Inline Quasi-Elliptic Single- and Dual-Band Monoblock Dielectric Stub-Loaded Resonator Filters

This article proposes a new class of monoblock dielectric stub-loaded resonators (MDSLRs) to realize highly selective single- and dual-band filters. The proposed MDSLR can be chosen flexibly for both single- and dual-mode operations, enabling the design of single- and dual-band filters. For single-band filter design, frequency-dependent coupling (FDC) can be generated easily in a strictly inline configuration. Thus, a series of transmission zeros (TZs) are introduced and can be precisely controlled to enhance the selectivity. For dual-band filter design, the MDSLR offers independent control for two passbands with good selectivity and isolation. Moreover, a mixed input/output coupling structure is presented, effectively improving the tuning range of external quality factors (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q_{e}$</tex-math> </inline-formula>). To demonstrate the above design concept, an inline fourth-order single-band filter and an inline fourth-order dual-band filter are designed and manufactured. Measurement results agree with the full-wave simulation ones.