CA1043877A - N-way power divider with remote isolating resistors - Google Patents

Abstract

N-WAY POWER DIVIDER WITH
REMOTE ISOLATING RESISTORS

ABSTRACT OF THE INVENTION

Disclosed is an isolated N-way power divider for operation at high frequencies. The power divider has iso-lating resistive terminations in the form of transmission line terminations connected to a set of transmission lines.
The termination and transmission line arrangement eliminates the need for a set of "star connected" resistors charac-teristic of prior art isolated power dividers.

Description

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~f~3~3flL~f7~7 ; Docket R3927 BACK~RQU~D OF THE. INVENTION

This inventioIl relates to isolated power dividers and more particularl~ to such power dividers designed for ~ -use with electrical s~gnals at high frequencies3 for exam-ple above 100 MHz. -: -In various high ~requency systems it is often desirable to d~ride a high frequency sign~l on one trans .` mission line in~o a number of substantially identi~al sig-.~ nalsi on a like number of transmission lines. This type o~
s~gr~l division may take place as part of an antenna system . .
where ~t is desirable to supply a portion of the original signal to a munber of individual antenna units, in a power a~ ifar system where it is desired to driLve a r~umber of ~ .
solid sltate famplifiers wlth the same signal, or in a cable -tria~smission system wherein the original sifffgnal is to be fsupplied ~o a selected number o~ cables.
,: ~ Among the rarif~us devices ~or accomplishing pf~er 1~; di~rision there are~ "hybrid junctions", directional couplers i~ and pawer dividers,, both isolated and refsctive. Directîonal i~20 ~ couplers are commonly u~ed at microwave ~requencies ~or supplying ~aw?er from an input port to a palr o~ pUt ports, in a selec~ed power ra~io, called the coupli~g ¦~ ~ ratio. A coupler has ~n additional port, which ls usually 1 te~minated~ Whlch is called the "isolated" por~ sin~e sig-?,'~25 ~ n~ls supplied to th0 input port are not coupled to the iso- :
1~:: lated port. ~11 of the ports of a directional coupler are impedance match2d to their correspond~n~ ~ransmis~ion : line~. me output ports of ~ directlo~al coupler are also mutually isola~ed, that iS7 a ?31gIIal ~uppl~ed to one ~utput .:~
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port will not appear at the other output port, but will appear at both the input port and the isolated port. The directional coupler has two inherent disadvantages ~or use i~ many power divider applications. First, there is pro- -vided only a two-way power divlsion~ hence many couplers may be required to achie~e a many-way power split. Second, the signals in the output ports of the directlonal coupler -~
have a quadrature phase relation, and phase correction is required where it is desired to ha~e equal-phase output signals.
Hybrid ~unctions are similar to directional coup ~;
lers in that the two output ports are impedance matched and ~;
mutually isolated. Hybrid junctions are dif~erent by rea-~son o~ the ~act that ~he output signals are identical in both amplitude and phase. Hybrid ~unctions are there~ore limlted to binary power divlsion and like the directional ~ ;
coupler h~ve only two output ports.
.
Power dividers have a single input port and two or more output ports. There are two general types of power ~ dividers, commonly known a5 3'reactive power divldcrs" and "lsolated power di~iders." In it~ usual ~orm a reactive p~war diuider has a ~ingle input port and a set of N output ports. Each o~ the output ports i5 co~nected to ~he input ports b~ a quarter-wavelength transmission llne whlch is cho~en ~o hav~ ~n lmpedance to match the input port to the collect~e output impedance o~ the N output ports~ m e reactive power divider does not have matchad or isolated :~ .
output por~s. When a signal i~ supplied to only one o~ the output ports, a portion o~ the ~i~nal wlll be re~lected and ~30 a p~rtlon o~ the signal will appear at each of the other : , : , . ': . .
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' output port~ as well as at the input port. me device will be matched ~or signals applied to the output ports only on the condition that signale o~ equal amplltude and phase be supplied simultaneously to all o~ the output ports. -me isolated power di~ider overcomes the deflciencies - -of the reactive power divider by providing resistive terminations ~or unequal signals applied to the output ports. These terminations perform the same ~unction as the isolated port on a directional coupler or h~brid ~unct~on and enable the output ports ~o be impedance matched and iso- -lated. In prior art power div~ders the re~istive termina-tions usually take the ~orm o~ resietors "star connected"
to the output po~ts as is described below. These resistors are usually not cap~ble of dissipatlng high average power without overheating and becau e o~ the star connection ~-.,; ..
', arrangement these resistors ca~not be conveniently mounted on a conductive "heat sink" for use with si~nale of high ~ -1, . . .
average p~wer. Further the star connected resietors in a hlgh-~requency power divider mu~t often be located in cloee prox~m~ty to each other~, there~y creating additional heating problem~ in a hi~h power system.

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It is there~ore an ob~ect o~ the presen~ in~ention to . .
provlde an isolated N~way power d~vider.
It is a further ob~ect o~ the present invent:Lon to - --~; provide such a pow~r divider ~Iherein the isolating resistive ~ ,:
terminatlons o~ the power dlvider m~y be remotely located from each other. :~ ~

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It is a still further object o~ the present lnvention .:
to provide such a power di~ider wherein the resistive ter-minations may be high power transmission-line terminations. - ~:
In accordance with the present inven~ion there i~ ~:
provided an isolated N-way po~er di~ider for operation over a selec~ed frequenc~ band. The p~wer divider includes an ~ ~ .
input port and a set of N-output ports, each comprising flrst and second output terminals. There is further ~nclu~-ed a ~irst set o~ N transmission lines each for coupling wa~e energy signals from the input port ~o a corresponding one o~ the output ports, each of the transmission lines ha~ng an electrical length o~ an odd integral multiple o~
one-quarter wavelength at a selected frequen y within the ~:
frequenc~ band. There is also i~cluded a second set o~ N
transmission lines~ each comprislng ~ ~irst conductor con-. .
: nected to one o~ the flrst output terminals and a second conductor connected to a re~erence terminal~ the re~erence texml~al being common ~o all o~ the second conductor~ ln the second ~et. There is *urther provided means for ter~
minatlng each o~ the transmission llne~ o~ the second set ., .
o~ transmi~ion lines to presen~ a sub~tantially resisti~e -impedance between ~ai~ ~ir~t output terminal ~nd æaid re~er~
ence termlnal and mean~ ~or presentlng an open circuit im-pedance between each o~ the second output terml~als and the re~erence terminal.
For a better u~derstanding o~ the present ~nvention~
together wlth o~har and ~urther ob~ectB theraof, re~erence : is had to the ~ollowing d~criptlon, taken in connection .-:
~ wikh the accomp~nying drawlngs, and its ~cope will be ;~ 30 pointed out in the appended clalms. ~ .:
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. - 5 -1 BRIEF DESCRIPTION OF TIIE F;IGURES
Figure 1 is a prior art isolated power divider.
Figure 2 is a prior art isolated power divider wherein the "star connected" resistors are remotely located from the output ports.
Figure 3 is a plan view of an isolated power divider constructed in accordance with the present invention.
Figure 3A is a cross-sectional view taken along section A-A of the isolated power divider of Figure 3.
Figure 4A is a plan view of another isolated power divider constructed in accordance with the present invention.
Figure 4B is a side view of the isolated power divider of Figure 4A.
DESCRIPTION OF FIGURES 1 AND 2 (PRIOR ART) -~, Figure 1 shows an isolated power divider constructed in accordance with prior art. By way of example, the Figure 1 power divider utilizes microstrip transmission line, but it ' ":".: ' is well recognized in the art that this type of power divider -may be constructed using other types of transmission lines including tri-plate strip line or coa~ial cable. The Figure 1 power di~ider is constructed by depositing a print circuit open '`~
one surface of a dielectric substrate 10. The other surface of ;~
the dielectric substrate is covered with conductive material to form a ground plane. The Figure 1 power divider includes an input port 11 comprising first and second input terminals.
The first input terminal is a circular spot of metal de-posited on the substrate which may be seen in Figure 1 and the second input terminal is the conductive ground plane on the other side of substrate 10 which is not shown ''' .- "

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in Figure 1. Co~nection to this type of terminal is uæually ~acilitated by use of a coaxial connector mounted on the side of substrate 10 having the conductiYe ground plan~.
The outer conductor of the coaxial connector is connected to the ground plane while the inner conductor is connected to the input terminal 11 shown ln Figure 1.
The power divider of Figure 1 also has output ports 13a, 13b and 13c which are of the same type as input ~! port 11 and have ~iræt and second output terminals similar '' 10 to the termlnals of input port 11. Ou~put ports 13a~ 13b a~d 13c are connected to input port 11 by transml~slon lineæ ~ ~-l?a, 12b and 12c. Transmiss~on llnes l? comprise a ~irst ~' cond~ctor, which is a ætrlp o~ metal deposited on substrate10~ as shown ln Flgure 1, and a æecond conductor which com~
prlses the conductive ground plane on the other slde of ~ ~
~ sub~trate 10. Transmission Iines l?a, 12b and 12c are ~:
3 æelected to be a quarter-wa~elength in length at a æelected~requency within the operating band o~ the Figure 1 power .~.
d~v~der ~ me lmpedance of these transmission line~ 12 i5 selected so that the transmlsslon line~ 1? ~orm a quar~er~
~avele~gth trans~ormer bet~æen the collective impedance of output ports 13a, 13b and 13e and the ~ped~nce o~ i~put j~ port 11.
Those skilled ln the art wlll recognize that ..
}~ 25 transmis~ion llnes 12 will alæo act as a trans~ormer 1~
seleeted ~o have a length which is an odd integral multiple ~:- of a quarter-wavelength~ but trans~ormers of more than one quarter~warelength tend to operate over relat~vely narr~wer ~requenc~ bands~
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1 In addition to operating as an impedance trans- -former, the odd-multiple of ~uarter-wavelength length of transmission lines 12 results in an odd-multiple of a half-wavelength electrical length for signals coupled between output ports 13 by input port 11. Thus, signals coupled by this path are out-of-phase with signals directly coupled between output ports 13 by star connected resistors 14, described below. The result is isolation between the ;
output ports since these signals tend to cancel. -In order to provide isolation between output ports 13a, 13b and 13c there is provided in the Figure 1 ; ;~
power divider "star connected" resistors 14a, 14b and 14c Each of these resistors 14 is connected to a corresponding one of the output ports and they are all connected to refer-ence terminal 15. For proper operation of the power divider ~ , ; ,:;-, . ..
reference terminal 15 must be an open circuit with respect to the ground plane on the other side of substrate -10. Since the other side of substrate 10 i5 also one of the output terminals of output ports 13a, 13b and 13c there ;
is provided an open circuit impedance between reference terminal 15 and the second terminals of output ports 13a, - ;
13b and 13c. This open circuit condition is necessary for the proper operation of the "star connected" resistors 14 `
and to provide isolation between the output ports 13 as 25 described above. -Figure 2 i5 another prior art isolated power divid-er. In addition to the elements of Figure 1 power divider : ,, . .:
the Figure 2 power divider has transmission lines 16a, 16b - ;
and 16c connected between "star connected" resistors 14 and -30 output ports 13. These transmission lines are chosen to ~
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be approxlmately one-half wavelength in length so that the lmpedance o~ the "star co~nected" resistors 14 at terminals 30a, 30b and 30c is presented to corresponding output ports 13. The electrical e~fect is therefore the same as in the Figure 1 power divider, but the resistors 14 are located remote from output ports 13.
The Figure 1 and 2 power dividers have been shown in embodiments of 3-way power dividers for purposes o~
illustration and the same type o~ design technique may be ~;
used to construct dividers having any number of output ports.
One problem associated with constructing the Figure 1 and 2 pcwer di~iders at high ~requen~ies is asso-ciated with the capabilit~ of resistors 14 to handle mod- -er&te or high power signals. SincP the resistors 14 are "star connected", the~ cannot be con~eniently cooled when dissipatlng hlgh p~wer signals.

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Figure 3 shows an isolated N~wa~ powe~ di~ider con-structed in accordance with the pre~ent invention wherein the i~olatlng resistive termlnations take the ~orm o~ trans-misslon line kermi~ations. me Figure 3 power dlvider has an l~put port 11, tran~mission lines 12 and output ports 13 which are sub~tantially identical to the corresponding ele-ments in the prior art power divider o~ Flgure 1. In the F~gure 3 power d~vider the "star connected" resistors 14 ~;-have been repl~ced by a set of three ~ransmisslon lines 18a, 18b and 18c. me transmission lines 18 are in the ~orm o~

_ 9 _ coaxial cables ha~ing a first conductor 19~ which is the j inner conductor and a second conductor which is the outer conductor. me inner conductor 19 of each coaxial cable 18 :~
is connected to a corresponding one of the ~irst output ~ .
terminals o~ the output ports 13 of the power divider. The - ;~
outer conductors o~ the transmission lineæ 18 are each electrically connected to re~erence terminal 157, which in the Figure 3 embodiment is the end of the inner conductor . ~:~
20 o~ a transmission line 220 Each of the coaxial cables 18 is ~erminated in its characterlstic impedance. A~ a cons~quence~ ea h of these cables i~ the electrical equiva-lent o~ a xeslstor connected between a corresponding first output terminal 13 and re~erence terminal 15~
Those skilled in the art will recognize that.~:
terminating tr~nsmission lines 18 ln their characterlstic , .
imped~ncel. re~ult ln the desired ef~ect o~ presenting a ~; .
resist~ve impedance between the flrst output terminals o~
, . :.
output ports 13 and re~erence terminal 151. Thi6 result ~
may, o~ course3 be achie~ed by other than a ch~racteristic ..
impedanca load, utilizing appropriate ~rans~ormer or matching tech~ique~ on transmission lines 18.
Tran~miææion line 22 is a coaxlal line, selected to:have a length "L", which i~ a quarter~ravelength at a :-:
, selected frequency withln the ~requenc~ band and is ter~ ;
: 25 minated by a short clrcuit 2~. The result o~ thi~ ~hort ~-circulted quarter~wavelength tran~mi~sion line 22 i~ to -present an open circuited im~edance between reference ter~
mlnal 151 and the ~econd termlnal~ o~ output ports 13 o~ ~.
. ..
~ the power divider. In the Figure 3 embodiment the ~econd ,' ....:

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~ r terminals o~ output ports 13 comprise the conductive ground plane 17 on substrate 10, which is electricall~ connected to the outer conductor 26 o~ coaxial output connector 27.
me open c~rcuit impedance condition results in re~erence terminal 15' being the electrlcal equ~valent o~ reference terminal 15 in the prior art power divider of Figure 1. - .
me combination o~ short circuited transmission line 22 and ~- -termlnated tr~nsmlsslo~ lines 18 is there~ore an electrlcal equivalent o~ star-connected resistors 14 of the prior art power divider of Figure 1.
The transmission lines 18 o~ the Figure 3 embodi-ment are terminated in transmission llne termlnations 28a, 28b and 28c, which may be con~eniently locate~ remote ~rom each other and from the output ports 13 o~ the p~wer divider.
It ma~ also be seen that since these terminabions are of the con~entional transmission line type, they may be selected to accommodate a high average power signal and may be cooled b~ an~ conventional method uaed in such te~mi~ations, ~or example, radiation cooling, convection cooling, liquld ~ cooling or conduction cooling to a heat sink. B~ having this ~orm o~ isolating resistlve termination~ the embodimen~ ;
o~ Figure 3 has remo~ed the requirement ~or ~'star-connected~
reslstors which was a limiting ~actor to the p~er capablllty o~ the prior art isolated power dividers. .~ .
Shown in Flgure 4 is ~nother embodiment o~ the ~ :
present invention, which corresponds to the prior ~rt power divider o~ Figure 2. Included in the Figure 4 power divlder are tran~mi~sion lines 16a, 16b and 16c between ou~put port~
13 and the second ~et o~ tra~smi~slon lines 18~ mis set ., .

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o~ transmission lines 16 i~ a hal~-wavelength in length at a selected *requency within the operating fre~uency band ~ ~ .
and, as in the ~igure 2 prior art power divider, cause the . .
impedance presented at terminals 30a9 30b and 30c to be presented to the corresponding output ports 13. ~he Figure ~' 4 embod~ment is also d~stinguished ~rom the Figure 3 embodi- -ment in that the second set of transmission lines 18 is ;~
in the fo~m of microstr~p, rather than coaxial lineO In this ~orm~ one conductor Or each o~ the second set of trans~ ~ :
mission lines 18 is connected to one terminal o~ output ports ;~
13 b~ hal~wavelength transmission line 16. me other con~
ductor of transmission lines 18 comprises a conductive ,! .: , . .. .
, ground plane 32, which is connected to re~erence terminal i 15", which in the Figure 4 embodiment comprises o~e edge . :
o~ ground plane 32. In the Figure 4 embod~me~t an open ~ circuit impedance is prese~ted be~ween reference terminal ;! 15" and the ground plane o~ the terminals 30 by a shor~
circui~ed parallel pla~e ~ransmisslon line ~ormed be~ween conductive ~round plane 32 and conducti~e ground plane 17, I 20 having a length t'L", which ls a quarter~wavelength at a '~! selected frequency within the frequene~r band. mis parallel plate ~ransmlssio~ llne is termin~ted b~ short clrcuit 34.
In the Figure 4 embodiment the impedance presen~ed ..
S ~o transmi~sion line~ 16 at termln~l 30 is also presented ~ ~;
,~ 25 to output ports 13. ~he result is the electrical equlvalent o~ the ~tar-connected resistors ~cross output ports 13 of ,~ the Figure 1 prlor art power divider. Ihe use o~ half~ ;
~avelength transmassion llnes 16~ as shown in Figure 4, to separate tran~m~s~ion lines 18 and reference terminal 15"

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from o~tput ports 13, is most useful in power dividers having - -many output ports, where ph~sical co-location is di~icult.
While the embodiments o~ ~he invention which have been described all consist o~ three~way power dividers, it will be eviden~ to those skilled in the art that such power dividers ma~ be constructed h~ing any number N of output terminals ~o ~orm an N-way divider3 ~here N is any interger greater than 1. It will also be evident that although the :
presen~ ln~e~tion is re~erred to as a "power divider," such devlces are inherentl~ reciprocal and may also be used as a power combiner and de~ices inte~ded ~or such application are withln the ~cope o~ this invention.
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Claims (12)

WHAT IS CLAIMED IS:

1. An isolated N-way power divider, for operation over a selected frequency band, comprising:
an input port;
a set of N output ports, each comprising first and second output terminals;
a first set of N transmission lines, each for coup-ling wave energy signals from said input port to a corres-ponding one of said output ports, each of said transmission lines having an electrical length of an odd integral multiple of one-quarter wavelength at a selected frequency within said frequency band;
a second set of N transmission lines each com-prising a first conductor connected to one of said first output terminals and a second conductor connected to a reference terminal, said reference terminal being common to all of said second conductors in said second set;
means for terminating each of the transmission lines of said second set of transmission lines to present a substantially resistive impedance between said first out-put terminal and said reference terminal;
and means for presenting an open-circuit imped-ance between each of said second output terminals and said reference terminal.

2. An isolated N-way power divider as specified in claim 1 wherein each of said transmission lines of said first set of N transmission lines has an electrical length of on-quarter wavelength at a selected frequency within said frequency band.

3. An isolated N-way power divider as specified in claim 1 wherein said means for terminating each of the transmission lines of said second set of transmission lines comprises means for terminating each of said transmission lines in its characteristic impedance.

4. An isolated N-way power divider as specified in claim 1 wherein said means for presenting an open cir-cuit impedance comprises a short-circuited transmission line having an electrical length of a quarter-wavelength at a selected frequency within said frequency band.

5. An isolated N-way power divider as specified in claim 1 wherein said second set of transmission lines comprises a set of N coaxial cables, and said first con-ductor comprises the inner conductor of each of said cables and said second conductor comprises the outer conductor of each of said cables.

6. An isolated N-way power divider as specified in claim 1 wherein said second set of transmission lines comprises a set of microstrip transmission lines, each com-prising a first conductor on a dielectric substrate and a second conductor comprising a ground plane on the opposite side of said substrate, said second conductor being common to all of the transmission lines in said second set.

7. An isolated N-way power divider, for operation over a selected frequency band, comprising:
an input port;
a set of N output ports, each comprising first and second output terminals;

a first set of N transmission lines, each for coupling wave energy signals from said input port to a corresponding one of said output ports, each of said transmission lines having an electrical length of an odd integral multiple of one-quarter wavelength at a selected frequency within said frequency band, a second set of N transmission lines, each compris-ing a first conductor and a second conductor connected to a reference terminal, said reference terminal being common to all of said second conductors in said second set, a third set of N transmission lines, each having a length which is an integral multiple of a half-wavelength at a selected frequency within said frequency bands and each comprising a first conductor connected between one of said first output terminals and the first conductor of a corre-sponding one of said second set of transmission lines, and a second conductor connected to a corresponding one of said second output terminals;
means for terminating each of the transmission lines of said second set of transmission lines to present a sub-stantially resistive impedance between said first conductor of said third set of transmission lines and said reference terminal;
and means for presenting an open-circuit impedance between each of said second conductors in said third set of transmission lines and said reference terminal.

8. An isolated N-way power divider as specified in claim 7 wherein each of said transmission lines of said first set of N transmission lines has an electrical length of one-quarter wavelength at a selected frequency within said frequency band.

9. An isolated N-way power divider as specified in claim 7 wherein said means for terminating each of the transmission lines of said second set of transmission lines comprises means for terminating each of said transmission lines in its characteristic impedance.

10. An isolated N-way power divider as specified in claim 7 wherein said means for presenting an open cir-cuit impedance comprises a short circuited transmission line having an electrical length of a quarter-wavelength at a selected frequency within said frequency band.

11. An isolated N-way power divider as specified in claim 7 wherein said second set of transmission lines comprises a set of microstrip transmission lines, each com-prising a first conductor on a dielectric substrate and a second conductor comprising a ground plane on the opposite side of said substrate, said second conductor being common to all of the transmission lines in said second set.

12. An isolated N-way power divider as specified in claim 7 wherein said third set of transmission lines comprises a set of microstrip transmission lines, each comprising a first conductor on a dielectric substrate and a second conductor comprising a ground plane on the oppo-side side of said substrate, said second conductor being common to all of the transmission lines in said third set.