US2912619A

US2912619A - High frequency apparatus

Info

Publication number: US2912619A
Application number: US502336A
Authority: US
Inventors: Collard John
Original assignee: EMI Ltd
Current assignee: EMI Ltd; Electrical and Musical Industries Ltd
Priority date: 1954-04-22
Filing date: 1955-04-19
Publication date: 1959-11-10
Anticipated expiration: 1976-11-10

Description

Nov. 10, 1959 J. COLLARD 2,912,619

HIGH FREQUENCY APPARATUS Filed April 19, 1955 FIG. 2.

. HIGH FREQU-ENCY APPARATUS John Collard, Hammersinitli, London, England, assignor to Electric 8: Musical Industries Limited, Hayes, Middle'sex, England, a company of Great Britain Application April 19,1955, Serial No. 502,336 Claims priority, application Great Britain- April 22, 1954 10 Claims. (Cl. 315-39) The present invention relates to high frequency apparatus in which a high frequency is set up and the invention being particularly but not exclusively concerned with measuring the power propagated along waveguides.

For the purpose of measuring power it has been a commonpractice in the past to employ germanium crystals as'rectifiers but such arrangements suffer from the objection that the crystals are easily damaged by overload conditions. An object of the present invention is to provide simple and convenient apparatus for power measurement and other purposes which does not employ a crystal rectifier. v V

According to the present invention there is provided high frequency apparatus in which a thermionic electron discharge device is arranged within the field set up by said apparatus, said device including a cathode and an anode which is influenced in potential only by said alternating electric field and which is large compared with said cathode and disposed in relation to said cathode so that said high frequency field existing in the space between said cathode and anode becomes progressively weaker towards said anode, whereby electrons emitted by said cathode and accelerated therefrom by said field continue to move-towards said anode despite reversal of said field. As applied to the measurement of power propagated along a waveguide said thermionic electron discharge device-maytake the form of a small thermionic diode in an evacuated glass tube which is arranged within the waveguide and with the cathode of the diode disposed coaxially with the axis of the waveguide. Such an arrangement is convenient not only for the measurement of power but is convenient also for the detection, mixing and modulation of oscillations.

In order that the invention may be more clearly understood the same will now be described by way of example with reference to the accompanying drawing, in which:

Figure 1 shows an arrangement in accordance with the invention,

Figure 2 shows a side elevation of a thermionic diode for use in accordance with the invention, and

Figure 3 illustrates the manner of mounting the diode shown in Figure 2 in a waveguide.

Referring to Figure l, the invention is shown as applied to high frequency apparatus in the form of a waveguide. The waveguide is of rectangular cross-section having broad walls as indicated by the reference numerals 1 and '1' and narrow walls indicated by the numerals 2 and 2', the guide being excited so that a field of H type is set up within it. With a field of this type the electric vector is normally parallel to the narrow walls and there is located in a region where the field is a maximum, namely, at the centre of the guide 3, a thermionic diode of which the dotted line indicates the evacuated glass envelope and reference numerals 4 and 5 indicate the cathode and anode respectively. The cathode is in the form of a filament extending coaxially with the axis of the guide and the anode is of elongated arcuate form in cross-section and located on the side of the cathode towardsone of the broad walls of the waveguide. As will be seen the anode 5 subtends an angle with respect to'the cathode 4 which is substantially less than 360.

The diode is shown in greater detail in Figure 2 of the drawings and as shown therein, the diode comprises a glass tubular envelope 6 which in a typical example may be approximately 1%" long and A" in diameter. The

anode 5 is mounted between a pair of mica spacers 7 and 8 between which is also arranged the filament 4. The two leads for the filament 4 are indicated at 9 and 10 and the lead for the anode at 11. The filament 4 should be as small in diameter as possible and is preferably of the directly heated type. The anode 5 in a typical example may have a radius of A2" and the cathode 4 is disposed at the radial point of the anode. The anode should be a half wavelength long at the frequency of the electro-magnetic waves propagated through the waveguide.

Figure. 3 of the:drawings illustrates the manner of mounting the diode in the waveguide and as shown, the

leads

9, 10 and 11 are arranged to support the diode in the waveguide, the leads being bent so that they are disposed at right angles to the electric field set up within the waveguide and pass through apertures in one of the walls 2 and 2' of the waveguide, two of the apertures being indicated in Figure 3 at 12 and 13, the leads being suitably insulated from the Waveguide.

As shown in Figure 1, the presence of the cathode 4 results in the convergence upon it of those lines of electric force presentin the region of the diode 3 and in consequence the field existing in the space between the cathode 4 and the anode 5 of the diode is of radial form so that the field between cathode and anode becomes progressively weaker towards the anode. The weakening of the field towards the anode is essential to the operation of the invention and with this form of field it will be seen that while an electron may be accelerated by the field strongly away from the cathode upon emission it is not possible for the reversal of the field to bring the electron to rest or return it towards the cathode since the electron will by that time have reached a point where the field is too weak for this purpose. Thus despite reversals of the field the electron retains a forward velocity and continues to move towards the anode so that the anode continues to charge up by theaccession of emitted electrons until its potential is such that on the average as many electrons are driven off as are being received. The potential of the anode in this way is a function of the power propagated along the guide.

As stated above, the invention may be employed as a signal detector and the manner of operation when so employed is similar to that described above as applied to the measurement of power, and the arrangement is of similar construction. The same form of apparatus may be employed for the purpose of mixing and here it is merely necessary to arrange that two fields of different frequencies are introduced into the waveguide so as to be effective upon the diode.

Although the invention has been described above as applied to a rectangular waveguide it will be appreciated that the invention can be employed in any device in which a high frequency field exists, such as in coaxial lines, cavity resonators and other devices where the electric field can converge onto the cathode of the diode.

What I claim is:

1. High frequency apparatus including a wave-guide adapted to be excited to set up an alternating electric field and a thermionic electron discharge device arranged Within said field, saiddevice including a cathode and an anode spaced from said cathode and which is influenced in potential only by said alternating electric field and which is large compared with said cathode and subtends an angle with respect to said cathode which is substantially less than 360, to expose said cathode to said field, the shape of said anode and said spacing and" angle being chosen to cause the field in the space between said cathode and anode to become progressively weaker towards said anode thereby to cause electrons emitted by said cathode and accelerated therefrom by said field to continue to move towards said anode despite reversals of said field.

2. High frequency apparatus according to claim 1, wherein said anode is of arcuate form in cross-section with the concavity of said' anode facing said cathode.

3'. High frequency apparatus according to claim 1, wherein said cathode is of filamentary form and said an ode is of said arcuate elongated form with the concavity of said anode facing said cathode.

4. A high frequency transmission line adapted to transmit an alternating electric field and a thermionicelectron discharge device arranged within said field, said device including a cathode and an anode spaced from said cathode and which is influenced in potential only by said alternating electric field and which is large compared with said cathode and subtends an angle with respect to said cathode of substantially less than 360, to expose said cathode to said field, the shape of said anode and said spacing and angle being chosen to cause the field between said cathode and anode to become progressively weaker towards said anode thereby to cause electrons emitted by said cathode and accelerated therefrom by said field to continue to move towards said cathode d espite reversals of said field.

5. A transmission line according to claim 4, wherein said anode is of arcuate form with the concavity of said anode facing said cathode.

6. A transmission line according to claim 4 wherein said cathode is of filamentary form with its axis substantially parallel to the axis of said line and said anode is of arcuate elongated form with its longitudinal axis substantially parallel to the axis of said line and with the concavity of said anode facing said cathode.

7. A waveguide of rectangular form in cross-section adapted to be excited to said up an alternating electric 4% field with the lines of said field substantially parallel to the narrow walls of said'waveguide, and' a thermionic electron discharge device arranged within said field, said device including a cathode and an anode spaced from said cathode and which is influenced in potential only by said alternating electric field; and which is large com pared with said cathode and subtends an angle with re* spect to said cathode of substantially less: than 360, to

expose said cathode to said field thelshape of said an-,

ode and said spacing and. angle being chosentocause the field between said cathode and anodeto. becomeprw gressively weaker towards said anode thereby to cause electrons emitted by said cathode and. accelerated therefrom by said field to continue to movetowardssaid,catlr ode despite reversals of said field.

8. A waveguide according. to claim 7, wherein said anode is disposed on the side of said cathode facing one of the broad walls of said waveguide.

9'. A waveguide according to claim 7; whereinsaid anode is of arcuate form in cross-section and is disposed on the side of said cathode facing one ofthe broad; walls of said waveguide.

10. A waveguide according to claim 7', wherein said cathode is of filamentary form with its axis substantially parallel to the axis of said waveguide and said anodeisof arcuate elongated form with its longitudinal axis substantially parallel to the axis of said waveguide and'with,

the concavity of said anode facing said cathode and disposedon the side of said cathode facing one of the broad walls of said waveguide.

References Cited in the'file ofthis patent UNITED STATES PATENTS