New bandstop/bandpass microstrip structures with harmonic
suppression are presented in this article. By replacing the series
quarter-wavelength connecting lines of conventional open-stub bandpass/
bandstop filters with the equivalent
-shaped line section, compact
open-stub bandstop/bandpass filters with second harmonic suppression
are achieved. Transmission-line theory is used to derive the design
equations of the equivalent
-shaped lines. Simulation and experiments
have also been done to validate the proposed design concept. When
compared with the conventional open-stub Bandpass/Bandstop filters,
the second harmonic is suppressed and size reduction is achieved in
both the Bandstop/bandpass structures. Moreover, results confirm that
the proposed shaped bandpass filter achieves a further third harmonic
rejection