EP2731192A1 - Filtre coupe-bande pour interférence de signaux - Google Patents

Filtre coupe-bande pour interférence de signaux Download PDF

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Publication number
EP2731192A1
EP2731192A1 EP12382438.5A EP12382438A EP2731192A1 EP 2731192 A1 EP2731192 A1 EP 2731192A1 EP 12382438 A EP12382438 A EP 12382438A EP 2731192 A1 EP2731192 A1 EP 2731192A1
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EP
European Patent Office
Prior art keywords
resonator
bandstop filter
transmission line
conductive wire
resonant frequency
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP12382438.5A
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German (de)
English (en)
Inventor
José Damboriena Jesús María San
Luciano Lavado Garcia
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Angel Iglesias SA
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Angel Iglesias SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Angel Iglesias SA filed Critical Angel Iglesias SA
Priority to EP12382438.5A priority Critical patent/EP2731192A1/fr
Publication of EP2731192A1 publication Critical patent/EP2731192A1/fr
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01P—WAVEGUIDES; RESONATORS, LINES, OR OTHER DEVICES OF THE WAVEGUIDE TYPE
    • H01P1/00—Auxiliary devices
    • H01P1/20—Frequency-selective devices, e.g. filters
    • H01P1/201—Filters for transverse electromagnetic waves
    • H01P1/205—Comb or interdigital filters; Cascaded coaxial cavities
    • H01P1/2053—Comb or interdigital filters; Cascaded coaxial cavities the coaxial cavity resonators being disposed parall to each other

Definitions

  • the present invention relates to filtering of unwanted electrical signals and, in particular, to filters based on helical elements configured as bandstop filters.
  • Compression systems in current digital television systems are designed to support several normal digital television channels (usually up to six, depending on the used coding and modulating techniques) of acceptable quality, in the spectrum of radioelectric frequencies previously used for a single analog channel.
  • Digital Dividend originally Spanish term "Dividendo Digital"
  • New coding, compression and modulating techniques for broadcasting of terrestrial digital television have indirectly contributed to the process of creating the mentioned digital dividend.
  • the precursor Recommendation UIT-R BT.798 says that "terrestrial broadcasting for digital television be accommodated in the channels (with bandwidths of 6, 7 and 8 MHz) dedicated to the broadcasting of analog television in the bands of metric and decimetric waves.
  • This Recommendation in which it is forbidden that the bandwidth used for digital programs be greater than the bandwidth used for analog channels, has open a way to the development of advanced techniques of digital compression.
  • the digital dividend is due to the fact that digital compression systems allow to multiplex the transmission of several television programs in the spectrum previously used for a single analog television channel.
  • digital compression systems allow to multiplex the transmission of several television programs in the spectrum previously used for a single analog television channel.
  • This means that the possibilities of accessing to the spectrum of the digital dividend are still growing, as more advanced rules for terrestrial television (for infrastructure and compression) are progressively developed and introduced (for example, the second generation of systems for broadcasting transmission of digital terrestrial television, TDT), which offer greater binary capacity per Hertz than existing systems.
  • the amount of liberated spectrum due to the change from analog to digital transmission depends mainly on the national peculiarities, such as the geography and topography of the country, grade of penetration of the digital transmission services, needs of the regional or minority television services, and use of the spectrum by neighbor countries.
  • This amount of liberated spectrum also depends on the digital television technology chosen for migrating the analog services.
  • the size of the digital dividend also changes from region to region and from country to country.
  • the specific location of the digital dividend also varies from one country (or region) to another one, because it depends on the frequency assignation in each country/region, normally between 200 MHz and 1 GHz. In particular in Europe, this liberated band (dividend) is placed in the range between 790 and 862 MHz.
  • the spectrum created with this digital dividend can be used for any type of services, such as additional terrestrial broadcasting services (which might even include the delivery of new interactive television programs and of high quality), mobile multimedia applications, mobile communications, wireless broad-band access systems (for example, it could be used to offer broad-band access to Internet, ubiquitous in areas not yet reached by terrestrial lines, which would help reducing the digital breach) and so on.
  • additional terrestrial broadcasting services which might even include the delivery of new interactive television programs and of high quality
  • mobile multimedia applications for mobile communications
  • wireless broad-band access systems for example, it could be used to offer broad-band access to Internet, ubiquitous in areas not yet reached by terrestrial lines, which would help reducing the digital breach
  • the mobile telephony sector the most interested one in this digital dividend, given the number of new mobile services which are being offered (mobile television, access to Internet through mobile terminals, massive data transmission).
  • the liberated frequencies in the digital dividend (which, as already explained, are usually in the band between 200 MHz and 1 GHz), have better characteristics of the signals propagation than the characteristics of, for example, 2.4 GHz.
  • the mobile sector has shown its interest in using these lower frequencies in order to improve capacity and thus to achieve an optimal balance between transmission capacity and operational scope. This way, less infrastructure would be required for obtaining wider mobile coverage, with the resulting reduction in costs of communication services, especially in rural areas.
  • the liberated spectrum has been mainly assigned to mobile telephony communications and, in particular, to new generation mobile telephony, also known as LTE (Long Term Evolution), and also to other types of technologies, such as 4G mobile telephony or WiMAX.
  • LTE Long Term Evolution
  • WiMAX WiMAX
  • the interference caused by these new signals on the digital television signals is important, because the new signals are very different from the television ones and besides are very close by (in some cases, at a distance of 1 MHz), causing the following undesired effects:
  • they since they are high-power signals compared to the digital television signals, they normally cause saturation in the wide-band amplifiers and in the tuners of the television receiving system.
  • these signals usually have a bandwidth which occupies frequencies out of the assigned channel, thus causing interference (co-channel interference) in the television channels, consequently deteriorating the signal-to-noise ratio of the received TV signal.
  • the power of the received TV signal can be increased (for example, by means of repeaters), but this is an expensive solution.
  • the reception of TDT signals can also be improved by using filters with adequate responses, in order to eliminate the interfering signals. Due to the limited separation in frequency between the useful signal and the interfering one, such filters are currently only achieved using cavities of great volume and high cost.
  • Patent US5932522 describes a bandstop filter formed by three resonators, each of which is composed of a transmission line and two capacitors.
  • the transmission lines can be helical.
  • the electrical length of the transmission lines is chosen to be between one-quarter wavelength and one-half wavelength of the resonant frequency.
  • this filter neither achieves rejection of the unwanted frequency band in a manner as sharp as required in the described circumstances.
  • the maximum electrical length suggested in this document is one-half wavelength of the resonant frequency. Longer lengths are discouraged because of their inherent disadvantage: they occupy too much space. Tuning of the resonators is achieved by means of screws acting as capacitors.
  • a filtering system is needed, which enables to solve in an efficient way, the problem of worsening in the quality of reception of digital television signals, in the scenario described above.
  • a bandstop filter comprising: a signal input; a signal output; connecting means for connecting the signal input and the signal output; at least one resonator connected to the connecting means, the at least one resonator having a resonant frequency with a corresponding wavelength, said at least one resonator comprising a helical transmission line;
  • the helical transmission line of the at least one resonator has an electrical length of n times one-quarter wavelength of the resonant frequency, n being an odd number different from 1.
  • the bandstop filter is preferably placed in a housing. More particularly, the at least one resonator is located within a cavity of said housing.
  • the at least one resonator preferably comprising a capacitor, more preferably an adjustable capacitor in order to vary the resonant frequency of said at least one resonator.
  • the capacitor is implemented by means of a first conductive wire and a second conductive wire.
  • the first conductive wire is preferably configured to achieve rough tuning of the resonant frequency of the at least one resonator, said first conductive wire being connected as a prolongation of the helical transmission line.
  • the second conductive wire is preferably configured to achieve fine tuning of the resonant frequency of the at least one resonator, said second conductive wire being connected to ground.
  • the helical transmission line of the at least one resonator has an electrical length of 3 times one-quarter wavelength of the resonant frequency.
  • the bandstop filter comprises a plurality of resonators connected to the connecting means, each of the plurality of resonators comprising a helical transmission line.
  • the bandstop filter is configured to reject the frequencies of the frequency band between 791 MHz and 821 MHz.
  • the term “approximately” and terms of its family should be understood as indicating values very near to those which accompany the aforementioned term. That is to say, a deviation within reasonable limits from an exact value should be accepted, because a skilled person in the art will understand that such a deviation from the values indicated is inevitable due to measurement inaccuracies, etc. The same applies to the terms “about” and “around” and “substantially”.
  • a filter of the present invention includes an input 10 and an output 11 connected by connecting means 12.
  • a plurality of resonators 13 1 13 2 13 3 13 4 are connected to respective terminals 14 1 14 2 14 3 14 4 at connecting means 12. It is remarked that connecting means 12 presents an electrically small connection.
  • Each resonator 13 1 13 2 13 3 13 4 has a helical transmission line 17 1 17 2 17 3 17 4 coupled to one of the terminals 14 1 14 2 14 3 14 4 .
  • the resonators have a resonant frequency with a corresponding wavelength.
  • the helical shape of the transmission line 17 1 17 2 17 3 17 4 is selected because it permits the use of a relatively long transmission line in a relatively small amount of space.
  • the helical transmission lines 17 1 17 2 17 3 17 4 are configured in a bandstop configuration and are tuned to work at n times ⁇ /4 (n times one-quarter of wavelength), n being an odd number different from 1.
  • Each resonator 13 1 13 2 13 3 13 4 also has a capacitor 15 1 15 2 15 3 15 4.
  • the capacitors 15 1 15 2 15 3 15 4 are adjustable. They are used for fixing the tuning of the resonators. This is explained in detail later.
  • the filter of figure 1 is designed to work in frequencies up to 1 GHz. In a preferred embodiment, it is designed to have a bandstop which rejects the LTE downlink band (791-821 MHz).
  • Figure 2 shows the physical aspect of the filter of figure 1 . Elements shown in figure 2 have been provided with equivalent numerals of the same elements shown in figure 1 (for instance, resonator 13 1 23 1 ).
  • the filter is placed in a housing 28.
  • the housing 28 is shown with an open top so that the filter can be seen. Outside the housing 28 are an input terminal 20 and an output terminal 21. Connecting means 22 is connected between the input and output terminals 20 21 from which resonators 23 1 23 2 23 3 23 4 are connected at terminals 24 1 24 2 24 3 24 4 .
  • the resonators 23 1 23 2 23 3 23 4 are each located in a cavity. Each resonator 23 1 23 2 23 3 23 4 has a helical transmission line 27 1 27 2 27 3 27 4 connected to one of the terminals 24 1 24 2 24 3 24 4 .
  • the helical transmission lines 27 1 27 2 27 3 27 4 in the resonators 23 1 23 2 23 3 23 4 are preferably manufactured from any material conventionally used in the manufacture of current helical transmission lines, such as copper wire (or silvered copper wire).
  • the resonators have a resonant frequency with a corresponding wavelength.
  • figure 2 shows a particular embodiment in which the filter is formed by four resonators, a different number of resonators can be implemented (also one single resonator).
  • each helical transmission line 27 1 27 2 27 3 27 4 is open (to the air). Its connection to ground is achieved thanks to the capacitors provided by conductive wires.
  • the helical transmission line 27 1 27 2 27 3 27 4 , conductive wires 25 1 25 2 25 3 25 4 26 1 26 2 26 3 26 4 (explained in detail later) and metallic walls of each resonator cavity are mounted and soldered on a double layered printed circuit board (PCB).
  • the PCB is located within a metallic housing (or chassis) which comprises the input and output terminals 20 21.
  • the chassis is closed by two metallic covers.
  • a single layered PCB can be used, or even no PCB can be used (other mechanical supports and electrical connections are possible).
  • the metallic walls which delimit the cavities can either be an integral part of the chassis or be independent from the chassis.
  • each helical element helical transmission lines 27 1 27 2 27 3 27 4
  • Fixing the tuning of each helical element (helical transmission lines 27 1 27 2 27 3 27 4 ) in each resonator is achieved by means of two conductive wires 25 1 25 2 25 3 25 4 26 1 26 2 26 3 26 4 which act as variable capacitors (in figure 1 , capacitors 15 1 15 2 15 3 15 4 ).
  • One of the conductive wires (or capacitors) in each resonator allows for quick approach to the tuning (rough tuning) and the other one allows for fine tuning.
  • the conductive wire 26 1 26 2 26 3 26 4 which allows for rough tuning is connected as a prolongation of the helical transmission line 27 1 27 2 27 3 27 4 in its open end (represented by a little circle having reference 18 1 18 2 18 3 18 4 in figure 1 ).
  • the conductive wire 26 1 26 2 26 3 26 4 is connected by a galvanic connection to the open end of the helical transmission line 27 1 27 2 27 3 27 4 (in a particular embodiment, through the PCB). This wire permits to lengthen a bit the length of the helical transmission 27 1 27 2 27 3 27 4 itself.
  • This conductive wire 26 1 26 2 26 3 26 4 becomes thus an integral part of the helical resonator and can besides be coupled with variable (tunable) capacitor to the main body of the helical transmission line and to the walls of the cavity within which the helical element is housed. Adjusting the tuning of the resonator is thus achieved.
  • Exemplary ways of adjusting the tuning of the resonator is done moving the conductive wire 26 1 26 2 26 3 26 4 , for example bending it, or cutting it. In a preferred embodiment, it is done by moving it, either reducing or increasing the distance between the conductive wire and the helical transmission line.
  • the second conductive wire 25 1 25 2 25 3 25 4 is connected to ground (represented by a little circle having reference 19 1 19 2 19 3 19 4 in figure 1 ).and also acts as a variable (tunable) capacitor at the open end of the helical transmission line 27 1 27 2 27 3 27 4 .
  • this second conductive wire 25 1 25 2 25 3 25 4 is weaker than the one of the first conductive wire.
  • the fixing in the tuning is thus finer.
  • Exemplary ways of adjusting the tuning of the resonator is done moving the conductive wire 25 1 25 2 25 3 25 4 , for example bending it, or cutting it. In a preferred embodiment, it is done by moving it, either reducing or increasing the distance between the conductive wire and the helical transmission line.
  • first and second conductive wires 25 1 25 2 25 3 25 4 26 1 26 2 26 3 26 4 serve as adjustable capacitors.
  • Conductive wires 26 1 26 2 26 3 26 4 are electrically connected to the open end of the helical transmission line and conductive wires 25 1 25 2 25 3 25 4 are electrically connected to ground. Both serve as each capacitor in figure 1 .
  • first conductive wires 26 1 26 2 26 3 26 4 and second conductive wires 25 1 25 2 25 3 25 4 are disposed parallel to the helical transmission line 27 1 27 2 27 3 27 4 , as shown in figure 2 . This position provides an optimal compromise between capacity and movement.
  • each resonator 23 1 23 2 23 3 23 4 may be tuned to its proper bandwidth and center frequency by adjusting respective first and second conductive wires.
  • tuning is achieved by means of screws inserted in the cavity of the resonator, as explained for example in US5932522 .
  • tuning the resonator with the wires of the present invention provides with several advantages, such as mechanical simplicity derived from several aspects, such as the absence of physical contact between different parts of the filter, absence of friction, and so on. Considerable reduction in manufacturing and maintenance costs is thus achieved.
  • the inventive filter occupies a bit more space than conventional filters tuned at ⁇ /4, but offers impressive advantages in terms of its response. Besides, the inventive filter occupies less space than conventional filters (having cavities of great volume) designed to correctly separate the useful signal from the interfering one at the mentioned frequencies.
  • the filter is formed by four resonators, the number of resonators can vary, including having one single resonator, depending on the requirements (mainly loss in the band-pass and rejection in the stop-band) of each application and on the available physical space.
EP12382438.5A 2012-11-08 2012-11-08 Filtre coupe-bande pour interférence de signaux Withdrawn EP2731192A1 (fr)

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EP12382438.5A EP2731192A1 (fr) 2012-11-08 2012-11-08 Filtre coupe-bande pour interférence de signaux

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
EP12382438.5A EP2731192A1 (fr) 2012-11-08 2012-11-08 Filtre coupe-bande pour interférence de signaux

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EP2731192A1 true EP2731192A1 (fr) 2014-05-14

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Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3763447A (en) * 1970-12-16 1973-10-02 Yagi Antenna High frequency helical filter
US3876963A (en) * 1973-12-03 1975-04-08 Gerald Graham Frequency filter apparatus and method
JPS52125253A (en) * 1977-01-18 1977-10-20 Alps Electric Co Ltd Device for adjusting coupling coefficient of helical resonator
US4459571A (en) * 1982-12-20 1984-07-10 Motorola, Inc. Varactor-tuned helical resonator filter
EP0660435A2 (fr) * 1993-12-23 1995-06-28 Lk-Products Oy Filtre électrique
EP0673077A1 (fr) * 1994-03-15 1995-09-20 Lk-Products Oy Dispositif à résonateur
EP0741431A1 (fr) * 1995-05-03 1996-11-06 Lk-Products Oy Filtre à resonateur du type de ligne de transmission
US5932522A (en) 1996-09-27 1999-08-03 Illinois Superconductor Corporation Superconducting radio-frequency bandstop filter

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3763447A (en) * 1970-12-16 1973-10-02 Yagi Antenna High frequency helical filter
US3876963A (en) * 1973-12-03 1975-04-08 Gerald Graham Frequency filter apparatus and method
JPS52125253A (en) * 1977-01-18 1977-10-20 Alps Electric Co Ltd Device for adjusting coupling coefficient of helical resonator
US4459571A (en) * 1982-12-20 1984-07-10 Motorola, Inc. Varactor-tuned helical resonator filter
EP0660435A2 (fr) * 1993-12-23 1995-06-28 Lk-Products Oy Filtre électrique
EP0673077A1 (fr) * 1994-03-15 1995-09-20 Lk-Products Oy Dispositif à résonateur
EP0741431A1 (fr) * 1995-05-03 1996-11-06 Lk-Products Oy Filtre à resonateur du type de ligne de transmission
US5932522A (en) 1996-09-27 1999-08-03 Illinois Superconductor Corporation Superconducting radio-frequency bandstop filter

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
MING YU ET AL: "High performance helical resonator filters", MICROWAVE CONFERENCE, 2004. 34TH EUROPEAN AMSTERDAM, THE NETHERLANDS 13 OCT. 2004, PISCATAWAY, NJ, USA,IEEE, 14 October 2004 (2004-10-14), pages 989 - 992, XP031996385, ISBN: 978-1-58053-992-0 *

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