Miniaturized dual-mode bandpass filter with harmonic control

This letter presents a miniaturized dual-mode microstrip bandpass filter with the right crossed slots. The right crossed slots perturb and reduce the fundamental resonant frequency, but the second resonance is not affected. Therefore, the second resonance will be effectively higher than 2f(o), where f(o) is the fundamental frequency. Since the fundamental frequency is lower, the bandpass filter is smaller than the conventional filter. The proposed filter shows a 4.4% fractional bandwidth at 1.595 GHz with a return loss of better than 10 dB and an insertion loss of less than 2.5 dB, while the second passband is located around 2.88f(o) = 4.6 GHz. Compared with the conventional square patch filter, the proposed filter also shows a 58% size reduction.