Design of a Compact Ultrawideband U-Shaped Slot Etched on a Circular Patch Antenna with Notch Band Characteristics for Ultrawideband Applications

Interference between ultrawideband (UWB) antennas and other narrowband communication systems has spurred growth in designing UWB antennas with notch characteristics and complicated designs consisting of irregular etched slots and larger physical size. This article presents a simplified notched design method for existing UWB antennas exhibiting four frequency-band-rejecting characteristics. The investigation has been conducted by introducing four semicircular U-shaped slot structures based on a theoretical formulation. The formulation is validated with the equivalent LC lumped parameters responsible for yielding the notched frequency. A novel feature of our approach is that the frequency notch can be adjusted to the desired values by changing the radial length based on the value calculated using a derived formula for each semietched U-slot, which is very simple in structure and design. Additionally, by introducing the rectangular notch at the ground plane, the upper passband spectrum is suppressed while maintaining the wide impedance bandwidth of the antenna applicable for next-generation wireless communications, 5G. The measured result shows that the antenna has a wide impedance bandwidth of 149% from 2.9 to 20 GHz, apart from the four-notched frequencies at 3.49, 3.92, 4.57, and 5.23 GHz for a voltage standing wave ratio (VSWR) of