EP3972048A1

EP3972048A1 - Bias tee apparatus and method of use thereof

Info

Publication number: EP3972048A1
Application number: EP21275100.2A
Authority: EP
Inventors: James Parish
Original assignee: Radio Design Ltd
Current assignee: Radio Design Ltd
Priority date: 2020-09-21
Filing date: 2021-07-27
Publication date: 2022-03-23
Also published as: GB202014836D0

Abstract

Bias tee apparatus is provided for radio frequency (RF) apparatus. The bias tee apparatus includes an input pathway for the passage of one or more radio frequency (RF) communication signals and direct current (DC) therealong in use. The input pathway divides into a DC bypass pathway to allow the passage of direct current (DC) therealong in use and an RF communication signal pathway for the passage of one or more RF communication signals therealong in use. The DC bypass pathway including at least a first inductor means for helping to prevent the passage of one or more RF communication signals therealong in use, and the RF signal pathway including at least first and second capacitor means for helping to prevent the passage of DC therealong in use. At least one of the at least first or second capacitor means includes a sleeve or tube member and at least a second inductor means is located in an interior of the sleeve or tube member.

Description

This invention relates to bias tee apparatus for use in radio frequency (RF) apparatus and to a method of using the same.
Although the following description refers almost exclusively to bias tee apparatus for use in radio frequency (RF) filter apparatus, it will be appreciated by persons skilled in the art that the bias tee apparatus could be used in any apparatus where at least direct current (DC) is required to be separated from one or more radio frequency signals that are being transmitted and/or received via the RF apparatus in use.
Wireless telecommunication networks that are transmitting and/or receiving one or more radio frequency signals typically utilise RF filter apparatus to allow the transmission and/or receiving of one or more RF communication signals, typically high frequency RF signals in the range of 400MHz or greater, at a particular desired radio frequency therethrough but which prevent or substantially prevent the transmission and/or receiving of one or more RF signals outside the particular desired radio frequency. RF filter apparatus is typically located on a telecommunication mast that contains other electronic equipment, such as tower mounted amplifiers (TMAs) for amplifying RF communication signals, RF combiners, antennas for transmitting and/or receiving the RF communication signals, motorised antenna position equipment (i.e. Remote Electrical Tilt (RET) motors) and/or the like. This electronic equipment often requires a direct current (DC) supply and/or one or more low frequency control signals (typically below 15MHz) for operation of the same. The low frequency control signals are often referred to as Antenna Interface Standards Group (AISG) control signals and relate to standard based control signals for digital remote control and monitoring of antenna line devices in wireless communication systems. The DC and low frequency control signals are typically passed through the RF filter apparatus (i.e. between an input and output of the RF filter apparatus) in order to power and/or control the electronic equipment above the RF filter apparatus on the mast. A bias tee arrangement is often used in the RF filter apparatus so that the DC and low frequency control signals can be separated out from the higher frequency RF communication signals.
A conventional bias tee arrangement typically comprises a DC and low frequency control signal bypass path that allows the DC and lower frequency control (LF) signals to pass along the same rather than through the main RF communication signal pathway. The bypass path can be fed back into the RF communication signal pathway at a higher point in the network. The RF communication signal pathway and filter apparatus will often contain DC and LF short circuits. It is therefore necessary in many cases to isolate the DC and LF signals from the RF communication signal pathway to avoid short-circuiting the DC and LF signals. If there is insufficient isolation between the bypass path and the RF cavities, intermodulation (IM) products are generated by non-linear elements that are connected to the bypass path, such as LEDs. The IM products leak back into the RF communication signal and significantly effects the functionality and efficiency of the RF filter.
A conventional bias tee arrangement 2 for use with RF filter apparatus is shown in Figures 1a and 1b. Input pathway 4 allows the passage of the RF communication signal, the DC and the low frequency control signals along the same. The pathway 4 then splits at junction 6 to provide pathway 8 for the passage of RF communication signals therealong and bypass pathway 10 for passage of the DC and control signals therealong. The bypass pathway 10 typically includes a series inductor in the form of an inductive coil 12 which aims to provide sufficient impedance to prevent or substantially prevent the passage of RF signals therealong but allow the passage of DC and the one or more control signals therealong. A series capacitor 14 is provided in the RF communication signal pathway 8 to prevent or substantially prevent the DC and control signals from passing along the same.
Figure 1b shows how the conventional bias tee arrangement in Figure 1a fits into typical RF filter apparatus 16. The filter apparatus 16 includes a housing body 18 with a lid 20 covering an open end of body 18. A plurality of resonant cavities 22 are defined in housing body 18, each cavity 22 having a resonator 24 that resonates at a desired frequency for the apparatus 16. An input port 26 of the filter apparatus 16 includes a connector body 28 with an input connector pin 30 provided therethrough which passes into the first resonator cavity 22. The connector pin 30 represents the input pathway 4 for the RF signals, DC and control signals to pass along the same.
The bypass pathway 10 is connected to the input connector pin 30 at one end and to a printed circuit board (PCB) 32 provided externally of the housing body 18 on the lid 20 at an opposite end. A coupling disk 34 is provided in the RF communication signal pathway 8 in the resonator cavity 22 to form the capacitor 14 of the bias tee.
The arrangements shown above can provide good isolation between the RF communication signal pathway 8 and the DC/control signal pathway 10 in the RF filter apparatus for frequencies above 1GHz, and particularly above 2GHz. However, for frequencies below 1GHz, there is insufficient isolation between the pathways 8 and 10 and RF leaks onto the PCB and generates intermodulation distortion (IMD). The IMD can then leak back onto the RF communication signal pathway 8 and cause interference in the RF receiver connected to the RF filter apparatus. In order to help overcome this problem, a number of capacitors and inductors could be provided. However, space is normally very limited in RF apparatus and there is often insufficient space to provide sufficient numbers of inductors and capacitors to provide the required level of isolation between the bypass pathway and the RF communication signal pathway.
In an attempt to overcome this problem and provide improved isolation between the bypass pathway 10 and the RF communication signal pathway 8, it is known to provide a second capacitor in the form of a sleeve or tube 36 with a wire located through the same, the tube 36 being located in a cavity 38 of the filter body housing 18, as shown in figures 2a and 2b. The second capacitor helps to ground (and therefore helps to block) residual RF from passing along the bypass pathway 10. However, this bias tee arrangement still provides insufficient isolation between the bypass pathway 10 and the RF communication signal pathway 8 for frequencies in the range of 400MHz to 1GHz.
It is therefore an aim of the present invention to provide bias tee apparatus that overcomes the abovementioned problems.
It is a further aim of the present invention to provide a method of using bias tee apparatus that overcomes the abovementioned problems.
It is a further aim of the present invention to provide electronic apparatus, and preferably RF apparatus, and yet further preferably RF filter apparatus, including bias tee apparatus.
It is a further aim of the present invention to provide a method of using electronic apparatus, and preferably RF apparatus, and yet further preferably RF filter apparatus, including bias tee apparatus.
According to a first aspect of the present invention there is provided a bias tee apparatus for radio frequency (RF) apparatus, said bias tee apparatus including an input pathway for the passage of one or more radio frequency (RF) communication signals and direct current (DC) therealong in use, the input pathway dividing into a DC bypass pathway to allow the passage of direct current (DC) therealong in use and an RF communication signal pathway for the passage of one or more RF communication signals therealong in use, the DC bypass pathway including at least a first inductor means for helping to prevent the passage of one or more RF communication signals therealong in use, and the RF signal pathway including at least first and second capacitor means for helping to prevent the passage of DC therealong in use, characterized in that at least one of the at least first or second capacitor means includes a sleeve or tube member and at least a second inductor means is located in an interior of the sleeve or tube member.
The provision of the at least second inductor means located in the tube or sleeve member of at least one of the capacitor means provides improved isolation between the DC bypass pathway and the RF communication signal pathway, without taking up additional space within the RF apparatus housing and without requiring additional bias tee components to be provided external to the RF apparatus housing. This prevents or significantly reduces IMD associated with prior art bias tee arrangements, which in turn reduces any adverse effects of the RF response in low RF band applications. This allows for greater flexibility in the cavity design in the RF filter apparatus. In addition, with improved isolation of the DC bypass pathway and the RF signal pathway, fewer bias tee components are required in the apparatus overall, thereby saving both space and cost.
In one embodiment the DC bypass pathway can rejoin with the RF communication signal pathway to form an output pathway which may be within the RF apparatus or may be external to the RF apparatus.
Preferably the output pathway is arranged to allow the passage of one or more RF signals and DC therealong in use.
Preferably the input pathway, bypass pathway, RF pathway and/or output pathway can include any or any combination of a transmission line, co-axial structure, microstrip (PCB), stripline, wire, electrically conductive track member and/or the like
Preferably the at least first inductor means is any component that provides inductance or a required level of inductance, such as for example, an inductor, a series inductor, a coil and/or the like.
Preferably the inductance provided by the first inductor means provides sufficient inductance to reduce, prevent or substantially prevent the passage of one or more RF signals through the same in use.
Preferably one of the at least first and second capacitors is in the form of a series capacitor and/or a coupling disk and the other of the at least first and second capacitors is in the form of the sleeve or tube member.
Preferably the at least first capacitor means is in the form of a series capacitor, coupling disk and/or the like.
Preferably the at least second capacitor means is in the form of the sleeve or tube member.
Preferably the sleeve or tube member includes a body having a first open end and a second open end opposite to the first open end.
Preferably the at least second inductor means is in the form of an inductor, a series inductor, a coil and/or the like.
Preferably the at least second inductor means or coil is provided centrally or substantially centrally of the sleeve or tube member.
Preferably the at least second inductor means or coil is co-axial with the sleeve or tube member.
Preferably a central axis of the second inductor means or coil is provided parallel or substantially parallel to one or more interior walls of the sleeve or tube member.
Preferably a main body portion of the second inductor means or coil is provided a spaced distance apart from interior walls of the sleeve or tube member.
Preferably the length of the at least second inductor means or coil, the diameter of the at least second inductor means or coil, the diameter of the wiring forming the at least second inductor means or coil, the number of coil turns of the at least second inductor means or coil and/or the like can be adjusted to control the inductance of the bias tee apparatus. This in turn allows the isolation between the bypass pathway and the RF communication signal pathway to be controlled, adjusted and/or improved.
Preferably a coil is a length of material (such as for example ― wire) in a joined sequence of concentric rings. Preferably a turn is provided between each ring of the sequence of concentric rings.
Preferably the sleeve or tube member of the at least first and/or second capacitor means is referred to as a blocking sleeve or tube member in that is helps to block the passage of DC and grounds residual RF signals via a RF apparatus housing in use.
In one embodiment one of the at least first and second capacitor means is a series capacitor and blocks DC and LF signals from entering the RF apparatus, thereby avoiding short-circuiting of the DC and LF signals, while allowing RF communication signals to pass through the RF apparatus. The other of the at least first and second capacitor means is a shunt capacitor and short-circuits residual RF signals, thereby attenuating the RF signals in the DC and LF signal pathway (increasing the effective isolation). The capacitance value of the second capacitor is preferably such that it presents a high enough impedance to the LF signals to avoid attenuating the LF signals (i.e. it prevents leaking of the signals through to ground)).
Preferably the sleeve or tube member is arranged so as to provide sufficient capacitance (i.e. to block or substantially block the passage of DC and LF through the same in use).
In one embodiment the sleeve or tube member is cylindrical or substantially cylindrical in form. However, the sleeve or tube member could have any cross sectional shape as required, such as for example be square, oval, triangular, rectangular and/or the like.
Preferably the sleeve or tube member is made from, consists of or includes an electrically conductive material, such as for example metal.
Further preferably the sleeve or tube member is made from, consists of or includes copper.
Preferably the sleeve or tube member is arranged to be electrically insulated from a housing of the RF apparatus by insulating means.
Preferably at least an external surface of the sleeve or tube member is provided with insulating means thereon and/or associated therewith.
Preferably the insulating means includes any or any combination of a dielectric material, dielectric member, dielectric coating, dielectric layer and/or the like. For example, in one example, the insulating means is a heat-shrink material, such as a plastic material, Polytetrafluoroethylene (PTFE) and/or the like.
In one embodiment the heat-shrink material is in the form of a heat-shrink sleeve that is heat-shrunk onto an external surface of the sleeve or tube member.
Preferably the heat-shrink material is arranged to overlap or cover a hole or substantially a whole of at least the wall edges defining at least one of the open ends of the sleeve or tube member when fitted to the same in use. This helps to prevent the sleeve or tube member from short circuiting when located in a housing of the RF apparatus in use.
Preferably a free end of the at least second inductor means or coil is connected to an interior surface of the sleeve or tube member.
Preferably the interior surface of the sleeve or tube member to which the free end of the at least second inductor means or coil is connected to is an internal side wall or internal base wall of the sleeve or tube member.
Preferably the at least second inductor means or coil is a spaced distance apart from the internal walls of the sleeve or tube member, with the exception of the free end that connects to an internal wall of the sleeve or tube member.
Preferably the sleeve or tube member is held in place in the housing of the RF apparatus via friction fit, via a compressive force provided between a lid and base of the RF apparatus in use and/or the like.
In one embodiment fixing means are provided on and/or associated with the sleeve or tube member or the apparatus housing to allow the sleeve or tube member to be fixed in position in the RF apparatus housing in use. For example, the fixing means can include any or any combination of adhesive, welding, one or more clips, screws, nuts and bolts, inter-engaging members, guide members, apertures, protrusions and/or the like.
Preferably the sleeve or tube member is located in an electrically grounded hole in the housing of the RF apparatus in use.
Preferably an end of the first inductor means is connected to a surface, and preferably an external surface, of the sleeve or tube member.
Preferably the end of the first inductor means is connected to the external surface of the sleeve or tube member via solder and/or the like.
Preferably the first inductor means and second inductor means are not connected directly together.
Preferably a third or further capacitor means is provided in the bias tee apparatus.
In one embodiment a third or further inductor means is provided in the bias tee apparatus.
Preferably the RF apparatus is RF filter apparatus, RF multiplexing or duplexing filter apparatus and/or the like.
Preferably the bypass pathway allows the passage of one or more low frequency control signals therealong in addition to the DC, such as for example one or more AISG control signals. The one or more low frequency control signals are prevented from passing along the RF communication signal pathway in a similar manner to the DC.
According to a second aspect of the present invention there is provided a method of using bias tee apparatus, said method including the steps of passing one or more radio frequency (RF) communication signals and direct current (DC) along an input pathway, dividing the input pathway into a DC bypass pathway such that direct current (DC) passes along the same and an RF communication signal pathway such that one or more RF communication signals passes along the same, the DC bypass pathway including at least a first inductor means for helping to prevent the passage of one or more RF communication signals therealong, and the RF signal pathway including at least first and second capacitor means for helping to prevent the passage of DC therealong, characterized in that at least one of the at least first or second capacitor means includes a sleeve or tube member and at least a second inductor means is located in an interior of the sleeve or tube member.
According to a further aspect of the present invention there is provided RF apparatus including bias tee apparatus.
Preferably the RF apparatus is RF filter apparatus including one or more RF filters therein.
According to a yet further aspect of the present invention there is provided a method of using RF apparatus including bias tee apparatus.
Embodiments of the present invention will now be described with reference to the following figures, wherein:

Figures 1a and 1b (PRIOR ART) show an example of a conventional bias tee arrangement, and the bias tee arrangement in RF filter apparatus, respectively;
Figures 2a and 2b (PRIOR ART) show a further example of a conventional bias tee arrangement, and the bias tee arrangement in RF filter apparatus, respectively;
Figures 3a-3d show a side view, cross sectional view, top plan view and perspective view of a blocking tube and inductor arrangement according to an embodiment of the present invention;
Figure 4 is a graph showing a comparison of the RF frequency response of three prior art bias tee arrangements (dotted lines) compared to the RF frequency of three bias tee arrangements according to the present invention (solid lines);
Figures 5a and 5b show an embodiment of a bias tee arrangement according to the present invention, and the bias tee arrangement in RF filter apparatus, respectively.

Referring to figures 3a-3d and 5a-5b, there is illustrated improved bias tee apparatus 102 according to an embodiment of the present invention. The bias tee apparatus 102 includes a first inductor coil 12, a first capacitor in the form of a coupling disk 34, and a second capacitor in the form of a blocking tube 36. The first inductor in the form of coil 12 has a first end 106 forming part of a bypass pathway 10 and a second end 108 connected to an external surface 109 of the blocking tube 36. The blocking tube 36 has side walls defining a first open end 112 and an opposite second open end 114. The blocking tube 36 is linear or substantially linear in form in this example.
Electrical insulating material in the form of a plastic or PTFE heat-shrink material is provided around the external surface of the blocking tube 36.
A second inductor in the form of coil 116 is located in the interior space of the blocking tube 36. More particularly, a first end 118 of inductor coil 116 is connected to an internal side wall surface of the blocking tube 36 and a second end of inductor coil 116 is connected to the bypass pathway 10.
The length of the inductor coil 116, the diameter of the inductor coil 116, the diameter of the wiring forming the inductor coil 116, the number of turns of the inductor coil and/or the like effect the isolation provided between the bypass pathway 10 and the RF communication signal pathway 8 and can be controlled accordingly.
Referring to figure 4, there is shown a graph showing a comparison of the RF frequency response of three prior art bias tee arrangements (dotted lines) compared to the RF frequency of three bias tee arrangements according to the present invention (solid lines). Frequency in MHz is shown on the X axis and isolation in dB is shown on the Y axis. Lines A, B, C show a blocking tube of length 19mm, 22mm and 25mm used with a second inductor coil located therein according to the present invention respectively. Lines A', B', C' show a blocking tube of length 19mm, 22mm and 25mm used without an inductor coil therein but with a simple linear wire passing through according to the prior art.
At 700Mhz, the isolation value is 32.4372dB in A' and 51.9239dB in A. At 945.461MHz, the isolation value is 50dB in B' and at 634.95MHz, the isolation value is 50dB in B. At 894.254MHz, the isolation value is 50dB in C' and at 603.765MHz, the isolation value is 50dB in C. At 670.395MHz, the isolation value is 50dB in A and at 1010.69MHz, the isolation value is 50dB for A'. Thus, it can be seen that the bias tee arrangement of the present invention improves isolation between the bypass pathway and the input and output pathways of RF filter apparatus by 20dB at 700MHz. The bias tee arrangement of the present invention also provides a 50dB isolation cut off frequency that is reduced by more than 30% compared to the prior art arrangements.

Claims

Bias tee apparatus for radio frequency (RF) apparatus, said bias tee apparatus including an input pathway for the passage of one or more radio frequency (RF) communication signals and direct current (DC) therealong in use, the input pathway dividing into a DC bypass pathway to allow the passage of direct current (DC) therealong in use and an RF communication signal pathway for the passage of one or more RF communication signals therealong in use, the DC bypass pathway including at least a first inductor means for helping to prevent the passage of one or more RF communication signals therealong in use, and the RF signal pathway including at least first and second capacitor means for helping to prevent the passage of DC therealong in use, characterized in that at least one of the at least first or second capacitor means includes a sleeve or tube member and at least a second inductor means is located in an interior of the sleeve or tube member.
Bias tee apparatus according to claim 1, wherein the first and/or second inductor means is in the form of an inductor, a series inductor and/or a coil.
Bias tee apparatus according to claims 1 or 2, wherein one of the at least first and second capacitors is in the form of a series capacitor and/or a coupling disk and the other of the at least first and second capacitors is in the form of the sleeve or tube member.
Bias tee apparatus according to any preceding claim, wherein the at least second inductor means is provided centrally or substantially centrally of the sleeve or tube member; is coaxial with the sleeve or tube member; a central axis of the at least second inductor means is provided parallel or substantially parallel to one or more interior walls of the sleeve or tube member; and/or a main body portion of the second inductor means is provided a spaced distance apart from interior walls of the sleeve or tube member.
Bias tee apparatus according to any preceding claim, wherein the length of the at least second inductor means, the diameter of the at least second inductor means, the diameter of wiring forming the at least second inductor means and/or the number of any coil turns of the at least second inductor means is adjustable to control the inductance of the apparatus.
Bias tee apparatus according to any preceding claim, wherein the sleeve or tube member is made from, consists of or includes an electrically conductive material, metal and/or copper.
Bias tee apparatus according to any preceding claim, wherein the sleeve or tube member is arranged to be electrically insulated from a housing of the RF apparatus and/or an external surface of the sleeve or tube member is provided with insulating means thereon and/or associated therewith.
Bias tee apparatus according to claim 7, wherein the insulating means includes any or any combination of a dielectric material, dielectric member, dielectric coating, dielectric layer, heat shrink material, plastic material or polytetrafluoroethylene.
Bias tee apparatus according to claim 8 wherein the heat-shrink material is arranged to overlap or cover at least edges of walls defining open ends of the sleeve or tube member.
Bias tee apparatus according to any preceding claim, wherein a free end of the at least second inductor means is connected to an interior surface, an interior side wall or an interior base wall of the sleeve or tube member.
Bias tee apparatus according to any preceding claim, wherein the sleeve or tube member is arranged such that it can be held in place in a housing of RF apparatus via friction fit or via a compressive force provided between a lid and a base of the RF apparatus in use; or wherein fixing means are provided on or associated with the sleeve or tube member to allow the same to be fixed in position in a housing of RF apparatus in use.
Bias tee apparatus according to any preceding claim, wherein an end of the first inductor means is connected to a surface or external surface of the sleeve or tube member.
Bias tee apparatus according to any preceding claim, wherein the bypass pathway is arranged to allow the passage of one or more low frequency control signals and/or Antenna Interface Standards Group (AISG) control signals therealong in addition to the DC in use.
Radio frequency apparatus including bias tee apparatus according to claim 1.
A method of using bias tee apparatus, said method including the steps of passing one or more radio frequency (RF) communication signals and direct current (DC) along an input pathway, dividing the input pathway into a DC bypass pathway such that direct current (DC) passes along the same and an RF communication signal pathway such that one or more RF communication signals passes along the same, the DC bypass pathway including at least a first inductor means for helping to prevent the passage of one or more RF communication signals therealong, and the RF signal pathway including at least first and second capacitor means for helping to prevent the passage of DC therealong, characterized in that at least one of the at least first or second capacitor means includes a sleeve or tube member and at least a second inductor means is located in an interior of the sleeve or tube member.