**1. Introduction**

The recent explosion in information technology and wireless communications has created many opportunities for enhancing the performance of existing signal transmission and processing systems and has provided a strong motivation for developing novel antenna structure for systems that require wider bandwidths and higher data transmission.

In today's modern communication systems, miniaturized and lightweight subsystems covering broad bandwidth are in much demand as they lead to realization of very compact and lightweight systems. To accomplish this, small and lightweight antennas which cover wide bandwidth without much degradation in their performance are required to be designed and realized. As antenna

dimensions are governed by wavelength of operating frequency, antenna miniaturization is a challenging and difficult task. Planar/printed antennas offer good solutions for the above class of problem. Vivaldi antennas are preferable in many applications due to high gain, simple structure and easy fabrication. They are mostly used in ultra-wideband and broadband applications. Printed antennas are being increasingly used as they are low profile and can be integrated on any printed circuit easily.

Most of the wireless communication systems suffer from co-channel interference and multipath effects. The co channel interference and multipath effects are addressed by using horn antennas that are placed in LOS, but these antennas are too bulky to be integrated with the rest of the wireless systems and suffer high cost of fabrication. For military and commercial applications wideband width antennas with high gain are preferred and Vivaldi antenna or planar tapered slot antenna (TSA) are better choice. As these antennas are support for multifunction communication applications because of their consistent impedance matching over a very broad operating frequency range, stable directional patterns, low profile and planar structures.

The Vivaldi and TSA's offer broadband operation, with low sidelobes but moderate gain.

**Problem definition:** The objective is to design the single cavity and double cavity Vivaldi antenna operating from 8 to 18 GHz frequency to achieve VSWR less than 3:1 and comparison of antenna performance for single cavity and double cavity Vivaldi antenna.
