Patent Application
20120229229
The present invention relates to a directional filter assembly, which may be used for combining or separating signals in a microwave transmission assembly. More particularly, but not exclusively, the present invention relates to a power-dependent reflective protection device that selectively reflects power away from a termination load of the directional filter assembly.
Base stations for generating microwave signals are known in the field of mobile telephony. Such base stations are connected to an antenna for transmitting the signals generated by the base stations to mobile telephones.
Often a plurality of base stations is connected to a single antenna. Each of the base stations may generate a microwave signal at a different frequency and different modulation scheme as is known in the art. In this case, each of the plurality of base stations is connected to an associated input port of a combiner. The combiner combines the signals from the input ports together and presents them at an output port, which is in turn connected to the antenna.
It is possible that the base stations may be incorrectly connected to the combiner or that transmit frequencies are incorrectly configured with respect to the respective pass-bands of the combiner. For example a base station adapted to generate a signal at one frequency may be accidentally connected to an input port of the combiner adapted to receive a signal at a different frequency. In such cases, and for certain types of combiners, such as directional-filter type combiners, the power from the incorrectly connected base station is delivered to an internal termination load in the combiner.
If some or all of the power from a base station is delivered to the internal termination load in the combiner then the apparatus will not operate correctly or possibly not at all. Permanent damage to the combiner, and especially to the internal termination load, may occur. Further, it can be difficult to determine the cause of such problems, and complex diagnostic systems may be required.
In one aspect of the teachings presented herein, a directional filter assembly is configured to prevent excessive power dissipation in its internal termination load by selectively reflecting power away from the internal termination load in a power-dependent fashion. For example, if the power that otherwise would be directed into the internal termination load is below a certain threshold, the directional filter assembly does not reflect that power away from the internal termination load. This can be understood as normal, non-reflective operation of the directional filter assembly. On the other hand, if the power level exceeds a certain threshold, the directional filter assembly reflects power away from the internal termination load, thereby preventing excessive power dissipation in the internal termination load.
Accordingly, in one embodiment, a reflective protection device is configured to protect the internal termination load of a directional filter assembly. The reflective protection device comprises, for example, a power-dependent reflective circuit that is coupled to the internal output port of the directional filter assembly, where the internal output port is also referred to as an “isolated” port of the directional filter assembly. The power-dependent reflective device directly or indirectly senses the incident out-of-band signal power level with respect to the internal termination load. As one example, thermal sensing is used. As another example, a microwave power sensor is used.
In any case, the sensed level of power can serve as a trigger, for changing the operation of the reflective protection device from a non-reflective state, where it may be transparent in a circuit sense and does not interfere with power absorption by the internal termination load, to a reflective state, where it reflects the out-of-band signal power away from the internal termination load. Here, it will be understood that “away from the internal termination load” means that out-of-band signal power that otherwise would be dissipated in the internal termination load is instead reflected elsewhere, such as back into the isolated port.
Such operational features make the contemplated directional filter assembly advantageous for a number of applications. In a non-limiting example, the directional filter assembly is configured as a combiner within a microwave transmission assembly. The combiner includes first and second input ports and internal and external output ports; the combiner being adapted to transfer a signal received at a microwave frequency range f1 at the first input port to the external output port, which is also referred to as a common port, and signals received at other frequencies to the internal output port, which is also referred to as an isolated port; the combiner being further adapted to transfer a signal received at a microwave frequency range f2 at the second input port to the external output port and signals received at other frequencies to the isolated port; a resistive load connected to the isolated port as the earlier-named internal termination load; and, a power dependent reflective protection device configured to protect the resistive load from being overloaded, based on the reflective protection device changing reflectivity as a function of the power being dissipated in the resistive load.
In at least one embodiment, the reflective protection device is configured to protect the resistive load from being overpowered by incident power from the isolated port, based on being configured to switch from a non-reflective state wherein incident power passes to said resistive load, to a reflective state wherein incident power is reflected away from the resistive load. The changeover in behavior is tied to the level of out-of-band signal power at the resistive load. As such, the reflective protection device protects the resistive load from damage that could otherwise arise from excessive power dissipation in the resistive load, such as might occur when a base station is incorrectly coupled to the combiner or the transmit frequencies are incorrectly allocated.
One or more of the embodiments taught herein are particularly well suited for use in remotely controlled combiners. This is because remote control of combiner pass-band frequency and transmit frequency allocation may increase the risk of mistakes and makes validation of retuning and reallocation more difficult or even impossible.
In at least one embodiment taught herein, the reflective protection device is configured as a shunt device that appears as a high-impedance shunt when in the non-reflective or standby state, and appears as a low-impedance shunt when in the reflective or active state. In at least one such embodiment, a thermal sensor or another control sensor monitors power dissipation in the resistive load, for triggering the change from non-reflective to reflective states. In another embodiment, the reflective protection device is self-triggered, e.g., it changes from the non-reflective state to the reflective state based on, for example, the voltage at the resistive load.
Generally, it will be understood, for example, that injecting the wrong frequency signal into one of the combiner's input ports will cause power dissipation in the resistive load to increase. Excessive power dissipation in the resistive load because of such error causes the reflective protection device to switchover from its non-reflective or standby state to its reflective state or active state.
As such, if a base station is incorrectly connected to the combiner of the microwave transmission assembly according to the invention, then the power transmitted to the resistive load will increase and, beyond a given threshold, causing the reflective protection device to reflect power back to the incorrectly connected base station. This action provides an immediate indication that the base station has been incorrectly connected to the combiner.
Preferably, the microwave transmission assembly further comprises an antenna for transmitting a microwave signal, the antenna being connected to the external output port. Preferably, at least one of the input ports has a base station connected thereto, the base station being adapted to provide a microwave signal to the combiner.
Preferably, the power limit which causes the reflective protection device to switchover is at least 10% and less than 90% of the power in the microwave signal generated by the base station, and more preferably greater than 20% and less than 75%. The base station can comprise a detector for detecting power reflected from the combiner. The base station can be adapted to provide a modulated microwave signal, preferably a Global System for Mobile Communications (GSM), Wideband Code Division Multiple Access (W-CDMA) or Long Term Evolution (LTE) modulated signal.
The present invention will now be described by way of example only and not in any limitative sense with reference to the accompanying drawings in which:
Directional filters are used for combining or separating signals at given frequency ranges or sub-bands and it is broadly contemplated herein to include a reflective protection device in a directional filter assembly, to provide protection for the filter's internal termination load.
As is known for directional filters, the directional filter assembly 10 directs out-of-band signals to its internal output port, which is referred to as an isolated port and is identified by reference number 20 in the illustration. One sees band-pass filter circuits 19 in the multi-port filter circuit 12, to provide for desired pass-band/out-of-band behavior.
The out-of-band signals are passed to the isolated port 20 and the directional filter assembly 10 includes an internal termination load for dissipating out-of-band signal power from the isolated port 20. In the illustration, the internal termination load is represented by a resistive load 22.
Advantageously, the directional filter assembly 10 includes a reflective protection device 24, which functions as a power dependent reflective load and thereby protects the resistive load 22 from dissipating excessive, potentially damaging levels of out-of-band signal power. As an example, the resistive load 22 comprises a 50 Ohm resistor or other impedance-matching termination that, in normal operation of the directional filter assembly 10, prevents out-of-band signals from being reflected from the directional filter 12. As such, it will be understood that the directional filter assembly 10 is sometimes also referred to as a “non-reflective” filter. However, the injection of excessive out-of-band signal power into the directional filter assembly 10 can overpower the resistive load 22. Correspondingly, the reflective protection device 24 operates in a non-reflective state or in a reflective state, and it changes from the non-reflective state to the reflective state in dependence on the out-of-band signal power level, to protect the resistive load 22 from damage.
One also sees in the illustration that the reflective protection device 24 is depicted as having an optional ground configuration. This aspect of the illustration is meant to indicate that some embodiments of the reflective protection device 24 use a ground connection, while others do not necessary have such a connection. In embodiments that use a ground connection, the reflective protection device 24 may be physically configured to have good thermal conduction into that ground connection, thus making it more robust.
With the above arrangement in mind, one or more embodiments of the teachings presented herein provide a directional filter assembly 10 comprising a multi-port filter circuit 12 for combining or separating signals in specified pass bands and an isolated port 20 having a resistive load 22, for absorbing out-of-band signals. The directional filter assembly 10 further comprises a reflective protection device 24 that is configured to protect the resistive load 22 from being overpowered by out-of-band signal power, based on being configured to reflect or not reflect the out-of-band signals in dependence on the level of out-of-band signal power.
The reflective protection device 24 may be triggered based on a sensor or other detector that is configured to directly or indirectly sense the out-of-band signal power level. In another embodiment, the reflective protection device 24 is self-triggering, e.g., it switches from its non-reflective state to its reflective state responsive to the voltage level at the resistive load, or responsive to another parameter that depends on out-of-band signal power level.
However, at a certain out-of-band signal level, the GDT 28 will become active and then appear as a low-impedance shunt on the transmission line 30 coupling the isolated port 20 to the resistive load 22. This can be understood as the reflective state of operation for the reflective protection device 24 in this embodiment. That action causes reflection of the out-of-band signals back into the isolated port 20, thereby protecting the resistive load 22.
This arrangement forms a low-pass filter that improves a return loss of the reflective protection device 24. The impedance scaling provided by the inductors 32 and 34 can be used to set the trip point of the GDT 28 to a desired power level. As a further option, a capacitor 36 (C1) couples the shunt-connected GDT 28 to a common node 38 between the first and second inductive elements 32 and 34. The capacitor 36 is configured to mitigate an inductance of the shunt-connected GDT 28 in its reflective state; however, leadless implementations of the GDT 28 are inherently low-inductance and the capacitor 36 will not be needed in at least some implementations.
It will be understood that the reflective protection device 24 can use either sensor 42 or 44 and that both sensors generally would not need to be used. It will also be understood that the power level at which it is desired to trigger reflective state operation of the electrical circuit 40 can be set in terms of a temperature level, in cases where the heat sensor 44 is used for triggering. Also, it should be noted that the electrical circuit 40 is depicted as interrupting the transmission line 30 but that is not a limitation of the embodiment. The electrical circuit 40 may comprise one or more shunt-connected electrical circuits, similar to that depicted in
In this regard, the electrical circuits 26 and 40 may be understood as to operate as “triggered reflectors” that change from a non-reflective state to a reflective state in dependence on the out-of-band signal power level, with the difference being whether they are self-triggered or rely on an associated sensor for triggering. Broadly, it is contemplated to implement the reflective protection device 24 using a range of triggered reflectors, which may be implemented in shunt or series configurations with respect to connection between the isolated port 20 and the resistive load 22. Non-limiting examples include the use of shunt-configured electrical circuits, such as circuit 26. Within that configuration, a variety of electrical circuits are contemplated, including two-terminal devices such as pull-down transistors, GDTs, etc.
As another variation using GDTs,
Some embodiments of the band-pass filter circuit 60 are self-triggered, while others use an associated sensor for triggering the switchover from the non-reflective state to the reflective state. By way of example,
In this regard, the band-pass filter circuit 60 is controlled to operate in the non-reflective state or in the reflective state via a de-tuning device 112, which operates on one or more tuning screws 114 that control operation of resonators 110. Thus, by actuating or otherwise triggering the de-tuning device 112, the band-pass filter circuit 60 operates in its non-reflective state or in its reflective state in dependence on the out-of-band signal power level.
These and other contemplated configurations offer specific operational advantages. It should also be understood that the band-pass filter circuit 60 can be configured to be self-triggering, such as by including a GDT 28 or other self-triggering circuit configured to operate on one or more resonators within the band-pass filter circuit 60. For example,
In
The position of the GDT 28 along the longitudinal dimension of the resonator rod 122 can be used to set the trip point to a desired power level. Also, note that the coaxial resonator 120 also may be enclosed by a cavity lid 128, and may include a tuning screw 130 to tune its band-pass characteristics.
Thus, one sees a first base station 130 connected to a first input port 16 of the directional filter assembly 10, and a second base station 132 connected to a second input port 18 of the directional filter assembly 10. The common output port 14, which also may be referred to as an external output port, is connected to one or more transmit antennas 134, and the isolated port 20 is connected to a reflective protection device 24, to protect the resistive load 22 as previously described.
This configuration is suitable for combining microwave signals from the two base stations 130 and 132, for transmission from the antenna 134. For example, the first base station 130 applies microwave signals in a first frequency range f1 to the first input port 16, while the second base station 132 applies microwave signals in a second frequency range f2 to the second input port 18.
In normal operation, signals applied to the first input port 16 that are out-of-band with respect to the first frequency range f1 are directed to the isolated port 20 for dissipation by the resistive load 22 and signals applied to the second input port 18 that are out-of-band with respect to the second frequency range f2 are also directed to the isolated port 20 for dissipation by the resistive load 22. Further, it will be understood that in normal operation, some amount of signal power generally is passed out of the isolated port 20, even in the absence of incorrect signal frequencies or base station misconnections.
In any case, in operation, the first base station 130 generates a microwave signal at a frequency range f1. Typically this is modulated according to a modulation scheme, for example W-CDMA modulation, as is known in the art. The multi-port filter circuit 12 functions as a microwave combiner and receives this modulation signal and transfers it to the antenna 134. The second base station 132 also generates a microwave signal, which is received by the multi-port filter circuit 12 of the directional filter assembly 10, where it is combined with the first signal, and passed to the antenna 134. As noted, the microwave signal generated by the second base station 132 is typically of a different frequency range f2 and may be modulated according to a different modulation scheme than the first microwave signal at frequency range f1.
In this sense, the directional filter assembly 10 “expects” to receive a particular frequency range microwave signal at each input port 16 and 18. If a base station 130, 132 is connected to the wrong port 16, 18, or is set to provide the incorrect range of microwave frequencies, then the directional filter assembly 10 will not pass the microwave signal to the antenna 134. Instead, the multi-port filter circuit 12 of the directional filter assembly 10 will pass the out-of-band signal to the resistive load 22 where it is dissipated—at least, it will do so subject to the level of out-of-band signal power dissipation that triggers the reflective protection device 24 and causes it to change from its non-reflective state to its reflective state.
By controlling whether the protective reflection device 24 operates in the reflective state or in the non-reflective state as a function of the out-of-band signal power level, the directional filter assembly 10 offers built-in protection against overpowering the resistive load 22, such as might happen with improperly connected base station signals. In this regard, the reflective protection device 24 can be understood as a power dependent reflective load that acts to protect the resistive load 22. Also, as earlier noted, the reflective protection device 24 may be configured to generate and output an indicator or alarm signal, to alert a connected base station to the out-of-band signal problem.
Of course, even in correct operation the directional filter assembly 10 may pass a small amount of power to the isolated port 20 at frequencies at or close to the f1 or f2 frequency ranges. At these low levels of out-of-band signal power, the reflective protection device 24 is in its non-reflective state. In this state, the resistive load 22 dissipates the out-of-band signal power and it may be chosen or otherwise dimensioned in view of some normally expected level of out-of-band signal power for normal operation of the directional filter assembly 10.
If a base station 130, 132 is incorrectly connected to the directional filter assembly 10 then the signal generated by the base station 130, 132 is out-of-band with respect to the input port 16, 18 to which it is applied and it is therefore passed to the isolated port 20 and hence to the reflective protection device 24 and resistive load 22. In that case, if the power generated by the base station 130, 132 exceeds a defined power limit, then the reflective protection device 24 will be triggered, i.e., caused to change from the non-reflective state to the reflective state. In an example configuration, the reflective protection device 24 reflects out-of-band signals back into the isolated port 20, rather than allowing them to pass to the resistive load 22.
The out-of-band signal power level at which the reflective protection device 24 is triggered may be configured in consideration of expected normal power levels. In one embodiment, the reflective protection device 24 is adapted such that the triggering power level is less than the power generated by at least one correctly connected base station 130, 132. It therefore switches from the non-reflective state to the reflective state when, for example, the out-of-band power level is more than 10% and less than 90% of the power level in the microwave signal generated by the base station 130, 132. More preferably, the triggering power level or triggering threshold is more than 20% and less than 75%. A typical base station 130, 132 generates an average power level of the order 100 Watt (W). The power level at which the reflective protection device 24 triggers is therefore typically in the range 10 to 90 W, preferably in the range 20 to 75 W for an incorrectly connected base station 130, 132.
Thus, in at least one embodiment contemplated herein, the directional filter assembly 10 is configured as a microwave transmission assembly 140, wherein its multi-port filter circuit 12 is configured as a microwave combiner, for combining signals from, e.g., two different base stations 130, 132. In this configuration, the reflective protection device 24 of the directional filter assembly 10 is configured to switch from a low impedance state to a high impedance state when the incident microwave power of the out-of-band signals exceeds a power limit. In this manner, the reflective protection device 24 prevents the resistive load 22 of the directional filter assembly 10 from excessive power dissipation in the presence of abnormally high levels of out-of-band signal energy.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0920545.1 | Nov 2009 | GB | national |
| 1001150.0 | Jan 2010 | GB | national |
| 1003764.6 | Mar 2010 | GB | national |
| 1004062.4 | Mar 2010 | GB | national |
| 1004129.1 | Mar 2010 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2010/051291 | 11/23/2010 | WO | 00 | 5/22/2012 |
