High‐performance two‐pole filter using self‐coupled resonators with frequency‐variant internal and external couplings

Abstract In this article, a two‐pole filter with very high selectivity and second harmonic suppression is presented. The design based on novel configuration using self‐coupled half‐wave resonators external frequency‐variant coupling (EFVC) structures. self‐coupling allows placing two transmission zeros, produced by interresonator the tapped feeds, close to passband edges. EFVC structure enables arbitrary positioning of these zeros without affecting in‐band performance. Thus, high‐selectivity passbands can be realized. Additionally, structures provide more which are used suppress spurious harmonics. fabricated prototype second‐order at 2.35 GHz center frequency 5.6% bandwidth shows factor (ratio 3‐ 20‐dB bandwidths) 0.535 stopband up 2.8 times minimum rejection.