RADIAL LOADED TRANSFORMED RADIAL STUB FOR LPF STOPBAND EXTENSION

A low pass fllter with ultra-wide band rejection and compact size using a proposed radial loaded transformed radial stubs is introduced and investigated. The implemented unite cell low pass fllter with 1-dB cutofi frequency fc of 3.2GHz demonstrates stopband rejection up to 11.8 fc, i.e., 38GHz. The design is further extended to the high-order LPF through cell cascading. The implemented four-cell LPF with fc of 3.6GHz demonstrated 35dB rejection from 4.8GHz to 39GHz, 50dB rejection from 5.4GHz to 26GHz (7.2 fc) and 20dB rejection from 4.4GHz to 50GHz (13.8 fc). The measured passband insertion loss is less than 1.7dB, and group delay is 0:45 » 0:8nS. The size of the four-cell low pass fllter is only 0:33‚g £ 0:135‚g, (‚g is the guide wavelength at center cutofi frequency) without using any lumped elements.