A PHYSICALLY SMALL DUAL CIRCULAR MICROSTRIP ANTENNA

Abstract

The microstrip antenna has recently gained popularity because it offers the advantage of flush mounting, small size, and low cost when fabricated by etched circuit techniques. In an effort to further reduce the aperture requirements, two circular microstrip antennas were placed one on the other and fed independently. Utilization of the field null at the center of the circular disk antenna allows independent excitation. In this configuration, two different frequencies can be transmitted simultaneously while sharing the same physical aperture. Polarization of the antennas is linear with well behaved radiation patterns exhibiting gains of 6 dBi. Moderate power levels can be accommodated by selection of suitable substrates and control of dielectric thickness. As a result of the reduced size, the antenna can now be placed in areas otherwise thought impractical. Placement in front of certain antennas or retrodirective reflectors has a very minor effect on their performance.