dc.description.abstract |
Circularly polarized antennas are used in mobile communication, satellite communication
and in other communication systems. The receiver is then able to pick the transmitted
signals without a polarization mismatch due to the alignments of the antennas. It can also
mitigate multi path interference. In multi path conditions, the reflected signal changes the
hand of the circularity giving a polarization mismatch with respect to the signal that
arrives from the direct path. Therefore a circularly polarized receiving antenna will pick
only the direct path signal which has the desired hand of circularity.//
Circularly polarized micro strip antennas can be used in communication systems where the
geometry and the size are constraints because it is lightweight, miniature in profile and
etched on a double sided printed circuit board.//
Analysis, design and implementations are presented of square, nearly square and circular
single feed circularly polarized micro strip antennas. In order to get familiarized with the
basic theory. A linearly polarized micro strip antennas were first made. Circularly
polarized 4 patch planner array antenna, circularly polarized circular patch antenna,
circularly polarized micro strip Yagi array antenna and a circularly polarized micro strip
frequency scanning antenna were designed with the help of the single patch designs.
Transmission line model and resonance cavity model were used in the analysis while the
mode detuning method was used to obtain circular polarization.//
The single square patch and the single circular patch antennas designed for 9.4 GHz for
RHCP showed broad radiation patterns, both in the E- plane and the H -plane, as expected
from theory. The polarization was nearly circular while no measurable gain was observed.//
The circular patch with protruding perturbations for mode detuning behaved very similar
to the circular patches having perturbations with depression. Therefore both methods
appear equally good to produce circular polarization.//
The circular patch antenna designed for RHCP for 1.4 GHz had a total gain of 5.74 dBi
Its radiation pattern is broad and hemispherical and thus this antenna could be fixed on a
vehicle for MSAT applications.//
The 4-square patch planner array designed for RHCP for 9.4 GHz had a gain of 4.5 dBi.
Its measured radiation pattern had 2 major lobes as expected but it also showed minor
lobes which was not seen in the theoretical radiation pattern. This could also be a useful
antenna for MSAT applications.//
The micro strip Yagi antenna for RHCP designed for a frequency of 1.150 GHz had a
total gain of 6.2 dBi and its major lobe was tilted by 35° from the broadside direction. By
suitable alteration to the element separations, it is possible to tilt the beam by a desired
angle.
I
A 2-element square patch array for RHCP designed for a frequency of 1.4 GHz showed a
gain of 4.88 dBi. The measured radiation patterns obtained for the frequency rage from
1.17 GHz to 1.625 GHz had a significant similarity with the theoretical radiation patterns
and demonstrated the possibility of frequency scanning with the antenna. |
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