**4.1 VSWR**

The numerical simulation of directional antenna is done using CST software. The performance of the antenna does not improve monotonically as the parameters of the antenna changes. It must be optimized through analysis during simulation to get the optimum parameters.

The simulations for Vivaldi antenna operating in the band 8–18 GHz are done using CST. The obtained VSWR simulation results for the respective antenna are as shown in **Figure 7(a)** and **(b)**.

As shown in **Figure 7(a)** and **(b)**, the VSWR-frequency plot for the Vivaldi antenna without SMA connector seems to have a high VSWR, which means the reflection of power is more and the reflected wave amplitude is high from frequency 8 to 18 GHz.

To lower the VSWR, a connector is attached to the antenna for the required band of frequencies. **Figure 8(a)** and **(b)** shows the VSWR with SMA connector in CST software for single cavity and double cavity respectively.
