CERAMIC MONOBLOCK FILTER WITH METALLIZATION PATTERN PROVIDING INCREASED POWER LOAD HANDLING

Cross-Reference to Related Application This application claims the benefit of the filing date of U.S. Provisional

Application Serial No. 60/934,863 filed on June 15, 2007, which is explicitly incorporated herein by reference as are all references cited therein.

Field of the Invention This invention relates to electrical filters and, in particular, to a dielectric ceramic monoblock filter which incorporates a metallization pattern on the top surface thereof adapted and structured to provide an increase in a filter's power load handling capability.

Background of the Invention

Ceramic dielectric block filters offer several advantages over air- dielectric cavity filters. The blocks are relatively easy to manufacture, rugged, and relatively compact. In the basic ceramic block filter design, resonators are formed by cylindrical passages called through-holes which extend between opposed top and bottom surfaces of the block. The block is substantially plated with a conductive material (i.e., metallized) on all but one of its six (outer) sides and on the interior walls of the resonator through-holes. The top surface is not fully metallized but instead bears a metallization pattern designed to couple input and output signals through the series of resonators. In some designs, the pattern may extend to the sides of the block, where input/output electrodes or pads are formed.

The reactive coupling between adjacent resonators is dictated, at least to some extent, by the physical dimensions of each resonator, by the orientation of each resonator with respect to the other resonators, and by aspects of the top surface metallization pattern.

Although such RF signal filters have received widespread commercial acceptance since the 1970s, efforts at improvement on this basic design have continued to the present.

For example, there continues to exist a need to increase power- handling capabilities of ceramic filters for higher power applications.

Currently, increasing the ceramic body size and/or the top pattern gaps to their maximum is the primary method used to increase the power handling capability of monoblock filters. Increasing the gaps in some cases, however, reduces the electrical performance of the filter and creates manufacturing sensitivity issues. Moreover, and where size and space is a limitation, increasing the size of the ceramic body is not an option.

Therefore, the need continues for an improved RF monoblock filter which can offer improved and increased power handling capabilities without either an increase in the size of the filter or an increase in the size of the gaps in the top metallization pattern.

Summary of the Invention

It is a feature of the invention to provide a ceramic monoblock filter comprising a block of dielectric material defined by top, bottom, and side surfaces wherein the side and bottom surfaces are substantially covered with a conductive material.

A plurality of spaced-apart resonators are defined by a plurality of spaced-apart resonator through-holes extending between the top and bottom surfaces of the block and surrounded on the top surface by conductive material defining conductive resonator plates. A pattern of conductive material on the top surface defines at least an input/output transmission line defined by a first elongate strip of conductive material extending on the top surface between, and spaced from, first and second ones of the plurality of resonators.

The pattern additionally defines a bar on the top surface defined by a second strip of conductive material. The bar extends above and is spaced from the resonator plates defining the first and second resonators. The bar is

located generally opposite and spaced from a top edge of the input/output transmission line.

The pattern still further defines a ground plate defined by one or more additional strips of conductive material on the top surface. The ground plate is coupled to the conductive material covering the side surfaces and is located generally opposite and spaced from the bar.

In one embodiment, the ground plate and the bar include respective interdigitated extension strips of conductive material defining a load splitting capacitor between the bar and the ground plate. In one embodiment, the respective interdigitated spaced-apart extension strips are generally spiral- shaped.

The input/output transmission line and the bar may additionally define respective interdigitated spaced-apart extension strips of conductive material defining a load splitting capacitor between the bar and the input/output transmission line.

Additional load splitting capacitors may be defined by extending terminal end portions of the bar over respective portions of the first and second resonators.

There are other advantages and features of this invention, which will be more readily apparent from the following detailed description of preferred embodiments of the invention, the drawings, and the appended claims.

Brief Description of the Drawings

These and other features of the invention can best be understood by the following description and the accompanying FIGURES as follows:

FIGURE 1 is an enlarged perspective view of a ceramic monoblock filter incorporating the features of the present invention;

FIGURE 2 is a top plan view of the top face of a filter incorporating a prior art input port capacitive loading metallization pattern; FIGURE 3 is an enlarged top plan view of the metallization pattern on the top surface of the ceramic monoblock filter shown in FIGURE 1 ;

FIGURE 4 is an enlarged, broken, top plan view of the input port capacitive loading metallization pattern of the filter shown in FIGURE 1 ;

FIGURE 5 is a schematic of the electrical circuit defined by the input port metallization pattern of the prior art filter shown in FIGURE 2;

FIGURE 6 is a schematic of the electrical circuit defined by the input port metallization pattern of the filter of the present invention shown in FIGURES 1 and 4;

FIGURE 7 is a graph depicting the power handling characteristics of the prior art filter of FIGURE 2;

FIGURE 8 is a graph depicting the power handling characteristics of the filter of FIGURE 1 ; FIGURE 9 is a graph comparing the performance characteristics of the filters of FIGURES 1 and 2; and

FIGURE 10 is a graph comparing the delay characteristics of the filters of FIGURES I and 2.

Detailed Description of the Preferred Embodiment

While this invention is susceptible to embodiment in many different forms, this specification and the accompanying FIGURES disclose only one preferred form as an example of the invention. The invention is not intended to be limited to the embodiment so described, however. The scope of the invention is identified in the appended claims.

FIGURES 1 , 3, and 4 show a preferred embodiment of a filter 100 which incorporates the increased and improved power handling metallization pattern features of the present invention.

Filter 100 includes a block 110 composed of a dielectric material and selectively plated with a conductive material. Block 110 has a top surface or face 112, a bottom surface (not shown) and four side surfaces or faces 116, 117, 120, and 122. Filter 100 can be constructed of a suitable dielectric material that has low loss, a high dielectric constant, and a low temperature coefficient. The plating or material on block 110 is electrically conductive, preferably copper, silver or an alloy thereof. Such plating or material preferably covers all surfaces of the block 110 to define ground with the

exception of top surface 112, the plating of which is described in some detail below.

In the embodiment of FIGURES 1 , 3, and 4 block 110 includes eight (8) through-holes 101 , 102, 103, 104, 105, 106, 107, and 108 (101-108), each extending from the top surface 112 to the bottom surface (not shown). The interior walls defining through-holes (101-108) are likewise plated with an electrically conductive material. Each of the plated through-holes 101-108 is essentially a transmission line resonator/pole comprised of a short-circuited coaxial transmission line having a length selected for desired filter response characteristics. For an additional description of the through-holes 101-108, reference may be made to U.S. Patent No. 4,431 ,977, to Sokola et al. Although block 110 is shown with eight plated through-holes 101-108, the present invention is not so limited and encompasses filters with more or fewer through-holes. Top surface 112 of block 110 defines opposed peripheral longitudinal edges 130 and 133, opposed peripheral side edges 115 and 119, and is selectively plated with an electrically conductive material similar to the plating on block 110. The selective plating includes and defines respective RF signal input-output (I/O) transmission lines/ pads/plates, specifically input electrode/port/line 114 and output electrode/port/line 118. Also included are conductive resonator plates 121 , 122, 123, 124, 125, 126, 127, and 128 (121- 128) that surround respective through-holes 101 , 102, 103, 104, 105, 106, 107, and 108 and in combination define respective resonators. Each of the plates 121 , 122, 123, 124, 125, 126, 127, and 128 are separated by regions devoid of conductive material and each defines respective opposed and spaced-apart plate edges such as, for example, as depicted in FIGURE 3 which identifies edge 126A of plate 126, edge 127A of plate 127 and unmetallized region 112A therebetween.

Top surface 112 additionally defines at least four ground plates 131 , 132, 134, and 135. Plates 121-128 are used to capacitively couple the transmission line resonators, provided by the plated through-holes 101-108, to ground plating or strips 131 , 132, 134, and 135 which are coupled to the ground material which covers the respective side and bottom surfaces.

Portions of plates 121-128 also couple the associated resonators of through- holes 101-108 to the input electrode 114 and the output electrode 118.

Ground plate or strip 131 is located on the top filter surface 112 and extends along a central portion of the peripheral lower edge of top surface 112 generally longitudinally between the input and output ports 114 and 118. Opposed terminal ends of plate 131 are spaced from the ports 114 and 118. Ground plate 132 is also located on the filter top surface 112 and extends generally longitudinally along the lower edge of top surface 112 generally between the edge of side surface 120 and the output port 118. Plate 132 is spaced from the port 118. Ground plate 134 is located on the top filter surface 112 and extends along the lower edge of surface 112 generally between the edge of opposed side surface 122 and the input port 114. Plate 134 is spaced from the port 114. Ground plate or strip 135 is located on the top surface 112 and extends the full length of the filter along the top longitudinal edge 133 of the filter 100.

Coupling between the transmission line resonators, provided by the plated through-holes 101-108, is accomplished at least in part through the dielectric material of block 110 and is varied by varying the width of the dielectric material and the distance between adjacent transmission line resonators. The width of the dielectric material between adjacent through- holes 101-108 can be adjusted in any suitable regular or irregular manner as is known in the art, such as, for example, by the use of slots, cylindrical holes, square or rectangular holes, or irregular-shaped holes.

The present invention is directed to the metallization pattern on the top surface 112 of filter 100 and, more specifically, the portion of the metallization pattern in the region of the input pad or port 114 which, as described in more detail below, is adapted to improve input capacitive coupling to ground which, in turn, increases the power load characteristics and abilities of the filter.

Referring to FIGURE 4, it is understood that input transmission port or pad or line 114 is defined by an elongate strip of metallized/conductive material which bridges the top and side surfaces 112 and 118 respectively. More specifically, input port 114 defines a first portion of a strip of conductive material located on the side surface 118; a second strip which wraps around

and bridges the edge between side surface 118 and top surface 112; and a third elongate strip portion which extends generally between and spaced from the metallized resonator plates 127 and 128. Input port or pad 114 preferably extends in a relationship spaced from and parallel to the resonator plates 127 and 128 and a relationship generally transverse to the top lower and upper longitudinal filter edges 130 and 133 respectively.

In the particular embodiment of FIGURES 1 and 4, the input pad 114 additionally defines strips of metallized material defining a plurality of fingers 136, 138, and 140 extending generally perpendicularly outwardly from opposed sides of the top portion of input pad 114 extending between respective resonator plates 127 and 128. Fingers 136, 138, and 140 are interdigitated into (i.e., protrude into) respective grooves 142, 144, and 146 defined in respective resonator plates 127 and 128. The grooves 142, 144, and 146 of course define regions devoid of metallized material. The fingers 136, 138, 140 are spaced from the metallized material defining the plates 122 and 128.

The top portion of input pad 114 extending between respective resonator plates 127 and 128 still further defines a central elongate groove 142 defining a fork having at least two tines 144 and 146 extending in a direction generally perpendicular to the upper top longitudinal filter edges 130 and 133. Groove 142 defines a region devoid of conductive material.

The metallization pattern on the input side of the filter 100 is still further defined by an elongate strip or bar 148 of metallized conductive material located above the respective resonator plates 127 and 128 and extending in an orientation and placement generally parallel to and spaced from the upper edges of respective resonator plates 127 and 128. Bar 148 extends in a direction parallel to the lower and upper longitudinal filter edges 130 and 133.

Bar 148 more specifically defines a central portion and respective opposed terminal end portions 150 and 152. The central portion is located and positioned generally opposite the ends of bar tines 144 and 146, and the respective end portions 150 and 152 extend and overlie at least about 1/4 of the length of the respective resonator plates 127 and 128 in a generally

spaced-apart and parallel relationship thereto. Bar 148 is spaced from the top of the plates 127 and 128.

Resonator plate 127 additionally defines a strip or finger or extension 154 of metallized conductive material protruding generally perpendicularly outwardly and upwardly from the top longitudinal edge thereof in a generally transverse relationship to the bar 148 and spaced from the terminal end portion 150 of bar 148. The resonator plate 128 in turn defines an upper shoulder 156 which is spaced from the opposed terminal end portion 152 of bar 148. Bar 148 still further defines a generally centrally located elongate first extension or strip or finger 157 of metallized conductive material extending generally perpendicularly outwardly and downwardly from a lower edge of the bar 148. Extension 157 is interdigitated into (i.e., protrudes into) the elongate groove 142 defined in the top portion of input pad 114. Extension 157 is spaced from the conductive material defining input pad 114.

Bar 148 still further defines a pair of second and third elongate metallization extensions/strips/fingers 158 and 160 protruding and extending generally perpendicularly upwardly and outwardly from a top longitudinal edge of each of the respective bar terminal end portions 150 and 152. Bar extensions 158 and 160 are oriented and located relative to each other in a spaced-apart, parallel relationship. A pair of further metallization extensions/strips/fingers 162 and 164 protrude generally normally inwardly from the opposed respective inner edges of bar extensions 158 and 160. Extensions 162 and 164 define bent, curved, or spiral-shaped fingers. Bar 148 still further defines a plurality of grooves 166, 168, and 170 protruding into the top edge thereof and extending along the length thereof in a generally spaced-apart and parallel relationship. Grooves 166, 168, and 170 define regions devoid of conductive material.

The metallization pattern in accordance with the present invention still further comprises a grounded plate extension 172 composed of one or more strips or bars or extensions or fingers of metallized material on the top filter surface 112 which protrude unitarily inwardly and outwardly from the grounding plate 135 extending along the top edge 133 of filter 100.

The grounded plate extension 172 is located generally opposite and spaced from the bar 148. In the embodiment of FIGURES 1 and 4, grounded plate extension 172 is defined by respective strips 174, 176, and 178 of metallized material which in combination define an "I-beam" shaped metallization pattern. Strip 174 is a unitary, integral extension of plate 135, extends along the top filter edge 133 of filter 100 and preferably has a width greater than the width of the ground plate 135. Strip 178 is spaced from the strip 174 and is intercoupled thereto by the strip 176 which extends therebetween in a generally transverse relationship. In accordance with the present invention, grounded plate extension

172 and, more specifically, strips 174 and 178 thereof, are spaced and split from the bar 148.

Grounded plate extension 172 is still further defined by a pair of strips, extensions, or fingers of metallized material extending downwardly and inwardly from opposed terminal end portions of the strip 174 and defining respective curved or spiral-shaped terminal fingers 180 and 182 which, in the embodiment shown, are similar in shape and configuration to, but mirror images of, the fingers 162 and 164 defined on bar 148.

Spiral-shaped fingers 162 and 164 and fingers 180 and 182 are respectively meshed/interwoven/interconnected/interdigitated together in a spaced-apart relationship and are separated and surrounded by regions devoid of conductive material so as to define an indirect capacitive coupling between the bar 148 and ground plate 135 as described in more detail below. In the embodiment of FIGURE 4, grounded plate extension 172 is located generally in the space defined between the fingers 158 and 160 of bar 148 in a relationship wherein the strip 178 of grounded plate extension 172 is spaced from and parallel to the bar 148; tabs or fingers 200 on strip 178 are interdigitated into (i.e., protrude into) the respective grooves 166, 168, and 170 defined in bar 148 in a relationship spaced from the conductive material defining the bar 148 and the fingers 180 and 182 of grounded plate extension 172 are spaced from the respective fingers 158 and 160 of bar 148. Taps 200 extend generally normally outwardly from the strip 178.

Top surface 112 defines an additional strip 202 of conductive material extending normally inwardly from the top ground plate 135. Strip 202 is located between and spaced from bar extension 160 on one side and the left side edge of resonator plate 128 on the other side. Strip 202 and bar extension 160 are disposed relative to each in a parallel relationship.

By way of background, it is known that the power handling of filters is directly related to the component with the greatest increase in stored energy. In ceramic monoblock filters, the circuit pattern incorporated onto the ceramic block forms capacitors to ground and capacitors between resonators. The capacitors with the most stored energy are the components with the greatest likelihood of arcing from high power. The input pad metallization pattern of the present invention increases the power handling of ceramic monoblock filters by modifying the components with the greatest chance of arcing. This is done by splitting the stored energy among two or more series connected capacitors.

Illustration A below shows a 1 Farad capacitor with 1 volt applied. In this example, the stored energy "E" is equal to the 1/2 CV ² . This calculates to (1/2)*(1 F)*(1 V) = 1/2 Joule. If the circuit of Illustration A is changed to the equivalent electrical circuit shown in Illustration B, the arcing potential is reduced.

Illustration A

V = 1 Volt

C = 1F

In Illustration B below, the total stored energy in the circuit is still 1/2 Joule. However, the stored energy in each of the capacitors (C 1 and C2) is equal to 1/2 C1*V1 ² = 1/2 C2*V2 ² . This calculates to (1/2) ^* (2F) ^* (1/2) ² = 1/4 Joule. Each capacitor now has 1/2 the stored energy of the Illustration A capacitor. Note that the stored energy is related to the squared voltage (V ² ).

In electromagnetic theory, the electric field strength is directly related to the voltage. Arcing occurs when the electric field strength increases such that the breakdown voltage of air (29000V/cm) is exceeded, creating a conductive path between the two metallic plates of the capacitor. The breakdown of air has units of volts-per-centimeter which, of course, means that the spacing of the capacitive plates is an important variable in arcing. As the capacitive plates are moved closer together, the probability of arcing increases.

llustration B

V1 = - 1/2 Volt V2.= = 1/2 Volt

C1 = 2 F C2 = 2 F

The Illustration B capacitive values are greater than the Illustration A capacitor value. The larger the capacitive value, the closer the metallic plates have to be located. This decreases the power handling. However, where space permits on the monoblock filter, the plate's surface area can be increased to maintain the desired capacitive value and still keep the wider plate spacing. The wide plate spacing in combination with the lower capacitive stored energy can increase the power handling of a filter.

In accordance with the present invention and referring to FIGURES 4 and 6 in particular, it is understood that input transmission line or port 114, resonators 127 and 128, and grounded plate extension 172 in combination define multiple sources of capacitive loading to the input transmission line or port 114 via the power load distribution bar 148. More specifically, it is understood that the polarity of ground extension plate 172 is negative and that the polarity of the input pad 114 is positive. When a load is applied to the filter 100, the polarity of the metallization pattern defining bar 148 will change to positive. Because the bar 148 is capacitively loaded to multiple sources as described above, the effect is the same as directly loading the

input to ground as is known in the art and shown in the input port metallization pattern 302 of the prior art filter 300 shown in FIGURE 2.

FIGURE 5 is a schematic diagram of the electrical methodology and circuit of the input metallization pattern 302 of the prior art filter 300. FIGURE 6 is a schematic diagram of the splitting electrical methodology and circuit of the input metallization pattern of the present invention.

The metallization pattern in accordance with the present invention, however, affords the advantage of facilitating the distribution of the power load over the full length of the bar 148, thus increasing the amount of power load which the filter can handle.

Specifically, and still with reference to FIGURES 4 and 6 in particular, it is understood that, in accordance with the principles shown in Illustration B: downward extension 157 of bar 148 defines a capacitor 210 between bar 148 and input port 114 for splitting the power load between bar 148 and input port 114; terminal end portions 150 and 152 of bar 148 extend and overlie portions of respective resonator plates 127 and 128 to define additional respective capacitors 212 and 214 between the bar 148 and resonator plates 127 and 128 for splitting the load between the respective resonator plates 127 and 128; and extensions 158 and 160 of bar 148 in combination with ground plate extension 172 define an additional capacitor 216 which splits the load between the input port 114 and ground plate 135.

In accordance with a preferred embodiment of the metallization pattern of the present invention, the distance, generally designated X in FIGURE 4 between the finger 154 on resonator 127 and the terminal edge 150 of bar 148 is about 0.007 inches; the distance generally designated Y in FIGURE 4, between the ground bar 178 and the power load distribution bar 148 is also preferably about 0.007 inches; and the distance, generally designated Z in FIGURE 4, between the ground bar 178 and the top terminal edge of input transmission port 114 is preferably about 0.03 inches. FIGURES 7 and 8 in combination illustrate that the metallization pattern in accordance with the present invention has been shown to provide an increase from about 47 dbm/50 watts (as shown in FIGURE 7 for the

FIGURE 2 prior art filter) to about 49 dbm/79 watts (as shown in FIGURE 8 for the FIGURE 1 filter) before there is a catastrophic failure.

FIGURE 9 in turn illustrates that the metallization pattern in accordance with the present invention has also been shown to create a filter exhibiting "in band" performance characteristics similar to the prior art filter of FIGURE 2 while, however, providing increased "out of band" rejection resulting from heavier loading to ground and source splitting via the bar 148. Line 400 in FIGURE 9 represents the performance of the filter shown in FIGURE 2. Line 402 in FIGURE 9 represents the performance of the filter of the present invention.

FIGURE 10 illustrates that the metallization pattern in accordance with the present invention not only allows the filter to handle increased power loads but also additionally advantageously causes an increase in the delay experienced by the filter 100 thus, of course, allowing the filter 100 to handle a higher power load for a longer period of time. Lines 500 in FIGURE 10 represent the performance of the filter shown in FIGURE 2. Lines 502 in FIGURE 10 represent the performance of the filter of the present invention. Numerous variations and modifications of the embodiment described above may be effected without departing from the spirit and scope of the novel features of the invention. No limitations with respect to the specific module illustrated herein are intended or should be inferred.