Broadband Microwave Passive Step Attenuator Based on Imperfect Matching Theory

Abstract

This paper presents an innovative design approach for a broadband passive step attenuator, utilizing the imperfect matching theory in the design process. To bring the actual performance of the attenuator closer to theoretical predictions, TaN resistors with the low parasitic capacitance have been redesigned. Measurement results demonstrate that the attenuator designed in this study delivers attenuation values ranging from 0 to 11 dB, with a step value of 0.5 dB. Over the wide operating frequency band from 9.65 to 30.8 GHz, the attenuator consistently maintains return losses all better than 15 dB, and insertion loss flatness within ±0.3 dB, particularly when attenuation values exceeding 3 dB. The attenuator can be realized simply with an uncut microstrip transmission line and a grounding structure, requiring no external power supply or control signals. Furthermore, it can be integrated into conventional RF circuit manufacturing processes, offering a low-cost and high-performance solution for a required attenuation with a straightforward design.