Study On Waveguide Slot Array And Printed Slot Element Antennas

As an important antenna form, slot antenna has been widely used in modern radarand mobile communication systems. Waveguide slot antenna array, notched on thebroad wall of rectangular waveguides, shows remarkable advantages such as highaperture efficiency, compact structure, low losses, high power capacity, easy tomanufacture and assemble. Thus, it has become a promising candidate forhigh-performance radar antennas. On the other hand, printed slot antenna has recentlyfound extensive applications in wireless terminal devices and mobile base stations,because of its attractive characteristics including small size, low profile and low cost,etc. Moreover, by employing different types of slot structures, the printed slot antennascan also achieve multiband and dual-polarized performance. In consideration ofresearch subjects and practical requirements of commercial and military wirelesscommunication systems, this dissertation is mainly concerned with the fast analysis andsynthesis of waveguide slot array and the novel design of printed slot element antennas.The author’s major works and contributions are as follows:1. Waveguide slot antenna array is investigated, and a monopulse waveguide slotantenna array with irregular-shaped aperture is further designed. Firstly, a novelself-adaptive competitive differential evolution (SaCDE) algorithm is proposed forpattern synthesis of antenna array. Self-adaptive scaling factor, self-adaptive crossoverprobability, and competitive mutant strategy are combined in SaCDE to improve thealgorithm’s optimization efficiency. Then, collaborative simulation between SaCDEalgorithm and HFSS software is employed for the pattern synthesis of irregular-shapedwaveguide slot antenna array. In the optimization procedure, the element patterns in theactual irregular-shaped array have been taken into account, which can reduce the errorcaused by the neglect of the mutual coupling among elements and improve the accuracyof the simulation. At last, low sidelobe pattern synthesis of the array can be optimizedefficiently to satisfy the requirements of antenna performance.2. Waveguide monopulse comparator is researched, and a novel cross-shapeddual-layer waveguide structure is applied in the monopulse comparator design. Thiscomparator is composed of four trapezoidal matching short-slot directional coupler andfour delay lines, which exhibits features such as simplicity in design concept, ease ofcontrol and use. The results show that the proposed dual-layer waveguide comparator has the capability to generate precise radar sum and difference signals.3. Multiband printed slot antennas are studied. Three methods are proposed forantenna design to realize multiband operation and miniaturization, including thefollowing:(1) Loading L-strips on slot structure. By embedding pairs of L-shapedresonant strips in a wide open U-slot or a square slot, an independent resonance can beintroduced additionally in multiband antenna with the restriction of not changing theoverall size of the original antenna.(2) Improving a compact RF choke. A novel slotedge resonator inspired by the RF choke structure has been successfully employed intwo multiband antenna designs to realize miniaturization. The experimental resultsshow this type of slot resonator is compact in size and flexible in use.(3) Usingasymmetric design. Special asymmetric configurations applied in microstrip-fed andCPW-fed multiband antennas are able to further reduce their sizes based on methods (1)and (2). Measured results show reasonable agreements with simulated results,manifesting high reliability and validity of the aforementioned approaches.4. Dual-polarized printed slot antennas are investigated. By loading slots incircular patch and adopting two coaxial feeding combined with shorting pins, a noveldual-polarized slot antenna with high isolation and low cross-polarization is presented.Subsequently, on the basis of the proposed dual-polarized slot antenna, dual-polarizedantennas with broad beamwidth and multiband operation are further developed, byusing parasitical metal rods and dual-frequency aperture-shared elements, respectively.The proposed dual-polarized slot antennas exhibit the virtue of superior performance,convenient design and low fabrication cost, indicating their extensive applications invarious wireless communication systems including mobile base stations,WLAN/WiMAX hot spots, etc.