Research On Broadband Unidirectional Microstrip Printed Circularly Polarized Antenna

Some researches and analyses corresponding to broadband unidirectional microstrip printed CP antenna have been present in this thesis. The radiative mechanisms about various CP antennas fabricated by printed circuit board(PCB) technique are explained briefly. Diversified desgins have been presented coincided with the theoretical analysis, and the experimental results of someone have been given. Some research achievements have been published in foreign journals. The main researches are organized as follows:1. A novel Unidirectional CP antenna with broadband feature has been proposed for the Third-generation System(TD-SCDMA, WCDMA, CDMA 2000), Wireless Local Area Network(WLAN 2.45 GHz), and Long-term Evolution(band 1, 39, 40) applications. Based on rotation feed technique of orthogonal dipole, four rotated orthogonal printed dipoles are connected through an annular strip whose length is 3/4 λ. This can provide the precondition of CP radiation. A gradually varied feed balun is applied to realize good impedence matching. In addition, the dipole’s arms are designed as folded form to decrease antenna’s transverse size tremendously. Measured 3 d B axial ratio(AR) bandwidth is 35% within an average gain 6.3 d Bic.2. A dual-band dual-sense coplanar waveguide(CPW) fed printed CP antenna is proposed for WALN(2.45 GHz and 5.8 GHz) applications. A dual-L shaped stub is designed to create dual broadband operation. What’s more, the grounded perturbations are embedded to realize dual circular polarization. Study shows that the spherical cap reflector can achieve better directional characteristic and gains than plane reflector especially in a large frequency ratio. So a spherical cap reflector which is corresponded to concerned frequency is proposed to obtain higher gains and better unidirectional radiation in a large frequency ratio.3. According to the P, L, S, C band application demands, an ultra-wide bandwidth printed spiral antenna covered 0.5~6 GHz is studied. Due to the frequency-independent theory, two-arm archimedean spiral printed antenna is chosen as an original type to realize ultra-wide bandwidth CP communication. Combing the hybrid substrate loaded technique with a novel stacked cavity, better unidirectional CP radiation is obtained. Results shows antenna’s voltage standing wave ratio(VSWR) is less than 2 within the concerned bandwidth 0.43~6.5 GHz, and the 3 d B AR bandwidth covers 0.9~6.2 GHz.4. For satellite communication system in Ku-band, antennas regarded as receiver and transmitter should be lower profile and less cross polarization, while the CP antennas are usually used to recede interference. Therefore, a 2×2 printed CP array based on rotated feed for Ku-band satellite communication is present. The microstrip slot coupling feed technique and stacked printed patch are applied to enlarge antenna’s bandwidth. Two kinds of power divider for 90° phase shift and 180° phase shift which have wideband characteristic are designed carefully for rotation feed technology. Results indicate that the proposed array has a 2 d B CP band of 34.5%.