Compact ultra-wideband filter using coupled-line and short-ended stub

A compact ultra-wideband filter is presented. The filter consists of a section of coupled microstrip-line and a short-ended stub. It has a simple structure and small size (4.7 × 6.2 mm²), but exhibits good performance. The filter has been investigated numerically using the simulator IE3D, and samples were fabricated and measured. Measured results show that the filter has a fractional bandwidth of 103.2% (from 3.05 to 9.55 GHz) and minimal insertion loss of -0.4 dB. The measured in-band return loss is better than -15.0 dB.