Design of Wideband Filtering Power Dividers with Harmonic Suppression Based on the Parallel-Coupled Line Structures

This paper presents a wideband filtering power divider with harmonic suppression. By embedding two coupled-line sections to each way of the conventional Wilkinson structure, four resonant modes excited by two coupled lines and one original mode of the Wilkinson structure are incorporated to improve the in-band filtering responses. In order to enhance the frequency selectivity, a pair of long open stubs are inserted between these coupled-line sections to produce a pair of transmission zeros on both sides of the passband. Meanwhile, two additional transmission zeros at the upper stopband can be introduced to broaden the bandwidth of the stopband. Moreover, a short open stub is installed at the input port, which can also introduce one transmission zero to enhance upper stopband rejection. Finally, a prototype of the wideband filtering power divider operating at the center frequency of 3 GHz is designed and fabricated. The measured results show a 15-dB bandwidth of 56%, an isolation better than 18-dB and a 35-dB wide stopband from 4.44 to 7.73 GHz.