WO2000016432A1

WO2000016432A1 - Metal dielectric composite resonator

Info

Publication number: WO2000016432A1
Application number: PCT/US1998/019106
Authority: WO
Inventors: Richard V. Snyder; Charlotte Alvarez
Original assignee: New Jersey Institute of Technology
Current assignee: New Jersey Institute of Technology
Priority date: 1998-09-15
Filing date: 1998-09-15
Publication date: 2000-03-23
Anticipated expiration: 2001-03-15
Also published as: AU9482298A

Abstract

A composite resonator (10) consisting of a conducting metal (14) and a dielectric material (12) is used to provide resonant frequencies lower than can be obtained using the same volume of dielectric alone and with higher unloaded Q than can be obtained using the same volume of metal imbedded into a cavity and used as a resonator. This significantly reduces the cost and size of the resonator (10) without degrading its performance. An inexpensive metal (14), such as aluminum, can be substituted for more than half of hte dielectric (12) and stille form a resonator (10) with substantially equivalent resonant properties. The operative embodiments of the resonator invention (1) cover composites with doughnut-shaped, i.e., cylindrical, configurations, with the 'doughnut' either metal (14) or dielectric (12), and the 'hole' either dielectric (314) or metal (312), respectively.

Description

TITLE; METAL DIELECTRIC COMPOSITE RESONATOR

BACKGROUND OF THE INVENTION

1. Field of the Invention The invention relates to a resonator composed of a conducting metal ring surrounding a cylindrical dielectric core material which can be incorporated into multi- cavity filters for frequency separation.

2. Description of Related Art Dielectric resonator filters are a class of stable microwave filters that are frequently used in radar and communications systems. Dielectric resonators are often utilized in filter circuits because of an intrinsically high Q value. These characteristics allow a filter employing a dielectric resonator to have excellent frequency stability with only a small amount of frequency drift over a wide range of temperatures and environmental conditions. The Q value of a dielectric resonator is defined as the ratio between the energy stored per cycle to the energy dissipated per cycle.

Dielectric resonators are typically made of a ceramic type material having a high dielectric constant (ε_r = 20 to 90) and a low dissipative loss. These characteristics allow the dielectric resonator to store energy with relatively little internal energy

dissipation. This corresponds to a high Q value.

One significant limitation of the practical use of dielectric resonator filters is the cost of the dielectric itself. The cost of a typical prior art 6" ceramic dielectric cylindrical resonator can cost three hundred dollars or more. In addition, the size of the resonator substantially increases the size of any multi-cavity filter in which it might be employed.

The following patents are generally representative of typical prior art dielectric resonators: 4,757,289; 5,140,285; and, 5,356,844.

Resonators are typically employed in filters for the wireless communication industry. Such filters typically include a plurality of resonators located in adjacent cavities and coupled to each other through a variety of different means. One coupling mechanism known in the prior art is the use of a tunable iris as described in U.S. Patent 5,220,300 entitled "RESONATOR FILTERS WITH WIDE STOPBANDS" and issued on June 15, 1993 and assigned by Richard V. Snyder to RS Microwave Company, Inc., the entire contents and substance of which is incorporated herein by reference. Other cutoff means are also known, but few are known that would be suitable for composite resonators such

as described in this disclosure.

What is clearly missing in the prior art, therefore, is a relatively inexpensive resonator, of reasonably small size, that can be used in a multi-cavity filter

structure without appreciable loss in performance.

SUMMARY OF THE INVENTION

Briefly described, the invention comprises a composite resonator preferably including a cylindrical ceramic core and an exterior metal layer that surrounds most of the exterior circumference of the core and wherein the resonator resonates in substantially bound modes. This composite configuration is used to provide resonant frequencies lower than can be obtained using the same volume of dielectric alone and with higher unloaded Q than can be obtained using the same volume of metal imbedded into a cavity and used

as a resonator. An inexpensive metal, such as aluminum, can be substituted for more than half of the dielectric and still form a resonator with substantially equivalent resonance properties.

According to alternative embodiments of the invention, the resonators are incorporated into spectrum filters for separation of frequencies. As contrasted to conventional prior art implementations, the new technique achieves similar, or better,

electrical performance; similar, or reduced, size; and significantly reduced cost for applications in the frequency range below 2.5 Ghz, thus including PC, wireless, AMPS and GSM applications, as well as a myriad of other applications in this frequency range. With spectrum currently selling for up to $45.00 per Hz, filters are very valuable for providing users the opportunity to utilize all spectrum available. Yet, the cost of the filters must ultimately be borne by the users, so reductions in cost are important to commercial applications. The present invention in its various embodiments contributes to such a

reduction in cost.

These and other features of the invention will be more fully understood by

reference to the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a prior art ceramic resonator core. Fig. 2 is a perspective view of a prior art multi-cavity filter including four prior art ceramic resonators.

Fig. 3 a is a perspective view of a composite resonator that comprises a dielectric core surrounded by an exterior metal layer according to the preferred embodiment of the invention.

Fig. 3b is a vertical cross-sectional view of the preferred embodiment of the resonator shown in Fig. 3 a.

Fig. 3 c is a top cross-sectional view of the resonator according to the preferred embodiment as illustrated in Figs. 3a and 3b.

Fig. 4 is a perspective view of one embodiment of the invention showing the metal dielectric composite resonator according to the preferred embodiment utilized in a basic filter resonator having a ferrite or garnet disk, magnetically tunable in frequency.

Fig. 5 is a perspective view of an alternate embodiment illustrating two metal dielectric composite resonators according to the present invention, each with a window facing one another in their metallized circumference, thereby permitting coupling

of energy between the two resonators.

Fig. 6 is a perspective view of another alternate embodiment of the invention illustrating a coupled filter in which two metal dielectric composite resonators according to the present invention are coupled by means of a tunable iris. Figs. 7, 8 and 9 are perspective views of other alternative, hybrid embodiments illustrating cross coupled array filters in which four metal dielectric composite resonators according to the present invention are coupled by various means. Fig. 10 is a perspective view of another alternative embodiment illustrating a metal dielectric composite resonator according to the present invention employed in a dual mode filter configuration.

Fig. 1 la is a perspective view of an alternative embodiment of a resonator with a shape similar to the preferred embodiment shown in Figs. 3a - 3c but having a metallic core and an external layer of dielectric material surrounding most of the surface of the metallic core.

Fig. 1 lb is a vertical cross-sectional view of the alternative embodiment of the resonator shown in Fig. 11a. Fig. 11 c is a top cross-sectional view of the alternative embodiment of the resonator shown in Figs. 1 la and 1 lb.

Fig. 12 is a resonator characteristic graph providing an example of how a typical resonator, according to the preferred embodiment of the invention, is structured and designed.

DETAILED DESCRIPTION OF THE INVENTION

During the course of this description like numbers will be used to identify like elements according to the different figures that illustrate the invention.

Fig. 1 illustrates a typical prior art dielectric resonator. Such prior art resonators are typically relatively large and made of a single material, such as ceramic.

Because of their size they can be relatively expensive to manufacture. In addition, their larger size in turn dictates that any filter in which they are used will also be relatively large, and thus display undesirable spurious responses in close proximity to the resonant frequency of the resonator. See Fig. 2 for a typical prior art multi-cavity four-stage filter including four prior art dielectric resonators.

A composite resonator 10, according to the preferred embodiment of the invention, is illustrated in Figs. 3a - 3c. The preferred resonator 10 includes a ceramic core 12 surrounded by a metal layer 14 to form a "doughnut" or "hockey puck" shape. The core 12 includes a top surface or face 22, a bottom surface or face 24, and an interior sidewall surface or face 26. As best seen in Fig. 3b, the circumference 26 of the core 12 is surrounded by a sidewall metallic band or layer 18. The metallic layer 14 is, of course, the side layer 18. The metallic layer 14, i.e., ring 18, is preferably at least 2 - 3 skin depths thick or deep. Ring 18 can be much thicker but must be at least 2-3 skin depths to operate

properly. The term skin depth is well known in the prior art and defined as - . e

Fig. 4 illustrates a relatively simple, basic embodiment 30 in which the resonator 10 is employed as a filter. The resonator 10, which includes the core 12 and the surrounding metal layer 14, as described with regard to Figs. 3a - 3b, is located in a structure, or housing, 32 and fed by a conventional probe 36 supported at anchor point 34. The ε_r, and μ can be chosen to vary the characteristics of the resonator. The resonator 10

comprises a ferrite or garnet disk, magnetically tunable in frequency.

According to the preferred embodiment of the present invention, composite resonators are used in a resonator apparatus that operates in a substantially bound mode. In a substantially bound mode, the signal is essentially contained within the high dielectric material and is essentially non-radiating. This is due to the almost perfect reflecting boundary conditions resulting from both the selective use of conductive metallization on

the periphery and the critical angle of reflection at the non-metallized boundaries of high dielectric constant material (ε_r > 10, and typically ε_r = 24 or greater) with the low dielectric (ε_r = 1) air filling the enclosures. What is important is the ratio of dielectric constant filling the resonator to that filling the cavity, external to the resonator. To ensure almost perfect

reflection and thus resonance of substantially bound modes, the ratio should be at least 15:1. Examples of substantially bound modes function in this application are the TE_oln modes which exist substantially without leakage in the structure described herein. In the example mode, the subscripts refer to the number of circumferential, radial and longitudinal magnetic field variations (for the case of a cylinder).

The invention 10 is not limited to round doughnut shapes, as the principle also applies to planar configurations or parallelepiped resonator configurations. The invention also applies to planar configurations in which metal dielectric composites are used to form artificial dielectric screens for application to antennas and similar devices.

Substantially bound modes become unbound only at specific interfaces wherein coupling mechanisms such as irises, tuning screws, or other perturbations are present, and then only for purposes of enhancing coupling of a portion of the substantially bound mode to another structure such as another resonator or port. Figs. 5 - 10 depict such

coupling mechanisms in various combinations.

The foregoing invention is described primarily in the context of a cylindrical example. It should be understood, however, that it can operate in any of the recognized nine "separable geometries". "Separable geometries" is a term known in the prior art and is described, for example, in "Methods of Theoretical Physics", by Morse and

Feshbach, McGraw Hill, 1953. The geometries, which are included in the nine separable modes, are believed to be the only ones which can support more than one orthogonal mode simultaneously.

Fig. 5 illustrates a filter embodiment 40 housed in a structure 42 having a cavity 49 and a standard energy feed port 44. A first and a second composite resonator 46a and 46b are attached at opposite ends of the cavity 49. The first resonator 46a includes a small window 48a located in the metallic sidewall sufficient to expose the underlying dielectric core 12. Similarly, the second composite resonator 46b includes a window 48b in its metallic sidewall that faces window 48a of the first resonator 46a. Energy from the first resonator 46a is coupled through window 48a to window 48b of the second composite resonator 46b.

Another coupling embodiment 50 is illustrated in Fig. 6. Filter, or coupling, embodiment 50 comprises a housing structure 52 that includes a pair of cavities 60a and 60b. Energy is coupled into the cavity by a standard fitting 54. Cavity 60a includes a composite resonator 56a which sits atop a pedestal support 58. Similarly, a second composite resonator 56b sits atop a pedestal 58 in cavity 60b. In real life, all resonators 10 et seq. shown in Figs. 4 - 10 sit on pedestals like 58 but are not shown because they are well known in the prior art. Such pedestals, sometimes refeπed to as "toadstools", typically have a low ε (in range of 2 - 6) and are made of foam or B_eO. Partition, or wall, 62 separates cavity 60a from 60b. A window 64 is located in wall 62 and includes a tunable iris 66 for selectively coupling energy from composite resonator 56b to composite resonator 56a. A tunable resonator having an acceptable iris structure is described in U.S. Patent 5,220,300 issued on June 15, 1993 and assigned by Richard V.

Snyder to RS Microwave, Inc., Butler, New Jersey. A cross-coupled array filter 70 embodiment is illustrated in Fig. 7. The housing structure 72 includes a standard energy port 74 and defines a pair of interior cavities 78a and 78b. A first and a second composite resonator 76a and 76b, respectively, are located within cavity 78b. Similarly, a third and fourth composite resonator 76c and

76d are located within cavity 78a. A partition, or wall, 82 separates cavities 78a and 78b.

A pair of windows 82a and 82b is located in partition 82. Window 82a includes a tunable iris 84a. Likewise, window 82b includes a tunable iris 84b. Tunable irises 84a and 84b can be identical to those described in U.S. Patent 5,220,330. Energy from the first composite resonator 76a can be selectively coupled through iris 84a to the third composite resonator 76c. Likewise, energy from the second composite resonator 76b can be coupled through iris 84b to the fourth composite resonator 76d.

Fig. 8 illustrates another alternative embodiment 100 which is a combination, or hybrid, of the window and iris coupling mechanisms. As illustrated in Fig.

8, the combination embodiment 100 is housed in a structure 102 and includes a standard energy coupling 104. Housing 102 includes interior cavities 110a and 110b. Cavity 110b houses a first, second, and fourth composite resonator 106a, 106b and 106d, respectively.

Cavity 110a houses third composite resonator 106c. The second and fourth resonators

106b and 106d each include a window 108b and 108d, respectively, which face each other and which couple energy from the second composite resonator 106b to the fourth composite resonator 106d in the manner previously described with reference to Fig. 5. The interior cavity 110a is defined by right angle panels or partitions 112 and 114, respectively.

Panel 112 includes a window 116 and a tunable iris 118, similar to that described in U.S.

Patent 5,220,300 for coupling energy from the first composite resonator 106a to the third composite resonator 106c. Similarly, panel 114 includes a window 120, and a tunable iris 122, for selectively coupling energy from the fourth composite resonator 106d to the third composite resonator 106c.

Another combination or hybrid coupling embodiment 150 is illustrated in Fig. 9. The resonators are located within a housing structure 152 which includes the standard energy port 154. Housing 152 defines a single interior cavity 160 which houses a first, second, third and fourth composite resonator 156a, 156b, 156c and 156d, respectively. The second and fourth composite resonators 156b and 156d each include windows, or apertures, 158b and 158d, respectively, which couple energy from the second composite resonator 156b to the fourth composite resonator 156d. A partition, or wall, 162 separates the first composite resonator 156a from the third composite resonator 156c. A window 164 is located in the wall 162 and includes a tunable iris 166, similar to that described in U.S. Patent 5,220,300 for coupling energy from the first composite resonator 156a to the third composite resonator 156c. Fig. 10 illustrates a single resonator 204, dual mode, configuration 200 that takes advantage of the fact that substantially bound modes become unbound where perturbations are present. The resonator 204 has a distinctly rectangular shape and is located within housing 202. It is feed energy by a conventional probe 206 and includes a rectangular dielectric core 208 partially, but not entirely, surrounded by a metallized peripheral layer 210. A three-dimensional orthogonal notch 212 is taken out of one corner of the composite resonator 204. The notch 212 provides for coupling of dual TM_π modes in the resonator 204. A high dielectric constant structure can support more than one bound mode simultaneously, either as degenerate (i.e., field orthogonal, but resonant, at the same frequency) or as separate modes separated in the frequency domain. Consequently, multimode filter configurations are attainable, as depicted in Fig. 10.

As depicted in each of Figs. 4-10, the structure of the apparatus's enclosure is too small to be resonant at frequencies at or below that of the high dielectric constant structure. Consequently, the enclosure is not a fundamental resonator in itself, but rather is below cutoff (i.e. only propagation of evanescent modes is possible within the enclosure, external to the high dielectric constant structure).

A composite resonator element 300, according to an alternative embodiment of the invention, is illustrated in Figs. 11a - l ie. The size and shape of

resonator 300 is essentially the same as the prefeπed embodiment 10 shown in Figs. 3a - 3c except with the metallic and dielectric materials reversing roles and positions. Accordingly, the alternative resonator 300 includes a metallic core 312 surrounded by a dielectric layer 314 to form a "doughnut" or "hockey puck" shape. The metallic core includes a top surface or face 322, a bottom surface or face 324 and an interior sidewall surface or face 326. As best seen in Fig. 1 lb, the circumference 326 of metallic core 312 is suπounded by a sidewall dielectric band or layer 318. The dielectric layer 314 is, therefore, composed of the sidewall band or layer 318.

Example 1 :

For comparison purposes, a calculation was made with the standard Trans-

Tech Dielectric Resonator Design package (available from Trans-Tech, 552 Adamstown

Road, Adamstown, Maryland 21710) for a conventional prior art resonator with an ε =80 to obtain a desired frequency of 0.733 GHz. The ultimate dielectric required a width of

1.940" by 0.873". The volume then is πr²h = 2.58in³. In contrast, using commercial available Mathcad™ 7 program distributed by MathSoft, Inc., 101 Main Street, Cambridge, Massachusetts 02142, the following calculations were obtained:

Structure Inputs: radius in inches a : = .784 height in inches d : = .63

relative permittivity of dielectric ε_r : = 80 conductivity of metal met : = 3 metal = 1 aluminum .3817 = 2 silver .6173 = 3 copper .58 relative permittivity of metal μmet : = .9999736 cut plane distance zd : = 1 d

(decimal percentage of total height)

Field Plot Inputs:

Choose a value [0, 1] for TE: TE : = 1

TE=1 for TE calculations TE=1 for TM calculations check : "Enter in a 0 or 1 value only" if TE>1 "okay" otherwise

check = "okay"

Choose Mode number

N is the number of circumferential variations in the field N : = 0 M : = l L : = l

M is the number of radial variations

L is the number of axial variations check : "Enter in a L>=1" ifL<l "Enter in a M>l" ifM<l TE_nml=root_NM "EnterinaM>=l" ifM<l TE ^■^„n_mrnl, root NM "okay" otherwise

TM_φ„=root_NM check = "okay"

Define cutplane for field plots: Option 1 - φ cut with φ = 90° option : = 3

Option 2 - φ cut with ψ = 0° Option 3 - Z cut with 0<z<d

Constants: ε0: = 8.854187817-10 12 μ0 4-π- 10 j:=V-l

Calculate Bessel function:

guess (n,r) : = π r +

TOL:= 10

jn(n,x) : = root( Jn(n,x),x)

jroot(n,r) : = jn (n,guess(n,r))

range variables: n : = 0..4 m: = l ..4

roots_nm:=jroot(n,m) roots_NW= 2.405

0 2.405 5.52 8.654 11.792

0 3.832 7.016 10.173 13.324 roots = 0 5.136 8.417 11.62 14.796

0 6.38 9.761 13.015 16.223

0 7.588 11.065 14.373 17.616 guess (n,m) : = π •

TOL:= 10

f d ^ j'n(n,x): = root — Jn(n,x),x j'0(x): = root(-Jl(x),x) y x )

j'root(n,m): = if(n = 0,j'0(guess(l,m)),j'n(n,guess(n-l,m))) ^r°ots'_n,m:=j'root(n,m)

^f 0 3.832 7.016 10.173 13.324 ^Λ 0 1.841 5.332 8.535 11.705 roots' = 0 3.056 6.707 9.97 13.168 roots'_NM = 3.832 0 4.199 8.016 11.346 14.581 0 5.318 9.285 12.682 15.964 J

Parti: Calculate Cutoff Frequency:

- 1

Part 2: Calculate Resonant Frequency: roots ' N ,M L • π if TE = 1

4 • π acm dcm

roots ² ( L - 7τ ²

+ if TE ≠ 1

4 • π acm v dcm

fres = 7.332^»10⁸

Here the volume is πr²h = 1.21 in³. Therefore, the metal ring resonator 10

has 1.21/2.58 = 47% of the volume of a conventional all dielectric resonator as shown in

Fig. 1 with the same εr = 80.

While the invention has been described with reference to the prefened embodiment thereof, it will be appreciated by those of ordinary skill in the art that various modifications can be made to the structure and function of the individual parts of the system without departing from the spirit and scope of the invention as a whole.

Claims

WE CLAIM:

1. A resonator apparatus ( 10) that resonates in a substantially bound mode for use inside of a structure having at least one cavity, said resonator comprising: a dielectric core (12) having an exterior surface with at least two faces (22, 24, 26); and, a metallic layer (14) covering substantially all of at least one face ( 18), wherein said resonator (10) resonates in the substantially bound mode.

2. The apparatus of claim 1 wherein said dielectric core (12) comprises a ceramic material.

3. The apparatus of claim 1 wherein said dielectric core (12) has a substantially cylindrical shape having two end faces (22, 24) and a side face (26) and wherein said side face (26) is substantially covered by said metallic layer (18).

4. The apparatus of claim 1 wherein said metallic layer (14) comprises a metal selected from the group consisting of gold, silver and copper.

5. The apparatus of claim 3 wherein said metallic layer (14) is sputtered on said side face (26).

6. The apparatus of claim 3 wherein said metallic layer (14) comprises a solid ring of metal.

7. The apparatus of claim 3 wherein said metallic layer (14) comprises a sandwich of copper, silver and gold.

8. The apparatus of claim 1 wherein said structure comprises a multi-cavity structure (50, 70, 100, 150, 200) and wherein each of said cavities in said multi-cavity structure includes at least one resonator (10).

9. The apparatus of claim 1 further comprising: means for producing a disturbance (212) on one of said exterior faces of said dielectric core (208),

wherein said resonator (204) resonates at at least two peak frequencies and wherein said resonant frequency is below the normal cutoff resonant frequency of said cavity.

10. The apparatus of claim 1 wherein none of the said at least one cavity (49, 60a, 60b, 78a, 78b, 110a, 110b, 160) is a fundamental resonator.

11. A dielectrically loaded metal resonator (10) that resonates in a substantially bound mode, said resonator comprising:

a dielectric core (12) having an exterior surface; and, a metallic layer (14) covering a substantial portion of the exterior surface (22, 24, 26), wherein said resonator resonates in the substantially bound mode.

12. The apparatus of claim 11 wherein said dielectric core comprises a ceramic

material.

13. The apparatus of claim 12 wherein said substantially bound mode comprises a mode of resonance selected from the group consisting of transverse magnetic (TM),

transverse electric (TE) and a hybrid of TM and TE modes. 14. The apparatus of claim 11 wherein said metallic layer (14) further functions

as a heat sink.

15. A resonator apparatus (10) that resonates in a substantially bound mode,

said resonator comprising: a metallic core having an exterior surface; and, a dielectric layer covering a substantial portion of the exterior surface, wherein said resonator resonates in the substantially bound mode.

16. A resonator apparatus (30) comprising at least a first resonator (10) that resonates in a substantially bound mode for use inside of a structure (32) having at least one cavity, said first resonator comprising:

a dielectric core (12) having an exterior surface with at least two faces; and, a metallic layer (14) covering substantially all of at least one face (22, 24, 26), wherein said first resonator resonates in a substantially bound mode. 17. The apparatus of claim 16 further comprising: a second resonator (46b) in addition to said first resonator (46a), both located within said structure (42), wherein said first and second resonators (46a, 46b) each have windows (48a, 48b) in said metallic layers (14) and further wherein the windows (48a, 48b) in said resonators (46a, 46b) face each other so as to couple energy from said first resonator (46a)

to said second resonator (46b).

18. The apparatus of claim 16 further comprising: a second resonator (56b) in addition to said first resonator (56a), each resonator comprising a dielectric core (12) and an exterior surface with at least two faces,

and a metallic layer covering substantially all of at least one face, wherein said first resonator (56b) is located in a first cavity (60b) in said

structure and said second resonator (56a) is located in a second cavity (60a) in said structure (50) separated from said first cavity (60b) by a tunable iris (66), whereby energy from said first resonator (56b) is selectively coupled to said second resonator (56a).

19. The apparatus of claim 16 further comprising a second (76b), third (76c), and fourth (76d) resonator in addition to said first resonator (76a), each resonator comprising a dielectric core having an exterior surface with at least two faces, and a metallic layer covering substantially all of at least one face, wherein said first (76a) and second (76b) resonators are located in a first cavity (78b) in said structure (72) and said third (76c) and fourth (76d) resonators are located in a second cavity (78a) in said structure (70) and wherein a tunable (84a) iris is located between said first (76a) and third (76c) resonators and a second tunable iris (84b) is located between said second (76b) and fourth (76d) resonators, whereby energy is coupled from said first resonator (76a) to said third (76c) resonator and from said second (76b) resonator to said fourth (76d) resonator selectively through said tunable irises (84a,

84b). 20. The apparatus of claim 16 further comprising: a second (106b), third (106c), and fourth (106d) resonator in addition to said first resonator (106a), each resonator comprising a dielectric core having an exterior surface with at least two faces, and a metallic layer covering substantially all of at least one

face, wherein said first (106a), second (106b) and fourth (106d) resonators are located in a first cavity (110b) and said third resonator (106c) is located in a second cavity

(110a), and said second (106b) and fourth resonators (106d) include windows (108b, 108d) in their metallic layers facing each other so as to couple energy from said second resonator (106b) to said fourth resonator (106d), and said first resonator (106a) is separated from said third resonator (106c) by an intervening tunable iris (118) which couples energy from said first resonator (106a) to said third (106c) resonator.

21. The apparatus of claim 16 further comprising: a second (156b), third (156c) and fourth (156d) resonator in addition to said first resonator (156a), each resonator comprising a dielectric core having an exterior surface with at least two faces, and a metallic layer covering substantially all of at least one

face, wherein said second (156b) and fourth (156d) resonators each include windows (158b, 158d) in their metallic layers facing each other so as to couple energy from said second resonator (156b) to said fourth (156c) resonator, and, wherein said first (156a) resonator is separated from said third (156c) resonator by a barrier (162) which includes a tunable iris (166) therein for selectively coupling energy from said first (156a) resonator to said third (156c) resonator. 22. The apparatus of claim 16 wherein said dielectric core (208) has a

substantially rectangular shape having at least four corners, and, wherein at least one of said corners includes a notch (212) for coupling dual

TM_π modes, wherein said resonator resonates in at least two modes.

AMENDED CLAIMS

[received by the International Bureau on 17 January 1999 (17.01.99); original claims 1 ,1 1 ,13 and 16. amended; remaining claims unchanged (5 pages)]

1. A resonator apparatus (10) that resonates in a substantially bound mode for use inside of a structure having at least one cavity, said resonator comprising: a dielectric core (12) having an exterior surface with at least two faces (22, 24, 26); and, a metallic layer (14) covering substantially all of at least one face (18), wherein said resonator (10) resonates in a substantially bound mode selected from the group consisting of the form of TE_01n and TM_{l ln}.

6. The apparatus of claim 3 wherein said metallic layer (14) comprises a solid ring of metal. 7. The apparatus of claim 3 wherein said metallic layer ( 14) comprises a sandwich of copper, silver and gold.

9. The apparatus of claim 1 further comprising: means for producing a disturbance (212) on one of said exterior faces of said dielectric core (208), wherein said resonator (204) resonates at at least two peak frequencies and wherein said resonant frequency is below the normal cutoff resonant frequency of said cavity.

11. A dielectrically loaded metal resonator (10) that resonates in a substantially bound mode, said resonator comprising: a dielectric core (12) having an exterior surface; and, a metallic layer (14) covering a substantial portion of the exterior surface (22, 24,

26), wherein said resonator resonates in a substantially bound mode selected from the

group consisting of the form of TE_01π and TM_nn.

12. The apparatus of claim 11 wherein said dielectric core comprises a ceramic material. 13. The apparatus of claim 12 wherein said substantially bound mode comprises a

mode of resonance selected from the group consisting of said transverse magnetic TM_{l lτι}, said

transverse electric TE_01n and a hybrid of said TM_{l ln} and TE_01n modes.

14. The apparatus of claim 11 wherein said metallic layer (14) further functions as a heat sink.

15. A resonator apparatus (10) that resonates in a substantially bound mode, said resonator comprising: a metallic core having an exterior surface; and, a dielectric layer covering a substantial portion of the exterior surface, wherein said resonator resonates in the substantially bound mode.

16. A resonator apparatus (30) comprising at least a first resonator (10) that resonates in a substantially bound mode for use inside of a structure (32) having at least one cavity, said first resonator comprising: a dielectric core (12) having an exterior surface with at least two faces; and, a metallic layer (14) covering substantially all of at least one face (22, 24, 26), wherein said first resonator resonates in a substantially bound mode selected from the group

consisting of the form of TE_0]n and TM_Un.

17. The apparatus of claim 16 further comprising: a second resonator (46b) in addition to said first resonator (46a), both located within said structure (42), wherein said first and second resonators (46a, 46b) each have windows (48a, 48b) in said metallic layers (1 ) and further wherein the windows (48a, 48b) in said resonators (46a, 46b) face each other so as to couple energy from said first resonator (46a) to said second resonator (46b).

18. The apparatus of claim 16 further comprising: a second resonator (56b) in addition to said first resonator (56a), each resonator comprising a dielectric core (12) and an exterior surface with at least two faces, and a metallic layer covering substantially all of at least one face, wherein said first resonator (56b) is located in a first cavity (60b) in said structure and said second resonator (56a) is located in a second cavity (60a) in said structure (50) separated from said first cavity (60b) by a tunable iris (66), whereby energy from said first resonator (56b) is selectively coupled to said second resonator (56a).

19. The apparatus of claim 16 further comprising a second (76b), third (76c), and fourth (76d) resonator in addition to said first resonator (76a), each resonator comprising a dielectric core having an exterior surface with at least two faces, and a metallic layer covering substantially all of at least one face, wherein said first (76a) and second (76b) resonators are located in a first cavity (78b) in said structure (72) and said third (76c) and fourth (76d) resonators are located in a second cavity (78a) in said structure (70) and wherein a tunable (84a) iris is located between said first (76a) and third (76c) resonators and a second tunable iris (84b) is located between said second (76b) and fourth (76d) resonators, whereby energy is coupled from said first resonator (76a) to said third (76c) resonator and from said second (76b) resonator to said fourth (76d) resonator selectively through said tunable irises (84a, 84b).

20. The apparatus of claim 16 further comprising: a second (106b), third (106c), and fourth (106d) resonator in addition to said first resonator ( 06a), each resonator comprising a dielectric core having an exterior surface with at least two faces, and a metallic layer covering substantially all of at least one face, wherein said first (106a), second (106b) and fourth (106d) resonators are located in a first cavity (110b) and said third resonator (106c) is located in a second cavity (110a), and said second (106b) and fourth resonators (106d) include windows (108b, 108d) in their metallic layers facing each other so as to couple energy from said second resonator (106b) to said fourth resonator (106d), and said first resonator (106a) is separated from said third resonator (106c) by an intervening tunable iris (118) which couples energy from said first resonator (106a) to said third (106c) resonator.

21. The apparatus of claim 16 further comprising: a second (156b), third (156c) and fourth (156d) resonator in addition to said first resonator (156a)_s each resonator comprising a dielectric core having an exterior surface with at least two faces, and a metallic layer covering substantially all of at least one face, wherein said second (156b) and fourth (156d) resonators each include windows (158b, 158d) in their metallic layers facing each other so as to couple energy from said second resonator (156b) to said fourth (156c) resonator, and, wherein said first (156a) resonator is separated from said third (156c) resonator by a barrier (162) which includes a tunable iris (166) therein for selectively coupling energy from said first (156a) resonator to said third (156c) resonator.

22. The apparatus of claim 16 wherein said dielectric core (208) has a substantially rectangular shape having at least four corners, and, wherein at least one of said corners includes a notch (212) for coupling dual TM_π modes, wherein said resonator resonates in at least two modes.