Patent Application
20160072169
1. Field
The current disclosure relates to cavity-resonator filters, and more specifically, but not exclusively, to cavity-resonator filters with pedestal-based dielectric resonators.
2. Description of the Related Art
Conventional dielectric-loaded cavity resonators are devices that include one dielectric posts inside one metallic chamber, while conventional dielectric-loaded cavity filters are devices that include one or more dielectric-loaded resonators interconnected in metallic chambers. Dielectric-loaded cavity resonators are used as radio-frequency (RF) filters thanks to their high Q factors. The Q, or quality, factor is a parameter that indicates a resonator's level of under-damping, where a higher Q factor indicates that resonant oscillations in the resonator die out more slowly.
Conventional dielectric-loaded cavity resonators use cylindrical dielectric posts. Individual dielectric-loaded resonators may couple to other dielectric-loaded resonators by capacitive coupling or inductive coupling. Couplings between resonators of a filter correspond to zeros and poles in the frequency-response characteristics of the filter. The numbers of poles in the frequency-response characteristics of a resonant filter may be increased by increasing the number of resonators. The number of zeros in the frequency-response characteristics of a resonant filter may be increased by increasing the number of cross coupled dielectric-loaded resonators as opposed to serial coupled resonators. Generally, the greater the number of zeros and poles in the frequency-response characteristics, the more flexibly the frequency-response curve can be shaped. More zeros can help define a sharper drop-off from the pass-band and, consequently, provide a higher Q factor.
Capacitive coupling between dielectric-loaded resonators is conventionally accomplished using a conductor between the coupled posts. Inductive coupling is conventionally accomplished using openings between the chambers of the coupled resonators. These openings are sometimes referred to as irises.
Some of the walls separating adjoining resonant cavities have openings between them, such as opening 104(1) between cavities 103(1) and 103(2). As noted above, opening 104(1) between cavities 103(1) and 103(2) allows for inductive coupling between the corresponding dielectric resonators 102(1) and 102(2).
Capacitive coupling between pairs of dielectric resonators may be accomplished using coupling conductive wires, such as conductor 106 between dielectric resonators 102(1) and 102(4). Note that coupling conductor 106 comes close to, but does not contact, dielectric resonators 102(1) and 102(4). The incorporation of conductor 106 into filter 100 increases the costs of production for filter 100 and restricts the filter topology such that length of 106 is short.
One embodiment of the disclosure can be a cavity-resonator filter comprising (1) a first set of one or more pedestal-based dielectric resonators, each mounted in a corresponding resonant cavity and oriented in a first direction and (2) a second set of one or more pedestal-based dielectric resonators, each mounted in corresponding resonant cavity and oriented in a second direction opposite to the first direction. Each dielectric resonator of the first and second sets comprises only one post connected to only one pedestal.
Another embodiment of the disclosure can be a method for filtering a signal to generate a filtered signal, the method comprising applying the signal to a filter comprising (1) a first set of one or more pedestal-based dielectric resonators mounted in corresponding resonant cavities and oriented in a first direction and (2) a second set of one or more pedestal-based dielectric resonators mounted in corresponding resonant cavities and oriented in a second direction opposite to the first direction. Each dielectric resonator of the first and second sets comprises only one post connected to only one pedestal. The method further comprises receiving the filtered signal from the filter.
Other embodiments of the invention will become apparent. In the accompanying drawings, like reference numerals identify similar or identical elements.
Dielectric resonator 201 may be made of a suitable ceramic material having a dielectric constant greater than but not limited to 10. In one implementation, the ceramic material has a dielectric constant of 43. Resonant cavity 202 may be made of a suitable metal, for example, copper or aluminum. The bottom of post 203 is placed on the thin layer of insulator supports (not shown) which are in contact with the inner surface of the bottom side 206 of cavity 202 and form gap 205 between the distal end of post 203 and the inner surface of bottom side 206 of cavity 202. In one implementation, the thin insulator has a thickness of 200 μm. In alternative embodiments, the insulator supports can be omitted and the bottom of post 203 can be in direct contact with the inner surface of the bottom side 206 of cavity 202. The top of pedestal 204 is separated from the inner surface of the top side 207 of cavity 202 by air gap 208. In one implementation, air gap 208 is 0.2 mm and is maintained by a plurality of 0.2 mm thick insulating pads (not shown) that may be made of a suitable insulating material, such as, for example, polytetrafluoroethylene (PTFE) or an Alumina-based ceramic or thin film material, and located between the top of pedestal 204 and the top side 207 of cavity 202. In one implementation, the inner dimensions of cavity 202 are 20 mm (long)×20 mm (wide)×15 mm (high). Note that the dominant mode of the fundamental resonance of the dielectric-loaded resonator described above is the TM (transversal magnetic) mode.
Dielectric resonator 301 may be made of a suitable ceramic material, as described above. Cavity 302 may be substantially similar to cavity 202 of
Particular novel configurations of pluralities of single-pedestal dielectric-loaded cavity resonators such as resonator 200 of
Specifically, (i) exemplary curve 501 plots the power loss, in decibels shown on the right vertical axis, from an input signal at source port 404, at the frequencies shown on the horizontal axis, as measured at load port 405 and (ii) exemplary curve 502 plots the phase shift, in degrees shown on the left vertical axis, from an input signal at source port 404, at the frequencies shown on the horizontal axis, as measured at load port 405. Note that additional harmonic modes occur at higher frequencies. Frequency-response curve 501 shows the forward-gain coefficient—sometimes referred to as S21—for filter 400 over a range of frequencies. As can be seen, the center frequency for filter 400 is approximately 2.6 GHz, and there are two transmission zeros at approximately 2.44 GHz and 2.77 GHz.
The distal ends of the posts of the dielectric resonators are separated by a thin insulator (not shown) from the near walls of the corresponding resonant chambers, and the distal ends of the pedestals of the dielectric resonators are similarly separated by thin insulators (not shown) from the opposing walls, as discussed above. In other words, (i) the bottoms of the posts of dielectric resonators 601(2)-601(4) are separated by thin insulators from the bottom sides of resonant cavities 602(2)-602(4), (ii) the top of the post of dielectric resonator 601(1) is separated by a thin insulator from the top side of resonant cavity 602(1), (iii) the tops of the pedestals of dielectric resonators 601(2)-601(4) are separated by an air gap from the top sides of resonant cavities 602(2)-602(4), and (iv) the bottom of the pedestal of dielectric resonator 601(1) is separated by an air gap from the bottom side of resonant cavity 602(1). This configuration of the flipped pedestal-based dielectric resonators 601(1)-601(4) in filter 600 allows for capacitive coupling between pairs of dielectric resonators 601(1)-601(4) without the use of conductive wires.
Filter 600 further comprises coaxial source port 604—whose center line couples to dielectric resonator 601(1)—and coaxial load port 605—whose center line couples to dielectric resonator 601(4). The center lines of the source and load ports 604 and 605 are bent—or L-shaped —so that their respective terminal lengths 604a and 605a run parallel to the posts of the corresponding dielectric resonators 601(1)-601(4) and their respective ends 604b and 605b point away from the corresponding pedestal. This bending of the center lines helps enhance coupling between the center line and the corresponding dielectric resonator. Note that terminal lengths 604a and 605a come close to, but do not contact, the posts of dielectric resonators 601(1) and 601(4).
Similarly to the dielectric resonators 601(1)-601(4) of
Filter 700 further includes coaxial source port 704 and coaxial load port 705. Similarly to the center lines of the ports of filter 600 described above, the center lines of the ports are bent so that their terminal lengths run parallel to the posts of the corresponding dielectric resonators 701(1)-701(4) and their ends point away from the corresponding pedestal. Dielectric resonator 701(1) forms a first set of dielectric resonators oriented in one direction and dielectric resonators 701(2)-701(4) form a second set of dielectric resonators oriented in the opposite direction. As can be seen, in this embodiment, (i) source port 704 couples with a resonator of the first set and (ii) load port 705 couples with a resonator of the second set of the filter 700. In alternative embodiments, both source and load ports might couple to two dielectric resonators of the same set—in other words, to two dielectric resonators oriented in the same direction.
Using the same exemplary dimensions for dielectric resonators 701(1)-701(4) and cavities 702(1)-702(4) as for resonators 601(1)-601(4) and cavities 602(1)-602(4) of
Embodiments of the disclosure have been described where the pedestal is separated from the top side or bottom side of the corresponding resonant cavity by an air gap. However, the invention is not so limited. In some alternative embodiments, the distal end of the pedestal—i.e., the pedestal end away from the post—is in contact with the top side or bottom side of the corresponding resonant cavity. In some alternative embodiments, the distal ends of both the pedestal and the post are separated from the nearby sides of the corresponding resonant cavity by respective air gaps.
Embodiments of the disclosure have been described where the post and the corresponding pedestal of a dielectric resonator are solid. However, the invention is not so limited. In some alternative embodiments, the post and/or pedestal have hollowed-out centers. The hollows may be cylindrical or of other shapes.
Embodiments of the disclosure have been described where the pedestals of the dielectric resonators are either circular or square and extend to the side walls of the corresponding cavity. However, the invention is not so limited. In some alternative embodiments, the pedestals have other shapes and/or are of a shape and/or size that does not contact the side walls of the corresponding cavity. In some embodiments, the area of the cross-section of the pedestal is greater than the area of the cross-section of the post so that the pedestal extends beyond the post. In some embodiments, the area of the cross-section of the pedestal that extends beyond the post is at least as great as the area of the cross-section of the post. In other words, in these embodiments, if the cross-sectional area of the post is x, then the cross-sectional area of the pedestal is at least 2x and the area of the pedestal overhang is at least x.
Embodiments of the disclosure have been described where the plurality of dielectric resonators and corresponding resonator cavities are arranged either in-line or in a rectangular grid. However, the invention is not so limited. In alternative embodiments, the dielectric resonators are arranged in non-rectangular-grid patterns.
Embodiments of the disclosure have been described where the filter comprises two or four dielectric resonators and corresponding resonant cavities. However, the invention is not so limited. In alternative embodiments, filters have different numbers of dielectric resonators and corresponding resonant cavities.
Embodiments of the disclosure have been described where only one dielectric resonator has an orientation opposite to the orientation of the other dielectric resonators. However, the invention is not so limited. In alternative embodiments, a first plurality of dielectric resonators is oriented in a first direction and a second plurality of dielectric resonators is oriented in a second direction that is the reverse of the first direction.
Embodiments of the disclosure have been described where coaxial ports are used to feed the dielectric and cavity resonators. However, the invention is not so limited. In some alternative embodiments, other feed means—such as, for example, micro-strip lines—are used to feed the resonators.
Embodiments of the disclosure have been described where all of the pedestal-based dielectric resonators of a filter are substantially identical. However, the invention is not so limited. In some alternative embodiments, one or more of the dielectric resonators of a filter are different from other dielectric resonators of the filter. For example, in some embodiments, a filter comprises some resonators with a cylindrical pedestal and some resonators with a rectangular-prism pedestal.
Embodiments of the disclosure have been described where the separation—via air gap or thin insulator—between parts of a dielectric resonator and a near wall is 0.2 mm (or 200 m). In some alternative embodiments, the separation may as narrow as 50 μm or as wide as 300 μm.
In some embodiments of the disclosure, the Q factor associated with the ceramic material of the dielectric resonator is greater than 1000.
Signals and corresponding nodes or ports may be referred to by the same name and are interchangeable for purposes here.
It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of this invention may be made by those skilled in the art without departing from the scope of the invention as expressed in the following claims.
Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. The same applies to the term “implementation.”
Unless explicitly stated otherwise, each numerical value and range should be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range. As used in this application, unless otherwise explicitly indicated, the term “connected” is intended to cover both direct and indirect connections between elements.
For purposes of this description, the terms “couple,” “coupling,” “coupled,” “connect,” “connecting,” or “connected” refer to any manner known in the art or later developed in which energy is allowed to be transferred between two or more elements, and the interposition of one or more additional elements is contemplated, although not required. The terms “directly coupled,” “directly connected,” etc., imply that the connected elements are either contiguous or connected via a conductor for the transferred energy.
The use of figure numbers and/or figure reference labels in the claims is intended to identify one or more possible embodiments of the claimed subject matter in order to facilitate the interpretation of the claims. Such use is not to be construed as limiting the scope of those claims to the embodiments shown in the corresponding figures.
The embodiments covered by the claims in this application are limited to embodiments that (1) are enabled by this specification and (2) correspond to statutory subject matter. Non-enabled embodiments and embodiments that correspond to non-statutory subject matter are explicitly disclaimed even if they fall within the scope of the claims.
Although the steps in the following method claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those steps, those steps are not necessarily intended to be limited to being implemented in that particular sequence.
