A small dielectric filter suitable for use in a high frequency band equal to or higher than 3 GHz. An input/output electrode made up of island type of conductive film is formed on one surface of the dielectric located on each end portion. In each of the dielectrics located on each end respectively, an earth electrode is formed on almost all of the remaining area of the one surface so as to be isolated from the input/output electrode and is also formed on all of the other surfaces with an exception of connecting surfaces. In an intermediate dielectric, an earth electrode is formed on all surfaces other than the connecting surface, and a conductive film connected to the earth electrode is formed on a part of at least one of the connecting surfaces of the dielectrics to be connected. Three or more elements of resonators may be integrally formed on a dielectric block, and, in that case, a through-hole is formed between the resonators.
A dielectric block includes a plurality of plated through holes each having an inner conductor formed thereon to form respective plated through holes. At least one of the plated through holes branches into two legs at the short circuit side thereof so that the two legs are close to the short circuit side of the plated through holes adjacent thereto. This allows the resonators formed of the plated through holes to be strongly inductively coupled with each other.
A hybrid filter assembly is provided having a first ceramic triple-mode mono-block resonator, a second ceramic triple-mode mono-block resonator and at least one metallic resonator coupled to at least one of the first and second mono-block resonators. Each triple-mode mono-block resonator supports three resonant modes and each metallic resonator supports an additional mode, thereby providing a hybrid filter assembly of reduced size having more than six poles.
A delay filter uses the dielectric mono-block triple-mode resonator and unique inter-resonator coupling structure, having smaller volume and higher power handling capacity. The triple-mode mono-block resonator has three resonators in one block. An input/output probe is connected to each metal plated dielectric block to transmit microwave signals. Corner cuts couple a mode oriented in one direction to a mode oriented in a second, mutually orthogonal direction. An aperture between two blocks couples all six resonant modes, and generates two inductive couplings by magnetic fields between two modes, and one capacitive coupling by electric fields. The input/output probes, coupling corner cuts and aperture are aligned such that all six resonators are coupled in the desired value and sign, so constant delay on the transmitted signal within certain bandwidth can be achieved. By connecting the input and output probes to the base printed circuit board, the delay filter is surface mountable.
The present invention incorporates triple-mode, mono-block resonators that are tunable. Four novel and unobvious methods of tuning are disclosed. The first tuning method is to mechanically grind areas on three orthogonal faces of the mono-block in order to change the resonant frequencies of the three modes in each block. Another method of tuning frequency is to cut a slot within a face of the resonator. A third method of tuning the mono-block is to tune the resonant frequency of a particular mode by removing small circular areas of the conductive surface from a particular face of the mono-block. The fourth, tuning method is the use of discrete tuning elements, with 3 elements distributed among three orthogonal faces of the mono-block, to affect the necessary change of the resonant frequencies.
