Compact microstrip dual‐band bandpass filter using short‐circuited stub‐loaded open loop resonators

Abstract

attributed to the mode conversion at the output taper section which was not prevented at all from inserting the metal post in the middle of the cavity as the TE 10,1 mode has its most energy distributed close to the cavity wall. The spectral separation of the TE 6,2 mode and the TE 10,1 mode is around 300 MHz, which is very close to each other.To eliminate the unwanted TE 10,1 mode, we redesigned a cylindrical type cavity for the mode generator. The new cavity has less abrupt change in the uptaper section of the cavity with a reduced aperture radius. The measured field pattern at 1 mm from the aperture was shown in Figure 5. The measured mode pattern does not contain any mixture of modes, and the sole excitation of the TE 6,2 mode was observed. Figure 6 proves that the generated field from the newly shaped cavity only excites the TE 6,2 mode by comparison with the simulated TE 6,2 mode. The unwrapped field data as a function of the azimuthal angle shows an excellent agreement between the measurement and the simulation. CONCLUSIONWe report a simple scheme for generating higher order mode, TE 6,2 mode at W-band frequency. The direct waveguide feeding to the resonant cavity was used for exciting the wanted mode. To prohibit excitation of neighboring modes, the metal post has been inserted in the middle of the cavity. The measured field pattern at the aperture of the mode generator shows very good agreement with the simulation results except for the mixing with the TE 10,1 mode happening at the second radial peak. Profiling the uptaper section of the mode generator cavity eliminates the TE 10,1 mode, and produces sole excitation of the TE 6,2 mode. The suggested direct waveguide feeding will be suitable for a mode generator for higher order mode at millimeter or higher frequency regime.ABSTRACT: In this article, a compact dual-band microstrip bandpass filter is proposed using two short-circuited stub-loaded open loop resonators and two common open loop resonators. The short-circuited stubloaded resonators can generate two resonant modes. Under odd mode, the short-circuited stub at the central does not affect the resonant frequencies, and four resonators tightly coupling with each other work at the same frequencies, a wideband passband is obtained. Whereas under the even mode, considering the influences from short-circuited stubs, the resonant frequencies are decided only by two short-circuited stub-loaded resonators, two common resonators are seen as parts of feedlines connected to 50 X. A new transmission zero is created between two passbands to improve the selectivity. Good agreement is achieved between simulation and measurement. Figure 6The comparison results of the azimuthal field intensity between experiments and simulation. The experimentally measured electric field intensity (red solid line) (a) at the first radial peak and (b) at the second radial peak compared to the simulated TE 6,2 mode (blue dashed line) as a function of azimuthal angle. [Color figure can be viewed in the online issue, which is available...