Design of filtering power dividers for desired filter responses using parallel coupled-line filters

This paper presents a design method for using two parallel coupled-line bandpass filters to realize a filtering power divider. For a specified filter response that involves the fractional bandwidth Δ and the element values g
₁
, g
₂
, ..., and g
_n+1
, an n-pole filtering power divider can be readily designed using the design equations derived in this paper. As demonstrated by a proof-of-concept microstrip filtering power divider, the design method leads to an isolation network that needs only a resistor to achieve wideband isolation. The measured isolation is better than 15 dB from DC to 7.5f
_c
, or is better than 12 dB from DC to 10f
_c
, where f
_c
is the center frequency of the passband.