US1725915A - Radiation prevention - Google Patents

Description

Aug. 27, 1929. Y

C. W. HANSELL RADIATION PREVENTION Filed May 2, 1927 6 "Li/12 I E 10 10 10 10 2 E g 5 29 Fay. 2

INVENTOR c.w. HANSELL ORNEY Patented Aug. 27, 1929.

UNITED STATES CLARENCE W. HANSELL, OF ROCKY POINT, 'NEW YORK, ASSIGNOR TO RADIO CORPO- RATION OF AMERICA, A CORPORATIONOF DELAWARE.

RADIATION PREVENTION.

Application filed May 2,

Y This invention relates to prevention of radiation, and more particularly the prevention of undesired radiation from a por tion of an antenna feed line.

It frequently happens that the energy radiated from a conductor supplying energy to an antenna is in an undesirable phase relative to the energy being radiated from the antenna itself. With any type of antenna this leads to reduced efiiciency, and in the case of a directive antenna it further serves to modify the directivity of the antenna. It is an object of my invention to prevent undesired radiation from a conductor. This is most simply accomplished by surrounding the conductor with a shield which is tuned to the working frequency. From the aspect of the method employed it consists in using the radiated energy to induce currents which themselves give rise to a field in opposition to the original radiated field.

The more detailed specification which fol lows is accompanied by a drawing in which Figure 1 schematically represents my in vention in simplest form;

Figure 2 is an equivalent circuit;

Figure 3 is a polar diagram indicating radiation characteristics; and

Figure 4 is a vector diagram explanatory of the neutralizing action.

Referring to Figure 1, energy from a source 2 is supplied through any convenient coupling means 4 to a suitable transmission line 6. This is used to carry the energy to a directive antenna which, in this instance, has been exemplified by a wave antenna provided with transverse radiators, such as is more fully described in my copending application Serial No. 161,771, filed January 18, 1927. Such an antenna is made up of a pair of listributing conductors or a wire return line 8 to which there are transversely coupled a series of short wave radiators 10. Only a few of these are shown in Figure 1, which is intended merely to indicate the idea involved. The transmission line 6 is connected to the wire return line 8 by means of the transverse feed conductor 12.

From a superficial examination it might be supposed that the transverse feed conductors 12 would constitute a good first transverse radiator for the antenna, but in practice this is found not to be so because 1927. Serial No, 188,157.

of the incorrect phase of the energy flowing in this first transversal.

This phase difference may be explained follows: An equivalent circuit for each of the radiators 10 would be an inductance and a capacitance in parallel. Each radiator takes from the line 8 substantially only the energy which it radiates, and this energy is radiated from a reactive circuit and therefore has a corresponding phase displacement comparedwith a resistive load. As the antenna is adjusted in use, the summation of the radiation energy taken by all of the radiators is, with reference to thetransmission line 6, a substantially resistive load. The energy radiated from the entire antenna traverses the feed conductors 12, which, while themselves reactive in characteristic, have flowing through them the large total radiation current the phase of which is determined by the characteristics of the antenna, and but very slightly by the feed conductors themselves.

This has been indicated in the equivalent circuit shown in Figure 2, and referring to this, it is seen that the feed conductors 12 may be represented by the inductances 20, 20, and the capacitance 22. The antenna load has been shown as the resistance 24-.

It follows that the energy radiated from the feed conductors 12 will be greatly out of phase with that desired successively in the series of radiators 10, and therefore it will act as an independent radiator, and not as one which contributes in proper phase to increase the directivity of the antenna system as a whole. This is suggested by the polar radiation diagram shown in Figure 3, to which attention is now directed. In this the wave antenna is indicated at 8, and the feed conductors are indicated at 12. The outline 30 represents the directive propagation taking place, from the antenna system exclusive of the conductors 12, and outline 32 represents the independent radiation which takes place from the latter. clear from this diagram that radiation from the feed conductors modifies the directivity of propagation, broadening the directive characteristics of the antenna, and substantially is wasted energy.

My invention consists in preventing radiation from the feedconductors 12 by resonant shielding, and again adverting to Figure 1, this is most simply done by surrounding the conductors 12 by a concentric pipe approximately onehalf wave in length, indicated at 14. Instead of a complete pipe there may equally well be used a plurality of parallel conductors arranged around the feed conductors 12, or any other desired shielding device, the only requirement being that such device be tuned to the working frequency. This is necessary in order to obtain a field from the shield which is in direct phase opposition to the field originally radiated from the surrounded con ductor.

The action involved may be explained by reference to the vector diagram shown in Figure l. In this figure 2' represents the radio frequency current flowing in the feed conductors, and (,5 is the field caused by this current. The lluX a has been shown in phase with the current because of the fact, before explained, that the antenna load is substantially resistive. This flux, cutting the pipe or shield 14, induces therein a potential 6,, which is 180 degrees out of phase with the flux As a result of this potential a current i flows in the pipe, and this current is in phase with the potential because, as explained, the pipe is tuned to the worring frequency. The current 2', sets up a field in phase with itself, and this field is directly opposed to the radiation field of the feed conductors 12.

It is to be understood that although my invention has been disclosed in connection with a transmission wave antenna, it is not necessarily restricted thereto, but is equally applicable to the prevention of radiation from any conductor. It is especially applicable to the prevention of radiation from a feed conductor which is supplying energy to an antenna, and from which conductor radiation would be injurious because of incorrect phase relative to that of the energy being radiated from the antenna itself.

The foregoing is disclosed by way of illustration and not limitation of my invention, which I claim is:

1. The combination with an antenna. having a feed conductor the energy in which, if radiated, would be in undesired phase relative to that in the antenna, of means to prevent radiation from the feed conductor comprising a conducting shield surrounding the feed conductor and tuned to the frequency of the propagated energy.

2. In combination, an antenna system for directively propagating high frequency energy including a plurality of radiators adjusted to radiate in desired phase relation and a feed conductor the energy in which, if radiated, would be in undesired phase relative to that in the radiators to obtain maximum directivity, of means to prevent radiation from the feed conductor comprising a conducting shield surrounding the feed conductor and tuned to the frequency of the propagated energy.

3. The combination with an antenna system comprising a distributing conductor to which there are transversely coupled radiating and feed conductors, of a radiation-preventing shield cooperating with a feed conductor to prevent radiation therefrom.

4. The combination with an antenna system comprising a wire-return line, a plurality of radiators transversely coupled thereto, and transverse feed conductors coupled thereto, of a radiation-preventing shield. cooperating with said transverse feed conductors to prevent radiation therefrom.

5. In combination, an antenna system comprising a Wire-return line and a plurality of short wave radiators coupled thereto, a source of energy, a transmission line coupled thereto, feed conductors connected to the transmission line and the wirereturn line, and a radiationpreventing shield surrounding the feed conductors to prevent radiation therefrom.

6. In combination, an antenna system com prising a wirereturn line and a plurality of short wave radiators coupled thereto, a source of energy, a transmission line coupled thereto, feed conductors connected to the transmission line and the wire-return line, and a conducting shield tuned to the working frequency and concentrically surrounding the feed conductors to prevent radiation therefrom.

7. The method of preventing radiation from a conductor carrying energy of a given frequency which includes utilizing the radiated energy to induce a potential, causing a current flow by applying the potential to a conducting medium surrounding the conductor and tuned to the given frequency, and using the current flow to set up a field in phase opposition to the field originally radiated from the conductor.

8. The combination with a conductor carrying high frequency energy of means to prevent radiation of the high frequency energy comprising a conducting shield surrounding the conductor and of proper length to be resonant to the frequency of the energy the radiation of which is to be prevented.

CLARENCE W. HANSELL.

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