WO2022117212A1 - Tunable resonator, tunable frequency filter and method of tuning thereof - Google Patents

Tunable resonator, tunable frequency filter and method of tuning thereof Download PDF

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Publication number
WO2022117212A1
WO2022117212A1 PCT/EP2020/084702 EP2020084702W WO2022117212A1 WO 2022117212 A1 WO2022117212 A1 WO 2022117212A1 EP 2020084702 W EP2020084702 W EP 2020084702W WO 2022117212 A1 WO2022117212 A1 WO 2022117212A1
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Prior art keywords
tunable
resonator
inner hole
liquid metal
frequency
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PCT/EP2020/084702
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French (fr)
Inventor
Abdulrahman WIDAA
Michael Höft
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Christian-Albrechts-Universität Zu Kiel
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Priority to PCT/EP2020/084702 priority Critical patent/WO2022117212A1/en
Publication of WO2022117212A1 publication Critical patent/WO2022117212A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P7/00—Resonators of the waveguide type
    • H01P7/04—Coaxial resonators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P7/00—Resonators of the waveguide type
    • H01P7/10—Dielectric resonators

Definitions

  • Tunable resonator Tunable frequency filter and method of tuning thereof
  • the invention relates to the area of tunable frequency filters for electronic circuits, for example in the area of wireless and microwave systems and components, e.g. for communication systems.
  • An embodiment of the invention is a tunable resonator comprising a hollow ceramic resonator having an inner hole, a reservoir at least partially filled with a liquid metal, a fluid connection between the reservoir and the inner hole and a transport device for transporting liquid metal from the reservoir into the inner hole or from the inner hole to the reservoir, the tunable resonator being tunable to a desired resonance frequency by changing the amount of liquid metal filled into the inner hole.
  • the invention comprises a liquid metal actuated widely tunable bandpass filter maintaining low loss and high quality factors over the whole wide tuning range of frequency.
  • This allows for a new liquid metal-based tuning mechanism for TM mode or other hollow ceramic resonators where the inner hole of the resonator is used as a channel for the liquid metals.
  • This mechanism provides the advantage of getting the highest possible achievable frequency tuning range with minimal losses and high quality factors.
  • the presented tuning mechanism is applied in a simple, low- cost, and efficient configuration where can be controlled using either manual or electrical transport device, e.g. by a pump.
  • the liquid metal can be e.g.
  • a nontoxic gallium-based metal for example, eutectic gallium indium (EGain) and/or Galinstan (GalnSn).
  • EGain eutectic gallium indium
  • GalnSn Galinstan
  • the liquid metal is in direct contact to the functional ceramic material when filled into the inner hole.
  • Mechanical tuning of TM mode-hollow ceramics have been introduced by intruding a screw into the inner hole. The screw cannot have tight contact to the ceramic, which lowers the performance.
  • the use of the inner hole to fill it with a liquid metal to obtain close contact overcomes this problem.
  • guiding the liquid metal with direct contact to the functional ceramic material instead of guiding by a relatively thick Teflon tube (as usually done in most other cases), a simplification of the setup and an increased effect are obtained.
  • the inner hole is covered by a thin layer of covering material, for example, a thin Teflon or lacquer layer.
  • the thin layer shall be thin compared to the diameter of the inner hole, e.g. thin layer shall have a thickness less than 10% or less than 5% of the diameter of the inner hole.
  • the liquid metal is not used only as a movable resonator to tune the frequency, but as a means which directly tunes the resonator, similar to a mechanical tuning screw, but with the benefit of having tighter contact to the ceramic, which significantly increases the tuning range.
  • the liquid metal does not only form an inner part of the resonator but directly influences the tuning.
  • the present invention allows in a first step to design the fixed filter with the order of interest and then employ the liquid metal similar to conventional tuning screws.
  • the tunable resonator comprises a control device which is arranged for tuning the tunable resonator to a desired resonance frequency by changing the amount of liquid metal filled into the inner hole through controlling the transport device.
  • the control device allows for automatic and/or remote tuning of the tunable resonator.
  • the control device can be an electronic control device, e.g. a device with a processor or the like.
  • the hollow ceramic resonator is at least partially covered with metal.
  • the tunable resonator can have a metallic housing. This protects the tunable resonator from external influences, in particular electromagnetic interferences.
  • the tunable resonator is a TM mode resonator.
  • the tunable resonator is a TE mode resonator.
  • the hollow ceramic resonator can be a cylindrical hollow ceramic resonator or any other shape.
  • the transport device is an electrically controllable pump, e.g. a manual or electrical pump, for example, a reciprocating pump, a syringe, or a rotating pump.
  • the pump can be a pneumatic pump which is used to pneumatically control the movement of the liquid metal inside the inner hole of the resonator.
  • the presented invention offers the highest achievable frequency tuning range (more than 100%) with high Q, high power handling capabilities, reduced complexity, and lower cost. Such advantages are highly required in most of the current and future communication systems which make the presented invention a really promising candidate in the tunable filters industry.
  • the tunable resonator can be tuned between a first frequency value and a second frequency value, the first frequency value being less than 50% of the second frequency value. This allows for a wide tuning range.
  • the resonant mode of the tunable resonator can be switched off by filling a defined amount of liquid metal into the inner hole.
  • This provides for an advantageous intrinsic-switching feature of the tunable resonator, which does not require additional hardware.
  • the passband can be easily switched off by just filling a major part, or the whole inner hole, with liquid metal cutting all field lines. Then the resonant mode is “short-circuited” and no more present.
  • Another embodiment of the invention is a tunable frequency filter having one or more tunable resonators of any of the aforementioned embodiments, wherein the resonance frequency of the frequency filter is tunable to a desired value by changing an amount of liquid metal filled into the inner hole of one, more or all hollow ceramic resonators of the tunable resonators.
  • the tunable frequency filter can be a bandpass filter. Also, the tunable frequency filter can be tuned in a wide tuning range of more than 100%.
  • the several tunable resonators may each have its own reservoir and transport device, or one or more groups of several tunable resonators may share a common reservoir and/or transport device. It is also possible that all tunable resonators share the same common reservoir and/or transport device.
  • An embodiment of the invention is a method for tuning a tunable frequency filter having one or more tunable resonators each comprising a hollow ceramic resonator having an inner hole, wherein the resonance frequency of the frequency filter is tuned to a desired value by changing an amount of liquid metal filled into the inner hole of one, more or all hollow ceramic resonators.
  • the tunable frequency filter is tuned to a desired resonance frequency by changing the amount of liquid metal filled into the inner hole of one, more or all hollow ceramic resonators through controlling the transport device or transport devices.
  • the resonant mode of one, more or all of the tunable resonators is switched off by filling a defined amount of liquid metal into the inner hole.
  • Filter units represent a key and essential part of any wireless communication system.
  • tunable filters have gained more attention and rapidly increasing demand in development and industry due to their significant role in improving the efficiency and capabilities of current and future communication systems in comparison with the conventional fixed and switched-bank filters [2], This includes more efficient and flexible spectrum utilization, reduced system complexity, more compact size and reduced power consumption, lower loss and higher capacity, easier to optimize the system performance and apply post-processing, more relaxed specification requirements of components, and better capability to apply softwarebased remote control.
  • Suitable uses of the invention are e.g. in wireless and microwave systems and components, telecommunication systems, wideband transceivers, multi-band transceivers, cognitive radio (CR) systems, next-generation cellular systems, wideband RADAR and satellite payloads, and flexible radio systems like software defined radios (SDR).
  • the invention provides for a high quality factor, high power, and low loss at low cost.
  • the tunable resonator and/or tunable frequency filter of the invention can be used for applications in the frequency range from 0,1 GHz to 100 GHz.
  • Figure 1 shows an electronic circuit with a tunable bandpass filter
  • Figure 2 shows a sectional view of a tunable resonator.
  • the embodiment depicted in figure 1 comprises an input circuitry 1 , a tunable bandpass filter 2, and an output circuitry 3.
  • the input circuitry 1 feeds the tunable bandpass filter 2 with radio frequency (RF) signals having a first bandwidth.
  • RF radio frequency
  • the tunable bandpass filter 2 filters out certain upper and lower frequency ranges from the RF signals, depending on the actual tuning state of the tunable bandpass filter 2, with the result that RF signals having a second bandwidth reach the output circuitry 3 from the tunable bandpass filter 2.
  • the second bandwidth is smaller than the first bandwidth.
  • the tunable bandpass filter 2 is a liquid metal actuated tunable bandpass filter which includes one or more tunable resonators 4 of the type depicted in figure 2.
  • the tunable resonator 4 comprises a hollow cylindrical TM mode ceramic resonator 5, a metallic housing 6, a liquid metal 7, a reservoir 8, a pump 9, a control device 10, and a tube 12.
  • the ceramic resonator 5 is metalized with the bottom and top walls of the metallic housing 6.
  • the ceramic resonator 5 has an inner hole 11 , like an inner chamber.
  • the inner hole 11 is connected on its bottom side opening through a tube 12 to the reservoir 8.
  • the reservoir 8 contains an amount of liquid metal 7.
  • the upper side of the inner hole 11 is open and may be connected through an opening 13 in the metallic housing 6 to the atmosphere.
  • the inner hole 11 of the ceramic resonator 5 is utilized as a channel for the flowing of the liquid metal 7 from the reservoir 8 through the tube 12 to the bottom of the metallic housing 6 and into the inner hole 11 , or back from the inner hole 11 to the reservoir 8.
  • the transport of the liquid metal 7 into the inner hole 11 and back is driven by the pump 9 which is electrically controlled by the control device 10.
  • the amount of liquid metal 7 within the inner hole 11 tunes the frequency of the tunable resonator 4 to a desired value.
  • the ingoing liquid metal 7 functionalizes as a tuning post to change the resonant frequency of the resonator. As liquid metal level increases inside the inner hole 11 , the electromagnetic field is perturbed resulting in a decrease of the resonant frequency.
  • the presented filter demonstrates a wide frequency tuning from 2.33 GHz to 0.67 GHz maintaining low insertion loss ⁇ 1 dB allover the tuning window.
  • the fundamental resonance frequency can be varied by changing the (cross-sectional) dimensions of either the housing or the ceramic.
  • the choice of the dielectric constant of the ceramic has an impact on the resonance frequency.

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Abstract

The invention relates to the area of tunable frequency filters for electronic circuits, for example in the area of wireless and microwave systems and components, e.g. for communication systems. An embodiment of the invention is a tunable resonator comprising a hollow ceramic resonator having an inner hole, a reservoir at least partially filled with a liquid metal, a fluid connection between the reservoir and the inner hole and a transport device for transporting liquid metal from the reservoir into the inner hole or from the inner hole to the reservoir, the tunable resonator being tunable to a desired resonance frequency by changing the amount of liquid metal filled into the inner hole. Another embodiment of the invention is a tunable frequency filter having one or more of such tunable resonators.

Description

Tunable resonator, tunable frequency filter and method of tuning thereof
The invention relates to the area of tunable frequency filters for electronic circuits, for example in the area of wireless and microwave systems and components, e.g. for communication systems.
The project leading to this application has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 811232.
Prior Art
[1] Y. Kobayashi and S. Yoshida, "Bandpass Filters Using TM/sub 010/ Dielectric Rod Resonators," 1978 IEEE-MTT-S International Microwave Symposium Digest, Ottawa, ON, Canada, 1978, pp. 233-235, doi:
10.1109/MWSYM.1978.1123848.
[2] J. Hong, "Reconfigurable planar filters," in IEEE Microwave Magazine, vol. 10, no. 6, pp. 73-83, Oct. 2009, doi: 10.1109/MMM.2009.933590.
[3] Mansour, 2018, “Rod - switched tunable filter*, US 9 , 979 , 063 B2, United states patent.
[4] Huang et al., 2014, “Three dimensional tunable filters with an absolute constant bandwidth and method", US 2016/0049710 A1 , United states patent application publication.
[5] William Weldon Cavey, 2000, “Tunable ceramic filters", 6,147,577, United states patent.
[6] Azarnaminy et al., 2016, “Tunable bandpass filter device and method", US 9.236,846 B2, United states patent.
[7] Schwab et al., 2007, “Electronically tunable dielectric resonator circuits", US 2008/ US 7,352,264 B2, United states patent. [8] F. Huang and R. Mansour, "A novel varactor tuned dielectric resonator filter," 2013 IEEE MTT-S International Microwave Symposium Digest (MTT), Seattle, WA, 2013, pp. 1-3, doi: 10.1109/MWSYM.2013.6697775.
[9] W. D. Yan and R. R. Mansour, "Tunable Dielectric Resonator Bandpass Filter With Embedded MEMS Tuning Elements," in IEEE Transactions on Microwave Theory and Techniques, vol. 55, no. 1 , pp. 154-160, Jan. 2007, doi: 10.1109/TMTT.2006.888582.
[10] F. Huang, S. Fouladi and R. R. Mansour, "High-Q Tunable Dielectric Resonator Filters Using MEMS Technology," in IEEE Transactions on Microwave Theory and Techniques, vol. 59, no. 12, pp. 3401-3409, Dec. 2011 , doi: 10.1109/TMTT.2011 .2171984.
[11] R. R. Mansour, "High-Q tunable dielectric resonator filters," in IEEE Microwave Magazine, vol. 10, no. 6, pp. 84-98, Oct. 2009, doi:
10.1109/MMM.2009.933591 .
[12] R. R. Mansour, F. Huang, S. Fouladi, W. D. Yan and M. Nasr, "High-Q Tunable Filters: Challenges and Potential," in IEEE Microwave Magazine, vol. 15, no. 5, pp. 70-82, July-Aug. 2014, doi: 10.1109/MMM.2014.2321101 .
[13] R. C. Gough, A. M. Morishita, J. H. Dang, W. Hu, W. A. Shiroma and A. T. Ohta, "Continuous electrowetting of non-toxic liquid metal for RF applications", IEEE Access, vol. 2, pp. 874-882, Aug. 2014, doi:
10.1109/ACCESS.2014.2350531 .
[14] C.-H. Chen, J. Whalen and D. Peroulis, "Non-toxic liquid-metal 2-100 GHz MEMS switch", IEEE MTT-S Int. Microw. Symp. Dig., pp. 363-366, Jun. 2007, doi: 10.1109/MWSYM.2007.380446.
[15] G. Mumcu, A. Dey and T. Palomo, "Frequency-agile bandpass filters using liquid metal tunable broadside coupled split ring resonators", IEEE Microw. Wireless Compon. Lett., vol. 23, no. 4, pp. 187-189, Apr. 2013, doi:
10.1109/LMWC.2013.2247750.
[16] A. Pourghorban Saghati, J. Batra, J. Kameoka and K. Entesari, "A miniaturized m icrofluidically reconfigurable coplanar waveguide bandpass filter with maximum power handling of 10 watts", IEEE Trans. Microw. Theory Techn., vol. 63, no. 8, pp. 2515-2525, Aug. 2015, doi:
10.1109/TMTT.2015.2446477. [17] T. Palomo and G. Mumcu, "Microfluidically reconfigurable microstrip line combline filters with wide frequency tuning capabilities", IEEE Trans. Microw. Theory Techn., vol. 65, no. 10, pp. 3561-3568, Oct. 2017, doi:
10.1109/TMTT.2017.2730181 .
[18] N. Mcclung, S. Saeedi and H. H. Sigmarsson, "Band-reconfigurable filter with liquid metal actuation", IEEE Trans. Microw. Theory Techn., vol. 66, no. 6, pp. 3073-3080, Jun. 2018, doi: 10.1109/TMTT.2018.2823307.
[19] N. Vahabisani, S. Khan and M. Daneshmand, "Microfluidically reconfigurable rectangular waveguide filter using liquid metal posts", IEEE Microw. Wireless Compon. Lett., vol. 26, no. 10, pp. 801-803, Oct. 2016, doi:
10.1109/LMWC.2016.2605450.
[20] D. Psychogiou and K. Sadasivan, "Tunable Coaxial Cavity Resonator-Based Filters Using Actuated Liquid Metal Posts," in IEEE Microwave and Wireless Components Letters, vol. 29, no. 12, pp. 763-766, Dec. 2019, doi:
10.1109/LMWC.2019.2950540.
[21] S. Fouladi, F. Huang, W. D. Yan and R. R. Mansour, "High-Q Narrowband Tunable Combline Bandpass Filters Using MEMS Capacitor Banks and Piezomotors," in IEEE Transactions on Microwave Theory and Techniques, vol. 61 , no. 1 , pp. 393-402, Jan. 2013, doi: 10.1109/TMTT.2012.2226601 .
[22] J. Xu, L. Yang, Y. Yang and X. Y. Zhang, "High- Q -Factor Tunable Bandpass Filter With Constant Absolute Bandwidth and Wide Tuning Range Based on Coaxial Resonators," in IEEE Transactions on Microwave Theory and Techniques, vol. 67, no. 10, pp. 4186-4195, Oct. 2019, doi:
10.1109/TMTT.2019.2926251 .
[23] L. Pelliccia, F. Cacciamani, P. Farinelli and R. Sorrentino, "High - Q Tunable Waveguide Filters Using Ohmic RF MEMS Switches," in IEEE Transactions on Microwave Theory and Techniques, vol. 63, no. 10, pp. 3381-3390, Oct. 2015, doi: 10.1109/TMTT.2015.2459689.
[24] G. Basavarajappa and R. R. Mansour, "Design Methodology of a Tunable Waveguide Filter With a Constant Absolute Bandwidth Using a Single Tuning Element," in IEEE Transactions on Microwave Theory and Techniques, vol. 66, no. 12, pp. 5632-5639, Dec. 2018, doi: 10.1109/TMTT.2018.2873383.
[25] Laplanche et al., "Tunable Filtering Devices in Satellite Payloads: A Review of Recent Advanced Fabrication Technologies and Designs of Tunable Cavity Filters and Multiplexers Using Mechanical Actuation," in IEEE Microwave Magazine, vol. 21 , no. 3, pp. 69-83, March 2020, doi: 10.1109/MMM.2019.2958706.
[26] http://www.colemanmw.com/tun_wave_filt.asp
[27] https://www.wainwright-filters.com/standard-filters/digitally-tunable-band-pass- fi Iters
[28] https://www.smithsinterconnect.com/products/rf-mw-mmw-components/rf- filters/rf-tunable-filters/
[29] http://www.klmicrowave.com/
[30] https://www. pastemack. com/nsearch.aspx?Category=Tunable+Filters&sort=y &view_type=grid
[31 ] https://www.bench.com/lark/tunable-filters
[32] https://www.fairviewmicrowave.com/nsearch.aspx?Category=Tunable+Filters& sort=y&view_type=grid
[33] https://nuwaves.com/rf-microwave-product-solutions-catalog/hipertuner-rf- broadband-preselector/
[34] TESAT.de/
[35] https://www.spinner-group.com/en/
[36] rfmicrotech.com/
Object of the invention
Many tunable dielectric bandpass filters have been introduced previously in [3] - [12], Generally, the tuning methods can be categorized into two main techniques: mechanical tuning and electrical tuning. In the mechanical tuning method, the frequency is tuned by using manually or motor-based movable tuning screws/discs. Despite its straightforward tuning and high power handling capability, it’s burdened by the bulky size, high complexity, high cost, and low-speed of tuning. Further, such devices have a very small and limited frequency tuning range.
On the other hand, electrical tuning methods (e.g. semiconductor varactors, RF MEMS) bring the advantages of higher tuning speed, reduced cost and size. However, this category has major drawbacks in terms of linearity, quality factor, and high power handling capability. Also, the challenging integration of semiconductor and MEMS circuits with the resonator structure leads to an increasing loss and significant degradation in the overall quality factor. All of these drawbacks also limit the capability of achieving wide tuning ranges and low losses. [3] presented a hybrid tuning method combining both techniques by proposing an electrically switchable tuning rods to improve the speed of tuning. However, this also shares the same limitations of bulky, complex structure, and small tuning range.
Recently, Liquid metal has been explored as a promising switching and reconfiguration candidate [13] - [20], mainly because of its linear properties, low loss, and high power handling capabilities. Planar and hybrid reconfigurable/tunable filters were introduced with good tuning capabilities [15] - [20], However, in addition to the limited quality factor (Q) and power handling capabilities of such structures, wide tuning ranges cannot be achieved due to the highly increasing loss and significantly degraded Q.
It is therefore an object of the invention to provide for a tunable resonator, a tunable frequency filter and a method for tuning a tunable frequency filter which overcomes at least some of the aforementioned drawbacks.
Embodiments of the invention
An embodiment of the invention is a tunable resonator comprising a hollow ceramic resonator having an inner hole, a reservoir at least partially filled with a liquid metal, a fluid connection between the reservoir and the inner hole and a transport device for transporting liquid metal from the reservoir into the inner hole or from the inner hole to the reservoir, the tunable resonator being tunable to a desired resonance frequency by changing the amount of liquid metal filled into the inner hole.
As a result, the invention comprises a liquid metal actuated widely tunable bandpass filter maintaining low loss and high quality factors over the whole wide tuning range of frequency. This allows for a new liquid metal-based tuning mechanism for TM mode or other hollow ceramic resonators where the inner hole of the resonator is used as a channel for the liquid metals. This mechanism provides the advantage of getting the highest possible achievable frequency tuning range with minimal losses and high quality factors. Besides, the presented tuning mechanism is applied in a simple, low- cost, and efficient configuration where can be controlled using either manual or electrical transport device, e.g. by a pump. The liquid metal can be e.g. a nontoxic gallium-based metal, for example, eutectic gallium indium (EGain) and/or Galinstan (GalnSn). In an exemplary embodiment, a microfluidic eutectic alloy of gallium, indium, and tin — commercially known as “Galinstan” — is chosen due to its advantages of high electrical conductivity (a = 3.46 x 106 Sim) and non-toxic characteristics.
According to an embodiment of the invention, the liquid metal is in direct contact to the functional ceramic material when filled into the inner hole. Mechanical tuning of TM mode-hollow ceramics have been introduced by intruding a screw into the inner hole. The screw cannot have tight contact to the ceramic, which lowers the performance. The use of the inner hole to fill it with a liquid metal to obtain close contact overcomes this problem. By guiding the liquid metal with direct contact to the functional ceramic material instead of guiding by a relatively thick Teflon tube (as usually done in most other cases), a simplification of the setup and an increased effect are obtained.
It is also possible that the inner hole is covered by a thin layer of covering material, for example, a thin Teflon or lacquer layer. The thin layer shall be thin compared to the diameter of the inner hole, e.g. thin layer shall have a thickness less than 10% or less than 5% of the diameter of the inner hole.
However, in contrast to known applications of liquid metal in filters, in the present invention the liquid metal is not used only as a movable resonator to tune the frequency, but as a means which directly tunes the resonator, similar to a mechanical tuning screw, but with the benefit of having tighter contact to the ceramic, which significantly increases the tuning range. In contrast to known applications, in the present invention, the liquid metal does not only form an inner part of the resonator but directly influences the tuning. In contrast to known applications, in the present invention, there are less variations in the IO coupling and the inter-resonator coupling. This positively affects the tuning range, and also it will get less variation in the bandwidth of the bandpass filter. All these become more challenging and critical with higher orders of a filter. The present invention allows in a first step to design the fixed filter with the order of interest and then employ the liquid metal similar to conventional tuning screws.
According to an embodiment of the invention, the tunable resonator comprises a control device which is arranged for tuning the tunable resonator to a desired resonance frequency by changing the amount of liquid metal filled into the inner hole through controlling the transport device. The control device allows for automatic and/or remote tuning of the tunable resonator. The control device can be an electronic control device, e.g. a device with a processor or the like.
According to an embodiment of the invention, the hollow ceramic resonator is at least partially covered with metal. For example, the tunable resonator can have a metallic housing. This protects the tunable resonator from external influences, in particular electromagnetic interferences.
According to an embodiment of the invention, the tunable resonator is a TM mode resonator. Alternatively, the tunable resonator is a TE mode resonator. The hollow ceramic resonator can be a cylindrical hollow ceramic resonator or any other shape.
According to an embodiment of the invention, the transport device is an electrically controllable pump, e.g. a manual or electrical pump, for example, a reciprocating pump, a syringe, or a rotating pump. For example, the pump can be a pneumatic pump which is used to pneumatically control the movement of the liquid metal inside the inner hole of the resonator.
In comparison with the all available high Q state-of-the-art and inventions as in [3] - [12], [21] - [25], and also to the commercially available tunable bandpass filters as [26] - [29], the presented invention offers the highest achievable frequency tuning range (more than 100%) with high Q, high power handling capabilities, reduced complexity, and lower cost. Such advantages are highly required in most of the current and future communication systems which make the presented invention a really promising candidate in the tunable filters industry.
According to an embodiment of the invention, the tunable resonator can be tuned between a first frequency value and a second frequency value, the first frequency value being less than 50% of the second frequency value. This allows for a wide tuning range.
According to an embodiment of the invention, the resonant mode of the tunable resonator can be switched off by filling a defined amount of liquid metal into the inner hole. This provides for an advantageous intrinsic-switching feature of the tunable resonator, which does not require additional hardware. For example, the passband can be easily switched off by just filling a major part, or the whole inner hole, with liquid metal cutting all field lines. Then the resonant mode is “short-circuited” and no more present.
Another embodiment of the invention is a tunable frequency filter having one or more tunable resonators of any of the aforementioned embodiments, wherein the resonance frequency of the frequency filter is tunable to a desired value by changing an amount of liquid metal filled into the inner hole of one, more or all hollow ceramic resonators of the tunable resonators. The tunable frequency filter can be a bandpass filter. Also, the tunable frequency filter can be tuned in a wide tuning range of more than 100%.
In such a tunable frequency filter the several tunable resonators may each have its own reservoir and transport device, or one or more groups of several tunable resonators may share a common reservoir and/or transport device. It is also possible that all tunable resonators share the same common reservoir and/or transport device.
An embodiment of the invention is a method for tuning a tunable frequency filter having one or more tunable resonators each comprising a hollow ceramic resonator having an inner hole, wherein the resonance frequency of the frequency filter is tuned to a desired value by changing an amount of liquid metal filled into the inner hole of one, more or all hollow ceramic resonators. According to an embodiment of the invention, the tunable frequency filter is tuned to a desired resonance frequency by changing the amount of liquid metal filled into the inner hole of one, more or all hollow ceramic resonators through controlling the transport device or transport devices.
According to an embodiment of the invention, the resonant mode of one, more or all of the tunable resonators is switched off by filling a defined amount of liquid metal into the inner hole. This provides for the advantageous intrinsic-switching feature which is already mentioned above. In such a way the tunable frequency filter can be switched off.
Filter units represent a key and essential part of any wireless communication system. In recent years, tunable filters have gained more attention and rapidly increasing demand in development and industry due to their significant role in improving the efficiency and capabilities of current and future communication systems in comparison with the conventional fixed and switched-bank filters [2], This includes more efficient and flexible spectrum utilization, reduced system complexity, more compact size and reduced power consumption, lower loss and higher capacity, easier to optimize the system performance and apply post-processing, more relaxed specification requirements of components, and better capability to apply softwarebased remote control.
Suitable uses of the invention are e.g. in wireless and microwave systems and components, telecommunication systems, wideband transceivers, multi-band transceivers, cognitive radio (CR) systems, next-generation cellular systems, wideband RADAR and satellite payloads, and flexible radio systems like software defined radios (SDR). In any of such cases, the invention provides for a high quality factor, high power, and low loss at low cost. The tunable resonator and/or tunable frequency filter of the invention can be used for applications in the frequency range from 0,1 GHz to 100 GHz.
Further embodiment of the invention is depicted in the drawings. Figure 1 shows an electronic circuit with a tunable bandpass filter, Figure 2 shows a sectional view of a tunable resonator.
The embodiment depicted in figure 1 comprises an input circuitry 1 , a tunable bandpass filter 2, and an output circuitry 3. The input circuitry 1 feeds the tunable bandpass filter 2 with radio frequency (RF) signals having a first bandwidth. The tunable bandpass filter 2 filters out certain upper and lower frequency ranges from the RF signals, depending on the actual tuning state of the tunable bandpass filter 2, with the result that RF signals having a second bandwidth reach the output circuitry 3 from the tunable bandpass filter 2. The second bandwidth is smaller than the first bandwidth.
The tunable bandpass filter 2 is a liquid metal actuated tunable bandpass filter which includes one or more tunable resonators 4 of the type depicted in figure 2.
The tunable resonator 4 comprises a hollow cylindrical TM mode ceramic resonator 5, a metallic housing 6, a liquid metal 7, a reservoir 8, a pump 9, a control device 10, and a tube 12. The ceramic resonator 5 is metalized with the bottom and top walls of the metallic housing 6. The ceramic resonator 5 has an inner hole 11 , like an inner chamber. The inner hole 11 is connected on its bottom side opening through a tube 12 to the reservoir 8. The reservoir 8 contains an amount of liquid metal 7. The upper side of the inner hole 11 is open and may be connected through an opening 13 in the metallic housing 6 to the atmosphere.
The inner hole 11 of the ceramic resonator 5 is utilized as a channel for the flowing of the liquid metal 7 from the reservoir 8 through the tube 12 to the bottom of the metallic housing 6 and into the inner hole 11 , or back from the inner hole 11 to the reservoir 8. The transport of the liquid metal 7 into the inner hole 11 and back is driven by the pump 9 which is electrically controlled by the control device 10. The amount of liquid metal 7 within the inner hole 11 tunes the frequency of the tunable resonator 4 to a desired value. The ingoing liquid metal 7 functionalizes as a tuning post to change the resonant frequency of the resonator. As liquid metal level increases inside the inner hole 11 , the electromagnetic field is perturbed resulting in a decrease of the resonant frequency. The presented filter demonstrates a wide frequency tuning from 2.33 GHz to 0.67 GHz maintaining low insertion loss < 1 dB allover the tuning window. Generally it can be said that for TM-mode resonators, the fundamental resonance frequency can be varied by changing the (cross-sectional) dimensions of either the housing or the ceramic. Furthermore the choice of the dielectric constant of the ceramic has an impact on the resonance frequency.

Claims

Claims:
1 . A tunable resonator (4) comprising a hollow ceramic resonator (5) having an inner hole (11 ), a reservoir (8) at least partially filled with a liquid metal (7), a fluid connection (12) between the reservoir (8) and the inner hole (11 ) and a transport device (9) for transporting liquid metal (7) from the reservoir (8) into the inner hole (11 ) or from the inner hole (11 ) to the reservoir (8), the tunable resonator (4) being tunable to a desired resonance frequency by changing the amount of liquid metal (7) filled into the inner hole (11 ).
2. The tunable resonator of claim 1 , comprising a control device (10) which is arranged for tuning the tunable resonator (4) to a desired resonance frequency by changing the amount of liquid metal (7) filled into the inner hole (11 ) through controlling the transport device (9).
3. The tunable resonator of any of the preceding claims, wherein the liquid metal (7) being in direct contact to the functional ceramic material of the ceramic resonator (5) when filled into the inner hole (11 ).
4. The tunable resonator of any of the preceding claims, wherein the hollow ceramic resonator (5) is at least partially covered with metal (6).
5. The tunable resonator of any of the preceding claims, wherein the tunable resonator (4) is a TM mode resonator.
6. The tunable resonator of any of the preceding claims, wherein the hollow ceramic resonator (5) is a cylindrical hollow ceramic resonator.
7. The tunable resonator of any of the preceding claims, wherein the transport device (9) is an electrically controllable pump. The tunable resonator of any of the preceding claims, wherein the tunable resonator (4) can be tuned between a first frequency value and a second frequency value, the first frequency value being less than 50% of the second frequency value. The tunable resonator of any of the preceding claims, wherein the resonant mode of the tunable resonator (4) can be switched off by filling a defined amount of liquid metal (7) into the inner hole (11 ). A tunable frequency filter (2) having one or more tunable resonators (4) of any of the preceding claims, wherein the resonance frequency of the frequency filter (2) is tunable to a desired value by changing an amount of liquid metal (7) filled into the inner hole (11 ) of one, more or all hollow ceramic resonators (5) of the tunable resonators (4). The tunable frequency filter of claim 10, wherein the tunable frequency filter (2) is a bandpass filter. A method for tuning a tunable frequency filter of claim 10 or 11 , wherein the resonance frequency of the frequency filter (2) is tuned to a desired value by changing an amount of liquid metal (7) filled into the inner hole (11 ) of one, more or all hollow ceramic resonators (5). The method of claim 12, wherein the tunable frequency filter (2) is tuned to a desired resonance frequency by changing the amount of liquid metal (7) filled into the inner hole (11 ) of one, more or all hollow ceramic resonators (5) through controlling the transport device (9) or transport devices (9). The method of claim 12 or 13, wherein the tunable frequency filter (2) is switched off by filling a defined amount of liquid metal (7) into the inner hole (11 ) one, more or all hollow ceramic resonators (5).
PCT/EP2020/084702 2020-12-04 2020-12-04 Tunable resonator, tunable frequency filter and method of tuning thereof WO2022117212A1 (en)

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