Microstrip realization of trisection synthesis with frequency-dependent admittance inverter

Frequency-dependent admittance (J-) inverter is in corporated in synthesis of micro strip trisection filters to achieve a quasielliptic function response. In the admittance matrix of the low pass proto type, certain coupling is modeled by a constant J-inverter multiplied by the complex frequency variable s. Direct synthesis of three low pass prototypes is presented. Based on the standard low pass to band pass transformation, coupled micro strip resonators with both electric and magnetic coupling are devised to implement the J-inverter with desired frequency-dependent characteristics. Tapped-line input/output is used and several transmission zeros can be created in the upper and lower rejection bands. In experiments, a third-order filter with four zeros, a fourth-order circuit with three zeros, and a fourth-order filter with five zeros are designed and fabricated. Measured results are compared with the simulation responses to validate the theory.