US2193859A - Ultra short wave antenna - Google Patents

Description

March 19, 1940. w. BUSCHBECK ULTRA SHORT WAVE ANTENNA Filed Nov. 16, 1937 INVENTOR. Wig}? BUSCHBEC K BY ATTORNEY.

Patented Mar. 19, 1940 UNITED STATES ULTRA SHORT WAVE ANTENNA Werner Buschbeck, Berlin, Germany, assignor to Telel'unken Gesellscliait i'iir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application November 16, 1937, Serial No. 174,751 In Germany November 28, 1936 7 Claims.

One of the chief difiiculties attendant upon television resides in the attempt to obtain a frequency characteristic as free as feasible from both amplitude and phase distortions inside the wide frequency band required in television practice and which roughly covers 12x10 cps. What proves particularly diflicult in an attempt to attain the said aim and end are the energy feeder leads needed between the transmitter and the antenna. For while it would seem possible to reduce the length of these lines or leads, say by mounting the transmitter at an elevated point, there will always remain in practice a line length equal to at least one to two wavelengths of the ultra short wave. The influence of such a line will be immaterial whenever it is possible to properly terminate the same throughout the entire range occupied by the side-bands. In case of improper matching, however, rather serious amplitude and phase defects result. One serious fact to be noted is that adaptation cannot be correct throughout the whole range or band,'for even if the inherently inappreciable differences in the radiation resistances for the upper and the lower side band be disregarded, alone the base reactance of an antenna (for instance a V4 antenna) correctly tuned to the carrier wave and which will arise additionally for the side bands, results in intolerable defects in matching. The said reactance for a given percentage side band width is directly proportional to the characteristic impedance of the antenna arrangement; hence, the latter should as far as feasible be minimized. To this end, special types of antennas arrangement, for example, inverted cones or the like, have been suggested in the art. In practice, however, in schemes of this sort the values of the characteristic impedance cannot be reduced to less than 200 ohms approximately, and this value, as later calculations will demonstrate, still results in unduly serious matching errors. Hence, additional ways and means must be found to compensate the base reactance. According to this invention there is used with this end in view a suitably proportioned parallel resonance circuit connected with the end of the cable, or its equivalent comprising one or several parallel connected leads of suitable length.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which Figure 1 illustrates an equivalent circuit scheme for an antenna and energy lead constructed according to my invention, Figure 2 illustrates an embodiment of the invention, while Figure 3 is a cross-sectional view of Figure 2 taken along lines 3-3.

Referring to Fig. 1, E denotes the energy lead or feeder. To the end of the latter is connected the aerial A and also the parallel or shunt circuit P tuned to the carrier frequency according to the present invention. Suppose the aerial is a V4 wave antenna tuned to the carrier wave frequency. In other words, in the neighborhood of its natural wave, it may be replaced by a simple series scheme or mesh comprising L, C and R, indicated by the mesh A, Fig. l. R corresponds to the radiation resistance which thus is =37 ohms.

is proportional to the characteristic impedance WA of the antenna arrangement. Denoting by Af y n "N f0 where w n== o the so-called detuning measure of the circuit, then, for the series circuit A the reactance will be X1=iX1 z/, for the parallel circuit For the upper side band, in other words, for a frequency which is higher than the carrier wave frequency, the antenna becomes inductive as illustrated by the substitute or equivalent circuit scheme, whereas the parallel circuit P tuned to the carrier wave becomes capacitive in nature. Inasmuch as the series connection of antennae ohm resistance and reactance may always be replaced for a given frequency by a parallel arrangement, that is, in our instance, by connecting in parallel a slightly increased ohm resistance and an inductive reactance (inductance), it follows that for a given side band frequency perfect compensation of the reactance must be possible. Thus the antenna reactance is Z1=R+jX1 y and The ensuing parallel susceptance thus becomes: 1 1 1. fr" i R +X,g Designating by the total-antenna attenuation (damping measure) and by 111 the detuning at which compensation of the reactance is to be brought about,

then

Since as a general rule the characteristic (surge) impedance'of the antenna arrangement rather than X1 will be the known quantity, it may be convenient here to derive the formulae for the requisite calculations. From the conductance equations, the base reactance of an open V4 type antenna, in first approximation, results to be In the present instance, for small percentage discrepancies there will be:

As shall be demonstrated by a practical calculation, X2 is of such small size that an attempt to provide the same by means of concentrated capacities or inductances may occasionally meet with practical difliculties. Wherever this happens, the stopper circuit could be replaced by an equivalent circuit, in other words, by a shortcircuited M4 line; or in order that inevitable concentrated inductances at the junction point may be still further reduced by the parallel connection of several lines with a correspondingly raised characteristic impedance, the outer conductors (or outers) of which could in such a case be used to act at the same time as a counterpoise. (Fig. 2.) The necessary recalculation quantities flow from the following formula: In the case of a short-circulted low-loss ./4 line Now, the actual situation shall be demonstrated and illustrated by the aid of a practical instance. Suppose that a U4 arrangement of 200 ohm characteristic impedance is compensated by a parallel circuit for w==%. The remnants of effective (ohm) resistance and reactance values are calculated in terms of series values, while there shall be indicated at the same time, for the sake of comparison, such values as are found for the same aerial without compensation.

Without With compensation compensation 9% X 0 Re Xs R1. Xi ohm ohm ohm ohm ohm ohm 37 0 37 O 37. 1 +0. 0605 37 +1. 67 37. 2 +0. 106 37 +3. 34 37. 6 +0. 123 37 +5. il 38. 0 +0. 93 37 +6. 68 38. 6 0 37 +8.35 39. 3 -l. 70 37 +9. 42 40. 0 4. 61 37 +1i.0 39. 4 -8. 32 37 +12. 11 37. 8 2. 8 37 +14. 1 34.8 -17. 5 37 +15. 7

and thus ym=8%. For this reason another calculation shall be made and tabulated for which there is chosen 1Ik=8%. These are the findings:

Without With compensation compensation 1/ 0 Rs XI BL X Also in this instance there will be noted a striking improvement. This improvement will become especially obvious if the faulty matching is determined which would result for the extreme side-band frequency in both of the instances hereinbefore considered. What shall here be taken as the faulty adaptation is the ratio of the maximum nodal resistance arising at a voltage loop and the characteristic impedance, or, what is tatamount, the relationship between the potentials or the currents prevailing at the nodal points. In the presence of compensation the same is given solely by the ohmic matching fault or deficiency, in other words in other words 11.3%, whereas the same would amount to 39% in the absence of compensation, this value being exclusively caused by the additional reactance. If the line is of a length so that the nodes are liable or likely to lie at the input end of the cable, this circumstance in the first instance would lead to extreme values of 33.4 and 41.2 ohms, respectively, while in the absence of compensation they would amount to 26.7 and 51.4 ohms, respectively.

Of course, it will be evident that in lieu of the parallel circuit provided directly at the cable output, it would also be practicable to employ a series circuit through a U4 line (or a plurality of paralleled arrangements of this kind), seeing that by virtue of the property of a M4 line of changing an impedance into its reciprocal there becomes in line with what is required .for compensation.

Fig. 2 illustrates a practical embodiment of the invention by way of example. E is the concentric (coaxial) energy feeder line whose inner conductor is united with the antenna A. The latter, as already indicated above, consists of an inverted cone placed upon its apex in a perpendicular position. The characteristic impedance as known in the art is very low and stable throughout its length. As a compensation circuit for the antenna reactance at the side band frequencies serve four lines L1, La, etc., each thereof consisting of two concentric or coaxial lines short-circuited at their ends and having a length equal to M4. The outers are interconnected at their ends by the ring K so that there is a resemblance to the spokes of 'a wheel. This wheel serves at the same time as'a counterpoise for the antenna A. It is only by the use and adoption of ways and means hereinbefore disclosed to the end of improving adaptation or matching that it becomes possible to utilize energy feeder lines of more than moderate or average length. In fact, it is only feasible by the aid of compensation schemes as here disclosed to design directional antenna arrays suited for broad band modulation.

What is claimed is:

l. The combination with an antenna having substantially a conical surface of revolution and adapted to receive or transmit a wide band of radio frequency waves, of a coaxial feeder line whose inner conductor is connected to the apex of said conical surface of revolution, and a pluralityof other coaxial lines each of which is connected at one end in shunt to the conductors of said feeder line for compensating for the antenna reactance at the side band frequencies. said plurality of coaxial lines each being onequarter of a wavelength long at the carrier frequency and short-circuited at the other end thereof.

2. The combination with an antenna having substantially a conical surface of revolution and adapted to receive or transmit a wide band of radio frequency waves, of a coaxial feeder line whose inner conductor is connected to the apex of said conical surface of revolution, and another coaxial line one-quarter of a wavelength long at the carrier frequency connected at one end in shunt to the conductors of said feeder line for compensating for the antenna reactance at the side band frequencies, the conductors of said last coaxial line being short circuited at the other end of said line.

3. An arrangement in accordance with claim 1, including a conductor inter-connecting all the outer conductors of said plurality of coaxial lines at the short-circuited ends.

4. The combination with an antenna having substantially a conical surface of revolution and adapted to receive or transmit a wide band of radio frequency waves, of a coaxial feeder line whose inner conductor is connected to the apex of said conical surface of revolution, and a plurality of other coaxial lines symmetrically disposed around said antenna, each of which is connected at one end in shunt to the conductors of said feeder line for compensating for the antenna reactance at the side band frequencies,

said plurality of coaxial lines each being onequarter of a wavelength long at the carrier frequency and short-circuited at the other end thereof.

5. The combination with an antenna adapted to radiate or receive a band of high radio frequencies and a radio frequency feeder coupled thereto, of an oscillation circuit tuned to the mid frequency of said band and connected to said feeder near the junction of said feeder to said antenna, said oscillation circuit being so proportioned with respect to the impedance of said antenna at a predetermined side frequency of said band that such antenna reactance is substantially compensated at all frequencies between said mid frequency and said side frequency.

6. The combination with an antenna adapted to radiate or receive a band of high radio frequencies and a two-conductor radio frequency feeder connected thereto, of an oscillation circuit tuned to the mid frequency of said band and connected in parallel relation to the conductors of said feeder near the junction of said feeder to said antenna, said oscillation circuit being so proportioned with respect to the impedance of said antenna at a predetermined side frequency of said band that such antenna reactance is substantially compensated at all frequencies between said mid frequency and said side frequency.

7. The combination with an antenna adapted to radiate or receive a band of high radio frequencies and a two-conductor radio frequency feeder coupled thereto, of a series tuned oscillation circuit tuned to the mid frequency of said band and connected to said feeder through a line having a length equal to the quarter of the length of the mid band frequency near the Junetion of said feeder to said antenna, said oscillation circuit having such impedance with respect to the impedance of said antenna at a predetermined side frequency of said band that said antenna reactance is substantially compensated at all frequencies between said mid frequency and said side frequency.

WERNER BUBCHBECK.

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