Microstrip Broadband Thin-Film Attenuators without Via-hole-ground at Millimeter Wave Frequencies

A comprehensive design methodology for microstrip broadband attenuators is presented. Closed-form design equations are given for two types of distributed attenuators. The attenuators are based on a cascade connection of thin-film resistors and microstrip line sections. The structure provides maximally flat attenuation and wideband performance without the need of plated via holes to ground, facilitating manufacture as well as achieving proper performance at millimeter wave frequencies. Experimental results demonstrate the validity of the technique applied to 3 dB and 13 dB broadband attenuators on alumina substrate up to 67 GHz. The proposed topology can be applied not only to MIC, but also to MMIC designs at the highest frequencies.