US3742392A - Self loaded uneven power divider - Google Patents

Abstract

An uneven power divider in strip transmission line is provided by branching the narrow conductor into, for example, two appropriately uneven width mutually coupled narrower conductor sections with a distributed resistance therebetween.

Description

United States Patent 1 Schwarzmann SELF LOADED UNEVEN POWER DIVIDER [75] Inventor: Alfred Schwarzmann, Mt. Laurel Township, NJ.

[73] Assignee: RCA Corporation, New York, NY.

[22] Filed: Dec. 13, 1971 [21] Appl. No.: 207,405

52 us. Cl. .Q 333/9, 333/84 M 511 int. Cl. H0lp 5/12 [58] Field at Search...., ..333/6, 8, 9, 84 M [56] References Cited UNITED STATES PATENTS 3,089,103 5/l963 Oline'r.; ..333/9 1 June 26, 1973 Vient 333/9 Le Vine 333/9 Primary Examiner-Paul L. Gensler Attorney-Edward J. Norton [57] ABSTRACT An uneven power divider in strip transmission line is provided by branching the narrow conductor into, for example, two appropriately 'uneven width mutually coupled narrower conductor sections with a distributed resistance therebetween.

3 Claims, 2 Drawing Figures 1 SELF LOADED UNEVEN POWER DIVIDER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a strip transmission line power divider and more particularly to a self loaded, uneven power divider.

2. Description of Prior Art Equal power division using strip transmission lines is well known. In such arrangements when using microstrip transmission line, for example, the narrow striplike conductor is branched at a junction into a selected plurality of equal width narrower conductors which provide equal power division. Some system arrangements, such as monitoring systems for example, require uneven power division with isolation.

SUMMARY OF INVENTION Briefly, a self loaded uneven power divider is provided by a strip transmission line wherein the narrow conductor is branched at a junction into at least two closely spaced mutually coupled narrower conductor sections. The width of each of the branched narrow conductor sections at the junction is proportional to the power division. A distributed resistance is located in the mutual space between the branched narrow conductor sections.

DETAILED DESCRIPTION A more detailed description follows in conjunction with the following drawings wherein:

FIG. 1 is a perspective view of a self-loaded uneven power divider.

' FIG. 2 is a perspective view of an impedance tapered, self-loaded uneven power divider. Referring to FIG. 1, there is illustrated a mic'rostrip transmission line power divider 10. The power divider includes a dielectric substrate 11 having on one surface a broad conductor sheet 13. On the opposite surface there is placed a narrow strip-like conductor 17. The incident signal power is applied to one end 16 of narrow strip-like conductor 17, between the conductors 17 and 13 of the line. The,

width of the narrow conductor 17 is selected so as to provide an impedance matching input such-as, for example, 50 ohms. At point A, the narrow conductor 17 is branched into sections AB and AC. The power division of the applied input signals along the two branched sections AB and AC is proportional to the widths of these narrow conductors at the branching point A. The width (w) of conductor AB near point A is much smaller than the width nw of conductor AC. Therefore most of the power is coupled along conductor section AC.

The branched section AC is divided into two portions AE and EC. Portion AE of branched section AC is. closely spaced so as to be mutually coupled to portion AF of section AB. A distributed resistance AD is located between portions AF and AE to provide self loading of the reflected power in the odd mode from ends 23 and 25 of the branched sections. In the branch section AC, there is located a narrow slit 21 which extends trom about branching point A to the point C, the slit 21 being about a half transmission line wavelength (A /2) long. The narrow slit 21 provides the same potential on the AEC conductor section as on the AF section and the resistiveload AD does not provide any substantial attenuation to the incident or forward direc tion signals.

It is required that each of the output ends 23 and 25 be matched to their loads. If the output loads at ends 23 and 25 are 50 ohms, some impedance transformation is required for line sections AB and AC. Line section AB includes two major portions AF and FE. Section PE is a wider conductive portion mitered to a higher impedance section AF. The coupled sections AE and AF transform the impedance to the output 25 at B to be 50 ohms. By increasing the width of section AC at the edge 18 by l or 2 mils, an impedance of 50 ohms is presented at point C and at end 23. The raised edge 18 extends for one half transmission line wave length (A /2) as shown in FIG. 1.

When viewing the circuit of FIG. 1 at point F, the line section AF is a single edge coupled quarter wave transformer. The section AB is a double edge coupled transmission line continuing in a single edge coupled line section EC. The line section EC is wider than section AE by the amount of the equivalent coupling capacitance of section AB. The coupled length AE or AF is about a quarter transmission line wavelength. The solution to the line widths for the coupled sections AF and AB is the even and odd mode solution of a coupled transformer. The width of the line AF is the even and odd mode solution for the single edge coupled pair of microstrip lines. For the embodiment shown in FIG. 1, by way of example, the thickness of the substrate 11 canbe 25 mils. The width w of the section AF equals 6 to 7 mils. The width of section AB is the even and odd mode double edge coupled solution which, for the above example with a 25 mil substrate, is about 6 to 7 mils. The spacing (S) between section AF and section AB is about 4 mils and is also from the above solution. The width of the slit 21 is approximately 2 to 3 mils.

In the above described arrangement for operating between 4 to 5 GHz, the slit length 21 is about 0.5 inch and the length of section AC is 0.5 inch. The width nw is about 23 mils with the 2 to 3 mil slit 21 therein. Sections AF and AE are 0.25 inch long. Resistive material AD is 0.2 inch long. The width of narrow conductor 17 7 at ends 19, 23 and 25 is 25 mils. The section AC has a raised edge 18 that is about 2 mils wide. The raised edge 18 extends for about a one half transmission line wavelength or in this case about 0.5 inch. The dielectric material of substrate 11 is 25 mil thick alumina (dielectric constant of about 9.6). The even and odd mode solutions can be solved generally using any of the well known solutions such as taught in the following references T. G. Bryant and J. A. Weiss, Parameters of Microstrip Transmission Lines and of Coupled Pairs of Microstrip Lines, IEEE Transactions on Microwave Theory and Techniques, Vol. MTT-16, page 1021, December .1968; L. S. Napoli and .I. J. Hughes, Characteristics of Coupled Microstrip Lines," RCA Review, September 1970, Vol. 3i, No. 3, pages 479-498.

The single edge coupled solution is approximately that of the double edge coupled solution. Slight modifications are however usually required to optimize impedance transformation. This is done by an iterative process of making estimated changes and testing and based on that test making other estimated changes.

Referring to FIG. 2, there is illustrated an uneven power divider 31 in which'the stepped impedance transformation shown in FIG. 1 is performed by a tapered impedance profile. Again a narrow strip-like conductor 33 is placed on a dielectric substrate 35 having on the opposite surface thereof a sheet of conductive material. The incident power is applied at terminal end 37 and is coupled to point A of FIG. 2. A tapered section AB transforms the impedance at point A to a useable impedance at point B such as 50 ohms. In the mutual coupling region AD between sections AB and AC there is located a distributive resistance which absorbs reflected power from either port B or port C. Section ABC is tapered and extends for a length of about one half transmission line wavelength and provides with the narrow slit AC and branched line conductor section AC impedance transformation to 50 ohms at point C. By the use of slit AC the potential along AEC is approximately equal to AF and consequently there is low forward attenuation and good reflected power attentuation.

What is claimed is:

l. A microstrip power divider responsive to applied input signals at one end for providing uneven power division of said signals at the opposite end with low signal reflection back to said one end comprising:

a narrow strip-like conductor spaced by a dielectric substrate from only one broad conductor, said narrow conductor being branched at a junction point into at least two mutually coupled narrow conductor sections, the width of each of said branched sections being proportional to the desired power division, a distributed resistance located in the mutual space between said branched narrow conductor sections for loading said reflected signals, said divider exhibiting a substantial attenuation of signals in the forward direction when said width of the branched sections are unequal, and means including a narrow slit in the wider of said branched nar row conductor sections for providing the same RF potential on either side of the space between said two mutually coupled narrow conductor sections to thereby prevent any substantial attentuation of said signals in the forward direction.

2. The combination claimed in claim 1 wherein said slit extends from said junction toward the output end of said broader narrow conductor.

3. The combination claimed in claim 2 wherein said slit is one half a transmission line wavelength long at an operating frequency of said input signals.

Claims (3)

1. A microstrip power divider responsive to applied input signals at one end for providing uneven power division of said signals at the opposite end with low signal reflection back to said one end comprising: a narrow strip-like conductor spaced by a dielectric substrate from only one broad conductor, said narrow conductor being branched at a junction point into at least two mutually coupled narrow conductor sections, the width of each of said branched sections being proportional to the desired power division, a distributed resistance located in the mutual space between said branched narrow conductor sections for loading said reflected signals, said divider exhibiting a substantial attenuation of signals in the forward direction when said width of the branched sections are unequal, and means including a narrow slit in the wider of said branched narrow conductor sections for providing the same RF potential on either side of the space between said two mutually coupled narrow conductor sections to thereby prevent any substantial attentuation of said signals in the forward direction.

2. The combination claimed in claim 1 wherein said slit extends from said junction toward the output end of said broader narrow conductor.

3. The combination claimed in claim 2 wherein said slit is one half a transmission line wavelength long at an operating frequency of said input signals.

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