With the rapid development of wireless communication technology, Ultra Wideband (UWB) systems occupy an important position in the field of short-range wireless communication due to their advantages such as high speed, low power consumption, and strong penetration capability. However, in practical applications, the frequency overlap problem between ultra wideband systems and narrowband communication systems often leads to mutual interference and affects communication quality. To solve this problem, notch technology has become one of the hotspots in the design and research of ultra wideband antennas.
The notch technology aims to form a stopband within a specific frequency band of an ultra wideband antenna through specific design methods, thereby avoiding frequency conflicts with narrowband communication systems. In recent years, various notch design methods have emerged, and the following will introduce several common notch techniques.
1、 Slotting technology
Slotting technology is the etching of specific shaped slots on antenna radiation patches, feed lines, or ground planes, such as "C-shaped slots", "L-shaped slots", "U-shaped slots", and "H-shaped slots". The total length of these slots is usually designed to be half or quarter of the wavelength of the notch center frequency to achieve a specific notch effect. This method, while maintaining the overall size of the antenna, introduces additional resonance points by changing the current distribution on the antenna surface, thereby forming a stopband in a specific frequency band.
2、 Load parasitic units
Loading parasitic units is another effective method for implementing notch filtering. The principle is to place parasitic elements in areas where the antenna current distribution is dense, and the size of these parasitic elements is usually designed based on the 1/2 or 1/4 wavelength corresponding to the center frequency of the notch. When electromagnetic energy flows through the antenna, some of the energy couples to parasitic elements and generates currents in the opposite direction. These reverse currents cancel each other out with the current on the antenna, forming a notch in a specific frequency band.
3、 Electromagnetic bandgap structure (EBG)
Electromagnetic Band Gap (EBG) structure is a special structure added near both sides of the microstrip feeder line, which can effectively control the antenna bandwidth and reduce the impact on the radiation pattern. EBG structures typically have compact dimensions and strong coupling capabilities. The closer they are to the feed line, the stronger the coupling effect, and the lower the center frequency of the notch frequency band. By designing the size and position of the EBG structure reasonably, precise control of the antenna bandwidth can be achieved, and a notch can be formed within a specific frequency band.
4、 Embedded Open Circuit Short Wire Method
This method can form a notch at a specific frequency by embedding specific open circuit stubs in the antenna design. The principle is to use the reflection effect of an open circuit stub on a specific frequency to achieve a stopband effect. Due to its advantages in integration and simple process, this method has been widely applied.
5、 Asymmetric input-output coupling structure method
By designing asymmetric input-output coupling structures, specific frequency notches can be achieved. This method utilizes the special response of asymmetric structures to electromagnetic waves, and by adjusting structural parameters, a stopband can be formed within a specific frequency band.
6、 Loading resonator method
Loading resonators is another effective method for implementing notch filters. By incorporating resonators into antenna design, resonance points can be introduced at specific frequencies to form stopbands near that frequency. The method of loading resonators may increase the volume of the filter, but this effect can be reduced by optimizing the design.
7、 Defective Ground (DGS) Method
The Defective Ground Structure (DGS) method involves etching specific patterns or structures on the ground plane of a microstrip antenna to alter the current distribution on the ground plane, thereby forming a notch in a specific frequency band. This method fully utilizes the dual layer structure of microstrip and is a direction for future development.
The above notch techniques each have their own characteristics, and suitable techniques can be selected according to specific application scenarios and requirements to achieve them. Meanwhile, with the continuous development of wireless communication technology, new notch techniques will continue to emerge, providing more choices for the design of ultra wideband antennas.
