DIRECTIONAL COUPLER AND POWER SPLITTER MADE THEREFROM

Abstract

A directional coupler including at least two coupled lines and at least three ports is disclosed. A first coupled line of the at least two coupled lines includes at least two ports such as an input port and an output port. A second coupled line of the at least two coupled lines includes a forward path and a backward path that are joined together at a third port to form a loop. To achieve a constant coupling attenuation over a broad frequency band and to minimize dimensions, the second coupled line includes a higher line impedance than the first coupled line, at least two times higher, and a coupling resistor is connected in series either in the forward path or in the backward path. In a multichannel power splitter, directional couplers are arranged in series with one another.

Claims

1. A directional coupler comprising: at least two coupled lines including a first coupled line and a second coupled line; and at least three ports including an input port, an output port, and a coupled port, wherein the first coupled line includes the input port and the output port, wherein the second coupled line includes a forward path and a backward path that is joined together at the coupled port to form a loop, and wherein in the second coupled line, a coupling resistor is connected in series in one of the forward path or the backward path.

2. The directional coupler of claim 1, further comprising a grounded inductance and a capacitance to form an LC-element, the grounded inductance and capacitance being connected to the loop between the coupling resistor and the coupled port.

3. The directional coupler of claim 2 further comprising a grounded resistor that is connected to the loop on a side of the coupling resistor.

4. A power splitter comprising at least two directional couplers including a first directional coupler and a second directional coupler, each of the first directional coupler and the second directional coupler including the directional coupler of claim 1.

5. The power splitter of claim 4, wherein the first directional coupler and the second directional coupler are connected in series and wherein each of the first directional coupler and the second directional coupler include a customized coupling attenuation.

6. The power splitter of claim 5, further comprising a slope compensator and an attenuator being connected in series about an output of the power splitter.

7. The power splitter of claim 6, wherein the attenuator is by-passed by a lossless path via radio frequency (RF) switches placed on both a first side and a second side of the attenuator.

8. The power splitter of claim 4 further comprising an additional directional coupler, a first radio frequency (RF) switch, a slope compensator, and a second RF switch that are connected in series with one another.

9. The power splitter of claim 8 wherein the first coupled line of the additional direct coupler is connectable to a grounded resistor via the first RF switch and the second coupled line of the additional directional coupler leads to a by-pass that is connected to the second RF switch.

10. A directional coupler comprising: a first coupled line; a second coupled line; and at least three ports including an input port, an output port, and a coupled port, wherein the first coupled line includes the input port and the output port, wherein the second coupled line includes a forward path and a backward path that is joined together at the coupled port to form a loop, and wherein in the second coupled line, a coupling resistor is connected in series in one of the forward path or the backward path.

11. The directional coupler of claim 10 further comprising a grounded inductance and a capacitance to form an LC-element, the grounded inductance and capacitance being connected to the loop between the coupling resistor and the coupled port.

12. The directional coupler of claim 11 further comprising a grounded resistor that is connected to the loop on a side of the coupling resistor.

13. A power splitter comprising: a first directional coupler; and a second directional coupler, wherein each of the first directional coupler and the second directional coupler include: a first coupled line; a second coupled line; and at least three ports including a first input port, a first output port, and a first coupled port, wherein the first coupled line includes the first input port and the first output port, and wherein the second coupled line includes a first forward path and a first backward path that is joined together at the first coupled port to form a loop.

14. The power splitter of claim 13, wherein each of the first directional coupler and the second directional coupler include a grounded inductance and a capacitance to form an LC-element, the grounded inductance and the capacitance being connected to the loop between a coupling resistor and the first coupled port.

15. The power splitter of claim 14, wherein each of the first directional coupler and the second directional coupler further include a grounded resistor that is connected to the loop on a side of the coupling resistor.

16. The power splitter of claim 13 wherein the first directional coupler and the second directional coupler are connected in series and wherein each of the first directional coupler and the second directional coupler include a customized coupling attenuation.

17. The power splitter of claim 13, further comprising a slope compensator and an attenuator being connected in series about an output of the power splitter.

18. The power splitter of claim 17, wherein the attenuator is by-passed by a lossless path via radio frequency (RF) switches placed on both a first side and a second side of the attenuator.

19. The power splitter of claim 13 further comprising an additional directional coupler, a first radio frequency (RF) switch, a slope compensator, and a second RF switch that are connected in series with one another.

20. The power splitter of claim 19 wherein the first coupled line of the additional direct coupler is connectable to a grounded resistor via the first RF-switch and the second coupled line of the additional directional coupler leads to a by-pass that is connected to the second RF switch.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIGS. 1 to 3 show in principle different embodiments of directional couplers according to the invention.

[0019] FIG. 4 is a diagram illustrating the technical progress of the invention over the state of art.

[0020] FIG. 5 shows another advantageous embodiment of the invention.

[0021] FIG. 6 is a diagramm of the frequency response of the circuit according to FIG. 5.

[0022] FIGS. 7 and 8 illustrate two inventive embodiments of a power splitter comprising directional couplers according to the invention.

DETAILED DESCRIPTION

[0023] FIG. 1 shows in principle an inventive directional coupler 1 in stripline technology. It consists of a first coupled line 2 the main line, having an input port P1 and a transmitted port P2, and a second coupled line 3 forming a loop and having a forward path 4 and a backward path 5 connected to a coupled port P3. In the backward path 5, is a coupling resistor 6, connected in series. A radio frequency signal is transmitted from the first coupled line 2 to the second coupled line 3. The second coupled line 3 has a higher impedance resulting in a thinner conductor track width than that of the first coupled line 2. To achieve broadband coupling, a line impedance of the second coupled line 3 is chosen at least two times higher than a line impedance of the first coupled line 2.

[0024] FIG. 2 shows an analogous directional coupler 7 in which the coupling resistor 6 is placed, in the forward path 4 for coupling-in of a signal from the second line 3 into the first line 2. FIG. 3 shows a combination of the examples of FIGS. 1 and 2.

[0025] The loop of the second coupled line 3 can be modified with respect to length, width, track width, distance of a coupling structure to set the desired frequency and a frequency response compensation. A position of the coupled port P3 of the forward path 4 and backward path 5 can be used as well to set the frequency response compensation. In other words, the wave impedance of the second coupled line 3, the length of the forward path 4, the length of backward path 5 and the resistor 6 which can be placed in the forward path 4 or the backward path 5 determine the transmission properties, especially the bandwidth of the coupler 1. The desired frequency range and frequency response can be tuned by determining these parameters. A coupling attenuation is adjusted only by the distance between the two coupling lines 2, 3.

[0026] Typical values for UHF application (470-950 MHz):

[0027] coupling resistor 220Ω

[0028] loop length 65 mm

[0029] loop width 5 mm

[0030] track width main line 2 mm

[0031] track width loop line 0,5 mm

[0032] coupling distance 0,5 mm

[0033] With parameters like these, a high coupling factor, almost constant over a wide frequency range, can be achieved as shown in FIG. 4. For comparison reasons, the frequency response of a conventional directional coupler is shown in broken lines which has an optimum between 0.60 and 0.70 GHz. In contrast thereto, the directional coupler of the invention has a more or less constant coupling factor nearly at the same level between about 0.35 to 0.95 GHz. In contrast to the state of art, the directional coupler according to the invention is a real broadband directional coupler.

[0034] FIG. 5 shows an embodiment of the directional coupler 8 according to the invention in which a grounded inductance 9 and a capacitance 10, forming a LC-element, are connected to the loop between the coupling resistor 6 and the third port P3 and a grounded resistor 11 is connected to the loop on the opposite side of the coupling resistor 6. The transmission characteristics can advantageously be adjusted by the value of these components which allows even greater flexibility of tunability of the frequency response.

[0035] Typical value for this embodiment are:

[0036] substrate . . . FR 4, 1.6 mm thick

[0037] coupling resistor 6 . . . 220Ω

[0038] inductance 9 . . . 20 nH

[0039] capacitance 10 . . . 1.2 pF

[0040] grounded resistor 11 . . . 330Ω

[0041] loop length . . . 53 mm

[0042] loop width . . . 4.5 mm

[0043] coupling distance . . . 0.5 mm

[0044] The frequency response achieved with these parameters is shown in FIG. 6. As can be gathered from the broken line, the coupling factor is almost constant in the wide range from 0.6 to 1.0 GHz. The mentioned parameters lead to active coupling structure dimensions of 55×12 mm or total external dimensions of 84×38 mm. Thus, the present broadband directional coupler 8 is just half as large as a conventional directional coupler whose length would have to be at least 110 mm at the same mean frequency of about 700 MHz.

[0045] To sum up, the directional coupler of the present invention has a nearly constant coupling factor over a wider frequency range than the state of art. Moreover, the directional coupler can be produced much smaller than comparable conventional directional couplers.

[0046] Due to the extraordinary properties of the directional coupler according to the invention several such couplers that each have a customized coupling attenuation, can be connected in series to form a broadband power splitter 12 as shown in FIG. 7. The number of series elements depends on the power input, i.e., as shown in FIG. 7, on the gain of a (low noise) amplifier 13 receiving the broadband signal from an antenna 14. As already mentioned before, the galvanic isolation of the outputs of the directional couplers result in high decoupling attenuations which cannot be realized with conventional power splitter technologies such as the Wilkinson divider. Moreover, the coupling attenuation can be exactly adjusted by the distance of the first coupling line and the main line, to the other coupling lines to extract only as much energy as necessary. The power with which the low noise amplifier provides is optimally utilized which minimizes losses.

[0047] The energy saved at the final output of the main line of power splitter 12, in comparison to the output of conventional power splitters with, for example, a tree structure, can, according to the invention, be used to provide additional receivers. As shown in FIG. 7, a slope compensator 15 and an attenuator 16 are connected in series, whereby the attenuator 16 is by-passed by a lossless path 17 by means of RF-switches 18, 19 placed on both of its sides. The slope compensator 15 serves to equalize the frequency response caused by the directional couplers 1. When the radio frequency-switch 18 connects the slope compensator 15 to the attenuator 16, and the RF-switch 19 connects the attenuator 16 to the output, then the output is used as one additional receiver channel. When, on the other hand, the RF-switches 18, 19 take the position as shown in FIG. 7, then the slope compensator 15 is directly connected to the output via the lossless path 17 so that the output is used as high power output to which e.g., a passive Wilkinson divider providing at least eight further receivers with a signal may be connected.

[0048] FIG. 8 shows a more advantageous arrangement in which the power splitter 12 includes directional couplers 1 that are followed in series by an additional directional coupler 20, a first RF-switch 21, a slope compensator 22 and a second RF-switch 23. The first coupled line of the additional directional coupler 20 is connectable to a grounded resistor 24. The ground resistor may be a 50 Ohm resistor, e.g., 50Ω. The second coupled line of the additional directional coupler 20 leads to a by-pass 25 of slope compensator 22 that is connected to the second RF-switch 23. In the position of the RF-switches 21 and 23, as shown in FIG. 8, the output of the first coupled line of the additional directional coupler 20 (the main line) is connected to the grounded resistor 24 that acts as wave absorber and the output of its second coupled line is switched to the final output. Thus, unwanted reflections in the main line are eliminated. In the other position of the RF-switches 21, 23; the main line of the additional directional coupler 20 is connected to the slope compensator 22 which is switched to the final output. In this constellation, the output is used as a high-power output to operate, for example, a Wilkinson divider which in turn may distribute the signal to at least eight further receivers.

[0049] To sum up, the power splitter according to the invention saves energy, in comparison with conventional power splitters, which can be used to provide additional receivers including additional splitters such as a passive Wilkinson divider.

[0050] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.