Tuesday, June 10, 2008

Microstrip Antenna Configurations

Microstrip antennas are characterized by a large number of physical parameters as compared to conventional microwave antennas. They can be design to have varied geometrical shapes and sizes. They can be broadly divided into four main categories.

 

Microstrip Patch Antenna

 A microstrip patch antenna is essentially a conducting patch of planar or non planar geometry on one side of dielectric substrate with a ground plane on other side. The radiation characteristics of different shapes of patch are similar despite the difference in geometrical shape because fundamentally all of them behave like a dipole. The figure below shows a rectangular patch having microstrip line feeding and a circular patch with coaxial feeding.

Microstrip or Printed Dipole Antenna

 Microstrip or printed dipoles differ from rectangular patch antenna in their length-to-width ratio. The width of dipole is typically less than 0.05 of wavelength. The radiation pattern of a dipole and patch are similar due to similar longitudinal current distributions, but on the contrary, radiation resistance, bandwidth and cross polar radiation between the two types differ. Microstrip dipoles are attractive elements owing to their desirable properties such as small size and linear polarization. They are well suited for higher frequencies for which the substrate can be electrically thick, and can therefore attend significant bandwidth.

 

Printed Slot Antenna

 Printed slot antennas comprise a slot in the ground plane of a grounded substrate. The slot can have any shape. Theoretically most of the microstrip patch can be realized in the form of a printed slot. Like patch antennas, slot antennas can either be fed microstrip line or coplanar waveguide. They are generally bidirectional radiators: unidirectional radiation is obtained by using a reflector plate on one side of the slot.


Microstrip Traveling Wave Antenna

 Microstrip traveling wave antennas consist of chain shaped periodic conductors or a long microstrip line of sufficient width to support a TE mode. The other end of traveling wave antenna is terminated in a matched resistive load to avoid the standing waves on the antenna. Traveling wave microstrip antenna can be designed so that the main beam lies in any direction from broadside to end fire.

 

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