GB2528390A

GB2528390A - Ceramic filter apparatus and method of use thereof

Info

Publication number: GB2528390A
Application number: GB1512166.8A
Authority: GB
Inventors: Elizabeth Francis Phillips
Original assignee: Radio Design Ltd
Current assignee: Radio Design Ltd
Priority date: 2014-07-17
Filing date: 2015-07-13
Publication date: 2016-01-20
Also published as: GB201412682D0; GB201512166D0

Abstract

Ceramic filter apparatus, said filter including a first ceramic filter means having one or more resonating means defined therein and arranged to resonate at at least a first radio frequency, and at least a second filter means having one or more resonating means defined therein and arranged to resonate at at least a second radio frequency, characterised in that the first ceramic filter means is multiplexed to the second filter means using one or more transmission lines. The one or more transmission lines include any or any combination of any structure that is arranged or is capable of carrying alternating current of radio frequency therealong, a printed circuit board with one or more electrical conductive strips provided thereon, a micro-strip, a coaxial cable, a stripline, a trough line, or any suitable transmission line of a particular or pre-determined electrical length. Preferably the one or more transmission lines are provided externally of the filter bodies. By using one or more transmission lines to multiplex or couple the first and at least second filter means together, the filter means have no required orientation and can therefore be provided in any suitable orientation to provide a compact filter design.

Description

CERAMIC FILTER APPARATUS AND METHOD OF USE

THEREOF

This invention relates to ceraniic filter apparatus and to a method of use thereof Although the following description refers almost exclusively to ceramic filter apparatus for use as part of a telecommunications system or network, it will be appreciated by persons skilled in the art that the ceramic filter apparatus could be used in any suitable system or network as required and/ or could be combined with non-ceramic filter apparatus.

lelecommunication networks rely on base transceiver stations (ETS) 2 to transmit and receive signals via a mast mounted antenna 4 to mobile electronic devices, as shown in figure 1.

Transmission and receive radio frequency signa's pass a'ong coaxial cables 5 between the BTS 2 and the antenna 4. The technology within BTSs has advanced significantly and for many of the constituent modules, has also reduced in size considerably. The size reduction has meant that some of the equipment that previous'y occupied a ground based rack (i.e. at the base of mast 6), as shown in figure 1, is now sufficiently compact to be housed in a single box known as a remote radio head (RRTT) 8, which can be mounted at the top of a cefl site mast 6, as shown in figure 2. A vital component of any BTS/RRH is the front end filter. The front end filter can take the form of a bandpass fflter for time divisiona' duplex systems ((TDD), meaning that the system transmits and receives radio frequency signals on the same frequency but at different times) or a diplexer for frequency division duplex systems (ftl)1)), meaning that the system is capable of transmitting and receiving radio frequency signals simultaneously but at different ftc q u en ci es).

Filters are electronic devices which allow an electromagnetic wave to be transmitted therethrough. They arc designed in such a manner so as to aHow radio frequency signals at one or more pre-determined frequencies to pass through the device (passband frequencies) and to substantially prevent radio frequency signals at frequencies other than the one or more pre-determined frequencies from passing through the device (stop band frequencies). The frequency selectivity of a filter can be optimised by locating transmission zeros at both or either side of the nassband freuuencv at finite non-zero freuuencies. A

I I I

transmission zero can be defined as one or more frequencies at which attenuation of a filter is infinite. This improves the performance of the filter to stop interference and prevent blocking. However, conventional filters that provide the required frequency sdectivity are typicafly large and there is a requirement in the industry to optimise both the size of the filter and the frequency selectivity of the filter.

An exampk of a conventional Rh front end apparatus 10 found within a BTS or RRTI is shown in figure 3. Apparatus 10 includes a diplexer arrangement shown by dotted line 9 comprising a transmission bandpass filter 12 in a first transmission signa' pathway 14 and a receive bandpass fflter 16 in a first receive signal pathway 18. The filters 12, 16 are diplexed together at a common junction 20. The common junction 20 is connected to an apparatus input/output port 22.

Diplexer 9 has input/output ports 34 in the transmission pathway and input/output ports 36 in the receive pathway. The transmission bandpass filter 12 is connected via port 34 to a transmission signal source 24 via a power amplifier 26 in the transmission signal pathway 14. The receive bandpass filter 16 is connected via port 36 to a signal receiver 28 via a low noise amplifier 30 in the receive signal pathway 18. The filter arrangement 10 has tough performance requirements including low passband loss and high rejection characteristics that are used to suppress spurious emissions arid protect the receiver 28 from interference and blockers. The filter technology used in BTSs and 1IHHs has remained largely the same since the start of mobile telecommunication systems and is dominated by air cavity filter technology. As such, the filter block is taking up an increasingly large proportion of the BTS and RRH as other components of the BTS and RRI I arc able to be reduced in size.

It is therefore a requirement to provide alternative filter technology that is smaller in size than conventional filter technology while maintaining the filter performance.

It is known to use ceramic waveguide filters to provide a more compact filter design. Ceramic filters are typically formed from a sofld block of high permittivity tow-loss ceramic, the exterior of which is coated in a conducting material, such as metal. The ceramic is typically formed by pressing and firing, and is then coated in a high conductivity adhesive paint. As the relative permittivity of the ceramic materia' is increased, the guide wavekngth will reduce, thus a'so reducing the physica' size of the filter for a specific resonant frequency, but this is offset by a reduction in resonator Q factor. This is particularly advantageous if an aim is to reduce the space required for the filter apparatus and/or apparatus with which the filter is associated in use. For example, if the permittivity of the ceramic materia' is chosen such that the ceramic waveguide resonator filter has the same Q factor as a conventional TEM or combline filter, then it will be physically less than half the volume of the conventional lNM filter. However, a problem with ceramic waveguide filters is that in order to couple two ceramic filters together, such as for example when providing a common junction between the transmission and receive band pass filters in a RRII, the physical layout of the coupled filters is very restrictive. This is because the filters have to be physically coupled by their common ports and the first resonating sections next to the common ports have to be in line with each other. In the prior art example shown in figure 4, in order to achieve the required coupling between two ceramic filters 12, 16 at the common junction 20, the ceramic filters are joined in such a way that they protrude outwardly in opposite directions (shown by arrows 29, 31) from a common port 20 connecting the two filters together. This results in a physical layout where the individual input/output ports 34, 36 of the filter are arranged at opposite ends of the coupied filter assembly and are significantly separated in space, which is inconvenient when integrating the filter equipment within a RRI I or B'lS and makes it difficult to produce a compact filter design. In figure 4, filter 12 is a rectangular ceramic waveguide filter comprising a ceramic body portion 11 with a plurality of resonating sections 13 defined therein. A plurality of electrically conductive apertures 15 are defined between resonating sections 13. This filter is typically not capable of having cross couplings between resonating means. Filter 16 is a'so a rectangular ceramic waveguide filter comprising a ceramic body portion 11 with resonating sections 13 provided in a different arrangement to that of filter 12 to allow cross coupling between resonating sections. A plurahty of electricafly conductive apertures 15 are defined between resonating sections 13.

It is therefore an aim of the present invention to provide ceramic filter apparatus that overcomes the abovementioned problem.

It is a further aim of the present invention to provide a method of using ceramic filter apparatus that overcomes the abovementioned problem.

According to a first aspect of the present invention there is provided ceramic filter apparatus, said filter apparatus including a first ceramic filter means having one or more resonating means defined therein and arranged to resonate at at least a First radio frequency, and at least a second filter means having one or more resonating means defined therein and arranged to resonate at at least a second radio frequency, characterised in that the first ceramic filter means is multiplexed to the second filter means using one or more transrrussion lines.

The advantage of the present invention over the prior art is that by using one or more transmission lines to multiplex or couple the first and at least second filter means together, the filter means have no required orlentatu)n and can therefore be provided in any suitable orientation to provide a compact filter design. This arrangement has not previously been used for ceramic filter technology. Ihus, the resonating means/sections adjacent to the common port of each filter means are not required to be in-line (i.e. they can be out of line or in a non-linear arrangement) with each other when the fillers are muhipexed together. This is in contrast to conventional ceramic wavegtude filter arrangements where two or more filters are coupled together and wherein the resonang means/secñons and the common ports of the ceramic \vaveguide filter means have to be in-line or in a linear arrangement with each other.

Preferably the one or more transmission lines is/are an external structure to a body of the first ceramic filter means and the second filter means. thus, the one or more transmission hnes are located externally of the First ceramic filter means and the second filter means.

The common port of the first and at least second filter means are typically the ports of the filter that are multiplexed or coupled to each other in use.

The at least second filter means can include ceramic filter means or non-ceramic filter means. Thus, the present invention can allow multiplexing of at least two ceramic filter means together or can allow multiplexing of a ceramic filter means with one or more other types of filter means. The other types of Filter means can include one or more air cavity filters and/or the like.

Preferably at least one of the ceramic filter means is in the form of a ceramic waveguide filter means but could include or be in the form of a combline ceramic filter means.

Thus, in one embodiment at least one ceramic waveguide filter means is multiplexed to at least one other ceramic waveguide filter means.

In one embodiment at least one ceramic waveguide filter means is multiplexed to at least one combline ceramic filter means.

In one embodiment at least one ceramic waveguide filter means is multiplexed to at least one non-ceramic filter means.

In one embodiment at least one combline ceramic filter means is multiplexed to at least one non-ceramic filter means.

Tn one embodiment at least one combhne ceramic lifter means is muftiplexed to at least one further combline ceramic filter means.

in one embodiment the ceramic filter means includes a ceramic body portion or a body portion consisting of or induding ceramic materia' with one or more resonating means or sections contained or defined therein.

PreferaNy the one or more transmission hnes are ocated externally of said ceramic body portion.

Preferably the ceramic body portion is a continuous, substantially continuous or a solid block of ceramic material.

One or more electrically conductive apertures, channels, holes and/or blind holes can be defined in the ceramic filter means or ceramic body porthon and can be located between two or more resonating means or sections. Ihis typically enables cross coupling between non-adjacent or non-sequentially numbered resonating means within the ceramic body portion, thereby allowing transmission zeros at finite, non-zero frequencies and optimising the frequency selectivity of the filter apparatus.

Preferably the entire exterior surface of the ceramic material, substantially the entire exterior surface of the ceramic material, or at least the external surface of the filter in the area or boundary in which the resonating means are provided, is metallised and/or is provided with an electrically conductive material, layer(s) and/or coating(s) thereon.

Preferably the entire surface(s) or substantially the entire surface (s) of the electrically c onductive through apertures, channds, ho'es and/or blind ho'es are provided with an electrically conductive material, layer(s) and/ or coating(s) and/or are metallised thereon. Thus, the interior walls of the apertures, channels, holes and/or blind holes have one or more meta' layers provided thereon in one exampk. The provision of the electricafly conductive through apertures, channels, holes, and/ or blind holes allows the same to act in an equivalent manner to metallic rods provided in conventional air filled waveguide fflters.

Preferably the first ceramic filter means has a radio frequency passband that is distinct, different, substantially different and/or separate to the radio frequency passband of the at least second filter means (i.e. the two radio frequency passbands do not overlap, although the radio frequency passbands could be adjacent to each other in the electromagnetic spectrum).

Preferably a plurality of resonating means within the first ceramic filter means resonate at the same or substantially the same or similar frequencies so that the first ceramic filter means operates at the First radio frequency.

Preferably a plurality of resonadng means within the second filter means resonate at the same or substantially the same or similar frequencies so that the second filter means operates at the second radio frequency.

Preferably the one or more transmission lines include any or any combination of any structure that is arranged or is capable of carrying alternating current of radio frequency therealong, a printed circuit board CB) with one or more electrical conductive strips provided thereon, a micro-strip, a coaxial cable, a stripline, a trough line, or any other suitable transmission line of a particular or pre-determined electrical length.

Preferably the one or 1m)re transmission lines are provided externally of the filter bodies.

The transmission line can be any required shape, such as linear, I-shaped, Y-shaped and/or the like.

Tn one embodiment each of the First and at kast second lifter means has a First input/output port arranged at or adjacent one end of the Filter or lifter body and a second input/output port arranged at or adjacent an opposite end of the filter or filter body.

Preferably the second input/output port of the first filter means is the common port for coupling or multiplexing to the common port or first input/output port of the second lifter means.

Preferably the input/output ports of each filter is/are typically coupled to the first or last resonating means of the filter and allows for the input/output of an electromagnetic wave therethrough. For example, one of the input or output ports is

S

coupled to one of the first or last resonating means of the filter and the other of the input or output ports is coupled to the other of the first or last resonating means.

The first and at least second filter means can be provided in-line (i.e. in a linear arrangement or where the common ports are arranged adjacent to each other but the first input/output port or non-common port of the first filter means is arranged at an opposite end to the second input/output port or non-common port of the second filter means), back to back (i.e. in a non-linear arrangement or where the common ports are arranged adjacent to each other and the first input/output port or non-common port of the first filter means is arranged adjacent to the second input/output port or non-common port of the second filter means) or in any orientadon that allows a pre-determined electrical length (phase length) to be provided between that at least two separate filter means.

Preferably the first and at least second filter means are arranged so that the non-common input/output ports, or the First input/ output port of the First filter means and the second input/output port of the second filter means, are arranged relatively close together, such as being adjacent to each other, side by side and/or the like. the term "relatively close together" in one embodiment can mean any distance doser than when the non-common input/output ports are at opposite ends of an in-line, ilnear or substantiafly linear filter arrangement.

Tn one embodiment the first and at kast second Filter means are elongate or substantially elongate in form having a longitudinal axis. Preferably a longitudinal side of each filter means of the at least two filter means are arranged in abutting rdationship, parad, substantially parafld and/or adjacent to each other.

Preferably each resonating means is a portion or section of the filter which is capable of undergoing resonance at a particular electromagnetic frequency or frequencies. Preferably the resonating means arc substantially cuboid in shape in the ceramic waveguide filter means.

According to a second aspect of the present invention there is provided a method of using ceramic filter apparatus, said filter apparatus including a first ceramic filter means having one or more resonating means defined therein and arranged to resonate at at least a first radio frequency, and at least a second filter means having one or more resonaang means defined therein and arranged to resonate at at least a second radio frequency, said method including the steps of multiplexing the first ceramic filter means to the second filter means using one or more transmission lines.

Embodiments of the present invention will now be described with reference to the accompanying figures, wherein: Figure 1 (PRIOR ART) is a simplified view of a conventional telecommunication cell site arrangement; Figure 2 (PRIOR ART) is a simplified view of a fhrther conventional telecomn-iunicathn cell site arrangements; Figure 3 (PRTOR ART) is a simphfied internal view of conventional RF front end apparatus found within a BTS or RRT I; Figure 4 (PRIOR ARt) is a plan view of the two filter means in figure 5 joined together to form a common junction; Figure 5 is a perspective view of two filter means multiplexed together according to an embodiment of the present invention; Figure 6 is a circuit diagram of two filter means multiplexed together as shown in figure 5 and figure 7; Figure 7 is a perspective of two filter means multiplexed together according to a further embodiment of the present lflvefltlnrl.

Referring to Figures 5-7, there is shown a Filter arrangement which aflows a ceramic Filter to be multiplexed with at least one other ceramic Filter and/or with at least one non-cerarmc filter.

In figure 5, a first ceramic waveguide filter 38 is multiplexed with a second ceramic \vaveguide filter 40 and is arranged in line, such that the input/output common port 42 of first filter 38 is multiplexed or coupled to input/output common port 44 of second filter 40 via a T-shaped transmission line 46 to form a common junction. lhe I-shaped transmission line 46 is arranged externally of the filter body pordons.

Both first and second ceramic waveguide filters 38, 40 includes a ceramic body portion 11 having resonating sections 13 contained therein. A plurality of elecfrically conductive apertures 15 are arranged between the resonatng sections 13 to allow cross coupling to take place between non-adjacent resonating sections.

f-shaped transmission line 46 has a common input/output port 48 on a central leg portion 50 and the two input/output ports 42, 44 on an arm portion 52 arranged at one end of central leg portion and substantially transverse or perpendicular thereto.

I"irst ceramic filter 38 also has a first input/output port 39 arranged at an opposite end of the Filter from second common input/output port 42.

Second ceramic filter 40 also has a first input/output port 41 arranged at an opposite end of the filter from second common input/output port 44. All the input/output ports 29, 42, 44, 41 are in-line or substantiafly in-line with each other in this arrangement.

I bach filter 38, 40 has a longitudinal axis and the axes of each filter are typically co-axial with each other. Each filter has at least one long side 888, 88' or side parallel to the longitudinal axis of the filter and at least one short cnd 90, 90'. Short ends 90 of filter 38 is adjacent to and oppositc short end 90' of filter 40.

Figure 6 is an illustration of a circuit diagram of a filter arrangement according to an cmbodirnent of thc prescnt lflVClltiOn. The top circuit 70 represents the first ceramic waveguide filter and the bottom circuit 72 represents the second ceramic waveguide filter. Each filter has a plurality of resonating sections 74 which are electromagnetically coupled together (shown by reference numeral 76). The common input/output port of the two filters is shown by reference numeral 78 and the common input/output ports arc joined togcther by transmission lines 80. 1he first input/output port of the first filter is shown by reference numeral 82 and the second input/output port of the second filter is shown by reference numeral 84.

Cross coupling can take place between some resonating sections 74, as shown by reference numeral 86.

In the further embodiment of a filtet arrangement shown in figure 7, first and second ceramic filters 38, 40 arc arrangcd back to back, such that a rear or longitudinal edge 54, or longitudinal side 88, of first ceramic filter 38 is adjacent to, parallel with and in abutting relationship with a rear or longitudinal edge 56, or longitudinal side 88', of second filter 40. This produccs a significantly more compact physical hyout of the fiftcrs than the arrangement shown in figurc 5 and in thc prior art hyout shown in figure 4.

Non-common input/output ports 39, 41 of the two filters 38, 40 are arranged side by side to each other (i.e. relatively close together compared to the arrangcmcnt in figure 4). Tn addition common input/output ports 42, 44 are arranged side by side of each other (i.e. relatively close together).

Tn the embodimcnt shown in fiire 7, a Y-shapcd transmission ilne 58 is provided to multiplex the input/output ports 42, 44 of the two ceramic filters 38, 41) together to form a COflMTh)fl junction. Y-shaped transmission line 58 has a common input/output pot-f 60 on a central leg portion 62 and the two input/output ports 42, 44 on two arm portions 64, 66 arranged at one end of central leg portion and at an acute angle thereto. Arm portions 64, 66 diverge outwardly from central leg portion 62. Transmission line 58 is located externally of the filters 38, 40.

lhus, it can be seen that by using external transmission lines to multiplex the two ceramic filters together, the filters can be arranged in-line to each other or out of line to each other, thereby allowing a range of different filter designs to be produced in which the filters are provided in different orientations with respect to each other.

Claims

Claims 1. Ceramic filter apparatus, said Liter apparatus including a first ceramic filter means having one or mote resonating means defined therein and arranged to resonate at at least a first radio frequency, and at least a second filter means having one or more resonating means defined therein and arranged to resonate at at least a second radio frequency, characterised in that the first ceramic filter means is multiplexed to the second filter means using one or more transmission lines.
2. Ceramic filter apparatus according to claim 1, wherein the second filter means is a ceramic filter means.
3. Ceramic filter apparatus according to claim 1, wherein the second filter means is a non-ceramic filter means.
4. Ceramic filter apparatus according to claim 3, wherein the second filter means is or includes one or more air cavity filters.
5. Ceramic filter apparatus according to claim 1, wherein the first and/or at least second filter means is a ceramic waveguide filter means and/or a combline ceramic filter means.
6. Ceramic filter apparatus according to claim 1, wherein the ceramic filter means includes a ceramic body portion or a body portion consisting of or including ceramic material with one or more resonating means or sections contained or defined therein.
7. Ceramic filter apparatus according to claim 6, wherein ceramic body portion is a continuous or substantially continuous block of ceramic material.
8. Ceramic filter apparatus according to claim 6, wherein one or more electrically conductive apertures, channels, holes and/or blind holes are defined in the ceramic filter means or ceramic body portion, and said electrically conductive apertures, channels, holes and/or blind holes are located between two or more resonating means or sections of the filter.
9. Ceramic filter apparatus according to claim 1, wherein an entire exterior surface, substantially the entire exterior surface, or at least the external surface in the area of the filter in which the resonating means are provided, is metallised and/or is provided with an electrically conductive material, layer(s) and/or coating(s) thereon.
10. Ceramic filter apparatus according to claim 8, wherein the entire surface(s) or substantially the entire surface(s) of the electrically conductive through apertures, channels, holes and/or blind holes are provided with an electrically conductive material, layer(s) and/or coaling(s) thereon.
11. Ceramic filter apparatus according to claim 1, wherein the first ceramic filter means has a radio frequency passband that is distinct, different to or separate to the radio frequency passband of the at least second filter means.
12. Ceramic filter apparatus according to claim 1, wherein a plurality of resonating means within the first ceramic filter means resonate at the same or substantially the same or similar frequencies so that the first ceramic filter means operates at a first radio frequency.
13. Ceramic filter apparatus according to claim 1, wherein a plurality of resonating means within the second filter means resonate at the same or substantially the same or similar frequencies so that the second ceramic filter means operates at a second radio frequency.
14. Ceramic filter apparatus according to claim 1, wherein the one or more transmission lines is any or any combination of a structure capable of carrying an alternating current of radio frequency therealong in use, a printed circuit board with one or mote electrical conductive strips provided thereon, a micro-strip, a coaxial cable, a stripline, a trough line, or a transmission line of a particular or pre-determined electrical length.
15. Ceramic filter apparatus according to claim I wherein the one or mote transmission lines is/are an external structure to a body of the first ceramic filter means and the second filter means.
16. Ceramic filter apparatus according to claim 1, wherein each of the first and at least second filter means has a first input/output port arranged at or adjacent one end of the filter or filter body and a second input/output port arranged at or adjacent an opposite end of the filter or filter body.
17. Ceramic filter apparatus according to claim 16, wherein the second input/output port of the first filter means is the common port for coupling or multiplexing to the common port or first input/output port of the second Liter means.
18. Ceramic filter apparatus according to claim 16, wherein the input/output ports of each filter is/are coupled to the first or last resonating means of the Liter.
19. Ceramic filter apparatus according to claim 1, wherein the first and at least second filter means can be provided in-line, back to back, or in any orientation that allows a pre-determined electrical length to be provided between the first and at least second filter means.
20. Ceramic Liter apparatus according to claim 1, wherein the first and at least second filter means are arranged so that non-common input/output ports, or the first input/output port of the first filter means and the second input/output port of the second Liter means, are arranged closer to each other compared to an arrangement where the non-common input/output ports, or the first input/output port of the first filter means and the second input/output port of the second filter means, are at opposite ends of an in-line, linear or substantially linear filter arrangement.
21. Ceramic filter apparatus according to claim 1, wherein the first and at least second filter means are elongate or substantially elongate in form having a longitudinal axis, a longitudinal side of each filter means being abutting, relationship, parallel, substantially parallel, and/or adjacent to each other.
22. A method of using ceramic filter apparatus, said filter apparatus including a first ceramic filter means having one or more resonating means defined therein and arranged to resonate at at least a first radio frequency, and at least a second filter means having one or more resonating means defined therein and arranged to resonate at at least a second radio frequency, said method including the steps of multiplexing the first ceramic filter means to the second filter means using one or more transmission lines.