HK1075330B - A device for coupling radio frequency energy from various transmission lines using variable impedance transmission lines - Google Patents

Description

Apparatus for coupling radio frequency energy from various transmission lines using variable impedance transmission lines

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patent application No.09/563,328 filed on 3.5.2000, claiming the benefit of U.S. provisional patent application No.60/169,722 filed on 8.12.1999.

Technical Field

The present invention relates to radio frequency devices, and more particularly to methods and apparatus for coupling radio frequency energy from a transmission line.

Background

Prior to the present invention, the coaxial taps and couplers were installed by cutting the RF cable and then connecting with a coaxial jumper. The main disadvantage of this method is the excessive loss to the main cable. Later, U.S. patent 5,729,184 to Stein et al disclosed that taps could be used without connectorization, however, Stein et al still resulted in over 1dB loss to the main cable. Stein et al mention that it is theoretically possible to design taps with coupling losses as high as 20dB, but do not disclose a method of manufacturing such a device.

What is needed, therefore, are methods and apparatus having the ability to select the coupling loss and accompanying insertion loss in an RF system. In particular, such a method and apparatus should not only allow the wireless system to be tuned but should also allow the need for RF illumination of a device to be minimized with amplifiers and active devices.

Summary of The Invention

The present invention relates generally to coupling devices that derive energy from transmission lines. In one embodiment, the coupling device includes a contact that contacts the inner conductor of the transmission line through an aperture in the outer conductor of the transmission line. At least a portion of the contacts include a coil having a preselected shape defining at least one property of the energy transferred. The coupling device also includes a connector having an inner conductor coupled to the contact.

In another embodiment, the coupling device includes a length of wire having a preselected shape positioned between the contact and the connector. The length of wire is spaced from the ground plane to form a selected parasitic capacitance, and the shape of the wire at least partially defines the center frequency of the coupling device.

Brief description of the drawings

For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings. In these drawings:

FIG. 1A is a schematic diagram of a first coupling device according to the principles of the present invention;

FIG. 1B is a schematic diagram of a second coupling device according to the principles of the present invention;

FIG. 1C is a schematic diagram of a third coupling device according to the principles of the present invention;

FIG. 1D is a schematic diagram of a fourth coupling device according to the principles of the present invention;

FIG. 2 illustrates an assembled and cross-sectional view of a coupling device according to the principles of the present invention;

FIG. 3A illustrates an electronic assembly of an ultra-low insertion loss, high coupling loss coupling device such as that schematically illustrated in FIG. 1B;

FIG. 3B illustrates the electronic assembly of a low insertion loss, medium coupling loss coupling device such as that schematically illustrated in FIG. 1B;

FIG. 3C illustrates an electronic assembly of a low insertion loss, low coupling loss coupling device such as that schematically illustrated in FIG. 1C;

FIG. 3D illustrates the electronic assembly of a low insertion loss high frequency coupling device such as that schematically illustrated in FIG. 1A;

FIGS. 4A and 4B illustrate a cross-sectional side view and a top view, respectively, of a fifth coupling device;

FIGS. 5A and 5B illustrate a cross-sectional side view and a top view, respectively, of a sixth coupling device;

FIGS. 6A and 6B illustrate a cross-sectional side view and a top view, respectively, of a seventh coupling device;

7A-7C illustrate a cross-sectional side view, a top view, and a close-up view, respectively, of an eighth coupling device;

FIG. 8 illustrates another embodiment of the coupling device of FIGS. 7A-7C;

FIG. 9 is a graph illustrating two exemplary insertion loss samples using a variation of the coupling arrangement of FIG. 8;

FIG. 10 is a graph illustrating two exemplary coupling response samples using a variation of the coupling device of FIG. 8;

fig. 11A-C illustrate a cross-sectional unassembled side view, an assembled side view, and a top view, respectively, of the ninth coupling device.

Description of The Preferred Embodiment

The principles of the present invention and its advantages are best understood from the exemplary embodiments shown in figures 1-3 of the drawings. Like numbers refer to like elements throughout.

Fig. 1A and 3D show a schematic diagram and a configuration diagram, respectively, of a coupling device for coupling RF energy from one coaxial cable to a second coaxial cable, RF radiator or RF amplifier. Although coaxial cables are shown, it is understood that any transmission line may be and tapped from. A hole is formed through the outer conductor 100 of the main transmission line and a contact 104(300 of fig. 3D) is inserted into the hole to contact the center conductor 102 of the main transmission line. The contacts may be spring loaded, but it will be appreciated that any means of contacting the center conductor may be used. It is preferred that center conductor contact 104(300) be insulated, but this is not required in accordance with the principles of the present invention. The shaft of contact 104(300) is insulated to prevent inadvertent contact with outer conductor 100.

The inner transmission line 106(326 of fig. 3D) of the coupler is a length of low-loss wire. The length and diameter of the wire determine the frequency response of the device and, to some extent, the coupling and insertion losses of the device. The wires of the transmission line may be insulated so that the wires may be longer for lower frequencies while still being desirable for the purposes of the present invention.

One principle of the invention is to use highly conductive wires. This prevents dielectric loss due to insulation.

The wire is connected to the center conductor pin 111(310) of the output connector, represented by outer conductor 110 and center conductor 111 (310). It will be appreciated that the output may be a hard-wired cable, a directly connected antenna, an amplifier or equivalent load. Whichever load is in accordance with the principles of the present invention.

Lossy elements 112(314) are connected between the center pin 111(310) of the output connector and the outer shield 110 to provide better impedance matching with devices connected to the output connector. A loss element is added to the implementation of the invention, but this is not essential in terms of the principle of the invention.

The configurations of fig. 1A and 3D are for coupling devices with coupling values from approximately-15 dB to-6 dB. The lossy elements of the internal transmission lines 106(306) are low-loss wires. The length and diameter of the wire determine the frequency response of the device and, to some extent, the coupling and insertion losses of the device. The wires of the transmission line may be insulated so that the wires may be longer for lower frequencies while still being desirable for the purposes of the present invention. Fig. 1B, 3A and 3B are schematic and layout views, respectively, of another coupling device designed in accordance with the principles of the present invention to couple very little RF energy from a main cable to an output connector, thereby greatly reducing insertion loss within the main cable.

A hole is formed through the main transmission line outer conductor 100 and a contact 104(300) is inserted into the hole to contact the main transmission line center conductor 102. The contacts may be spring loaded, but it will be appreciated that any means of contacting the center conductor may be used. It is preferred that center conductor contact 102 be insulated, but this is not necessary to meet the principles of the present invention.

The internal transmission line 114 (306 and 320 in fig. 3A and 3B) is a length of low loss, non-insulated wire, but may be insulated for longer lengths to accommodate lower frequencies while still being in accordance with the principles of the present invention. The transmission line wire is not in contact with any medium except at the connection to the termination point.

The configurations of fig. 1A and 3D are for coupling devices with coupling values from approximately-15 dB to-6 dB. The lossy elements of the inner transmission lines 106(326) are low loss wires. The length and diameter of the wire determine the frequency response of the device and to some extent also the coupling loss and insertion loss of the device. The parasitic capacitance 105 depends on the diameter of the wire and the distance from the ground plane 108(308) (202 in fig. 2) shown in fig. 3D. The parasitic capacitance and shape of the wire determine the center frequency response of the device. The wires of the transmission line may be insulated so that the wires may be longer for lower frequencies while still being desirable for the purposes of the present invention. As shown in FIG. 3D, the PC board 312 includes a number of holes 316, the function of which will be described below.

One principle of the invention is to use highly conductive wires. This prevents dielectric loss due to insulation. Another principle of the invention is to avoid contact of the transmission line wire with any dielectric surface except at the connection points.

The wire is connected to the center conductor pin 111(310) of the output connector, represented by outer conductor 110 and center conductor 111 (310). It will be appreciated that the output may be a hard-wired cable, a directly connected antenna, an amplifier or equivalent load. Whichever load is in accordance with the principles of the present invention.

Yet another principle of the present invention is to sample the field around the pin 102, as shown in particular at 302 in fig. 3A and 318 in fig. 3B, by capacitive coupling instead of connecting the transmission line to the center contact 102 (300). The heavier the sampling, the greater the coupling energy.

In fig. 1B, element 132 represents the complex impedance of the dc blocking connection between the transmission line 114 and the pin 104 connected to the main cable center conductor 102. This connection is also shown in fig. 3A and 3B. This connection may be a shallow connection allowing a small amount of power to be coupled (from 20 to 30dB) as shown in fig. 3A, or a deep connection allowing a coupling value of from 15 to 20dB as shown in fig. 3B. High coupling losses result in insertion losses of 0.3 to 0.05 dB.

The configuration of fig. 1C and 3C allows the coupling device to transmit several selected frequencies with low insertion loss at those frequencies. The internal transmission line is labeled 116 in fig. 1C and 322 in fig. 3C. The lumped impedance 117 in fig. 1C and the coil 325 shown in fig. 3C allow the coupling device to be configured to emphasize a selected frequency while substantially reducing insertion loss at the selected frequency.

Yet another principle of the present invention is to use lumped impedance inputs such as those shown in fig. 1C and 3C and the selective coupling of fig. 1B and 3A and 3B, which allows the designer to select not only the coupling, insertion loss, but also the desired frequency so that several frequencies can be transmitted and received on the same cable.

Fig. 1D generally relates to the present invention with dc blocking complex impedance 119 at the input of the coupled port. This allows the designer to configure the coupling device to set the reflection loss and to some extent the frequency response. Here, the transmission line (internal) is labeled 118.

Fig. 3D generally relates to the coupling arrangement of the present invention for a single frequency around 2 GHz. This device, like the other devices described herein, applies the principle that different wire sizes are required for selecting coupling loss and insertion loss. It is to be understood that any combination of these principles of the invention is also an integral part of the invention.

Fig. 2 relates generally to the mechanical aspects of the invention. This assembly comprises three plastic parts, a bottom 210, a top 206 and a top seal 214. Coupling port connector 200 is shown as an "N" connector, but any suitable RF connector may be used. The connection to the coupling port may also be "squished" or "hard wired". The connection to the main cable is indicated at 208, but it is understood that any probe or other device that contacts the center conductor of the main cable is also contemplated as falling within the principles of the present invention.

Tie-down screws 212 are used to connect the top and bottom of the device to the main cable. The use of tie-down screws facilitates installation.

Screws 216 are disposed at opposite corners of the attachment flange and pass through holes 316 in the PC board 312 (204 in fig. 2) to act as anti-rotation and also provide a ground path from the main cable to the outer conductor of the coupling port. While anti-rotation is not required for the device to work, it adds to the overall strength. Grounding is not required for operation above 400MHz, but improves overall electrical stability. The screws 216 are typically partially installed at the time of manufacture and are installed last at the time of installation.

Referring now to fig. 4-9, additional embodiments are illustrated, as will be described in detail below.

Turning first to fig. 4A and 4B, in one embodiment, a coupling device 400 contacts a center conductor (not shown) of a coaxial cable with a length of wire wound coil 402 (e.g., a spring). The coupling device 400 may include a housing of plastic or non-ferromagnetic material, but the housing is not shown for clarity. The spring 402 may be a non-ferromagnetic material spring with a constant or variable pitch. The spring 402 in this example includes a coil portion 412, a straighter extension atop the coil portion 412, and a straighter extension 412 below the coil portion 412. The wire diameter, coil diameter, and number of turns of the spring 402 may be selected according to the desired effect, such as coupling and insertion loss.

The bottom extension 416 of the spring 402 is connected to the center conductor pin 406 through the secondary transmission line 404. A Printed Circuit Board (PCB)408 may be used to provide a mounting surface for the spring 402, the secondary transmission line 404, and the center conductor pin 408. In this example, an RF interface connector 410 is mounted on the opposite side of the spring 402, connected to the spring 402 by the center conductor pin 408 and the secondary transmission line 404. One or more holes (not shown) are provided in the PCB 408 to provide signal connection paths to both sides of the PCB 408 and to serve as mounting holes.

In operation, the spring 402 may transform the impedance from the transmission line characteristic impedance of the coaxial cable (e.g., approximately 50 or 75 ohms) to a higher desired value. This transformation is achieved substantially in the imaginary plane and the complex impedance of the spring 402 determines the overall frequency response and the energy extracted from the coaxial cable. Specifically, the transformation is in the imaginary plane because the complex impedance is primarily a series inductance with the inter-turn parasitic capacitance. Thus, in general, the impedance has almost no resistive real plane component.

The ratio of the complex impedance to the transmission line impedance determines the amount of energy extracted from the transmission line. This complex impedance is in part a function of the spring 402 and the diameter, pitch, number of turns, and wire length. In addition, the top and bottom extensions 414, 416 of the spring 402 may provide second order control of the total complex impedance. In addition, the secondary transmission line 404 may be used to perform a transformation to bring the complex impedance to a desired value. For example, the secondary transmission line 404 may control the frequency response and the power extracted/fed into the coaxial cable from the coaxial cable.

Turning now to fig. 5A and 5B, in another embodiment, a coupling device 500 includes a coil 502, a secondary transmission line 504, a center conductor pin 506, a PCB 508, and an RF interface connector 510, connected in a similar manner as described with respect to fig. 4A and 4B. In this example, the secondary transmission line 504 can be shaped in any manner that allows the desired complex impedance to be obtained over the desired frequency band. For example, the coil 502 acts as a primary impedance transformer, while the secondary transmission line 504 may be a transmission line or any passive element (such as a lumped element resistor, capacitor, or inductor) that may be used to achieve the desired insertion and coupling losses.

Turning now to fig. 6A and 6B, in yet another embodiment, the coupling device 600 includes a coil 602, which may be similar to the coils 402 and 502 described with respect to fig. 4 and 5, respectively. The coil 602 may comprise a single fixed or variable pitch non-ferromagnetic coil, and may be fixed or variable in diameter. The coil 602 is directly connected to the center pin 604 of the RF interface connector 606. As previously explained, the insertion loss and coupling loss of the coupling device 600 may be determined by designing the wire length, coil diameter, number of turns, and pitch of the coil 602.

This example may be constructed without a PCB. This may simplify the manufacture of the coupling device 600, reducing costs, but with similar benefits. Furthermore, the direct connection of the coil 602 to the RF interface connector 606 avoids the energy loss that would occur through a PCB connection. Furthermore, the frequency response due to the presence of the coil 602 may be broadband. The broadband frequency response arises in part because the direct connection approach described above eliminates the circuit board and the use of secondary coils/transmission lines, which reduces the total secondary/parasitic impedance. This reduction raises the resonant frequency of the coil 602 itself outside the frequency band of interest, resulting in a wide frequency band of frequency response.

Referring now to fig. 7A-7C, in yet another embodiment, the coupling device 700 includes a coil 702 directly connected to a center pin 704 of an RF interface connector 706. A portion of the coil 702 is encapsulated within a material 708, such as a low-loss plastic (e.g., polystyrene). In this example, only a small portion of the coil 702 near the bottom is left unencapsulated, while the majority of the top is encapsulated.

The upper portion of the coil 702 acts as the primary impedance transformer, whose complex impedance can be maintained by mechanically constraining the size of the coil with material 708. The lower portion of the spring 702 acts as a secondary impedance transformer but allows compression, it is this portion of the coil 702 that actually maintains contact with the center conductor of the main cable. Referring specifically to fig. 7C, for purposes of illustration, coil 702 is wound 14 turns with american wire diameter (AWG)25 gauge wire, with an outer diameter of 0.120 inches. The portion of the coil 702 labeled "a" represents the upper 12.5 turns, encapsulated with material 708. The portion of the coil 702 labeled "B" represents the next 1.5 turns, without encapsulation.

Such encapsulation may be characterized as allowing the coupling device 700 to be mounted to a coaxial cable (e.g., the non-sealing portion may be compressed or expanded to engage the cable) by varying the thickness of the dielectric sheath while controlling the coil 702. Furthermore, the frequency response due to the presence of the coil 702 may be broadband. The broadband frequency response arises in part because the direct connection approach described above eliminates the circuit board and the use of secondary coils/transmission lines, which reduces the total secondary/parasitic impedance. This reduction raises the resonant frequency of the coil 702 itself outside the frequency band of interest, resulting in a wide frequency band frequency response.

Referring now to fig. 8, in yet another embodiment, the coupling device 700 of fig. 7A-7C includes a tubular extension 710 that can extend from the device 700 into a coaxial cable. The extension 710 may be formed as part of the coupling device 700 or may be added to the coupling device as a separate assembly. The extension 710 can serve various functions, such as serving as a stabilizer for the coil 702 and as an anti-rotation device.

Additionally, a cavity 712 may be formed within the housing 714 of the coupling device 700. The frequency response can be fine tuned by adjusting the cavity 712 size to adjust the parasitic capacitance. More specifically, the cavity 712 may form an electromagnetic resonant circuit. When the coil 702 (or transmission line) is loaded into the cavity 712, the field surrounding the coil 702 is limited (e.g., due to electromagnetic boundary conditions that are not present in free space). Thus, the cavity 702 will present a substantially imaginary complex impedance, which may be capacitive.

Turning now to fig. 9, a graph 900 illustrates a typical insertion loss due to a tap. The X-axis 902 of the graph 900 represents frequency (MHz) and the Y-axis 904 represents insertion loss (dB). The two samples 906 and 908 each represent typical performance conditions for two different variations of the coupling device 700 of FIG. 8. The sample 906 illustrates the result when the nominal power is extracted, and the sample 908 illustrates the result when the extracted power is increased by around 3 dB.

Turning now to fig. 10, a graph 1000 illustrates a typical coupling response due to a tap. The X-axis 1002 of the graph 1000 represents frequency (MHz) and the Y-axis 1004 represents coupling loss (dB). The two curves 1006 and 1008 each represent typical performance behavior for two different variations of the coupling device 700 of fig. 8. Curve 1006 illustrates the results when the nominal power is extracted, while curve 1008 illustrates the results when the extracted power is increased by around 3 dB.

The samples 906, 908 and 1006, 1008 in the graphs of fig. 9 and 10, respectively, are derived from the two variants of fig. 8. The samples 906 and 1006 correspond to results from one variation, while the samples 908 and 1008 correspond to results from another variation. For example, the variation represented by samples 906 and 1006 may be fabricated with one coil base length, coil inner diameter, coil wire length, and coil turns. In the case of baseline determination, the samples 908 and 1008 were obtained when making a modification of the same coil length but with 20% reduction in coil turns, 10% increase in coil diameter, and 5% increase in coil wire length. These two variants are derived from the fact that the diameter and the pitch of the coil are constant. Similar results may be obtained with one or both of these parameters in place of or in combination with the changed parameters. In addition, it is to be understood that various parameters may be used to produce a desired variation.

Referring now to fig. 11A-C, in yet another embodiment, an exemplary coupling device 1100 includes a coil 1102, a secondary transmission line 1104, a center conductor pin 1106, a PCB 1108, and an RF interface connector 1110 connected in a similar manner as described with respect to fig. 4 and 5. As previously explained, the secondary transmission line 1104 may be shaped in any manner that allows the desired complex impedance to be obtained over the desired frequency band. For example, the coil 1102 acts as a primary impedance transformer, while the secondary transmission line 1104 may be a transmission line or any passive element (such as a lumped resistive, capacitive, or inductive element) that may be used to achieve the desired insertion and coupling losses.

The device 1100 includes a housing 1112. In this example, the housing 1112 includes a lower housing 1112a, an upper housing 1112b, and a top plate 1112 c. The top plate 1112c may be secured to the upper housing 1112b by a plurality of screws 1114, and the upper housing 1112b may be secured to the lower housing 1112a by a plurality of screws 1116. Other fastening means may be used in place of or in addition to screws 1114 and 1116.

The device 1100 may also include a tubular extension 1118 and a cavity 1120 as described with respect to fig. 8. The tubular extension 1118 may extend from the device 1100 into the coaxial cable. The extension 1118 may be formed as part of the coupling device 1118 or may be added to the coupling device as a separate assembly. The extension 1118 can serve various functions, such as serving as a stabilizer for the coil 1102 and as an anti-rotation device. A cavity 1120 may be formed within the housing 1112 of the coupling device 1100. For example, a cavity may be formed within the upper housing 1112b, as shown. The frequency response can be fine tuned by adjusting the size of the cavity 1120 to adjust the parasitic capacitance, as previously described.

While the invention has been described in conjunction with specific embodiments, the description is not intended to be construed in a limiting sense. These disclosed embodiments and others of the present invention will become apparent to those skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other devices for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.

Claims (18)

1. A coupling device for deriving energy from a transmission line, the coupling device comprising:

a contact for contacting the inner conductor of the transmission line through an aperture in the outer conductor of the transmission line, wherein a first portion of the contact comprises a coil having a preselected shape defining a property of the transmitted energy selected from the group consisting of frequency, coupling loss, and insertion loss, and wherein a second portion of the contact is configured to form a connection between the inner conductor of the transmission line and the first portion of the contact; and

a connector having an inner conductor coupled to the contact.

2. The coupling device of claim 1, further comprising a length of wire having a preselected shape disposed between said contact and said connector, wherein said wire is spaced from a ground plane to form a selected parasitic capacitance, said shape of said wire operable to at least partially define a center frequency of said coupling device.

3. The coupling arrangement of claim 2, wherein said wire is a passive component.

4. The coupling device of claim 1, further comprising:

a housing; and

a cavity within said housing, wherein said cavity receives said contact and wherein said cavity is operable to induce said parasitic capacitance.

5. The coupling device of claim 1, further comprising an enclosure surrounding at least a portion of the coil, the enclosure mechanically confining the surrounded portion of the coil.

6. The coupling arrangement of claim 1 wherein said coil has a variable pitch.

7. The coupling arrangement of claim 1 wherein said coil has a variable diameter.

8. The coupling arrangement of claim 1 wherein the second portion of the contact is a first straight end portion, the contact further comprising a second straight end portion, the first and second straight end portions being located at respective ends of the coil, the first straight end portion engaging the transmission line and the second straight end portion being coupled to the inner conductor of the connector.

9. A radio frequency coupling device, the radio frequency coupling device comprising:

a housing; and

a circuit at least partially within the housing, the circuit comprising:

a contact for engaging a transmission line for transmitting energy, said contact package

Comprising a coil part configured to define properties of the transmitted energy, said properties being selected

From the group consisting of frequency, coupling loss, and insertion loss;

a conductor pin coupled to the contact; and

an interface connector coupled to the conductor pin.

10. The radio frequency coupling device of claim 9 wherein said housing further comprises an extension extending from said radio frequency coupling device into said transmission line, said extension at least partially surrounding said contact and operable to limit lateral movement of said contact relative to said housing.

11. The radio frequency coupling device of claim 10 wherein the extension is tubular.

12. The radio frequency coupling device of claim 10 wherein said extension is operable to prevent rotation of said radio frequency coupling device relative to said transmission line.

13. The radio frequency coupling device of claim 9, further comprising a wire positioned between the contact and the conductor pin, the wire being separated from the ground plane at least in part by an air gap and configured to further define a property of the transmitted energy.

14. The radio frequency coupling device of claim 9, further comprising a cavity within the housing, wherein the cavity receives the contact, and wherein the cavity is sized to adjust a parasitic capacitance of the radio frequency coupling device.

15. A method of coupling energy from a transmission line having separate inner and outer conductors, said method comprising the steps of:

forming a hole through the outer conductor of the transmission line to expose a portion of the inner conductor;

inserting a coil contact through the aperture;

changing the position of the coil contact relative to the inner conductor to engage the inner conductor, the changing being performed automatically by the coil contact; and

electrically coupling the coil contact with an interface.

16. The method of claim 15, further comprising inserting an extension into the transmission line, the extension extending from the interface and at least partially surrounding the contact.

17. The method of claim 15, further comprising altering with the coil a property of the transmitted energy selected from the group consisting of frequency, coupling loss, and insertion loss.

18. The method of claim 15, wherein the step of electrically coupling the coil contact with the interface comprises disposing a length of wire between the coil contact and the interface.