Translated Abstract
Circularly polarized (CP) antennas have various advantages including mitigated polarization mismatch loss, suppressed multipath interferences, insensitivity to Faraday rotation effects and reduced orientation constraints between transmitter and receiver antennas. With the rapid development of modern satellite navigation and communication systems and modern mobile communications, multiband or wideband CP antennas have attracted more and more interests from the industry. In addition, modern electronic devices demand antennas with more compact sizes. To meet the requirements of some practical projects, researches and designs of various CP microstrip patch antennas and slot antennas have been conducted in this work. The details and innovation points of this dissertation are summarized as follows:
1. Multiband CP microstrip antennas with dual feeds have been studied. A quadband shorted stacked microstrip antenna with circular polarization is investigated for Global Navigation Satellite Systems (GNSS) applications. Quadrature phase feeding network is employed to produce CP radiation, and four shorted annular patches are stacked to achieve quadband operation and compactness. Another key feature of this design is the stepped-radius shorting pillar introduced to avoid the inductive effects as a result of longer feeding probes when penetrating thick substrates. The feeding network is implemented by stripline to reduce the antenna structure complexity, the number of feeding ports as well as the electromagnetic coupling between the radiating patch and feeding network. The simulations and measurements demonstrate that the antenna can operate at CNSS L, CNSS S, GPS L1, GLONASS L1, BDS B1 and BDS B3 at the same time.
2. Compact dualband CP microstrip antennas have been researched. A compact dualband CP microstrip antenna is proposed for BeiDou Satellite Navigation System (BDS) applications. The antenna is based on quadrature proximity-coupled feeding structure, and the slot-loading technique is used to achieve dualband operation. To obtain compactness, high permittivity ceramic substrates are employed and the meandered cross-shaped slots are introduced. The antenna aperture is less than λ0/9. In order to generate CP radiation property and maintain compactness, a wideband quadrature phase feeding network is implemented by using a small commercial quadrature hybrid coupler. The simulations and measurements validate that the antenna achieves excellent right-hand circular polarization (RHCP) performance within the BDS B1 and BDS B3 bands.
3. Aperture-coupled CP microstrip antennas have been investigated. A miniaturized cross-aperture coupled CP microstrip antenna loaded by shorting strips and shorting pins is proposed. Under the help of the capacitance and the inductance produced by the loading structures, the overall size and the patch size of the proposed antenna have been significantly reduced by 69% and 75%, respectively, when compared with the conventional antenna. The overall size and the patch size of this antenna are only 0.317λ0?0.317λ0?0.048λ0 and 0.186λ0?0.176λ0. The measured results validate that the impedance and axial ratio (AR) bandwidths are 4.8% and 1.5%, respectively. Through further improving the feeding network of this antenna to be a quadrature microstrip line hybrid, its wideband counterpart has been obtained. The measured impedance, AR and gain bandwidths of the antenna are 18.6%, 26.3% and 12.0%, respectively, which implies a global bandwidth of 12.0%. The global bandwidth of the antenna has been improved by eight times whereas the antenna size is almost kept the same.
4. CP annular-ring microstrip slot antennas have been investigated. Two CP annular-ring slot antennas loaded by proper lumped capacitor and inductor, respectively, are proposed. The efficiency of reactive loading in design CP annular-ring slot antennas has been verified. The prototypes have been fabricated and measured. The measured results demonstrate that the impedance and AR bandwidths for the capacitor-loaded slot antenna are 30.8% and 5.5%, respectively; while those for the inductor-loaded antenna are 34.2% and 6.7%, respectively. Furthermore, a dual-band dual-sense CP annular-ring slot antenna is developed. The antenna consists of two concentric annular-ring slots to achieve dual-band operation. The dual-sense circular polarization can be obtained by loading two suitable lumped capacitors along the outer and inner ring-slots. The experimental results show that the antenna achieves good left-hand circular polarization (LHCP) for the lower band and RHCP for the upper band. The measured impedance bandwidths for the lower and upper bands are 22.2% and 22.6%; and the measured AR bandwidths are 3.6% and 5.6%, respectively, for the lower and upper bands.
5. Adaptive anti-jamming antenna array has been researched and implemented. A prototype for a four-element adaptive space-time antenna array has been designed and implemented for BDS receivers to improve their robustness to interfering signals. First of all, the systematic framework and schematic diagram of the adaptive antenna array is presented. Then, an four-element microstrip antenna array is designed, and the adaptive space-time signal processing algorithm is validated by simulations. In the end, the prototype has been implemented, and the outfield experiments have been carried out. The experimental results demonstrate that the prototype exhibits anti-jamming margins of greater than 70dB and 65dB, respectively, in the presence of single and three wideband interfering signals.
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