Ultra-wide rejection band lowpass cell

Abstract

A novel lowpass cell with ultra-wide band rejection and compact size by using proposed radial loaded transformed radial stubs is proposed. The implemented lowpass filter with 1dB cutoff frequency fc of 3.2 GHz demonstrates stopband rejection up to 11.8 fc, i.e. 38 GHz. The measured passband insertion loss, including the connector loss, is less than 1.0 dB. The effective size of the unit cell lowpass filter is only about 310×170mil, i.e. 0.12 λg × 0.063 λg (λg is the guide wavelength at cutoff frequency) without using any lumped elements.