Highly compact UWB-BPF with a wide notch-band using a rectangular ring structure and two Y-shaped open stub resonators

Abstract

A miniaturized ultra-wideband bandpass filter (UWB-BPF) with a high rejection notched band is proposed in this article. It is composed of a rectangular ring with two grounded vias, a microstrip line with two open radial stubs, a pair of interdigital feedlines with two lumped capacitors and two open-loaded Y-shaped stub resonators (YSSR), as well as a defected ground structure (DGS). This filter was simulated and fabricated by using a practical printed circuit board (PCB) process with the substrate of FR4. The measurement results agree well with the simulation data. The measured 3-dB passbands cover 2.73–4.36 and 6.82–11.78 GHz, the in-band insertion loss is less than 1.13 dB except at the edges of the bands, and the return loss is better than 10 dB. It is found that the filter’s lower and upper transmission zeros occur at 0.8 and 13.95 GHz with the magnitudes of −87.2 and −45.6 dB, respectively. This makes the filter exhibit high selectivity with the steep skirt characteristics. It is also worth noting that the proposed filter possesses a wide 10-dB notch band ranging from 4.87 to 6.93 GHz with the highest rejection of 46.3 dB at 5.9 GHz. This feature can effectively and simultaneously inhibit the unwanted signals coming from the C-band 5G mobile communication, 5-GHz WiFi, WLAN, and 6-GHz satellite systems. Furthermore, the presented filter is highly compact with the dimensions of 13.2 mm × 11.8 mm and has a very wide upper stopband spanning from 13.4 to 28 GHz with rejection of 20 dB or higher.