Design of compact planar power divider with wideband bandpass response and high in‐band isolation

Abstract In this study, a compact planar power divider (PD) with wideband bandpass response is proposed based on a coupled three‐line filtering prototype. With two back‐to‐back microstrip feeding lines and a coplanar waveguide resonator located in the middle ground plane, the filtering structure is constructed. According to the synthesis approach, the proposed filtering structure can achieve an equal in‐band ripple response with three transmission poles and four out‐of‐band transmission zeros. In order to make the proposed PD inherit the designed filtering performance, one of the output lines in the filter network is modified to realize a 50 to 25 Ω impedance transformation in the passband first. Then, for good in‐band isolation and impedance matching at output ports, the modified output line is split into two separated lines by a slot so that a lumped resistor can be loaded at the ends of the two separated output lines. By properly setting the slot width and the resistance with guidance, high isolation level over an ultra‐wide passband is attained. For demonstration, three cases of the PDs with different bandwidths are designed on the basis of the corresponding filter designs. Finally, two bandpass PDs are fabricated and tested to verify the design concept