Novel dual-mode square-loop resonator filter using spurline and slot techniques

A new type of microstrip dual-mode microstrip filter using spurlines and L-shape slot is proposed in this letter. It is found interestingly that the embedded spurlines and slot can excite, couple and split the degenerate modes. Moreover, the transmission characteristics of the loop resonator can be controlled by adjusting the length of the embedded L-shaped slot appropriately. Parameter study of the transmission characteristics using this L-shaped slot technique are discussed also. Details of the filter design are presented and experimental results are given to demonstrate the performance of the proposed filter.