Printed antennas are the most commonly used antennas in wireless applications where size is a constraint. The most basic form of printed antenna is the microstrip antenna that comprises a printed patch on the grounded substrate (Fig. A.1). In this text, a microstrip antenna will be designed. An antenna's performance is controlled by various parameters. The overall goal of any design is to obtain a stable output in the desired band. In order to achieve this goal, different factors on which the characteristic depends need to be examined and decided properly

The important considerations in the design of microstrip antenna are as follows

I. Substrate selection: Substrate in antenna design is principally needed for mechanical support of the antenna metallization. However, it also affects the performance of the antenna. There is no ideal substrate that will work equally well for all applications; in fact, the choice is completely determined by the application. The following points should be kept in mind before selecting any substrate.

• • Substrate thickness (h): A thicker substrate, besides being mechanically strong, will increase the radiated power, reduce conductor loss and improve impedance bandwidth. However, it will also increase the weight, dielectric loss, surface wave loss and extraneous radiation from probe feed.

• • Substrate dielectric constant (er): Low value of dielectric constant for substrate will increase the fringing field at the patch periphery and thus, the radiated power.

• • Loss tangent: A high loss tangent will increase dielectric loss and therefore reduces antenna efficiency.