Patent Description:
Filters are known to provide attenuation of signals having frequencies outside of a particular frequency range and little attenuation to signals having frequencies within the particular range of interest. As is also known, these filters may be fabricated from ceramic materials having one or more resonators formed therein. A ceramic filter may be constructed to provide a lowpass filter, a bandpass filter, or a highpass filter, for example.

Dielectric filters typically employ quarter-wavelength type resonators with one end electrically open and the other end shorted to ground in combline like design. This design offers compact size and rugged construction in a slim, low-profile component. Moreover, this design offers transmission zeros between pairs of resonators and only requires a printed pattern on one surface of the filter block.

Nevertheless, conventional resonator in dielectric filter is usually designed in column shape, which is formed by filling up or plating preformed cavities in a dielectric block with metal materials. The size and weight of these kinds of conventional resonators are considerably large and heavy, which is not suitable for the application of <NUM> telecommunication systems that employs Massive MIMO requiring individual filters for each antenna unit.

In addition, conventional dielectric filter is usually manufactured by forming process, which is difficult for mass and customized production. Mechanical hole drilling is required in forming process to form resonant cavities, which is susceptible to the drilling process with low yield and poor uniformity. Also, secondary processing like manual tuning and calibration are also required after forming and drilling since it is difficult to control the accuracy of filling (or plating) process and drilling process. These disadvantages make conventional dielectric filter unsuitable for current <NUM> application.

There is still room for improvement when it comes to dielectric filter with multilayer resonator such as Document D1 (<CIT>) or Document D2 (<CIT>).

In order to solve the aforementioned disadvantages in prior art and develop a dielectric filter well suited for the <NUM> application nowadays, the present invention hereby provides a novel dielectric filter, featuring multiple metal layers forming in a dielectric block to constitute the columned resonators with excellent light-weight and miniaturization properties as well as improved yield and excellent uniformity.

The objective of present invention is to provide a dielectric filter with multilayer resonator, according to the present claims.

The accompanying drawings are included to provide a further understanding of the embodiments, and are incorporated in and constitute a part of this specification. The drawings illustrate some of the embodiments and, together with the description, serve to explain their principles. In the drawings:.

It should be noted that all the figures are diagrammatic. Relative dimensions and proportions of parts of the drawings have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. The same reference signs are generally used to refer to corresponding or similar features in modified and different embodiments.

In following detailed description of the present invention, reference is made to the accompanying drawings which form a part hereof and is shown by way of illustration and specific embodiments in which the invention may be practiced. These embodiments are described in sufficient details to enable those skilled in the art to practice the invention. Dimensions and proportions of certain parts of the drawings may have been shown exaggerated or reduced in size, for the sake of clarity and convenience in the drawings. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

As used in various embodiments of the present disclosure, the expressions "include", "may include" and other conjugates refer to the existence of a corresponding disclosed function, operation, or constituent element, and do not limit one or more additional functions, operations, or constituent elements. Further, as used in various embodiments of the present disclosure, the terms "include", "have", and their conjugates are intended merely to denote a certain feature, numeral, step, operation, element, component, or a combination thereof, and should not be construed to initially exclude the existence of or a possibility of addition of one or more other features, numerals, steps, operations, elements, components, or combinations thereof.

Spatially relative terms, such as "beneath," "below," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It should be readily understood that these meanings such as "on," "above," and "over" in the present disclosure should be interpreted in the broadest manner such that "on" not only means "directly on" something but also includes the meaning of "on" something with an intermediate feature or a layer therebetween, and that "above" or "over" not only means the meaning of "above" or "over" something but can also include the meaning it is "above" or "over" something with no intermediate feature or layer therebetween (i.e., directly on something).

While expressions including ordinal numbers, such as "first" and "second", as used in various embodiments of the present disclosure may modify various constituent elements, such constituent elements are not limited by the above expressions. For example, the above expressions do not limit the sequence and/or importance of the elements. The above expressions are used merely for the purpose of distinguishing an element from the other elements. For example, a first user device and a second user device indicate different user devices although both of them are user devices. For example, a first element may be termed a second element, and likewise a second element may also be termed a first element without departing from the scope of various embodiments of the present disclosure.

It should be noted that if it is described that an element is "coupled" or "connected" to another element, the first element may be directly coupled or connected to the second element, and a third element may be "coupled" or "connected" between the first and second elements. Conversely, when one component element is "directly coupled" or "directly connected" to another component element, it may be construed that a third component element does not exist between the first component element and the second component element.

Firstly, please refer collectively to <FIG>, which are the schematic isometric view, cross-sectional view in a first direction D1 and cross-sectional view in a second direction D2 of a combline filter respectively in accordance with the preferred embodiment of present invention. The filter <NUM> of present invention includes a dielectric block <NUM> as the main body. As shown in <FIG>, the dielectric block <NUM> is preferably a low-profile rectangular cuboid bounded by six quadrilateral faces and with its length, depth and height extending respectively in a third direction D3, the first direction D1 and the second direction D2, wherein the first, second and third directions D1, D2, D3 are preferably perpendicular to each other. The material of dielectric block <NUM> may be ceramic, such as BaSmTi, ZrTiSn or MgSi with loss tangent ranging from <NUM>-<NUM> to <NUM>-<NUM>. In comparison to common FR4 material used in PCB with loss tangent of <NUM>-<NUM>, these materials are more suitable for high-frequency and high-rejection bandpass filter required in the application of <NUM> telecommunication. It should be note that the present invention may also be implemented using PCB process.

Refer still to <FIG>. A series of multilayer resonators <NUM> are formed in the dielectric block <NUM>. In the present invention, the multilayer resonators <NUM> are preferably aligned and closely spaced in the third direction D3 in the dielectric block <NUM>. The multilayer resonator <NUM> may be a transverse electromagnetic resonator in a column shape extending in the first direction D1 into the dielectric block <NUM>. One end of the columned multilayer resonator <NUM> is electrically opened inside the dielectric block <NUM> and the other end of the columned multilayer resonator <NUM> is shorted to a ground electrode <NUM>. In the present invention, the ground electrode <NUM> may be a metallic shielding cladding or soldering on the outer surface of the dielectric block <NUM> to minimize the noise coupling and to achieve acceptable stopbands and satisfactory harmonic performance. The multilayer resonators <NUM> in the dielectric block <NUM> connect the ground electrode <NUM> at the surface of dielectric block <NUM> through its ground terminal 104c at rear end. The ground terminal 104c may be electrically connected with the ground electrode <NUM> through ground structures (not shown) like ground path or ground layer. Alternatively, in some embodiments, the ground terminal 104c of the multilayer resonator <NUM> may not extend outside of the dielectric block <NUM>. The material of ground electrode <NUM> may be the conductive material including but not limited to aluminum, steel, copper, silver and nickel, as well as metal alloys. During use, wireless/microwave signals enter the filter shielding and follow a signal pathway around/through the multilayer resonators <NUM>. Depending on the position and configuration of the resonators, the frequency response of the filter can be tailored to suit specific operational needs.

Refer still to <FIG>. In the preferred embodiment of present invention, the multilayer resonators <NUM> are capacitively coupled with each other in series through capacitors <NUM> set between the multilayer resonators <NUM>. Alternatively, in other embodiment, the multilayer resonators <NUM> may be directly connected with each other in series through the metal layers extending from and between the multilayer resonators <NUM>. More specifically, in the embodiment of present invention, each multilayer resonator <NUM> has a first signal terminal 104a and a second signal terminal 104b at two lateral ends respectively. The first signal terminal 104a of one multilayer resonator <NUM> and the second signal terminal 104b of an adjacent multilayer resonator <NUM> may be directly connected through a metal layer or capacitively coupled through capacitor or inductively coupled through inductor. The resonance characteristic of LC or RLC is provided between the first signal terminal 104a and the second signal terminal 104b. The bandwidth and response of the filter is determined by the amount of coupling of each multilayer resonator <NUM> to its immediate neighbor, which in turn is dependent on resonator size, resonator spacing, and ground plane separation. Furthermore, a first signal electrode <NUM> and a second signal electrode <NUM> are set respectively at opposite sides of the dielectric block <NUM> in the third direction D3. In the preferred embodiment of present invention, the first signal electrode <NUM> may be an input pad and the second signal electrode <NUM> may be an output pad to input and output the signals to be filtered and resonated by the filter <NUM>. Similarly, the first signal electrode <NUM> and the second signal electrode <NUM> may be directly connected or capacitively or inductively coupled to the first signal terminal 104a or second signal terminal 104b of the multilayer resonators <NUM> through metal layers or capacitors. In combline filter, the first signal (input) electrode <NUM> is coupled to the first signal terminal 104a of the first multilayer resonators <NUM> on one side of the dielectric block <NUM> and the second signal electrode <NUM> is coupled to the second signal terminal 104b of the last multilayer resonators <NUM> on the other side of the dielectric block <NUM> in the series. The first signal electrode <NUM> and the second signal electrode <NUM> may be further electrically connected to external PCB or devices to receive and transmit signals. Please note that the first signal electrode <NUM> and the second signal electrode <NUM> are not electrically connected with the ground terminal (shielding) <NUM> although they are all set on outer surfaces of the dielectric block <NUM>.

Please refer to <FIG>. In the embodiment of present invention, the ratio of a total height H of the multilayer resonator <NUM> in the second direction D2 and a spacing S between the multilayer resonator <NUM> and an outer surface of the dielectric block <NUM> (shielded by the ground electrode <NUM> like a ground structure) in the second direction D2 is preferred <NUM>:<NUM> to <NUM>:<NUM> (H:S), in order to achieve an optimal filtration efficiency. In addition, please refer to <FIG>, the length L of multilayer resonators <NUM> in the first direction D1 is preferably and nominally λ/<NUM> at the centre frequency, wherein λ is the wavelength of the signal.

Now, please refer to <FIG>, which is an enlarged cross-sectional view of the multilayer resonator <NUM> in the preferred embodiment of present invention. The multilayer resonator <NUM> of the present invention is particularly constituted by multiple metal layers <NUM>. As shown in the figure, the metal layers <NUM> preferably parallel and overlap each other in the second direction D2, which is perpendicular to the first direction D1 in which the multilayer resonator <NUM> extends. The metal layers <NUM> may have the same length in the first direction D1, however, their width in the third direction D3 may be different in order to render required cross-sectional shape for the multilayer resonator <NUM>. Take the circular cross-sectional shape in the figure for example, the metal layer <NUM> has a width different in the third direction D3 from the widths of adjacent metal layers. The percentage difference of lengths in the first direction D1 of adjacent metal layers <NUM> in each multilayer resonator <NUM> may be <NUM>%~<NUM>%, and the multilayer resonator <NUM> is preferably constituted by at least six metal layers <NUM> in order to provide good resonant efficiency. The first signal terminal 104a and the second signal terminal 104b of a multilayer resonator <NUM> may be two ends of a metal layer <NUM>, especially the metal layer <NUM> with max width in the third direction D3 in a multilayer resonator <NUM>.

In addition, as shown in <FIG>, a straight via <NUM> is formed extending in the second direction D2 from a topmost metal layer <NUM> to a bottommost metal layer <NUM> in each multilayer resonator <NUM>. The via <NUM> electrically connects every metal layers <NUM> in the multilayer resonator <NUM> so that these metal layers <NUM> may constitute and function in entirety like a normal cylindrical resonator. The via <NUM> is preferably formed in the middle of the multilayer resonator <NUM> in the width direction (third direction D3), that is, aligning with a vertical diameter of the circular multilayer resonator <NUM>. In some embodiments, a via <NUM> in a multilayer resonator <NUM> may be divided into several via sections (not shown) offset each other in the third direction D3 and connecting all of the metal layer <NUM> in the multilayer resonator <NUM> (i.e. the metal layers <NUM> are not connected by a single, straight via). The via sections connecting three adjacent metal layers may have overlapping portions in the second direction D2. Moreover, please refer to <FIG>, a multilayer resonator <NUM> may include a plurality of vias <NUM>, wherein these vias <NUM> are preferably aligned and spaced apart in the first (length) direction D1 to provide better resonant efficiency. Also, in order to improve manufacturing yield, these vias <NUM> are preferably set at a position at least half length of the multilayer resonator <NUM> in the first direction D1 away from the ground electrode <NUM> or ground terminal 104c (i.e. the ground-shorted end). In some embodiments, these vias <NUM> may be set along the whole length in the first direction D1 with the same spacing to achieve better characteristics. For the same reason, as shown in the figure, the capacitors <NUM> or metal layers coupling or connecting the first or second signal terminals 104a, 104b of the multilayer resonators <NUM> are preferably set at the open-circuited end of the multilayer structures <NUM>, and the via <NUM> may be set at a position on <NUM>%~<NUM>% width of the multilayer resonator <NUM> in the third direction D3, preferably the position on <NUM>% width (i.e. middle position).

Please refer back to <FIG>. In the embodiment of present invention, the capacitor <NUM> between multilayer resonators <NUM> may also be constituted by the metal layers <NUM>. As shown in the figure, the capacitor <NUM> between the two multilayer resonators <NUM> is constituted by three metal layers <NUM>, wherein some of these metal layers <NUM> may be a part of metal layers <NUM> extending from the multilayer resonators <NUM> (especially the metal layer for providing the first signal terminal 104a and the second signal terminal 104b). In other embodiment, the two multilayer resonators <NUM> may be directly connected through common metal layers with the first signal terminal 104a and the second signal terminal 104b rather than capacitively coupled by the capacitor <NUM>. In the present invention, the material of metal layers <NUM> may be the conductive material including but not limited to aluminum, steel, silver, copper and nickel, as well as metal alloys.

In addition, the cross-sectional shape of the multilayer resonators <NUM> is preferably but not limited to circular. For example, in other embodiments as shown in <FIG>, the cross-sectional shape of the multilayer resonator <NUM> is oval constituted by the metal layers <NUM> with different widths in the third direction D3. In fact, any regular shape such as rectangle or polygon in bilateral symmetry is well suited for the multilayer resonators <NUM> in the present invention.

In the present invention, the multilayer resonators <NUM> formed of multiple metal layers <NUM> in the dielectric block <NUM> may be realized by using PCB (printed circuit board) process or LTCC (low temperature co-fired ceramics) process. In comparison to conventional forming process that the resonators are formed by filling up or plating inner surface of the drilled resonant cavities in the dielectric block with metal materials, the components of resonators in the present invention, including metal layers <NUM> and vias <NUM>, may be formed and patterned layer by layer through image transfer and screen printing on multiple thin green tapes in LTCC process. The entire dielectric block <NUM> is formed by sintering laminated green tapes having patterns of the resonators formed therein. The advantage of this approach is that it can easily manufacture the resonators in complex and customized patterns or shapes with great accuracy. No secondary processing or machining like manual tuning and calibration are required after the resonators are formed. Furthermore, the concept of constituting a resonator through multiple metal layers makes it possible to reduce the weight and scale the size of whole dielectric filter, thereby making it well suited for the application of <NUM> telecommunication systems that employs Massive MIMO requiring individual filters for compact antenna units.

Next, please refer collectively to <FIG>, which are respectively the schematic isometric view, cross-sectional view in the first direction D1 and cross-sectional view in the second direction D2 of a combline filter in accordance with another embodiment of present invention. In this embodiment, coupling structures are added in the filter <NUM> to enhance or tuning the coupling degree between the multilayer resonators <NUM>. As shown in the figure, a coupling structure <NUM> is formed above (or below) every two of the multilayer resonators <NUM>, wherein each of the coupling structures <NUM> consists of a short metal bar 116a formed in an additional dielectric layer <NUM> on the dielectric block <NUM> and two coupling vias 116b connecting two end of the metal bar 116a and extending in the second direction D2 into the dielectric block <NUM> toward the corresponding two multilayer resonators <NUM>. Please refer to <FIG>. The dielectric layer <NUM> may be a part of the dielectric block <NUM>, with a ground layer <NUM> set therebetween to isolate the metal bar 116a and the dielectric block <NUM>. The material of dielectric layer <NUM> may be the same or different from the material of dielectric block <NUM>. Furthermore, the two coupling vias 116b of the coupling structure <NUM> may extend and pass in the second direction D2 through the holes on the ground layer <NUM> toward the multilayer resonators <NUM>. Preferably, the coupling via 116b is set right above or below the vias <NUM> that connects the metal layers in the multilayer resonator <NUM>, especially the via <NUM> closest to the open-circuited end of the multilayer resonator <NUM>.

In addition to the coupling structures <NUM>, please refer still to <FIG>, a coupling metal bar <NUM> may be formed below (or above) the multilayer resonators <NUM> in the dielectric block <NUM>. Unlike the coupling structure <NUM> that couples only two multilayer resonators <NUM>, the coupling metal bar <NUM> extends in the third direction D3 over at least two or all multilayer resonators <NUM> and couples them collectively. Preferably, the coupling metal bar <NUM> is set behind or not overlapping the multilayer resonators <NUM> in the first direction D1 or in the second direction D2 as shown in <FIG>.

Lastly, please refer to <FIG>, which is a frequency response curves for the combline dielectric filter <NUM> of the present invention. A frequency response is provided having frequency measured in gigahertz (GHz) along the x-axis between <NUM> and <NUM>. Insertion/Return loss, measured in dB, is provided along the y-axis and ranges between <NUM> and -<NUM> along the area of interest. As shown in the figure, the graph reveals that a viable filter response for a high rejection dielectric filter may be achieved in the frequency range of interest. At <NUM> frequencies, for example, a bandwidth of about <NUM> is realized. The graph also shows reasonable insertion loss values and good stopbands.

According to the embodiments described above, the present invention provides a novel combline dielectric filter with enhanced high rejection and excellent selectivity in the filter's frequency response. The dielectric filter may offer greater design freedom and options to produce custom filters with unique specification requirements, and the accuracy of the dielectric filter may be well-controlled to provide improved yield and excellent uniformity since it is not formed by conventional mechanical drilling method. The present invention is particularly well suited for <NUM> wireless telecommunications field involving equipment that operates at higher and higher frequencies and which requires filters that are smaller in volume, contain less material, have smaller footprints, and have a lower profile on the circuit board, while still providing high performance and meeting increasingly strict specifications.

Claim 1:
A dielectric filter (<NUM>) comprising
a dielectric block (<NUM>);
more than one multilayer resonator (<NUM>) formed in said dielectric block (<NUM>), wherein each said multilayer resonator (<NUM>) is in a column shape extending in a first direction (D1) into said dielectric block (<NUM>) and is formed of multiple metal layers (<NUM>) paralleling and overlapping each other in a second direction (D2) perpendicular to said first direction (D1), and each said multilayer resonator (<NUM>) is provided with a first signal terminal (104a), a second signal terminal (104b) and a ground terminal (104c), wherein said first signal terminal (104a) of one said multilayer resonator (<NUM>) and said second signal terminal (104b) of one adjacent said multilayer resonator (<NUM>) are directly connected, inductively coupled or capacitively coupled;
a plurality of vias (<NUM>) extending in said second direction (D2) and connecting said metal layers (<NUM>) in each said multilayer resonator (<NUM>); and
a ground electrode (<NUM>), wherein said ground terminal (104c) of each said multilayer resonator (<NUM>) extends in the same said first direction (D1) to a side of said dielectric block (<NUM>) and connected with said ground electrode (<NUM>);
wherein a third direction (D3) is perpendicular to said first direction (D1) and said second direction (D2), and widths in said third direction (D3) of said metal layers (<NUM>) at two outermost sides in said second direction (D2) of said multiple metal layers (<NUM>) are smaller than widths in said third direction (D3) of other said metal layers (<NUM>).