Study And Design On Planar Circularly Polarized Combined Dipole Antenna

Circularly polarized(CP) antennas have been widely used in mobile communication systems, satellite communication systems and radio frequency identification systems owing to its unique advantages. In general, most planar, small-element CP antennas have broadside radiation patterns or end-fire beam in perpendicular with the plane of the antenna. If an end-fire CP beam in parallel with the plane of the antenna is desired, additional orthogonal elements will be introduced and they may lead to non-planar configurations. Therefore, it is challenging to design a planar CP antenna with an end-fire beam in parallel with its plane while maintaining a simple, planar structure and a relatively small size as well. In this thesis, a loop-parallel plate combined antenna is analyzed at first. It is found that the gain of the loop-parallel plate combined antenna is too low to get practical. Then, a loop-aperture combined antenna is analyzed. The operation principle of the loop-aperture combined antenna is analyzed at first. Then, an optimized loop-aperture combined antenna is designed and demonstrated to exhibit an end-fire beam in parallel with its plane. The main content of this thesis is organized as follows:1. A novel planar CP antenna with an end-fire beam in parallel with the antenna’s plane based on orthogonal magnetic dipoles combination is proposed. At first, an equivalent sources model is analyzed and used to deduce a loop-aperture combined antenna configuration. Then, the antenna is designed with parametric studies.2. Based on the design approach, the initial parameters are determined. Parametric studies are carried out and the optimized dimensions are chosen to simultaneously obtain the best reflection coefficient and 3dB axial ratio bandwidth. The parameters are analyzed and optimized by using HFSS.3. The prototypes of one kind of the antenna are fabricated and measured by Agilent’s 8720 ET vector network analyzer, NSI’s NSI-800F-10 x far-field antenna measurement systems and Satimo Starlab near field antenna measurement systems. The simulated and measured results agree well with each other. The |S11| is lower than-10 dB and axial ratio is smaller than 3dB in 5.73-5.90 GHz. The proposed antenna can be used as a low-profile, cost-effective, hand-held reader antenna for radio frequency identification(RFID) systems.