US3747026A - Two input combiner having useful and dummy load outputs - Google Patents

Abstract

A four-port combining network which utilizes a single transformer element. The two input ports are supplied with radio frequency signals of the same frequency and phase. One output port is connected to a useful load such as an antenna. The other output port is connected to a dissipative ''''dummy'''' load. Under normal operating conditions the two input signals add to provide a single high power output and essentially no signal is fed to the dummy load. In the event of failure of one input signal the remaining operating input signal is divided between the two output ports. Respective isolation under all conditions is maintained between the two inputs ports.

Description

United States Patent [191 Covill [451 July 17, 1973 TWO INPUT COMBINER HAVING USEFUL AND DUMMY LOAD OUTPUTS [75] inventor: Dennis H. Covill, Nova Scotia,

' Canada [73] As'signee: Nautical Electronics Laboratories Limited, Nova Scotia, Canada [22] Filed: Nov. 2, 1971 I 211 Appl. 190.; 194,985

[ 52] U.S. Cl 333/6, 333/11, 336/181 [51] Int. Cl. H0311 7/48 [58] Field of Search 333/6, 8, 11; 336/171, 181

[56], r References Cited 3 UNITED STATES PATENTS 3,037,173 5/1962 Ruthroff 333/11 FOREIGN PATENTS OR APPLICATIONS 329,905 1/1952 .Germany. 333/11 Primary Etaminer-Paul L. Gensler Attorney-Christopher Robinson et a1;

[5 7] ABSTRACT A four-port combining network which utilizes a single transformerelement. The two input ports are supplied with radio frequency signals of the same frequencyand phase. One output port is connected to a useful load such as an antenna. The other output port is connected to a dissipative dummy" load. Under normal operating conditions the two input signals add to provide a single high power output and essentially no signal is fed to the dummy load. in the event of failure of one input signal the remaining operating input signal is divided betweenthe two output ports. Respective isolation under all conditions is maintained between the two in puts ports.

3 Claims, 2 Drawing Figures TWO INPUT COMBINER HAVING USEFUL AND DUMMY LOAD OUTPUTS FIELD OF THE INVENTION 7 This invention relates to an improved four-port combiner used to combine two synchronous, coherent AC signals to form a single AC signal.

Known combining networks can be broken down into two categories. The first category contains combiners usedto combine narrow band signals and comprises one quarter wave transmission line sections arranged generally in the form of a bridge circuit. The second category of combining network and the category in which the present invention is contained, includes the four-port transformer-wound, broad-band combiner. As inthe first category, the transformers are generally arranged ina bridge circuit. An example of the combiners of the second category is described in US. Pat. No. 3,503,016, which issued to A.F. PODELL on 24 Mar. 1970.

Known broad-band combining networks have the disadvantage that they are relatively complicated arrangements of a plurality of individual transformers. The individual windings of these transformers must be .capable of handling the power output of one of the inputs. In contrast, the combiner of the present invention utilizes a single transformer having three windings and therefore represents a considerable simplification of known prior art devices. The individual windings of the combiner in accordance with the present invention needv only be capable of handling a fraction of the power of either input and in fact during normal operating conditions, onlya fraction of the power output of an individual source.

SUMMARY OF THE INVENTION In accordance with the present invention there is provided a combiner network comprising an output port having a first terminal and a second terminal for supplying a load, a first input port having first and second terminals, a second input port having first and second terminals, thesecond terminals of the said input ports and the secondterminal of the output port being directly connected together; a single transformer having a first winding and a second winding, the first winding being connected between the first terminal of the first input port and the first terminal of the output port, the second windingbeing connected between the first terminal of the output port and the first terminal of the second input port, said windings being oppositely wound .with respect to current flow from the first and second input ports and having a respective turns'ratio in inverse proportion to the respective rated input powers of the first and second input ports whereby under rated operating conditions the net flux attributable to current flow through said windings is substantially zero; dissipative impedance means having an impedance selected to balance rated load impedance and connected in a series loop with a third winding of said transformer, said third winding being mutually transformer-coupled with said first and second windings whereby, in response to non-zero net flux in said windings caused by flux imbalance between said windings, said dissipative impedance means is operative to dissipate a portion of the power supplied by said input ports so as to maintain an impedance balance between said input ports.

' signal will appear at both output ports 20 and 21. At

DESCRIPTION OF THE DRAWINGS The invention will be described in detail herein below with the aid of the accompanying drawings in which:

FIG. 1 is a schematic diagram of a known broadband, wound transformer combiner; and

FIG. 2.is a schematic diagram of a particular embodiment of a broad-band combiner according to the present invention.

DETAILED DESCRIPTION The combiner shown in FIG. 1 is comprised of two individual transformers l0 and 11. Transformer 10 has two primary windings 12 and 13 and a secondary wind ing 14. Similarly, transformer 11 has primary windings 15 and 16 and secondary winding 17. The combiner network is comprised of two input ports 18 and 19 and two output ports 20 and 21. In operation, two coherent and synchronous AC signals are applied to input ports 18 and 19.-The amplitudes of the signals need not be the same but it is important that the frequency and phase'. of the two signals be identical. The current sense of the AC signals is indicated by the arrows leading away from input ports 18 and 19 respectively. The currents circulating in the two primary windings 15 and 16 of transformer 11 are wound in aiding sense and produce a net flux circulating in the magnetic core of transformer 11 whose intensity isproportional the sum of the two currents. As a result, there is induced into the secondary winding 17 'of transformer 11 a current which is proportional'to the sum-of the two individual input currents. This summation current is fed to a load R via output port 21. The same input currents which additively combine in transformer 11 exactly oppose one another in transformer 10. The flux created by the current in winding 12 is opposite in sense to the flux created by the current flowing in winding 13. It can be seen that if the frequency and phase of the two input signals are identical, and the flux created by the two input ports are identical, there will be no net flux circulating in the magnetic circuit of transformer 10 and as a result, there will be no current induced into the secondary winding l4.-

However, if one of the input signals should fail, the power of the remaining input signal will be divided between the two transformers 10 and 11 and the output such time, a dummy load" dissipative impedance element R will dissipate a portion of the remaining input signal. In this manner, the two input ports will remain mutually isolated.

A similar action takes place in the combiner according to the present invention, which is shown schematically in FIG. 2. However, it can be readily seenthat the complexity of the circuit shown in FIG. 2 is considerably less than that shown in FIG. I.

Referring to FIG. 2, there are shown input ports 18 and 19 and output ports 20 and 21. Similar reference numerals are used for similar components throughout the drawings. The combiner network comprises a transformer 30 having three mutually coupled windings 31, 32 and 33. Winding 31 is connected with source 19 and winding 32 is connected with source 18 to obtain mutually opposing senses of current flow in transformer 30. Two coherent and synchronous AC signals are applied to input ports 18 and 19 to produce signal currents whose instantaneous sense is represented by arrows.

The flux created in winding 31 by the current from input port 19 will be opposite in sense to the flux created in winding 32 by the current flowing from input port 18. If the magnitude of the two fluxes is identical, there will be no net flux circulating in transformer 30. This criteria is satisfied if:

where N represents the number of turns of winding 31;

N represents the number of turns of winding 32;

and

i and i represents the two input signal currents. (Note that by properly selecting the turns ratio, it-is possible to produce a zero net magnetic flux in the transformer 30 by applying two input signals which are of the same frequency and phase but of different magnitudes.)

Since no net flux is normally (i.e., under rated operating conditions) present in the magnetic circuit of the transformer 30, the two input currents add at the connection point 34 to produce an output current substantially equal to the sum of the input currents at the output port 21. This summation current is then fed to the load R When one of the input signals fail, the remaining signal produces a net flux in the transformer 30 and a cur rent is induced into winding 33, which in turn is absorbed by dummy load R via the output port 20. By properly choosing the turns ratios in transformer 30, the combined effect of the new impedance presented by the dummy load and the impedance created by the load R can be arranged to present, at the remaining operating input port, an impedance equal to the impedance presented when both input signals were supplying current. In this manner, input ports 18 and 19 are mutually isolated. I

The input impedanceof the circuit shown inFIG. 2 for input port 18 is:

ia Z1. azl N31) and the input impedance for port 19 is:

where Z, is the impedance of load R (The turns ratio for N and N is determined by the relative input power ratio to the two input ports by equation I, above.)

The isolation can now be obtained by the correct selection of the number of turns N for the third winding, and the value Z,, of the dummy load R If it is assumed that transformer 30 is an ideal transformer (i.e. having a unity coupling coefficient and negligible magnetizing current), the voltage transfer coefficient C from input port 18 to input port 19 with input port 19 opencircuited is given as follows:

|s+1o ss 1. a: a: u) a:; ZL 32 n) It can be seen from equation 4 that no coupling will be present, (i.e., C +19 will be zero), if Z 2,, (N 31 We?) The condition for zero coupling from input port 19 to input port 18, (i.e., C M8 0), is identical with the above result.

The transformer 11 shown in FIG. 1 must be capable of handling the entire power from the input ports 18 and 19. However, transformer 10, will, under the worst conditions only be required to handle one half of the power of the remaining input which has not failed. Under these conditions, the power of the remaining input will be divided between both transformers l1 and 10. In the combining network according to the present invention, as shown in FIG. 2, there is no one winding which must be capable of handling the complete power input of the two ports 18 and 19. As a result, not only has one transformer been eliminated using the combining network according to the present invention but the remaining transformer may be reduced in size.

The embodiment of the present invention described above is concerned with the objective of coupling together a number of coherent RF signal inputs to an antenna (the load). Clearly the frequency range for which the invention is useful will be limited by the operating characteristics of available wire-wound transformers.

What I claim as my invention is:

l. A combiner network comprising an output port having a first terminal and a second terminal for supplying a load, a first input port having first and second terminals, a second input port having first andsecond terminals, the second terminals of the said input ports and the second terminal of the output port being directly connected together; a single transformer having a first winding and a second winding, the first wirlding being connected between the first terminal of the first input port and the first terminal of the output port, the second winding being connected between the first terminal of the output port and the first terminal of the second input port, said windings being oppositely wound with respect to current flow from the first and second input ports and having a respective turns ratio in inverse proportion to the respective rated input powers of the first and second input ports whereby under rated operating conditions the net fluxattributable to current flow through said windings is substantially zero; dissipative impedance means having an impedance selected to balance rated'load impedance and connected in a series loop with a third winding of said transformer, said third winding being mutually transformer-coupled with said first and second windings whereby, in response to non-zero net flux in said windings caused by flux imbalance between said windings, said dissipative impedance means is operative to dissipate a portion of the power supplied by said input ports so as to maintain an impedance balance between said input ports.

2. A combiner network according to claim 1 wherein the rated input powers of the first and second input ports are substantially the same and the said first and second windings have substantially the same number of turns.

3. A combiner network as defined in claim 1, wherein tion at R.F. signal frequencies.

t l i

Claims (3)

1. A combiner network comprising an output port having a first terminal and a second terminal for supplying a load, a first input port having first and second terminals, a second input port having first and second terminals, the second terminals of the said input ports and the second terminal of the output port being directly connected together; a single transformer having a first winding and a second winding, the first winding being connected between the first terminal of the first input port and the first terminal of the output port, the second winding being connected between the first terminal of the output port and the first terminal of the second input port, said windings being oppositely wound with respect to current flow from the first and second input ports and having a respective turns ratio in inverse proportion to the respective rated input powers of the first and second input ports whereby under rated operating conditions the net flux attributable to current flow through said windings is substantially zero; dissipative impedance means having an impedance selected to balance rated load impedance and connected in a series loop with a third winding of said transformer, said third winding being mutually transformer-coupled with said first and second windings whereby, in response to non-zero net flux in said windings caused by flux imbalance between said windings, said dissipative impedance means is operative to dissipate a portion of the power supplied by said input ports so as to maintain an impedance balance between said input ports.

2. A combiner network according to claim 1 wherein the rated input powers of the first and second input ports are substantially the same and the said first and second windings have substantially the same number of turns.

3. A combiner network as defined in claim 1, wherein said transformer and windings are selected for operation at R.F. signal frequencies.

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