CN109155450B

CN109155450B - Radio frequency filter

Info

Publication number: CN109155450B
Application number: CN201680085836.3A
Authority: CN
Inventors: 迈克尔·格斯
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2016-06-14
Filing date: 2016-06-14
Publication date: 2020-02-21
Anticipated expiration: 2036-06-14
Also published as: CN109155450A; WO2017215742A1

Abstract

A radio frequency filter (100) is described. The radio frequency filter comprises a first dual-mode resonator (102) having a first mode (1a), a second mode (2a) and a first parasitic mode (Sa), wherein the first dual-mode resonator (102) comprises a first in-coupling element (112) coupling the first mode (1a) to the first parasitic mode (Sa), a second dual-mode resonator (104) having a third mode (3b) and a fourth mode (4b), and a mutual coupling element (106) arranged between the first dual-mode resonator (102) and the second dual-mode resonator (104), the mutual coupling elements (106) coupling the first mode (1a) to the fourth mode (4b), the second mode (2a) to the third mode (3b), and coupling the first parasitic mode (Sa) to the third mode (3 b).

Description

Radio frequency filter

Technical Field

The present invention relates to a radio frequency filter and a communication device comprising such a radio frequency filter.

Background

As radios become more miniaturized and integrated, there is a renewed need to produce low loss, high power filters that are small or slim in size. First, this is to allow the assembly to be tightly packed and used with large antenna arrays of MIM0 systems.

However, the rejection performance specifications of such filters are stringent in order to simultaneously meet stringent regulatory emission requirements and provide the necessary protection for sensitive receiver electronics multiplexed with high power transmitter amplifiers.

To provide suitable filtering, higher order filters are required to achieve acceptable passband roll-off and out-of-band rejection. However, as the order of the filter increases, the overall capacity of the filter also increases. To address this problem, multimode solid dielectric waveguide filters are being developed that combine the poles of multiple resonance or filtering functions within a single physical section. This solution improves the space efficiency more significantly due to the concentration of the high permittivity electric field of certain bulk materials used.

However, in general the filter specifications are so stringent that it is not feasible to implement the filter function using a basic band-pass filter with the theoretically necessary order. Instead, an additional transmission path, called cross-coupling, is introduced into the filter providing a method of implementing the transmission zero specified by the filter transfer function. These transmission zeroes can be selectively placed around the pass band to provide significant additional rejection at design requirements.

However, in the solid-state multimode dielectric filter, it is not easy to implement the required additional coupling path due to the limitation of the physical structure. In particular in a bimodal waveguide filter, the dominant modes used are orthogonal to each other, coupling being easily achieved only between two modes that are similarly aligned. Often, complex external ancillary components or structures must be used to achieve the required cross-coupling, adding significant production cost through the requirement of additional components themselves, and adding complexity to configuring them during manufacture.

Alternatively, the designer may intentionally limit the number of transmission zeroes used to a number that is naturally and easily obtainable from a given physical structure. Although simple and low cost, the result is that implementation is not as space-saving as theoretically possible.

Disclosure of Invention

It is an object of embodiments of the present invention to provide a radio frequency filter that reduces the problems with conventional solutions.

It is a further object of embodiments of the present invention to provide a radio frequency filter that provides an additional coupling path relative to conventional radio frequency filters.

It is a further object of embodiments of the present invention to provide a radio frequency filter having a desired arbitrary filter topology using a first dual-mode resonator and a second dual-mode resonator.

It is an additional object of embodiments of the present invention to provide a radio frequency filter with any desired filter topology using solid dielectric bimodal waveguide technology.

The above object is achieved by the subject matter of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.

According to a first aspect of the invention, a radio frequency filter is provided. The radio frequency filter includes a first dual-mode resonator having a first mode, a second mode, and a first parasitic mode. The first dual-mode resonator includes a first in-coupling element coupling a first mode to a first parasitic mode, a second dual-mode resonator having a third mode and a fourth mode, and an inter-coupling element disposed between the first dual-mode resonator and the second dual-mode resonator, the inter-coupling element coupling the first mode to the fourth mode, the second mode to the third mode, and the first parasitic mode to the third mode.

With the radio frequency filter according to the first aspect, a narrower filter function may be provided. This is due to the possibility of coupling the first mode to the third mode through the first parasitic mode.

In a first possible implementation form of the radio frequency filter according to the first aspect, the first dual-mode resonator and the second dual-mode resonator are arranged with their respective centers along a common central axis. The mutual coupling element includes a first elongated iris centered about a common central axis and a second elongated iris disposed perpendicular to the first elongated iris and offset from the common central axis.

With the radio frequency filter according to the first possible implementation form, the magnetic field lines of the first parasitic mode are parallel to the magnetic field lines of the third mode at the mutual coupling element, thereby providing coupling between the first parasitic mode and the third mode.

According to a first possible implementation form, in a second possible implementation form of the radio frequency filter, along the common central axis, the magnetic field strength of the first parasitic mode is at its minimum and the electric field strength of the first parasitic mode is at its maximum. This is an advantageous tendency for the first parasitic mode to provide the desired coupling between the first parasitic mode and the third mode.

In a third possible implementation form of the radio frequency filter according to the first or the second possible implementation form, the second elongated iris is offset from the common central axis in the direction of the length component of the first elongated iris. The first and second elongated irises are connected to each other or a gap is provided between the first and second elongated irises. The first elongated iris has the longest dimension along the length component. As described above, the second elongated iris is disposed perpendicular to the first elongated iris. In the case where the first and second elongated irises are connected to each other, the two irises together form a T-shape.

Another advantage of the moving second elongated iris is that the coupling strength between the second mode and the third mode 3b is constant for its position, since the magnetic field vectors of the second mode and the third mode have a constant magnitude and direction for all iris positions. This means that the coupling between the second and third modes can be controlled by varying the iris length and the coupling from the parasitic mode can be controlled by the position of the second elongated iris, allowing independent control of the two couplings according to a single characteristic.

In a fourth possible implementation form of the radio frequency filter according to any of the first to third possible implementation forms the length component of the first elongated iris is arranged in parallel with the electric field vector of the second mode. The length component of the second elongated iris is disposed in parallel with the electric field vector of the first mode.

In a fifth possible implementation form of the radio frequency filter according to any of the first to fourth possible implementation forms or the first aspect as such, the first in-coupling element is arranged at a boundary region between the first side and the second side of the first double-mode resonator where the magnetic field lines of the first parasitic mode and the first mode are at least partially parallel. This is an advantageous position of the in-coupling element in order to obtain a high coupling efficiency between the first mode and the first parasitic mode.

According to a fifth possible implementation form, in a sixth possible implementation form of the radio frequency filter, the first in-coupling element is one of a notch, at least one local chamfer and at least one local cut. These forms of the in-coupling element are advantageous in order to obtain a high coupling efficiency between the first mode and the first parasitic mode and to obtain a desired low coupling efficiency between the other modes. To obtain low coupling efficiency between other modes, notches may be most preferred; while other forms may be more desirable in order to achieve the highest coupling efficiency possible between the first mode and the first parasitic mode.

The first dual mode resonator may comprise a block of dielectric material in which the in-coupling element is disposed.

In a seventh possible implementation form of the radio frequency filter according to the fifth or sixth possible implementation form, the second dual-mode resonator has a second parasitic mode and comprises a second in-coupling element coupling the second parasitic mode to the third mode.

The second in-coupling element is arranged at a boundary region between the first side and the second side of the second dual-mode resonator, at which boundary region the magnetic field lines of the second parasitic mode and the third mode are at least partially parallel. This is an advantageous position of the in-coupling element in order to obtain a high coupling efficiency between the second parasitic mode and the third mode.

The second inner coupling element is one of a notch, at least one partial chamfer and at least one partial cut. These forms of the in-coupling element are advantageous in order to obtain a high coupling efficiency between the second parasitic mode and the third mode and to obtain a desired low coupling efficiency between the other modes. To obtain low coupling efficiency between other modes, notches may be most preferred; while the other forms mentioned may be more desirable in order to achieve the highest coupling efficiency possible between the second parasitic mode and the third mode.

The second dual-mode resonator may comprise a block of dielectric material in which the internal coupling element is disposed.

According to a seventh possible implementation form, in an eighth possible implementation form of the radio frequency filter, the second in-coupling element is one of a notch, at least one local chamfer and at least one local cut. These forms of the in-coupling element are advantageous in order to obtain a high coupling efficiency between the first mode and the first parasitic mode and to obtain a desired low coupling efficiency between the other modes. To obtain low coupling efficiency between other modes, notches may be most preferred; while other forms may be more desirable in order to achieve the highest coupling efficiency possible between the first mode and the first parasitic mode.

In a ninth possible implementation form of the radio frequency filter according to the seventh or eighth possible implementation form, the mutual coupling element further couples the first parasitic mode to the second parasitic mode. This is an alternative to the possible implementation forms described above.

In a tenth possible implementation form of the radio frequency filter according to the ninth possible implementation form, the mutual coupling element comprises a third elongated iris arranged parallel to the second elongated iris and moving from a central axis on the opposite side of the central axis with respect to the second elongated iris.

The third elongated iris functions to avoid direct coupling from the first parasitic mode to the third mode. The magnetic field of the first parasitic mode rotates about a common central axis, and the magnetic field of the third mode rotates about an axis perpendicular to the common central axis and parallel to the second and third elongated irises. Thus, any positive coupling from the first parasitic mode to the third mode by the second elongated iris is largely cancelled by a similar negative coupling from the first parasitic mode to the third mode by the third elongated iris.

It may be preferred to arrange the second elongated iris and the third elongated iris symmetrically around a common central axis in order to optimize the cancellation of the coupling from the first parasitic mode to the third mode. This optimization is due to the radial dependence of the magnetic field strength.

In an eleventh possible implementation form of the radio frequency filter according to any of the seventh to tenth possible implementation forms the first mode, the second mode, the third mode and the fourth mode together form a filter passband, and wherein the frequency of the first spurious mode and the frequency of the second spurious mode are outside the filter passband.

In a twelfth possible implementation form of the radio frequency filter according to any of the seventh to eleventh possible implementation forms, at least one of the electric field vector of the first parasitic mode and the electric field vector of the second parasitic mode is parallel to the common central axis.

In a thirteenth possible implementation form of the radio frequency filter according to any one of the first to twelfth possible implementation forms or the first aspect as such, the first dual-mode resonator comprises a third in-coupling element coupling the first mode to the second mode.

Strong coupling between the first mode and the second mode is facilitated.

The third in-coupling element is arranged at a border region between the sides of the first double-mode resonator, where the magnetic field lines of the first and second modes are at least partially parallel. This is an advantageous position of the third in-coupling element in order to obtain a high coupling efficiency between the first mode and the second mode.

The third inner coupling element is one of a notch, at least one partial chamfer and at least one partial cut. These forms of the in-coupling element are advantageous in order to obtain a high coupling efficiency between the first mode and the first parasitic mode and to obtain a desired low coupling efficiency between the other modes.

In a fourteenth possible implementation form of the radio frequency filter according to any of the first to thirteenth possible implementation forms or the first aspect as such, the second dual-mode resonator comprises a fourth in-coupling element coupling the third mode to the fourth mode. Strong coupling between the third mode and the fourth mode is facilitated.

The fourth in-coupling element is arranged at a border region between the sides of the second double-mode resonator where the magnetic field lines of the third and fourth modes are at least partially parallel. This is an advantageous position of the fourth in-coupling element in order to obtain a high coupling efficiency between the third mode and the fourth mode.

The fourth inner coupling element is one of a notch, at least one partial chamfer and at least one partial cut. These forms of the in-coupling element are advantageous in order to obtain a high coupling efficiency between the third mode and the fourth mode and to obtain a desired low coupling efficiency between the other modes.

In a fifteenth possible implementation form of the radio frequency filter according to any one of the first to fourteenth possible implementation forms or the first aspect as such, the first dual-mode resonator comprises a first monolithic block of solid dielectric material and a first conductive layer covering the first monolithic block, and the second dual-mode resonator comprises a second monolithic block of solid dielectric material and a second conductive layer covering the second monolithic block.

By having a first monolithic block of dielectric material in the first dual-mode resonator and a second monolithic block of dielectric material in the second dual-mode resonator, the dimensions of the first and second dual-mode resonators depend on the dielectric constant in the monolithic blocks.

In a sixteenth possible implementation form of the radio frequency filter according to the fourteenth or fifteenth possible implementation form the first monolithic block, the second monolithic block and the mutual coupling element together form a monolithic unit. The manufacture of the radio frequency filter may be facilitated by the first monolithic block, the second monolithic block and the mutual coupling element together forming a monolithic unit.

According to a second aspect, there is provided a communication device for a wireless communication system, the communication device comprising a radio frequency filter according to any one of the first to sixteenth possible implementation forms of the first aspect or the first aspect itself.

Drawings

Figure 1a shows a dual mode resonator having a first mode and a second mode.

Figure 1b shows an alternative dual mode resonator having a first mode and a second mode.

Figure 2a shows the dual-mode resonator of figure 1a showing the first parasitic mode.

Figure 2b shows the dual-mode resonator of figure 1b showing the first parasitic mode.

Fig. 3 is a view of a first dual-mode resonator along a first parasitic electric field line.

Fig. 4 is a view of a first dual-mode resonator along first parasitic electric field lines in accordance with an alternative embodiment.

Fig. 5 schematically shows a radio frequency filter according to an embodiment of the invention.

Fig. 6 shows the concept of a mutual coupling element arranged between a first dual-mode resonator and a second dual-mode resonator.

Figure 7 is a view of the first dual-mode resonator of figure 6 along a common central axis.

Fig. 8 shows a radio frequency filter according to an embodiment of the invention.

Fig. 9 shows the coupling characteristics through the mutual coupling elements in the radio frequency filter in fig. 8.

Fig. 10 schematically shows a radio frequency filter according to an embodiment of the invention.

Fig. 11 schematically shows a radio frequency filter according to an embodiment of the invention.

Fig. 12 schematically shows a radio frequency filter according to an embodiment of the invention.

Fig. 13 schematically shows a first resonator with a different form of the third incoupling element.

Fig. 14 to 18 schematically show different examples of filter functions implemented with radio frequency filters according to different embodiments of the present invention.

Fig. 19 schematically shows a radio frequency filter according to an embodiment of the invention.

Fig. 20 shows a radio frequency filter according to the embodiment of fig. 19.

Fig. 21 schematically shows a communication device in a wireless communication system.

Detailed description of the preferred embodiments

In the following description of embodiments of the invention, the same reference numerals will be used for the same or equivalent features in the different drawings.

In the following description of the embodiments, electromagnetic modes in the dielectric monolith will be described to explain the embodiments.

Figure 1a shows a dual-mode resonator 102 having a first mode 1a and a second mode 2 a. Figure 1b shows an alternative dual-mode resonator 102 having a first mode 1a and a second mode 2 a. The first pattern 1a has a first electric field vector E1 and a first magnetic field vector H1. The second pattern 2a has a second electric field vector E2 and a second magnetic field vector H2. The first electric field vector E1 is perpendicular to the second electric field vector E2. The frequency of first mode 1a is similar to the frequency of second mode 2a and depends on the size of dual-mode resonator 102 and the dielectric constant of dual-mode resonator 102. So that the size of dual-mode resonator 102 will be larger in the case where dual-mode resonator 102 is composed of air surrounded by reflective sides than in the case where dual-mode resonator 102 is composed of a material having a higher dielectric constant.

Fig. 2a shows the dual-mode resonator 102 of fig. 1a showing the first parasitic mode Sa. Fig. 2b shows the dual-mode resonator 102 of fig. 1b showing the first parasitic mode Sa. The first parasitic mode Sa includes a first parasitic electric field vector Es and a first parasitic magnetic field vector Hs. The first parasitic electric field vector Es is perpendicular to the first electric field vector E1 and the second electric field vector E2. In the embodiment shown in fig. 1a and 2a, the frequency of the first parasitic mode Sa is lower than the frequency of the first mode 1a and lower than the frequency of the second mode 2a, since the size of the first dual-mode resonator 102 along the first parasitic electric field lines Es is smaller than the size of the first dual-mode resonator 102 along the first electric field lines E1 and along the second electric field lines E2. In the embodiment shown in fig. 1b and 2b, the frequency of the first parasitic mode Sa is higher than the frequency of the first mode 1a and higher than the frequency of the second mode 2a, because the size of the first dual-mode resonator 102 along the first parasitic electric field lines Es is larger than the size of the first dual-mode resonator 102 along the first electric field lines E1 and along the second electric field lines E2.

Fig. 3 is a view of the first dual-mode resonator 102 along the first parasitic electric field lines Es and the common central axis 126. The first parasitic magnetic field vector Hs is shown in fig. 3. Also shown in fig. 3 are a first elongated iris 128 centered about a common central axis 126 and a second elongated iris 130 disposed perpendicular to the first elongated iris 128 and offset from the common central axis 126. The first dual-mode resonator 102 has a first conductive layer 110 covering the dual-mode resonator 102. The first elongated iris 128 and the second elongated iris 130 are openings in the conductive layer 110. As shown in fig. 3, the first elongated iris 128 (in its lengthwise extension) is at least partially perpendicular to the first parasitic magnetic field vector Hs. The second elongated iris 130 is at least partially parallel (in its length extension) to the first parasitic magnetic field vector Hs. This is due to the offset of the second elongated iris 130 from the common central axis 126.

Typically, the coupling of the first parasitic mode and the second parasitic mode through the first elongated iris 128 is minimal when the width of the first elongated iris 128 is small. This is due to the fact that there is no magnetic field component along the greater length (length extension) of the first elongated iris 128, and only a small component across the short length (width extension), which is below the cut-off frequency of the first elongated iris 128.

Figure 4 shows an alternative embodiment of the first dual mode resonator 102. The difference between the embodiment in fig. 3 and the embodiment in fig. 4 is that the second elongated iris 130 is located on the opposite side of the first elongated iris 128.

In both embodiments shown in fig. 3 and 4, the first elongated iris 128 and the second elongated iris 130 are not connected. A gap d is provided between the first elongated iris 128 and the second elongated iris 130. In further embodiments, the first elongated iris 128 and the second elongated iris 130 may be connected to form a T-shape. In another embodiment, the concepts of fig. 3 and 4 may be combined. In such an embodiment, the first dual-mode resonator 102 has two second elongated irises 130, one arranged as shown in fig. 3 and the other arranged as shown in fig. 4. Also in this embodiment, the first elongated iris 128 and the second elongated iris 130 may be isolated from each other or connected to each other (forming an H-shape). In all embodiments, although the

elongated irises

128, 130 disposed between the two dual-mode resonators form a mutual coupling to couple the (wanted and parasitic) modes from the first dual-mode resonator to the second dual-mode resonator.

Fig. 5 schematically shows a radio frequency filter 100 according to an embodiment of the invention. The radio frequency filter 100 includes: a first dual-mode resonator 102 having a first mode 1a, a second mode 2a, and a first parasitic mode Sa, wherein the first dual-mode resonator 102 includes a first in-coupling element 112 coupling the first mode 1a to the first parasitic mode Sa; a second dual-mode resonator 104 having a third mode 3b and a fourth mode 4 b; and a mutual coupling element 106 disposed between the first dual-mode resonator 102 and the second dual-mode 104, the mutual coupling element 106 coupling the first mode 1a to the fourth mode 4b, the second mode 2a to the third mode 3b, and the first parasitic mode Sa to the third mode 3 b. The frequency of the first parasitic mode Sa is lower than the frequency of the first mode 1a and lower than the frequency of the second mode 2a, because the size of the first dual-mode resonator 102 along the first parasitic electric field lines Es is smaller as shown in fig. 1a and 2 a. As shown in fig. 1b and 2b, the size of the first dual-mode resonator 102 along the parasitic electric field lines Es may also be larger. In this case, the frequency of the first spurious mode Sa is higher than the frequency of the first mode 1a and higher than the frequency of the second mode 2 a. The coupling between the first parasitic modes is not immediately beneficial because they are significantly different from the main two-mode resonant frequencies used to form the filter function. In fact, these spurious frequencies tend to be problematic and undesirable when they occur. However, if energy from a parasitic mode can be transferred to an adjacent cavity oscillator (e.g., from the first dual-mode resonator 102 to the second dual-mode resonator 104), then it is possible to use the parasitic resonance as a bypass resonator in order to provide diagonal cross-coupling. This concept is schematically illustrated in fig. 5. The coupling between the first mode 1a and the fourth mode 4b is provided by a first elongated iris 128 between the first dual-mode resonator 102 and the second dual-mode resonator 104. The coupling between the second mode 2a and the third mode 3b and the coupling between the first parasitic mode Sa and the third mode 3b are provided by the second elongated iris 130 between the first dual-mode resonator 102 and the second dual-mode resonator 104. The first elongated iris 128 and the second elongated iris 130 will be explained in further detail below. The third inner coupling element 154 couples the first mode 1a to the second mode 2 a. Fourth inner coupling element 156 couples third mode 3b to fourth mode 4 b. The third internal coupling element 154 and the fourth internal coupling element 156 will be explained in further detail below.

Fig. 6 visualizes the concept of the mutual coupling element 106 (formed by the elongated

irises

128, 130 described above) arranged between the first and second double-

mode resonators

102, 104 of the radio frequency filter 100. The radio frequency filter 100 includes a first dual-mode resonator 102 and a second dual-mode resonator 104. The first dual-mode resonator 102 and the second dual-mode resonator 104 are disposed with their respective centers along a common central axis 126. The intercoupling element 106 includes a first elongated iris 128 centered about a common central axis 126 and a second elongated iris 130 disposed perpendicular to the first elongated iris 128 and offset from the common central axis 126. The first parasitic electric field vector Es is parallel to the common central axis. The first elongated iris 128 is a distance d from the second elongated iris 130. The first parasitic magnetic field vector Hs is oriented around the first parasitic electric field vector Es. Thus, the first parasitic electric field vector Es is substantially parallel to the second elongated iris 130. Along the common central axis 126, the magnetic field strength of the first parasitic mode Sa is at its minimum and the electric field strength of the first parasitic mode Sa is at its maximum.

The second elongated iris 130 is offset from the common central axis 126 in a direction of a length component of the first elongated iris 128, wherein a gap is provided between the first elongated iris 128 and the second elongated iris 130.

The length component of the first elongated iris 128 is disposed parallel to the electric field vector E2 of the second mode 2 a. The length component of the second elongated iris 130 is disposed parallel to the electric field vector E1 of the first pattern 1 a. The length component of the first elongated iris 128 is disposed parallel to the electric field vector E3 of the third mode 3 b. The length component of the second elongated iris 130 is disposed parallel to the electric field vector of the fourth pattern 4 b. This allows coupling the first mode 1a to the fourth mode 4b via the first elongated iris 128 and the second mode 2a to the third mode 3b via the second elongated iris 130. Further, the first parasitic mode Sa is coupled to the third mode via the second elongated iris 130.

By being off-center (i.e., common central axis 126), the second iris slivers 130 provides coupling between mode 2a and mode 3b, and the flux vector from the first parasitic mode Sa is substantially aligned with both the flux vectors of the second iris slivers 130 and mode 3 b.

The incoupling elements are not shown in fig. 6. These will be shown and described in association with fig. 8 and 10-13. The in-coupling element couples modes within dual-mode resonator 102.

Figure 7 is a view of a first dual-mode resonator along a common central axis. In fig. 7, the first parasitic magnetic field vector Hs and the third magnetic field vector H3 are shown as being substantially parallel to each other at the second elongated iris 130.

Fig. 8 shows an embodiment of the radio frequency filter 100. Only features not described with reference to fig. 6 will be described. In the embodiment of fig. 8, the first elongated iris 128 and the second elongated iris 130 are connected to each other and together form a T. As previously described, the two

elongated irises

128 and 130 together form the intercoupling element 106. Also shown in fig. 8 is the first in-coupling element 112 disposed at the border region between the first side 134 and the second side 136 of the first dual-mode resonator 102 where the magnetic field lines of the first parasitic mode Sa and the first mode 1a are at least partially parallel. The first inner coupling element 112 is a notch in the embodiment shown in fig. 8. Since the first parasitic mode Sa is significantly separated in frequency from the main mode, a large chamfer/cut/notch is required in order to couple sufficient energy between the modes. As such, the notch is advantageous over a cut or chamfer along the entire length of the first dual-mode resonator 102 because it significantly reduces parasitic coupling or interaction between other modes within the resonator mass, thereby enabling precise filter design using these features.

The first dual-mode resonator 102 includes a third in-coupling element 154 that couples the first mode 1a to the second mode 2 a. The third in-coupling element 154 is arranged at a border region between the second side 136 and the third side 168 of the first double-mode resonator 102, where the magnetic field lines of the first mode 1a (fig. 5) and the second mode 2a (fig. 5) are at least partially parallel. This is an advantageous position of the third in-coupling element in order to obtain a high coupling efficiency between the first mode 1a and the second mode 2 a. In the embodiment shown in fig. 8, the third inner coupling element 154 is in the form of a cut-out.

The second dual-mode resonator 104 includes a fourth in-coupling element 156 that couples the third mode 3b to the fourth mode 4 b. The fourth in-coupling element 156 is arranged at the border region between the first side 158 and the second side 160 of the second dual-mode resonator 104. In this boundary region, the magnetic field lines of the third mode 3b and the fourth mode 4b are at least partially parallel. This is an advantageous position of the fourth inner coupling element 156 in order to obtain a high coupling efficiency between the third mode 3b and the fourth mode 4 b. In the embodiment shown in fig. 8, the fourth inner coupling element 156 is in the form of a cut-out.

Fig. 9 shows the coupling characteristics through the mutual coupling element 106 in the radio frequency filter of fig. 8, depending on the position of the second elongated iris 130 with respect to the common central axis 126. The coupling characteristic is expressed in MHz on the vertical axis. The solid line shows the coupling efficiency between the first parasitic mode Sa and the second parasitic mode Sb for different lengths L2 (fig. 3, 4) of the second elongated iris 130. The dashed lines depict the coupling between the second mode 2a and the third mode 3b for different lengths L2 (fig. 3, 4) of the second elongated iris 130. For convenience, the coupling efficiency of the first parasitic mode Sa to the second parasitic mode Sb is shown because the two resonances are at the same frequency. Even at different frequencies, the coupling of the first parasitic mode Sa to the third mode 3b is proportional to the coupling of the first parasitic mode Sa to the second parasitic mode Sb and has a similar dependence on the position of the iris. It is clear that although the magnetic flux density of mode 3b is substantially uniform across the iris cross-section and has the same magnitude for all iris bridge positions, the magnetic flux component of the parasitic mode Sa is not. Thus, as the second elongated iris 130 is moved further from the common central axis 126, the magnitude of the coupling from Sa to 3b will correspondingly increase, as is evident and shown in fig. 9. Furthermore, since the parasitic mode Sa has vertical and horizontal components of flux on either side of the common central axis 126, moving the mutual coupling element 106 in one direction will result in an opposite sign coupling with respect to that obtained by moving it in the other direction.

Another advantage of the moving second elongated iris 130 is that the coupling strength between the second mode 2a and the third mode 3b is constant for its position, since the magnetic field vectors of the second mode 2a and the third mode 3b have constant magnitude and direction for all positions of the iris. This means that the main coupling from the second mode 2a to the third mode 3b can be controlled by varying the length L2 (fig. 3, 4) of the second elongated iris 130, and the coupling between the first parasitic mode and the second parasitic mode can be controlled by the position of the second elongated iris, allowing independent control of the two couplings according to a single characteristic.

Fig. 10 schematically shows a radio frequency filter 100 according to an alternative embodiment of the invention. Only the differences between the embodiment in fig. 8 and the embodiment in fig. 10 will be described. In fig. 10, the third incoupling element 154 has been arranged on the opposite side of the second side 136, on which opposite side 136 the magnetic field lines of the first mode 1a and the second mode 2a are at least partly parallel.

Fig. 11 schematically shows a radio frequency filter 100 according to an alternative embodiment of the invention. Only the differences between the embodiment in fig. 10 and the embodiment in fig. 11 will be described. In fig. 11, the first in-coupling element 112 has been arranged on the opposite side of the first resonator 102, on which opposite side of the first resonator 102 the magnetic field lines of the first mode 1a and the first parasitic mode Sa are at least partially parallel.

Fig. 12 schematically shows a radio frequency filter 100 according to an alternative embodiment of the invention. Only the differences between the embodiment in fig. 11 and the embodiment in fig. 12 will be described. In fig. 12, the second elongated iris 130 is placed on the opposite side of the first elongated iris 128 as compared to the previous embodiment in fig. 11.

The operation of the radio frequency filter 100 according to the embodiments of fig. 8 and 10 to 12 is as follows. The first dual-mode resonator 102 is fed with an electromagnetic wave that is to be filtered to the first mode 1 a. The first in-coupling element 112 will provide coupling from the first mode 1a to the first parasitic mode Sa and the third in-coupling element 154 will provide coupling from the first mode 1a to the second mode 2 a. Then, the mutual coupling element 106 will provide coupling from the first mode 1a to the fourth mode 4b, coupling from the first parasitic mode Sa to the third mode 3b, and coupling from the second mode 2a to the third mode 3 b. More specifically, the first iris strip 128 provides coupling from the first mode 1a to the fourth mode 4b, and the second iris strip 130 provides coupling between the second mode 2a and the third mode 3b, and coupling between the first parasitic mode Sa and the third mode 3 b. Finally, the fourth in-coupling element 156 will provide coupling from the third mode 3b to the fourth mode 4 b. The first mode 1a, the second mode 2a, the third mode 3b and the fourth mode 4b together form a filter passband. The frequency of the first spurious mode Sa and the frequency of the second spurious mode Sb are outside the filter passband.

Fig. 13 schematically shows a first dual-mode resonator 102 with a different form of the third in-coupling element 154. In contrast to the third in-coupling element 154 described above, the third in-coupling element 154 in fig. 13 is in the form of a full length chamfer.

Fig. 14-18 show different examples of filter functions implemented with the radio frequency filter 100 according to different embodiments of the invention. The different filter functions show the transmission (in dB) through the different rf filters 100 as a function of frequency (in GHz). The filter function shows the transmission s21 (in dB) as a function of frequency (in GHz). The single transmission zeroes or pairs of transmission zeroes shown in fig. 14-18 can be formed with many different combinations of circuit topologies and slot offsets-there is no specific location for the slot offset or notch positioning required for a given transmission zero positioning-depending on the complete circuit. In fig. 14 to 18, the solid and dashed lines show typical variations obtainable with variations in the notch and offset parameters, i.e. the transmission zero position can be controlled by design.

Figure 14 illustrates one example of strong and weak inductive triplets implemented according to one embodiment of the invention. As can be seen in fig. 14, the filter function has a transmission dip above the transmission peak.

Figure 15 illustrates one example of strong and weak capacitive triplets implemented according to one embodiment of this disclosure. As can be seen in fig. 15, the filter function has a transmission dip below the transmission peak.

Fig. 16 illustrates an example of strong and weak inductance quads implemented according to an embodiment of the invention. As can be seen in fig. 16, the filter function has two transmission dips above the transmission peak.

Figure 17 illustrates one example of strong and weak inductive triplets implemented according to one embodiment of this disclosure. As can be seen in fig. 17, the filter function has two transmission dips below the transmission peak.

FIG. 18 illustrates one example of a strong and weak capacitance quad-state implemented according to one embodiment of the invention. As can be seen in fig. 18, the filter function has a transmission dip below the transmission peak and a transmission dip above the transmission peak. Fig. 18 shows an example with respect to significant high-side and low-side tilt.

Fig. 19 schematically illustrates a radio frequency filter 100 according to an alternative embodiment. The radio frequency filter 100 includes: a first dual-mode resonator 102 having a first mode 1a, a second mode 2a, and a first parasitic mode Sa, wherein the first dual-mode resonator 102 includes a first in-coupling element 112 coupling the mode 1a to the first parasitic mode Sa; a second dual-mode resonator 104 having a third mode 3b, a fourth mode 4b, and a second parasitic mode Sb; and a mutual coupling element 106 disposed between the first dual-mode resonator 102 and the second dual-mode resonator 104, the mutual coupling element 106 coupling the first mode 1a to the fourth mode 4b, the second mode 2a to the third mode 3b, and the first parasitic mode Sa to the second parasitic mode Sb. The second dual-mode resonator 104 has a second parasitic mode Sb and includes a second in-coupling element 132 that couples the second parasitic mode Sb to the third mode 3 b. The first parasitic electric field vector Es is parallel to the common central axis 126 (as shown in fig. 20). The first elongated iris 128 is a distance d from the second elongated iris 130. The first parasitic magnetic field vector Hs is oriented around the first parasitic electric field vector Es. Thus, the first parasitic electric field vector is substantially perpendicular to the second elongated iris 130. Along the common central axis, the magnetic field strength of the first parasitic mode Sa is at its minimum, and the electric field strength of the first parasitic mode Sa is at its maximum. The coupling between the first mode 1a and the fourth mode 4b is provided by the first elongated iris 128. The coupling between the second mode 2a and the third mode 3b and the coupling between the first parasitic mode Sa and the second parasitic mode Sb are provided by the second elongated iris 130 and the third elongated iris 138. The first, second, and third

elongated irises

128, 130, 138 forming the mutual coupling element 106 will be explained in further detail with reference to fig. 20. The third inner coupling element 154 couples the first mode 1a to the second mode 2 a. Fourth inner coupling element 156 couples third mode 3b to fourth mode 4 b. The third and fourth

inner coupling elements

154, 156 will be explained in further detail with reference to fig. 20.

Fig. 20 shows a radio frequency filter 100 according to the embodiment of fig. 19. The first dual-mode resonator 102 comprises a first monolithic block 108 of solid dielectric material and a first conductive layer 110 overlying the first monolithic block 108, and the second dual-mode resonator 104 comprises a second monolithic block 114 of solid dielectric material and a second conductive layer 116 overlying the second monolithic block 114. The first monolithic block 108, the second monolithic block 114 and the mutual coupling element 106 together form a monolithic unit, which may facilitate the manufacture of the radio frequency filter.

The first dual-mode resonator 102 and the second dual-mode resonator 104 are disposed with their respective centers along a common central axis 126. The mutual coupling element 106 includes a first elongated iris 128 centered about a common central axis 126, an elongated iris 130 disposed perpendicular to the first elongated iris 128 and offset from the common central axis 126, and a third elongated iris 138, the third elongated iris 138 disposed parallel to the second elongated iris 130 and offset from the central axis 126 on an opposite side of the central axis 126 relative to the second elongated iris 130. The second elongated iris 130 couples the first parasitic mode Sa to the second parasitic mode Sb. The third elongated iris 138 couples the first parasitic mode Sa to the second parasitic mode Sb. Thus, both the second elongated iris 130 and the third elongated iris 138 couple the first parasitic mode Sa to the third mode 3 b. The magnetic field vector of the first parasitic mode Sa rotates about the common central axis 126, while the electric field vector of the third mode 3b is orthogonal (but in the same plane) to the common central axis 126. This means that the second elongated iris 130 will contribute to the positive coupling, while the third elongated iris 138 will contribute to the negative coupling. If the second elongated iris 130 and the third elongated iris 138 are positioned at the same distance from the common central axis 126, the contribution of the second elongated iris 130 will cancel the contribution of the third elongated iris 130.

The magnetic field vector of the first parasitic mode Sa and the magnetic field vector of the second parasitic mode Sb encircle a common central axis 126.

The first internal coupling element 112 is arranged at a boundary region between the fifth side 170 and the sixth side 172 of the first dual-mode resonator 102 where the magnetic field lines of the first parasitic mode Sa and the first mode 1a are at least partially parallel. The first inner coupling element 112 is a notch in the embodiment shown in fig. 20. Since the parasitic modes are significantly separated in frequency from the primary modes, large chamfers/cuts/notches are required in order to couple sufficient energy between the modes. As such, the notch is advantageous over a cut or chamfer along the entire length of the first dual-mode resonator 102 because it results in significantly reduced parasitic coupling or interaction between other modes within the resonator mass, thereby enabling precise filter design using these features.

The second internal coupling element 132 is disposed at a boundary region between the first side 158 and the third side 162 of the second dual-mode resonator 104 where magnetic field lines of the second parasitic mode Sa and the third mode 3b are at least partially parallel. The second inner coupling element 132 is a notch in the embodiment shown in fig. 20 for the same reason as the first inner coupling element.

The first dual-mode resonator 102 includes a third in-coupling element 154 that couples the first mode 1a to the second mode 2 a. The third in-coupling element 154 is arranged at a boundary region between the second side 136 and the fourth side 140 of the first dual-mode resonator 102, where the magnetic field lines of the first and second modes are at least partially parallel. This is an advantageous position of the third in-coupling element in order to obtain a high coupling efficiency between the first mode and the second mode. In the embodiment shown in fig. 20, the third inner coupling element is in the form of a cut-out.

The second dual-mode resonator 104 includes a fourth in-coupling element 156 that couples the third mode 3b to the fourth mode 4 b. The fourth in-coupling element 156 is arranged at a boundary region between the first side 158 and the second side 160 of the second dual-mode resonator 104, where the magnetic field lines of the third mode 3b and the fourth mode 4b are at least partially parallel. This is an advantageous position of the fourth inner coupling element 156 in order to obtain a high coupling efficiency between the third mode 3b and the fourth mode 4 b. In the embodiment shown in fig. 20, the fourth inner coupling element 156 is in the form of a cut-out.

In operation, the first dual-mode resonator 102 is fed with an electromagnetic wave that is to be filtered to the first mode 1 a. The first in-coupling element 112 will provide coupling from the first mode 1a to the first parasitic mode and the third in-coupling element will provide coupling from the first mode 1a to the second mode 2 a. Then, the mutual coupling element 106 will provide coupling from the first mode 1a to the fourth mode 4b, coupling from the first parasitic mode Sa to the second parasitic mode Sb and coupling from the second mode 2a and the third mode 3 b. More specifically, the first elongated iris 128 provides coupling between the first mode 1a and the fourth mode 4b, and the second elongated iris 130 and the third elongated iris 138 provide coupling between the second mode 2a and the third mode 3b and coupling between the first parasitic mode Sa and the second parasitic mode Sb. Finally, the second in-coupling element 132 will provide coupling from the second parasitic mode Sb to the third mode 3b, and the fourth in-coupling element 156 will provide coupling from the third mode 3b to the fourth mode 4 b. The first mode 1a, the second mode 2a, the third mode 3b and the fourth mode 4b together form a filter passband. The frequency of the first spurious mode Sa and the frequency of the second spurious mode Sb are outside the filter passband.

Fig. 21 schematically illustrates a communication device 300 in a wireless communication system 400. The communication device 300 comprises a radio frequency filter 100 according to an embodiment of the present invention. The wireless communication system 400 further comprises a communication device 500, which communication device 500 may also comprise a radio frequency filter 100 according to any of the embodiments described above. Dashed arrow a1 represents a transmission from communication device 300 to communication device 500, commonly referred to as an uplink transmission. Full arrow a2 represents a transmission from communication device 500 to communication device 300, commonly referred to as a downlink transmission.

The communication device 300 may be any of a User Equipment (UE), a Mobile Station (MS), a wireless terminal, or a mobile terminal capable of performing wireless communication in a wireless communication system (sometimes referred to as a cellular radio system) in Long Term Evolution (LTE). The UE may further be referred to as a mobile phone, a cellular phone, a computer tablet, or a laptop with wireless capabilities. A UE herein may be, for example, a portable, pocket, hand-held, computer-included, or car-mounted mobile device capable of communicating voice or data with another entity, such as another receiver or server, via a radio access network. The UE may be a Station (STA), which is any device that contains a Media Access Control (MAC) compliant IEEE 802.11 and a Physical Layer (PHY) interface to the Wireless Medium (WM).

The present communication device 500 may also be a Base Station (Radio) network node or access point or Base Station, e.g. a Radio Base Station (RBS), which in some networks may be referred to as transmitter, "eNB", "eNodeB", "NodeB" or "B node", depending on the technology and terminology used. Based on the transmit power and thus on the cell size, the radio network nodes may have different categories, e.g. macro eNodeB, home eNodeB or pico base station. The radio network node may be a Station (STA), which is any device comprising a Medium Access Control (MAC) compliant with IEEE 802.11 and a physical layer (PHY) interface to the Wireless Medium (WM).

Claims

1. A radio frequency filter (100) comprising:

a first dual-mode resonator (102) having a first mode (1a), a second mode (2a) and a first parasitic mode (Sa), wherein the first dual-mode resonator (102) comprises a first in-coupling element (112) coupling the first mode (1a) to the first parasitic mode (Sa);

a second dual-mode resonator (104) having a third mode (3b) and a fourth mode (4 b); and

a mutual coupling element (106) disposed between the first dual-mode resonator (102) and the second dual-mode resonator (104), the mutual coupling element (106) coupling the first mode (1a) to the fourth mode (4b), the second mode (2a) to the third mode (3b), and the first parasitic mode (Sa) to the third mode (3 b);

wherein the first in-coupling element (112) is arranged at a border region between a first side (134) and a second side (136) of the first dual-mode resonator (102) where magnetic field lines of the first parasitic mode (Sa) and the first mode (1a) are at least partially parallel;

wherein the second dual-mode resonator (104) has a second parasitic mode (Sb) and comprises a second in-coupling element (132) coupling the second parasitic mode (Sb) to the third mode (3 b);

wherein the mutual coupling element (106) further couples the first parasitic mode (Sa) to the second parasitic mode (Sb);

wherein the first dual-mode resonator (102) and the second dual-mode resonator (104) are disposed with their respective centers along a common central axis (126), the mutual coupling element (106) comprising a first elongated iris (128) centered on the common central axis (126) and a second elongated iris axis (130) perpendicular to the first elongated iris (128) and offset from the common central axis (126); the mutual coupling element (106) comprises a third elongated iris (138), the third elongated iris (138) being arranged parallel to the second elongated iris (130) and being displaced from the central axis (126) on an opposite side of the central axis (126) with respect to the second elongated iris (130).

2. The radio frequency filter (100) of claim 1,

wherein, along the common central axis (126), the magnetic field strength of the first parasitic mode (Sa) is at its minimum and the electric field strength of the first parasitic mode (Sa) is at its maximum.

3. The radio frequency filter (100) of claim 1 or 2,

wherein the second elongated iris (130) is offset from the common central axis (126) in a direction of a length component of the first elongated iris (128);

wherein the first elongated iris (128) and the second elongated iris (130) are connected to each other or a gap is provided between the first elongated iris (128) and the second elongated iris (130).

4. The radio frequency filter (100) of claim 1 or 2,

wherein a length component of the first elongated iris (128) is arranged in parallel with an electric field vector of the second mode (2 a);

wherein a length component of the second elongated iris (130) is arranged in parallel with an electric field vector of the first mode (1 a).

5. The radio frequency filter (100) of claim 1,

wherein the first inner coupling element (112) is one of a notch, at least one local chamfer and at least one local cut-out.

6. The radio frequency filter (100) of claim 1, wherein the second in-coupling element (132) is one of a notch, at least one local chamfer and at least one local cut.

7. The radio frequency filter (100) according to any of claims 1, 2, 5 and 6, wherein the first mode (1a), the second mode (2a), the third mode (3b) and the fourth mode (4b) together form a filter passband, and wherein the frequency of the first parasitic mode (Sa) and the frequency of the second parasitic mode (Sb) are outside the filter passband.

8. The radio frequency filter (100) according to any of claims 1, 2, 5 and 6, wherein at least one of the electric field vector of the first parasitic mode (Sa) and the electric field vector of the second parasitic mode (Sb) is parallel to the common central axis (126).

9. The radio frequency filter (100) of any of claims 1, 2, 5 and 6, wherein the first dual-mode resonator (102) comprises a third in-coupling element (154) coupling the first mode (1a) to the second mode (2 a).

10. The radio frequency filter (100) of any of claims 1, 2, 5 and 6, wherein the second dual-mode resonator (104) comprises a fourth in-coupling element (156) coupling the third mode (3b) to the fourth mode (4 b).

11. The radio frequency filter (100) of any of claims 1, 2, 5 and 6, wherein the first dual-mode resonator (102) comprises a first monolithic block (108) of solid dielectric material and a first conductive layer (110) covering the first monolithic block (108), and wherein the second dual-mode resonator (104) comprises a second monolithic block (114) of solid dielectric material and a second conductive layer (116) covering the second monolithic block (114).

12. The radio frequency filter (100) of claim 11, wherein the first monolithic block (108), the second monolithic block (114) and the mutual coupling element (106) together form a monolithic unit.

13. A communication device (300) for a wireless communication system (400), the communication device (300) comprising a radio frequency filter (100) according to any of the preceding claims.