Molded resonator

The molded resonator includes at least one formed resonator element having an resonator portion and opposed end leg portions which provide electrical connections to the main portion. A dielectric portion is molded about the resonator element. A conductive ground plane is carried by the dielectric portion and electrically shields the resonator element. The resonator element is formed of wire having a circular cross-section.

BACKGROUND OF THE INVENTION 
This invention relates to transmission line resonators in general and 
particularly to molded resonators. Prior art transmission line resonators, 
such as stripline resonators having solid dielectric materials were 
constructed by a lamination process. For example, in one known method, a 
circuit trace is formed on a dielectric substrate, a second dielectric 
substrate is placed over and bonded to the first substrate, and an outer 
ground plane is then bonded to the substrates. This prior art approach 
includes a number of limitations such as expense of manufacture, limited 
electrical specifications, difficulties in making the external connections 
to the stripline elements, and microphonics (i.e. electrical instability 
during mechanical vibration). These limitations are overcome by the molded 
resonator. 
SUMMARY OF THE INVENTION 
This molded resonator includes at least one preformed resonator element 
that is molded into a monolithic dielectric structure. 
This molded resonator includes at least one formed resonator element having 
a main resonator portion and opposed end leg portions for providing 
electrical connections to the main portion. The dielectric material is 
molded about the resonator element. A conductive ground plane is carried 
by the dielectric portion and electrically shields the resonator element. 
In one aspect of the invention, the resonator element is formed of wire 
having a circular cross-section. In another aspect of the invention, the 
resonator includes two formed resonator elements. In still another aspect 
of the invention, one of the leg portions is connected to the conductive 
ground plane. 
A method of manufacturing a resonator includes the steps of forming at 
least one resonator element; placing the one resonator element in a mold; 
injecting a dielectric material to form a first molded member having 
corner support portions for precisely locating the member in a second 
mold; placing the first molded member in a second mold and injecting 
additional dielectric material to form a second molded member; and 
metallizing the second molded member to provide a ground plane for 
shielding the resonator element. 
In one aspect of the method of manufacturing a resonator, the first molding 
member is formed with through holes and the additional dielectric 
materials is injected into the through holes thereby interconnecting the 
additional dielectric material on opposite sides of the resonator.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now by characters of reference to the drawings and first to FIG. 
1, it will be understood that the molded resonator includes first and 
second resonator elements 11 and 12 that are preformed into predetermined 
shapes for providing desired electrical characteristics. The resonator 
elements 11 and 12 are formed of conductive material which, in the 
preferred embodiment, is hard drawn copper wire having a circular 
cross-section. While two resonator elements are illustrated in the 
preferred embodiment, a single resonator element or three or more can be 
utilized. 
Each of the resonator elements 11 and 12 includes a main resonator portion, 
13 and 14 respectively, which is formed in a single plane. In the 
illustrated embodiment, both portions 13 and 14 are substantially "U" 
shaped. Any other shape including a straight line can be utilized provided 
the shape and length are properly choosen to achieve the desired 
electrical characteristics in the finished resonator. 
As more clearly illustrated in FIGS. 2 and 3, resonator element 11 includes 
depending legs 15 and 16 located at opposite ends of the main resonator 
portion 13 and extending substantially perpendicular to the plane of the 
main portion 13. Likewise, resonator element 12 includes, depending legs 
17 and 18. The legs 15-18 provide the necessary electrical connections 
between the resonator main portions 13 and 14 and external circuits. 
The resonator elements 11 and 12 are placed in a precision mold (not shown) 
which locates the legs 15-18 while opposed side mold locating pins clamp 
and support the main resonator portions 13 and 14 in a precise 
predetermined location. A dielectric material is then injected into the 
mold to form the first molded member 19. After the first molding 
operation, the first molded member 19 has a plurality of holes 20 
resulting from the mold locating pins that engage the main portions 13 and 
14. Through holes 22 are provided in the first molded member 19, which 
also includes support protrusions 23 used for mechanical support in the 
second molding operation as well as, corner support portions 24 that are 
used to provide for exact location of the first molded portion 19 during 
the second molding operation. 
The first molded portion 19 is then placed in a second mold (not shown) and 
additional dielectric material is injected to form the second molded 
member 25, illustrated in FIGS. 4 and 5. The second molded member 25 
provides a substantially parallelepiped structure that includes on its 
lower surface, two locating protrusions 26 and 27 used for positioning the 
molded resonator when used in a circuit such as a two-way portable radio. 
The legs 15-18 are sheared off substantially even with the surface of the 
second molded member 25. At legs 15 and 17, the second molded member 25 
includes island portions 30 that have their surfaces in the plane of the 
surface of the second molded member. The island portions 30 are surrounded 
by ring depressions 31 in the surface of second molded member 25. A layer 
of resist material is deposited in the depressions 31. The exterior of a 
second molded member 25 is then metallized as by sputtering to provide an 
electrical shield or ground plane 32 around the resonator elements 11 and 
12 thereby completing the molded resonator 10, as illustrated in FIG. 6. 
The metallized ground plane 32 makes electrical connection to the legs 16 
and 18. The metallization at islands 30 provides electrical connection to 
legs 15 and 17. The resist in depressions 31 prevent metallization of that 
area thereby electrically isolating islands 30 from the ground plane 32 on 
the surfaces of molded resonator 10. In the event that the legs 16 and 18 
are not to be grounded, they can also be connected at islands 30 like legs 
15 and 18. 
It is thought that the structural feature and functional advantages of the 
improved molded resonator have become fully apparent from the foregoing 
description of parts, but for completeness of disclosure a brief 
description of the manufacture operation of the resonator will be given. 
It will be understood that the particular form of the resonator elements 
13 and 14 depend upon the desired operating characteristics of the molded 
resonator 10. The arrangement once chosen provides a high Q resonator due 
in part to the circular cross-section of the resonator elements 11 and 12. 
The first molding, illustrated in FIGS. 1-3, is used for the precise 
positioning of the resonator elements 11 and 12. During the second molding 
the corner portions 24 are used to precisely locate and support the first 
molded member 19 in the mold. The protrusions 23 by engaging the mold 
prevent flexing, bending or movement of the first molded member 19 during 
the high pressure molding operation. During the second molding operation, 
a substantially continuous and smooth outer surface is formed to provide a 
uniform surface for the application of the metallized ground plane 32 to 
complete the resonator 10. The support protrusions 23 and, corner support 
portions 24 are spaced from the resonator elements 11 and 12. This spacing 
is important to minimize the effects of discontinuities in the ground 
plane 32 that can exist at boundaries of the dielectric material from the 
first and second molding processes. 
The through holes 22 provide direct interconnection of the dielectric 
material of the second molding process in addition to the interconnection 
that occurs at the periphery of the second molded member 25, thereby 
providing increased structural integrity of the resonator. In the 
preferred embodiment, the dielectric material used in both molding 
processes is polyetherimide having a 10% fiberglass content such as that 
sold under the tradename ULTEM 2100 by General Electric Company. 
After metallization, the high Q, mechanically stable resonator 10 can be 
incorporated into a circuit such as a two-way portable radio by making 
electrical connections at pads 30 and to the ground plane 32.