WO2022229450A1

WO2022229450A1 - Filter with mixed ceramic waveguide and metal technique

Info

Publication number: WO2022229450A1
Application number: PCT/EP2022/061607
Authority: WO
Inventors: Juandi SONG; Yuhua XIAO
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2021-04-30
Filing date: 2022-04-29
Publication date: 2022-11-03

Abstract

A filter unit (4) is formed with ceramic waveguide and sheet metal waveguide technique. The filter unit (4) comprises one or more ceramic waveguide resonators (302) and one or more sheet metal resonators (301, 303). The ceramic waveguide resonator and sheet metal resonator is coupled together by a coupling window, a printed metal strip line on a printed circuit board or a metal pin.

Description

FILTER WITH MIXED CERAMIC WAVEGUIDE AND METAL TECHNIQUE

TECHNICAL FIELD

Embodiments herein relate to filters. In particular, they relate to ceramic waveguide filter and sheet metal filter.

BACKGROUND

In 5G communication, two types of frequency ranges have been defined, Frequency Range-1 , i.e. Sub-6 GHz, which is less than 6GHz, and Frequency Range-2, i.e. millimeter wave, which is above 24GHz. With the development of 5G communication, multiple-input and multiple-output (MIMO) technology is widely used in Sub-6 GHz base station product, in which amount of filter unites (FUs) need to be integrated with antenna unit (AU) or radio unit (RU). To get size, weight and cost benefit, ceramic waveguide filter unit (CWG FU) become popular instead of metal FU. It is easy to solder onto radio mother board, low pass filter (LPF) board or antenna calibration network (AC) or power splitter board, which will reduce the radio unit size and weight.

However, there are so many limitations of CWG FU. The first is the size limitation due to reliability issue, since ceramic material is easy to crack when soldering on board with big size. If more poles are needed to realize better out of band attenuation, CWG FU may not be a good solution. The second is the loss limitation, CWG FU is usually soldered with a printed circuit board (PCB) low pass filter (LPF) to suppress remote harmonics. Strip line PCB LPF usually has big loss compared with metal LPF and microstrip line PCB LPF will bring extra coupling from one batch to another. Thirdly, CWG FU has limitation for coupling achievement. It’s very difficult to use CWG technique to achieve wide band filter with multi transmission zeros. Fourthly, with the technical development of Advanced Antenna Systems (AAS), there are more and more multiband Time Division Duplexing (TDD) or Frequency Division Duplexing (FDD) application cases require multiband filter. The fifth, the 2nd harmonic of CWG FU is closer to the pass band of a radio unit. A multipoles LPF needs to be added to recede the harmonic. To find a way to get farther or weaker harmonic and reduce LPF poles is necessary. Due to those limitations, radio products can use CWG filter are limited.

Traditional metal FU has good performance and reliability. However, it has big size or volume and higher cost and is not a good solution for MIMO system. CWG FU and sheet metal FU is popular in 5G AAS system to filter out unwanted signal. But Both CWG FU and sheet metal FU has usage defects.

SUMMARY

As a part of developing embodiments herein, problems and limitations with CWG FU and traditional metal FU will further be discussed.

CWG FU has some limitations in design, such as the number of poles, the number of transmission zeros, bandwidth, transmission zeros achievement etc. It is necessary to find a suitable method to solve these limitations and increase the advantages of CWG FU. To find a way to connect CWG technique with other technique will benefit those products greatly.

CWG FU also has limitation factors in production, which cannot be used in complex radio systems. If the length and width of CWG FU in mass production are more than 60mm, it is so easy to crack when the FU is soldered on board. It is also unreliable during long-term radio work progress. CWG FU is always soldered with a PCB LPF to get better out of band attenuation, the LPF will bring much loss and extra coupling from two near paths.

Sheet metal FU has good reliability in production, but it has worser power handing capacity and bigger size or volume compared with CWG FU. Sheet metal band pass filter (BPF) is usually combined with a sheet metal LPF to get better out of band attenuation, the sheet metal LPF has smaller insertion loss compared with the PCB LPF.

Mixed filter with CWG technique and other technique such as sheet metal to solve CWG’s limitation above will be a good way. One FU unit can be composed of two parts:

CWG part and sheet metal parts. The mixed FU will have both advantages of CWG and sheet metal. The design solution can be flexible according to different specifications of radio.

The FU with mixed material will have better insertion loss and power handling compare with small size sheet metal or benefit for reliability compared with CWG FU. This kind of FU also can be used for indoor small base station and traditional macro base station. To further reduce the radio unit size and weight, integrate two different passbands or multiple passbands to one radio unit is a new popular way. But multiple passbands CWG FU will have big size, which has reliability risk in production. The mixed material FU, e.g. one band is CWG FU and another band is sheet metal FU, is a suitable solution to get multiple passbands.

There is no doubt that mixed material FUs will be a new popular solution in base station and will be more and more widely used with the better development of ceramic manufacturing technology. To introduce sheet metal together with CWG material in one filter can solve those design issues and provide advantages to use different techniques in different bands in a multiband radio.

As discussed in the background, CWG FU has harmonic close to the 2nd harmonic of the pass band and need to add multipoles LPF to get better attenuation. To introduce sheet metal together with CWG in one filter can get farther and weaker harmonic, which will reduce the number of poles of LPF needed and get a better FU with less loss.

Therefore, it is an objective of embodiments herein to provide a filter with both CWG and metal materials to improve the performance.

According to one aspect, the object is achieved by a filter unit composed with CWG and metal materials. The filter unit comprises one or more ceramic waveguide resonators and one or more sheet metal resonators. The CWG resonators and sheet metal resonators may be cascaded with each other.

According to embodiments herein, in order to make full use of the advantages of both CWG FU and sheet metal FU, a filter unit with mixed CWG material and sheet metal is formed. Several kinds of filter units have been provided according to embodiments herein.

According to some embodiments herein, the filter unit may be formed by applying a sheet metal resonator before a first CWG resonator and after the last CWG resonator. That is a sheet metal resonator may be placed before a first CWG resonator and after a last CWG resonator. The numbers of sheet metal resonator may be random depends on design requirement. All sheet metal resonators and ceramic resonators form one filter unit, which will reduce the ceramic volume to get better reliability compared with a filter unit with all ceramic resonators. This kind of mixed FU will also have better power handing capacity compared with the FU with all sheet metal resonators. Compared with the CWG filter, the mixed filter also will get better 2nd harmonic attenuation and easy to realize wide band filter.

According to some embodiments herein, the filter unit may be formed by combining one sheet metal band pass filter with another CWG band pass filter to form a dual band FU. In other words, the dual band filter unit may comprise a first and second band pass filters. The first band pass filter comprises one or more ceramic waveguide resonators, and the second band pass filter comprises one or more sheet metal resonators. According to some embodiments herein, the filter unit may be formed by combining two band pass filters, each band pass filter may be a mixed filter comprising one or more ceramic waveguide resonators and one or more sheet metal resonators.

The two band pass filters may be soldered together directly or combined by PCB strip line. The dual band filter unit may be used for both TDD system and FDD system. The filter type and the number of resonators of two bands may be adjusted according to radio requirement. This kind of dual band FU will get better reliability than the dual band FU with two CWG filters when the FU need to realize more poles. If the dual band FU is composed with all ceramic resonators, it will have big size and is hard to production. If the dual band FU is composed with all sheet metal resonators, it will have big size, volume, weight and worser power handling capacity.

According to some embodiments herein, the filter unit may be formed by combining a sheet metal LPF with a CWG band pass filter to suppress remote harmonics. That is the one or more ceramic waveguide resonators may form a band pass filter, and the one or more sheet metal resonators may form a low pass filter. The sheet metal LPF will bring lower loss compared with a PCB LPF. Two methods may be used to implement the combined filter, e.g. soldering by PCB pad or connecting by RF connectors. This kind of filter unit formed by CWG BPF and sheet metal LPF will have both reduced insertion loss and increased out of band attenuation.

According to some embodiments herein, a CWG resonator may be a single mode CWG resonator or a multimode CWG resonator, and the filter unit may comprise one or more multimode CWG resonator.

The filter with mixed CWG and sheet metal according to embodiments herein have some advantages, for examples:

• Reduced size and weight for radio unit with ceramic resonators.

• Solving the design limitations of CWG filter such as the number of poles and zeros, bandwidth, capacitive zero achieving etc. Providing more chance to use CWG technique.

• Easy to get wide bandwidth and better harmonic attenuation.

• Getting better reliability while reducing the size of ceramic part.

• Realizing complex multiband FU.

• Getting better power handing capacity with small size or volume.

• Realizing better out of band attenuation and getting better insertion loss compared with PCB LPF. • Providing flexible assembling solution for filters, as well as high level building practice solutions, e.g. the mixed filter may be soldered on PCB, or use screw fasten solution by the metal part when connecting with other function units.

• Good performance with appropriate cost.

Therefore, embodiments herein provide a filter unit with improved performance and advantages on bandwidth, out of band attenuation, power handing capacity and reliability with reduced size, flexible assembling and building practice etc.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments herein are described in more detail with reference to attached drawings in which:

Figure 1 shows an example of a sheet metal resonator;

Figure 2 shows an example of a ceramic resonator;

Figure 3 shows an example coupling type between a sheet metal resonator and a ceramic resonator according to embodiments herein;

Figure 4 shows example coupling types between a sheet metal resonator and a ceramic resonator according to embodiments herein;

Figure 5 shows an example filter unit and the frequency response of the filter unit according to embodiments herein;

Figure 6 shows example filter units according to embodiments herein;

Figure 7 shows example filter units according to embodiments herein;

Figure 8 shows an example filter unit according to embodiments herein;

Figure 9 shows an example filter unit comprising a multimode CWG resonator according to embodiments herein; and

Figure 10 is a block diagram illustrating a device in which filter units according to embodiments herein may be implemented.

DETAILED DESCRIPTION

According to embodiments herein, a new kind of mixed FU is formed with cascaded

CWG and sheet metal waveguide technique. Each filter is composed with one or more CWG resonators and one or more sheet metal resonators. The surface of a CWG resonator is provided with a shielding layer such as silver, the magnetic field travels inside the shield. The material of CWG always has high permittivity and several kinds of materials can be used, which will reduce the filter size with same electromagnetic wavelength and resonant frequency. The CWG resonator coupling is achieved by removing the silver coating between two near resonators. The sheet metal waveguide resonator is composed by metal material with silver surface and the coupling may be achieved by a window on metal wall.

Figure 1 shows an example of a metal waveguide resonator made by metal material. The metal waveguide resonator has conductive surface or metal plating such as silver etc. The resonant frequency may be changed by a metal cavity with a metal slot, and the metal slot may be any shape to get property frequency. The fine-tuning of frequency may be achieved by tuning screw (not shown) on the top of the cavity or other methods. Tuning screws are screws inserted into resonant cavities which can be adjusted externally. The direction of Electromagnetic field (E-filed) is from the metal slot to the cavity wall as shown by the black arrows.

Figure 2 shows an example of a ceramic waveguide resonator. The ceramic waveguide resonator comprises a ceramic body and a tuning hole with conductive material or metal plating such as silver etc. on the surface of the ceramic body and tuning hole. The resonant frequency may be adjusted by the size of the ceramic body and height of the tuning hole. The direction of E-filed is from the bottom of the ceramic body to the tuning hole. The tuning hole may be any shape to get property frequency.

Figure 3 shows an example of a coupling type between a sheet metal resonator 1 and a ceramic resonator 2 according to embodiments herein. The coupling between two different resonators in this example is a coupling widow 3. A part of metal plating on the sheet metal resonator 1 may be removed to realize a coupling window on the metal resonator and some area of the metal plating on the surface of the ceramic resonator 2 may be removed to realize a coupling window on the ceramic resonator. The two coupling windows with the same size are related to the actual coupling value, which will influence the filter response.

Slot indicated with 101 is the capacitive load of the metal resonator 1 and hole indicated with 201 is the capacitive load of the ceramic resonator 2. The slot 101 and hole 201 can reduce the resonator size, which also has silver plating.

The size of the slot 101 and the shape of the hole 201 will influence the frequency of the resonators. The location and size of the coupling window 3 may be adjusted based on different required coupling values. As shown in Figure 3, the coupling window 3 on the sheet metal wall of the metal resonator 1 is towards the no-silver-surface of the ceramic resonator 2. Two different resonators may be soldered together or connected by conducting resin at the coupling window 3 to form one filter unit.

Figure 4 (a) shows another example of a coupling type between a sheet metal resonator 1 and a ceramic resonator 2 according to embodiments herein. These two kinds of resonators may be soldered on a PCB and the coupling between these two kinds of resonators is realized with a printed metal strip line 3a on the PCB. The shape and size of the printed strip line 3 will influence the coupling value.

According to some embodiments herein, metal pins may be assembled or soldered together with the metal and ceramic resonators and used to connect the metal and ceramic resonators. Figure 4 (b) shows such an example, where a metal pin 3b connects a sheet metal resonator 1 and a ceramic resonator 2 together according to embodiments herein.

An electronic signal transfers from air in the metal resonator 1 to the ceramic resonator 2 through e.g., a coupling window, a PCB strip line, metal pins or any other types of coupling structures.

Figure 5 (a) shows an example of a filter unit 4 combined with two kinds of resonators, i.e. ceramic resonators and sheet metal resonators according to embodiments herein. The filter unit 4 comprises two sheet metal resonators 301, 303 and one ceramic resonator 302, and these resonators 301 , 302, 303 are composed to form a 3-order filter. The coupling windows between the sheet metal resonators 301 , 303 and the ceramic resonator 302 are indicated with 311 and 312 respectively. RF ports to connect with the metal cavities 301 , 303 are indicated with 321 and 322, respectively. The frequency response of the composed 3- order filter unit 500 is shown in Figure 5 (b).

Figure 6 (a) shows another example of a filter unit 5 combined with two kinds of resonators, i.e. ceramic resonators and sheet metal resonators according to embodiments herein. There are two sheet metal resonators 501 and 506 and four ceramic resonators 502-505. The coupling windows between the sheet metal and ceramic resonators are indicted with 511, 515. The coupling windows between the ceramic resonators are indicated with 512-514. RF ports are indicated with 521, 522.

Figure 6 (b) shows an example of a filter unit 6 combined with two kinds of resonators, i.e. ceramic resonators and sheet metal resonators according to embodiments herein. Different from the filter unit 5 shown in Figure 6(a), the sheet metal resonators 601, 608 may also be soldered on two sides of a ceramic body. The ceramic body comprises six ceramic resonators 602-607. The two sheet metal resonators 601 , 608 and six ceramic resonators 602-607 are combined to form an 8-order filter. The two sheet metal resonators 601 , 608 of the filter unit 6 are assigned to the different sides of the ceramic body. The coupling windows between the sheet metal and ceramic resonators are indicted with 611, 621. RF ports are indicated with 631 , 641.

Figure 7 (a) shows a dual band filter unit 7 combined with two kinds of filter, a sheet metal filter 701 and a ceramic filter 702 according to embodiments herein. The sheet metal filter 701 and ceramic filter 702 both are soldered on a printed circuit board. The PCB coupling between these two kinds of filters is indicated with 711. The metal filter 701 may comprise one or more resonators, and in this example, 4 resonators. The ceramic filter 702 may comprise one or more resonators, and in this example, 4 resonators.

Figure 7(b) shows another dual band filter unit 8 comprises a sheet metal filter 801 and a ceramic filter 802 combined to compose the dual band filter unit 8. The coupling between the metal resonator and ceramic resonator is indicated with 811 , which is a coupling widow, i.e. an area without metal plating, and is easy to combine the two kinds of resonators. The metal filter 801 may comprise one or more resonators, and in this example, 6 resonators. The ceramic filter 802 may comprise one or more resonators, and in this example, 6 resonators.

Figure 8 shows a filter unit 9 combined with a CWG BPF 901 and a sheet metal LPF 902. The cover of the sheet metal LPF 902 is indicated with 907, which may be a metal type or a PCB type. Two metal pins 903 and 904 are to connect the sheet metal LPF 902 and the CWG BPF 901. If the material of the LPF 902 cover is PCB, the two pins are connected to PCB pad and the CWG BPF 901 is soldered on the PCB. If the material of LPF 902 cover is metal, the two pins are connected to two 50W connectors and soldered together with the CWG BPF part. The final input port and output port of the filter unit 9 are indicated with 905 and 906. These two ports are 50W RF connectors, which can be joint with other parts from radio unit.

According to some embodiments herein, a multiband filter unit with any number of channels may be composed by these two kinds of resonators, i.e. one or more ceramic resonators and one or more sheet metal resonators may be combined to achieve a multiband filter. Figure 9 (a) shows a mixed filter unit 10 combining one or more multimode and single mode CWG resonators and one or more sheet metal resonators. Compare with a single mode CWG resonator which has one resonate frequency, a multimode CWG resonator has multiple resonate frequencies and has good insertion loss in small size, but the spurious is very close to the pass band. A mixed filter structure combining multimode CWG resonator with sheet metal resonators provides improved out band performance. As shown in Figure 9 (a), the mixed filter unit 10 comprises a triple modes CWG resonator 1001 with 3 resonate frequencies, two single mode CWG resonators 1002, 1003, two single mode sheet metal filters 1004, 1005. The sheet metal filter 1004 comprises a metal chassis 1008, a sheet metal resonator 1006 and a cover 1010. The sheet metal filter 1005 comprises a metal chassis 1009, a sheet metal resonator 1007 and a cover 1011.

The surface of CWG resonators 1001 , 1002, 1003 are metalized or partly metalized. The single mode CWG resonators 1002, 1003 are coupling with the multimode CWG resonator 1001 by coupling structures such like windows 1014, 1015 or patterns.

The sheet metal resonator 1006 is coupling with the CWG resonator 1002 by a window 1012 in the sheet metal chassis 1008 which towards the CWG resonator 1002. The sheet metal resonator 1007 is coupling with the CWG resonator 1003 by a window 1013 in the sheet metal chassis 1009 which towards the CWG resonator 1003. And the CWG resonators 1002, 1003 have at least a pattern without metallization which toward the coupling window 1012, 1013.

Figure 9 (b) shows the topology of the mixed filter unit 10, where the coupling of the resonators comprised in the mixed filter unit 10 are indicted by number 1, 2, 3, 4, 5, 6, 7. As shown in Figure 9(b), the input In of the mixed filter unit 10 is at the 1 st filter 1 , i.e. the single mode sheet metal filter 1004, and the output Out of the mixed filter unit 10 is at the 7th filter 7, i.e. the single mode sheet metal filter 1005. As can be seen in the topology, the single mode CWG resonator 1002 is coupling with the 3th, 4th, 5th filters, which is realized with the three modes of CWG resonator 1001 , and the single mode sheet metal filter 1005 is coupling with all three modes of CWG resonator 1001 as well. This topology can achieve a BPF with transmission zero.

Some advantages of using a triple mode resonator include smaller in size, better in loss and better in loss to volume rate compared to only using single mode resonator.

One can see from Figure 9 (a), a triple mode resonator has larger size than a single mode resonator, which means each mode has a better quality (Q) value, and that means less loss compared with the single mode resonator. Although the triple mode resonator has larger size, the total size of the mixed filter unit may be reduced since the total number of resonators is decreased, and therefore a better in the loss to volume rate is achieved.

The mixed filter unit 10 may be used as a BPF. The triple modes CWG resonator 1001 can achieve 3 poles in the BPF.

To summarize, to make full use of the advantages of both CWG FU and sheet metal FU, a mixed or combined FU according to embodiments herein is formed with one or more CWG FU(s) and one or more sheet metal FU(s). That is one FU may contain two kinds of resonators: one or more sheet metal resonators and one or more CWG resonators.

According to some embodiments herein, to realize complex filter requirement with better performance, two different kinds of filters may be combined to form a dual band FU, where each filter may be a mixed filter with CWG FU(s) and sheet metal FU(s) or not.

According to embodiments herein, the coupling between two filters with different materials may be achieved by a coupling window, a strip line on a PCB, metal pins or any other suitable techniques. The coupling window may be any shape not limited to what is shown in this application.

The one or more sheet metal and ceramic resonators may be any structure, not limited to what have been shown in this application.

By adding sheet metal resonator, the size of CWG filter part is reduced appropriately which solves the reliability issue of a big size CWG filter. The mixed or combined FU according to embodiments herein will reduce the ceramic volume to get better reliability compared with the FU with only ceramic resonators. This kind of mixed material FU will also have better power handing capacity compared with the FU with only sheet metal resonators. This kind of mixed material FU is also easy to get wider bandwidth and increased harmonic attenuation.

By combining a CWG BPF with a sheet metal LPF, a mixed FU according to embodiments herein with reduced insertion loss and increased out of band attenuation may be achieved.

According to embodiments herein, the numbers of poles or zeros may be added based on this kind of mixed material FU. It’s easy to realize dual band filters with ceramic technology.

The filter unit 4,5,6,7,8,9,10 according to the embodiments herein may be employed in various electronic devices or any devices or apparatus where filtering is needed. Figure 10 shows a block diagram for a device 900. The device 900 may comprise a radio unit 910, which may comprise an antenna unit 912, a transmitter, a receiver or both, i.e. a transceiver Rx/Tx 9140 etc. The device 900 comprises the filter unit 4, 5, 6, 7, 8, 9, 10. The filter unit 4, 5, 6, 7, 8, 9, 10 may be comprised in the radio unit 910, in the antenna unit 912, or in the transceiver Rx/Tx 914. The device 900 may comprise other units, where a memory 920, a processing unit 930 are shown. The device 900 may be a radio base station for a cellular communication system or any device where a filter is needed for radio frequency.

The word "comprise" or “comprising”, when used herein, shall be interpreted as non limiting, i.e. meaning "consist at least of".

The embodiments herein are not limited to the above described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appended claims.

Claims

1. A filter unit (4, 5, 6, 7, 8, 9, 10) comprising one or more ceramic waveguide resonators and one or more sheet metal resonators.

2. The filter unit (4, 5, 6, 7, 8, 9, 10) according to claim 1 , where a coupling between a ceramic waveguide resonator and a sheet metal resonator is achieved by a coupling window.

3. The filter unit (4, 5, 6, 7, 8, 9, 10) according to claim 1 , where a coupling between a ceramic waveguide resonator and a sheet metal resonator is achieved by a printed metal strip line on a printed circuit board or a metal pin.

4. The filter unit (4, 5, 6, 7, 8, 9, 10) according to any one of claims 1 -3, wherein the ceramic waveguide resonators and sheet metal resonators are cascaded with each other.

5. The filter unit (4, 5, 6, 7, 8, 9, 10) according to any one of claims 1 -3, wherein a sheet metal resonator is placed before a first ceramic waveguide resonator and after a last ceramic waveguide resonator.

6. The filter unit (4, 5, 6, 7, 8, 9, 10) according to any one of claims 1-3 is a multiband filter unit comprising at least a first and second band pass filters, wherein the first band pass filter comprises one or more ceramic waveguide resonators, and the second band pass filter comprises one or more sheet metal resonators.

7. The filter unit (4, 5, 6, 7, 8, 9, 10) according to any one of claims 1 -3 is a multiband filter unit comprising at least a first and second band pass filters, wherein each band pass filter comprises one or more ceramic waveguide resonators and one or more sheet metal resonators.

8. The filter unit (4, 5, 6, 7, 8, 9, 10) according to any one of claims 1 -3, wherein the one or more ceramic waveguide resonators form a band pass filter, and the one or more sheet metal resonators form a low pass filter.

9. The filter unit (4, 5, 6, 7, 8, 9, 10) according to any one of claims 1-8, wherein one or more ceramic waveguide resonators is a multimode ceramic waveguide resonator.

10. A multiband filter unit comprising one or more filter units (4, 5, 6, 7, 8, 9, 10) according to any one of claims 1 -9.

11 . An antenna unit (912) comprising one or more filter units (4, 5, 6, 7, 8, 9, 10) according to any one of claims 1 -9.

12. A radio unit (910) comprising one or more filter units (4, 5, 6, 7, 8, 9, 10) according to any one of claims 1 -9.

13. A device (900) comprising one or more filter units (4, 5, 6, 7, 8, 9, 10) according to any one of claims 1-9.

14. The device (900) according to claim 13, wherein the electronic device is a base station for a cellular communication system.