1. Field of Invention
The present invention relates to a radio frequency (“RF”) combiner/divider capable of automatic impedance transformation for impedance-matching and, more particularly, to a combiner/divider for use in an RF system that includes a changeable number of combiner/divider branches.
2. Related Prior Art
An RF combiner/divider is used to combine several RF signals into a single output RF signal and divide a single RF signal into several output RF signals. The operation of a divider is opposite to that of a combiner. That is, the structure of a divider can be derived from that of a combiner. The combiner combines several input ports into a single output port while the divider divides a single input port into several output ports.
Impedance transformation networks are used in the combiners or dividers. When the characteristic impedance at the input port is not matched with the output impedance at the output port, an impedance transformation circuit increases or reduces the impedance stage between the input and output ports to match the output impedance with the characteristic impedance as much as possible. Impedance-matching is important to ensure the maximum power transformation and minimum signal distortion and/or reflection between input and output circuits.
Korean Patents KR20040069816 and KR20040098857 both describe Wilkinson combiner/dividers based on the Wilkinson Principle. For convenience of description, only the combiners will be discussed for example. Each input branch includes a quarter-wavelength impedance transformer for impedance transformation to match the output impedance with the input impedance. The impedance transformer of each input branch is given limitation. Hence, when the number of the input branches that are combined is changed, the impedance transformer of each input branch must be changed, and this is impractical because such a structure includes a certain number of transformers based on a certain number of channels to be combined, and the impedances of all of the transformers are based on the number of the channels to be combined. Hence, the Wilkinson combiner/dividers based on the Wilkinson Principle are not suitable for systems that include changeable numbers of combined/divided branches.
U.S. Pat. No. 7,046,101 (“'101”) discloses a combiner/divider that is based on the concept of a series/shunt network instead of the Wilkinson Principle. There is disclosed a divider that includes a single-pole N-way RF switch and a switchable impedance-matching network. The switchable impedance-matching network includes N−1 switch-selectable impedance-matching elements. The impedance-matching elements are arranged along a transmission line that includes an input port at an end and a switching connection point at another end. The switching connection point is for selective contact with several output-port reeds. The impedance-matching elements include different impedance-matching lengths. An impedance-matching distance exists between each impedance-matching element and the switching connection point. In operation, when only one output-port reed is in contact with the transmission line, i.e., only one output port is connected to the input port, the load impedance is matched with the source impedance, without having to activate any impedance-matching element. If the number of output ports connected to the input port is changed, the transmission line is connected to an impedance-matching element in a certain position determined by the number of the output ports that are combined, thus initiating an impedance-modulation mechanism for impedance-matching. In practice, the manufacturing and location of the impedance-matching elements require precision.
U.S. Pat. No. 6,323,742 discloses an RF combiner that includes N input channels 126a, 126b, 126c and 126d for receiving input signals. These input channels are electrically connected to an electrical connection point 22 or 132. All of the input signals are combined with one another at the electrical connection point 22 or 132. Then, a quarter-wavelength impedance transformer 34 or 150 transfers the combination of the input signals to an output port. Each input channel includes a grounding switch 26, 28, 30 or 32. There will be high impedance in an input channel if the respective grounding switch is connected to an electrical ground. Hence, the electrical connection point is only connected to an input channel where the grounding switch is open-circuited. An input channel ready for transferring an input signal is defined as an “active input channel.” According to the number of the active input channels, a control circuit 116 controls the connection of a first combiner switch 144 and a second combiner switch 154 to the corresponding impedance transformation line to match the output impedance with the input. The grounding switch provides high impedance to interfere with the ability of the input channels to transfer the signals. That is, the input channels are not actually cut off from the electrical connection point although they cannot smoothly transfer the input signals to the electrical connection point. This practice could easily damage the combiner. Moreover, the structure of the first combiner switch 144 and how it works are not described although it is actually part of an impedance transformer.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.
It is an objective of the present invention to provide an inexpensive and efficient RF combiner/divider.
It is another objective of the present invention to provide an RF combiner/divider for use in an RF system that includes a changeable number of combiner/divider branches, wherein the RF combiner/divider is used for automatic impedance transformation for impedance-matching.
To achieve the foregoing objective, the RF combiner includes an input switch, an output switch, an impedance matching transmission network and a control circuit. The input switch includes several input channels for receiving input signals. The output switch includes the same number of input channels as the input channels of the input switch. All of the input channels of the output switch are electrically connected to an output port. The impedance matching transmission network includes switching elements and impedance transmission lines. The number of the switching elements is identical to that of the input channels. The impedance transmission lines are arranged between the switching elements and the input channels of the output switch. The control circuit controls the number of the input channels of the input switch that are electrically connected to a center connection point, and selectively connects an impedance-matched one of the switching elements to the center connection point based on the number.
The control circuit controls the on/off of the input channels via digital inputs at the input channels electrically connected to the input switch.
Other objectives, advantages and features of the present invention will be apparent from the following description referring to the attached drawings.
The present invention will be described via detailed illustration of four embodiments referring to the drawings wherein:
The present invention is related to an RF combiner/divider. Only a combiner is however described referring to the drawings since a divider and a combiner are identical to each other regarding the structure but opposite to each other regarding the operation.
Referring to
The input switch 10 is preferably a single-poled 2N-throw RF switch such as a single-poled 8-throw (“SP8T”) switch. Half of the stationary contacts of the single-poled 2N-throw RF switch are used as input channels 11, 12, 13 and 14 of the input switch 10. The other stationary contacts of the single-poled 2N-throw RF switch are used as switching elements 21, 22, 23 and 24 of the impedance-matching transmission network 30. The input channels 11, 12, 13 and 14 and the switching elements 21, 22, 23 and 24 are connected to a center connection point 20 under the control of the control circuit 80.
Each of the input channels 11, 12, 13 and 14 of the input switch 10 receives an input signal. Thus, there is characteristic impedance Z0 at each of the input channels 11, 12, 13 and 14. The input signals include but not limited to RF signals, microwave frequency signals and signals at higher frequencies.
There is respective transformation impedance at each of the switching elements 21, 22, 23 and 24 as part of the impedance-matching transmission network 30. To this end, each of the switching elements 21, 22, 23 and 24 is sized according to the respective transformation impedance. The size includes length and/or cross-sectional width.
The output switch 60 is preferably a high-power single-pole N-throw switch such as single-pole 4-throw (“SP4T”) switch. The single-pole N-throw switch includes four input channels 61, 62, 63 and 64 which are all connected to an output port 65 electrically. The input channels 61, 62, 63 and 64 are connected to the switching elements 21, 22, 23 and 24 via impedance transmission lines 31, 32, 33 and 34, respectively. Hence, impedance at each of the input channels 61, 62, 63 and 64 is identical to the impedance at a corresponding one of the input channels 11, 12, 13 and 14 of the input switch 10.
The impedance-matching transmission network 30 includes the switching elements 21, 22, 23 and 24 and the impedance transmission lines 31, 32, 33 and 34 for connecting the switching elements 21, 22, 23 and 24 to the input channels 61, 62, 63 and 64. The impedance transmission lines 31, 32, 33 and 34 are impedance-controlled RF transmission lines including but not limited to coaxial cables, coaxial structures built therein, circuit board transmission lines and microstriplines.
The on/off of the input channels 11, 12, 13 and 14 of the input switch 10 are under the control of the control circuit 80 based on digital inputs 81, 82, 83 and 84 thereat. The digital input at each of the digital inputs 81, 82, 83 and 84 may be “1” to represent the turning on of a corresponding one of the input channels 11, 12, 13 and 14. The digital input at each of the digital inputs 81, 82, 83 and 84 may alternatively be “0” to represent the turning off of a corresponding one of the input channels 11, 12, 13 and 14.
A selector 85 is connected to the control circuit 80 and operable to select a number of the input channels 11, 12, 13 and 14 to be turned on. Based on the selected number, the control circuit 80 turns on at least some of the input channels 11, 12, 13, 14 and connects the input switch 10 to the output switch 60 via a selected one of the impedance transformers 35, 36, 37 and 38 of the impedance-matching transmission network 30 for impedance transformation in an impedance-matched manner.
For example, three of the input channels of the input switch 10 may be turned on. The characteristic impedance Z0 at each turned-on input channel is 50 Ω (Z0=50 Ω). The total impedance at the center connection point 20 is Z0/N (50 Ω/3=16.66 Ω). By using the impedance-matching transmission network 30 for impedance transformation, the output impedance at the output switch 60 is matched with the characteristic impedance Z0, i.e., Z0/N is transformed to Z0 for output.
For example, only one of the input channels of the input switch 10 is turned on. The control circuit 80 connects the input switch 10 to the output switch 60 via the impedance transformer 35 where the impedance is Z0/√{square root over (1)}.
For example, two of the input channels of the input switch 10 are turned on. The control circuit 80 connects the input switch 10 to the output switch 60 via the impedance transformer 36 where the impedance is Z0/√{square root over (2)}.
For example, three of the input channels of the input switch 10 are turned on. The control circuit 80 connects the input switch 10 to the output switch 60 via the impedance transformer 37 where the impedance is Z0/√{square root over (3)}.
For example, four of the input channels of the input switch 10 are turned on. The control circuit 80 connects the input switch 10 to the output switch 60 via the impedance transformer 38 where the impedance is Z0/√{square root over (4)}.
Referring to
Each of the switching elements 21, 22, 23 and 24 is connected to a corresponding one of the impedance transmission lines 31, 32, 33 and 34 to form a corresponding one of the quarter-wavelength impedance transformers 35, 36, 37 and 38 as in the embodiment shown in
Each of the impedance-switching elements 21, 22, 23 and 24 forms a corresponding one of the quarter-wavelength impedance transformers 35, 36, 37 and 38 according to another embodiment of the present invention referring to
Each of the switching elements 21, 22, 23 and 24, a corresponding one of the impedance transmission lines 31, 32, 33 and 34 and a corresponding one of the input channels 61, 62, 63 and 64 are interconnected serially to form a corresponding one of the quarter-wavelength impedance transformers 35, 36, 37 and 38 according to another embodiment of the present invention referring to
The present invention has been described via the detailed illustration of the embodiments. Those skilled in the art can derive variations from the embodiments without departing from the scope of the present invention. Therefore, the embodiments shall not limit the scope of the present invention defined in the claims.
Number | Date | Country | Kind |
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101146748 A | Dec 2012 | TW | national |
Number | Name | Date | Kind |
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5872491 | Kim et al. | Feb 1999 | A |
6323742 | Ke | Nov 2001 | B1 |
7046101 | Mruz et al. | May 2006 | B2 |
Number | Date | Country |
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20040069816 | Aug 2004 | KR |
20040098857 | Nov 2004 | KR |
Number | Date | Country | |
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20140159830 A1 | Jun 2014 | US |