US2679591A - Ultrahigh-frequency apparatus - Google Patents

Description

y 25, 1954 G. D. ONEILL 2,679,591

ULTRAHIGH-FREQUENCY APPARATUS Filed March 13, 1948 2 Sheets-Sheet l I N V EN TOR. George .0. 071/911 Z May 25, 1954 G. D. O'NEILL ULTRAHIGH-FREQUENCY APPARATUS 2 Sheets-Sheet 2 Filed March 13, 1948 INVENTpR.

G'earyefl 0M!!! Patented May 25, 1954 ULTRAHIGH-FREQUENCY APPARATUS George D. ONeill, Port Washington, N. Y., assignor to Sylvania Electric Products Inc., a corporation of Massachusetts Application March 13, 1948, Serial No. 14,807

14 Claims. 1

The present invention relates to radio circuits.

In a useful form of high-frequency circuit, a planar-grid electron-discharge device is partly enclosed in a high-frequency resonator and a capacitor is interposed between the annular terminal of the planar gridand the resonator to block direct and low-frequency currents and to bypass the radio-frequency currents. The capacitor ordinarily takes the form of a dielectric annulus sandwiched between a metallic wall of the resonator and a metallic extension of the annular terminal.

Many difiiculties are inherent in the foregoing arrangement. The capacitor is ordinarily de signed to have a minimum impedance. This bypass, at its exterior edge, couples to space, so that, unfortunately, a part of the high-frequency power is unintentionally radiated, representing losses and uncontrolled local high-frequency fields. The path also provides coupling between moving bodies outside the resonator and its interior, resulting in variable reflections and operational instability.

One phase of the present invention aims at providing a novel construction for blocking direct-current and low-frequency signals and for connecting an annular-terminal vacuum tube to a high-frequency resonator, thereby minimizing one or more of the difficulties inherent in the comparable prior-art construction.

As to this phase of the invention it is proposed that an annular quarter-wave transmission line, having an open termination, be used, providing insulation circumferentially around the annular terminal of the vacuum tube at the input end of 1 the line.

The outer end of the line, which is open to the surrounding space, may be said to terminate in a high impedance. Hereinafter I shall refer to this arrangement as an open termination, which results in a low value of input impedance when the physical construction is suitably adjusted to the signal frequency involved.

The term annular transmission line is intended to identify two-walled transmission lines wherein the input edges of the walls are spaced apart and. close on themselves to constitute loops, and may take various forms, such as the cylindrical form of a coaxial line or the flat form of a radial line as more fully described below.

The bypass results obtained with this open quarter-wave annular line may be deficient for some purposes. The lower limit of the input impedance that is injected into the high-frequency circuit such as a resonator depends on the approach to perfect reflection at the open termination. Radiation losses and leakage may transform to a small but appreciable impedance at the input end of the open-ended quarter-wave line, and to reduce this effect is another object of this invention. An annular shorted quarterwave line advantageously is joined circumferentially to a wall of the annular open-ended line adjacent the open termination. Its impedance is effectively in series with the high impedance of the open termination. At the frequency at which the open-ended line and the shorted line are effectively one-quarter wave-length long, the transformed impedance at the input end of the bypass is very nearly zero, whereas the directcurrent insulation is unimpaired.

If the circuit is to be operated over a band of frequencies, the open line and the shorted line will not be equal to an electrical quarter wavelength for any except a single frequency. But if the open line is breached at a point near the open end by the input end of a first shorted annular quarter-wave line having maximum impedance at one frequency and again at a point very near the open end by a second annular shorted quarter-wave line having maximum impedance at a lower frequency, the impedance looking into the bypass will be low for a band of frequencies. The two shorted lines are effectively series-connected, and their impedances are added to the impedance of the open end of the nominally quarter-wave open line. This broad-banding of annular lines is another broad purpose of the invention.

The invention in its several aspects will be better understood from the following detailed description of various illustrative forms. In the drawings:

Fig. 1 is a longitudinal section of a cylindrically symmetrical combination of a planar-grid tube and a cavity resonator, showing the improved blocking or bypass construction, and Fig. 2 is an enlarged fragmentary view of that construction with a partial external view of the tube.

Fig. 3 is a diagrammatic view of a planar-grid tube-and-resonator combination, with a quarterwave open annular line between the annular grid terminal and the resonator, and Figs. 4, 5, and 6 are like views of similar bypass arrangements improved by the addition of quarter-wave shorted annular lines.

Fig. 7 is a graphical aid to the proportioning of the radial quarter-wave lines forming part of some forms of this invention.

Figs. 8 and 9 are wiring diagrams of lumpedconstant analogies of two forms of radio frequency bypass constructions.

A simple embodiment of one phase of the invention is shown in Fig. 3. Resonator I is associated with a tube including a dynode or secondary-emitting anode l2, a positive planar grid I4, and a cathode I6, the interior metallic surface of resonator I!) being breached circumferentially about positive grid I 4 at gap l1 filled with dielectric material. Output from resonator it is optionally obtained by loop 20 and guided along coaxial line 22 to the load. In accordance with one phase of the invention, the efiective length of dielectric I8, sandwiched between two metal plates 24 and 26, is equal to an electrical quarterwave when measured from the breach in the metallic surface of resonator t0 toward the outer edges of those plates 24, 26.

This combination of parts is diagrammatically shown in Fig. 8 with the direct-current circuit completed to constitute a dynatron oscillator of the type in my cepending application, Serial No. 681,454 filed July 5, 1946. Dynode l2, positive grid I 4, and cathode I6 form a vacuum tube (the envelope not being shown) which. when connected through choke Z to direct current power supply E and to the resonator represented by L, C, constitute the dynatron oscillator. The capacitor designated C represents total circuit shunt ca pacitance including that between electrodes I2 and I4 and for this reason it is shown dotted. The resonator circuit is completed, across the gap shown, by a quarter-wave line S which phys ically surrounds the annular terminal of the planar grid in the actual construction but which is represented by an open=circuit two=wire quarter-wave line. Dyn'ode l2, a secondaryemissive electrode, is connected to a tap in the directcurrent supply through choke Z, the extremities of supply E being connected to positive grid I4 and to cathode IS. The secondary emission from dyno'd'e l2 promotes the functioning of the tube as part of the dynatron oscillator in the illustrative circuit, the operation of which is described in detail in my above-mentioned copen'din'g application.

It should be understood that the use of this tube and other tubes in combination with a resonator and the novel high frequency bypass arrangement is not limited to the generation of oscillations, but extends also to other applica tions such as modulation and amplification with circuits that will be obvious to those skilled in the art, including applications requiring more than one resonator. Furthermore, the physical arrangement of the annular open=ended quarterwave line replacing the usual bypass capacitor is applicable to both positiveand negative-grid tubes, to diodes, and to multiple-grid tubes of the so-called planar grid type having an annular terminal for at least one grid.

From transmission line theory it will be understood that the impedance Z1 of line S at its input end is low where line S is made an electrical quarter-wave in length, and is terminated in a very high impedance at the other end, and is minimum with a termination of infinite impedance.

In order that the impedance Z1 may be held to a minimum for the mechanical arrangement shown in Fig. 3, consideration must be given to the material of the dielectric l8, the high-freouency conductivity of conducting plates 24 and 26, their distance apart, their inner and outer radii 11 and T2 respectively, and the resonant wavelength A of the cavity. The following discussion of wave-guide bypass design applies specifically to the radial form of Fig. 3, although the same general considerations are involved in a cylindrical quarter-wave (coaxial) bypass in Figs. 5 and 6 and to other forms of quarter-wave bypass providing an insulating loop about an annular terminal of a tube or like device.

As previously indicated, an open quarter-wave section to have minimum input impedance should have maximum impedance at the end from which the waves are reflected. Consequently, the bypass formed by conducting members 24 and 2S,

between-which is preferably sandwiched the plate T8 of dielectric material such as polystyrene, are so dimensioned that the time required for a wave to travel from 1'1 to m is one quarter of the time of one cycle at average cavity frequency. Considering the terminal impedance, by which is here meant the impedance an outward-traveling wave encounters at the periphery, or a lossless radialtr'ansmi'ssion line as being infinite, the input impedance is given by the relation 01 sin (in-"1 1) Where Z01 is the surge impedance and the angles are defined by for any other dielectric having a specific inductive capacity 6 times greater than that of air, the value X is inversely proportional to Vs.

Since the input impedance Z1 is to be minimum. Equation 1 is set equal to zero; then and it is seen that tan 9z=c0t I L (5) Substitution by Equations 2 and 4 gives N X.- N 0( l( L) values of X1. corresponding to the values of iii are then determined by finding the values of Ni(XL) /J1(XL) which correspond to the duoti'ents' No(Xi) /Jo(X1) and the results plotted as fi/"A against rz/x as shown in '7, and as i i/k against (Ta-11)) The curve, Fig. '7, is plotted with air dielectric. When the dielectric medium between plates of the racial line is some other material having a specific inductive capacity 6' times greater than that "of air, the yaiueof is "changed to X', which is the wavelength in the new dielectric medium and which is expressed by the relation /e.

It will be understood that practical limitations prevent full realization of the results predicted when only the foregoing ideal relations are considered. Three of these limitations of fundamental importance are:

1. Variations in electron tubes cause variations in the wavelength of the oscillations with the result that bypass dimensions may not be ideal for all tubes.

2. The terminating impedance of the radial transmission line can never be infinite, since the open-ended line couples into space.

3. No line is quite lossless due to surface resistance, dielectric losses and the like.

Thus, so far as the bypass is concerned, these limitations translated into Equation 1 show that the characteristic impedance Z01 is desirably held low, indicating the use c; small spacing between the conducting members of the bypass and the use of a material having high dielectric constant. For the radial shorted line to be considered with Fig. 5, the reverse is true; i. e., separation of the conducting members is relatively great and air dielectric is preferred.

If a transverse electromagnetic wave is sent out between the inner surfaces of plates 21! and 26 from gap l1 adjacent grid M, and reaches a point of infinite impedance at the radial extremity of the system, the wave is reflected back to the input gap and will then be 180 out of phase with the voltage by which it was excited, provided the dimensions of the conductors and the dielectric constant of the insulating ma terial are properly related to the wavelength. To the extent that there are no losses in the dielectric medium or on the inner surfaces of plates 24 and 26, the exciting and fully-reflected voltages are equal in magnitude and, being 180 out of phase, mutually cancel and the system is said to have zero impedance. However, to the extent that the impedance of the termination is not infinite, the reactance of the bypass is greater than zero, so that energy is radiated. Just as the impedance of an antenna is a function not only of its dimensions but also of its surroundings, so the terminating impedance of the gap is affected by the surroundings and varies to some extent when surrounding objects are moved. These variations in terminating impedance are reflected back into the cavity as variations of the impedance into which the electron tube operates with resultant instability of developed power or frequency or both.

Fig. 4 illustrates one form of improvement over the open quarter-wave bypass shown in Fig. 3. In Fig. 4 there are shown the same resonator, output coupling, and tube, including a dynode, grid and cathode, as in Fig. 3. Replacing plates 24 and 26 in Fig. 3 are plates 28 and 30. A metal ring 32 is attached to plate 30, having two circular grooves 34 and 36. These grooves are of different depths, the shallower groove 34 being connected closer to input gap 38 than the other. The upper edge of ring 32 radially outward of grooves 34 and 36 provides two extensions to and 42 of the inner surface of plate 30. A layer of dielectric material All such as polystyrene separates plate 30 and ring 32 from plate 28 and the rest of the resonator.

A wave of a certain frequency travelling radially outward from gap 38 will have travelled onequarter of a wavelength by the time it reaches groove 34. By making groove 34 effective as a quarter-wave short-circuited line for that frequency, the open-ended terminal impedance of the arrangement in Fig. 3 would be increased for the arrangement in Fig. 4 by the effective impedance of the shorted quarterwave line. At the frequency for which the first groove is truly a quarter of a wave in electrical length, the bypass is terminated in a much higher impedance than was the case for Fig 3, hence the impedance at gap 38, Fig. 4, is much lower.

For other frequencies than that for which groove is electrically one-quarter of a wavelength long and is connected to plate 30 one-quarter of a wavelength from input gap 38, groove 34 will present a high series impedance to an outwardly-- travelling wave. The longer one 36 of the two grooves, connected further from gap 38 than groove 34, should preferably be made equal to one quarter of a wave in electrical length for a lower frequency than that which matches groove 3 5. Groove 36 should be connected to the openended line bounded by plates 23 and 30 at a quarter Wave distance from gap 38 for that lower frequency.

At frequencies between or slightly above or below the resonant frequencies of shorted coaxial lines as and 35, such lines are effectively reactances of less than maximum impedance, connected in series with each other and with the open termination of plates 28 and 30 as extended by surfaces 40 and 42. This arrangement preserves the insulating properties of the bypass but minimizes unintended radiation and coupling of the resonator to the surroundings. The analogous lumped-constant circuit is shown in Fig. 9, including the open quarter-wave annular line S and the series annular reactors 34' and 36'. There is considerable reflection of the input wave by those reactors, and for this reason there is a considerable reduction in coupling to the exterior and in radiation through the bypass. The leakage fields are indicated by the dotted lines in Figs. 8 and 9 in a manner intended only to show their comparative strengths.

Referring to Fig. 4, the lengths of the two coaxial-line reactors depend upon the maximum and minimum wavelengths of the oscillations generated in the cavity. They are not, however, made one-fourth as long as these wavelengths, since this would result in a lowered performance at average wavelength than at the extremes. A good compromise is to make one reactor of electrical length L1 such that it has maximum impedance at a wavelength v9. Which is intermediate between the average wavelength 'Y and the minimum wavelength min. Thus It will be evident that if T2 of Fig. 4 is computed for "/a with the aid of the curve, Fig. 7, and the length of the innermost reactor also has an electrical length 79/41, the shunt impedance at gap 38, Fig. 4, is minimum when the wavelength 1S a.

As a first approximation, 12" may be determined for 'yb using the curve if the series impedance offered by the short reactor to the long wavelength be ignored. This results in a solution for m" which is too large. A rigorous solution is obtained by setting up the equationfor the input impedance of the gap 36 for wavelength 115 with the impedance of the small reactor placed in series at the radius 1'2 and setting this equal to zero. The solution for T2" is obtained graphically with the expenditure of more time than would ordinarily be warranted, since plots must be made from points determined from Bessel functions having small, closely-spaced arguments and hen'ee by careful interpolation of the values given in such tables as those of Jahnke and Emde. However, solution of a few practie'al cases results in the conclusion that, when X's and Rh differ from the average wavelength A by approximately which represents ample spread, one may compute r2"- r1 ignoring the short rea'ctor, then use 95% of this figure in specifying m". t should be noted that such a relation cannot be strictly accurate since a rigorous solution must take full consideration of the surge impedances both of the by-pass and of the shorter reactor.

The broad-banding of the radial bypass is es-= pecially useful, with the dielectric shown, for cavities divided by insulation to provide for difierent direct-current potentials on the several electrodes of a tube; but the arrangement of multiple quarter-wave shorted lines on a common axis and encircling a quarter-Wave open transmission line will be found useful in other high-frequency applications not involving direct-current insulation requirements.

Figs. 5 and 6 illustrate other arrangements of the open quarter-wave line completely surround ing' the planar grid and multiple shorted quarter wave lines adjacent the open termination of the open duarter wave line. In Fig. 5 the open line comprises a pair of cylinders 46 and as, the for mer being insulated from most of the resonator by dielectric spacer 50. Cylinder t3 does not extend to the open termination but is connected to disc 52, grooved to provide a shorted radial quarter wave line 54 for maximum effectiveness at the shorter wavelength M, and a somewhat longer short-circuited quarter-wave line 5%, which corresponds to wavelength Ab. In Fig. 6 the open line is similarly comprised of inner and outer metal cylinders 58 and 6B separated by an insulating passage 82, and, replacing radial series 'conneoted shorted lines 54 and 55, is a first shorted quarter-wave line 64 within cylin der 58 and a second, somewhat longer, shortcircuited quarter-wave line 66 outside cylinder 60. Lines 54 and 66 are folded back on the open quarter-wave line; all three lines may be filled with any suitable dielectric material. The use of a solid dielectric filler serves as a mechanical strengthener and in reducing the dimensions of the lines.

The radial quarter-wave reactors of Fig. 5 may have air as the dielectric in order that the surge impedance Z01 be maximum. Taking the terminating impedanceas' zero, the input impedance as a lossless line will be Sill (er-01,)

is taken to be infinity when the distance from input to the short is electrically a quarterwavelength. Hence the curves of Fig. '7 apply to the proportioning of radial reactors as to radial open quarter-wave lines. The wave-lengths 7m and M) used in the design procedure are taken the same manner as was explained for the case of Big. 4 described above. v

The system shown i'nFig. 6 is more amenable to numerical solution than are those of Figs. 4

and 5. A more rigorous solution will be given as it illustrates the general method of attack on any of the systems discussed or which might be envisioned. V V

In order to avoid the need for considering the dielectric constant throughout the manipulations to follow, it may be considered unityfor air dielectric-and surge impedances and lengths will be recognized as varying inversely as the square root of 6. Also, the conductance ofthe dielectric and resistance of the conductors may both be considered zero.

Certain mechanical and electrical dimensions are as follows:

A=average wavelength Amm=minimum useful wavelength generated in the resonator ka= (X-I-Xmin) xmx=maximum useful wavelength generated Ln=distance from the input gap to the first shorted quarter-wave line L1=length of the shorter quarter-wave shorted line Lz length of the longer shorted quarter-wave line L3=length of the bypass (that is, the length from gap to the longer line) zub surge impedance of bypass Zoc= urge impedance of shorted lines The impedance of the shorter line at a wavelength )i will be z1=izoc tan (arm/m ('83 where 200:6!) ZnO'b/ri) in which m is the inside radius of the outer conductor and Ti is the outside radius of the inner conductor.

Since Z1 is to be infinite at wavelength hi, it is seen from (8) that this may be accomplished by making L1=')\s/4. Similarly, the impedance of the longer shorted line is made infinite for )lb by making L2= \b/4.

Consider the impedance at the gap for wavelength Aa. Since it is terminated in an infinite impedance, we have:

Z=-'- 'Ztz cotfizarLo/xa') (9) where Z0b=60Zn 7'o/n) To and n this time referring to the conductors of the bypass. It is evident that if Z=0, then Lo=Aa/1.

N ow for wavelength 7\b, the longer shorted line has a finite impedance which is inductive, andthis is in series with a short additional length of line LI:L3Lo, which, being less than a quarter wavelength long and terminated in the innnite impedance of the second shorted line, is

capacitive. The sum v, of these impedances we may designate as Z'i. Then, since L0=Xa/4,

. 'lrX, ZWLX) 7AM W Z,, JZM tan Z cot M (1.))

9 Eliminating Z8. between (10) and (11) and setting As an example, if 7m=0.95 and Ab=1.05)\, and Zoc=Zob, L3=0.93 \t/4. In general, the surge impedance Zoo of the shorted lines will be set higher than that of the bypass, Zob, and the result will be a somewhat lower value of L3.

It will be remembered that the system was described for air dielectric. For any other medium having dielectric constant e, L3 will be multiplied by It may be well to remark again that the corrections just described are ordinarily a secondorder eilect, and in those cases where a radial transmission line is part of the device, such as in Figs. 4 and 5, the correction may be approximated. The correction to the case where all coaxial lines are used is simple enough so that the more exact computation given by (12) is simple enough to warrant its use.

The several arrangements in Figs. 3 to 6 will find varied application depending on space and design factors. A further but particularly useful arrangement of the open quarter-wave line of Fig. 3, further modified to include multiple shorted quarter-wave lines as part of the termination of the open quarter-wave line is shown in Figs. 1 and 2. In Fig. 1, resonator l includes a rod 66 supporting dynode I2 adjacent positive planar grid I 4'. Diaphragm B! has a central portion threaded to support 66 and is joined to the walls of resonator I0 by threaded cap 69, this construction serving to facilitate assembly without stressing the glass unduly. Planar grid I4 is insulated from most of the resonator by a layer of dielectric material 68 such as polystyrene. Cathode I6, is supported below grid l4 and these three electrodes are enclosed in an evacuated envelope. The upper part of the envelope is in the form of a generally cylindrical or conical glass wall In the bottom of which is sealed to the annular extension. corresponding to the usual terminal for a planar grid. The apex of the conical glass wall 10 is of somewhat thicker glass stock and provides a relatively long seal with support 66 of the dynode. This glass shape is well calculated to resist abrupt upward acceleration.

The planar grid terminal is extended downward to strengthen the seat for wall 10, and the metallic planar grid extension constitutes the axial wall 12 (see Fig. 2) of the lower part of the envelope. This extension constitutes one wall of the open quarter-wave line corresponding to plate 26 of Fig. 3, and the other plate of that open line is in the form of a complementary metal ring I4. The bottom of the envelope includes a formed metal annulus l6 fused to wall 12 and a glass exhaust tube portion 18 which also provides separate seals for the terminals of filamentary cathode l6 and for a getter-flashing lead that also serves as a direct-current lead for the grid. Annulus l6 and planar grid extension 12 constitute a shield substantially enclosing cathode l6. Annulus 16 further extends the open quarterwave line by providing a short radial bearing for dielectric ring 82. This is pressed by a composite 1i tube 84 which is threaded into ring 12 against the triode envelope which in turn is seated against polystyrene layer 68 within ring 14. Tube 84 includes a pair of shorted lines 86 and 88 adjacent the termination of the open line and provides a length of shielding for leads 80.

Of the form in Figs. 1 and 2 it will be noted that the open quarter-wave line may be other than radial or cylindrical as in Figs. 3-6; and in like sense the shorted quarter-wave lines at the open termination that impart broad-band effectiveness are similarly not necessarily confined to the fiat radial or to the concentric cylindrical forms. The particular arrangement in Fig. 1, whereby the metallic portion of the tube envelope serves as one of the walls of the, bypass, is claimed in copending application, Serial No. 14,726, filed March 13, 1948 of Paul Haas assigned to the assignee of this application.

Lines having lengths of any odd multiples of a quarter-Wave may be substituted for the onequarter Wave lines described. Further detailed variations, as well as other applications of the novel subject matter in this case, will occur to those skilled in the art; and for this reason I desire the appended claims to be broadly interpreted consistent with the spirit and scope of the invention.

What is claimed is:

1. In combination, a resonator having a conductive end wall, and a planar grid electron discharge device a grid of which has an annular terminal approximately in the plane of said wall, said terminal and said wall being separated by a high-frequency bypassing and direct-current blocking construction comprising an annular transmission line surrounding said terminal and extending externally of said resonator to an open termination electrically one quarter of a wave length away from said terminal.

2. In combination, an electron-discharge device having a planar grid and another electrode the terminal of which is spaced from said planar grid, a resonator completing a high-frequency circuit between said electrode and said planar grid, and a quarter-wave transmission line surrounding said planar grid and insulating it from said resonator, said line extending externally of said resonator and having an open termination.

3. The combination in claim 1 including a short-circuited annular transmission line one quarter of a wave in length breaching a wall of said transmission line adjacent said open termination.

4. The combination according to claim 1 including a pair of short-circuited annular transmission lines each circumierentially breaching a wall of said annular transmission line adjacent the open termination of said open transmission line, said short-circuited lines being of different efiective lengths and being displaced from the said planar grid terminal an electrical distance equal to their electrical lengths, respectively.

5. In combination a triode having a planar grid between a cathode and a secondary emissive electrode arranged along an axis, said planar grid having an annular terminal, a metallic resonator connected between said terminal and said anode and enclosing the space between them, a circumferential breach between said grid terminal and said metallic resonator, and a two-walled transmission line having its walls insulated apart and connected to said terminal and to said resonator respectively but extending externally of said resi onator, said line ending in an open termination at a point electrically an odd multiple of quarter wavelengths from said breach.

6. In combination a high frequency circuit including an apertured conductive cavity, a device having multiple terminals at least one of which is annular and is set in the aperture of said cavity, an annular insulator encircling said annular terminal, and a pair of conductive walls at opposite surfaces of said insulator joined to said terminal and to said cavity at said aperture, said insulator and said conductive walls extending externally of said cavity and being dimensioned to constitute an open quarter-wave transmission line at the operative frequency of said circuit.

7. A high frequency circuit having a portion elfective over a band of operating wavelengths, said portion including an annular transmission line having two conductive walls insulated apart, and closely adjoining series-connected shorted transmission lines each circumferentially breaching a wall of said annular transmission line respectively equal in length to one-quarter of different operating wavelengths in said band.

8. A high frequency circuit having a portion effective over a band of operating wavelengths,

including a first two-walled transmission line having an annular terminal, and second and third annular transmission lines joined circumferentially each to a wall of said first line at distances from said terminal respectively equal to onequarter of different wavelengths in said band and having maximum input impedance at said junction at said respective wavelengths.

9. A high frequency circuit having a broadband construction including an annular twowalled transmission line having an open termination and multiple annular short-circuited transmission lines of electrical lengths equalling a quarter of an operating wavelength at different points in said band joined circumferentially to said two-walled line adjacent and in series with said open termination.

10. A high frequency circuit having a broadband construction including an annular twowalled quarter-wave line having an open termination and multiple annular short-circuited transmission lines of electrical lengths equalling a quarter of an operating wavelength at different points in said band joined circumferentially to said two-walled line adjacent and in series with said open termination.

11. A high frequency network including a twowalled annular transmission line having an input gap, a first short-circuited annular transmission line joined to said two-walled line circumferentially at a quarter-wave distance from said input gap at one frequency, and a second shortcircuited annular transmission line joined to said two-walled line circumferentially at a quarterwave distance from said gap at a second frequency.

12. A high frequency network including an annular quarter-wave transmission line having two walls insulated from each other and having an open termination, and a short-circuited quarterwave line circumferentially joined to each wall of said open line adjacent and in series with said termination and connected in series with said open termination.

13. A high frequency network including an annular quarter-wave transmission line having two walls insulated from each other and having an open termination, and a short-circuited quarter-wave line circumferentially joined to a wall of said open. line adjacent to and in series with said open termination.

14. A high frequency network including ar annular transmission line having an input gay and an open. termination in combination with a pair of short-circuited coaxial. lines arranged one within the other breaching said annular line at distances from said gap electrically an odd multiple of quarter-waves from said gap at different frequencies, said short-circuited lines being odd. multiples of quarter-waves in length at said dif ferent frequencies, respectively.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,415,962 Okress Feb. 18, 1947 2,422,160 Woodward, Jr June 10, 1947 2,429,811 Guarrera Oct. 28, 1947 2,438,912 Hansen et a1 Apr. 6, 1948 2,438,914 Hansen Q Apr. 6, 1948 2,446,982 Pound Aug. 10, 1948

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