CA2015945A1 - Radio frequency network - Google Patents
Radio frequency networkInfo
- Publication number
- CA2015945A1 CA2015945A1 CA 2015945 CA2015945A CA2015945A1 CA 2015945 A1 CA2015945 A1 CA 2015945A1 CA 2015945 CA2015945 CA 2015945 CA 2015945 A CA2015945 A CA 2015945A CA 2015945 A1 CA2015945 A1 CA 2015945A1
- Authority
- CA
- Canada
- Prior art keywords
- branch
- node
- common
- radio frequency
- common node
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
- H01P5/00—Coupling devices of the waveguide type
- H01P5/12—Coupling devices having more than two ports
- H01P5/16—Conjugate devices, i.e. devices having at least one port decoupled from one other port
Landscapes
- Microwave Amplifiers (AREA)
- Amplifiers (AREA)
- Transmitters (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A radio frequency network, comprises a first common node connected to a common input or output port, a second common node, and at least three identical branches therebetween, each branch comprising a first branch node, to which is connected a balance load, and a second branch node spaced therefrom and connected to a branch output or input port, the network being dimensioned and arranged such that an r.f. signal of a specific frequency input at the common input port is divided equally between all the branch output ports, and a plurality of identical r.f. signals of the specific frequency applied in phase to all the branch input ports appear combined at the common output port.
A radio frequency network, comprises a first common node connected to a common input or output port, a second common node, and at least three identical branches therebetween, each branch comprising a first branch node, to which is connected a balance load, and a second branch node spaced therefrom and connected to a branch output or input port, the network being dimensioned and arranged such that an r.f. signal of a specific frequency input at the common input port is divided equally between all the branch output ports, and a plurality of identical r.f. signals of the specific frequency applied in phase to all the branch input ports appear combined at the common output port.
Description
, Field of the Invention This invention relates to a radio frequency network usable for splitting an r.f. signal or ~or combining a plurality of r.f. signals.
- . , A particular application for a combiner is in transmitters, for example television transmitters.
Conventionally, a television transmitter uses a klystron in the r.f output stage to amplify the signal to be passed to the antenna. While klystrons generally perform this function satisfactorily and reliably, they require complex cooling arrangements, usually employing circulating water, and these require regular maintenance. In addition, failure of the klystron -renders the transmitter inoperative.
:' For these reasons, there has been a move towards the use of arrays of solid state r.f. amplifiers operating in parallel in place of the klystron. With an array of parallel solid state amplifiers, it is necessary to combine the output signals in phase in such a way that failure of individual amplifiers does not jeopardize the total output.
- , , .
- .:
I/ 7 6 3 5/MCS L/ CAN .-' 2 -- ~
.,~ ' .
summary of the Invention The present invention provides a radio frequency network, comprising a first common node connected to a common input or output port, a second common node, and at least three identical branches therebetween, each branch comprising a first branch node, to which is connected a balance load, and a second branch node spaced therefrom and connected to a branch output or input port, the network being dimensioned and arranged such that an r.f. signal of a specific frequency input at the common input port is divided equally between all the branch output ports, and a plurality of identical r.f. signals of the specific frequency applied in phase to all the branch input ports appear combined at the common output port.
. ;
All the inter-nodal distances are preferably equal to one quarter of the operating wavelength of the input signal or signals. However, for many applications, a narrow network bandwidth is unsatisfactory. It has been found that~the values of the impedances of the portions ;~
. .
of the branches between the second common nodes and each first branch node have some influence on the bandwidth ..
' ' :' ' ` , ,, '., '::, ::, ::, :;: : ' ' ' ' . ' :. , , .. , . ' . : ' : ,: " .. ": ' , ' ' ' ,~ ' ,1, ', ' ' .' ' . ' ' ' .'" , , ' ' .
of the network. By selection of suitable impedances for these portions, the bandwidth may b~e increased. The impedance is preferably low relative to the other portions of the network.
A greater increase in bandwidth may be achieved by providing a quarter wavelength transEormer between the first common node and the common input/output port, the length of the line added being a quarter of the wavelength at the centre of the bandwidth. Still further improvement of the bandwidth may be obtained by connecting to the first common node a short circuited stub, preferably having a length equal to a quarter wavelength. By way of example, using this construction, a twenty way combiner with a bandwidth of 88 to 108 NHz for an input VSWR of less than 1.02:1 can be achieved.
When the network is used as a splitter, as each output load fails, the input match deteriorates, but all the other inputs stay at the same amplitude and phase.
This input deterioration could be cleaned up by, for example, using a circulator.
', ' When the network is used as a combiner, as each input; fails~, the output power drops by somewhat more , .:
.., ,~, . ' _ 4 than this input amount, depending on the number of already failed inputs. Most of the surplus power appears in the load adjacent to the failed input, with :
the remainder spread evenly around the other loads.
The network of the invention may be formed of coaxial cable, multi-wire cable, waveguide, or even LC
circuits to give a 90 phase shift. The ~larter wavelength lines may conveniently be any odd multiple of quarter wavelengths where this makes the network physically easier to realise. The use of greater lengths carries the disadvantage, however, that the ;
opera~ing bandwidth becomes narrower.
Brief Description of the Drawings In the drawings:
:'`
Figure 1 is a diagrammatic representation of a sixteen-way combiner in accordance with one embodiment of the invention;
Figure 2 is a diagram of a modified form of the combiner illostrated in Figore l; and ~j : :"
: ' _ 5 _ :
Figures 3, 4 and 5 are graphs of insertion loss and .
VSWR against frequency respectively for the network as shown in Figure 1, the network shown in Figure 2, but without the stub, and the network shown in Figure 2 with the stub. .:
Description o~ the Preferred Embodiments Referring to Figure 1 the network comprises sixteen identical branches la to lp extending between a first ~
common node 2 and a second common node 3. Each branch 1 :
comprises three equal lengths of coaxial cable joined at a first branch node 4 and at a second branch node 5. A
balance load 6 is connected to the first branch node 4, :
while a branch input port 7 is connected to the second : :
..
branch node 5. The inter-nodal length is in each case one quarter of the wavelength at the centre of the operating bandwidth for the network, thus giving a 90 phase shift in each portion of the network for that wavelength. The first common node 2 is connected to an output port ~.
~, . .
In use, sixteen identical r.~. signals are applled in phase to the branch input ports 7a to 7p. The signal appearing~ at~the output port 8 is substantially the sum ,~,.
. ~ : :
::
of the input signals.
:
Referring now to Figure 2, the bandwidth of the network may be increased by connecting a quarter wavelength transformer 9 between the first common node 2 of the network illustrated in Figure l, and the output port 8. A further improvement may be achieved by connecting a short circuited quarter wavelength stub lO
to the first common node 2. Adjustment of the impedances of the lines extending between the second common node 3 and each of the first branch nodes 4a to 4p can also improve the bandwidth. The effects of these modifications are illustrated by Figures 3, 4 and 5.
Figure 3 illustrates insertion loss and input VSWR
against ~requency for the network illustrated in Figure 1, where, in each branch, the impedance of the line from the second common node 3 to the first branch node 4 is 280 ohms, the impedance of the line between the two branch nodes 4 and 5 is 50 ohms, and the impedance of the third line is 12.5 ohms. It will ~e seen that, moving away ~rom the central frequency of approximately 670 MHz, one encounters rapidly increasing loss and VSWR.
.
~ ~ , .:
:
--:I/7635/MCSL~CAN
Figure 4 shows the effect of a circuit in accordance with Figure 2, but without the short circuited stub. The impedances are set in each branch, from the second common node 3 to the iirst common node 2 as 5 ohms, 50 ohms and 100 ohms respectivelyO The quarter wavelength transformer has an impedance of 25 ohms. It will be seen that the bandwidth over which -very low loss is experienced is very much greater, extending from about 470 MHz to about 860 MHz the VSWR
over this range is also substantially reduced.
Figure 5 shows the effect of adding a short-circuit stub, having an impedance of 49 ohms. The impedance of the line in each branch extending ~rom the second common node to the first branch node is increased to 50 ohms, with all other impedances remaining the same. It will be seen that, while the loss is very slightly increased over the bandwidth of 470 to 860 MHz, the VSWR is significantly reducad further. `
', While the networks described with reference to the ;
drawings are symmetrically arranged with respect to impedance, it has been found that by varying the ratio o~ the impedances in one branch to those in any of the remaining ~branches,~the power in that branch will vary ~-'- ' ... . .
~ -....
relative to that in each of the other branches. This is of particular application in a splitter, if an uneven distribution of output power is desirled.
It should be noted that the network of the application, although particularly described with reference to television transmitters, will find application in many other types of transmitter, and generally where a plurality of r.f. signals are to be combined together or produced from a single such signal.
:
?
:::
: ' . '', ' . : ' . ~
',.' ,.
- . , A particular application for a combiner is in transmitters, for example television transmitters.
Conventionally, a television transmitter uses a klystron in the r.f output stage to amplify the signal to be passed to the antenna. While klystrons generally perform this function satisfactorily and reliably, they require complex cooling arrangements, usually employing circulating water, and these require regular maintenance. In addition, failure of the klystron -renders the transmitter inoperative.
:' For these reasons, there has been a move towards the use of arrays of solid state r.f. amplifiers operating in parallel in place of the klystron. With an array of parallel solid state amplifiers, it is necessary to combine the output signals in phase in such a way that failure of individual amplifiers does not jeopardize the total output.
- , , .
- .:
I/ 7 6 3 5/MCS L/ CAN .-' 2 -- ~
.,~ ' .
summary of the Invention The present invention provides a radio frequency network, comprising a first common node connected to a common input or output port, a second common node, and at least three identical branches therebetween, each branch comprising a first branch node, to which is connected a balance load, and a second branch node spaced therefrom and connected to a branch output or input port, the network being dimensioned and arranged such that an r.f. signal of a specific frequency input at the common input port is divided equally between all the branch output ports, and a plurality of identical r.f. signals of the specific frequency applied in phase to all the branch input ports appear combined at the common output port.
. ;
All the inter-nodal distances are preferably equal to one quarter of the operating wavelength of the input signal or signals. However, for many applications, a narrow network bandwidth is unsatisfactory. It has been found that~the values of the impedances of the portions ;~
. .
of the branches between the second common nodes and each first branch node have some influence on the bandwidth ..
' ' :' ' ` , ,, '., '::, ::, ::, :;: : ' ' ' ' . ' :. , , .. , . ' . : ' : ,: " .. ": ' , ' ' ' ,~ ' ,1, ', ' ' .' ' . ' ' ' .'" , , ' ' .
of the network. By selection of suitable impedances for these portions, the bandwidth may b~e increased. The impedance is preferably low relative to the other portions of the network.
A greater increase in bandwidth may be achieved by providing a quarter wavelength transEormer between the first common node and the common input/output port, the length of the line added being a quarter of the wavelength at the centre of the bandwidth. Still further improvement of the bandwidth may be obtained by connecting to the first common node a short circuited stub, preferably having a length equal to a quarter wavelength. By way of example, using this construction, a twenty way combiner with a bandwidth of 88 to 108 NHz for an input VSWR of less than 1.02:1 can be achieved.
When the network is used as a splitter, as each output load fails, the input match deteriorates, but all the other inputs stay at the same amplitude and phase.
This input deterioration could be cleaned up by, for example, using a circulator.
', ' When the network is used as a combiner, as each input; fails~, the output power drops by somewhat more , .:
.., ,~, . ' _ 4 than this input amount, depending on the number of already failed inputs. Most of the surplus power appears in the load adjacent to the failed input, with :
the remainder spread evenly around the other loads.
The network of the invention may be formed of coaxial cable, multi-wire cable, waveguide, or even LC
circuits to give a 90 phase shift. The ~larter wavelength lines may conveniently be any odd multiple of quarter wavelengths where this makes the network physically easier to realise. The use of greater lengths carries the disadvantage, however, that the ;
opera~ing bandwidth becomes narrower.
Brief Description of the Drawings In the drawings:
:'`
Figure 1 is a diagrammatic representation of a sixteen-way combiner in accordance with one embodiment of the invention;
Figure 2 is a diagram of a modified form of the combiner illostrated in Figore l; and ~j : :"
: ' _ 5 _ :
Figures 3, 4 and 5 are graphs of insertion loss and .
VSWR against frequency respectively for the network as shown in Figure 1, the network shown in Figure 2, but without the stub, and the network shown in Figure 2 with the stub. .:
Description o~ the Preferred Embodiments Referring to Figure 1 the network comprises sixteen identical branches la to lp extending between a first ~
common node 2 and a second common node 3. Each branch 1 :
comprises three equal lengths of coaxial cable joined at a first branch node 4 and at a second branch node 5. A
balance load 6 is connected to the first branch node 4, :
while a branch input port 7 is connected to the second : :
..
branch node 5. The inter-nodal length is in each case one quarter of the wavelength at the centre of the operating bandwidth for the network, thus giving a 90 phase shift in each portion of the network for that wavelength. The first common node 2 is connected to an output port ~.
~, . .
In use, sixteen identical r.~. signals are applled in phase to the branch input ports 7a to 7p. The signal appearing~ at~the output port 8 is substantially the sum ,~,.
. ~ : :
::
of the input signals.
:
Referring now to Figure 2, the bandwidth of the network may be increased by connecting a quarter wavelength transformer 9 between the first common node 2 of the network illustrated in Figure l, and the output port 8. A further improvement may be achieved by connecting a short circuited quarter wavelength stub lO
to the first common node 2. Adjustment of the impedances of the lines extending between the second common node 3 and each of the first branch nodes 4a to 4p can also improve the bandwidth. The effects of these modifications are illustrated by Figures 3, 4 and 5.
Figure 3 illustrates insertion loss and input VSWR
against ~requency for the network illustrated in Figure 1, where, in each branch, the impedance of the line from the second common node 3 to the first branch node 4 is 280 ohms, the impedance of the line between the two branch nodes 4 and 5 is 50 ohms, and the impedance of the third line is 12.5 ohms. It will ~e seen that, moving away ~rom the central frequency of approximately 670 MHz, one encounters rapidly increasing loss and VSWR.
.
~ ~ , .:
:
--:I/7635/MCSL~CAN
Figure 4 shows the effect of a circuit in accordance with Figure 2, but without the short circuited stub. The impedances are set in each branch, from the second common node 3 to the iirst common node 2 as 5 ohms, 50 ohms and 100 ohms respectivelyO The quarter wavelength transformer has an impedance of 25 ohms. It will be seen that the bandwidth over which -very low loss is experienced is very much greater, extending from about 470 MHz to about 860 MHz the VSWR
over this range is also substantially reduced.
Figure 5 shows the effect of adding a short-circuit stub, having an impedance of 49 ohms. The impedance of the line in each branch extending ~rom the second common node to the first branch node is increased to 50 ohms, with all other impedances remaining the same. It will be seen that, while the loss is very slightly increased over the bandwidth of 470 to 860 MHz, the VSWR is significantly reducad further. `
', While the networks described with reference to the ;
drawings are symmetrically arranged with respect to impedance, it has been found that by varying the ratio o~ the impedances in one branch to those in any of the remaining ~branches,~the power in that branch will vary ~-'- ' ... . .
~ -....
relative to that in each of the other branches. This is of particular application in a splitter, if an uneven distribution of output power is desirled.
It should be noted that the network of the application, although particularly described with reference to television transmitters, will find application in many other types of transmitter, and generally where a plurality of r.f. signals are to be combined together or produced from a single such signal.
:
?
:::
: ' . '', ' . : ' . ~
',.' ,.
Claims (15)
1. A radio frequency splitter network, comprising a first common node connected to a common input port, a second common node, and at least three identical branches therebetween, each said branch comprising a first branch node, to which is connected a balance load, and a second branch node spaced therefrom and connected to a branch output port, said network being dimensioned and arranged such that an r.f. signal input at said first common node is divided equally between all said branch output porks.
2. A radio frequency splitter network according to Claim 1, wherein the impedances of the portions of the branches between said second common node and each said first branch node are such that substantially all of an r.f. signal having any one of a range of frequencies input at said common input port is divided equally between all said branch output ports.
3. A radio frequency splitter network according to Claim 2, wherein the impedance of the portion of each said branch between said second common node and said first branch node is substantially lower than the impedance of the portion of said branch between said first and said second branch nodes, and lower than that of the portion of said branch between said second branch node and said first common node.
4. A radio frequency network according to Claim 2, comprising a short circuited stub connected to said first common node.
5. A radio frequency splitter network according to Claim 4, wherein said stub is equal in length to the portion of any of the branches between said first common node and said second branch node.
6. A radio frequency splitter network according to Claim 2, comprising a quarter-wavelength transformer connected between said first common node and said common input port, the length of said transformer being a quarter of the centre wavelength of the said range.
7. A radio frequency splitter network according to Claim 2, wherein each said portion of each said branch has a length equivalent to one quarter of said centre wavelength of said range.
8. A radio frequency combiner network, comprising a first common node connected to a common output port, a second common node, and at least three identical branches therebetween, each said branch comprising a first branch node, to which is connected a balance load, and a second branch node spaced therefrom and connected to a branch input port, said network being dimensioned and arranged such that a plurality of identical r.f.
signals applied in phase to all said branch input ports appear combined at said first common node.
signals applied in phase to all said branch input ports appear combined at said first common node.
9. A radio frequency combiner network according to Claim 8, wherein the impedances of the portions of the branches between said second common node and each said first branch node are such that a plurality of identical r.f. signals, all of any one of a range of frequencies, applied in phase to all said branch input ports appear substantially combined at the common output port.
10. A radio frequency combiner network according to Claim 9, wherein the impedance of the portion of each said branch between said second common node and said first branch node is substantially lower than the impedance of the portion of said branch between said first and said second branch nodes, and lower than that of the portion of said branch between said second branch node and said first common node.
11. A radio frequency combiner network according to Claim 9, comprising a short circuited stub connected to said first common node.
12. A radio frequency combiner network according to Claim 11, wherein said stub is equal in length to the portion of any of the branches between said first common node and said second branch node.
13. A radio frequency combiner network according to Claim 9, comprising a quarter-wavelength transformer connected between said first common node and said common input port, the length of said transformer being a quarter of the centre wavelength of the said range.
14. A radio frequency combiner network according to Claim 9, wherein each said portion of each said branch has a length equivalent to one quarter of said centre wavelength of said range.
15. A television transmitter, comprising a vision modulated r.f. signal input, signal splitter means for splitting said signal into a plurality of equal signals, an amplification stage having a plurality of solid state amplifiers operating in parallel, each of said equal signals being input to a respective one of said solid state amplifiers and the output of each said amplifier being connected to a combiner network having a plurality of input ports and a common output port connected to a signal mixing stage for mixing a sound-modulated signal with the combined vision-modulated signal, said combiner network comprising a first common node connected to said common output port, a second common node, and a plurality of identical branches between said first and second common nodes, each said branch comprising a first branch node, to which is connected a balance load, and a second branch node spaced therefrom and connected to a respective one of said input ports, said combiner network being dimensioned and arranged such that said outputs from said solid state amplifiers appear combined at said output port.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8910410A GB2232028B (en) | 1989-05-05 | 1989-05-05 | Radio frequency network |
| GB8910410.3 | 1989-05-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2015945A1 true CA2015945A1 (en) | 1990-11-05 |
Family
ID=10656307
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2015945 Abandoned CA2015945A1 (en) | 1989-05-05 | 1990-05-02 | Radio frequency network |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0396430A3 (en) |
| JP (1) | JPH0388402A (en) |
| AU (1) | AU625827B2 (en) |
| CA (1) | CA2015945A1 (en) |
| GB (1) | GB2232028B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5164689A (en) * | 1991-04-11 | 1992-11-17 | Harris Corporation | N-way power combiner/divider |
| US6587013B1 (en) * | 2000-02-16 | 2003-07-01 | Signal Technology Corporation | RF power combiner circuit with spaced capacitive stub |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4156212A (en) * | 1977-12-19 | 1979-05-22 | Nautical Electronic Laboratories, Ltd. | Combiner system |
| US4163955A (en) * | 1978-01-16 | 1979-08-07 | International Telephone And Telegraph Corporation | Cylindrical mode power divider/combiner with isolation |
| GB2069244A (en) * | 1980-02-11 | 1981-08-19 | Decca Ltd | Radio frequency zero phase power combiner |
| DE3814744A1 (en) * | 1988-04-30 | 1989-11-09 | Grundig Emv | HYBRID PERFORMANCE DIVIDER, IN PARTICULAR THREE-TORCH HYBRID |
-
1989
- 1989-05-05 GB GB8910410A patent/GB2232028B/en not_active Expired - Lifetime
-
1990
- 1990-05-02 CA CA 2015945 patent/CA2015945A1/en not_active Abandoned
- 1990-05-04 EP EP19900304909 patent/EP0396430A3/en not_active Withdrawn
- 1990-05-04 AU AU54675/90A patent/AU625827B2/en not_active Ceased
- 1990-05-07 JP JP11733090A patent/JPH0388402A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| GB2232028B (en) | 1992-12-09 |
| JPH0388402A (en) | 1991-04-12 |
| EP0396430A3 (en) | 1992-02-05 |
| GB8910410D0 (en) | 1989-06-21 |
| EP0396430A2 (en) | 1990-11-07 |
| AU5467590A (en) | 1990-11-08 |
| GB2232028A (en) | 1990-11-28 |
| AU625827B2 (en) | 1992-07-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |