BACKGROUND
Dielectric resonator filters have been widely employed in space payloads and cellular base station equipment due to their compact size, good thermal stability and high Q performance.
Single-mode dielectric resonator filters, which have advantage in manufacturability and filter coupling configurations, have been widely used in wireless industry.
In recent years, multiple degenerate mode resonances in a dielectric resonator have also been explored, which utilize either the same type of modes with certain spatial symmetries or different types of modes resonating at the same frequency. U.S. Pat. No. 6,414,571 discloses a dual TM mode composite resonator for use in devices operating at microwave frequencies in the field of cellular telecommunications. U.S. patent application Ser. No. 12/479,263 discloses dielectric resonator filters and multiplexers realized using full cylindrical or half-cut dielectric resonators.
SUMMARY
One aspect of the disclosure is to provide a dielectric resonator filter. The dielectric resonator filter includes at least one dielectric resonator. The dielectric resonator includes a metal housing having a top surface and a bottom surface and defining a resonator cavity, and a dielectric rod located within the resonator cavity. The dielectric rod is short-circuited at both the top surface and the bottom surface. A plurality of holes is formed in the dielectric rod parallel to an axis of the dielectric rod and a plurality of apertures is formed on the top surface corresponding to the positions of the holes, respectively. A plurality of screws are inserted into the holes through the apertures, respectively. The dielectric resonator supports dual TM11 degenerate modes, each of which forms an electric resonator. An insertion depth of each of the screws is adjustable for adjusting resonance frequencies of the dual degenerate modes and coupling between the dual degenerate modes.
One aspect of the disclosure is to provide a dielectric resonator filter. The dielectric resonator filter includes a plurality of dielectric resonators in a common housing, wherein the housing including a top surface and a bottom surface. A separating wall is provided between each of two adjacent dielectric resonators to separate the housing into a plurality of resonator cavities. A coupling element is provided for coupling between two adjacent dielectric resonators. Each of the dielectric resonator comprises a dielectric rod located within the resonator cavity of the dielectric resonator, wherein the dielectric rod is short-circuited at both the top surface and the bottom surface; a plurality of holes is formed in the dielectric rod parallel to an axis of the dielectric rod and a plurality of apertures is formed on the top surface corresponding to the positions of the holes, respectively, a plurality of screws is inserted into the holes through the apertures, respectively. Each of the dielectric resonators supports dual TM11 degenerate modes, each of which forms an electric resonator, and an insertion depth of each of the screws is adjustable for adjusting resonance frequencies of the dual degenerate modes and coupling between the dual degenerate modes.
Another aspect of the disclosure is to provide a method of manufacturing a dielectric resonator filter. The method includes obtaining dimension parameters of the dielectric rod and the metal housing of the filter based on required center frequency, bandwidth, isolation and return loss; forming the dielectric rod with holes, the screws, the metal housing and the top surface with apertures according to the obtained dimension parameters; and assembling the filter by disposing the dielectric rods into the metal housing and inserting the screws into the holes of the dielectric rods. The dielectric resonator filter supports dual TM11 degenerate modes, each of which forms an electric resonator, and an insertion depth of each of the screws is adjustable for adjusting resonance frequencies of the dual degenerate modes and coupling between the dual degenerate modes.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a dielectric resonator filter including a dielectric resonator according to an embodiment of the present application.
FIG. 2
a is a plan view of a dielectric resonator according to an embodiment of the present application, FIG. 2b is a cross-sectional view along a line B-B′ of FIG. 2a, and FIG. 2c is a cross-sectional view along a line A-A′ of FIG. 2a.
FIG. 3
a is a plan view of a dielectric resonator according to an embodiment of the present application; and FIG. 3b is a plan view of a dielectric resonator according to an embodiment of the present application.
FIG. 4
a is a schematic view showing the arrangement of the screws according to an embodiment of the present application, FIG. 4b is a schematic view showing the electric and magnetic field of the two TM11 degenerate modes in a resonator according to an embodiment of the present application, FIG. 4c is a schematic view showing the electric and magnetic field of the two TM11 degenerate modes in a resonator according to an embodiment of the present application.
FIG. 5 is a schematic view showing an arrangement of the screws according to an embodiment of the present application.
FIG. 6 is a schematic view showing a filter with an input/output according to an embodiment of the present application.
FIG. 7
a is a schematic view showing a filter with two dielectric resonators according to an embodiment of the present application; and FIG. 7b is a schematic view showing a filter with two dielectric resonators according to another embodiment of the present application.
FIG. 8 is a schematic view showing a filter with two dielectric resonators according to an embodiment of the present application.
FIG. 9
a is a schematic view of a dielectric resonator filter with four dielectric resonators according to embodiments of the present application; and FIG. 9b is a plot of transmissions response for the dielectric resonator filter of FIG. 9a.
FIGS. 10
a-10d are schematic views showing a dielectric resonator filter with four dielectric resonators according to embodiments of the present application.
FIGS. 11
a-11d are plots of transmissions response for the dielectric resonator filters of FIGS. 10a-10d, respectively.
FIGS. 12
a-12d are schematic views showing a dielectric resonator filter with four dielectric resonators according to embodiments of the present application.
FIGS. 13
a-13d are plots of transmissions response for the dielectric resonator filters of FIGS. 12a-12d, respectively.
FIG. 14
a is a plot showing a typical measured in-band isolation responses for an 8-pole TM11 dual mode dielectric resonator filter according to an embodiment; FIG. 14b is a plot showing a typical measured broadband isolation response for an 8-pole TM11 dual mode dielectric resonator filter according to an embodiment.
FIG. 15 is a perspective view of a dielectric resonator filter according to an embodiment of the present application.
FIG. 16 is a plot showing broadband isolation response for an 8-pole TM11 dual mode dielectric resonator filter with spurious-suppression screws according to an embodiment.
FIG. 17 is a plan view of a diplexer/filter configuration by the TM11 dual-mode dielectric resonators according to an embodiment of the present application.
FIG. 18 is a flowchart of manufacturing a dielectric resonator filter including at least one dielectric resonator according to an embodiment of the present application.
DETAILED DESCRIPTION
Hereinafter, a detailed description will be given with reference to the appended drawings.
According to an embodiment of the present application, FIGS. 1 and 2 show a dielectric resonator filter including a dielectric resonator 100. The dielectric resonator 100 includes a metal housing 6 defining a resonator cavity 7. The metal housing 6 includes a top surface 15 and a bottom surface 16. A dielectric rod 1 is located within the resonator cavity 7. The dielectric rod 1 is a full height dielectric rod situated in the cavity 7. That is, the rod 1 is short-circuited at both the top surface 15 and the bottom surface 16. Holes 2, 3, 4 are formed in the dielectric rod parallel to an axis of the dielectric rod 1 and apertures 8, 9, 10 are formed on the top surface 15 corresponding to the positions of the holes 2, 3, 4, respectively. Screws 12, 13, 14 are inserted into the holes 2, 3, 4 through the apertures 8, 9, 10, respectively. The dielectric resonator 100 supports dual TM11 degenerate modes, each of which forms an electric resonator. A dual mode resonator works by coupling energy from one mode to its degenerate mode in the same resonator. In the embodiment, an insertion depth of each of the screws 12, 13, 14 is adjustable for coupling between the dual degenerate modes and adjusting resonance frequencies of the dual degenerate modes.
According to an embodiment, the holes formed in the dielectric rod include one coupling screw hole 2 sized and dimensioned for accommodating coupling screw 12 (e.g., threaded) and two tuning screw holes 3, 4 for accommodating tuning screws 13, 14 (e.g., threaded). In an example, the holes 2, 3, 4 are through holes formed in the rod 1. In another example, the holes 2, 3, 4 can be non-through holes. In an example, the diameter c of the tuning screws can be chosen by a tradeoff between the mechanical manufacturability and the filter tunability. If the diameter c is increased, the tuning and coupling capability of the screw will be increased.
According to an embodiment, as shown in FIG. 1, the resonator cavity 7 is a square resonator cavity and the dielectric rod 1 is a cylindrical dielectric rod situated in the center of the resonator cavity.
According to another embodiment, as shown in FIG. 3a, the resonator cavity 7′ is a cylindrical resonator cavity and the dielectric rod 1′ is a cylindrical dielectric rod situated in the center of the resonator cavity.
According to an embodiment, as shown in FIG. 3b, the resonator cavity 7″ is a square resonator cavity and the dielectric rod 1″ is a square dielectric rod situated in the center of the resonator cavity.
The behavior of the resonator 100 will be described with reference to FIGS. 4a, 4b, and 4c.
FIG. 4
a is a schematic view showing the arrangement of the screws/holes according to an embodiment of the present application. Here, a resonator having a square metal housing with a cylindrical dielectric rod is taken as an example, but the design principles can also be used in the other resonators as shown in FIGS. 3a and 3b.
As shown in FIG. 4a, R is the radius of the dielectric rod, point O is the resonator center, T1 and T2 are the positions for the two tuning screws, respectively (to tune the individual dual TM11 resonance frequencies), and T3 is the position for the coupling screw (to couple the dual TM11 resonances).
According to an embodiment, to effectively and independently realize the tuning and coupling functions, the positions of T1, T2 and T3 can be designed as: line OT1 is perpendicular to line OT2; line OT3 is either perpendicular to line T1T2 or be parallel to it; the length of lines OT1, OT2 and OT3 is between 0.5 R to 0.8 R.
In an embodiment, to facilitate the filter routing and manufacture, T1, T2 and T3 can be arranged on a same circle that is concentric with dielectric rod.
In an example, positions T1 and T2 for tuning screws can be laid along the diagonal lines of the resonator cavity, with the resultant EM fields of a pair of orthogonal degenerate TM11 modes as shown in FIG. 4b. The dots and crosses represent the electric field, which go into and out of the screen. The dashed lines represent the magnetic field. One of the modes is called h-mode (left), and the other is called v-mode (right) as shown in FIG. 4b.
In another example, positions T1 and T2 for tuning screws can follow the cavity side line directions, with the resultant EM fields of the resonator shown in FIG. 4c. The dots and crosses represent the electric field, which go into and out of the screen. The dashed lines represent the magnetic field. One of the modes is called h-mode (left), the other is called v-mode (right).
In an embodiment, the resonance frequencies of the h-mode and the v-mode can be adjusted by adjusting the insertion depths of the tuning screws located in positions T1 and T2, respectively. The coupling between the h-mode and the v-mode can be adjusted by adjusting the insertion depth of the coupling screw located in position T3. For example, as shown in FIGS. 2b and 2c, the insertion depth of the tuning screw 13 inserted into the tuning screw hole 3 can be adjusted for tuning the resonance frequency of the h-mode and the insertion depth tv of the tuning screw 14 inserted into the tuning screw hole 4 can be adjusted for tuning the resonance frequency of the v-mode. In addition, the insertion depth tf of the coupling screw 12 inserted into the coupling screw hole 2 can be adjusted for coupling between the h-mode and the v-mode. Thus, the self-coupling (resonance frequency tuning) and mutual coupling can be adjusted independently. Also, the tuning of both the self and mutual couplings can be accessible in a convenient way, i.e., from the top of the filter. That is, all the tuning/coupling structures can be realized by mechanical elements adjustable on the top surface of the dual mode filter.
In the above, a dielectric resonator with two tuning screws and one coupling screw is described. However, the arrangement of the screws of the dielectric resonator of the present application is not limited to this, only if at least one screw is positioned to tune the h-mode, at least one screw is positioned to tune the v-mode, and at least one screw is positioned to couple the h-mode and the v-mode. For example, as shown in FIG. 5, six screws are provided in the dielectric resonator. Locations T1A, T1B represent the tuning screws/holes for h-mode, T2A and T2B represent the tuning screws/holes for v-mode, and locations T3A and T3B represent the tuning screws/holes for two coupling screws/holes which couple the two modes (resonances) in the same dielectric resonator. In an embodiment, the six holes can be positioned substantially on a same circle that is concentric with the dielectric rod. The line T1AT1B is perpendicular to line T2AT2B and the line T3AT3B is either perpendicular to line T1AT2A, or in parallel with line T1AT2A.
According to an embodiment, as shown in FIG. 6, an input element 5 and an output element 5′ are provided in the filter with the dielectric resonator 100 for realizing the input and output coupling between the filter and other apparatus, respectively. The input/output 5/5′ includes a connector 17/17′, an input/output coupling strip 18/18′, and a wire 19/19′. In an example, the input/output coupling strip 18/18′ has an end connected to the SMA connector 17/17′ through the wire 19/19′, and another end grounded to the bottom surface 16. By designing the distance between the coupling strip 18/18′ and the dielectric rod 1, the required I/O coupling can be achieved.
According to an embodiment, the filter may comprise a plurality of dielectric resonators.
As shown in FIG. 7a, the filter comprises a first resonator 201 and a second resonator 202 in a common housing 203 with a top surface 215 and a bottom surface 216. A separating wall 210 is positioned between the two resonators to separate the housing 203 into two resonator cavities 211, 212. Each of the dielectric resonators includes cylindrical dielectric rod with three holes for accommodating two tuning screws and one coupling screw, which supports dual TM11 degenerate modes. The screws of a resonator are adjustable for adjusting resonance frequencies of the dual degenerate modes and coupling between the dual degenerate modes of the resonator. In order to efficiently use the space of the metal cavity for realizing the couplings between two dielectric resonators and reduce the stray coupling between two metal cavities, in an embodiment, the two frequency tuning screws of a resonator cavity are placed along the two diagonal lines of the resonator cavity.
In order to realize the coupling between the dielectric resonator 201 and the dielectric resonator 202, according to an embodiment, a coupling element 231 is provided as shown in FIG. 7a. In an embodiment, the coupling element 231 is a conductor loop for realizing an inter-cavity coupling for the dual mode TM11 dielectric resonator filter. The loop 231 is formed by a metal wire with one end connected to the upper surface of the resonator cavity 211 and the other end connected to the upper surface of the resonator cavity 212.
In an example, as shown in FIG. 7a, the coupling element 231 is a loop in a trapezoid shape, which is folded in the horizontal lower side and vertical straight in the upper side.
In another example, as shown in FIG. 7b, the coupling element 231 is a loop in a rectangular shape. This structure provides a convenient means for volume manufacturing and tuning without noticeable stray couplings.
The inter-cavity coupling structure can be controlled by changing the height H of the loop. By pulling up or pushing down the pair of straight wires forming the coupling loop outside of the top surface of the resonator cavity, the coupling between resonators 201 and 202 can be reduced or increased.
According to an embodiment, more than one coupling elements can be provided for coupling the resonators. As shown in FIG. 8, two coupling elements 231, 232 are disposed between the two adjacent dielectric resonators 201 and 202 for coupling the resonators 201 and 202. Since the degenerate mode coupling screws of the adjacent dielectric rods excite two pairs of oppositely polarized v and h modes in each individual cavity, the inter-cavity couplings M23 and M14 realized by the two loops are in opposite signs, which may result in a pair of symmetric transmission zeroes on both sides of a filter rejection band.
By choosing the number, the layout and the coupling manner of resonators in the filter, it is possible to realize various practical filter configurations with symmetric or asymmetric characteristics.
FIG. 9
a shows a filter including four resonators 301-304 positioned in a straight line layout, which provides an eight-pole symmetric filter characteristic. An input element 311 is disposed in the resonator 301 for inputting signals to the filter and an output element 312 is disposed in the resonator 304 for outputting signals from the filter. In this embodiment, one coupling element is provided between each of two adjacent resonators. FIG. 9b shows the transmission response for the dielectric resonator filter of FIG. 9a. The horizontal axis represents the frequency of the response and the vertical axis represents the isolation and the return loss of the response.
FIGS. 10
a-10d show several other practical layout schemes of an eight-pole symmetric filter. FIGS. 11a-11d are plots of transmissions response for the dielectric resonator filters of FIGS. 10a-10d, respectively. The filters illustrated in FIGS. 10a, 10b are in a straight line layout while those in FIGS. 10c, 10d are in a folded layout. The filters in FIGS. 10a, 10c are in folded coupling topology, whereas those in FIGS. 10b, 10d are in cascade-quartet (CQ) coupling topology.
FIGS. 12
a-12d show several practical layout schemes of a filter including four resonators, which provides an eight-pole asymmetric filter characteristic. FIGS. 13a-13d are plots of transmissions response for the dielectric resonator filters of FIGS. 12a-12d, respectively. The filters in FIGS. 12a, 12b are in box and extended-box coupling topologies, and are capable of generating two and three independent transmission zeroes, respectively. The filters in FIGS. 12c, 12d are in Cul-de-Sac and further Cul-de-Sac coupling topologies, and can generate five and three independent transmission zeroes, respectively. When the TM11 dual mode dielectric resonators are used for channel filters of a diplexer, filter characteristics with independently controllable asymmetric transmission zeroes are usually required.
Here, an example of an 8-pole symmetric filter in a folded coupling topology with straight line layout as shown in FIG. 10a will be described in details. The center frequency f0 and bandwidth BW for the filter is 1.948 GHz and 67 MHz, respectively. Four dielectric resonators with radius R=16.2 mm, relative permittivity ∈r=20.5 and loss tangent 2.5×10−5 are used to build the filter. For each metal cavity the inner size is 41×41×14(L×L×H) mm3. The coupling matrix which gives a 20 dB return loss and two 60 dB side lobe filter characteristic is synthesized with a standard procedure and given in Table I. As shown in Table I, M01 (M89) is the input (output) coupling. M23, M45, M67 are the inter-cavity mainline couplings, which are realized by metal loops. M12, M34, M56 and M78, are the dual degenerate mode mainline couplings in each dual mode dielectric resonators, respectively. The dual degenerate mode mainline couplings are realized by the coupling screws inserted into the dielectric rods.
TABLE I
|
|
COUPLING MATRIX FOR THE 8-
|
POLE FOLDED-COUPLED FILTER
|
|
|
M01
0.9882
|
M12
0.8178
|
M23
0.5877
|
M34
0.5393
|
M36
−0.1014
|
M45
0.6376
|
M56
0.5393
|
M67
0.5877
|
M78
0.8178
|
M89
0.9882
|
|
The designed filter is measured. The measured in-band isolation/return loss responses of the filter are shown in FIG. 14a and the measured broadband isolation response of the filter is shown in FIG. 14b. The measured isolation at f0 is less than 0.5 dB, and the extracted unloaded Q-factor from the measured data is a slightly more than 3,000. From the broadband response of the filter shown in FIG. 14b, it can be observed that the lower spurious mode TM01 is below 1.25 GHz and the higher spurious mode TM21 is above 2.55 GHz. These two spurious modes can be suppressed by cascading a wide band bandpass filter.
In an embodiment, the lower TM01 spurious mode can also be suppressed by a self-contained method, in which the spurious mode can be suppressed by introducing a hole at the center of each dielectric resonator and a tuning screw inserted into the hole.
FIG. 15 is a perspective view of a dielectric resonator filter 400 according to an embodiment of the present application. The filter 400 includes four resonators 401-404 positioned in a straight line layout, which provides an 8-pole symmetric filter characteristic. The resonators 401-404 include dielectric rods 411-414, respectively. An input element 421 is disposed in the resonator 401 for inputting signals to the filter and an output element 422 is disposed in the resonator 404 for outputting signals from the filter. In the embodiment, a coupling element 431 is provided between the resonator 401 and the resonator 402, two coupling elements 432, 433 are provided between the resonator 402 and the resonator 403, and a coupling element 434 is provided between the resonator 403 and the resonator 404. Each of the dielectric rods includes one coupling screw hole for accommodating coupling screw and two tuning screw holes for accommodating tuning screws.
In order to suppress the spurious mode TM01, as shown in FIG. 15, four holes 441-444 are formed at a center of the dielectric rods 411-414 for accommodating tuning screws 451-454, respectively. By adjusting insertion of the central tuning screws to different depths for the four resonators, the lower TM01 spurious resonance frequency in each dielectric resonator will be different and will be spread in a broad frequency range so that very weak signal carried by TM01 mode can pass through the filter. The suppression effect by this method has been demonstrated in FIG. 16, where the spurious resonance has been suppressed to below 60 dB.
In an embodiment, the dimension of the resonator cavity can be chosen by trading off the spurious mode location (HEH11 as shown in FIG. 14b) and the Q value of the resonator. For example, as shown in FIGS. 2b and 2c, the side length L of the square cavity as well as the height h of the cavity can be chosen by trading off the spurious mode location and the Q value of the TM11 dual-mode dielectric resonator.
In a communication system, especially in a modern wireless base station system, integrated diplexer/multiplexers are wildly used due to the stringent footprint/space/mass requirement.
According to an embodiment, an integrated diplexer/multiplexer can be realized by using the proposed filter. FIG. 17 shows a diplexer including three 8-pole single filters 510, 520, 530. Each of the filters includes four dielectric resonators positioned in a straight line layout. The filter 530 has two ports: Ante and Tx2. The filters 510 and 520 form two channels of a diplexer with port Ant1 as the common port, ports Tx1 and Rx1 as the other two ports. Being realized by the proposed dual mode resonator, the structure of the diplexer/multiplexer is compact. Since all the tuning and coupling elements are easily accessed from the top surface, rather than from the side walls, the tuning and coupling of the diplexer/filter is also convenient. Such dual mode resonator configuration easily enables the integration of even more filters laid on the horizontal plane.
According to an embodiment, a method of manufacturing a dielectric resonator filter including at least one dielectric resonator is provided. As shown in FIG. 18, dimension parameters of the TM11 dual-mode dielectric rod and the metal housing of the filter are obtained based on required center frequency, bandwidth, isolation and return loss in step 601. In an embodiment, a filter circuit model can be built up by using EM simulation software, for example, HFSS, and the dimension parameters can be obtained according the circuit model and the tradeoff between filter volume, Q-factor, spurious mode frequencies. In step 602, the dielectric rod with holes, the screws, the metal housing and the top surface with apertures are formed according to the obtained dimension parameters. In step 603, the filter is assembled by disposing the dielectric rods into the metal housing and inserting the screws into the holes of the dielectric rods. The dielectric resonator filter supports dual TM11 degenerate modes, each of which forms an electric resonator, and an insertion depth of each of the screws is adjustable for adjusting resonance frequencies of the dual degenerate modes and coupling between the dual degenerate modes.
In an embodiment, an input/output connector is formed in the filter for input/output coupling of the dielectric resonator filter.
In an embodiment, a coupling element is formed between two adjacent dielectric resonators for coupling the two adjacent dielectric resonators.
In an embodiment, a spurious-suppressing hole is formed at the center of the dielectric rod.
This application presents a compact dielectric resonator filter/multiplexer using TM11 dual-mode dielectric resonators. The resonator is suitable for a planar coupling configuration and effective heat dissipation. High Q dielectric resonator filters with versatile coupling schemes can be achieved using the proposed dual mode resonators and coupling mechanism. The tuning screws inserted into the holes in dielectric resonators can effectively control the required coupling of the two degenerate modes and the frequency-offsets. The transmission responses of the filter/multiplexer are adjustable through the insertion depths of the screws and metal coupling loops.
The various embodiments described above can be combined to provide further embodiments. All of the commonly assigned US patent application publications, US patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, including but not limited to U.S. Provisional Patent Application No. 61/615,728, filed Mar. 26, 2012, are incorporated herein by reference, in their entirety.
While the present application has been illustrated by the above description and embodiments or implementations, it is not intended to restrict or in any way limit the scope of the appended claims hereto.
Patent Application
20130249651
