Cavity filter with a slim and compact structure

1. A cavity filter comprising:

a resonant element comprising a coupling block;

a first casing comprising the resonant element therein;

a second casing disposed to cover one surface of the first casing;

a terminal unit passing through the first casing such that one end thereof protrudes to be connected to an electrode pad of an external member provided outside the first casing and the other end thereof is electrically connected to the coupling block of the resonant element provided in proximity to the second casing, the terminal unit being electrically insulated from the first casing; and

an assembly unit provided on either one side or both sides of the first casing in a longitudinal direction thereof and formed with a terminal insertion hole into which the terminal unit is inserted and installed,

wherein the assembly unit protrudes outward from a lower surface of the first casing.

2. The cavity filter according to claim 1 , wherein:

the terminal insertion hole is formed in such a manner that at least a portion of the first casing is recessed from the lower surface of the first casing or extends from the first casing toward a PCB; and

the terminal unit comprises:

a pin member disposed in the terminal insertion hole and configured such that one end thereof is connected to the coupling block of the resonant element and the other end thereof is connected to the PCB; and

a terminal body through which the pin member passes, and which is installed together with the pin member in the terminal insertion hole, the terminal body having an elastic member accommodated therein to apply an elastic force to the pin member.

3. The cavity filter according to claim 2 , wherein the terminal body is provided therein with a pin connector elastically supported toward the PCB by the elastic member.

4. The cavity filter according to claim 3 , wherein the pin connector has a tip further protruding outward from the terminal insertion hole by the elastic member.

5. The cavity filter according to claim 2 , wherein:

the terminal insertion hole comprises a first insertion hole having a relatively larger inner diameter on its side where the PCB is provided, and a second insertion hole having a relatively smaller inner diameter than the first insertion hole; and

the cavity filter further comprises a dielectric bush inserted into the second insertion hole.

6. The cavity filter according to claim 5 , further comprising a terminal head block coupled to the terminal body and seated in the first insertion hole.

7. The cavity filter according to claim 5 , further comprising a ground terminal electrically connected to the first casing,

wherein the first casing is formed with an annular groove surrounding the first insertion hole to have an installation surface on which the ground terminal is installed.

8. The cavity filter according to claim 7 , wherein:

the annular groove is in the form of an annular dovetail in which a circumferential surface diameter corresponding to its inner diameter increases in a depth direction; and

the annular groove has a minimum inlet inner diameter that allows the ground terminal to shrink by elasticity and be inserted into the annular groove, thereby preventing separation of the ground terminal.

9. The cavity filter according to claim 8 , wherein the ground terminal comprises:

a fixing ring seated on and fixed to the installation surface of the annular groove; and

a plurality of elastic grounds circumferentially formed on an inner peripheral end of the fixing ring and extending toward the center thereof while obliquely extending toward the PCB.

10. The cavity filter according to claim 2 , wherein:

the terminal insertion hole comprises a first insertion hole having the relatively largest diameter on its side where the PCB is provided, a second insertion hole having a relatively smaller inner diameter than the first insertion hole, and a third insertion hole having a relatively smaller inner diameter than the second insertion hole; and

the cavity filter further comprises a dielectric bush inserted into the second and third insertion holes, the dielectric bush being in the form of a two-stage cylinder.

11. The cavity filter according to claim 10 , wherein:

the terminal unit further comprises a pin member disposed in the terminal insertion hole and configured such that one end thereof is connected to the resonant element and the other end thereof is connected to the PCB; and

the pin member comprises:

a pin corresponding to the one end of the terminal unit and positioned over the second and third insertion holes such that the pin is connected to the resonant element;

a terminal body being in the form of a two-stage cylinder integral with the pin, the terminal body being formed therein with a socket having a cone-shaped opening, the terminal body being positioned over the first insertion hole; and

an elastic connector corresponding to the other end of the terminal unit and inserted and fixed into the socket, the elastic connector being connected to the PCB.

12. The cavity filter according to claim 11 , wherein the elastic connector is a cylindrical structure that is inserted into the socket, and comprises a truncated conical pin-socket contact portion inserted corresponding to the cone-shaped opening and an impedance matching portion extending from the pin-socket contact portion.

13. The cavity filter according to claim 12 , wherein the elastic connector is inserted into the socket while being in contact with the PCB, and comprises a circular spring formed to have a circular vertical cross-section in its constant width except for both ends and two plate projections protruding perpendicular to a circumference of the circular spring from two points adjacent thereto.