US2159627A - Shielding arrangement for high frequency transmission systems - Google Patents

Description

P. F. BYRNE SHIELDING ARRANGEMENT FOR HIGH FREQUENCY TRANSMISSION SYSTEMS Filed July 14, 1938 FIG. 1.

IN VEN TOR.

p401. F- amwz A TTORN Patented May 23, 1939 UNITED STATES PATENT OFFICE SHIELDIN G ARRANGEMENT FOR, HIGH FRE- QUENCY TRANSMISSION SYSTEMS Application July 14, 1938, Serial No. 219,132

8 Claims.

My invention relates to shielding arrangements for high frequency transmission systems, and more particularly to shielding arrangements adapted for use with simple transmission modifying networks used in connection with transmission lines and coupled thereto.

Certain forms of transmission modifying networks have been developed which comprise a conductor spaced from the transmission lines and coupled thereto differently at different ends of the networks. Such arrangements may comprise a plurality of different forms of network of different shape and arrangement. The simplest form of such coupled network generally in use with a two-conductor transmission line coinprises a section of transmission line spaced from the main transmission circuit and short circuited at one end. This transmission line section may be tuned by designing it with the proper length with respect to the wavelength at which the transmission system is to be modified, and may be further adjusted in tuning by means of a small trimming condenser bridged across the network at a point adjacent the short circuited end. The network itself may, however, have many other forms and other means for adjusting the tuning may be provided. The particular form of the network is not a feature of this in vention and for this reason a more particular description thereof is not made.

With these coupled transmission line sections used as wave modifying networks, it has been found that the tuning thereof is quite critical and that any foreign bodies adjacent the coupled network will disturb tuning and consequently change its wave modifying property. This change in tuning is particularly troublesome when the network is used in conjunction with other high frequency apparatus so that it is necessary for an attendant to approach the system to attend to other apparatus in the vicinity thereof. For example, when the coupled network is used as a filter for selectively coupling high frequency transmitting or receiving apparatus to the transmission line, it is desirable that the leads from the network to the high frequency apparatus be comparatively short and consequently anyone approaching the high frequency apparatus to make adjustments will cause an upset of the filter arrangement and the coupling of the apparatus to the transmission line.

It is an object of my invention to overcome this difficulty by providing a shielding arrangement to be used in conjunction with coupling network.

It is a further object of my invention to provide a shielding arrangement which will not interfere with the final adjustment and tuning of the coupled network.

It is a further object of my invention to provide a shielding arrangement for a coupled network which permits ready accessibility to the coupled network arrangement.

It is a still further object of my invention to provide a shielding arrangement for a coupled network which will permit an attendant to move about in close proximity to the network without upsetting the tuning thereof. 7

Other objects and advantages will be apparent from a reading of the particular description in connection with the accompanying drawing in which Fig. 1 diagrammatically illustrates one form of the coupled network arrangement and the shielding means therefor.

Fig. 2 illustrates a cross-sectional view of the network and shielding arrangement of Fig. 1, and

Fig. 3 illustrates an arrangement wherein the coupled network is used as a filter circuit connected to high frequency apparatus and is pro vided with a shielding arrangement in accord ance with my invention.

Turning now to Figs. 1 and 2, reference character l designates a grounded conducting surface which may be a wire screen. Spaced from the conducting surface I and arranged parallel thereto are the transmission line conductors 2. Spaced a proper distance from the transmission line and preferably arranged substantially parallel thereto, is the coupled wave modifying network 3. This network is properly designed and located with respect to transmission line 2 so as to produce desired modification of the waves in transmission line 2. This modification may consist of an impedance matching of the transmission line, or a filter coupling for waves of a desired frequency between said transmission line and high frequency apparatus or any other wave modification.

In the network there may be provided a short circuiting bar indicated at 4. With this con struction the voltage developed in the network is relatively high at the open end and approaches zero at the short circuited end. The network may itself be designed so as to completely and properly modify the wave transmission without further change. However, in order to secure the fine adjustment of the network, it is sometimes desirable to provide a trimming condenser such as indicated at 5 across the network at a point adjacent the short circuited end thereof.

When such a wave modifying network as has been described above is coupled to a transmission line, it has been found that the network is quite critical in tuning and that any foreign objects approaching the network will upset the tuning of the system and accordingly the coupling. This has been found to be true whether the object approaching the network is a dielectric or a conductive body. Such disturbances adversely react in the system and upset the whole circuit.

In order to eliminate these disturbances, in accordance with my invention, a screen 6, is provided about the coupled network. This screen may be of any desired conducting material shown, by way of example, in Figs. 1 and 2, as a mesh screen. I have discovered that when shielding of a coupled network is desired, it is not necessary to enclose the entire network within the screen, but it is sufficient to provide merely a substantially U-shaped screen extending outwardly from the grounded wall and about the transmission line and the network leaving the end wall of the screening arrangement open. Furthermore, it is not necessary that the screen extend the full length of the network, since at the low voltage end adjacent the short circuiting bar 4, the presence of foreign bodies does not exert much of an influence upon the tuning of the network. Furthermore, while the other end of the screen may extend as far as it is desired, I have discovered that it is not necessary to have this screen extend to a point beyond the end of the conductors of the coupled network. Accordingly, the screen may be provided so as to start at a point adjacent the short circuited end of the coupled network and terminate at a point in a plane with the open end of the network. When so designed I have found that a person may work immediately adjacent the open end of the conductor network without noticeably disturbing the tuning.

The spacing of the walls of the shield from the conductor arrangement is not critical and may be varied within wide limits. I have found that a very satisfactory result was obtained by providing a screen in which the side and end walls of the screen were spaced from the conductors a distance substantially equal to the spacing between the conductors. It should be distinctly understood, however, that other dimensions and spacings may be used within the spirit of my invention.

The fact that the shield may be terminated short of the closed end of the network permits that this end may be readily accessible for any small adjustments that may be necessary. If the tuning is to be adjusted wholly by varying the length of the conductors of the network, the short circuiting bar itself is readily available for movement to vary the effective length. Furthermore, if a trimming condenser is used to make the final adjustments of the network, the shield arrangement in accordance with my invention provides that this condenser will be readily accessible.

My invention is particularly useful when wave modifying networks such as described are used for filter circuits to couple high frequency apparatus with the transmission line. Such an arrangement is diagrammatically illustrated in Fig. 3. In this figure, 3!, represents a wall of a suitably provided building for housing high frequency transmitting and repeating apparatus.

The entire interior surface of the building, including wall 3|, is preferably lined with a conducting material which may be, for example, a suitable wire mesh. The conductive wall is grounded so as to maintain the entire interior surface and ground potential and to shield the apparatus from any outside influences. Adjacent wall 31 and suitably insulated thereupon by insulating supports 31 is transmission line 32. Spaced from transmission line 32 and likewise mounted on suitable insulated supports 31, is the coupled network 33. This network is provided with a short circuiting bar 34 and may be provided with a suitable tuning condenser 35. Positioned at a point directly opposite network 33 is high frequency apparatus 38. Connecting high frequency apparatus with the coupled network 33 is provided the lead-in conductors 39. These conductors are connected to the short circuiting bars and spaced apart by such an amount as to provide an impedance match between the coupled network and the high frequency apparatus. With an arrangement such as herein illustrated, it is clear that an attendant approaching high frequency apparatus 38 would at the same time move into close proximity to the coupled network This would badly interfere with the tuning of the network and if apparatus 33 comprised a receiver would substantially reduce if not entirely eliminate the reception of signals at such time. Likewise, if the apparatus 33 comprises a transmitter, the approach of an attendant to the transmitter would substantially cut the transmitter out from the line. In order to avoid such disturbances I provide a shielding arrangement 3'6 about the coupled network. This shielding arrangement is designed similar to that illustrated in Figs. 1 and 2 and may be of any suitable conducting material, for example, metal foil or wire mesh. This shield is fastened to the metallic screening on wall 3! and thus provides a grounded shield about the coupled network. With provision of this network, the high frequency apparatus is no longer substantially cut off from the transmission line upon approach to the arrange-ment for the purpose of making necessary adjustments.

Furthemore, by providing this shielding arrangement, it is much easier to properly adjust the tuning of the network itself since the approach thereto for adjusting purposes will not itself upset the tuning of the system. It is thus clear that with this arrangement the proper tuning and adjustment of the coupled network is greatly facilitated as likewise is the adjustment of other apparatus located adjacent thereto.

In each of Figs. 1, 2 and 3, I have illustrated the shielding arrangement in the form of a rectangular screen. It should be distinctly understood that the particular shape and form of the shield is not material and any desired shape, such for example, as cylindrical or elliptical forms may be used. It is preferable that the shields be made symmetrical with respect to the transmission line and network arrangement, since any dissymmetry would tend to upset the normal balance of the system. However, any slight dissymmetry may be taken care of by suitable adjustments of the network with respect to the transmission line. Furthermore, the positioning of the screening arrangement itself is not critical and any slight dissymmetry will not therefor unduly upset the balance of the system.

As shown in Figs. 1, 2 and 3, the coupled network has been illustrated as a simple straight conductor section. Since the network itself is not part of my invention, I have not illustrated the many forms that the network may assume. It should be distinctly understood, however, that the shielding arrangement in accordance with my arrangement, is not limited to any particular form of coupled network, but is equally applicable to all of the different forms of networks which may be used.

While I have described by way of example a preferred embodiment of my invention in connection with the illustrative drawing, it should be distinctly understood that this description is not intended as a definition of the scope of my invention. What I desire to claim as my invention and consider to be the scope thereof is embodied in the accompanying claims.

What I claim is:

1. A high frequency transmission system, comprising a transmission line, a wave modifying network spaced from said line and coupled thereto, said network being coupled diiferently at one end than at the other end, and means for preventing disturbance of said coupling comprising a grounded metal screen spaced from said network and said transmission line and extending about said section and the portion of the transmission line adjacent thereto.

2. A high frequency system according to claim 1, in which said metal screen, comprises a wall provided with a grounded screen, and a substantially U-shaped member covering said section and said transmission line, the open side of said U-shaped member being fastened to said wall.

3. A high frequency transmission arrangement comprising, a grounded conductive surface, a high frequency transmission line comprising a pair of conductors mounted on said wall and insulated therefrom, a network comprising a section of transmission line short circuited at one end, said network being spaced from said transmission line and extending substantially parallel thereto, connections from said network coupled to high frequency apparatus, and a conductive shield connected to said conductive surface arranged about said transmission line and said network.

4. A high frequency transmission arrangement comprising, a grounded conductive surface, a high frequency transmission line comprising a pair of conductors mounted on said wall and insulated therefrom, a network comprising a section of transmission line short circuited at one end, said network being spaced from said transmission line and extending substantially parallel thereto, connections from the short circuited ends of said network coupled to high frequency apparatus, a tuning means bridged across said network adjacent said short circuited end, and a conductive shield connected to said conductive surface arranged about said transmission line and said network, said shield terminating at the end adjacent said short circuited end of said network, short of the point of connection of said condenser.

5. A high frequency transmission system comprising a two conductor high frequency transmission line, a wave modifying network, tuned to a particular frequency which said line is adapted to carry, coupled to said line, said network extending along the direction of said transmission line and insulated therefrom, and a shielding means arranged about said network and said transmission line, said shield extending substantially over the entire length of said network and being open at its ends.

6. A high frequency transmission system ac cording to claim 5, in which said shielding means comprises a grounded metal screen of wire mesh.

'7. A transmission system according to claim 5, further comprising means for adjusting the tuning of said network, said shielding means terminating at one end at a point short of said tuning means, whereby easy adjustment is facilitated.

8. A high frequency transmission system according to claim 5, in which said shielding means comprises a grounded conductive screen the Walls of which are spaced from said transmission line and said network a distance of the same order of magnitude as the spacing between the conductors.

PAUL F. BYRNE.

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