Ultra-wideband power dividers with good isolation and improved sharp roll-off skirt

A novel class of ultra-wideband power dividers with good isolation and sharp roll-off skirt is proposed, analysed and designed on microstrip topology. By introducing a pair of quarter-wavelength short-circuited stubs and/or parallel coupled lines to two symmetrical output ports, good performance in terms of equal power splitting is achieved over the ultra-wideband range, that is 3.1-10.6-GHz. A single resistor is then placed between two output ports such that good isolation is achieved between them. By virtue of direct-current chocked and half-wavelength transmission zeros of short-circuited stubs and coupled lines, out-of-band roll-off skirt near the cut-off frequencies is sharpened to a great extent. Two types of these power dividers are analysed and optimised using the simple transmission-line based even- and odd-mode approach. Based on comparative study of these two types, an ultra-wide band divider with coupled lines has been designed and fabricated. Measured results evidently confirm the predicted features of the divider in terms of return losses at all the three ports, input-to-output insertion losses and output-to-output isolation.