FR2591392A1 - HIGH FREQUENCY FILTER COMPRISING A CERAMIC RESONATOR COMPENSATED IN TEMPERATURE - Google Patents

Abstract

A high frequency filter comprising a temperature compensated ceramic resonator is disclosed. The filter 100 includes a ceramic resonator 116 interposed between a first and a second compensator disc 114, 120 providing temperature compensation, low loss mounting and heat removal from the resonator. Good thermal contact between resonator 116 and disks 114, 120 is established by a compressive force applied by copper plates 112, 128 and a copper casing 124, the resonant frequency can be tuned by a tuning piston ceramic 118 positioned by a brass bush 134 in a copper tube 130, 132. The invention applies in particular to antenna combiners. (CF DRAWING IN BOPI)

Description

The present invention relates generally to

  high frequency (HF) filters and more particularly relates to a high frequency filter comprising

  a temperature-compensated ceramic resonator, capable of

  to be used in antenna combiners for coupling several high frequency transmitters with

a single antenna.

  To combine a number of high frequency transmitters, RF signals from each transmitter must be isolated from each other to avoid

  i; teermodulation and any possible damage to transmitters.

  Air-filled cavity type HF filters can be used to provide isolation between HF transmitters. Each of these cavity filters is tuned to let only the RF signal from the transmitter to which it is connected, each RF transmitter producing a signal.

  HF signal of different frequency. A conventional device

  used to compensate for these filters

  cavity is described in the United States patent of

  N ° 4 024 481. But these cavity-filled air filters are expensive and relatively bulky, so

  that they occupy a large valuable space in posi-

  distant antennas located at the top of buildings and

of Mountain.

  The dimensions of high frequency filters can

  be reduced using a ceramic resonator.

  Such a filter using a ceramic resonator

  that is described in the patent of the United States of America

  N 4 241 322. Although constituting a more com-

  pact, the ceramic resonator in such a filter is not compensated for temperature variations of the ceramic because of the power dissipation at

  high frequency in ceramics and so it can pre-

  the resonance frequency is large because of high frequency power dissipation and because the ceramic can not have a temperature coefficient exactly zero. Another filter described in U.S. Patent No. 4,019,161 uses conventional devices for temperature compensation of a ceramic resonator mounted on a micro-integrated circuit substrate, but without providing the same.

  heat dissipation in the ceramic resonator.

  An object of the invention is therefore to provide a compact and inexpensive HF filter comprising a resonator in

  ceramic temperature compensated.

  Another object of the invention is to propose a

  an improved HF filter comprising a ceramic resonator

  than compensated for in temperature and a tuning piston in ceramics

  to change linearly the frequency of

  resonance of the ceramic resonator.

  Another object of the invention is to propose

  an improved HF filter comprising a ceramic resonator

  temperature-compensated temperature coupled thermally with the

  filter housing so as to minimize the increase in

  temperature resulting from the dissipation of

  power in the ceramic resonator.

  In summary, the invention therefore relates to a high frequency filter having an interposed dielectric resonator

  between a first and a second dielectric compensating disc

  than. The resonator and the first compensating disc may

  have concentrically aligned holes in the

  which is introduced a ceramic tuning piston intended

  adjusting the resonance frequency of the ceramic resonator

  than. The resonator, the first and the second compensating disc

  the piston and the tuning piston are locked and

  mutual geometrical relationship by a metal case.

  Input and output signals can be coupled to the RF filter by means of respective input and output probes which can be positioned anywhere.

appropriate copper case.

  Other features and advantages of the invention

  tion will be better understood when reading the description

  following an example of implementation and referring to

  in the accompanying drawings in which: FIG. 1 is a perspective view in partial section of a preferred embodiment of an HF filter according to the invention, FIG. 2 is a simplified diagram of a combination apparatus that uses RF filters according to the invention

  to couple RF signals from transmitters

  with a combiner for application to a common antenna. FIG. 3 is a top view of the HF filter

illustrated in Figure 1.

  Fig. 1 is therefore a perspective view of an HF filter 100 according to the invention, part of the filter 100 has been

  cut to show more clearly the structure

  pool. The filter 100 of FIG. 1 is particularly suitable for use in the antenna combiner of Fig.2 which combines two or more RF transmitters operating in the frequency range 870-990 MHz. The postman

  The nominal uncharged Q of filter 100 is about 14,000.

  The frequency offset of the filter 100 in the ambient temperature range of -30 ° C. to + 60 ° C. is at most KHz relative to the nominal frequency at ambient temperature. The nominal dimensions of the filter 100 are 137.5 mm in diameter and 75 mm in length, compared to 150 mm in diameter and 325 mm in length of a conventional filter with cavities filled with air. In addition, the filter leads to a material cost saving of 60% per

  compared to a filter equivalent to cavities filled with air.

  According to FIG. 1, the filter 100 comprises a resonator

  116 ceramic interposed between a first compensating disk

  114 and a second compensator disc 120. The resonator

  is preferably a composite ceramic

  taking barium oxide, titanium oxide and zirconium oxide and having a dielectric constant

  at least twenty (20). A ceramic compound which

  comes for this use is described in an article by G.H. Jonker and W. Kwestroo, entitled "The Ternary Systems Ba0-TiO2-Sn02 and Ba0-Ti02ZrO2", published in the Journal of American Ceramic Society, Vol. 41, No. 10, October 1978, pages 390 to 394. Among the ceramic compounds described in this article, Ba2Ti9020 in Table VI having 18.5 mole percent BaO, 77.0 mole percent TiO2, and 4.5 mole percent of ZrO 2 and having a dielectric constant of 40 is suitable for resonator 116. Many of the other compositions of the type described in some

  titles may also be suitable. Compensating discs

  The cores 114 and 120 are preferably alumina-free / Al 2 O 3) because the alumina has a low dielectric loss,

  a high thermal conductivity compared to the resonant

  ceramic reactor 116 and a positive dielectric temperature coefficient with respect to that of the resonator

ceramic 116.

  According to an important characteristic of the invention, the negative dielectric temperature coefficient of the

  ceramic resonator 116 can be practically compensated

  se by the positive dielectric temperature coefficient

  compensating discs 114 and 120 of alumina. Other-

  In other words, the dielectric temperature coefficient of

  -36 ppm / C of the ceramic resonator 116 can be practiced

  compensated by the dielectric temperature coefficient

  +113 ppm / C of the compensating discs 114 and 120 in alumina, or the temperature frequency coefficient of +7 ppm / C of the ceramic resonator 116 can be substantially compensated by the temperature frequency coefficient of -63 ppm / C compensating discs 114 and 120 of alumina. As is known, the frequency temperature coefficient of a dielectric material

  has a polarity opposite to that of the temperature coefficient

  dielectric strength and is proportional to both

  physical dimensions and the dielectric temperature coefficient

  this material. Therefore, the desired compensation is achieved by selecting the appropriate thickness of the compensator disc 114 and 120 of alumina. In addition, the compensating discs 114 and 120 in alumina provide room temperature compensation, minimize the temperature increase due

  the high frequency power dissipation of the resonant

  ceramic resistor 116 by introducing a low thermal resistance between the ceramic resonator 116 and the top plate and bottom plate 112 and 128 of the filter housing, while minimizing the overall high frequency losses of the filter, by supporting the resonator 116 away from the plates 112 and 128 introducing

  losses with alumina at low loss. A force of com-

  pressure exerted by the plates 112 and 128 maintains a

  good thermal contact between the resonator 116 and the

  114 and 120 so that the thermal resistance between the resonator 116 and the filter housing is lower than

  at 1 C / W (that is, 0.68 C / W predicted by the analysis of

  reception). Therefore, according to another characteristic of the invention, the filter 100 can be associated with high power transmitters because the temperature rise due to the dissipation of energy in the resonator 116 is

  minimized by the relative thermal resistance

  low between the ceramic resonator and the housing

  of the filter. In other words, with a high frequency energy

  of twelve Watts dissipated in the filter 100, the temperature

  The temperature of the resonator 116 is only 8 C above

  above ambient temperature and filter frequency

- only shifts 42 KHz.

  To return to Fig. 1, the copper case

  filter 100 completely encloses the ceramic resonator

  116 and provides the compression force that maintains the geometric relationship between the resonator 116 and the compensating discs 114 and 120 of alumina. The casing has a copper top plate 112 which fits on a pot 124 of copper. The upper plate 112 is welded to the pot 124. The latter also has an inner ring 126 with tapped holes for receiving screws 138. The lower copper plate 128 is fixed to the pot 124 by the screws 138. The resonator 116 and the

  ceramic compensator discs 114 and 120 are now

  held against each other by a force of compro-

  by the lower plate 128. The resonator 116 and the ceramic compensating discs 114 and 120 may also be assembled by a suitable adhesive,

  for example sintered glass or an adhesive film.

  According to another characteristic of the invention, the resonator 116 with the disks 114 and 120 can be closed individually or collectively to avoid any degradation of the electrical characteristics of the filter, resulting from moisture. The resonator 116 and the disks 114 and 120 can be hermetically sealed

  with low-loss glass, such as dielectric ink

  that Engelhard A-3702 melted at high temperature.

  The resonance frequency of the resonator 116 in ceramics

  It can be adjusted linearly by means of a tuning rod 102 and a dielectric tuning piston 118 fixed thereto. The resonance frequency of the resonator 116 decreases linearly when the tuning piston 118 is introduced into the concentric holes of the disk 114 and the resonator 116. The tuning piston 118 is preferably

  made of the same ceramic as the resonator 116.

  But in other applications, the tuning piston 118 may be of any suitable dielectric material. The tuning piston 118 not only produces a variation

  linear resonance frequency but also eliminates

  parasitic resonance modes (maintaining

  stents the overall dimensions of the copper case when the resonator frequency 116 is set), it reduces to

  minimum reduction of the Q factor of the resonator (because it

  is a low loss dielectric) and allows

  114 and 120 to be in good thermal contact with the reflector 118 over the entire upper surface and the surface

  lower. Although resonator 116 is granted

  by means of the tuning piston 118, other arrangements

  Conventional agreements may also be appropriate.

  The tuning rod 102 is preferably made of nickel steel, such as Invar, plated with copper. The stem

  102 is threaded and is screwed into a

  corresponding die in the upper portion 108 of a socket 134. The sleeve 134 has a threaded lower portion which penetrates into a threaded portion of a copper lid 130. The lid 130 is welded to a tube of

  copper 132 welded in turn on the upper plate 112.

  The lower and inner part of the sleeve 134 is

  not tapped so that the tuning rod 102 is not

  held only in the upper and inner portion 108 of the sleeve 134. The upper portion 108 of the sleeve 134 is also slotted and threaded so that a locking nut 104 can be used to fix the position of the rod 102 and the piston agree 118 ceramic. A locking nut 106 is also used to secure the

  position of the lower part of the sleeve 134 by

port to the copper lid 130.

  According to another characteristic of the invention, the sleeve 134, the tuning rod 132 and the tube 130, 132 may be of different materials, each having different coefficients of expansion to compensate for the resonant frequency variations of the resonator 116. with the ambient temperature. For example, the tuning rod 102 is preferably a nickel plated copper steel while the socket 134 is preferably brass and the

2S91392

  tube 130, 132 preferably of copper. The movement of

  tuning piston 118 made of ceramic in the range of

  ambient conditions can be modified by changing the

  effective length of the brass sleeve 134. The length

  The effective amount of the brass sleeve 134 is adjusted by turning this sleeve 134 into or out of the tube 130, 132. Temperature compensation is thus obtained by the difference of the expansion coefficients and the respective dimensions between the shank. 132, the brass sleeve 134 and the copper tube 130, 132. This arrangement can compensate for the worst case of variation of 0.8 ppm / C of the coefficient

  frequency temperature of the entire filter.

  The high frequency signals are coupled with the filter 100 by means of two probes 122 accessible by respective connectors 136. In the present mode

  of the filter 100, two probes 122 are available.

  in front of the resonator 116 on the pot 124, at 90

  one of the other, illustrated by FIG.

  save space, the probes 122 can be arranged in any appropriate position of the cabinet of the

  filter, for example, on the upper plate 112.

  The dimensions of the different elements of an embodiment of the filter 100 intended to operate at frequencies between 865 and 900 MHz are indicated below in Table I. In this embodiment, the ionisator 116 and the piston of FIG. 118 are made of a Ba2Ti9020 ceramic compound, the disks 114 and 110 are made of alumina, the tuning rod 102 is made of copper-plated nickel steel, the sleeve is made of brass and

  the filter housing is made of copper. The exact dimensions

  elements of this filter embodiment

  depending on the desired operating frequency

  and materials chosen for each element. -

  Filter dimensions in millimeters Element Diam. ext. Diam. int. Length Resonator 116 68.07 32.00 19.61 Disc 114 71.12 32.00 28.93 Disc 120 71.12 - 28.62 Piston 118 31.11 - 34.42 Rod 102 9.52 - 88.9 Pot 124 142.87 139.7 79.88 Tube 132 41.27 38.1 25.4 Socket 134 19.05 9, 52 31.75

  Fig. 2 represents an apparatus combining

  A filter for coupling RF transmitters 201, 202 and 203 having different frequencies with a common antenna 231. Filters 211, 212 and 213 are preferably filters 100 according to the invention. The combiner 221 may be any suitable conventional antenna combiner, such as that described and illustrated in U.S. Patent No. 4,375,622. Using the HF filter of the invention for filters 211, 212 and 213 , the imperatives of global dimensions and congestion of

  the combination apparatus of FIG. 2 can be net-

  reduced. Since congestion is essential

  for remote antennas, a subdivided economy

  stantial can be achieved using the filter 100

according to the invention.

  In summary, a high frequency filter with a high Q factor has been described including a temperature compensated ceramic resonator. The whole filter

  is temperature compensated, it is optimized thermal-

  such that the rise in temperature due to the dissipation of energy in the resonator is reduced to

  minimum, and with low total losses in high frequency

  accordingly. In addition, this filter is significantly smaller than conventional filters with cavities filled with air. The HF filter according to the invention can be advantageously used in many applications, for example in a combiner apparatus for coupling several transmitters

  HF of different frequencies with a common antenna.

  Of course, various modifications can be made by those skilled in the art to the embodiment described and illustrated by way of non-limiting example.

  without departing from the scope of the invention.

he

Claims (16)

  1 - High frequency filter, characterized in that it comprises a resonator (116) comprising a   upper surface and a lower surface and   of a dielectric material having a predetermined rate of temperature-resonant frequency variation, a first and a second compensating device   (114, 120) each having a top surface and an   lower face respectively disposed above and below.   below the resonator, the first and the second compensating devices being made of a dielectric material having a rate of variation of resonant frequency with the temperature of direction opposite to that of the predefined rate   variation, and a housing comprising a larger surface area   (112), a bottom surface (128) and a side surface (124) for enclosing and holding under   compression the resonator between the first and the second dis-   compensating positives, the upper surface and the surface   lower part of said housing being thermally coupled   with the upper surface of the first   compensator and the lower surface of the second   compensator for discharging the heat of said resonator 2 - filter according to claim 1, characterized   in that said housing further comprises a probe of   trea (122) and an output probe (122) disposed at a predetermined distance from each other for coupling respective input and output signals with the high frequency filter, 3 - Filter according to claim 1, characterized in that said resonator (116) and the first compensator device (114) further comprise respective holes aligned concentrically with each other, said high frequency filter further comprising a tuning device (102, 118) constitated by a dielectric material and which   be introduced into the holes of the first   thinker and resonator to change the frequency of resonance of the resonator.   4 - Filter according to claim 3, characterized in that said tuning device comprises a tuning rod (102) and a tuning piston (118), the tuning piston being constituted by the same dielectric material than the resonator.   - Filter according to claim 4, characterized   in that the tuning rod (102) is threaded and said bolt-   tier further comprises a threaded bushing (134) for receiving said tuning rod.   6 - Filter according to claim 5, characterized in that said tuning rod (102), said sleeve (134) and the casing (124) consist of different materials having different coefficients of expansion with temperature to compensate for variations frequency   resonator resonance with temperature.   7 - A filter according to claim 3, characterized in that said housing c further comprises an input sensor (122) and an output sensor (122) disposed at a predetermined distance from each other for coupling signals respective input and output with said high frequency filter.   8 - Filter according to claim 1, characterized   in that said first and second devices   Thinkers (114, 120) are made of alumina.   9 - Filter according to claim 1, characterized in that said resonator (116) is made of a dielectric material comprising barium oxide BaO,   titanium oxide TiO2 and zirconium oxide ZrO2.   - High frequency filter, characterized in that   it comprises a resonator (116) with a larger surface area   a lower surface made of a   having a predetermined thermal conductivity, first and second compensating devices (114,   > each with an upper surface and an inner surface   located respectively above and below   below the resonator, the first and the second compensating devices being made of a dielectric material having a thermal conductivity greater than the thermal conductivity of the resonator's electrical material, and a housing comprising an upper surface (112), a surface   lower section (128) and a lateral surface (124) for   close and maintain under compression the resonator between   the first and the second compensating devices, the   upper face and the lower surface of the housing being   thermally coupled with the upper surface of the first   first compensating device and the lower surface of the second compensating device respectively to evacuate of the heat of said resonator.   11 - Filter according to claim 10, characterized   in that said housing further comprises a probe of   (122) and an output probe (122) arranged at a dis-   predetermined frequency of each other to couple signals   respective input and output levels with said filter at high frequency.   12 - Filter according to claim 10, characterized in that said resonator (116) and the first compensator device (114) further comprise respective holes aligned concentrically with each other, said filter comprising   furthermore, a tuning device (102, 118) makes a   dielectric electrode and being insertable into the holes of the first compensator device and the resonator to change the resonance frequency of the resonator 13 - Filter according to claim 12, characterized   in that said tuning device comprises a stem of   cord (102) and a tuning piston (118), the tuning piston being made of the same dielectric material as the resonator 14 - Filter according to claim 13, characterized in that said tuning rod (102) is threaded , the housing further comprising a threaded bushing (134) for receive the chord rod.   Filter according to claim 14, characterized   characterized in that the tuning rod (102), the socket (134) and the housing (124) are made of different materials having different coefficients of expansion with temperature to compensate for variations in the frequency   resonator resonance with temperature.   16 - Filter according to claim 12, characterized   in that said stacker further comprises an input sensor (122) and an output sensor (122) disposed at a predetermined distance from each other for coupling respective input and output signals with said high frequency filter,   17- Filter according to claim 10, characterized   in that said first and second devices   compensators (114, 120) are made of alumina.   18 - Filter according to claim 10, characterized   in that said resonator (116) is made of a material   dielectric material containing barium oxide BaO,   titanium oxide TiO2 and zirconium oxide ZrO2.   19 - High frequency filter, characterized in that it comprises a resonator (116) with an upper surface and a lower surface and a hole which pours it, the resonator being made of a ceramic material having a dielectric constant of minus twenty (20) and with a predetermined rate of resonant frequency variation with temperature, a first compensator device (114) with an upper surface and a lower surface and a hole therethrough, the surface   lower end of the first compensating device being   placed between the upper surface of the resonator so that the respective holes are aligned concentrically,   and the first compensating device being made of a   dielectric having a rate of change of resonant frequency with the temperature opposite to that of the predetermined rate of variation, a second compensating device 259139 2   (120) with an upper surface and a lower surface, the upper surface of the second compensator being disposed against the lower surface of the resonator   and the second compensating device being made of a   dielectric material with a frequency variation rate   resonance with the temperature opposite to the prede-   a variation device, a tuning device (102, 118) made of the same ceramic material as the resonator and   be introduced into the holes of the first compensating device   and resonator to change the frequency of reso-   of the resonator and a box comprising a surface   (112), a lower surface (128) and a   lateral face (124) for enclosing the first device   compensator, the resonator and to maintain   the resonator device between the first and the second   compensating devices, the upper surface and the   lower face of said housing being thermally coupled   respectively with the upper surface of the first   compensator and the lower surface of the second   compensator for removing heat from said resonator.   - Filter according to claim 19, characterized   in that said first and second compensating devices   (114, 120) are made of alumina.   21 - Filter according to claim 19, characterized   in that said resonator (116) is made of a material di-   Electrical containing barium oxide BaO, oxide   titanium TiO2 and zirconium oxide ZrO2.   22 - High frequency filter, characterized in that   it comprises a resonator (116) with a larger surface area   and a bottom surface and a hole therethrough the resonator being made of a dielectric material having   a predetermined thermal conductivity and a predetermined rate   end of resonance frequency variation with the time   a first compensating device (114) with an upper surface and a lower surface and a hole therethrough, the lower surface of the first state compensating device disposed against the upper surface of the resonator so that the respective holes are   concentrically aligned, the first compensating   the dielectric material having a resonant frequency variation rate with the temperature opposite the predetermined rate of change, and the dielectric material of the first compensating device having a   thermal conductivity greater than the thermal conductivity   of the dielectric material of the resonator, a second compensator device (120) with an upper surface and a lower surface, the upper surface of the second compensator device being disposed against the lower surface of the resonator, the second compensator device   being made of a dielectric material having a rate of   frequency of resonance with the temperature opposite   at the predetermined rate of change and the dielectric material   of the second compensator device having a further   thermal conductivity greater than the thermal conductivity   dielectric material of the resonator, a tuning device (102, 118) made of a dielectric material and insertable into the holes of the first compensator device and the resonator for changing the resonance frequency of the resonator and a housing comprising a surface   (112), a lower surface (128) and a   lateral face (124) for enclosing the first device   thinker, the resonator and to maintain under compression   the resonator between the first and second devices   thinkers, the upper surface and the lower surface   of the housing being thermally coupled with the surface   of the first compensating device and the lower surface of the second compensating device respectively   to evacuate the heat of said resonator.   23 - Filter according to claim 22, characterized in that the first and second compensating device (114, 120) are made of alumina.   24 - Filter according to claim 22, characterized   characterized in that said resonator (116) is made of a dielectric material containing barium oxide (BaO) of titanium oxide (TiO2) and zirconium oxide (ZrO2). -