Patent ID: 7889029

Claim:
An active bandpass filter, comprising: N transmission line circuits, each of the N transmission line circuits having a first end and a second end, wherein N≧2 and N is a natural number; N negative impedance circuits, each of the N negative impedance circuits having a third end and a fourth end, each of the N negative impedance circuits correspondingly coupling with each of the N transmission line circuits, wherein the third end correspondingly couples with the first end and the fourth end correspondingly couples with the second end, thereby forming N resonators with negative impedances; a Direct Current (DC) circuit for providing a DC bias for the N negative impedance circuits, wherein the DC circuit correspondingly couples with the N resonators with negative impedances via N coupling elements; and at least (N−1) first coupling circuits, each of the at least (N−1) first coupling circuits having a fifth end and a sixth end, each of the at least (N−1) first coupling circuits coupling with a corresponding two of the N resonators with negative impedances, wherein the fifth end of a first of the (N−1) first coupling circuits couples with the second end and the fourth end of a first of the N negative impedance circuits, and the sixth end of the first of the (N−1) first coupling circuits couples with the first end and the third end of a second of the N negative impedance circuits, wherein successive ones of the coupling circuit of the (N−1) first coupling circuits are singly coupled between successive neighboring pairs of the N negative impedance circuits.