US3551856A

US3551856A - Miniaturized circuit device

Info

Publication number: US3551856A
Application number: US763227A
Authority: US
Inventors: Gary R Hoffman
Original assignee: Bendix Corp
Current assignee: Bendix Corp
Priority date: 1968-09-27
Filing date: 1968-09-27
Publication date: 1970-12-29
Anticipated expiration: 1987-12-29

Description

United States Patent O U.S. Cl. 333-'35 3 Claims ABSTRACT F THE DISCLOSURE This invention describes a circuit device which is useful with miniature circuits. Depending upon the structure of the device it can be used as either an impedance transformer or as a directional coupler. When used as an impedance transformer an impedance matching center conductor is sandwiched between two dielectric elements and a ground plane is added to the opposite sides of the dielectric elements. A slotted spindle is placed transversely across the several layers of material at the approximate center of the longitudinal dimension of the device. The layers are then rolled around the spindle in a bifilar manner. This type of rolling accomplishes two purposes: firstly, it allows a substantial decrease in the longest dimension of the layers of material, and secondly, the bifilar winding serves to cancel out the inductive reactance which would be formed due to the winding. For use as a. directional coupler two stripline elements are placed in a substantially parallel relationship and then inserted between the two dielectric elements. Two conductive elements are then positioned on the opposite sides of the dielectric elements to serve as ground planes after the element is rolled around the slotted spindle.

It is well known that the best operating efficiency of an electrical system is obtained when the impedance of the circuit receiving a signal is matched to that of the circuit supplying the signal. When the impedances are thus matched the efficiency of the overall system is maximized and is at its theoretical maximum. However, as is well known, it is very difficult to design two different circuits having distinct and separate functions which at the same time have the same impedance. For this reason the use of impedance matching networks, often called impedance transformers, has become very common in order to improve the system eiciency by matching the impedance of the two circuits. Such systems are quite satisfactory for their intended purpose; however, when working with waveguide or stripline transmission systems the impedance transformation network must be approximately onequarter wavelength long. The wavelength is dependent upon circuit reactance and operating frequency. The impedance transformation network will therefore ordinarily be anywhere from one to two feet in length and sometimes even greater, depending upon the frequency at which the system is intended to operate. This obviously is a mechanical Vdisadvantage and makes distributed matching useless for use with miniaturized circuitry.

A similar problem exists with directional couplers wherein the energy from the energy supplying circuit is directed to any one of two existing output terminals of the directional coupler. When used in a stripline configuration a directional coupler must also be approximately a quarter wavelength long. These elements are also therefore very cumbersome to use with miniaturized circuitry in their presently existing form.

It is therefore an object of this invention to provide a circuit element ordinarily having large physical dimensions, but which is physically reduced in size while maintaining its electrical size so that it is useful with miniaturized circuitry.

3,551,856 Patented Dec. 29, 1970 ICC It is another object to provide such a device which ordinarily has a length in the order of a quarter wavelength of its operating frequency, but which is wound in a bilar manner to substantially reduce the physical length.

It is another object to provide such a device having a center conductor which is properly dimensioned in width and length to serve as an impedance transformer.

It is another object to provide such a device having an impedance matching conductor positioned between two dielectric members and two ground members positioned on the opposite sides of the dielectric elements.

It is another object to provide such a device having two parallel signal conductive members positioned in a substantially parallel relationship between two dielectric members and which is useful with miniaturized circuitry.

Further objects, features and advantages of the invention will become apparent from the following description and claims when read in view of the accompanying drawings, wherein like numbers indicate like parts and in which:

FIG. 1 is a cross-sectional view of the device taken along the longitudinal axis thereof.

FIG. 2 is a pictorial view looking straight down upon the inventive device.

FIG. 3 is a transverse, cross-sectional View taken along the line III-III of FIG. 2.

FIG. 4 is a pictorial view showing the use of a spindle for rolling the layered device into a bifilar wound device.

The structure of the inventive device can be best understood by viewing FIG. l. In this figure the device is generally indicated by reference numeral 10 and is composed of a plurality of thin layers respectively labeled 11 through 15. The three

conductive layers

11, 12 and 13 are shown to be separated by two

dielectric layers

14 and 15. These layers can be made of any suitably ilexible material. Conductor 12 is seen to be the longest of the three conductive layers. This allows the conductor 12 to extend beyond the ends of the rolled device after it has been wound around cylinder 17 as shown in FIG. 4. Conductor 12 serves as the signal conductor, while conductors 11 and 13 serve as ground planes. The additional length of conductor 12 provides a means for connectig the input and output circuits of the device. Conductor 11 is much shorter than the other four layers of material. This is so because the layer serves as a ground plane on the inside of the device and therefore need only be long enough to effect one complete turn when the device is wound around the spindle 17. After the initial turn the conductor 13 serves as the ground plane on both sides of the dielectric layers. Dielectric 15 is shown to be longer than any of the other layers. By extending the dielectric 15 beyond the length of conductor 12 it serves as an insulating element after the device is wound about the spindle 17 As best seen in FIGS. 2 and 3 the two conductors 11 and 13 are of substantially equal width and extend beyond the width of

dielectrics

14 and 15. The width of the

dielectrics

14 and 15 is substantially greater than the width W of center conductor 12. The narrow portions of conductors 11 and 13 which extend beyond the width of the

dielectrics

14 and 15 are provided with a plurality of thin slots or serrations 16. These serrations provide a good contact between the two conductive layers and also provide a good ground contact as the layered device is rolled about the spindle 17. It should be noted that, although in FIG. 3 the layers 11 through 15 appear to be relatively thick and therefore provide distinct separations between the

dielectrics

14 and 15, as a practical matter this separation is extremely small. In an actual embodiment of the invention the

conductors

11, 12 and 13 were 0.002

inch thick and the

dielectrics

14 and 15 were 0.010 inch thick. With a center conductor 12 of this nominal thickness the two dielectric 14 and 15 almost completely enclose the center conductor 12 so that, for practical purposes, no air spacing exists anywhere in the device. The only exception to this is a very small cross-sectional area at the edges of the enclosed materials. Also the extended edges of the conductors 11 and 13 are intended to be in electrical Contact. This is easily accomplished when using the very thin materials.

FIG. 4 illustrates the manner in which the layered device is rolled into a single unitary device having a longitudinal dimension substantially less than the dimension L shown in FIG. 2. The rolling procedure is accomplished by using a spindle 17 including a slot 18. The spindle 17 is placed across the transverse dimension of the various layers at the approximate longitudinal center thereof such that the device is enclosed in slot 18. The device is then rolled in a direction indicated by the arrow 19 in FIG. 4. A bifilar type of winding is therefore formed. Because of the bifilar type of winding the inductive reactance created due to the winding is substantially reduced because the inductors formed by the winding step are wound in opposite directions. With the spindle at the longitudinal center of the device the two opposed inductors are of essentially equal inductances at any frequency and therefore the inductive reactance is substantially cancelled.

Transmission line theory requires that the longitudinal length indicated as L in FIG. 2 of conductor 12 must be consistent with the equation:

where: L is the length, A is the wavelength of the operating frequency, and s is the dielectric constant of the propagating medium.

The factor e is present `because it affects the propagation velocity, and therefore the wavelength, of the transmitted signal. The length L of the device would therefore ordinarily be anywhere from one to three feet in length, depending primarily upon the frequency at which it was intended to operate. The advantage of the inventive device is therefore quite evident when it is realized that the length is reduced to less than one inch after the device is rolled in the bilar manner.

Because the device is intended to serve as an impedance transformer it must be consistent with the usual impedance transformer theory. It therefore must obey the equation:

equation:

h ,i 1 W-(.) (E) a Z=the required matching impedance, determined in accordance with Equation l,

h=the thickness of the dielectric material,

e=the dielectric constant of the dielectric materials,

,u=the permeability of the dielectric materials, and

W=the required width of the stripline conductor 12.

whe re The critical dimensions L and W, respectively shown in FIGS. 2 and 3 of the conductor 12 are therefore easily calculated by use of the Expressions l and 2 presented hereinabove. The lengths and widths of the

other layers

11, 13, 14 and 15 are chosen as a matter of convenience only and are not critical to the operation of the device.

After the layered device is rolled about the spindle 17 the ends of conductor 12 which extend beyond the rolled portion provide connecting terminals for the input and output circuitry. The invention thus provides a very small impedance transformer which is useful with either coax or stripline transmission media. Center conductor 12 therefore preferably has a rectangular cross-sectional area and is a stripline conductor. It should also be noted that the device is a two terminal bilateral device and therefore it can be connected into the system in any manner convenient. The device also has the advantages of being very light in weight and low in cost. Another distinct advantage is the simplicity of its construction and the lack of critical dimensions other than the length and width of center conductor 12, even those dimensions are not critical from a fabrication point of view.

The device shown and described this far uses a single center conductor 12 and therefore serves as an impedance transformer. A directional coupler can be fabricated simply by adding a second conductor parallel to and along side of the center conductor 12. In all other respects the construction of the directional coupler would be identical to that of the impedance transformer. As is well known, the mutual coupling between the two center conductors is a function of the spacing between the two conductors and the dielectric constant of the

layers

14 and 15. The spacing between the conductors 12 therefore, in part, determines the total width of the directional coupler. This is so because a minimum width is then required. The length L is again calculated in accordance with the theory presented hereinabove.

This invention relates to non-inductively wound stripline circuits and can be applied to any such stripline circuits of which the hereinabove described are two examples.

The invention claimed is:

1. A non-inductively wound, spatially compact, stripline impedance transformer comprising: three electrically conductive members providing a signal path and an electrically continuous shield for said signal path;

said signal path having a longitudinal dimension which is approximately 1 being the wavelength at the desired operating frequency and e being the dielectric constant of the propagating medium; said shield being provided by two of said three conductive members, one of said two members having a longitudinal dimension substantially shorter than the other, the width dimensions of said two members being essentially equal to each other and substantially grlter than the width dimension of said signal path; an a plurality of dielectric members, said dielectric members being positioned so that said signal path and said shield are insulated from each other; said conductive members and said dielectric members being flexible and planar in form; said conductive members and said dielectric members being wound in a bilar relationship from approximately the center of said signal path to form a unitary device having physical dimensions which are substantially less than the largest physical dimension of said device prior to said winding.

2. The impedance transformer of claim 1 wherein the width of said signal path is determined in accordance with the equation:

l l W" (zo) (e) 2 Z=impedance of the transformer W: width of the signal path ,U.:perrneability of the dielectric members e=dielectric constant of the dielectric members h=thickness of the dielectric members.

where:

3. The impedance transformer of claim 2 wherein the impedance of said transformer is determined in accordance with the equation:

Z0=impedance of the transformer Z1=impedance of the input circuit Z2=impedance of the load circuit;

UNITED STATES PATENTS References Cited Brooks 338-61X Eversheim 338-61X Tarpiey et al. 338-61 Snow 338-61X Dickson, Jr., et al. 29-618X Pusch 333-84M Kalstein 317-260 PAUL L. GENSLER, Primary Examiner U.S. Cl. X.R.