New Method to Control the Passband and the Stopband of UWB Ring Resonator Based Bandpass Filters

Abstract

In this article, resonance frequencies, stopband rejection level, and the passband of ultra-wideband compact ring resonator-based bandpass filters are controlled by a new and understandable method. In this method, the passage and the rejection of resonance frequencies are controlled by the ports' positions. This can be achieved by investigating the electric field distribution of the successive resonant frequencies of the ring resonator considering symmetrical excitation. Then, decide which resonant frequencies will be passed and which will be rejected according to the electric field distribution. For size reduction, the Sierpinski space-filling curve is used. The stopband rejection level is controlled by inserting a bandstop filter with the resultant bandpass filter with the minimum extra area. Band-pass filter passband width is controlled by the attenuation poles' frequency positions that are controlled by inserting open stubs without the need for any further area. For verification, the proposed filter passband is chosen to cover the S-band frequency spectrum. The proposed bandpass filter has an ultra-wide 3 dB passband of 2.11 GHz (2.27 GHz - 4.38 GHz) and a 15 dB ultra-wide stopband of 5.36 GHz (4.64 - 10 GHz). The proposed bandpass filter is fabricated, measured, and the results are in good harmony with their simulated counterparts.