Broadband Filtering Attenuator With Bandwidth Enhancement in High Attenuation Level

In this letter, a new broadband filtering attenuator designed to enhance bandwidth performance in high attenuation levels is proposed. By adjusting the resistors, attenuation is achieved that is inversely proportional to their resistance values. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda $ </tex-math></inline-formula>/4 open-circuited stubs (OSs) are employed instead of traditional grounding techniques to overcome the problem of bandwidth narrowing in high attenuation levels. Due to the symmetry of the circuit, the odd- and even-mode methods are used for analysis. To demonstrate the concept, a filtering attenuator was fabricated, which operates from 1.2 to 2.75 GHz, offering attenuation from 0.55 to 15.7 dB. Notably, by maintaining the filtering shape and mitigating the narrowing of bandwidth in high attenuation levels, it preserves the fractional bandwidth of 78.5% across all attenuation levels.