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Title:
A METHOD FOR PROVIDING ABILITY OF TUNING RESONANCE FREQUENCY FOR DIFFERENT APPLICATIONS
Document Type and Number:
WIPO Patent Application WO/2005/091429
Kind Code:
A1
Abstract:
Disclosed is a method for providing ability of tuning resonance frequency in different applications. The method according to the invention at least comprises the step of adding ferroelectric disks in the resonators. Here, the ferroelectric disks have the relative dielectric constants varying according to change of ambient environment. In the invention, since the resonance frequency can vary according to the ambient environment, the tuning range of filters and duplexers/multiplexers having the resonators with ferroelectric disks is large. In addition, the resonance frequency can be changed in high frequency environment according to the invention. So, the invention can be used to improve the size and cost of the filters and duplexers/multiplexers in different applications, especially in low noise environment.

Inventors:
ABBAS FARHAT (SE)
NEJATIAN ALIREZA (SE)
Application Number:
PCT/CN2004/000231
Publication Date:
September 29, 2005
Filing Date:
March 19, 2004
Export Citation:
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Assignee:
HUAWEI TECH CO LTD (CN)
ABBAS FARHAT (SE)
NEJATIAN ALIREZA (SE)
International Classes:
H01P1/208; H01P7/06; (IPC1-7): H01P7/06; H01P1/208
Domestic Patent References:
WO2003028146A12003-04-03
Foreign References:
US5900390A1999-05-04
GB2380069A2003-03-26
US5459123A1995-10-17
Attorney, Agent or Firm:
DEQI INTELLECTUAL PROPERTY LAW CORPORATION (No. 1 Zhichun Road Haidian District, Beijing 3, CN)
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Claims:
Claims
1. A method for providing ability of tuning resonance frequency in different applications, at least comprising the step of adding ferroelectric disks in the resonators, wherein the ferroelectric disks have the relative dielectric constants varying according to change of ambient environment.
2. The method according to claim 1, wherein the resonators are respectively located in cylindrical metallic cavities of a fourpole filter with two input/output coaxial probes, the method further comprising the step of respectively forming a notch on each resonator to couple the two polarizations of each mode exciting the resonators.
3. The method according to claim 2, wherein the notch is at a 135 degree from the probes.
4. The method according to claim 2, further comprising the step of respectively forming another notch on each resonator to rectify the perturbation due to the coaxial probes.
5. The method according to claim 4, wherein the notch is at a 90 degree from the probes.
6. The method according to any one of claims 2 to 5, wherein the notch is rectangular or circular.
7. The method according to claim 1, further comprising the step of using full electromagnetic simulators to optimize the response.
8. The method according to claim I3 wherein said ambient environment includes applied direct current bias electric field and the ambient temperature.
Description:
A Method for Providing Ability of Tuning Resonance Frequency for Different Applications

Field of the Technology

The present invention generally relates to frequency tuning technology, and more particularly to a method for providing ability of tuning the resonance frequency for different applications.

Background of the Invention

At present, resonators are widely employed in filters and duplexers/multiplexers, especially in filters. A good filter has three desired characteristics, namely, low insertion loss, high return loss and high rejection band. For example, a super filter can provide a 3dB improvement to the channel quality, which can increase the speed of data transmission to twice the original rate. To a service provider, this will increase the size of the "sweet spot" where users can enjoy the highest speed connection and will increase the average data rate throughout the network.

There are number of technologies in use including cavity resonators, multi- coupled cavities, dielectric resonators, etc. for low insertion loss and multi mode resonators for low size. It is sometimes desirable to include couplings between non- adjacent resonators to obtain more optimum filter transfer functions.

Taking a fourth order dielectric resonator design as example, this design incorporates a single capacitive cross coupling. Of course, it is understood that inductive coupling can be achieved similarly. The filter employs a short, single- section evanescent mode filter to couple the first resonator and the last one. The couplings between other resonators are tuned but not resonated inductive irises. The evanescent filter coupling between the first resonator and the last one employs a re¬ entrant section of coaxial line to provide the capacitance required to resonate the equivalent shunt inductance of the below cutoff section of wave guide which is what the iris really represents.

The single cross coupling in this fourth order provides a pair of transmission zeros which emphasize the attenuation close to the pass band. Both capacitive coupling and inductive coupling produce the response shown in Fig. 1 and Fig.2 for UMTS RX and TX band respectively, with respective effects on stop band attenuation or on pass band group delay and amplitude flatness.

With the development of communication application, the filters and duplexers/multiplexers are required to have different bandwidth and center frequencies for different applications. For example, 5 MHz bandwidth is required for one carrier and 10 MHz bandwidth is required for two carriers. Nevertheless, in prior art, the tuning of resonance frequency usually be implemented by means of varactor diode. There are several problems in this technical scheme. First, there is low tuning range which cannot satisfy the requirements for more applications, for example, the method can not achieve 60MHz bandwidth which is needed in Wideband Code Division Multiple Access (WCDMA) system. Secondly, the center frequency is not very high, which is not suitable for the development of the resonator also. All of the shortcomings limit the development of filters and duplexers/ multiplexers.

Summary of the Invention

Accordingly, in order to overcome the shortcomings in prior art, an object of the invention is to provide a method for providing ability of tuning the resonance frequency for different applications.

A method according to the invention comprises the step of adding ferroelectric disks in the resonators, wherein the ferroelectric disks have the relative dielectric constants varying according to change of ambient environment.

In the above-mentioned method, the resonators are respectively located in cylindrical metallic cavities of a four-pole filter with two input/output coaxial probes, the method further comprises the step of respectively forming a notch on each resonator to couple the two polarizations of each mode exciting the resonators. The notch can be at a 135 degree from the probes.

The above-mentioned method may further comprise the step of respectively forming another notch on each resonator to rectify the perturbation due to the coaxial probes. The notch can be at 90 degree from the probes.

In the above-mentioned method the notch can be rectangular or circular. The method may further comprise the step of using full electromagnetic simulators to optimize the response.

In the above-mentioned method, the ambient environment includes applied direct current bias electric field and the ambient temperature.

It can be seen from the method according to the invention that the resonance frequency can vary according to the ambient environment through adding ferroelectric disks in resonator, for example, the resonance frequency can vary as a function of applied DC electric filed and the ambient temperature, so the tuning range is much larger compared with the prior art. In addition, the resonance frequency can be changed in high frequency environment according to the invention. For filters with resonators in high frequency environment, it is a passive component. When it is designed for specific center frequency and defined bandwidth, it should always be used for the same bandwidth and the same center frequency. If the' same bandwidth but different center frequency is required, the filter must be re-designed in prior art. But in this invention, since the center frequency can be altered in high frequency environment, it is much easier and also cost almost nothing to change the center frequency and have a new filter. So, the invention can be used to improve the size and cost of the filters and duplexers/multiplexers in low noise environment.

Brief Description of the Drawings

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings in which:

Fig.1 shows UMTS RX band response of a four-pole filter by using capacitive coupling;

Fig.2 shows UMTS RX band response of a four-pole filter by using inductive coupling;

Fig.3 is a general flowchart of a preferred embodiment according to the invention; and

Fig.4 illustrates an electronically tunable proposed filter design with ferroelectric disks. Detailed Description of the Invention

A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well- known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

The idea of the invention is to add ferroelectric disks in the resonators. Since the dielectric constant of the ferroelectric disk varies as a function of applied Direct Current (DC) electric field and the temperature, the dielectric constant is not a fixed value and can vary according to the ambient environment. So, the resonance frequency can vary also, which enables the center frequency of filters, duplexers or multiplexers can be changed. Meanwhile, a large tuning range can be obtained.

Referring to Fig.3 in which the general flowchart is illustrated and taking a four- pole filter composed of two cylindrical metallic cavities loaded by two supported Dielectric Resonators (DRs) as example, the method according to the embodiment comprises the following steps.

In step 301, ferroelectric disks are added in the resonators inside the filter.

In this example, the ferroelectric disks are respectively added in the two DRs. As shown in Fig.4 in which an electronically tunable proposed filter design with ferroelectric disks is illustrated, the two DRs are arranged along the axis of the cylindrical metallic cavities.

The dielectric constant of a ferroelectric disk can be altered by ambient temperature (K), as shown in the following formulation.

._,. M [TJl)COIh(T, /T) - T0

Here, Mis 9X 104K5 T0 is 38 K and T1 is 84 K.

In addition, the dielectric constant of a ferroelectric disk also can be altered by applied DC bias electric field (kV/cm), as shown in the following formulation.

ε(E) = ~429E2 +12992

It can be seen from the above two formulations that the ferroelectric disks have the property of nonlinearity. This property can be proposed to explore the temperature compensated variable phase shifters or adaptive filters to be considered. There is potential to exploit the use of the nonlinearity of ferroelectric materials with conducting surface for electronically tunable microwave device applications in low noise environment, such as shown in Fig.4 in this case of a filter design.

In step 302, a rectangular notch is formed on each DR at a 135 degree angle from the probes.

The filter shown in Fig.4 is excited with two input/output coaxial probes. The notched DRs are excited on their first hybrid HEMi i Δ dual modes. The two polarizations of each mode are coupled using a rectangular notch on the DRs, placed at a 135 degree angle from the probes. The couplings between cavities are provided by crossed rectangular irises.

In step 303, a rectangular notch is formed on each DR at a 90 degree angle from the probes.

In order to rectify the perturbation due to the coaxial probes, a rectangular notch is manufactured on each DR, placed at a 90 degree angle from the probes.

In step 304, full electromagnetic simulators are used to optimize the filter response.

A filter synthesis method could be developed and applied to design the filter as shown in Fig.4. The full electromagnetic simulators can be used to optimize the filter response, with the central frequency is equal to 2GHz, and the bandwidth at -3 dB is 0.25% (5 MHz) with the tuning ability of 3% (60 MHz) for UMTS band.

The configuration shown in Fig.4 can be designed for 5 MHz (one carrier), 10 MHz (two carriers) and 15 MHz (three carriers) for size and cost reductions and tuned into the whole UMTS band by the DC biased electric field. Also, the 60 MHz design can be tuned to- the wireless multi bands for software defined radio applications.

In addition to the applications, the present invention can also be used in the rigs where low noise tuning required. The full electromagnetic simulators can be used to optimize the filter response with the center frequency is equal to main wireless band, and the bandwidth at -3 dB is number of carriers considered with the tuning ability of all the wireless bands covered in software defined radio applications. The dielectric constant of ferroelectric disks varies as a function of frequency enabling microwave devices such as variable phase shifters or adaptive filters to be considered in high frequency environment. In addition, the dielectric constant varies as a function of applied DC electric field and the temperature enabling microwave devices such as electronically tunable and temperature compensated phase shifters and filters for low noise applications.

It can be understood for those skilled in the art that the notches formed in steps 302 and 303 can be circular shape or other shape besides the above-mentioned rectangular shape.

The present invention is described taking filter design as example. It also can be understood that the present invention can be used for duplexers/multiplexers also.

Accordingly, although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example, and is not to be taken by way of limitation. The spirit and scope of the present invention are to be limited only by the terms of the appended claims.