A 2.0-GHz wideband bandpass filter using ring resonator with the compound stub

This paper presents the 2.0-GHz wideband bandpass filter using ring resonator with the compound stub. The compound stub is connected to the upper path of the loop filter functioning as the capacitance. As the experimental results, it is found that the bandwidth of this filter is approximately 50 percent of the central frequency at the return loss of 20 dB and the insertion loss is about 0.65 dB. Additionally, the size of the filter is dramatically smaller than the filter using the conventional open-circuited stub at least a quarter wavelength.