US2749521A - Microwave coupling arrangements - Google Patents

Description

June 5, 1956 H. F. ENGELMANN ET AL 2,749,521

MICROWAVE COUPLING ARRANGEMENTS Filed March 5, 1952 INVENTORS HERBERT F. ENGELMANN JOHN A. KOSTRIZA United States Patent MICROWAVE COUPLING ARRANGEMENTS Herbert F. Engelmann, Mountain Lakes, N. J., and John A. Kostriza, New Dorp, N. Y., assignors to International Telephone and Telegraph Corporation, a corporation ofMaryland Application March 5, 1952, Serial No. 274,855

1 Claim. (Cl. 333-11 This invention relates to microwave transmission systems and more particularly to coupling arrangements equivalent to the magic T type of coupler.

In the patents to H. F. Engelmann, No. 2,654,842, dated October 6, 1953, and to D. D. Grieg and H. F. Engelmann, No. 2,721,312, dated October 18, 1955, a new principle of microwave transmission is disclosed, comprising in its simplest form twoconductors, the first as a line conductor and the second as a ground conductor, spaced close together in substantially parallel. relation. The so-called ground conductor, which may be at ground potential or some other given potential, is preferably considerably Wider than the line conductor so that the surface thereof provides in effect a mirror image reflection of the line conductor, whereby the distribution of the electric and magnetic field between the. conductors is substantially the same as the distribution between one conductor. and the neutral plane of a theoretically perfeet two-conductor parallel system. Small variations in size and shape of the. line conductor may produce variations in the characteristic impedance of the system but the field distribution with respect to the ground conductor is not materially disturbed. Likewise, certain variations in the surface of the ground conductordo not: materially disturb the field distribution with respect to the surface thereof since such variations either neutralize each other or do not adversely aliect the field distribution between the two conductors. By this system, microwaves can be propagated in substantially the TEM mode along the line-ground conductor system since the microwaves flow along the opposed surface or skin portions of the conductors which define the opposed conductive boundaries for the concentrated regions of the electro-magnetic field.

One of the objects of this invention is to provide an equivalent magic T coupling arrangement employing either the line-ground conductor feature of the transmission system referred to above or printed parallel conductors.

One of the features of the invention is the simplicity of construction and the economy of cost of the coupler as compared to the waveguide magic T coupler. The coupler according to the present invention comprises a dielectric sheet containing on opposite sides thereof the conductor configurations desired. For example, the conductor configuration on one side may comprise a closed conductor loop and branch conductors disposed laterally thereof at selected points on the loop. The conductor configuration on the other side may be identical to that on the one side or it may comprise a layer of conductive material so as to present a planar conductive surface parallel to the plane of the conductive loop. If desired, the loop and branch conductors may be so supported relative the planar conductor as to have air dielectric therebetween.

The above-mentioned and other features and objects of this invention will become more apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein: a

Fig. 1 is a view in plan of a loop form of coupling between.

arrangement in accordance with the principles of this invention;

Fig. 2 shows a cross-sectional view with parts broken away taken substantially along line 22 of Fig. 1;

Fig. 3 shows across-sectional view similar to Fig. 2 of a parallel strip loop coupler; and v Fig. 4 is a view in plan of a variation of the loop coupler shown in Figs. 1 and 2.

Referring to Figs. 1 and 20f the drawings, a loop form of coupler is shown comprising transmission lines of the line-above-ground type. Preferably the microwave transmission line is of the printed circuit type comprising a first or line conductor land a second or ground conductor 2 with a layer 3 of insulating material there- The. conductive material may bev applied to the layer of insulation, such. as polystyrene, polyethylene, Teflon, or other flexible insulation of high dielectric quality, in the form of conductive paint or ink, or the conductivematerial may be chemically deposited, sprayed through a stencil or dusted. onto selected prepared surfaces of the installation according to known printed circuit techniques. For relatively short lengths of lines or loop configurations, the conductive strips may be cut and applied by a clie-stan1ping operation. In some cable manufacturing-processes, the insulation may be extruded andsimultaneously or later coatedon the two sides thereof 'with conductive material of the desired thickness and widths. Where the widths. of the two coatings are the same and it is desired to reduce the width of one of the coatings, the portions of the two coatings that are to beretained may be coated with a chemically inert material exposing the parts to be removed, and thereafter passed through an etching bath, whereupon the exposed portionsof the conductivecoatings are removed. While the two conductive coatings 1 and 2- are shown in crosssection to be substantially rectangular, they may comprise different shapes so long as one of the conductors presents a planar surface with. respect to the other. Preferably, the ground conductor is two to three times the width of the line conductor 1, although two such conductors of equal width when printed on a sheet of dielectric will function as a two-wire parallel system. The electric field concentrated for a ratio of widths of line to ground conductors of l to 3 is found to range from about per cent to approximately 99 per cent. From the foregoing it is clear that a narrow ground conductor may be used without much radiation loss, and where it can be three or more times the width of the line conductor, an exceptionally low loss transmission line is assured. For further information on various line-above-grount cable constructions, reference may be had to the aforementioned Patent No. 2,721,312.

From the foregoing description of a line-above-ground transmission system, it will be clear that such a conductor arrangement is similar to a rectangular waveguide especially where the line conductor is of flat strip form. Whether or not the line conductor is round, oval, or fiat, wave propagation is predominantly of one polarization, that is, the concentration of lines of electrical force 4 are substantially perpendicular to the opposed surfaces of the line and ground conductors. It will be understood from this that the spacing of the two conductors cornprises a very small fraction of a wavelength of the micro wave propagated therealong and that this spacing is usually less than the diameter or width of the line conductor 1, thus incurring a high concentration of the electric field directly beneath the line conductor.

The loop coupler shown in Figs. 1 and 2 comprises a loop 5 of the line conductor 1 connected with four radially disposed branches 6, 7, 8, and 9. The branches 6 and 7 are connected at diametrically opposite points on the loop While the branches 8 and 9 are connected at spaced points at one side of the loop. The mid circumference of the loop is selected to be one and a half wavelengths so that the distance between branches 6 and 7 will be three-quarters of a wavelength. The location of branches 8 and 9 is such that these branches are spaced a quarter of a wavelength from adjacent branches. The loop and the branches 6, 7, 8, and 9 overlie the planar surface of conductor 2, the sheet of dielectric material 3 being disposed therebetween as the supporting medium. By disposing the line conductor of the loop and branches a small fraction of a quarter wavelength above the planar surface of conductor 2, the electric field 4 is highly concentrated between the opposed surfaces of the line conductors and the planar surface of the line conductor 2. This field approximates the field of the TEM mode so that microwaves are propagated along the skins of the conductors which bound the electric field. Any physical discontinuities in the line conductors 1 may tend to set up higher order modes but due to the close spacing of the conductors 1 with respect to the planar surface of conductor 2 these higher order modes are quickly attenuated.

Assuming that the source of microwave energy is received over branch 6, there is an outward flow of microwave energy over adjacent branches 7 and 8. Likewise, if a source of microwave energy is coupled to branch 7 an outward flow will be obtained over adjacent branches 6 and 9. v

In Fig. 3 a cross-section of a parallel strip line arrangement is shown similar to the cross-section of Fig. 2, it being understood that the strip 2a corresponds to the planar conductor 2 in the embodiment of Figs. 1 and 2. As shown in the cross-section the line conductor 1a and the so-called ground conductor 2a are of substantially the same width in cross-section and are held in true parallelism by a sheet of dielectric material, such as indicated at 30. The field distribution between the parallel strips is indicated at 4a. This field is highly concentrated in view of the fact that these conductor strips are purposely disposed a very small fraction of a quarter wavelength. The operation of the parallel strip loop coupler follows the same as for the line-planar conductor system of Figs. 1 and 2.

In Fig. 4, the loop is shown to be in the form of a rectangle 10. This form is shown to indicate that the loop need not be circular but may comprise any configuration so long as the current flow follows a closed circuit having a circumference dimension equal to one and a half wavelengths. The loop circumference, however, may be of other lengths so long as the lengths provide for max and null conditions at the junctions in accordance with the illustration of Fig. 1. For example, the loop dimensions may be five quarters wavelength for one half of the loop, with three quarters wavelength between branches 6, 8; 8, 9; and 9, 7.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made by way of example only and not as a limitation to the scope of our invention as set forth in the objects thereof and in the accompanying claim.

We claim:

A microwave coupler comprising first and second conductors only, a planar dielectric sheet supporting said first conductor on one surface thereof and said second conductor on the opposite surface thereof, the spacing between said conductors being a minor fraction of a wavelength at the mean frequency of waves applied to said coupler, said first conductor being a flat strip conductor in the form of a loop with a plurality of branches extending from said loop, two branches at diametrically opposite points, and two other branches each at a point distant in the order of one-quarter of a wavelength from the next adjacent branch, the loop having a mid-circumference in the order of one and a half wavelengths, the loop and its branches lying substantially in a given plane on said dielectric sheet, said second conductor being a planar sheet underlying the entire loop and at least a portion of each of said branches adjacent said loop.

References Cited in the file of this patent UNITED STATES PATENTS 2,409,449 Sanders et a1. Oct. 15, 946 2,445,895 Tyrrell July 27, 1948 2,611,822 Bliss Sept. 23, 1952

Images