HIGH FREQUENCY POWER DIVIDER/COMBINER CIRCUIT

Abstract

A high frequency power divider circuit for distributing an input signal to two or more signal output ports, comprising: a rat race coupler, wherein the rat race coupler is configured to couple an input signal provided at an input port of the rat race coupler to a first output of the rat race coupler and to a second output of the rat race coupler; a first coupling structure coupled to the first output of the rat race coupler, to couple the first output of the rat race coupler with a first signal output port; and a second coupling structure coupled to the second output of the rat race coupler, to couple the second output of the rat race coupler with a second signal output port; wherein a characteristic impedance of a first transmission line portion between the input port and the first output of the rat race coupler deviates from a nominal ring impedance of the rat race coupler in a first direction, and wherein a characteristic impedance of a second transmission line portion between the input port and the second output of the rat race coupler deviates from the nominal ring impedance of the rat race coupler in a second direction, which is opposite to the first direction.

Claims

1. A high frequency power divider circuit for distributing an input signal to two or more signal output ports, the circuit comprising: a rat race coupler configured to couple an input signal provided at an input port thereof to a first output and to a second output thereof; a first coupling structure coupled to the first output of the rat race coupler and configured to couple the first output of the rat race coupler with a first signal output port; and a second coupling structure coupled to the second output of the rat race coupler and configured to couple the second output of the rat race coupler with a second signal output port, wherein a characteristic impedance of a first transmission line portion between the input port and the first output of the rat race coupler deviates from a nominal ring impedance of the rat race coupler in a first direction, and wherein further a characteristic impedance of a second transmission line portion between the input port and the second output of the rat race coupler deviates from the nominal ring impedance of the rat race coupler in a second direction, which is opposite to the first direction.

2. The high frequency power divider circuit according to claim 1, wherein a characteristic impedance of a third transmission line portion between the second output of the rat race coupler and another port of the rat race coupler deviates from the nominal ring impedance in the same direction as the characteristic impedance of the first transmission line portion.

3. The high frequency power divider circuit according to claim 2, wherein a characteristic impedance of a fourth transmission line portion between the first output of the rat race coupler and yet another port of the rat race coupler deviates from the nominal ring impedance in the same direction as the characteristic impedance of the second transmission line portion.

4. The high frequency power divider circuit according to claim 2, wherein the characteristic impedance of the first transmission line portion differs from the characteristic impedance of the third transmission line portion by no more than ±25% of the characteristic impedance of the first transmission line portion and the characteristic impedance of the second transmission line portion.

5. The high frequency power divider circuit according to claim 1 wherein the characteristic impedance of the second transmission line portion differs from the characteristic impedance of the fourth transmission line portion by no more than ±25% of the characteristic impedance of the second transmission line portion and the characteristic impedance of the first transmission line portion.

6. The high frequency power divider circuit according to claim 1 wherein a multiplied value of the characteristic impedance of the first transmission line portion with the characteristic impedance of the second transmission line portion is equal to the square of the nominal ring impedance within a tolerance of ±10%.

7. The high frequency power divider circuit according to claim 1 wherein the characteristic impedance of the first transmission line portion is smaller than the characteristic impedance of the second transmission line portion.

8. The high frequency power divider circuit according to claim 1 wherein the deviation range of the characteristic impedance from the nominal ring impedance is within ±20% of the nominal ring impedance.

9. The high frequency power divider circuit according to claim 1, wherein the characteristic impedance of the first and the third transmission line portions deviate between +1% and +20% of the nominal ring impedance, and the characteristic impedance of the second and the fourth transmission line portions deviate between −1% and −20% of the nominal ring impedance.

10. A high frequency power divider circuit for distributing an input signal to two or more signal output ports, the circuit comprising: a rat race coupler configured to couple an input signal provided at an input port thereof to a first output to a second output thereof; a first coupling structure coupled to the first output for coupling the first output with a first signal output port; and a second coupling structure coupled to the second output for coupling the second output with a second signal output port, wherein the first coupling structure and the second coupling structure are adapted to provide different phase shift over frequency, and wherein further the first coupling structure comprises a phase shifter adapted to at least partially compensate for a frequency variation of a phase difference between signals at the first output of the rat race coupler and at the second output of the rat race coupler in a system configured to operate at a design frequency of the rat race coupler.

11. The high frequency power divider circuit according to claim 10, wherein the second coupling structure comprises a pair of coupled transmission lines, wherein a first end of a first coupled transmission line is coupled with the second output of the rat race coupler, wherein a second end of the first coupled transmission line is coupled to a second end of a second coupled transmission line, which is adjacent to the second end of the first coupled transmission line, and wherein the first end of the second coupled transmission line is coupled to the second signal output port.

12. The high frequency power divider circuit according to claim 10, wherein the first end of the first coupled transmission line is coupled with the second output of the rat race coupler via a further transmission line.

13. The high frequency power divider circuit according to claim 12, wherein a characteristic impedance of further transmission line deviates from a reference impedance by no more than ±5%.

14. The high frequency power divider circuit according to claim 10, wherein a product of an even mode impedance of the pair of coupled transmission lines and of an odd mode impedance of the pair of coupled transmission lines deviates from a square of the reference impedance by no more than ±5%.

15. The high frequency power divider circuit according to claim 12, wherein an electrical length of the coupled transmission lines of the pair of coupled transmission lines deviates from a fourth of a wavelength at a design centre frequency of the rat race coupler by no more than ±5%.

16. The high frequency power divider circuit according to claim 12, wherein a length of the further transmission line is selected to decouple stray fields of the pair of coupled transmission lines from the rat race coupler.

17. The high frequency power divider circuit according to claim 10, wherein an electrical length of a transmission line forming the first coupling structure is equal to an electrical length of the further transmission line plus half a wavelength, with a tolerance of ±a tenth of a wavelength.

18. A high frequency power combiner circuit for obtaining an output signal on the basis of input signals from two or more signal input ports, the circuit comprising: a rat race coupler configured to provide an output signal at an output port thereof on the basis of a signal at a first input thereof and on the basis of a signal at a second input thereof; a first coupling structure coupled to the first input thereof, to couple the first input thereof with a first signal input port; and a second coupling structure coupled to the second input thereof, to couple the second input thereof with a second signal input port, wherein a characteristic impedance of a first transmission line portion between the output port and the first input thereof deviates from a nominal ring impedance thereof in a first direction, and wherein a characteristic impedance of a second transmission line portion between the output port and the second input thereof deviates from the nominal ring impedance thereof in a second direction, which is opposite to the first direction.

19. A high frequency power combiner circuit for obtaining an output signal on the basis of input signals from two or more signal input ports, the circuit comprising: a rat race coupler, wherein the rat race coupler is configured to provide an output signal at an output port of the rat race coupler on the basis of signals at a first input at a signal at a second input thereof; a first coupling structure coupled to the first input of the rat race coupler, for coupling the first input of the rat race coupler with a first signal input port; and a second coupling structure coupled to the second input of the rat race coupler, for coupling the second input of the rat race coupler with a second signal input port, wherein the first coupling structure and the second coupling structure are adapted to provide different phase shift over frequency, and wherein the first coupling structure comprises a phase shifter adapted to at least partially compensate for a difference of frequency variations of transmission characteristics from the first input of the rat race coupler to the output port, and from the second input of the rat race coupler to the output port in a system configured to operated at a design frequency of the rat race coupler.

20. The high frequency power combiner circuit of claim 19, wherein the second coupling structure comprises a pair of coupled transmission lines, wherein a first end of a first coupled transmission line is coupled with the second output of the rat race coupler, wherein a second end of the first coupled transmission line is coupled to a second end of a second coupled transmission line, which is adjacent to the second end of the first coupled transmission line, and wherein a characteristic impedance of said first and second transmission lines varies by no more that ±25%.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0056] Embodiments according to the invention will subsequently be described taking reference to the enclosed figures.

[0057] FIGS. 1A, 1B, 1C, and 1D show schematic illustrations of possible structures for a radio frequency (RF) power divider according to the prior art.

[0058] FIGS. 2A, 2B, 2C, and 2D show schematic illustrations representing theoretical performances of the structures as shown in FIGS. 1A-1D.

[0059] FIGS. 3A and 3B show further theoretical performances of the structures as shown in FIGS. 1A-1D.

[0060] FIG. 4 shows a table indicating the relative bandwidth of the four circuits according to the structures as shown in FIGS. 1A-1D.

[0061] FIGS. 5A, 5B, 5C, and 5D show schematic illustrations indicating examples of physical layouts of the power dividers indicated in FIGS. 1A-1D.

[0062] FIGS. 6A1 and 6A2 show modification examples of the Branch-line according to the prior art shown in FIG. 1C.

[0063] FIGS. 7A and 7B show examples of Rat-race couplers according to embodiments of the present application.

[0064] FIGS. 8A, 8B, and 8C show performance of modified Rat-race (rat race) coupler(s) according to embodiments of the present application.

[0065] FIG. 9 shows a table to indicate an amplitude unbalance and a relative bandwidth in dependence on the value of K.sub.GB according to embodiments of the present application.

[0066] FIG. 10 shows performance of a modified Rat-race according to embodiments of the present application.

[0067] FIG. 11 shows further performance of a modified Rat-race according to embodiments of the present application.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0068] FIG. 7 shows examples of a Rat-race coupler according to an embodiment of the present application. FIG. 7 (a) indicates a standard Rat-race coupler which is the same as indicated in FIG. 1 (B), and FIG. 7 (b) indicates a modified Rat-race coupler, i.e., an improved Rat-race.

[0069] As shown in FIG. 7 (b), the Rat-race (rat race) coupler is coupled an input signal provided at an input port, P1, of the rat race coupler to a first output of the Rat-race coupler, e.g. a location where a transmission line portion TL7B is connected to the rat race coupler ring, and to a second output of the Rat-race coupler, e.g. a location where a transmission line portion TL8B is connected to the rat race coupler ring; a first coupling structure, TL7B, coupled to the first output of the rat race coupler, to couple the first output of the rat race coupler with a first signal output port, P2; and a second coupling structure, formed by the transmission lines TL8B, TL5B, TL6B, coupled to the second output of the Rat-race coupler, to couple the second output of the Rat-race coupler with a second signal output port, P3; wherein a characteristic impedance, e.g. Z.sub.0=1/K.sub.GB*sqrt(2)*R.sub.0 (R.sub.0 is most typically, but not always 50Ω), of a first transmission line portion, TL1B, between the input port P1 and the first output of the Rat-race coupler deviates from a nominal ring impedance, e.g. sqrt(2)*R.sub.0, of the Rat-race coupler in a first direction, e.g. is smaller than the nominal ring impedance, and wherein a characteristic impedance, e.g. Z.sub.0=K.sub.GB*sqrt(2)*R.sub.0, of a second transmission line portion, TL2B, between the input port P1 and the second output of the rat race coupler deviates from the nominal ring impedance, e.g. sqrt(2)*R.sub.0, of the Rat-race coupler in a second direction, which is opposite to the first direction, e.g. is larger than the nominal ring impedance such that, at the design frequency of the rat race coupler, a larger signal power of the input signal is coupled to the first output port P2 than to the second signal output port P3, and such that a signal power of the input signal coupled to the first output port decreases, to become smaller than the signal power of the input signal coupled to the second output port, when the frequency of the input signal moves away from the design frequency of the rat race coupler (within an environment of the design frequency).

[0070] The characteristic impedance of a third transmission line portion, TL3B, between the second output of the Rat-race coupler and a further port, e.g., terminated port, of the Rat-race coupler deviates from the nominal ring impedance in the same direction as the characteristic impedance of the first transmission line portion TL1B. The characteristic impedance of a fourth transmission line portion, TL4B, between the first output of the rat race coupler and a further port, e.g. terminated port, of the rat race coupler deviates from the nominal ring impedance in the same direction as the characteristic impedance of the second transmission line portion TL2B.

[0071] In addition, as shown in FIG. 7 (b), the Rat-race is inherently unsymmetrical; therefore the phase shift between the second and third ports P2, P3 is zero only at centre frequency f0. In order to flatten the phase difference, a variant of the Schiffman phase shifter can be used, as shown in FIG. 7 (b). The transmission portions TL5B, TL6B are coupled lines λ/4 at centre frequency f0 and with even (odd) mode impedance Z0E (Z0O) such that Z0E*Z0O=R0.sup.2. The transmission line portion TL8B is a transmission with Z0=R0, long enough to minimize the coupling between the transmission line portions TL5B, TL6B and the Rat-race itself. The transmission line portion TL7B is a transmission with Z0=R0, and length equal to TL8B+λ/2 at the centre frequency f0.

[0072] FIG. 8 shows a performance of modified Rat-race coupler according to the embodiment of the present application. As already mentioned above, the nominal ring impedance is sqrt(2)*R.sub.0 and the characteristic impedance of the first and the third transmission line portions TL1B, TL3B is Z.sub.0=K.sub.GB*sqrt(2)*R.sub.0 and the characteristic impedance of the second and the fourth transmission line portions TL2B, TL4B is Z.sub.0=K.sub.GB*sqrt(2)*R.sub.o. FIG. 8 (a) shows values of scattering parameters S21 and S31, FIG. 8 (b) shows a value of S31/S21, and FIG. 8 (c) shows an absolute value of S31/S21.

[0073] FIG. 9 shows a table to indicate an amplitude unbalance and a relative bandwidth in dependence on the value of K.sub.GB according to the embodiment of the present application. In case K.sub.GB=1 is a conventional circuit structure. As shown in FIG. 9, a reasonable value for the absolute amplitude balance could be between 1 and 2 dB. This means that the reasonable range of K.sub.GB is bounded between 1 (i.e. conventional design) and about 1.1 (or 1/1.1). In addition, replacing K.sub.GB with 1/K.sub.GB is almost equivalent to swap the first signal output port P2 and the second signal output port P3. The result is very similar to the table shown as FIG. 9.

[0074] As a modification, a value of the characteristic impedance of the first transmission line portion TL1B differs from a value of the characteristic impedance of the third transmission line portion TL3B by no more than ±25%, or by no more than ±10% of the characteristic impedance of the first transmission line portion TL1B and the characteristic impedance of the second transmission line portion TL2B. Furthermore, a value of the characteristic impedance of the second transmission line portion TL2B differs from a value of the characteristic impedance of the fourth transmission line portion TL4B by no more than ±25%, or by no more than ±10% of the characteristic impedance of the second transmission line portion TL2B and the characteristic impedance of the first transmission line portion TL1B.

[0075] In addition, a multiplied value of the characteristic impedance of the first transmission line portion TL1B or the characteristic impedance of the third transmission line portion TL3B with the characteristic impedance of the second transmission line portion TL2B or the characteristic impedance of the fourth transmission line portion TL4B is equal to the value of square of the nominal ring impedance within a tolerance of ±10%. The value of the characteristic impedance of the first transmission line portion TL1B or the characteristic impedance of the third transmission line portion TL3B is smaller than the value of the characteristic impedance of the second transmission line portion TL2B or the characteristic impedance of the fourth transmission line portion TL4B.

[0076] Furthermore, the deviation range of the characteristic impedance from the nominal ring impedance is within ±20% or within ±10% of the value of the nominal ring impedance. That is, the value of the characteristic impedance of the first and the third transmission line portion deviates between +1% and +20%, or between +1% to +10% of the value of the nominal ring impedance, and the characteristic impedance of the second and the fourth transmission line portion deviates between −1% and −20%, or between −1% to −10% of the value of the nominal ring impedance, or vice versa.

[0077] As a further embodiment, the Rat-race is inherently unsymmetrical (see FIG. 7 (b)), therefore the phase shift between the first and second signal output ports P2, P3 is zero only at the centre frequency f0. In order to flatten the phase difference, a variant of the Schiffman phase shifter can be used, as shown in FIG. 7 (b). Coupled transmission lines TL5B, TL6B are coupled lines having an electrical length λ/4 at the centre frequency f0 and with even (odd) mode impedance Z0E (Z0O) such that Z0E*Z0O=R0.sup.2.

[0078] That is, a high frequency power divider circuit for distributing an input signal to two or more signal output ports according to the embodiment is shown in FIG. 7 (b). The circuit comprises: a rat race coupler, wherein the rat race coupler is configured to couple an input signal provided at an input port, e.g. P1, of the rat race coupler to a first output of the rat race coupler, e.g. a location where TL7B is connected to the rat race coupler ring, and to a second output of the rat race coupler, e.g. a location where TL8B is connected to the rat race coupler ring; a first coupling structure, TL7B, coupled to the first output of the rat race coupler, to couple the first output of the rat race coupler with a first signal output port, P2; and a second coupling structure, i.e., configured by TL8B, TL5B, TL6B, coupled to the second output of the rat race coupler, to couple the second output of the rat race coupler with a second signal output port, P3; wherein the first coupling structure and the second coupling structure are adapted to provide different phase shift over frequency; wherein the first coupling structure comprises a phase shifter adapted to at least partially compensate for a frequency variation of a phase difference between signals at the first output of the rat race coupler and at the second output of the rat race coupler in an environment of a design frequency of the rat race coupler.

[0079] In addition, the second coupling structure comprises a pair of coupled transmission lines TL6B, TL5B, wherein a first end of a first coupled transmission line TL5B is connected e.g. via TL8B with the second output of the rat race coupler, wherein a second end of the first coupled transmission line is connected to a second end of a second coupled transmission line, which is adjacent to the second end of the first coupled transmission line, and wherein the first end of the second coupled transmission line TL6B is connected to second signal output port, or constitutes the second signal output port P3. The first end of the first coupled transmission line TL5B is connected, e.g. via TL8B, with the second output of the rat race coupler via a further transmission line TL8B.

[0080] Furthermore, a characteristic impedance of further transmission line deviates from a reference impedance, e.g. 50Ω, by no more than ±5% or by no more than ±10%. In addition, a product of an even mode impedance Z.sub.0E of the pair of coupled transmission lines and of an odd mode impedance Z.sub.0O of the pair of coupled transmission lines deviates from a square of the reference impedance by no more than ±5% or by no more than ±10% or by no more than ±15%.

[0081] As a modification, an electrical length of the coupled transmission lines of the pair of coupled transmission lines deviates from a fourth of a wavelength at a design centre frequency of the rat race coupler by no more than ±5%, or by no more than ±10%, in other words, the coupled transmission lines are lambda/4 transmission lines at a design centre frequency of the rat race coupler within a tolerance of ±5% or ±10%. In addition, a length of the further transmission line TL8B is chosen to decouple stray fields of the pair of coupled transmission lines from the rat race coupler. Furthermore, an electrical length of a transmission line forming the first coupling structure is equal to an electrical length of the further transmission line TL8B plus half a wavelength, with a tolerance of ±a tenth of a wavelength.

[0082] FIG. 10 shows a performance of the modified Rat-race according to the embodiment of the present application. As shown in FIG. 10, the modification on Z0 of the transmission line portions TL1B, . . . , TL4B has almost no impact on the phase. Furthermore, the addition of the phase-compensating network has not at all impact on the amplitude.

[0083] FIG. 11 also shows a performance of the modified Rat-race according to the embodiment of the present application. As shown in FIG. 11, the addition of the phase-compensating network, i.e., the addition of the first and the second coupling structure, has an impact on the phase shift.

[0084] The above mentioned embodiments are related to the high frequency power divider. However, the same structure is used as a high frequency power combiner circuit for obtaining an output signal on the basis of input signals from two or more signal input ports. For example, the combiner circuit comprises a rat race coupler, wherein the rat race coupler is configured to provide an output signal at an output port, e.g. P1, of the rat race coupler on the basis of a signal at a first input of the rat race coupler, e.g. a location where TL7B is connected to the rat race coupler ring, and on the basis of a signal at a second input of the rat race coupler, e.g. a location where TL8B is connected to the rat race coupler ring; a first coupling structure TL7B coupled to the first input of the rat race coupler, to couple the first input of the rat race coupler with a first signal input port P2; and a second coupling structure, e.g. configured by TL8B, TL5B, TL6B, coupled to the second input of the rat race coupler, to couple the second input of the rat race coupler with a second signal input port P3; wherein a characteristic impedance, e.g. Z.sub.0=1/K.sub.GB*sqrt(2)*R.sub.0 of a first transmission line portion TL1B between the output port P1 and the first input of the rat race coupler deviates from a nominal ring impedance, e.g. sqrt(2)*R.sub.0 of the rat race coupler in a first direction, e.g. is smaller than the nominal ring impedance, and wherein a characteristic impedance, e.g. Z.sub.0=K.sub.GB*sqrt(2)*R.sub.0 of a second transmission line portion TL2B between the output port P1 and the second input of the rat race coupler deviates from the nominal ring impedance, e.g. sqrt(2)*R.sub.0 of the rat race coupler in a second direction, which is opposite to the first direction, e.g. is larger than the nominal ring impedance.

[0085] As a further example of a high frequency power combiner circuit for obtaining an output signal on the basis of input signals from two or more signal input ports, the combiner circuit comprises: a rat race coupler, wherein the rat race coupler is configured to provide an output signal at an output port, e.g. P1, of the rat race coupler on the basis of a signal at a first input of the rat race coupler, e.g. a location where TL7B is connected to the rat race coupler ring, and on the basis of a signal at a second input of the rat race coupler, e.g. a location where TL8B is connected to the rat race coupler ring; a first coupling structure TL7B coupled to the first input of the rat race coupler, to couple the first input of the rat race coupler with a first signal input port P2; and a second coupling structure, e.g. configured by TL8B, TL5B, TL6B, coupled to the second input of the rat race coupler, to couple the second input of the rat race coupler with a second signal input port P3; wherein the first coupling structure and the second coupling structure are adapted to provide different phase shift over frequency; wherein the first coupling structure comprises a phase shifter adapted to at least partially compensate for a difference of frequency variations of transmission characteristics from the first input of the rat race coupler to the output port, and from the second input of the rat race coupler to the output port, e.g. which affect a combination of signals at the first input of the rat race coupler and at the second input of the rat race coupler, in an environment of a design frequency of the rat race coupler.