Question

What is a patch, or micro strip, antenna and how does it work?

Answer 1

In Microstrip antenna, It is the fringing fields that are responsible for the radiation. The fringing fields around the antenna can help explain why the microstrip antenna radiates. Consider the side view of a patch antenna, shown in Figure . The current at the end of the patch is zero and the current is maximum at the center of the half-wave patch. Since the patch antenna can be viewed as an open circuited transmission line, the voltage reflection coefficient will be 1 . When this occurs, the voltage and current are out of phase. Hence, at the end of the patch the voltage is at a maximum (say +V volts). At the start of the patch antenna (a half-wavelength away), the voltage must be at minimum (-V Volts). Hence, the fields underneath the patch will resemble , which roughly displays the fringing of the fields around the edges.

Note that the fringing fields near the surface of the patch antenna are both in the +y direction. Hence, the fringing E-fields on the edge of the microstrip antenna add up in phase and produce the radiation of the microstrip antenna. The microstrip antenna's radiation arises from the fringing fields, which are due to the advantageous voltage distribution; hence the radiation arises due to the voltage and not the current. The patch antenna is therefore a "voltage radiator", as opposed to the wire antennas, which radiate because the currents add up in phase and are therefore "current radiators".