Study And Design On Circularly Polarized Microstrip Antenna

The design of circularly polarized microstrip antenna is mainly studied in this thesis. Nowadays, circularly polarized antenna has been widely used in various wireless communication systems because of its unique characteristics in anti-jamming and anti-fading. As the quickly development of modern communications, circularly polarized antenna is required to have some new characteristics, including miniaturization, directional radiation and multi-band operation.The main works in this thesis are as follows:First of all, a reduced-size circularly polarized microstrip antenna for 2.45 GHz ISM applications with two feed points is designed. This proposed antenna is fed with a Wilkinson power divider and a phase shifter to generate circularly polarized radiation. A set of slits and slots are used on the patch to increases the length of the current streamlines associated with the fundamental mode of excitation, which effectively reduce the size of the patch. The area of the patch measured is reduced by 33%.Secondly, a directional dipole circularly polarized antenna is proposed. This antenna is designed based on coaxial-fed printed dipole antenna. Four resonant units with identical structure is used to generate two orthogonal modes with equal amplitude, which are connected by two quarter-wavelength microstrip to generate circularly polarized radiation. A reflector is placed beneath the antenna to transform bi- directional radiation into directional radiation. The measured gain on the main radiation direction reaches 9.2dBi.Finally, a dual-band slot circularly polarized microstrip antenna is proposed. This antenna generates two resonant frequencies by two concentric annular slots on the ground, and on the angular positions with 45 degrees inclined of each annular slot two bent structures are loaded to generate circularly polarized radiation. The radiation of this antenna is bi-directional and the directions of rotation are opposite on two directions.