Design of a compact UWB BPF with a Fractal Tree Stub Loaded Multimode Resonator

Abstract This paper presents a novel technique to design an ultra‐wideband bandpass filter (UWB BPF) based on fractal tree stub loaded multimode resonators. Two different topologies are opted to verify the relationships between resonant modes of the multimode resonators with different parameters of the fractal tree stub. UWB bandwidth is acquired by increasing iterations of the fractal tree without a significant effect on the filter's physical size. The proposed topologies provide design flexibility in terms of resonance and bandwidth, which are directly related to the iteration order of the fractal tree used. To verify all the features of fractal‐tree‐based UWB BPF, the proposed UWB BPF is parametrically studied using electromagnetic simulation, and a prototype is fabricated. The measured and simulated results are in close agreement. The actual size of the filters is 11.5 × 9.6 mm2. The proposed filter covers the whole band of UWB with a minimum insertion loss of 1 dB and return loss is better than 10 dB. The measured stopband extends up to 16 GHz.