US1952411A - Transmission network - Google Patents

Description

March 27, 1934. Q Q ET AL 1,952,411

TRANSMI S S ION NETWORK Filed March 16, 1928 2 Sheets-Sheet l INVENTORS OTTO BORN BY WI LM SER ATT N EY March 27, 1934. o, BQHM Er AL 1,952,411

TRANSMI S S ION NETWORK Filed March 16, 1928 2 Sheets-Sheet 2 24 jig. 2c

Patented Mar. 27, 1934 PATEil IFFICE 1,952,411 TRANSMISSION NETWORK Otto Biihm and Wilhelm Moser, Berlin, Germany,

assigncrs to Telefunken Gesellschaft fur Drahtlose Telegraphic m. b. H, Berlin, Germany, a corporation of Germany Application March 16, 1928, Serial No. 262,160 In Germany March 17, 1927 4 Claims.

It has been found in practice that in the case of short-wave work it is suitable to radiate the energy from a plurality of wires arranged a certain distance apart rather than from a single 5 antenna wire, it being immaterial so far as thepresent invention is concerned in What particular way these aerials are geometrically disposed.

However, all systems comprising a plurality of aerials have this feature in common that the constituent antennzeare equivalent with reference to one another, and that they must be identically coupled with the transmitter. The coupling is effected by means ,of energy. (feeder) wires, and these, of course, must be branched whenseveral antennae are employed.

In order that the energy of the transmitter may be totally transmitted to the different aerials, it isunecessary that the energy lines should be coupledwith one another and with the respective antennae in a way free from reflection. The same situation holds true if av receiver is to be coupled with a plurality of aerials. In other words, at each branchingpoint of the energy line, say, atrthe junction or transition point from 1 to 11. wires, the natural impedance of all of these n wiresmust be equal to that of. the main line, in other words, each individual line must possess the 'n-fold resistance of the main line. If each of these in many lines again divides into a number of others, the same condition holds true for such new branch point. Finally, however, also the useful, thatis, the antenna resistance'must be adapted to the energy line.

It has already been known from low-frequency -problems, ,f0r instance, from ordinary telephone lines that the natural impedance of the main energy'line maybe adapted to that of the branch nes by the aid of transformers having conveniently chosen transformation ratios. But the qi qu stion of dimensioning and disposing the lines was mainly solved from a viewpoint of insuring minimum cost of installation, indeed,such lack in agreement between the wave resistance as resulted from such policy and plan was corrected iby the convenient selection of the transformation ratios of coupling transformers.

Now, in the case of radio frequency work, especially with ultra-short waves, transformers, most preferably of the air-core type, could be employed 'ifor the said purpose. However, these involve the disadvantage that they establish coupling not in a purely inductive manner, but also capacitively, so that as a consequence the phase relations between the primary and the secondary bibecome uncertain. When the question of proper phase relationship is important (and this is the case of transmitting and receiving with a great number of antenna which are to bear well-defined phase relations with one another by being arranged at certain distances), it is a better plan 5 not to use such uncertain transformer coupling and to couple the energy lines at the junctionpoints directly with one another. v According to thedisclosures of the present invention, while dispensing with the said coupling transformers by establishingdirect connection between the input and output wires at the junction points, wave reflection is completely precluded by that the necessary conditions and relations as regards natural impedance are insured 7 simply bythe convenient selection of the line constants for themain and branch lines. The factors governing the line or wire constants are the cross-sections and the geometrical form of arrangement of the wire paths, the distances ductors, becomes higher whenever the geometrical size of the line path, for instance, in the case of wires, the cross-section is increased. Hence, by enlargingthe cross-section, the natural impedance can be diminished. A reduction in the distance between conductors, or an increase in the dielectric constant of the medium surrounding the line, would have the same effect. 9

For the supply of antennae according to the present invention, the following forms of line paths may be considered:

(a) Concentric tubes whose diameters are changed at each branch point in accordance with whatever change in natural impedance may be desired.

(b) Parallel wires or tubes whose mutual distanceor whose cross-sections are varied at each branching point.

(0) Parallel wires or tubes which are screened towards the outside by a common sheath or envelope. In this case, there is a further chance to utilize the influence of the envelope upon the line capacity for insuring the desired natural 119 Ra=120 ohms.

diameter). have a natural impedance each of Z3=120 ohms,

impedance, for instance, by varying the distance between the envelope and the lines.

(11) Lines consisting of several paths, parallel from both an electrical as well as spatial viewpoint with or without external screening or shielding by external envelopes. In this case, there is an additional chance to vary the natural impedance at the branching points by that the number of paralleled conductors may be altered.

All of the arrangements hereinbefore mentioned may be embedded in insulation materials possessing well defined dielectric constants, the value of the dielectric constant being taken into consideration in choosing the dimensions of the diiierent conductor parts.

As regards the last conductor section directly preceding the antenna, its natural impedance must suitably be so chosen that it will come as closely as possible to the antenna resistance. The coupling between the energy line and the antenna isthen to be chosen of the simplest possible form.

The following practical example furnishes numerical values for an energy line to be dimensioned according to the present invention and as shown in the accompanying drawings.

The problem to be solved is to establish coupling between a transmitter S and four identical antennae A, the latter to be excited at the same phase. Suppose the resistance of each aerial is Each antenna is to be coupled with the respective energy supply line directly without the insertion of a transformer.

According to the present invention, this is e1- fected by that the transmitter first works upon a main supply line having a natural impedance Z 1=30 ohms. This main line may consist of two concentric tubes, the outer tube having a diameter of 100 mm. and the inner tube a diameter of 60 mm. This main line is divided or branched into mm. The said two secondary lines are again branched each into two energy lines (consisting again, for instance, of concentric tubes, the outer one of 100 mm. and the inner conductor of 12.5 These last-named conductors so that they can be coupled directly with the antenna in a way afiording freedom from refiection.

Having thus described our invention what we a plurality of pairs of spaced aerials, a transmission line of known impedance coupled to high frequency apparatus, said transmission line comprising concentric conductors of known mutual capacity, direct connections between each antenna in each pair and an antenna in another pair, and a plurality of branch lines directly included in said connections and directly connecting said connections to the transmission line, said branch lines comprising concentric conductors of less mutual capacity than said transmission line and each having an overall impedance greater than the impedance of the transmission line.

2. An antenna system having, in combination, a plurality of pairs of spaced aerials, a transmission line of known impedance coupled to high frequency apparatus, direct connections extending between each antenna in each pair and an antenna in another pair, said direct connections including a plurality of branch lines directly connected to the transmission line, said branch lines each having an overall impedance greater than the impedance of the transmission line, said transmission line and branch lines comprising spaced conductors, the spacing between the branch line conductors being greater than the' including tubes having diameters different from said branch lines.

4. An antenna system having, in combination, a two wire transmission line connected to high frequency apparatus, two: pairs of antenna, idividual ground connections at each of said antenna of said pairs, a direct connection between an an-' tenna in each pair to the ground of the other antenna in the same pair, and a plurality of branch lines directly connected to said antenna connections and to said two wire transmission line, said branch lines taken alone each having an overall impedance greater than the impedance of said transmission line, but less than the overall impedance of said antenna connections taken alone.

o'rro BoHM. WILHELM MOSER.

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