Distribution element high-frequency filter

Abstract

A distribution element RF filter comprises one or more fully grounded half-wave resonators positioned between a first and a second resonator, which are electrically coupled to corresponding input / output (I / O) interfaces near corresponding ends of a dielectric substrate. Each of the one or more half-wave resonators includes a U-shaped or omega-shaped resonator section located between a first and a second end section, which are electrically connected to a base plate on a common side of the substrate. Each resonator has an electrical length that is nominally equal to half a wavelength of a center frequency of the filter. The filter may optionally include a conductive cover over the resonators.

Description

AREA OF REVELATION

[0001] The present disclosure relates generally to distributed element RF filters and in particular to those comprising grounded half-wave resonators. BACKGROUND

[0002] Distributed element RF filters generally comprise thick- or thin-film resonators and other conductive elements deposited on a dielectric substrate. Such filters are typically integrated with a microstrip line or other impedance-controlled transmission line on a printed circuit board (PCB) and are frequently used at or near the front end of communication and radar systems, where insertion loss, frequency selectivity, and power handling are of paramount importance. One such distributed element RF filter is a quarter-wave bandpass filter, which includes partially grounded resonators with one end grounded (short-circuited) and the other end ungrounded (open). However, quarter-wave resonators tend to result in less than desirable insertion loss, stopband rejection, and deviation from a desired flat and low-loss passband.Therefore, there is a desire to provide improved distribution element RF filters that, among other things, have lower insertion loss and improved frequency selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The objectives, features, and advantages of this disclosure are explained in more detail below with reference to the detailed description and the accompanying claims in conjunction with the accompanying drawings. The drawings show only representative embodiments and implementations and do not limit the application of the teachings of the disclosure, the scope of which is defined by the accompanying claims. Fig. Figure 1 is a perspective view of a representative distributed element RF filter. Fig. Figure 2 is a top view of the RF filter. Fig. 1 without cover. Fig. Figure 3 is a top view of a distributed element RF filter that includes an alternative resonator configuration. Fig. Figure 4 is a top view of a distributed element RF filter that includes another resonator configuration. Fig. Figure 5 is a top view of a distributed element RF filter that includes another resonator configuration. Fig. Figure 6 is a top view of a distributed element RF filter that includes an even further resonator configuration. Fig. Figure 7 is a top view of a distributed element RF filter that includes another resonator configuration. Fig. Figure 8 is a top view of a distributed element RF filter, which includes another alternative resonator configuration. Fig. Figure 9 is a top view of the grounding plate of the RF filter. Fig. 1. Fig. Figure 10 is a side view of a representative distribution element RF filter. Fig. Figure 11 is an end view of a distribution element RF filter that includes a cover. Fig. Figure 12 shows comparative simulated passband diagrams for a prior art bandpass filter having partially grounded quarter-wave resonators and a bandpass filter having fully grounded half-wave resonators according to the present disclosure.

[0004] Those skilled in the art will recognize that the drawings are presented for the sake of simplicity and clarity and may therefore not be to scale and may not include known features, that the sequence of actions or steps may differ from the sequence described, that some or all of these actions or steps may be carried out simultaneously unless otherwise stated, and that the terms and expressions used herein have meanings known to those skilled in the art unless a different meaning is expressly assigned to them. DETAILED DESCRIPTION

[0005] The disclosure relates generally to high frequency (HF), including microwave filters, and in particular to distributed element HF filters comprising grounded half-wave resonators on a dielectric substrate that can be mounted on a printed circuit board (PCB) or other host device or system. Such filters can be configured as microstrip, stripline, or other impedance-controlled transmission lines. Representative distributed element HF filters are further described herein. In this specification, HF also includes microwave frequencies.

[0006] The resonators and other conductors of distribution element RF filters can be deposited onto the substrate as thick or thin films using known fabrication methods. Thick-film filter elements typically have a thickness in the range of 0.5 mils to 2.0 mils and can be formed, for example, by screen printing a metal paste onto the substrate. Thin-film deposits can be structured in various ways and deposited onto the substrate by chemical vapor deposition, electron beam deposition, or sputtering, among other methods. Thin-film filters typically have a thickness of about two skin depths. A "skin depth" is the depth at which the current density is approximately 1 / e of the current density at the surface of the conductive film. A thickness of less than two skin depths can adversely affect insertion loss. A thickness of 3 to 5 skin depths is typical.A greater thickness may offer no significant advantage and can impair the accuracy of the metal deposition. In a 10 GHz filter with a conductive film (e.g., copper, silver, gold), four skin depths correspond to approximately 0.10 mil. Alternatively, the resonators can be formed by laser or chemical etching of a pattern projected onto the substrate. The resonators can also be formed from a rolled or electrolytically bonded conductive film adhered to a printed circuit board or other substrate.

[0007] In one embodiment, a distributed-element RF bandpass filter comprises a dielectric substrate between a grounding plate on one surface of the substrate and a plurality of resonators on an opposite surface of the substrate. One or more intermediate resonators may be arranged between first and second resonators, which are electrically coupled to corresponding input / output (I / O) interfaces near corresponding ends of the substrate. In the bandpass filter, each of the one or more intermediate resonators may have an electrical length that is nominally equal to half a wavelength of a center frequency of the bandpass filter.

[0008] The one or more intermediate resonators each comprise a resonator section between a first and a second resonator end section, which are electrically connected to the grounding plate via one or more conductors near a common side of the substrate, each of the one or more intermediate resonators at least partially surrounding a corresponding section of the surface of the substrate on which the resonator is located.

[0009] Dielectrics suitable for the RF filters disclosed herein generally exhibit a relatively high quality factor (Q-factor) and a stable temperature coefficient. One representative dielectric has a Q-factor greater than 400. A representative dielectric is a high-purity aluminum oxide ceramic (also known as "aluminum oxide"), which can exhibit a Q-factor of up to 5000 and a relative permittivity of about 10. Other known and future ceramics, as well as other dielectric materials, can also be used for the RF filters described herein.

[0010] Fig. Figure 1 shows a representative distribution element RF filter 100 configured as a microstrip transmission line, comprising a dielectric substrate 200 between a plurality of resonators on one side and a grounding plate on the opposite side. Fig. Figures 2-8 best show the resonators located on a top surface 202 of the substrate opposite a bottom surface 204, on which the grounding plate 206 is located (shown in Fig. 9-11). Adjacent resonators are separated from each other by a gap or space on the dielectric. In the Fig. In 2-8, a first resonator 208 is electrically coupled to an I / O interface 209 near a first end of the substrate, and a second resonator 210 is electrically coupled to an I / O interface 212 near a second end of the substrate. One or more fully grounded half-wave intermediate resonators are located between the first and second resonators 208 and 210, which are electrically coupled to the I / O interfaces. In other implementations, the filter can be configured as a stripline, with the resonators stacked between an upper and a lower grounding plate, which are interconnected by conductive vias. Fig. 2-8, for example, the filter can be configured as a stripline by adding a second dielectric substrate and a second grounding plate to the resonators.

[0011] The electromagnetic coupling between and below the resonators is a function of the dielectric gap between the resonators. Embodiments incorporating a plurality of intermediate resonators can reduce reflections due to impedance mismatches by providing a relatively large dielectric gap between one or more intermediate resonators and a relatively small dielectric gap between the outermost intermediate resonators and the resonators coupled to the I / O interfaces (e.g., 208 and 210). The filter order is related to the number of resonators. Fig. This illustrates a third-order bandpass filter, which comprises three resonators. Higher-order filters can be achieved by adding more resonators.

[0012] In one implementation, the distributed RF bandpass filter is a thin-film multipolar filter with a passband between 1 GHz and 60 GHz, and one or more intermediate resonators have an unloaded Q factor of more than 400.

[0013] In the Fig. 2-8 Each of the one or more intermediate resonators generally comprises a resonator section 214 between a first and a second end section 216 and 218, which are connected to the grounding plate via one or more conductors located near a common (i.e., the same) side of the substrate. In this configuration, each resonator is fully grounded and at least partially surrounds a section 220 of the substrate surface on which the resonator is located. The resonator section 214 may, among other configurations, have a U-shape or an omega-shaped form, as shown in the Fig. 2 or 3 shown.

[0014] In the Fig. 2-8 Each of the first and second resonators 208 and 210, which are coupled to the corresponding I / O interfaces, comprises a resonator section between the first and second end sections, which are connected to the grounding plate by a conductor on one side of the substrate, as described herein. In this configuration, the first and second resonators and the one or more intermediate resonators of the RF filter have the same shape. Alternatively, the first and second resonators may have a different configuration or shape than the one or more intermediate resonators. In general, the resonators may be arranged symmetrically on the surface 202 of the substrate around a reference point (e.g., one in Fig. The resonators are arranged at the midpoint 201 shown in Figure 1 between the I / O interfaces 209 and 212, with the resonators on one side of the reference point being a mirror image of the resonators on the other side of the reference point. The symmetrical configuration of the resonators can improve filter performance.

[0015] The insertion loss can be reduced if the resonators are directly coupled to the grounding plate by one or more conductors, rather than by capacitive coupling. The one or more conductors electrically connecting the first and second end sections of the resonators to the grounding plate can form a conductive wall near a common side of the substrate. Fig. In 2-8, a first conductive wall 222 is arranged on a first outer wall of the substrate, and a second conductive wall 224 is arranged on a second outer wall opposite the first outer wall of the substrate. In the Fig. 2-3 and 6, the conductive wall 222 extends between the grounding plate and the first and second end sections 216 and 218 of each resonator. In the Fig. 4-5 The first conductive side wall 222 connects the end sections 216 and 218 of the intermediate resonator to the grounding plate, and the second conductive side wall 224 electrically connects the end sections of the first and second resonators, which are coupled to the I / O interfaces, to the grounding plate. In the Fig. 7-8 comprise the one or more conductors comprising a series of discrete vias 226 extending through the substrate adjacent to the first outer sidewall. The discrete vias electrically connect the first and second end sections 216 and 218 of the resonators to the grounding plate on the opposite surface of the substrate. The conductive sidewalls or conductive vias can comprise thick or thin films deposited on selected surfaces (e.g., outer walls or vias) of the dielectric substrate.

[0016] The electrical length of a resonator generally depends on the physical length of the resonator and the wavelength of the signal at a given frequency or frequency band. In one implementation, at least one or more intermediate resonators have an electrical length nominally equal to half a wavelength of the center frequency of the bandpass filter, as described herein. The first and second resonators may also have an electrical length nominally equal to half the wavelength of the center frequency. The term "nominal" means that the electrical length of the resonator can be up to 8% more or less than half the wavelength of the center frequency of the bandpass filter. The resonators connected to the I / O interfaces may also have an electrical length nominally equal to half the wavelength of the center frequency.

[0017] In one implementation, all resonators have the same electrical length. In other implementations, the resonators have different electrical lengths. For example, one or more intermediate resonators may have a common electrical length that differs from the electrical lengths of the first and second resonators. The electrical length of the first and second resonators, which are connected to the I / O interfaces, may be greater than the electrical length of one or more intermediate resonators to compensate for, among other things, the electrical load from the I / O interfaces and external devices. Fig. In Figures 6-8, the first and second resonators coupled to the I / O interfaces have a common length that is longer than that of one or more intermediate resonators. Increasing the width of the resonators connected to the I / O interfaces relative to the width of one or more intermediate resonators can also compensate for the electrical load. For example, the first and second resonators can have a length-to-width ratio that is smaller than the length-to-width ratio of one or more intermediate resonators. In one implementation, one or more intermediate resonators have a length-to-width ratio of no more than 10.

[0018] In the Fig. In sections 2-8, the I / O interfaces are directly electrically connected to the resonators via corresponding conductive tracks 211 and 213, respectively. Alternatively, the I / O interfaces can be coupled to the resonators by one or more capacitive intermediate elements. The term "coupled" as used here means capacitive coupling or direct electrical connection (i.e., non-capacitive coupling) through a conductive track. The I / O interfaces each generally comprise a corresponding castel that extends through the substrate 200 between the surfaces on which the resonators and the base plate are located. Fig. Figures 2-9 show a first and a second castelation 209 and 212 formed at corresponding end walls of the substrate 200. Alternatively, the castelations can be configured as vias located within the end walls. Each castelation comprises a flange section on each of the opposing surfaces of the substrate. Fig. 2-8 are the flange sections on surface 202 connected to corresponding conductive traces, which are connected to a corresponding resonator. In Fig. In Figure 9, the flange sections 227 and 229 of the castelations are separated from the grounding plate 206 by corresponding gaps 228 and 230, respectively. The grounding plate 206 and the flange sections of the castelations can be electrically connected to appropriate conductors of a host device (e.g., contacts on a printed circuit board) by surface mounting the RF device in a backflow, wave soldering, or other assembly process. In other implementations, the I / O interfaces can alternatively be located on one side of the substrate or on the same surface as the resonators and electrically connected to a host circuit by wire bonding or another conductor connection technology. In RF and microwave filters, the characteristic impedance at the I / O interface is typically 50 ohms. However, in other filters, the impedance at the I / O interface may differ from 50 ohms depending on the application.

[0019] In some embodiments, a conductive cover is optionally placed over the resonators on the dielectric substrate, effectively creating a waveguide. In some embodiments, the conductive cover can improve the filter performance. Fig. 10-11 The filter includes a cover 250 that covers part of the resonators on the substrate 200. The cover comprises metal or another conductive material with a top wall 252 and opposing side walls 254 and 256, which are electrically connected to the grounding plate via the conductive side walls. Fig. 10. The side walls of the cover are connected to the corresponding conductive side wall of the substrate. The ends of the cover can remain open, allowing passage underneath.

[0020] Fig. Figure 12 shows a simulated passband diagram 300 for a prior art 4-pole distributed element RF bandpass filter having quarter-wave resonators, and a simulated passband diagram 310 for a representative 4-pole distributed element RF bandpass filter having half-wave resonators, as described in Fig. 2 are shown and described here. Both filters comprise a 0.02-inch thick ceramic substrate with a dielectric constant of approximately 25. Both filters include a 0.1 mil thin-film metallization layer. The resonators of the quarter-wave filter are connected to the base plate via conductive vias. The resonators of the half-wave filter are connected via a metallized side wall of the substrate shown in Figure 2. Fig.The type shown is connected to the base plate. The half-wave filter has a higher Q-factor than the quarter-wave filter, resulting in an insertion loss of approximately 1.7 dB for the half-wave filter compared to an insertion loss of approximately 2.1 dB for the quarter-wave filter according to the prior art.

[0021] In one embodiment, a distribution element RF filter (RF filter) comprises a ceramic substrate with a grounding plate on a first surface of the substrate and a first and a second resonator on a second surface opposite the first surface of the substrate. The first resonator is electrically connected to a first input / output interface (I / O interface) near a first end of the substrate, and a second resonator on the second surface of the substrate is electrically connected to a second I / O interface near a second end opposite the first end of the substrate. One or more intermediate resonators on the second surface of the substrate are located between the first and second resonators. Each of the first, second, and one or more intermediate resonators has an electrical length that is nominally half a wavelength of a center frequency of the filter.Each of the first, second and one or more intermediate resonators comprises a resonator section between first and second resonator end sections, which are electrically connected to the grounding plate by a conductive wall near a common side of the substrate, each resonator at least partially surrounding a section of the surface of the substrate on which the resonator is located.

[0022] Each resonator section can comprise a U-shaped or an omega-shaped resonator section. The first, second, and one or more intermediate resonators are all electrically connected to the grounding plate through a common conductive wall, configured as a multitude of vias extending through the substrate or a metallized sidewall of the substrate.

[0023] In another implementation, a distribution element RF filter comprises a dielectric substrate with a grounding plate located on one surface of the substrate, and a first and a second resonator located on a surface of the substrate opposite the grounding plate. The first and second resonators are each electrically coupled to a corresponding I / O interface near a corresponding end of the substrate. One or more U-shaped or omega-shaped resonators are located on the surface of the substrate opposite the grounding plate and between the first and second resonators.Each U-shaped or omega-shaped resonator comprises a first and a second resonator end section electrically connected to the base plate by one or more conductors near a common side of the substrate, each resonator having an electrical length nominally equal to half a wavelength of a center frequency of the filter.

[0024] A distribution element RF filter comprises a dielectric substrate between a grounding plate on one surface of the substrate and a plurality of resonators on an opposite surface of the substrate. The plurality of resonators includes a first and a second resonator, electrically coupled to a corresponding input / output (I / O) interface near a corresponding end of the substrate, and one or more intermediate resonators located between the first and second resonators. Each of the one or more intermediate resonators comprises a resonator section between a first and a second end section, electrically connected to the grounding plate by one or more conductors near a common side of the substrate.

[0025] In the various distributed-element RF filter implementations described here, the first and second resonators can have the same common electrical length, and one or more intermediate resonators can also have a common electrical length. The electrical length of the first and second resonators can be greater than the electrical length of one or more intermediate resonators. Furthermore, the first and second resonators can have a length-to-width ratio that is smaller than the length-to-width ratio of one or more intermediate resonators.

[0026] The various distribution element RF filters described here may optionally include a conductive cover that is attached to the substrate and electrically connected to the grounding plate, with the conductive cover being arranged over a surface of the substrate on which the resonators are located.

[0027] Each of the distribution element RF filters described here can be a thin-film multipolar filter with a passband between 1 GHz and 60 GHz, and one or more intermediate resonators exhibit, among other things, an unloaded quality factor (Q) of more than 400, as described here.

[0028] While the disclosure and the currently considered best embodiment have been described in a manner that establishes ownership and enables skilled persons to manufacture and use them, it is understood and appreciated that there are many equivalents to the representative embodiments described herein and that countless modifications and variations can be made to them without departing from the scope and spirit of the invention, which is limited not by the described embodiments but by the attached claims and their equivalents.

Claims

[1] Distribution element high-frequency (HF) filter, comprising: a ceramic substrate that has a grounding plate on a first surface of the substrate; a first resonator on a second surface of the substrate opposite the first surface, wherein the first resonator is electrically connected to a first input / output interface (I / O interface) near a first end of the substrate; a second resonator on the second surface of the substrate, wherein the second resonator is electrically connected to a second I / O interface near a second end of the substrate opposite the first end; one or more intermediate resonators on the second surface of the substrate, wherein the one or more intermediate resonators are located between the first and the second resonator, wherein each of the first, second and one or more intermediate resonators has an electrical length that nominally corresponds to half a wavelength of a center frequency of the filter, wherein each of the first, second and one or more intermediate resonators comprises a resonator section between first and second resonator end sections, which are electrically connected to the grounding plate by a conductive wall near a common side of the substrate, wherein each resonator at least partially surrounds a section of the surface of the substrate on which the resonator is located. [2] Distributed element RF filter according to claim 1, wherein each resonator section comprises a U-shaped resonator section. [3] Distributed element RF filter according to claim 1, wherein each resonator section comprises an omega-shaped resonator section. [4] Distribution element RF filter according to claim 1, wherein the first, the second and one or more intermediate resonators are all electrically connected to the grounding plate via a common conductive wall. [5] Distributed element RF filter according to claim 1, wherein the first and the second resonator have a common electrical length and the one or more intermediate resonators have a common electrical length. [6] Distribution element RF filter according to claim 1, wherein the electrical length of the first and second resonator is greater than the electrical length of one or more intermediate resonators. [7] Distributed element RF filter according to claim 5, wherein the first and second resonator have a length-to-width ratio that is smaller than the length-to-width ratio of one or more intermediate resonators. [8] Distributed element RF filter according to claim 1, which is a thin-film multipolar filter with a passband between 1 GHz and 60 GHz, and wherein one or more intermediate resonators have an unloaded quality factor of more than 400. [9] Distribution element RF filter according to claim 8, further comprising a conductive cover which is attached to the substrate and electrically connected to the grounding plate, wherein the conductive cover is arranged over the second surface of the substrate. [10] Distribution element high-frequency (HF) filter, comprising: a dielectric substrate with a grounding plate located on a surface of the substrate; a first and a second resonator located on a surface of the substrate opposite the grounding plate, the first and second resonators each being electrically connected to a corresponding I / O interface near a corresponding end of the substrate; and one or more U-shaped or omega-shaped resonators located on the surface opposite the grounding plate and between the first and second resonators, each U-shaped or omega-shaped resonator comprising a first and a second end section electrically connected to the grounding plate via one or more conductors near a common side of the substrate, wherein each of the resonators has an electrical length that nominally corresponds to half a wavelength of a center frequency of the filter. [11] Distributed element RF filter according to claim 10, wherein the first and the second resonator have a common electrical length and the one or more U-shaped or Omega-shaped resonators have a common electrical length. [12] Distributed element RF filter according to claim 11, wherein the electrical length of the first and second resonator is greater than the electrical length of one or more U-shaped or Omega-shaped resonators. [13] Distributed element RF filter according to claim 10, wherein the first and the second resonator have a length-to-width ratio that is smaller than the length-to-width ratio of one or more U-shaped or Omega-shaped resonators. [14] Distribution element RF filter according to claim 10, further comprising a conductive cover arranged above and spaced apart from the surface of the substrate on which the one or more resonators are located, wherein the conductive cover is electrically connected to the grounding plate. [15] Distributed element RF filter according to claim 10, which is a thin-film multipolar filter with a passband between 1 GHz and 60 GHz, wherein the U-shaped or Omega-shaped resonator(s) have an unloaded Q factor of more than 400. [16] Distribution element high-frequency (HF) filter, comprising: a dielectric substrate between a grounding plate on the surface of the substrate and a plurality of resonators on the opposite surface of the substrate; including the multitude of resonators: a first and a second resonator, each electrically coupled to a corresponding input / output (I / O) interface near a corresponding end of the substrate; and one or more intermediate resonators arranged between the first and second resonator, wherein each of the one or more intermediate resonators comprises a resonator section between a first and a second end section, which are electrically connected to the grounding plate by one or more conductors near a common side of the substrate. [17] Distributed element RF filter according to claim 16, wherein the resonator sections of each of the multiple resonators comprise a section with a U-shape or an Omega shape. [18] Distributed element RF filter according to claim 16, wherein the electrical length of the first and second resonator is greater than the electrical length of one or more intermediate resonators. [19] Distributed element RF filter according to claim 16, wherein the first and second resonator have a length-to-width ratio that is smaller than the length-to-width ratio of one or more intermediate resonators. [20] Distribution element RF filter according to claim 16, further comprising a conductive cover arranged above and spaced apart from the surface of the substrate on which a plurality of the resonators are located, wherein the conductive cover is electrically connected to the grounding plate. [21] Distributed element RF filter according to claim 16, which is a thin-film multipolar filter with a passband between 1 GHz and 60 GHz, wherein each of the one or more intermediate resonators has an electrical length that is nominally equal to half a wavelength of a center frequency of the bandpass filter.

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