Patent Publication Number: US-7583165-B2

Title: High Q cavity resonators for microelectronics

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of the filing date of U.S. Provisional Application No. 60/650,505 filed Feb. 7, 2005, the disclosure of which is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to filters, particularly filters which include cavity resonators, for use in microelectronic devices and assemblies, e.g., chips, substrates and circuit panels. 
     Filters play a critical role in the operation of radio receivers and transmitters. In receivers, high-Q filters are used to confine received signal energy to narrow passbands in order to reject noise and spurious harmonics that interfere with the reception of the intended signal. In transmitters, high-Q filters are used to restrict the bandwidth of signals to be amplified to designated channels, for example, for the purpose of increasing the signal to noise ratio of the transmitted signal and to avoid the transmitted signals from interfering with out-of-band signals. 
     Many filters used in microelectronics employ lumped components, e.g., capacitors and inductors, which are combined to form resonant circuits, for example, to select a narrow fixed passband of an intermediate frequency (“IF”) or baseband (“BB”) signal in a receiver. Lumped components may be provided as discrete components mounted to a circuit panel or other interconnection element. Alternatively, distributed components or both lumped and distributed components may be provided as elements of a chip or microelectronic substrate commonly known as “integrated passives on chip” (IPOC). The Q value of each component in a filter strongly influences the overall performance of the filter. In order for filters to provide good rejection of out-of-band energy and noise, they need to operate with a high “Q” value. High Q values generally result in the following benefits: a greater degree of signal isolation, the ability to achieve narrower passbands, and sharper filter roll-off. 
     Unfortunately, the Q value of traditional lumped components is inadequate for these purposes. Traditional lumped capacitors used in microelectronic devices, such as in capacitors of an IPOC, typically have unloaded Q values which are below 200. Lumped inductors used in microelectronics, e.g., inductors which are formed as traces on a microelectronic dielectric sheet, typically have unloaded Q values which are below 100. Such unloaded component Q values lead to circuit Q values of about 10 in resonant circuits which include the components. Circuit Q values of about 10 are inadequate to achieve the above-indicated goals. 
     Outside the field of microelectronics, one class of resonant circuits, the helical cavity resonator, has a characteristically high unloaded Q value. Such resonators typically have Q values ranging between about 500 and 1000 over frequencies selected between about 10 MHz and 1000 MHz. As used herein, a “cavity resonator” is defined as a chamber, which may be hollow, or, alternatively packed with a dielectric material, whose dimensions allow the resonant oscillation of electromagnetic waves, and in which is disposed an inductive element for exciting the electromagnetic waves. 
     An example of a two-stage helical cavity resonator  50  is illustrated schematically in a sectional view thereof in  FIG. 1 . As shown therein, the helical cavity resonator  50  includes a shielded enclosure  60 , which encloses a first volume  62  and a second volume  64  and having an internal shield  66  which separates the first volume  62  from the second volume  64 . The shielded enclosure  60  is cubic or cuboid in shape, having planar walls  61 , each of which presents a conductive surface to the first and/or second volumes  62 ,  64  enclosed by the shielded enclosure. The shielded enclosure  60  is typically held at a fixed potential, e.g., ground, thus forcing the conductive interior surfaces of the walls  61  of the enclosure to be held at that potential, e.g., ground. 
     A first helical coiled inductor  70  is disposed within the first volume  62  and a second helical coiled inductor  72  is disposed within the second volume  64 . The first inductor  70  has a ground end  71  mounted to the shielded enclosure  60 , shown here as being mounted to the internal shield  66 . Likewise, the second inductor  72  also has a ground end  73  mounted to the shielded enclosure  60 , also shown as being mounted to the internal shield  66 . In addition, the first inductor has an open end  74  and the second inductor has an open end  76 . Connected to the first inductor  70  is a first transmission line  80  having a characteristic impedance such as 50Ω. A second transmission line  82  is connected to the second inductor  72 , also having a characteristic impedance which is typically the same as that of the first transmission line  80 , e.g., an impedance of 50Ω. Each of the first and second transmission lines extends from inside the shielded enclosure  60  through openings  86 ,  88 , respectively, to the space  85  outside the shielded enclosure. Transmission line  80  includes an active conductor  87  and a grounded conductor  81 . Transmission line  82  includes an active conductor  89  and a grounded conductor  83 . The grounded conductors  81 ,  83  typically are in conductive communication with the shielded enclosure  60 , and/or one or more external ground points (not shown) in order to provide a stable ground for the transmission lines. 
     One requirement in fabricating the helical cavity resonator is to attach the active conductors  87 ,  89  of the transmission lines to the inductive elements  70 ,  72 , respectively, at a location which terminates the transmission lines in matched impedances. Unfortunately, achieving such terminations is difficult. Because the cavity resonator is very sensitive to variations in dimensions and the shape of the inductive element, painstaking manual adjustments must be made in order to achieve the matched impedance. Moreover, the same hand-tuning must be performed for each such cavity resonator being manufactured, because the dimensions and shape of the inductor (and hence, its impedance) are subject to variations. 
     The helical cavity resonator  50  operates to resonate at a predetermined resonant frequency f 0  which is determined by the inductance of the inductors  70 ,  72  and the dimensions and geometry of the shielded enclosure  60 . Due to the boundary conditions imposed by the walls  61  of the shielded enclosure, an electromagnetic field of standing waves is excited in the first volume at the resonant frequency f 0 . Such electromagnetic field is excited by an excitation current delivered onto the first inductor  70  by the first transmission line  80 . An opening  68  is provided in the internal shield  66  for the purpose of coupling energy from the electromagnetic field excited by the first inductor  70  onto the second inductor  72 . The first and second inductors  70 ,  72  and the shielded enclosure  60  cooperate together in exciting a current in the second inductor  72  having an amplitude which is very sensitive to the frequency of the excitation current present on the first inductor  70 . The excited current on inductor  72  is output onto the second transmission line  82 . The excited current output onto transmission line  82  is the same as or exceeds the excitation current provided onto inductor  70  when the frequency of the excitation current is at the resonant frequency of the cavity resonator  50 . However, very little excited current is produced in the second inductor  72  unless the frequency of the excitation current is at or near the resonant frequency. In this manner, the helical cavity resonator  50  operates as a filter to select a narrow passband between a signal arriving on first transmission line  80  and output onto second transmission line  82 . 
     The merits of the helical cavity resonator are best illustrated with reference to  FIG. 2 . As shown therein,  FIG. 2  is a chart comparing the frequency response of a first type of bandpass filter which employs a helical cavity resonator (curve  10 ), as compared to a second type of bandpass filter (curve  12 ) which employs lumped circuit elements. In addition, the first filter type has a much narrower passband. Each of the first and second filter types has a nominal center frequency f 0 . By convention, the passband is generally considered to be the range of frequencies which lie between a lower “3 dB frequency” and an upper “3 dB frequency”. The lower 3 dB frequency is the frequency below f 0  at which the frequency response is 3 dB lower than the peak frequency response (the frequency response at f 0 ). The upper “3 dB frequency” is a frequency above f 0  at which the frequency response is 3 dB lower than the peak frequency response. As illustrated in  FIG. 2 , the passband  20  of the first filter type lies between the lower 3 dB frequency  30  and the upper 3 dB frequency  32 . On the other hand, the passband  22  of the second filter type lies between the lower 3 dB frequency  40  and the upper 3 dB frequency  42 . As apparent from  FIG. 2 , the passband  20  of the first filter type, having a helical cavity resonator, is much narrower than the passband  22  of the second filter type having lumped circuit elements. 
     Unfortunately, the available helical cavity resonators available heretofore are heavy, expensive and bulky, typically being constructed of helical coils of copper tubing which is disposed within in metal chambers. Aside from that, fabrication of such resonators is difficult. In particular, the task of properly terminating the helical inductor element in such resonators is expensive and arduous, because the 50 ohm termination point is difficult to determine prior to constructing the helical coil and the metal chamber. Because of the size and weight of helical cavity resonators and the difficulties involved in providing the appropriate termination point, heretofore the use of such resonators has been limited to applications outside the field of microelectronic devices and microelectronic assemblies. 
     However, as explained above, there is a present need for resonant circuits in microelectronics having higher Q values. Accordingly, it would be desirable to provide a new high Q value resonator component suitable for use in or with microelectronic assemblies. 
     SUMMARY OF THE INVENTION 
     Therefore, according to an aspect of the invention, a cavity resonator is provided which includes a sheet-like dielectric element having one or more dielectric layers, and a shielded enclosure overlying at least a portion of the dielectric element, the shielded enclosure enclosing a first volume and a second volume and having a metallic divider separating the first volume from the second volume. 
     A first unitary trace is disposed within the first volume, the first unitary trace including a first transmission line trace extending along the dielectric element and a first inductor trace. A first reference trace extends along the dielectric element and is separated from the first transmission line trace by at least one dielectric layer of the dielectric element. 
     A second unitary trace is disposed within the second volume, the second unitary trace including a second transmission line trace extending along the dielectric element and a second inductor trace. A second reference trace extends along the dielectric element and is separated from the second transmission line trace by at least one dielectric layer of the dielectric element. 
     In addition, the metallic divider between the first and second volumes has an opening adapted to permit a predetermined proportion of energy of an electromagnetic field excited by the first inductor trace to be coupled onto the second inductor trace. 
     According to a particular aspect of the invention, the shielded enclosure includes a top enclosure which encloses portions of the first volume and the second volume above the dielectric element. In addition, a bottom enclosure encloses portions of the first volume and the second volume below the dielectric element. The metallic divider includes a top divider separating the first volume from the second volume within the top enclosure and a bottom divider separating the first volume from the second volume within the bottom enclosure. 
     In accordance with one or more further aspects of the invention, the dielectric element includes a plurality of third traces disposed outside the shielded enclosure for which at least some of the third traces are not connected to either the first unitary trace or the second unitary trace. In accordance with such aspect, the dielectric element may include a ground plane separated from the third traces by at least one dielectric layer of the dielectric element, the ground plane being connected to the first and second reference conductors. 
     In accordance with a particular aspect of the invention, each of the first inductor trace and the second inductor trace has a spiral form, or each of the first and second inductor traces has helical form, or even each of the first and second inductor traces has tapered helical form. 
     In accordance with one or more further aspects of the invention, the dielectric element includes a substantially planar surface that is disposed outside the shielded enclosure, as well as first and second frusto-conical inductor surfaces disposed inside the shielded enclosure. The first and second inductor surfaces have tops which are displaced vertically from the planar surface and the first and second inductor traces are each disposed in a spiral pattern along the first and second inductor surfaces, respectively. In accordance with such aspect of the invention, the first and second transmission line traces and the first and second reference traces are disposed on opposite sides of the substantially planar surface. The cavity resonator may further include a ground plane, in which the first and second reference traces are portions of the ground plane. 
     According to another aspect of the invention, a cavity resonator is provided which includes a shielded enclosure enclosing a first volume and a second volume, the shielded enclosure having a shield separating the first volume from the second volume. 
     A first unitary conductor and a first reference conductor are provided which extend within the first volume, the first unitary conductor having a first inductor portion disposed within the first volume and a first transmission line portion. A first dielectric element separates the first transmission line portion from the first reference conductor so that the first transmission line portion of the first unitary conductor, the first dielectric element and the first reference conductor define a first transmission line. 
     A second unitary conductor and a second reference conductor are provided which extend within the second volume, the second unitary conductor having a second inductor portion disposed within the second volume and a second transmission line portion. A second dielectric element separates the second transmission line portion from the second reference conductor so that the second transmission line portion of the second unitary conductor, the second dielectric element and the second reference conductor define a second transmission line. 
     The shield between the first and second enclosed volumes is further provided with an opening allowing a predetermined proportion of energy radiated by the first inductor portion to be radiatively coupled to the second inductor portion. 
     In a cavity resonator according to one or more further aspects of the invention, the first transmission line and the second transmission line extend through one or more openings in the shielded enclosure to locations outside the shielded enclosure. According to one or more further aspects of the invention, one or more encapsulating members insulate the first transmission line and the second transmission line at the one or more openings. 
     In a cavity resonator according to one or more further aspects of the invention, the first dielectric element and the second dielectric element are portions of a unitary dielectric element. 
     In a cavity resonator according to one or more further aspects of the invention, the first reference conductor and the second reference conductor are adapted to be connected to the same reference potential. 
     In a cavity resonator according to one or more further aspects of the invention, the first inductor portion and the second inductor portion include ground ends conductively bonded to the shielded enclosure. 
     In a cavity resonator according to one or more further aspects of the invention, the shielded enclosure includes an inner surface having a silver coating disposed thereon. In such aspect, the first inductor portion and the second inductor portion may further include silver coatings. 
     In a cavity resonator according to one or more further aspects of the invention, each of the first inductor portion and the second inductor portion has spiral form, or each of the first inductor portion and the second inductor portion has helical form, or each has a tapered helical form. 
     A cavity resonator according to one or more further aspects of the invention may further include a first dielectric mounting element and a second dielectric mounting element. In such aspect, the first inductor portion has a first open end and a first ground end opposite the first open end. The second inductor portion has a second open end and a second ground end opposite the second open end. The first open end is mounted to the first dielectric mounting element and insulated from the shielded enclosure thereby. The second open end is mounted to the second dielectric mounting element and insulated from the shielded enclosure thereby. 
     In a further preferred aspect of the invention, the first dielectric mounting element and the second dielectric mounting element are mounted to the shielded enclosure. 
     According to a preferred aspect of the invention, a dielectric loading material occupies at least a substantial portion of the first volume and the second volume. In a particular preferred aspect of the invention, the dielectric loading material includes a multiplicity of solid dielectric nodules. 
     In a cavity resonator according to one or more further aspects of the invention, the first reference conductor and the second reference conductor are portions of a unitary ground conductor that includes a ground plane portion disposed at an interior surface of the shielded enclosure. 
     In a cavity resonator in accordance with one or more further aspects of the invention, each of the first enclosed volume and the second enclosed volume has substantially cuboid shape. 
     According to a particular aspect of the invention, a assembly includes a cavity resonator according to one or more of the herein-described aspects of the invention. Such assembly further includes a circuit panel having a plurality of signal traces. The first transmission line portion and the second transmission line portion of the cavity resonator are mounted in conductive communication with respective ones of the plurality of signal traces. 
     In such assembly, the circuit panel may further have a major surface which is oriented in a horizontal direction. Such assembly further includes vertical interconnection elements, each having a ground plane oriented in a vertical direction and one or more signal conductors oriented in the vertical direction and separated from the ground plane by a dielectric. In such assembly, the first transmission line portion and the second transmission line portion are in conductive communication with the signal traces of the circuit panel through the signal conductors of the vertical interconnection elements. 
     In one assembly in accordance with an aspect of the invention, each vertical interconnection element has top and bottom surfaces and contacts disposed on the top and bottom surfaces. The contacts are conductively connected to the ground plane and to the signal traces. 
     A cavity resonator in accordance with another aspect of the invention includes a shielded enclosure enclosing a volume. A unitary conductor is disposed within the volume, such conductor having a first inductor portion and a transmission line portion included in a transmission line. The transmission line further includes a reference conductor which is separated from the transmission line portion by a dielectric element. An active semiconductor device is coupled to the unitary conductor and is operable to conduct a current to the unitary conductor at a resonant frequency of the unitary conductor. 
     A method of making a cavity resonator is provided in accordance with another aspect of the invention. In such method, a first dielectric element is provided which has a first unitary conductor and a first ground conductor disposed on first and second opposite sides of the first dielectric element. The first unitary conductor includes a first transmission line portion disposed on the first side opposite the first ground conductor and a first inductor portion disposed on the first side at locations not opposite the first ground conductor. A second dielectric element is provided in which a second unitary conductor and a second ground conductor are disposed on first and second opposite sides of the second dielectric element. The second unitary conductor includes a second transmission line portion disposed on the first side opposite the second ground conductor and a second inductor portion disposed on the first side at locations not opposite the second ground conductor. The first dielectric element is mounted within a first chamber of a shielded enclosure and the second dielectric element is mounted within a second chamber of a shielded enclosure. The first and second chambers are shielded from each other and have an opening allowing a predetermined proportion of energy to be coupled between the first chamber and the second chamber. 
     In accordance with one or more further aspects of the invention, each of the first dielectric element and the second dielectric element has sheet-like form and extends in horizontal directions of the cavity resonator. An end of the first inductor portion is vertically displaced a first predetermined height from the first dielectric element and an end of the second inductor portion is vertically displaced a second predetermined height from the second dielectric element. 
     In a particular aspect of the invention, the first predetermined height is equal to the second predetermined height. 
     In a method of making a cavity resonator in accordance with one or more further aspects of the invention, the first and second dielectric elements are mounted such that the first transmission line portion and the second transmission line portion extend through the openings in the shielded enclosure to locations outside the shielded enclosure. 
     In a method of making a cavity resonator in accordance with one or more further aspects of the invention, the first inductor portion is provided by forming a first spiral pattern on the first dielectric element, and the second inductor portion is provided by forming a second spiral pattern on the second dielectric element. A portion of the first dielectric element underlying the first spiral pattern is removed and a portion of the second dielectric element underlying the second spiral pattern is removed prior to vertically displacing ends of the spiral patterns so as to vertically displace the ends of the first inductor portion and the second inductor portion. 
     In a method of making a cavity resonator in accordance with one or more further aspects of the invention, the first and second dielectric elements are portions of a unitary dielectric element. 
     In a method of making a cavity resonator in accordance with one or more further aspects of the invention, the first and second dielectric elements are physically separated from each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view schematically illustrating a conventional cavity resonator. 
         FIG. 2  is a graph illustrating a frequency response of a cavity resonator relative to that of a lumped passive circuit element. 
         FIG. 3  is a cutaway perspective drawing illustrating a cavity resonator according to one embodiment of the invention. 
         FIG. 4  is a cutaway perspective drawing illustrating a cavity resonator according to another embodiment of the invention. 
         FIG. 5  is a sectional diagram illustrating a stage of fabrication of a cavity resonator according to one embodiment of the invention. 
         FIGS. 6 and 7  are a top-down view of a portion of a unitary conductor and a corresponding sectional diagram thereof, respectively, illustrating a stage of fabrication of a cavity resonator according to another embodiment of the invention. 
         FIG. 8  is a sectional view of a cavity resonator according to another embodiment of the invention. 
         FIG. 9  is an exterior view, through lines  9 - 9 , of a cavity resonator according to the embodiment of the invention illustrated in  FIG. 8 . 
         FIG. 10  is a schematic circuit diagram illustrating an application of a one chamber cavity resonator according to an embodiment of the invention. 
         FIG. 11  is a functional block diagram illustrating an application of a cavity resonator in a transceiver according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     As discussed above, good noise rejection and narrow passband operation is important to the operation of radio frequency receiving and transmitting equipment. As the size of such equipment is reduced with each new generation of devices such as cellular phones, two-way radios, wireless personal digital assistant (PDA) devices, and broadcast receivers, it is important that filters used in them meet the demands for both the high noise rejection and the small size. 
     The most preferred high Q cavity resonators according to the embodiments of the invention described herein satisfy these demands. In addition, cavity resonator structures and methods of fabricating them are provided herein which are less expensive to fabricate than the large, bulky cavity resonators described above as background to the invention. 
       FIG. 3  illustrates a first embodiment of a two-chamber cavity resonator  100  according to an embodiment of the invention. As shown therein, the cavity resonator  100  includes some of the features of the cavity resonator  50  which are described above as background to the invention. Thus, the cavity resonator  100  includes a shielded enclosure  110  which encloses a first volume  112  and a second volume  114 . The shielded enclosure is formed by stamping, folding, shaping, or otherwise forming metallic members, e.g., a metallic sheet, into a generally cubic or cuboid, i.e. “boxlike”, shape. Desirably, the shielded enclosure is formed of a metal such as copper or aluminum which is easily worked in such manner, has high conductivity and is readily available at a reasonable cost. In one embodiment, a silver coating is applied at least to the interior surfaces of the shielded enclosure, e.g., by electroplating or other widely used method. Silver is especially advantageous because it has higher conductivity than any other material at operating temperatures and conditions, i.e., between about −54° C. and 150° C. in which all but the most exotic of microelectronic devices are normally operated. In addition, oxides of silver are conductive such that some oxidation of the silver coating is permitted without causing the conductivity of the silver coating to degrade excessively. 
     The shielded enclosure includes a metallic divider  116  which functions to separate the first volume  112  from the second volume  114  except for an opening  118  through which a predetermined proportion of the electromagnetic wave energy present in the first volume is coupled into the second volume  114 . 
     As in the cavity resonator described in the background, the cavity resonator shown in  FIG. 3  has a transmission line which is joined to the inductive element of the resonator at a position which results in a matched impedance. A particular feature of this embodiment is the unitary construction in which the transmission line conductors of the cavity resonator are formed integrally with the inductive elements such that the transmission lines are terminated consistently in matching 50Ω impedances, thus eliminating the need for manual, hand-tuned adjustments to determine the attachment locations for the transmission lines. 
     The transmission line elements are provided on a sheet-like dielectric element  120  which extends within the first and second volumes  112 ,  114  of the shielded enclosure. In the embodiment shown in  FIG. 3 , the dielectric element  120  is disposed at a position at about midway between a bottom side  101  of the shielded enclosure and a top side  102  of the shielded enclosure. In a particular form of such embodiment, the shielded enclosure includes a top enclosure which encloses an upper portion  103  of the space within the shielded enclosure above the dielectric element  120 . A bottom enclosure encloses a lower portion  105  of the space within the shielded enclosure below the dielectric element  120 . In such embodiment, the metallic divider  116  includes a top divider  117  which divides a top portion of the first volume from a top portion of the second volume. In such embodiment, the metallic divider  116  further includes a bottom divider  119  which divides a bottom portion of the first volume from a bottom portion of the second volume. 
     The dielectric element  120  includes one or more dielectric layers, on which the below-described metallic traces are formed, such layers being formed of materials, such as polyimide and the like. Alternatively, the dielectric layers are formed, such as by electrophoretic deposition, onto a metallic layer of the dielectric element  120 . 
     A first unitary trace  122  is disposed within the first volume  112 , the first unitary trace  122  including a first transmission line trace  124  and a first inductor trace  126 . The first transmission line trace  124  includes an active conductor of a first transmission line. A first reference trace  128  also extends along the dielectric element  120  and is separated from the first transmission line trace  124  by a dielectric layer  130  of the dielectric element  120 . As coupled for operation in a circuit, the first reference trace  128  is coupled to a fixed potential such as ground, and provides a source of reference potential for the transmission line including itself and the first transmission line trace. The first transmission line trace may even be coupled to one or more walls of the shielded enclosure  110 . 
     Similarly, a second unitary trace  132  is disposed within the second volume  114 , the second unitary trace  132  including a second transmission line trace  134  and a second inductor trace  136 . A second reference trace  138  also extends along the dielectric element  120  and is separated from the second transmission line trace  134  by a dielectric layer  140  of the dielectric element  120 . The second transmission line trace  134  and the second reference trace  138  together form a transmission line, the second reference trace  138  being coupled to a fixed potential such as ground. 
     Each of the first and the second inductor traces  126 ,  136  have ground ends  127  which are grounded, such as by mounting them in conductive communication with the shielded enclosure  110 . In one embodiment, the ground ends  127  are mounted by adhesive or solder bonding to the metallic divider  116 , as shown in  FIG. 3 , or other interior wall of the shielded enclosure  110 . These mountings are provided in a manner with or without the inductor traces being bonded or mounted to one or more intermediate elements. 
     As shown in  FIG. 3 , the first and second inductor traces  126 ,  136  are spiral elements disposed on an upper surface  121  of the dielectric element  120 . The spiral arrangement helps maintain the geometry of the metallic inductor traces  126 ,  136 . Methods of providing inductive elements on various types of dielectric elements, including web-like or tape-like elements, are described in commonly assigned U.S. patent application Ser. Nos. 10/210,160 filed Aug. 1, 2002 and 10/452,333 filed Jun. 2, 2003, the entire contents of which are incorporated herein by reference. In one embodiment, the dielectric element  120  presents an upper surface  121  which is at least generally planar, such that the inductor traces are disposed in spiral patterns on the upper surface  121  of the dielectric element  120 . However, in some embodiments, as are described more fully below, the dielectric element  120  includes a raised or indented surface underlying the spiral inductive traces, so as to impart a somewhat helical geometry to the inductor traces. 
     Transmission lines including the transmission line traces  124  and  134  extend through openings  125 ,  137  from locations inside the shielded enclosure  110  to positions external thereto for the purpose of making external connections. As shown in  FIG. 3 , a transmission line  135  including the second transmission line trace  134 , dielectric layer  140  and reference trace  138  extends to a location external to the shielded enclosure  110 . At least the transmission line traces of the first and second transmission lines are insulated at the openings in walls of the shielded enclosure  110 . As further shown in  FIG. 3 , the transmission line  135  is conductively connected to a trace  142  on a circuit panel, which is, illustratively, any of many available types of boards, carriers, substrates having traces patterned thereon for conducting currents and voltages between elements affixed thereto. In this regard, the term “on” and “along” are meant broadly to include patterns either disposed on an exterior surface of such circuit panel or rather, disposed within the interior of the circuit panel. In one embodiment, the transmission line  135  is interconnected to trace  142  through an interconnection element  148  having a structure such as that described in commonly assigned U.S. Provisional Application No. 60/576,170 filed Jun. 2, 2004, the entire contents of which are hereby incorporated herein by reference. In some embodiments described therein, the interconnection element  148  has a structure similar to a sawed portion of a printed circuit board, such as an FR-4 type (e.g., epoxy resin) board, which has been up-turned onto one end and mounted to the circuit panel  150 . With such interconnection element  148 , the reference trace  138  of the transmission line is conductively connected to a vertically disposed ground plane  144  of the interconnection element  148  which in turn, is connected to a ground plane  146  of the circuit panel  150 . The ground plane  144  of the interconnection element is itself bonded to the ground plane  146  of the circuit panel, as by solder bond or conductive adhesive bond  151 . In the embodiment shown, the ground plane  146  of the circuit panel  150  extends under and is conductively bonded to the entire bottom side  101 , of the shielded enclosure  110 , e.g., by solder, so as to provide a stable and effective ground for the cavity resonator. Further, the transmission line trace  134 , which extends through the opening  137  in the wall of the shielded enclosure  110 , is conductively connected to a trace  152  of the interconnection element  148 , the trace  152 , in turn, being conductively connected to the trace  142  on the circuit panel, such as through a solder bond  154 . 
     As discussed above, one objective of cavity resonators according to some embodiments of the invention is to provide small-size resonators suitable for use in microelectronic assemblies. Another consideration, which can sometimes be at odds with reducing the size, is the need to manufacture a cavity resonator having a resonant frequency which is usable at frequencies used in microelectronic circuits today. Generally speaking, the smaller size that the cavity resonator has, the higher the resonant frequency will be. However, this relationship can be altered by loading the chamber that houses the inductive element with a dielectric material. In order to achieve the greatest reduction in the resonant frequency, high-K dielectric materials can be used, such as perovskite materials, ferroelectric dielectric materials, e.g., barium strontium titanate (BSTO), zeolites, and the like. Otherwise, medium-K materials such as various glasses and oxides can be used. In one embodiment, the dielectric loading material is formed into nodules, which may be ball-shaped or otherwise. At a near completion stage of manufacture, after the inductive elements have been formed and positioned within the chambers of the cavity resonator, the ball-shaped nodules  160  ( FIG. 3 ) are poured in a fluid manner into the chambers of the cavity resonator to fill the space between the inductive elements and the walls of the chamber. In another embodiment, the dielectric material is suspended in an extrudable material such as a self-curing polymer, thermoset polymer or other organic material. That material is extruded into the chambers of the cavity resonator, e.g., chambers  112 ,  114  of resonator  110 , or chambers  204  of resonator  200 , after the inductive elements are placed in their final positions, to fill the spaces between the inductive elements and the walls of the chambers. 
       FIG. 4  illustrates another embodiment of a cavity resonator  200  according to the invention. The cavity resonator according to this embodiment is similar to that shown and described above relative to  FIG. 3 , except for the number of inductive elements, the particular geometry of the inductive elements and of the shielded enclosure. In this embodiment, a shielded enclosure  201  houses three spiral helical inductive elements  202 , each of which is generally in the shape of a helix which is tapered from a larger coil  205  of the inductive element towards a smaller open end  210  of the coil. While three inductive elements  202  are shown in  FIG. 3 , fewer inductive elements may be provided, as described above relative to  FIG. 3 . Alternatively, more than three inductive elements may be provided in a manner similar to that described here. Each of the inductive elements  202  is disposed in a substantially separate chamber  204  of the shielded enclosure  201 , the chamber being cubic or cuboid in shape. Similar to the embodiment described above relative to  FIG. 3 , each chamber  204  is substantially separated by one or more metallic dividers  206  from the other two chambers  204  of the enclosure  201 , except for openings  208  provided in the metallic dividers  206 . 
     In a particular embodiment, the inductive elements  202  are disposed at least partially as inductive traces (e.g. at larger coils  205 ) on a sheet-like dielectric element  212  having portions which are bonded to a metallic sheet  216 . The open end  210  of each inductive trace is vertically displaced from the metallic sheet  216 . For example, the open end  210  may be mounted through a dielectric block  228  that is also mounted to the interior surface of a top side  234  of the shielded enclosure  201 . A ground end  214  of each inductive trace is conductively bonded to the shielded enclosure  201  or other available source of a fixed potential such as ground. The inductive element  202  is one part of a unitary trace  218  in each chamber  204  which includes the inductive trace, e.g. trace  205 , and a transmission line trace  215  that is disposed at an essentially fixed spacing in relation to the metallic sheet  216 , the metallic sheet  216  functioning as a reference trace or reference conductor for a transmission line including the transmission line trace  215 , the dielectric element  212  and the metallic sheet  216 . 
     The metallic sheet  216  forms a ground plane of a circuit panel, and also functions as a bottom side of the shielded enclosure  201 . Circuit traces  222  are also disposed on the dielectric element  212  in portions  220  thereof which extend externally to the shielded enclosure  201 . 
     The three-chambered cavity resonator  200  has an input end at a first transmission line  224  feeding into a first chamber of the shielded enclosure  201 , and an output end from a second transmission line  217  emerging from another chamber of the shielded enclosure  201 . As in the embodiment described above relative to  FIG. 3 , the three-chambered resonator  200  is mounted to the circuit panel  230  and conductively connected to traces on the circuit panel  230 , as through solder or adhesive bonding. 
       FIG. 5  is a sectional view illustrating a stage in the fabrication of a cavity resonator such as that shown in  FIG. 4 , according to an embodiment of the invention. In a particular embodiment, each inductive element  202  is formed as a spiral element disposed on the surface of a planar dielectric layer  300  of a dielectric element. Thereafter, the inductive trace is separated from the dielectric layer to form the inductive element having the desired spiral helical shape. As shown in  FIG. 5 , a dielectric sheet  300  is provided having a first patterned metal layer  302  thereon, the layer  302  including a unitary trace having a transmission line trace  304  and an inductive trace  306 . The inductive trace  306  is formed in a spiral pattern, such as that shown and described above as elements  126 ,  136  shown in  FIG. 3 . The inductive trace  306  is formed, e.g., in a subtractive process, from a layer of metal disposed on the dielectric sheet  300 , which is patterned, as by a masked etch. Thereafter, with the inductive trace  302  remaining in place over the dielectric sheet  300 , further etching is performed of the dielectric sheet  300  underlying the inductive trace  306 , using an etchant which does not etch or only slightly etches the metal of the inductive trace  302 . As a result of such etching, the metallic pattern of the inductive trace is undercut to reduce the area of the dielectric layer  300  in contact with the inductive trace, resulting in the structure as shown. In one embodiment, a reference trace  310  is formed on a bottom side of the dielectric element, such reference trace serving as a reference conductor of a transmission line including transmission line trace  304 , dielectric layer  300  and reference trace  310 . In another embodiment, such as described above with reference to  FIG. 4 , a portion of the dielectric layer of the dielectric element is bonded to a metallic bottom side of the shielded enclosure, allowing the metallic bottom side to function as the reference conductor for the transmission line. 
     As further shown in  FIG. 5 , a dielectric mounting block  320  is bonded, e.g., via an adhesive, to the open end  308  of the inductive trace, such mounting block  320  being used to mount the open end  308  to the interior wall of the shielded enclosure, such as shown and described above with respect to  FIG. 4 . Once the open end  308  is mounted to the mounting block  320  in this way, the inductive trace is gradually peeled from the surface of the dielectric layer  300 , such that the open end of the inductive trace becomes vertically displaced from the dielectric layer in the center of the inductive trace. In such manner, the inductive trace gradually acquires the desired spiral and helical shape and vertical displacement for installation within the shielded enclosure. Thereafter, the top surface of the dielectric mounting block is bonded, e.g., via an adhesive to the interior surface of the shielded enclosure. 
       FIG. 6  is a top view illustrating a stage of fabrication of a spiral helical cavity resonator according to another embodiment of the invention in which the inductive trace is formed from a spiral pattern disposed as traces  402  on a dielectric layer  400 .  FIG. 7  is a corresponding sectional view, through line  7 - 7  of  FIG. 6 . In this embodiment, the dielectric layer  400  is scored or severed along the dotted lines  404  between each of a plurality of adjacent traces  402  of the spiral pattern. A dielectric mounting block  406  is bonded to an open end  408  of the pattern in a manner as shown and described above relative to  FIG. 5 . In this arrangement, the traces  402  of the spiral pattern can be vertically displaced from a reference plane  405  of the dielectric element by moving the dielectric mounting block  406  away from the reference plane  405 . Once the mounting block  406 , with the open end  408  attached, has been vertically displaced, the mounting block  406  is bonded to an interior surface of the shielded enclosure in the manner set forth above relative to  FIG. 4 . 
       FIG. 8  is a sectional view illustrating a spiral helical cavity resonator according to still another embodiment of the invention.  FIG. 9  is a corresponding side view of the resonator, through line  9 - 9  of  FIG. 8 . In this embodiment, spiral helical inductive traces  802  is disposed on a surface of a dielectric layer  800  which includes portions  804  which are vertically displaced, as by indenting, from a reference plane  810  thereof on which a reference conductor  806  is disposed. As shown in  FIG. 8 , the inductive traces  802  are disposed within a first chamber  809  and a second chamber  811  of a shielded enclosure  812 . The shielded enclosure is similar to the shielded enclosure described above with respect to  FIG. 4 . However, flanges  814  are provided for mounting outer walls of the shielded enclosure  812 , as by solder or conductive adhesive, to a conductive member  816  disposed on a surface of the dielectric layer  800 . Through conductive member  816 , a conductive interconnection is provided to a ground plane  818  and to a circuit panel  820 , in turn, to which it is conductively bonded. The circuit panel  820  further includes metallic members  822 , e.g., posts and/or plated through holes, extending from a top side to a bottom side of the circuit panel, for the purpose of further extending the ground path in a series of low-resistance interconnects. 
     As shown in  FIG. 9 , a transmission line trace  830  emerges outside the shielded enclosure from a position inside a first chamber thereof. The transmission line trace  830  is electrically insulated from the metallic wall  832  of the shielded enclosure  812 , as by a dielectric encapsulating material  834  which is disposed between the transmission line trace  830  and the edge of an opening in the metallic wall from which the transmission line trace  830  emerges from the shielded enclosure. 
     Referring again to  FIG. 8 , a metallic divider  840  is disposed with a top end soldered or otherwise bonded to an interior surface  842  of the shielded enclosure. Desirably, the metallic divider  840  is mounted at a top end  838  to the shielded enclosure at a position disposed within a slot  845  formed in the wall of the shielded enclosure. At a lower end  844 , the metallic divider  840  is bonded, e.g., through solder or conductive adhesive bond, to the ground ends of conductive traces disposed on the dielectric sheet  800 . 
       FIG. 10  illustrates a further embodiment of the invention in which a filter  860  is constructed using a resonator  850  similar to the resonators provided according to one of the other embodiments described above with respect to  FIG. 3 ,  FIGS. 4-7  or  FIGS. 8-9 , except that the resonator includes a single chamber having a single inductive element disposed therein. In this embodiment, the values of the various resistors and capacitors of the circuit are selected to bias the transistor  862  in a manner which amplifies the frequency selected by the one chamber resonator  850 , as appears at the output  864  of the circuit. 
       FIG. 11  illustrates a transceiver  900  according to another embodiment of the invention, such transceiver  900  being as provided in a cellular telephone or other wireless telephone, or in a portable or non-portable computing device having a wireless interface, e.g., desktop or notebook computer, or as provided in a personal digital assistant, or other wireless communication device. As shown therein, transceiver  900  includes two helical cavity resonators  910 ,  920 . In such transceiver, a receiver portion  930  includes a resonator  910  such as that described above with respect to  FIG. 3 ,  4 , or  10  above, which is used to select the passband of the output of a mixer  912  used to downconvert a signal received over an antenna  914  through low noise amplifier  916 , as multiplied by the output of a variable frequency oscillator, e.g., VCO  918 . The output of resonator  910  is a bandlimited intermediate frequency (IF) signal having a narrow passband as determined by the characteristics of resonator  910 . The IF signal from resonator  910  is then input to baseband conversion and demodulation circuitry, shown collectively at  922 . Such circuitry  922  may, in one embodiment, utilize output of a local oscillator  924 . The output of that circuitry  922  is shown illustratively in  FIG. 11  as audio, video and data output, although other types of output, e.g., still-frame image can also be provided. 
     In a transmitter portion  940  of the transceiver, a resonator  920  is provided such as that described above with respect to  FIG. 3 ,  4 , or  10  above, the resonator  920  being used to select a narrow passband including the IF signal output of intermediate frequency conversion and modulation circuitry  932 . Illustratively, that IF signal is then converted to a transmission frequency by multiplication with the output of a VCO  934  through a mixer  936 , and then further amplified for transmission over an antenna  940  by amplifier  938 . Alternatively, the IF output signal of resonator  920  is provided to alternative modulation and transmission means including but not limited to any of the transmission means such as: amplitude modulation, frequency modulation, frequency hopping including that which satisfies one or more standards from the organization “GSM”, or is modulated according to spread spectrum techniques, e.g., code data multiple access (CDMA), and one or more data transmission standards such as General Packet Radio Service (“GPRS”) or cellular digital packet data “CDPD”). 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.