A lossy triple-mode microstrip filter with flat passband based on nonuniform Q-factors

In this paper, a lossy triple-mode microstrip filter is proposed, where the nonuniform-Q method is applied. By properly loading a resistor on the resonator, only the Q-factor of odd mode is reduced to its optimized value. The passband flatness can be significantly improved. In comparison with the conventional filter counterpart, our proposed filter shows an enhanced bandwidth with a small variation of 0.2 dB, as has been observed from the synthesized, simulated and measured results.