US1929878A

US1929878A - Microray wavemeter

Info

Publication number: US1929878A
Application number: US595764A
Authority: US
Inventors: Andre G Clavier
Original assignee: International Communications Laboratories Inc
Current assignee: International Communications Laboratories Inc
Priority date: 1932-02-29
Filing date: 1932-02-29
Publication date: 1933-10-10
Anticipated expiration: 1950-10-10

Description

Oct. 10, 1933. A. G. CLAVIER 1,929,878

MICRORAY WAVE-METER Filed Feb. 29. 1952 FIG. l g n FIG. 2

INVENTOR ANDRE G. CLAVIER ATTORNEY Patented Oct 1933 NITED STATES! PATIENT-"3 OFFICE I Andr G. jClavier,

to International Glen Ridge, N; J.,-'assignor Communications Laboratories, Inc., Newark, N. J., a corporation or New York Application February 2 ,1932. Serial no. 595,764

" 8 Claims. ,(olz 250-29)" This invention relates to micro-ray wavemeters and transmission lines. disclosure herein a micro-ray transmission line maybe so designed that the transmission characteristic of the line is a function of the length of the line and the length of the wave transmitted. over the line, so that, by adjusting the length of the'lin'e and measuring the adjustments, a suitable wavemeter is obtained. lnaccordance withthe disclosure herein, it is also possible toadesign a transmission'line so that its transmission characteristics are independent of the lengthof 'a certain section of the line.

With such a line itispossible to make adjustments in length without setting. up disturbances in other parts of a micro-ray signaling system.

Bymicro-rays is meant electromagnetic waves lying, generally, in the range between 1 and 100 centimeters. g

In my U. ,S. Patent'No. 1,928,408 there is disclosed a system for operation inthis range.

In the drawing: i

Fig. l is a diagrammatic sketch of a wavemeter which consists of van adjustable micro-ray trans- 2-{3 missionline connecting a wave receiving device or antenna to a current measuring device which, in this case, is a thermo-coupleconnected to'a galvanoineter Fig.2 is a diagram of a section of amicro-ray 3!) transmission line which may be'adjusted without changing the characteristic, impedance of any part of the same section of the'lineg-andfl Fig. 3 is a sketch of a wavemeter, similar generally to that shown in Fig. 1,. but in which a wider rangeof waves may be measured, with a reduced number of' adjustments. I

In designing a wavemeter in which an adjustable line connects an antenna to a thermocouple, it is necessary to know fithe current flow- 4( ing through the thermo-couple TC, Fig. 1, in

terms of thelength 1 of the adjustable line.

In U. 5. Patent No. 1,921,11'1 granted to Rene H. Darbord, such a waverneter is disclosed. In that patent the adjustable line is connected at each end to asection of; line approximately a quarter wave lengthlong, and these sections are connected, respectively, toan antenna and thermocouple. f

Such a system is n50, shown inFigjl, in which an adjustable antenna Z is connected to a quarter wavelength line 2. This, inturmis connected'to a line 3 which is adjustable as to length and con In, accordance with the p be theresistance of the tuned antenna;

and, finally:

Wave length line 6, and the thermo-couple TC is connected across the ends of this line.

' We want to find the current flowing through 60 p the thermo-couple TC in 1761111801 the length I of the adjustable line. Assume the line itself-dissipationless. v Let 65 'p'- be the high frequency resistance of the thermo-couple; y

Za bethe impedance looking into the wavemeter at point a;

Z1) be the impedance looking into the wavemeter at point I); l e e Zc be the impedance looking into thethermocouple at point c; I Z1 be the characteristic impedance of the first quarter wave length line;

Z2 be the characteristic impedance of the adjustable line;

Z3 be the characteristic impedance of theseo- 0nd quarters wave lengthline; and

We have the successive relations:

so that we find:

The amplitude of i4 is found to be:

Z1Z2Z3 Let:

A zzz (Zi p' +Z3 p) 2 (11) B (Z1 Z3 +pp'Z2 2 (12) Then:

This gives us the formula for the current through thermo-couple in terms of the characteristics of the lines, the length of the adjustable line, and the frequency of the wave received. We now Want to find the conditions for maximum transfer of energy from the antenna to the thermo-couple. Let:

The sign of B A depends on B-A, which may be written:

We then have to examine the cases in which the characteristic impedance of the adjustable line, the ratio of the square of the characteristic impedance of the first quarter wave length line to the resistance of the tuned antenna, and the ratio of the square of the characteristic impedance of the last quarter wave length line to the high frequency resistance of the thermo-couple, have different relative values. cases to examine, as follows:

In Cases a and b the sign of 15p is the same as the sign of sin 251. g In Cases 0 and. d the sign 15,: is apposite to the sign of sin 2131.

In Cases e and f bp is always equal to zero.

Let us first discuss Cases e and I. In these cases B =A and id is independent of Z and Z2 The maximum of is occurs when:

In these cases the current in the thermo-couple is independent of the adjustment of the length This gives us six of the adjustable line, because this line at one of its ends is looking into a resistance equal to its own characteristic impedance. These cases, then, furnish a means for designing a micro-ray transmission line which may be adjusted as to length without changing the transmission characteristics of the line. This is a valuable property and one which may be made use of .in various applications. It is not, however, suitable for use as a wavemeter. It will, therefore, not be considered further in connection with the design of a wavemeter.

Let us now consider Cases 0 and b. In these cases, the sign of Dp is the same as the sign of sin 2 Bl. Adjustment of the length of the adjustable line, then, gives us the following results, where M indicates, maximum and m indicates minimum:

It will be seen that maximum transfer of energy 1;;

occurs for adjustments of the length l of the adjustable line equal to a multiple of a half wave length of the received wave, that is, when A l 11c With this adjustment:

z,z FP'i' aP (28) 11' a The maximum transfer of energy is obtained when:

p p as in Cases 6 and ,f, with the same maximum value for id.

If we now consider Cases 0 and d, in the same manner we find:

l 251 sin 28! D1 D Id 0 0 0 0 i l 1 0 9 'm M (30 M2 21 if 0 M m am 31 0 0 m M The maximum current in the thermo-couple now occurs when the adjustable line has a length equal to an odd multiple of a quarter of a wave length, that is, when:

In this case the maximum current:

, The best adjustment of the lines is obtained when:

Z Z -=w pp' that is, when:

- should be chosen as small and, as before, the grand. maximum for I4 is We have now found, the conditions for the maximum transfer of energyfrom. the antenna to the thermo-couple, under different. conditions of the intermediate line, and have also found. that the conditions represented by Cases a, b, c and (1 above ofier possibilities as wavemet ers. The accuracy with which waves may be measured on a wavemeter depends on the sharpnessof the resonance curve of the meter. Let -'us,; therefore, now consider the conditionsforimaximurn sharpness of resonance withthe different possiblecases.

' Let usfirst consider the Cases a and b In these cases B -'A zero., In order to estimate the sharpness of the resonance curve, let us find the values of Z for which the thermo-c'ouple current s :11v /2 an. This condition "obtains when: I fixe on and ma A l We want the angle 51 to be as small as possible,

or rather, to differ from 1r by. as small a value as possible; so that we can write: v

In order to increase the sharpness of the curve, the value of should be made as large aspossibIa A haze +23%) 7 Differentiation with respect is v 2 2 fand Z3? v z 2 I Z has the sign of Za 2 5 (43) In Case a, I

a and P P should beas large aspossible while Z2 should be chosen as small as possible.

In Case b, p s I and as possible and Z2 as large as possible. The value of sharpness, as given by the change in I, required to reduce the value of current in the thermo-couple from a' maximum to r r In Case c practical cases. As seen in thedexpression 139*), the sharpness isbetterthe shorter the wave i ';-length. In order'to insure maximum transfer of energy at the same timemaximum sharpness is obtained, Zr and Z3: should be such. that 1 14 31, which gives cos fil== (l6) and ihas the sign of Z (49) 2 has the sign of.

i ofand 2 must be. small (52) 0 and z 'must belarge. (53) Maximum sharpness occurs when:

k a I ,7 0 and 2; must be small. a (5 6) Maximum sharpness occurs, as before, when:

' The value of maximum sharpness is given by the fact that maximum sharpness is finite, Cases 145 .c and d do not lead to as good a wavemeter decloses a -wavemeter designed in accordancewith 150 Y is) p Case b above. It has already been shown that Cases e and f are not suitable for wavemeters and that Cases 0 and d do not give as good results as Cases a and 12. Case a, however, oiferspossibilities of a wavemeter which is as sensitive as that disclosed in Darbords above-identified patent and which is more convenient to build and can be used for a wider range of wave lengths. Such a wavemeter is shown in Fig. 1, which has already been partially described.

Since the quarter wave length sections should have a larger characteristic impedance than the adjustable center section, these two sections may be parallel wire lines and the center section may be a concentric line so constructed that the ratio of the internal diameter of the outer conductor to the external diameter of the inner conductor is as small as possible. An antenna 1, which is adjustable in length so that each section of the antenna may be a quarter wave length long, is provided. Means for making such an adjustment in an antenna is disclosed in my co-pending application, Serial No. 581,362, filed December 16, 1931, and is simply illustrated in this application by the arrows shown through the dotted portions of the antenna in Fig. 1 of the drawings.

The quarter wave length line 2.is connected to the antenna 1- and is adjustable by sliding it in and out of the adjustable line 3. A suitable screw arrangement may be provided for making this adjustment. The antenna may also be designed to be rotated'through an angle of in order to intercept waves of any polarity which may be incident thereon. The quarter wave length line 6, connected to the opposite end of the adjustable line 3 to that to which the quarter wave length line 2 is connected, is also separately adjustable as to length by sliding it in and out of the adjustable line 3. A screening box 7 may be provided to prevent radiation loss from the section 6 of the line. The radius of this screening box is, preferably, equal to one-eighth of the smallest wave length to be measured, as explained in my U. S. Patent No. 1,928,408, previously mentioned.

A suitable arrangement, which may consist of a screw-drive 8, is provided for varying the adjustment of the adjustable line 3, and a suitable scale 9 and pointer 10 permit this adjustment to be measured accurately. A reflector 11, which may be plane or parabolic, concentrates the incident wave onto the antenna 1. A galvanometer G is connected to the end of the inner conductor of the adjustable line next to the thermo-couple on one side, and to any point on the outside of the external conductor of the adjustable line on the other side. The connection to the end of the inner conductor of the adjustable line should be perpendicular to the plane of the line 6, in order to avoid any undue losses due to induction of high frequency current from the line 6.

The operation of the device is as follows: the antenna 1 and the quarter

wave length sections

2 and 6 are first adjusted'so that they are approximately one-fourth the length of the wave to be measured. The adjustable line 3 is then adjusted by turning the handle connected to screw 8 until a point is reached where there is a maximum deflection in the galvanometer. When the adjustable line 3 is adjusted, the line 6 and screening box '7 all move as a unit. After the adjustment of the line 3 for maximum deflection on thegalvanometer is discovered, the antenna 1 and

lines

2 and 6 are again adjusted more carefully for this maximum deflection. The point on the scale corresponding to maximum deflection is then carefully noted. The adjustable line 3 is then re-adjusted by turning the handle connected to screw 8 until another point is reached where there is a maximum deflection in the galvanometer G. The point on dial 9 corresponding to this second adjustment is then also carefully noted and the distance between the two points of adjustment for maximum deflection is measured. This distance will be equal to onehalf the wave length of the received wave, with a high degree of accuracy. When the mechanical adjustments are carefully made, an accuracy of one part in tenthousand is obtainable.

For the best results with a wavemeter of this character, it is highly desirable to have an adjustable line 3, the characteristic impedance of which does not vary with changes in its adjustment. Such a line is shown in Fig. 2. The adjustable line shown in this figure is designed for use as the adjustable line of the wavemeter shown in Fig. l, which has already been described, and is adjusted in any suitable manner such as that shown in Fig. 1. It is also designed for use in the wavemeter of Fig. 3, yet to be described. The parts of the line in Fig. 2 which are shown not cross-hatched are designed to slide over the parts which are shown cross-hatched. In order to have the same characteristic impedance all through the length of an adjustable line, the following condition must obtain, using the notation shown on Fig. 2:

In order to dispense with the adjustment of the antenna in the type of wavemeter shown in Fig. 1, use may be made of a wavemeter such as that disclosed in Fig. 3, in which similar elements are marked with the same numbers used in Figs. 1 and 2. Instead of an adjustable antenna of the type shown in Fig. 1, a doublet is connected across the ends of the quarter wave length line 2 and the thermo-junction is connected in the line of the doublet. Line 2 is separately adjustable as before, and line 3, which is constructed as shown in Fig. 2, may be adjusted in the manner shown in Fig. 1. Line 6 is also separately adjustable, but this adjustment is now made by adjusting the length of the shielding cylinder '1 by moving its lid 12. Of course, at least one of the leads 6 should be insulated from the lid 12. With this arrangement, the wavemeter is sensitive and may be used conveniently for a wider range of wave lengths than is the case for a wavemeter of the type shown in Fig. 1.

In Fig. 3, if we assume the line 6 to be practically short circuited, the current flowing through the thermo-couple is found to be The operation of the device of Fig. 3 is as follows: The

lines

2 and 6 are adjusted for approximately one-fourth of the wave length of the wave tobe measured, the line 6 being adjusted, as just the device.

mentioned, by moving the. lid 12'. The line 3 is then adjusted for. maximum deflection on the galvanometer G and final adjustments of the

lines

2 and 6 are made. The line 3 is then readjusted for another point of maximum deflection on the galvanometer G, and the distance between the two positions of the line 3 formaximum deflection is one-half the length of the wave measured.

' In Fig. 3, the shield 7 may be replaced 'by'a plane reflector at the position of the plane portion of the lid 12. In this case the reflector slides along the line 6 just as thelid 12 did, and is positioned the same with respect to the rest of Again, at least one of the leads should be insulated from the reflector.

What is claimed is: 1

1. A micro-ray wavemeter comprising two lines havinga certain value of characteristic impedance and an intermediate adjustable line having a value of characteristic impedance less than the value of either of the two first-mentioned lines.

2. A micro-ray wavemeter comprising two sections of transmission line having equal values of characteristic impedance, and an intermediate section adjustable as to length having a value of characteristic. impedance less than the values of said two first-mentioned sections.

3. A micro-ray wavemeter comprising an adjustable antenna, an adjustable section of line having a large characteristic impedance, an adjustable section of line having a small characteristic impedance, a second adjustable section, of line having a large characteristic impedance, means connected to said last-mentioned section for measuring the current in said antenna, and means for indicating the adjustment of said low impedance portion whereby the length of an incident wave may be measured. 1 I

4. A micro-ray wavemeter comprising an adjustable section of line having a large characteristic impedance, a thermo-couple connected to said section, an adjustable sectionof line having a low characteristic impedance connected to said first section, and a third section of adjustable line having alarge characteristic impedance connected to said second section, and a galvanometer connected to said third section, and means for adjusting said second section of the line whereby an indication of the length of the received wave may be obtained. v

5. A micro-ray transmission line connecting two devices acting as resistances, said line comprising three sections, namely, two end sections each having a length equal to an odd number of quarter wave lengths and an intermediate section of variable length, the characteristic impedance of one of the end sections being equal to the square root of the product ofthe characteristic impedance of the intermediate section and the resistance of the adjacent device so as to ensure an energy transferv independent of the length. of the intermediate section. V

6. A micro-ray transmission line in accordance with claim 5, in which both end sections have the relationship mentioned with respect to the intermediate line andthe respective adjacent devices, so as to ensure maximum transfer of energy independently of the length of the intermediate line.

'7. A micro-ray wavemeter comprising two sections of line adjustable to a quarter wave length, and an intermediate section adjustable to half wave lengths, and means for effectively adjusting one of said quarter wave length sections comprising an adjustable shield surrounding said section.

8. A micro-ray wavemeter comprising two sections of line adjustable to a quarter wave length, and an intermediate section adjustable to half wavelengths, and means for effectively adjust- ANDRE G. CLAVIVER.