US 2428831 A
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Oct. 14, 1947. G, H, BROWN U M 2,428,831
RADIO POWER DIVISION NETWORK Filed Aug. 22, 1944 INVENTORS ATTORNEY Patented Oct. 14, 1947 eorg Princeton,
H. Brown and Donald N. J assignorstofiadio Corporat on Peterson,
of America, a corporation of Delaware Application August 2-2, 1944, Serial No. 550,556
This invention relates to radio frequency power dividing networks, such as are used to allocate the output of a transmitter between the various elements of a directional antenna array.
The principal object of the present invention is toprovide an improved type of power division network, simple in design and construction and capable of providing fiicient operation throughout a broad band of frequencies.
The invention will be described with reference to the accompanying drawing, which is a schematic perspective diagram of a structure embodying the invention.
A relatively common type of directive antenna array comprises four radiators, or groups of radiators, with their centers in line and spaced at equal intervals. Of the total power applied to the array, 10 percent is delivered to each of the outer radiators and 40 percent is delivered to each of the inner radiators. One array of this type is described in copending U. S. application Ser. No. 445,175, filed May 30, 1942, by G. H. Brown and entitled Antenna systems, now Patent No. 2,397,645, April 2, 1946.
It has been'the practice to allocate the power between the inner and outer groups of such antennas by connecting the outer groups to the source through a network of resonant length transmission lines, so. arranged as to cause the outer radiator groups to present to the source an impedance which is four times that presented by the inner radiator groups. The impedance mismatches introduced by this network are counteracted by means of matching stubs connected to the feed lines at suitable points and adjusted to eliminate standing waves thereon.
Systems of the above-described type operate satisfactorily, but only at the single frequency for which they are designed. At other frequencies the line sections of the network are no longer of resonant lengths, and the matching stubs are of incorrect lengths and improperly placed to function as intended, causing incorrect power division and generally inefficient operation of the system. In copending application Ser. No. 549,670 filed on Aug. 16, 1944, by G. H. Brown et a1. and entitled Radio frequency power division network, it is proposed to divide the power between four loads in the required 1:4:411 ratios by connecting two of the loads in parallel to the input circuit and connecting the other two loads effectively in series with each other across the input circuit. One means for providing said series connection is described in said copending application. Resonant length line sections are 6 Claims. (Cl. 178-4 4) also used in said system but for compensating variations with frequency of the reaotances of said lines. However, variations in theresistiv components of the impedances of the various elements are not compensated, and
means are provided these components decrease progressively with variation in frequency from the center of the. band through which the system is to operate. Although this variation in resistance does notdisturb, the ower division ratio of the system, the
' efiiciency is somewhat lower at the extremes of the frequency band than at the center.
, The present invention relates to improvements over the systemldescribed in said copending application, whereby a simpler construction may be used, at the same time providing compensation for variation of resistance as well as reactance.
Referring to the drawing, a source I is to be connected to four loads 3, 5, 1 and 9 in such manner that the loads 3 and 5 each receive 40 percent, and the loads 1 and 9 each receive 10 ma be aq at s o percent ofth'e output of the source I. The loads 3, 5,7 and 9 are represented in the drawing as esistors. It is to be understood, however, that they groups of radiators or in fact, any load devices. It is assumed that all of the loads are of equal impedance Z. The loads 3 and 5 ar c nnect d th ou axial line II and 3 respectively in parallel with each other to a coaxial input line l5, extending to the source I. The loads S! and 3 are connected to coaxial lines I 1 and JQrespectiVely. ,The outer conductor of theline i9 is surrounded at its input end by a tubular conductive sleeve 2|, approximately onequarter wavelength long at the center of the band of frequencies through which the system is' to operate. -The end of the sleeve 2| is closed by a conductive disc 23, connected to the outer conductor of the line 19 at a point one-quarter wavelength from the input end thereof. The other end ofthesleeye, 2| is connected to the outer conductors of the lines ll,v I3, 15 and I1. The inner conductors of the lines 11 and I9 are connected togetherat their input ends.
. The lines H, l3, Hand [9 are constructed so that their characteristic impedances are approxi mately'equal to the impedances Z of the loads 3, 5, 7,; 9. Thesleeve 2| cooperates with the outer conductors'of thefinal quarter wave section of the line l9 to act as a quarter wave line section short-circuited at its lower end by the disc 23. The ,diameter of thesleeve 21 is made as large as is conveniently practical, in order that the. characteristic impedance of the short-circuited quarter wave line'may be as high as possible.
Assuming that this impedance is four times the total resultant impedance of the loads 3, 5, 1 and 9, the final half wave section 25 of the line [5 is designed to have a characteristic impedance of approximately 44 percent of the'impedance Z of one of the loads. A quarter wave line section 21 is connected across the line l5 at the point 29 one-half wavelength from theend thereof. The other end of the line section 21 is short-circuited. The line section 27 is designed to have a characteristic impedance equal to that of the quarter wave line formed by the sleeve 2| conductor of the line l9.
Current flowing from the source I throughthe line i5 is divided three ways: One portion I1 flows through the line ,I I to the load 3, an equal portion I2 flows through the line I3 to the load 5, and a third portion I3 flows down the outer conductor 'of the line I 9, radially across the disc 23 and upward on the inner surface of the sleeve 2| t the outer conductors of the lines I, I3, l and H allof which are at ground potential. The flow of current downward through the final quarter wave portion of the outer conductor of the line I9 induces an equal and opposite current to flow in the inner conductor of the line l9. This current flows through the loads land 9 in series. Thus the loads 1 and 9 are effectively coupled in series with each other across the output end of the line l5, so that the current I3 is one-half each of the currents Irand I2.
The impedance of the quarter wave line comprising the outer conductor of the line I 9 and the sleeve 21 is also presented across the end of the line l5. It should be noted that this impedance.
will have no eifect on the power'division ratios, regardless of its value, since it shunts both pairs of loads. At resonant frequency, where the length of the line [9 enclosed by the sleeve 2| is exactly one-quarter wave, this impedance is substantially infinite with respect to the impedances of the loads 3, 5, 'l and 9. At other frequencies, however, thesleeve 2i provides a shunt reactance. This reactance is compensated by means of the onehalf wave line section 25 and the quarter wave stub 27. It is found that if the'characteristic impedance of the stub 21 is equal to that of the line formed by" the sleeve 2| 'and'the enclosed portion of the line [9 and is four times the'total impedance presented to the output end of the section 25-by the loads 3, 5, 1 and 9, the impedance looking into the section 25 from the source will be constant throughout a wide range of frequencies, providing that the characteristic impedance of the line 25 is 1.1 times the resonant impedance of the loads 3, 5, 1 and 9. It is to be understood that the above ratios are given merely by way of example, and that other characteristic im--,
pedances may be employed with the half wave line section 25 to provide equivalent reactance compensation. For example, if the characteristic impedances of the short-circuited quarter wave lines were equal to the total load impedancaa half wave section 25 having a characteristic impedance 1.5 times that value would provide the optimum broad-band compensation.
The invention has been described as an improved power division network, in which two loads are connected in parallel to each other across an input line and two further loads are connected effectively in series with each other across said line by means of a coaxial line balance convertor. The resonant characteristics of the line balance convertor are compensated by means of a terminating half wave section: on said input line and the outer shunted at one end with a short-circuited'quarter wave stub.
The invention covered herein may be manufactured and used by orfor the Government of the United States for any governmental purpose without payment to me or assigns of any royalty thereon. n
We claim as our invention: I
1. A radio frequency power division network including a coaxial input line and two pairs of coaxial output lines, and a line balance convertor connected across said input line, the first of said pairs of lines being connected in parallel with each other tosaid input line, and one of said second pair of lines being connected through said line balance convertor to the other line of said second pair.
2. A radio frequency power division network including a coaxial input line, a pair of coaxial output lines with their input ends connected in parallel to the output end of said input line, a second pair of coaxial output lines with theinput ends of their inner conductors connected together, the input end of the outer conductor of one of said second pair. of lines being connected to the inner conductor of .said inputline, and a quarter wavelength sleeve surrounding said lastmentioned line,connected at one of itsends to the outer conductor of said last mentioned line, and at its other end to the outer conductors of all of the others of 'saidlines.
3. A radio'frequency power division network including a coaxial line substantially one-half wavelength long at' the center of the band of frequencies over which .the system is to operate, a pair of unbalanced-to-ground load circuits connected in parallel with each other across. one end of said line,. av line balance convertor comprising a quarter wavelength line section shortci'rcuited at one of its ends and connected at its other end across said end of said half wavelength line, a second pair of load unbalanced-toground circuits connected in series with each other through said line balance convertor across said end of said line, and'a second quarter Wavelengthline section shortrcircuited at one of its ends and connected at its other-end across the other end of said half wave line.
4. The invention as set forth in claim 3, wherein said quarter wave line sections each have a characteristic impedance of 4Z, where Z is the resultant impedance of all of said load circuits, and said half wave line section has a characteristic impedance of 1.1Z.
5. Aradio frequencypower division network, including two pairs of coaxial'tra'nsmission lines, and an input line, each line including an inner conductor and a outer conductor, with the inner conductor of said input line connected at a common point to the inner conductors of the first of said pairs of lines, and to the outer conductor of one of said'second pair of lines; a sleeve surrounding'the end portion of said last mentioned line, connected at one of its ends to the outer conductor of said last mentioned line and con-,
impedance Z, four unbalanced loads, each of im-' pedance 2.5Z, a coaxial line section of characteristic impedance 1 .12 connected between the end of said input line and two of said loads in 5 parallel, said line section being one-half wavelength long at the center of the band of frequencies over which the system is to operate, a quarter wavelength coaxial line section shortcircuited at one of its ends and connected at its other end to the junction of said input line with said half wave line, said short-circuited quarter wave section having a characteristic impedance 4Z, a second quarter wavelength coaxial line section of characteristic impedance lZ short-circuited at one of its ends and connected at its other end to the other end of said half wave line section, the other two of said loads being connected in series with each other across the open end of said second quarter wave line section.
GEORGE H. BROWN. DONALD W. PETERSON.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,266,502 Lindenblad Dec. 16, 1941