NOVEL UWB ANTENNA DESIGNS WITH DOUBLE NOTCH FOR WLAN BAND REJECTION

Abstract

In this dissertation, we present several designs for a microstrip line monopole antenna and CPW fed monopole antenna. First, a monopole antenna to cover the entire UWB band of 3.1-10.6GHz is designed. Different types of tapers are investigated to achieve the impedance match over the desired band. A parametric study of various dimensional parameters is carried out on CST Microwave Studio with the aim of understanding their effect on antenna characteristics. The operating principle of the antenna is studied based upon the H-field distribution over the antenna. The UWB antenna interferes with WLAN frequency of 5.2 GHz (5150-5350 MHz) and 5.8 GHz (5725-5825 MHz). So UWB antenna with single notch centered at 5.5GHz and covering 5.1-5.8GHz is developed. The inherent disadvantage in this method is that frequency between 5.1 GHz and 5.8GHz cannot be used for transmission. To avoid this, UWB antenna with double notches at 5.2GHz and 5.8GHz has been developed. For UWB antenna with single notch, a T-shaped parasitic strip is introduced in the ground plane to reject the WLAN frequencies. Two cases of this antenna have been investigated by varying the distance between the parasitic strip and ground plane. When the distance between parasitic strip and ground plane is more, notch is sharp giving rise to increased ringing. In the second case where the distance is less, notch bandwidth increases and there is substantial reduction in the ringing. Next, two band-rejection notches at 5.2GHz and 5.8GHz are introduced by combining two traditional band-notching techniques. In microstrip line fed monopole antenna, by combining a T-shaped parasitic strip in the ground plane and a CSSRR in the radiating patch, a double notch has been achieved. In CPW fed monopole antenna by combining a slot in the patch and a CSSRR on both side of the ground plane, a double notch has been achieved. Performance of the proposed antenna has been investigated in both frequency and time domain. It is found that the antenna exhibits omnidirectional radiation in H-Plane, with a gain of 2-4dB except at the notch frequencies. It also exhibits low-level ringing and pulse distortion, making it suitable for UWB communication systems. The antenna parameters have been optimized with CST MICROWA VE STUDIO and an NH9338 substrate of thickness 1.524mm and relative permittivity of 3.38 has been used in simulation as well as for the fa