A low-loss serial power combiner using suspended stripline is described. It consists of novel broadside-coupled directional couplers which have shunt capacitances at the edges of the coupled sections. These additional shunt capacitances compensate for poor directivities of the couplers because of inhomogeneous dielectric in suspended stripline structure. The fabricated three-way power combiner has achieved good performance with insertion loss less than 0.23 dB over a bandwidth of 10% in 2 GHz band.