Filter tuning device and tuning plate including a number of such devices

The present invention relates to a tuning device in a radio filter equipment for mobile telephony in which one or more cavities in the equipment should be tuned to the right frequency. The invention also relates to a tuning plate including a number of such tuning devices. The tuning device (401) consists of preferably regular or square formed depressed parts (1, 6) in the tuning plate (300) of the filter equipment The depressed part converges each to a square formed central plate (5) which is provided with an elevation or bulb (3) upwards. By turning a timing screw on the equipment will then develop a force on the plate and the surrounding depressed parts. This implies that the tuning can be made automatically, more secure and with less risk for intermodulation. Different embodiments of the depressed parts are described.

FILTER TUNING DEVICE AND TUNING PLATE INCLUDING A NUMBER OF SUCH DEVICES

Technical field of the invention

The present invention relates generally to radio filters, e.g bandpass filters which may be in the HF-area, used in e.g. a mobile radio system, and more particularly to the tuning of such filters.

Description of background art . 15

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Some kind of tuning arrangement is needed to tune a HFfilter to the right frequency. This may for example be done with a tuning screw alone or with a tuning plate where a tuning screw moves a part of the tuning plate.

A conventional BP (bandpass)-filter includes a body, a lid, filter cavities, center conductors, tuning screws, an input loop, an output loop and connectors. The walls of the filter cavities are formed by the inner surfaces of a filter casing. The filter casing is formed from the hollowed-out body and the lid. Center conductors are placed inside the filter cavities. Tuning screws for tuning the filter, that is the center conductors, to the right frequency are arranged in the lid and extend into the filter cavities. One tuning screw is arranged in the lid for every center conductor in the filter. Each of the

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center conductors are intended to receive and/or transmit radio signals within different frequencies. The input loop and the output loop are connected to connectors and the connectors can be connected with cables to functional units, such as printed circuit boards (PCB:s) and antennas. The arrangement of the various elements in a filter as described above are well known in the art. In typical state of the art systems, tuning screws with locking nuts are used. The filter is tuned by tuning the screw until the right frequency for the corresponding center conductor is set. When this is done, the screw is fixed by tightening a locking nut on the screw. When the screw is turned the capacitance between the screw and the center conductor changes.

Figure 1 schematically illustrates a side cutaway view of a state of the art filter 20 for e.g a mobile telephone system. A conventional BP (bandpass) - filter includes a body 111, a lid 110, filter cavities 114, center conductors 112, tuning screws 113, an input loop 120, an output loop 121 and connectors 122, 123. The walls 124 of the filter cavities 114 are formed by the inner surfaces of a filter casing. The filter casing is formed from the hollowed-outbody 111 and the lid 110. Center conductors 112 are placed inside the filter cavities 114. Tuning screws 113 for tuning the filter, that is the center conductors 112 to the right frequency are arranged in the lid 110 and extend into the filter cavities 114. One tuning screw 113 is arranged in the lid 110 for every center conductor 11 in the filter. Each of the center conductors 112 are intended to receive and/or transmit radio signals within different frequencies. The input loop 120 and the output loop 121 are connected to connectors 122, 123 and the connectors 122, 123 can be connected with cables (not shown) to functional units (not shown), such as printed circuit boards (PCB:s) and antennas. The filter is tuned by turning the screw 113 until the right frequency for the corresponding center conductor 112 is set. When this is done, the screw 113 is fixed by tightening a locking nut 115 as can be seen in figure 3 on the screw 113. When the screw 113 is turned the capacitance between the screw 113 and the corresponding center conductor 112 changes.

The tuning of a filter with a tuning plate 100, 300 is made in the same way, by rotating a tuning screw 113 until the right frequency is set. In the filter the tuning plate is placed between the base and the lid as can be seen in Figure 11.

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• · · • · · • ··· · • · · • · · · • · · • · · · · • ·

The difference is that instead of using a locking nut 115 to fix the tuning screw 113 in position, a tuning plate 100,300 can be used. The screw 113 moves part of the tuning plate 100, 300 axially when the screw 113 is rotated. This creates a tension in the tuning plate 100, 300 which increase the friction for the tuning screw 113 when rotated and thus fixes the tuning screw 113 in position. If more friction is needed, a plastic coated screw, also called a stop screw, may be used. When using a tuning plate the capacitance is changed by moving part of the tuning plate, the tuning unit. In the state of the art tuning plate 100 shown in figure 2 the tuning unit 400 is equivalent with the area containing the bent slits

201 in a rose-pattern. The way the slits 201 are formed enables the central part

101 of the rose to move axially. The center 102, 302 of the tuning plate is placed above the center 142 of the corresponding center conductor. The screw 113 only moves the plate 100, 300 and does not have a major impact on the change of capacitance.

A mechanically adjustable capacitance is provided, for example a tuning screw 113 in combination with a tuning plate, where the tuning screw may or may not be in direct electrical contact with the tuning plate.

When a state of the art tuning plate 100 with bent slits 201 in a rose pattern is used, the resistance to earth is relatively high and the currents do not take the shortest route to earth. To avoid intermodulation, IM, some of the tuning screws 113 must be electronically isolated from the tuning plate, preferably with PTFE (teflon)-washers which are fastened on the tuning plate (not shown).

The prior art devices have various disadvantages. First, the tuning of the first type of state of the art filters that are tuned without using a tuning plate creates a problem when autotesting because of the need for two tools when tightening the locking nut. If a tuning screw with a locking nut is used, rotation of the locking nut by itself will also cause the screw to rotate. Therefore a second tool must be used to hold the screw while a first tool is used to tighten the locking nut. This method is cumbersome because it takes more time, more space, and the use of more tools than is necessary or optimal.

Secondly, when a state of the art tuning plate with bent slits in a rose pattern is used, the resistance to earth is relatively high and the currents do not

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3a take the shortest route to earth. To avoid intermodulation, IM, some of the tuning screws must be electronically isolated from the tuning

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• · · · ·

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WO 98/54783

PCT/SE98/OO918 plate, preferably with PTFE(tefIon)-washers which are fastened on the tuning plate.

Normally the parts in a filter are manufactured with high precision on the surfaces which form the contact surfaces between the tuning plate and the body, and the joining is made by using screws. To minimize the electromagnetic radiation (EMC) the electrical contact between the casted part, that is the body, and the tuning plate must be excellent. To fulfil the requirements for the high working frequencies (around 1.8 Ghz) for the filters, the distance between the screws must be relatively small (around 20 ram) which means that the number of screws needed in a filter is significant.

Another factor which also emphasizes the need for good contact between the body and the lid is the risk for intermodulation (IM). Holes in the tuning plate should be made with a minimal total area for minimizing the risk for

IM.

Accordingly, one object of the present invention is to minimize the problems of having slits in the tuning plate by minimizing the area of the slits. Another object of the invention is to minimize the problem of the currents not taking the shortest route to earth by using straight slits instead of the curved slits used in the state of the art tuning plate. Yet another object of the invention is the use of spring-elements integrated in the tuning plate to obtain good contact between the body and the tuning plate and in this way minimizing the risk for intermodulation (IM). To minimize the electromagnetic radiation (EMC) the electrical contact between the body and the tuning plate is excellent due to the springs in the tuning plate.

A further object of the invention is to alleviate at least one of the problems of prior art.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention a tuning device arranged on a tuning plate for use in a radio equipment in which tuning of the equipment is made by using a force directed substantially perpendicular towards said tuning, including:

a number of depressed parts said parts being depressed in relation to said plate, each part being so designed as to form a corrugate surface converging towards a common point;

a central plate integrated with each of said depressed parts in order to receive said tuning force, said depressed parts being separated from each other but integrated with said central plate and converging towards a center of the central plate.

In accordance with a second aspect of the invention a tuning plate in a radio equipment including a number of cavities, the electrical properties of which are to be tuned, and including a number of tuning devices as claimed in any one of the claims 1-5, wherein the tuning devices are arranged side by side integrated on the tuning plate and positioned in relation to each of the cavities.

The central idea in the invention is to make a tuning plate with tuning units with straight and narrow slits that reach out diagonally from a center square and to have multiple depressions in the tuning plate in each tuning unit so that the tuning plate is wave-formed around the center square in order to minimize the resistance to earth, to improve the IM characteristics and to allow a sufficient movement of the plate in the axial direction of a tuning screw. A sufficient movement in this case means at least 2-3 mm.

It is the combination of the slits and the depressions that makes a Afunctional and advantageous solution possible.

5a

The result will be a filter which is possible to tune automatically, which is more cost effective and which has less risk for intermodulation.

If the tuning plate with the tuning units and springs is designed according to the preferred embodiment of the invention, the number of fastening screws in the lid may

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WO 98/54783

PCT/SE98/00918 be reduced by approximately 60% compared to the state of the art solution.

Tuning and electrical sealing function is united in one detail, that is in the tuning plate.

When using the solution with depressions and four slits the area of the tuning plate cooperating with the center conductor is increased by 50% compared with the state of the art system. The filter is easier to tune if the area is larger (C = ε * A/d).

The force needed to tune the filter is decreased by a factor around 2-4 due to the easier movement of the tuning unit compared with the the rose-formed state of the art pattern which means that the thickness of the tuning plate may be decreased.

The area of the holes in the tuning plate may be decreased to around half the area needed today by using the straight and narrow slits that reach out diagonally from the center square.

No electrically isolating PTFE (teflon)-washers are needed on the tuning plate to isolate some of the tuning screws from the tuning plate because of the smaller area of the slits in the tuning plate and because of the better contact between the body and the tuning plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail with reference to preferred embodiments of the present invention, given only by way of example, and illustrated in the accompanying drawings, in which:

FIG.1 schematically illustrates a side cutaway view of a conventional state of the art filter for e.g. a mobile telephone system.

FIG.2 schematically illustrates a perspective view of a conventional state of the art tuning plate with holes for the screws joining body, tuning plate and lid for a filter in e.g a mobile telephone system^

FIG.3 schematically illustrates a side cutaway view of one cavity in a conventional state of the art filter for e.g a mobile telephone system.

FIG.4 schematically illustrates a perspective view of the preferred embodiment of the present invention.

FIG.5 schematically illustrates a top view of the preferred embodiment of 15 the tuning plate where depressions and slits in one tuning unit are shown.

FIG.6 schematically illustrates a side cutaway view of the depressions in one tuning unit of the preferred embodiment of the present invention.

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WO 98/54783

PCT/SE98/00918

FIG. 7 schematically illustrates a top view of the preferred embodiment of the tuning plate where springs between the tuning units, at the edge of the tuning plate, holes for screws for the joining of the base, lid and tuning plate and also depressions and slits in ten tuning units are shown.

FIG. 8 schematically illustrates the preferred embodiment of the spring-elements placed at the edge of the tuning plate of the present invention.

FIG. 9a schematically illustrates a side view of the preferred embodiment of the spring elements between two tuning units in the tuning plate.

FIG. 9b schematically illustrates a top view of the 15 preferred embodiment of the spring elements between two tuning units in the tuning plate.

FIG. 10 schematically illustrates a side view of one spring at the edge of a tuning plate of the present invention

FIG. 11 schematically illustrates a side cutaway view 20 showing where the present invention would be located in a filter for e.g a mobile telephone system.

FIG. 12 schematically illustrates a perspective view of a filter with a tuning plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Briefly described, the present invention provides an apparatus fortuning of radio/BP-filters used in e.g. mobile radio systems. The present invention focuses on the tuning plate 300 placed between the body 111 and the lid 110.

Figure 4 schematically illustrates a perspective view of the preferred embodiment of the invention. The tuning plate 300 has, in this embodiment, ten tuning units 401.

Figure 5 illustrates schematically a top view of the tuning plate 300 where depressions 1, slits 2 and the bump 3 in

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one tuning unit 401 accordning to one embodiment are shown.. The tuning plate has depressions 1 and slits 2 . The depressions 1 are integrated in the tuning plate 300 and formed with different lengths (a,b) as shown in figure 6 which is important in order to obtain a soft movement in the plate. The distance (a) should be longer than distance (b) and the angle between distance (a) and (b) should be around 9 0°, preferably more than 90 ° to obtain a soft movement.

In the center of a tuning unit an elevated area, a bump 3 is made in order to absorb the force (F) from the tuning screw. The bump is placed in the middle of a square 5. The slits 2 extend radially on the tuning plate andL beyond the ···· outmost depression 6 as can be seen in Figure 5. The tuning· • ·· ····

:..: : 15 plate is wave formed between the slits 2.

·· • · • · · · : ·... This means that the depressions 1 are formed as a series of ridges 7 and valleys 8 and that these ridges 7 and valleys ······ • ·

.. . 8 are formed as squares with slits 2 cutting the squares in • · • · · .··. : four substantially identical parts. Another geometrical • · *:··*: 20 forms , such as circles or polygons are also possible.

• «· • · · • · · • ·· ·;···· Figure 6 schematically illustrates a side cutaway view of the depressions around one tuning point of the preferred embodiment of the present invention.

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Figure 7 schematically illustrates a top view of the preferred embodiment of the tuning plate 300 where springs 4 at the edges of the tuning plate, springs 11 between the tuning units 401, holes 9 for screws for the joining of the base 111, lid 110 and tuning plate 3 00 and also depressions

I, . slits 2 and bumps 3 in ten tuning units 401 are shown.

The plate 300 is preferably 0.3 mm thick and is preferablymade of silver-electroplated-brass. The tuning plate is shielded, that is earthed with the help of the springs 4,

II. The central idea in the invention is to make a tuning plate 300 with tuning units 401 with straight and narrow slits 2 that reach out diagonally from a center square 5 and to have multiple depressions 1 in the tuning plate 300 in each tuning unit so that the tuning plate is wave-formed around the center square 5 in order to minimize the resistance to earth, to improve the IM characteristics and to allow a sufficient movement of the plate in the axial direction of a tuning screw 113. It is the combination of the slits 2 and the depressions 1 that makes a functional and advantageous solution possible.

The wave form consists of depressions with two ridges 7 arid two valleys 8 in the following order: level center square 5, ridge 7, valley 8, ridge 7,valley 8, level surface of the tuning plate 300. The ridges 7 are on the same level as the tuning plate and the valleys 8 are on the same level as the center square 5 as shown in figure 6.

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i· r

Figure 8 schematically illustrates the preferred embodiment of the springs 4 placed at the edge of the tuning plate.

The springs are integrated in the tuning plate and made byremoving material from the tuning plate. A hoLe 9 for a screw joining the base 111, lid 110 and the plate 300 together is also shown.

Figure 9a schematically illustrates a top view of the preferred embodiment of the springs 11 between two tuning units 401 in the tuning plate 3 00. These springs 11 are made by removing material from the tuning plate 300.

Figure 9b schematically illustrates a side view of the preferred embodiment of the spring elements 11 between two tuning Units 401 in the tuning plate 3 00. The figure shows ·*· · • · · ί ·ί·; how these springs 11 are bent to make better contact with ···· • · · *:Σ* *15 the base by contacting in one point 12.

• · • · · · ·· • · • ···

Figure 10 schematically illustrates a side view of one .;...: spring at the edge of the tuning plate 300. The tuning • · · plate is grounded in the boxwall of the filter. The spring • · · • ·· • : 4 is an elongated member integrated in a tuning plate 300 .

·· » * .·.··. 20 The springs improve the contact between the body 111 and • · · ·;···: the tuning plate 300. The spring 4 is simple to mannfaeturp and has a flexible design and a very good contact with a relatively short distance (around 1.5 mm) between the springs 4. Each spring 4 is bent as shown in Figure 10, so that contact between the base 111 and each spring 4 is made j

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only in a point 10 and not in a large area. Usually the filters for radio base stations which are tuned using a tuning plate are manufactured using a casted part with the filter cavities (here called the base 111), a tuning plate

300 and a lid 110.

Although the embodiments described above both use a screw to create the adjustment of the capacitance, other types of adjusting means and capacitance means may be used. The use of the screw especially provides a more convenient method for automatic testing by using robots to merely turn the screw. It also means that when tuning the filter only one tool is needed. Although the embodiments described above both use a screw to create the adjustment of the

...: capacitance, other types of adjusting means and. capacitance • · 9

9 9 • · · · 9

5..115 means may be used. The use of the screw especially provides • · · ···· · • · ;·. a more convenient method for automatic testing by using • · ·· : ·... robots to merely turn the screw. It also means that when tuning the filter only one tool is needed.

······ • · • · · • · • · *5.* .20 It is apparent that one or more tuning plates may be placed • ·· • ·

.....: in one filter, that each tuning plate has one or several • · · iJ.J tuning points, that the springs may be separate elements «····· which are fastened to the tuning plate or the fc&gt;ody, that a 5 filter may have one or more cavities and that the number of ridges and valleys in the wave-formed parts of the tuning

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plate may be one or more without departing from the spirit of the invention.

The embodiments described above serve merely as 5 illustration and not as limitation. It will be apparent to one of ordinary skill in the art that departures may be made from the embodiments described above without departing from the the spirit and scope of the invention. Therefore, the invention should not be regarded as being limited to the examples described, but should be regarded instead as being equal in scope to the following claims.

• r · « • · · • · * • · · · · • ·· • « » · • · · « · · · · • · &lt;'· • ·

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