CA1301865C - Transmission line coupling device - Google Patents

Abstract

ABSTRACT
A transformer and method of making same for coupling devices having differing impedances and comprising a pair of parallel conductors each constructed and arranged to have a standing wave in one which is a mirror image of the standing wave in the other so that the impedance varies from near zero at one end of the parallel conductors to a max-imum at their other end. The transformer having input ter-minals connected to points on one conductor having an im-pedance matching that of one device and having ouptut ter-minals connected to points on the other conductor having an impedance matching that of the other device.

Description

~301865 BE IT KNOWN that I, Donald H. Wells, a citizen of the United States of America residing at the City of Holland, County of Lucas, and State of Ohio, have invented a new and useful improvement entitled:
TRANSMISSION LINE COUPLING DEVICE
the following disclosure of which contains a correct and full description of the invention and the best mode known to the inventor of taking advantage of the same.
TECHNICAL FIELD
The present invention relates to coupling devices For transmission lines, and more particularly to such devices which will couple across a layer of dielectric material, such as plastic or glass.
BACKGROUND OF THE INVENTION
The prior art devices with which I am aware give off stray radiation such that their oscillating frequency is affected by structures adjacent the devices when installed, as well as by atmospheric conditions. Since such devices are sensitive to the environment in which they are installed, they must either be provided with means for adjustment after installation, or else are left to operate after installation at less than the best efficiency of which they are capable.
An object of the present invention is the provision of a new and improved device for coupling a two element trans-mission line of one impedance to an antenna or other device of another impedance by means of a transformer structure which will not be appreciably affected by surrounding structures.

130~86S

1 A further object of the present invention is the pro-vision of a new and improved device of the above described type wherein all of the elements of the tuned circuit are sheet metal stampings or printed circuits such that their dimensions as manufactured are precise, as is their frequency of oscillation when assembled.
Still further objects and advantages of the invention will become apparent to those skilled in the art to which the invention relates from the following description of the pre-ferred embodiments described with reference to the accompany-ing drawings forming a part of this specification.
BRIEF SUMMARY OF THE INVENTION
The transformer used in the coupling device of the pres-ent invention broadly comprises two electrical conductors arranged so that the magnetic and electrical fields of one interact and generally cancel the magnetic and electrical fields of the other. This can be accomplished by construct-ing and arranging the parallel conductors so as to produce standing waves in the conductors which are equal and opposite to each other. Preferably one end of the conductors are directly connected to each other. If the other ends of the conductors are not d;rectly connected, some additional means must be provided to reflect standing waves in an equal and opposite condition to each other. Most simply this is accom-plished by directly connecting the other ends together also,and causing the length of the conductors to be such as to oscillate at the desired frequency. An output connection from the two conductors may be provided for one plate of a coupling condensor later to be described. The output connect-i~n is physically located so that the standing wave at thatpoint will give the proper impedance to said one plate to match that of the other plate of the coupling condensor.
In the preferred embodiments of the present invention, the current in the two conductors at all points directly opposite each other is equal and opposite. This may be accomplished in a number of ways, but as stated, is believed most simply accomplished by directly connecting the ends of 1301~365 1 conductors of proper length and spacing. By so doing there is no phase shift at any point in the conductors, and this in mos~ cases is highly desirable.
In onè application, the invention is used to drive a whip antenna mounted on one side of a layer of dielectric material while the transformer is mounted on the other side of the layer of dielectric ~a~erial with no direct electrical connection therebetween. The whip antenna is connected to one plate of a coupling condensor which is adhered to one sur-face of the dielectric layer. The other plate of the couplingis adhered to the opposite side of the dielectric layer and is connected to the transformer. Obviously the impedance of the transformer connected plate of the coupling condensor must be specifically taylored to match that of the antenna connected plate.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a sectional view of one embodiment of the invention shown adhered to a glass panel with an antenna mount containing a condensor plate that is electrically connect-ed to a whip antenna adhered to the opposite side of the glass.
Figure 2 is a sectional view taken approximately on theline 2-2 of Figure 1.
Figure 3 is an oblique view of a plastic support body also shown in Figures 1 and 2 with a condensor plate and a terminal strip affixed to a coaxial cable connector.
Figure 4 is the terminal strip shown in Figures 1-3, but ;n its as stamped, unbent, condition.
Figure 5 is an edge view of the terminal strip shown in Figures 1-4.
Figure 6 is an oblique view of the condensor plate shown in Figures 1-3.
Figure 7 is a fragmentary oblique view of the electrical connection to the input coaxial connector.
Figure 8 is a plan view of the spirally wound twin transformer wires shown in Figures 1 and 2.
Figure 9 is a vertical sectional view similar to Figure 1 but showing another embodiment of the invention.

Figure 10 is a sectional view taken approximately on the line 10-10 of Figure 9.
Figure 11 is a plan view of a sheet metal stamping shown in Figures 9 and 10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
. . .
According to principles of the present invention, a transmission line of a given impedance is coupled to a device having another impedance by means of a transformer comprising a pair of generally parallel conductors each having a stand-10 ing wave which is equal and opposite to the standing wave inthe other; so that the electrical and magnetic fields sub-stantially completely cancel each other at a designed freq-uency. Also it is preferable that there should be no phase shift at any point in the device; so that the possibility of 15 stray radiation is eliminated at all parts of the device.
According to further principles of the invention, spaced apart input connections to the conductors are made at points having the same impedance as the impedance of the input transmission l;ne, and output connections to the conductors 20 are made at spaced apart points having an impedance matching that of the device to which they are to be connected. Pre-ferably the standing waves are produced at the deisred freq-uency without the addition of discrete components of capac-itance and inductance to avoid stray radiation from such 25 sources.
In the embodiment shown in Figures 1 through 8, the two conductors previously referred to are made from a pair of spirally coiled wires 10 and 12, and a stamped sheet metal terminal strip 14. In the transformer shown in the drawing, 30 the conductors 10 and 12 are supported by three pedestals 16, 18 and 20 that are molded onto a plastic base 22 having an integral plastic terminal support 24. The terminal support 24 has an opening 26 therethrough into which a coaxial cable receptable 28 is pressed. The receptable 28 comprises a 35 tubular conducting barrel 30, an inner tubular insulating sleeve 32, an axially extending conducting pin 34, and a threaded nut 36 for securing the usual coaxial cable terminal 38 to the receptacle 28.

13~865 1 The sheet metal terminal strip 14 has an opening 40 through one end for receiving the conducting metal barrel 30, a soldering tab 42 adjacent the opening 40, and a laterally extending leg 44 bent to form a U-shaped leg 46, the end of which is slotted as at 48 to receive conducting pin 34. The distance from the tab 42 to the opening 40, and the distance from the opening 40 to the terminal 34 are chosen so that their lengths when added to the lengths of the conductors 10 and 12 will give equal total conductor lengths to create equal but opposite standing waves in the conductors 10 and 12. The distance from opening 40 to the terminal 34 is chosen so that the distance therebetween relative to the total conductor length will give an impedance which matches that of the coaxial cable attached to terminal 38. The ter-minal strip is soldered to the conducting barrel 30, the endof conductor 10 is soldered to tab 42, the edge of slot 48 is soldered to terminal pin 34, and the end of conductor 12 is soldered to terminal pin 34-last.
The transformer shown in Figures 1-8 can be used to pass an RF signal through a panel of dielectric material, be it plastic, glass, etc. Because the transformer of the present invention does not put out stray radiation, it can be used to pass the signal to another section of coaxial cable, or to a discrete piece of RF equipment, such as an amplifier or antenna. Figure 1 illustrates how an antenna that is secured to a plastic base 50, similar to the plastic base 22 can be adhered to the dielectric panel (glass, etc.) directly opposite each other.
The transformer shown in the drawings is provided with a large size capacitive plate 52 received in a recess 54 in the base 22. The opposite plastic base 50 has a similar capacitive plate 56 connected to the antenna. The antenna and its capacitive plate 56 have a characteristic impedance depending on the type of antenna and its design. The trans-former of the present invention is easily taylor made tomatch the impedance of the device to which it is to be coupled by connecting its capacitive plate 52 to the appropriate im-pedance points of the conductor 10. As shown in the drawings ~3(~186S

1 this is accomplished by a branch wire 58 one end of which is soldered to the plate 52 and the other end of which is sold-ered to the conductor lQ at the appropriate length from the opening 40 in the terminal strip 14. The assembly so far described is protected from the weather by a square plastic cap 60 that is cemented to its base 22.
While it is not a necessary part of the invention, the t~ansformer shown in the drawings includes a shorting bar 62 that is crimped across the wires 10 and 12 to electrically a~just their lengths to provide a standing wave at a desired frequency. The shorting bar 62 permits a unit of basic man-ufacture to be tuned to a wide range of frequencies by a simple crimping operation. By making the length of the con-ductors 10 and 12 such that they oscillate at the desired frequency when the shorting bar 62 is positioned as shown in Fig. 2, the transformer can easily be changed to oscillate at a higher RF frequency by moving the shorting bar 62 to the position B, and can be made to oscillate at a lower fre-quency by moving to the position C. By a complete removal of the bar 62, a still lower frequency is provided.
In operation, standing waves are produced in the con-ductors 10 and 12 between the opening 40 in the sheet metal terminal strip 14 and their other electrical end be it their hair pin end union, or the shorting bar 62, as the case may be. There will be substantially zero impedance at opening 40 and a maximium impedance at a location in conductors 10 and 12 one quarter wave length away from opening 40 at the operating frequency. The point on slot 48 at which the co-axial cable conductor 34 is connected to conductor 12 has an impedance depending on the ratio of its distance from opening 40, relative to the total distance from opening 40 to the shorting bar 62. The impedance at the point where wire 58 is soldered to conductor 10 will be the ratio of the distance it is from the opening 40 to the distance between opening 40 and bar 62. This ratio is selected to match that at the cap-acitive plate 56 of the driven device. The precise locations of contact with leg 46 and the connection of wire 58 to con-ductor 10 are best precisely determined by actual measurement before production.

13C~1~65 1 is begun, since once so established, individual adjustment is not necessary.
The embodiment shown in Figures 9-11 is generally sim-ilar to the embodiment shown in Figures 1-8, but differs principally therefrom in that the electrical conduclors are made from a preform such as a sheet metal stamping, or from a printed circuit board. Those portions of the embodiment shown in Figures 9-11 which correspond to similar portions of the embodiment shown in Figures 1-8 are designated by a like reference numeral characterized further in that a suffix "a" is affixed thereto.
The sheet metal terminal strip 14a is generally similar to the terminal strip 14 excepting that the end of leg 46 on the top side of slot 48 is bent out to form a soldering terminal for conductor 12a. The conductors lOa and 12a are part of a sheet metal stamping that includes integral L-shaped projections 64 and 66, respectively, which are bent ~wn to make contact with tabs 42a and the tab on leg 46a.
Obviously, it is possible to replace the sheet metal terminal strip 14 with wire by making the conductors 10 and 12 longer, so that each extends all the way to the metal barrel 30 of the coaxial cable receptacle 28. This makes soldering very difficult however. Instead, the use of sheet metal terminal strip 14 permits metal barrel 30 to be solder-ed to strip 14, and leg 46 to be soldered to pin 34 before conductors 10 and 12 are in position. Thereafter conductor 10 can be more easily soldered to tab 42, and conductor 12 more easily soldered to leg 46, since they are at more accessible, yet precise locations.
In the embodiments above described, the length of the electrical conductors and legs of the sheet metal terminal strips to which they are connected gi,ve total electrical lengths that provide equal but opposite standing waves and in which all points of one conductor are opposite points on the other conductor having an equal but opposite charge and magnetic field.

1 It will now be apparent that there has been provided a new and improved coupling device and transformer which will transfer an RF signal across a dielectric body without stray radiation and without a direct electrical connection through the body.
It will also be apparent that because all components are formed from accurate stampings, or short lengths of pre-formed wire, or printed circuits, the oscillating fequency of the parts when assembled will be precise without a sub-sequent individual tuning operation. Also, because allportions of the electrically oscillating structure have points on one conductor that are directly opposite points on the other conductor having an equal and opposite charge and mag-netic field, the transformer is not appreciably affected by surrounding structures and does not have to be individually tuned after installation.
While thé invention has bee!n described in considerable detail, I do not wish to be limited to the particular embod iments shown and described, and it is my intention to cover hereby all adaptations, modifications and arrangements thereof which come within the practice of those skilled in the art to which the invention relates, and which fall within the ~rview of the following claims.

Claims (9)

1. An assembly for coupling a two element transmission line of characteristic impedance to a driven device having a given impedance, said assembly comprising: a pair of conductors having respective opposite ends, said pair of conductors being directly connected together at respective opposite ends to form a closed loop devoid of discontinuities, each one of said pair of conductors being adapted to resonate at a generally predetermined frequency to produce generally equal and opposite standing wave portions in the pair of conductors to provide a fixed range of impedance values which vary according to the position of the standing wave along the pair of conductors; an output terminal for driving said driven device, said output terminal being electrically connected to a point on one of said pair of conductors where said standing wave gives said given impedance; and said pair of conductors also having a pair of input terminals for respective elements of said two element transmission line and electrically connected at points where said standing wave has the characteristic impedance of the two element transmission line.

2. An assembly for coupling a two element transmission line of characteristic impedance to a first driven device having a given impedance, said assembly comprising: a closed loop conductor devoid of discontinuities at any point along the loop and constructed and arranged to have a standing wave therein to give a fixed range of impedance values along the loop; an output terminal disposed on said loop conductor at a point having said given impedance of said first driven device; and said closed loop conductor rn/ 9 also having a pair of input terminals for respective elements of said transmission line and which are disposed at spaced apart points on said loop and having therebetween the characteristic impedance of the two element transmission line.

3. The assembly of claim 1 wherein said pair of conductors comprise: a generally hairpin shaped conductor having two open ended legs forming said pair of conductors and integrally connected together by a center transverse section of said hairpin conductor; and a sheet metal terminal strip having said spaced apart input terminals and connected across the open end of said generally hairpin shaped conductor.

4. The assembly of claim 1 wherein each of said conductors has an electrical length of approximately a one half wave length of the transmitted frequency.

5. The assembly of claim 1 including a shorting bar disposed across said conductors intermediate their first and second ends to vary the effective electrical length of said pair of conductors.

6. The assembly of claim 1 wherein said conductors comprise integral legs of a sheet metal stamping to provide accurate conductor lengths and spacing.

7. The assembly of claim 6 including an integral shorting bar disposed between conductors of said pair which can be easily removed to increase the electrical length of said pair of conductors.

8. A method of producing an accurate impedance match between first and second two conductor transmission lines having first and second impedances, respectively, said method comprising: producing a preform having two conductor legs with each leg having respective first and second ends and with rn/ 10 respective first and second ends being connected together to form a closed loop, and said second ends providing a first terminal for attachment to one conductor of the first transmission line, said closed loop providing a fixed range of impedances therealong; attaching one conductor of said first transmission line to said first terminal and attaching the other conductor of the first transmission line to a point on said preform having the impedance of said first transmission line; and coupling a conductor of said second transmission line to a point on said preform having the impedance of said second transmission line.

9. A transmission line coupling device for electrical wave energy, comprising: a closed resonating conductive loop devoid of discontinuities and accommodating a wave of transmitted energy to provide a fixed range of impedance points which vary around the loop from approximately zero to a maximum, said loop having a pair of input terminals spaced apart along the loop by a distance corresponding to a given difference in impedance; and at least a first output terminal on said loop spaced apart from one of said input terminals by a distance having a desired output impedance.