies,

FIG. 3 is a schematic block diagram of modulation apparatus for use in the aerial assembly of FIG. 1 or FIG. 2,

FIG. 4 is a graphical representation of waveforms illustrating the operation of the modulation apparatus of FIG. 3, and

FIG. 5 is a schematic block circuit diagram showing the connections of the modulation apparatus of FIG. I to the tubes and cavities of the aerial assemblies.

FIG. 1 shows in cross section two similar resonant cavities 1 and 2, formed of quarter-wavelengths of coaxial line, arranged close together with their axes vertical, and short circuited at their lowest ends. The upper 3, 4 of the resonant cavities are open, and

radiator elements

3, 4 are mounted on top of their

inner conductors

5, 6 respectively. A number of electron beam accelerator-decelerator tubes are mounted radially across each cavity; two of these are shown and marked 7, 8. The

outer conductors

9, 10 of the cavities 1 and 2 are electrically connected togetherfat least at their upper and lower ends. The open ends of the cavities are covered by a hemispherical radome 11 of low loss dielectric material. The structure of the radome 11 incorporates a plurality of separate horizontal conductive annuli 12.

Each of the electron beam accelerator-decelerator tubes has an electron gun at one end and a water-cooled collector at the other. The electron guns each include a modulator or grid electrode, enabling their electron beams to be pulsed under the control of a comparatively low voltage signal. Each tube has an acceleration region between its electron gun and a principal and a deceleration region between its principal anode and its collector. The tubes also have

subsidiary collector electrodes

7a, 8a. The decelerating regions cross the resonant cavities radially, whereas the acceleration regions are screened from the radiofrequency fields within the cavities. The tubes are fitted with magnet coils (not shown) to counteract space-charge repulsion effects which tend to make the electron beams spread excessively especially in the deceleration region.

In the embodiment of FIG. 1, the electron guns and acceleration regions of the accelerator-decelerator tubes are mounted within the extensions of the

inner conductors

5, 6 which form the

radiator elements

3, 4. High direct voltage acceleration power supplies are conducted to the tubes through cables (not shown) within the

inner conductors

5,6.

A vertical conductive electrostatic screen 13, connected to the outer conductors 9, I0, is provided to reduce the capacitance between the

radiator elements

3 and 4. Adjustable sets of copper tapes l5, 16 are festooned and connected between the inner and outer conductors ofthe cavities l and 2 respectively, at their lower ends. Beam control units are mounted within the

radiator elements

3 and 4 and connected to the modulator electrodes of the accelerator-decelerator tubes. The radiator element 4 is shown partially cut away to reveal one of the beam control units, referenced 18. The beam control unit are controlled by a modulator 19. Signals from the modulator 19 are conveyed to the beam control units in the form of modulated beams of infrared light via

mirrors

20 and 21 respectively, along paths indicated by the chain-dotted

lines

27, 28. The line 24 represents ground level.

The aerial is intended to operate at approximately 1400 kHz.; this is the resonant frequency of the cavities l and 2, which are about 30 feet in diameter and I60 feet high. The high direct voltage applied between the principal anodes and the electron guns of the accelerator-decelerator tubes is about one million volts. The electron beams are pulsed at the operating frequency of 1400 kHz.; each pulse has a duration equivalent to a phase angle of the order of IO to 20 degrees at this frequency. The pulsed beam currents induce radiofrequency voltages in the two cavities which decelerate the electron beam and draw energy from them. The beam pulses are controlled by the signals from the modulator 19 so that the induced radiofrequency voltages in the two cavities l and 2 are in antiphase when a modulation signal has a minimum value, and have a relative phase displacement at other times which is decreased as the modulation signal increases. In each of the cavities I and 2, a feedback arrangement is provided which is responsive to the induced radiofrequency voltage and which controls the duration of the beam pulses, thus stabilizing the amount of energy fed to each cavity and thereby stabilizing the induced radiofrequency voltage therein so that its peak amplitude is somewhat less than the direct voltage applied across the acceleration regions of the acceleratordecelerator tubes. This is achieved by

connections

25, 26 from subsidiary collector electrodes 7a in 8a in the acceleratordecelerator tubes to the modulator 19. The subsidiary collector electrodes draw currents which are critically dependent on the spreading of the electron beams. The beam spreading is in turn critically dependent on the difference between the direct voltage and the induced radiofrequency voltage. Hence the cavities are made to produce signals of equal amplitudes, which combine vectorially to give a resultant whose amplitude is determined by the relative phase displacement of the beam pulses in the two cavities. The resultant transmitted wave is therefore amplitude modulated in accordance with the modulation signal from which the relative displacement is derived. The festoons of

copper tape

15, 16 are adjusted to make the cavities 1 and 2 resonant at the desired carrier frequency. The coupling between the cavities is adjusted by alterations to the screen 13 to achieve a desired bandwidth, preferably with transitional coupling.

The radiation from the radiator elements causes the exter nal surfaces ofthe

outer conductors

9, 10 of the cavities to be excited like a vertical monopole, but with a desirably high impedance and Q-factor. However, the horizontal separation of the

radiator elements

3, 4 would, in the absence of the conductive annuli l2, superimpose the effect ofa smaller horizontal dipole on the radiated field. The conductive annuli 12 short circuit the horizontal field components.

Harmonics of the desired frequency can be reduced by arranging that the impedance presented at the acceleratordecelerator tubes by the cavities to unwanted harmonics is low or as near as possible to a short circuit. This may be achieved by mounting suitable conductive sleeves (not shown) over the

inner conductors

5 and 6. The sleeves may each be arranged to produce a standing wave null, or to act as a series-tuned short circuit at a harmonic frequency. Alternatively, the lowest of the conductive annuli 12 (marked 12a in the drawing) may be connected by an inductance (not shown) to the

outer conductors

9, 10 or to earth so that it acts as a seriestuned short circuit at the harmonic frequency. Yet another possible method for suppressing harmonics would be to initiate subsidiary beam pulses in one or more of the accelerator-decelerator tubes, controlled in timing and duration so that they exactly counteract any harmonic frequency components ofthe signals induced by the main beam pulses.

Various modifications of the arrangement of FIG. 1 are possible. For instance, the accelerator-decelerator tubes could be all mounted the other way round, with their collectors connected to the inner conductors and their electron guns and acceleration regions outside the outer conductors. A better arrangement still has two sets of tubes in each cavity, with alternate tubes facing opposite ways and being pulsed in antiphase with each other. This doubles the duty cycle of the power input, enabling a given power to be obtained with half the accelerating voltage needed in an equivalent simple system. The impedance required to the cavities is reduced, and the bandwidth ofthe antenna increased.

Instead of being mounted radially across the open ends of the cavities l and 2, the accelerator-decelerator tubes may be mounted vertically in a squirrel cage formation on top of the cavities.

FIG. 2 shows an embodiment of this type. Parts of the transmitter assembly of FIG. 2 which correspond to similar parts in the transmitter of FIG. 1 are given the same reference numbers in both drawings, and need not again be described in detail.

FIG. 2 shows sections of two similar resonant cavities l and 2 formed, as in FIG. 1, of quarter wavelengths of coaxial line arranged close together with their axes vertical and short circuits at their lower ends. The accelerator-decelerator tubes are connected to a high-voltage supply 41 through high-voltage leads 38,39 which are supported within the

inner conductors

5, 6 and the spaces around them are pressurized with nitrogen or sulphur-hexaflouride. They are connected to a high-voltage power supply unit 41 which is immersed in oil in a tank 40. At the open ends of the cavities 1 and 2 are

conductive annuli

34 and 35 which connect squirrel cage formations of accelerator-

decelerator tubes

7, 8 supported vertically on disc-shaped

enlargements

30, 31 of the

inner conductors

5, 6. The

inner conductors

5, 6 are braced from the

outer conductors

9, 10 by a plurality of

radial quartz rods

36, 37.

Above the disc-shaped

enlargements

30, 31 are the

aforementioned radiator elements

3, 4.

Beam control units

18a, 18b are contained within the

radiator elements

3, 4 and

modulator units

19a, 19b are contained within the

conductive annuli

34, 35. The remaining structure is substantially similar to the embodiment of FIG. 1 already described, and the aerial assembly is operated in a similar way. Suitable pulse-timing circuits for performing the modulating and stabilizing functions into either of the above-described embodiments will now be described in greater detail with reference to FIGS. 3 and 4.

FIG. 3 shows a pulse generator 51 with an output connected to inputs of two fixed

monostable multivibrators

52 and 53. Outputs from the

multivibrators

52 and 53 are connected to inputs of

monostable multivibrators

54 and 55 respectively. Outputs from the

multivibrators

54 and 55 are connected to inputs of

monostable multivibrators

56 and 57 respectively. The

multivibrators

54, 55, 56 and 57 are variable, being constructed to produce pulses of duration dependent on a voltage applied to control inputs with which they are provided. The control inputs of

themultivibrators

56 and 57 are connected through rectifier and

filter units

58, 59 respectively to the

lines

25, 26 respectively, which receive signals from the subsidiary collector electrodes of the accelerator-decelerator tubesin the cavities 1 and 2 respectively. The control inputs of the

multivibrators

54 and 55 are both connected to a modulation input line 60. The

multivibrators

56, 57 have

output lines

66, 67 respectively.

Typical signals from the outputs of the above-described

units

51, 52, 54, 56, 53, 55 and 57 are represented graphically on a common horizontal time scale at (a), (b), (c), (d), (e), (j), and ('g) respectively of FIG. 4.

The pulse generator 51 generates a pulse train (shown at (a) in FIG. 4) having a recurrence period equal to the period of the radiofrequency signal which is to be transmitted by the aerial, and at which the cavities l and 2 are adjusted to resonate. This period is indicated in FIG. 4 and hereinafter by the symbol T. The trailing edge of each pulse from the pulse generator 51 is applied to trigger the

multivibrators

52 and 53. The multivibrator 52 produces pulses of duration T/2 as shown at (b) in FIG. 4; the trailing edges of these pulses are applied to trigger the multivibrator 54, causing it to produce pulses as shown at (c) in FIG. 4. The duration of each pulse produced by the multivibrator 54 is controlled by a modulation voltage Vm applied on the line 60 so that it is substantially equal to A;T+l Vm-V0) but never exceeds /zT, where k is a constant and V0 is the minimum value of the modulation voltage. The trailing edge of each pulse from the multivibrator 54 triggers the multivibrator 56, causing it to produce a pulse as shown at(d) in FIG.4. v

The multivibrator 53 produces pulses of duration equal to 3T/4, as shown at (e) in FIG. 4. The trailing edges of these pulses are applied to trigger the multivibrator 55, causing it to produce pulses as shown at (f) in FIG. 4. The duration of each pulse produced by the multivibrator 55 is controlled by the modulation voltage Vm so that it is substantially equal to VzT- k( VmVc), and never less than AT. The trailing edge of each pulse from the multivibrator 55 triggers the multivibrator57 causing it to produce a pulse as shown at (g) in FIG. 4.

To achieve the desired relationship between the modulation voltage and the durations of the pulses produced by the

variable multivibrators

54, 55 an inverting amplifier (not shown) may be connected in series with the control input to one of the

multivibrators

54 or 55, or alternatively their control inputs may be fed from push-pull modulation inputs.

The result of the actions described above is therefore to generate two pulse trains as shown at (d) and (g) in FIG. 4, each having a pulse recurrence frequency equal to the radio frequency to be transmitted and having a'phase displacement relative to each other which decreases proportionately as the modulation voltage increases. After suitable amplification in the beam control units 18, one of these pulse trains is used to switch on the electron beams in the tubes of one of the resonant cavities, and the other pulse train is used to switch on the electron beams in the accelerator-decelerator tubes of the other resonant cavity. This induces radiofrequency voltages which are radiated as hereinbefore described. As the modulating voltage V!" increases from its minimum value the amplitude of the resultant formed by the vectorial combination of the radiated waves increases having a relationship to the modulation voltage which is substantially linear over a useful range.

A feedback signal, derived from the currents drawn by the subsidiary collector electrodes of all the accelerator-decelerator tubes whose beams are controlled by the pulses from the multivibrator 56, is rectified and smoothed in the rectifier and filter unit 58 and applied to control the duration of each pulse produced by the multivibrator 56, so as to stabilize the power input to and the radiofrequency power developed in the associated cavity. Another feedback signal similarly derived from the tubes in the other cavity, is rectified and smoothed in the rectifier and filter units 59 and applied to control the duration of each pulse from the multivibrator 57, to stabilize the power in the other cavity.

The units 52 to 57 inclusive of FIG. 3 may be incorporated in the modulator unit 19 (FIG. 1) or divided between the modulator units 19a, 1912 (FIG. 2). The rectifier and filter units'58 and 59 may be mounted close to the collector ends of the accelerator-decelerator tubes or in the modulator unit 19 or the

modulator units

19a, 19b Bearing in mind that in the operation of the aerial there is expected to be a direct voltage of about 500 kilovolts between the cavity

inner conductors

5, 6 and the electron guns and modulator connections of the accelerator-decelerator tubes, and a radiofrequency voltage of about 500 kilovolts r.m.s. between the

radiator elements

3, 4 and the upper ends of the

outer conductors

9, 10, it will be understood that the transmission of the signals on at least two of the connection lines indicated in FIG. 3 may involve some conventional form of telemetry, for example an infrared link as hereinbefore described in connection with FIG. 1. FIG. 5 shows the connections required. In the modulator 19 the

outputs

66, 67 from the

multivibrators

56, 57 are applied to

conventional telemetry transmitters

70, 71 which transmit the modulator output signals, in the form of pulses of infrared light or other radiation, along the

paths

27, 28 to the

beam control units

18b, 18a respectively. The

beam control units

18a, 18b comprise conventional receivers and amplifiers for receiving the signals and reconverting them into electrical form and to a suitable voltage for pulsing the electron beams in the accelerator-

decelerator tubes

7 and 8, respectively. The

subsidiary collector electrodes

7a, 8a of the

acceleratordecelerator tubes

7 and 8 are connected by

lines

25, 26 to the rectifier and

filter units

59, 58 which control the periods of the

multivibrators

57, 56, respectively. Since the pulse-timing cir cuits (51 to 55) in the modulator unit 19 have already been fully described with respect to FIG. 3, it is unnecessary to describe them again and they are not fully shown in FIG. 5. The deceleration regions of the

tubes

7, 8 are indicated at 7d, 8d, respectively. The electrical connections formed by the

inner conductors

5, 6 and the

outer conductors

9, 10 of the cavities are indicated diagrammatically and out of proportion .in FIG.5.

suitably phased pulse trains for controlling the electron beams. If two sets of tubes are used in each cavity as hereinbefore suggested, the modulation system will have to be elaborated to provide one pulse train for each set of accelerator-decelerator tubes. Some pulse-timing circuits comprising multivibrators as shown in FIG. 3 may then be mounted in or adjacent to the units 18. The cavities may be made as compartments formed by one or more vertical subdivisions in an upright cylindrical structure, for example with an elliptical cross section subdivided along its minor axis. The acceleratordecelerator tubes may be air-cooled or water-cooled. In place of the infrared telemetry system, the output signals from the

multivibrators

56, 57 could be passed through suitable isolating transformers in the power supply tank 41 (FIG. 2) and transmitted by cables up the center of the high-voltage leads 38, 39 to the

beam control units

18a, 18b. In this case the beam control units would clearly not need to include telemetry receivers and they could be simple amplifiers.

Iclaim:

I. A radio transmitter antenna comprising two tunable open-ended quarter-wave coaxial electromagnetically resonant cavities both tuned to the same resonant frequency, each having an inner conductor and an outer conductor and disposed with their axes parallel and their open ends adjacent to each other,

a plurality of radiator elements, comprising one radiator element mounted on the inner conductor of each of the said resonant cavities and protruding from the open end thereof,

a plurality of accelerator-decelerator tubes, comprising at least one accelerator-decelerator tube for each one of the said resonant cavities, each tube having an evacuated envelope, a modulator electrode and a deceleration region within said envelope and between two further electrodes with external electrical connections, and being coupled to one only of the said cavities and being mounted thereon with the electrode at one end of its deceleration region electrically connected to the inner conductor of the cavity and the electrode at the other end of its deceleration region electrically connected to the outer conductor of the cavity,

means for applying a high-voltage power supply to each of the said accelerator-decelerator tubes,

pulse generator means for generating a first train of pulses having a recurrence frequency equal to the resonant frequency of said cavities,

further means, connected to the said pulse generator means and having a modulation input connection, for deriving a second train of pulses and a third train ofpulses both having the same recurrence frequency as the said first train of pulses but being phased relative to each other so that the phase difference between the said second train and the said third train is dependent on a modulation voltage applied to the said modulation input connections and will be substantially half a period of the recurrance frequency when the said modulation voltage has a predetermined minimum value and will decrease whenever the modulation voltage increases,

and means for applying the second train of pulses to the accelerator-decelerator tube or tubes in one of the said two cavities and for applying the third train of pulses to the accelerator-decelerator tube or tubes in the other of the said two cavities.

2. A radio transmitter antenna is claimed in claim 1 and wherein the said further means comprises a first monostable multivibrator circuit connected to the pulse generator means, and constructed to produce pulses of duration equal to half a period at the recurrance frequency,

a second monostable circuit connected to the pulse generator means and constructed to produce pulses of duration equal to three-quarters of a period at the recurrence frequency,

a third monostable multivibrator circuit connected to the first multivibrator circuit and to the modulation input connection, and constructed to produce pulses of duration substantially linearly increasing with the modulation voltage,

and a fourth monostable multivibrator circuit connected to the second multivibrator circuit and constructed to produce pulses of duration substantially linearly related to the modulation voltage but decreasing as the modulation voltage increases. i

3. A radio transmitter antenna as claimed in claim 2 and comprising a first detector means mounted in the said one of the said two cavities for deriving a first feedback signal indicative of the amplitude of radiofrequency signals developed therein,

a second detector means mounted in the said other of the said two cavities for deriving a second feedback signal indicative of the amplitude of radiofrequency signals developed therein, fifth monostable multivibrator circuit connected to the said first detector means and to the said third monostable multivibrator circuit and constructed to produce pulses of duration controlled by the said first feedback signal, and a sixth monostable multivibrator circuit connected to the said second detector means and to the said fourth monostable multivibrator circuit and constructed to produce pulses of duration controlled by the said second feedback signal,

and wherein the output of the fifth monostable multivibrator circuit is connected to the modulator electrode of the accelerator-decelerator tube or tubes in the said one of the resonant cavities, and the output of the sixth monostable multivibrator circuit is connected to the modulator electrode of the accelerator-decelerator tube or tubes in the said other of the resonant cavities.

4. A radio transmitter antenna as claimed in claim 1, and wherein a plurality of accelerator-decelerator tubes are mounted radially across the open end of each of the resonant cavities.

5. A radio transmitter antenna as claimed in claim 1 wherein each of the resonant cavities has an outer conductor formed with an inwardly extending annular lip at its open end, and an inner conductor formed with a disc like enlargement near the open end of the cavity, and wherein a plurality of accelerator-decelerator tubes are mounted substantially longitudinally in each cavity with their deceleration regions between the said annular lip and the said disc like enlargement.

6. A radio transmitter antenna as claimed in claim 1 and comprising a radome covering the said resonant cavities and the said radiator elements.

7. A radio transmitter antenna as claimed in claim 6 and comprising a plurality of conductive annuli mounted on the radome so that each annulus lies in a plane normal to the axes of the resonant cavities.

8. A radio transmitter antenna as claimed in claim 1 and comprising an electromagnetic screening element mounted between the radiator elements.

9. A radio transmitter antenna comprising a plurality of tunable open-ended quarter-wave coaxial electromagnetically resonant cavities, each having an inner conductor and an outer conductor, and all disposed with their axes parallel and their open ends adjacent to each other, plurality of radiator elements, comprising one radiator element mounted on and electrically connected to the inner conductor of each of the said resonant cavities and protruding from the open end thereof, and excitation means connected to the said cavities for directing at least one separate electron beam across each of the said cavities so that each electron beam crosses one only of the said cavities and causing the electron beam to be pulsed with a repetition rate related to the fundamental resonant frequency of the cavities,

the said excitation means comprising pulse-timing control means having a modulation input connection for causing a pulse position modulation of the pulses of the electron beams so that there will be a difference between the timing of the electron beam pulses in one of the cavities and the timing of the electron beam pulses in another of the cavities, and for varying the magnitude of the said difference in response to signals applied to the said modulation input connection.

10. A radio transmitter antenna comprising a plurality of tunable open-ended quarter-wave coaxial electromagnetically resonant cavities, each having an inner conductor and an outer conductor, and all disposed with their axes parallel and their open ends adjacent to each other,

plurality of accelerator-decelerator tubes, comprising at least one acceleratondecelerator tube for each one of the said resonant cavities, each tube having an evacuated envelope, a modulator electrode and a deceleration region within said envelope and between two further electrodes with external electrical connections, and being coupled to one only of the said cavities and being mounted thereon with the electrode at one end of itsdeceleration region electrically connected to the inner conductor of the cavityand the electrode at the other'end of its deceleration region electrically connected to the outer conductor of the cavity,

means for applying a high-voltage power supply to each of pulse position modulation of the pulses of the electron beams so that there will be a difference between the timing of the beam pulses in one of the said cavities and the timing of the beam pulses in another of the said cavities, and for varying the magnitude of the said difference in response to signals applied to the said modulation input connection.

ll. A radio transmitter antenna as claimed in claim 10 and comprising stabilization means, connected to each of the said cavities and responsive to the amplitude of radiofrequency oscillations induced therein by the electron beam pulses, and connected to the modulator means, for controlling the energy of the electron beam pulses so as to stabilize the said amplitude.

12. A radio transmitter antenna as claimed in claim 11 and wherein the said stabilization means comprises a detector means mounted in each ofthe said cavities for deriving a feedback signal indicative of the amplitude of radiofrequency oscillations induced therein, and pulse-width-controlling means connected to receive the said feedback signal from the said detecting means and connected to the said modulatormeans for controlling the duration of the electron beam pulses.

13. A radio transmitter antenna as claimed in claim 12 and wherein the said detector means comprises a subsidiary collector electrode in each of the said accelerator-decelerator tubes.

72 8? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3'597'69l D t d August 1971 Inventor) Harold Kilner Robin and Francis Michael Russell It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

7 In the title cancel "exiting" and insert -exciting--. I Column 2, line 39, cancel "not" and insert -now-,- line 55, cancel "3,4" and insert --ends--; line 72, after "principal" insert -anode-. Column 3, line 23, cancel "unit" and insert --units-. Column 4, line 66, cancel "into" and insert --in-. Colunm 5,

line 29, cancel "Vm" and insert --V line 40, cancel "Vc" and insert Vo--.

Signed and sealed this 28th day of March 1972.

(SEAL) \ttest:

EDWARD M.FLETCH ER,JR. ROBERT GOI'TSCHALK Ittesting Officer Commissioner of Patents

Claims

1. A radio transmitter antenna comprising two tunable open-ended quarter-wave coaxial electromagnetically resonant cavities both tuned to the same resonant frequency, each having an inner conductor and an outer conductor and disposed with their axes parallel and their open ends adjacent to each other, a plurality of radiator elements, comprising one radiator element mounted on the inner conductor of each of the said resonant cavities and protruding from the open end thereof, a plurality of accelerator-decelerator tubes, comprising at least one accelerator-decelerator tube for each one of the said resonant cavities, each tube having an evacuated envelope, a modulator electrode and a deceleration region within said envelope and between two further electrodes with external electrical connections, and being coupled to one only of the said cavities and being mounted thereon with the electrode at one end of its deceleration region electrically connected to the inner conductor of the cavity and the electrode at the other end of its deceleration region electrically connected to the outer conductor of the cavity, means for applying a high-voltage power supply to each of the said accelerator-decelerator tubes, pulse generator means for generating a first train of pulses having a recurrence frequency equal to the resonant frequency of said cavities, further means, connected to the said pulse generator means and having a modulation input connection, for deriving a second train of pulses and a third train of pulses both having the same recurrence frequency as the said first train of pulses but being phased relative to each other so that the phase difference between the said second train and the said third train is dependent on a modulation voltage applied to the said modulation input connections and will be substantially half a period of the recurrance frequency when the said modulation voltage has a predetermined minimum value and will decrease whenever the modulation voltage increases, and means for applying the second train of pulses to the accelerator-decelerator tube or tubes in one of the said two cavities and for applying the third train of pulses to the accelerator-decelerator tube or tubes in the other of the said two cavities.

2. A radio transmitter antenna is claimed in claim 1 and wherein the said further means comprises a first monostable multivibrator circuit connected to the pulse generator means, and constructed to produce pulses of duration equal to half a period at the recurrance frequency, a second monostable circuit connected to the pulse generator means and constructed to produce pulses of duration equal to three-quarters of a period at the recurrence frequency, a third monostable multivibrator circuit connected to the first multivibrator circuit and to the modulation input connection, and constructed to produce pulses of duration substantially linearly increasing with the modulation voltage, and a fourth monostable multivibrator circuit connected to the second multivibrator circuit and constructed to produce pulses of duration substantially linearly related to the modulation voltage but decreasing as the modulation voltage increases.

3. A radio transmitter antenna as claimed in claim 2 and comprising a first detector means mounted in the said one of the said two cavities for deriving a first feedback signal indicative of the amplitude of radiofrequency signals developed therein, a second detector means mounted in the said other of the said two cavities for deriving a second feedback signal indicative of the amplitude of radiofrequency signals developed therein, a fifth monostable multivibrator circuit connected to the said first detector means and to the said third monostable multivibrator circuit and constructed to produce pulses of duration controlled by the said first feedback signal, and a sixth monostable multivibrator circuit connected to the said second detector means and to the said fourth monostable multivibrator circuit and constructed to produce pulses of duration controlled by the said second feedback signal, and wherein the output of the fifth monostable multivibrator circuit is connected to the modulator electrode of the accelerator-decelerator tube or tubes in the said one of the resonant cavities, and the output of the sixth monostable multivibrator circuit is connected to the modulator electrode of the accelerator-decelerator tube or tubes in the said other of the resonant cavities.

9. A radio transmitter antenna comprising a plurality of tunable open-ended quarter-wave coaxial electromagnetically resonant cavities, each having an inner conductor and an outer conductor, and all disposed with their axes parallel and their open ends adjacent to each other, a plurality of radiator elements, comprising one radiator element mounted on and electrically connected to the inner conductor of each of the said resonant cavities and protruding from the open end thereof, and excitation means connected to the said cavities for directing at least one separate electron beam across each of the said cavities so that each electron beam crosses one only of the said cavities and causing the electron beam to be pulsed with a repetition rate related to the fundamental resonant frequency of the cavities, the said excitation means comprising pulse-timing control means having a modulation input connection for causing a pulse position modulation of the pulses of the electron beams so that there will be a difference between the timing of the electron beam pulses in one of the cavities and the timing of the electron beam pulses in another of the cavities, and for varying the magnitude of the said difference in response to signals applied to the said modulation input connection.

10. A radio transmitter antenna comprising a plurality of tunable open-ended quarter-wave coaxial electromagnetically resonant cavities, each having an inner conductor and an outer conductor, and all disposed with their axes parallel and their open ends adjacent to each other, a plurality of radiator elements, comprising one radiator element mounted on the inner conductor of each of the said resonant cavities and protruding from the open end thereof, a plurality of accelerator-decelerator tubes, comprising at least one accelerator-decelerator tube for each one of the said resonant cavities, each tube having an evacuated envelope, a modulator electrode and a deceleration region within said envelope and between two further electrodes with external electrical connections, and being coupled to one only of the said cavities and being mounted thereon with the electrode at one end of its deceleration region electrically connected to the inner conductor of the cavity and the electrode at the other end of its deceleration region electrically connected to the outer conductor of the cavity, means for applying a high-voltage power supply to each of the said accelerator-decelerator tubes, and modulator means having a modulation input connection and a plurality of outputs which are connected to the modulator electrodes of the said accelerator-decelerator tubes, for producing a pulsed electron beam within each of the said accelerator-decelerator tubes, said electron beam being pulsed at a repetition rate related to the resonant frequency of the said resonant cavities, the said modulator means comprising means for causing a pulse position modulation of the pulses of the electron beams so that there will be a difference between the timing of the beam pulses in one of the said cavities and the timing of the beam pulses in another of the said cavities, and for varying the magnitude of the said difference in response to signals applied to the said modulation input connection.

11. A radio transmitter antenna as claimed in claim 10 and comprising stabilization means, connected to each of the said cavities and responsive to the amplitude of radiofrequency oscillations induced therein by the electron beam pulses, and cOnnected to the modulator means, for controlling the energy of the electron beam pulses so as to stabilize the said amplitude.

12. A radio transmitter antenna as claimed in claim 11 and wherein the said stabilization means comprises a detector means mounted in each of the said cavities for deriving a feedback signal indicative of the amplitude of radiofrequency oscillations induced therein, and pulse-width-controlling means connected to receive the said feedback signal from the said detecting means and connected to the said modulator means for controlling the duration of the electron beam pulses.