SE528358C2 - Waveguide technology filter, e.g. for base station, has cast housing for filter with integral threaded input and output connectors and walls defining resonant cavities and DC isolating arrangement - Google Patents

Abstract

The filter housing is integrated with threaded input and output connectors and the walls defining the cavities. A first resonator (21) of the filter structure, preferably integrated with the lid, is supplied with an RF signal via an input connector (1) and a connecting rod (2), isolated from the housing, using a DC extracting arrangement for blocking a DC voltage or low frequency signal superimposed on the signal. The filter comprises a filter housing (3), preferably cast in zinc, having a lid (5) made from zinc which is preferably coated with silver, threaded input and output connectors, and at least one filter structure including cavities and resonators. A resonator (21) is provided with a cavity (22), is electrically grounded to the filter lid and the connecting rod (2) extends through an opening (23) into the resonator cavity. A low pass filter comprising an inductor (24) and a capacitor (25) is provided inside the cavity and the DC/LF signal is fed from the cavity through an opening (27) in the filter lid.

Description

intermodulation (PIM) and it is difficult to control the tolerances of the structure which limits the performance and makes the solutions described in connection with Figures 1 and 2 expensive to manufacture. In addition, RF tends to leak into the DC voltage and the low frequency communication signal due to the structure of the LP filter.

A structure similar to the present invention is described in US 5,023,579 by Salvatore et al. describes an integrated bandpass / lowpass filter where the first and last resonators are connected to associated connections. The low-pass filter is positioned within the first and last resonators and the RF signal fed into the resonators is subjected to low-pass filtering and thus forms a band-pass filter for the RF signal. Thus, the RF signal is subjected to low pass filtering which is not the object of the present invention.

Summary of the invention An object of the invention is to provide a new way of manufacturing a filter housing which results in a more compact filter compared to known solutions.

This object is achieved by a filter as defined in the characterizing part of claim 1.

An advantage of the filter according to the invention is that it is possible to further reduce the required tolerances in the manufacturing process, which in turn will minimize the size of the internal structures of the filter, and in addition the filter according to the invention makes it possible to integrate e.g. threaded connections in the filter housing during casting.

Another advantage is that it is cheaper to manufacture a complex structure by using Zinc. An advantage of a preferred embodiment of the filter is that it is easier to cast the casing in Zinc compared to casting it in aluminum, which will increase the life of the tools required to cast the casing.

The invention will now be described in connection with the accompanying drawings, which are provided in a non-limiting manner, in order to improve the understanding of the invention.

Brief Description of the Drawings Figure 1 shows a first known arrangement for extracting DC voltage or low frequency signals superimposed on an RF signal.

Figure 2 shows a second known arrangement for extracting DC voltage or low frequency signals superimposed on an RF signal.

Figure 3 shows a first embodiment of a DC extracting arrangement according to the present invention.

Figures 4a and 4b show a second and third embodiment of a DC extracting arrangement according to the present invention.

Figure 5 shows a fourth embodiment of a DC extracting arrangement implemented in a filter.

Figures 6a and 6b show cross-sectional views of the filter of Figure 5.

Figure 7 shows a block diagram of a first embodiment of a filter including a DC extracting arrangement.

Figure 8 shows a block diagram of a second embodiment of a filter including a DC extracting arrangement. Detailed Description of Preferred Embodiments »Figures 1 and 2 show known solutions for a DC extracting arrangement in an RF filter, where the signal to be extracted (DC voltage or a low frequency signal commonly used for communication purposes ) is superimposed on an RF signal.

Figure 1 shows a first type of known arrangement for extracting a DC voltage or low frequency signal in an RF filter 10 having a housing 3a, 3b and a cover 5. A common signal comprising an RF signal with superimposed DC voltage and / or low-frequency signal, is fed into an input terminal 1. A connection pin 2 is connected to the input connection 1 and the connection pin 2 is insulated from the filter housing 3a, 3b. A first resonator 4 is capacitively connected to the input terminal 1 via said connection pin 2 and a first capacitance Cmn A first end of an inductor Lm; is directly connected to the connection pin 2, usually by soldering, and a second end of the inductor LW is connected to a second capacitance Cm, which is arranged outside the RF filter 10.

The inductor LN is arranged inside a part of the filter housing 3a and extends through the filter cover 5, which is attached to the housing by screws or similar fastening means. The inductor Lm; and the second capacitance Cm; together form a low-pass filter (LP filter), and the DC voltage and / or the low-frequency communication signal (DC / Com signal) are available on the outside of the filter. The second capacitance CW may be implemented on a PCB circuit board (not shown) connected to the filter cover 5.

There are disadvantages to the described DC extracting arrangement, especially with respect to leakage of the RF signal into the DC / Com signal. In addition, it is difficult to make the connection of the first end of the inductor Lm due to the small available space to solder it to the connecting pin 2.

The second type of DC extracting arrangement shown in Figure 2 also comprises a filter 20, which has a housing 3 and a lid 5, an input connection 1 connected to a connecting pin 2. The lid 5 is attached to the housing 3 in a similar manner as described in connection with Figure 1, and a first resonator 14 arranged inside the filter 20.

The coupling pin 2, which is isolated from the housing 3, is directly connected to an isolated part 11 of the first resonator 14, which means that the common signal, including the RF signal with the superimposed DC voltage and / or the low frequency signal, is fed into the input connection 1 via the connecting pin 2 to the insulated part 11 of the first resonator 14. The first resonator further comprises a base part 12, which is electrically grounded to the cover 5 and insulated from the insulated part 11 of an insulating layer 13. A capacitance CM thus.

One end of a lead 15, which acts as an inductor LW, is connected to the insulated part 11 of the first resonator 14, and the lead 15 is arranged through a hole 16 in the cover 5.

The other end of the lead is connected to a second capacitance CBC, which is arranged outside the RF filter 20. The second capacitance Cm can of course be implemented on a circuit board PCB (not shown) if desired. The inductor Lm and the second capacitance Cm form, as described in connection with Figure 1, a low-pass filter.

The second type of DC extracting arrangement according to the prior art also has disadvantages, especially in terms of leakage in the DC / Com signal, but also in the complex structure of the DC extracting arrangement where soldering of the wire to 10 15 20 25 30 528 358 the first resonator 14 is necessary to obtain a good contact.

The basic idea of the invention, as described below, is to arrange the LP filter inside the first resonator and connect the RF signal to the outside of the first resonator.

This in turn will suppress the RF signal in the DC / Com signal, but also provide a simplified manufacturing method for the filter.

Figure 3 shows a first embodiment of a DC extracting arrangement according to the present invention arranged in a filter 30, which has a housing 3 and a lid 5. An input connection 1 and a connecting pin 2, isolated from the housing 3, are provided to feed the common the signal, including RF signal with superimposed DC / Com signal, into the filter 30.

A resonator 21, which may be a first resonator in a filter structure or a connecting pin for several filter structures, is provided with a cavity 22. The resonator 21 is electrically grounded to the filter cover 5 and the connecting pin 2 extends through an opening 23 in the resonator 21 in in the cavity 22. A low pass filter (LP filter) comprising an inductor 24 and a capacitance 25 is provided inside the cavity 22 and the DC / Com signal is output from the cavity 22 through an opening 27 in the filter cover 5.

The LP filter is realized by connecting a first end of the inductor 24 with the end of the connecting pin 2 extending into the cavity 22. The second end of the inductor 24 is connected in series with the capacitor 25, which is grounded to the cavity wall, and DC / Com The signal is extracted by connecting a line 26 to the other end of the inductor 24 and passing it through the opening 27 in the filter cover 5. The described embodiment illustrates the basic idea of the invention and Figure 4a shows a preferred embodiment. of the present invention.

In Figure 4a, similar components have the same reference numerals as used previously. The fundamental difference between the previously described embodiment in Figure 3 is that the LP filter is realized as a tubular LP filter 32. the connecting pin 2 is conductively connected to the lower part 33 of the tubular LP filter 32 and an insulating layer 36, for example PTFE or Teflon, is provided between the tubular LP filter and the cavity wall. An opening 37 in the insulating layer 36 is provided to enable the connection of the connecting pin 2 to the lower part 33 of the tubular LP filter 32.

The tubular LP filter 32 further comprises, in this embodiment, two disks 34, the disks and the lower part 33 being interconnected by narrow pins 35. Each disk will form a capacitance with the cavity wall and each narrow pin will form an inductance. , and thus an LP filter is formed. The DC / Com signal is located at the center 38 of the upper end of the tubular LP filter.

In this embodiment, the filter is provided with a modified cover 31 having the resonator 21 integrated with the cover 31 and in addition a DC connection 39 is provided on the outside of the cover 31 to which the LP filter output 38 is connected.

Figure 4b shows a third embodiment of the present invention. The embodiment of Figure 4b functions substantially in the same way as the embodiment of Figure 4a, and as in Figure 4a, similar components have the same reference numerals as previously used. The LP filter is realized as a tubular LP filter 32, as in Figure 4a. In this embodiment, however, the connecting pin is conductively connected to the lower part 33 of the tubular LP filter 32 of the resonator 21 from below in the figure instead of from the left side as in figure 4a. In addition, the insulating layer 36 has been omitted and the insulation is provided instead through an air gap between the cavity wall and the disks 34 and the lower part 33.

In addition, the lower part of the cavity wall has been omitted.

The DC / Com signal is retrieved, as in Figure 4b, at the upper end of the tubular LP filter, preferably from the center of the top disk 34. As shown in previous embodiments, the RF signal is coupled to the outside of the resonator 21 and may forwarded to a bandpass filter 41.

Figure 5 shows an exploded view of a fourth embodiment 50 of a filter having a DC extracting arrangement according to the present invention. The filter comprises five different parts: filter housing 51, a connecting pin 52, a filter cover 53, resonators 53 and LP filter 55.

A coupling pin 56 having a cavity 57 is integrated with the filter cover 53, as described in connection with Figure 4a, but in this embodiment the coupling pin instead extends through the cover 53 to form an edge 58 on the outside of the filter. An insulating layer (not shown) is mounted inside the cavity 57 to prevent shorting of the LP filter 55 when mounted inside the cavity. The filter housing 51 is provided with an opening 59 for inserting the connecting pin 52 upon connection to the LP filter 57 after the resonators 54 and the lid 53 have been mounted to the housing 51.

The filter cover may also be provided with tuning means, such as tuning screws, to tune the frequency of the coupling pin. The tuner is accessible from the filter when mounted.

Figures 6a and 6b show cross-sectional views of the filter of Figure 5.

Figure 6a is a cross-sectional view from above of the filter where the tuning means 60 is clearly shown. The connection pin 52 is connected to the LP filter in such a way that it ensures a good electrical contact, e.g. with threads. Figure 6b shows a partial cross-sectional view of the cover 53 comprising the mounted LP filter 55 and the connecting pin 52. The insulating layer 61 can be seen in the cavity 57 between the LP filter 55 and the integrated connecting pin 56. The insulating layer may be any material having a dielectric property.

The DC extracting arrangement has only been described as a way of extracting low frequency signals, e.g. DC signals or signals having a frequency up to a few MHz (2-4 MHz), but the same arrangement can of course be used to add DC and / or low frequency communication signals to an RF signal.

Figure 7 shows a block diagram illustrating a duplex filter 70 for mobile communication systems. The input 71 of the duplex filter 70 can be connected to a base station (BTS) and the output 72 can be connected to an antenna 73.

The duplex filter 70 comprises: a transmission filter structure TX, two reception filter structures Rx with a low noise amplifier LNA in between, an extracting arrangement 74 for DC / Com signal and an adding arrangement 75 for DC / Com signal.

The LNA requires a DC voltage to operate and it is provided by circuits 76. The low frequency communication signal is not normally used within the duplex filter 70 but is passed on from input 71 to output 72 by means of the DC extracting and adding arrangements.

Figure 8 illustrates a block diagram where no low frequency communication signal is present and the DC voltage is only used to drive the LNA.

The filter shown in Figure 5 is preferably made of cast Zinc, which makes it possible to reduce the size of the filter casing because thinner walls can be made by using Zinc instead of using traditional materials such as Aluminum. In addition, the use of Zinc makes it possible to integrate threaded input and output connections to the housing. The use of cast Zinc has the obvious advantage that the casting takes place at a lower pressure and temperature, compared to Aluminum, which in turn will increase the service life of the molds used during the manufacturing process.

Since it is possible to include complex structures in the cast filter housing, the result is a much cheaper product compared to traditional filters made of Aluminum.

In addition, it is more advantageous to cast the filter cover, which includes the DC extracting arrangement as described in connection with Figures 5, 6a and 6b, in Zinc.

The temperature coefficient of both the housing and the lid will thus be approximately equal, which will increase the performance of the filter during operation. However, the lid is preferably coated with a high conductivity material, such as Silver, to increase the performance of the filter.

Claims (22)

l0 l5 20 25 528 358 ll Patent claim A filter comprising a filter housing and a filter cover, said filter having a threaded input connection, a threaded output connection and at least one filter structure comprising cavities and resonators, characterized in that the filter housing is integrated with the threaded input / output connections and that the walls defines cavities, and where said filter housing is made of Zinc. The filter of claim 1, wherein said filter housing is molded. The filter of claim 1 or 2, wherein said filter cap is made of Zinc, preferably coated with Silver. The filter according to any one of claims 1 to 3, wherein a first resonator of the filter structure is integrated with the lid. The filter according to any one of claims 1 to 4, wherein a DC extracting arrangement for extracting a DC voltage or low frequency signal superimposed on a radio frequency signal (RF signal), said RF signal being input to a first resonator of The RF filter structure is mounted at the input to the filter. The filter according to any one of claims 1 to 5, wherein a DC adding arrangement for adding a DC voltage or low frequency signal superimposed on a radio frequency signal (RF signal), said RF signal being output from a final resonator of The RF filter structure is mounted at the output of the filter. 10 15 20 25 528 358 12 The filter according to any one of claims 1 to 6, wherein the input / output connections of the filter are manufactured during a casting procedure. The filter of claim 7, wherein the input / output connections are threaded during the casting procedure. The filter of claim 5, wherein said DC extracting arrangement comprises a low pass filter (LP filter) that provides the DC voltage or the low frequency signal outside the RF filter structure, the first resonator being provided with a cavity where said LP filter is arranged inside the cavity of the first resonator, and where the RF signal is coupled to the outside of the first resonator. The filter of claim 9, wherein said first resonator is integrated with the filter cover or filter housing. 11. ll. The filter of claim 10, wherein the first resonator is integrated with the lid and is made of Zinc (Zn). The filter according to any one of claims 9 to 11, wherein a tuning means for tuning the frequency of the first resonator is integrated in the first resonator. The filter of claim 12, wherein the tuning means is a tuning screw. The filter of any of claims 9 to 13, wherein the first resonator is a coupling pin that provides RF signals to a first filter structure (Rx), and receives RF signals from a second filter structure (TX). The filter of claim 6, wherein said DC adding arrangement comprises a low pass filter (LP filter) that superimposes the DC voltage or the low frequency signal provided outside the RF filter structure to the RF signal, the final the resonator is provided with a cavity where said LP filter is arranged inside the cavity of the final resonator, and where the RF signal is coupled to the outside of the final resonator. The filter of claim 15, wherein said final resonator of the adding arrangement is integrated with the filter cover or filter housing. The filter of claim 16, wherein the final resonator of the adding arrangement is integrated with the lid and is made of Zinc (Zn). The filter according to any one of claims 15 to 17, wherein a tuning means for tuning the frequency of the final resonator of the adding arrangement is integrated in the first resonator. The filter of claim 18, wherein the tuning means is a tuning screw. The filter according to any one of claims 15 to 19, wherein the final resonator of the adding arrangement is a coupling pin which receives RF signals from a first filter structure (Rx), and provides RF signals to a second filter structure (Tg). The filter according to any one of claims 9 to 20, wherein the LP filter is a tubular LP filter. The filter of claim 21, wherein the tubular LP filter is made of a one-piece material.