Four Dimensional Conformal Array Antenna Technology Research

With the continuously increasing requirement for advanced aerocrafts in modern electronic warfare, in order to keep the good aerodynamic performance and electromagnetic transmitting/receiving performance, antennas onboard aerocrafts are usually required to be conformal with the surfaces of the aerocrafts, thus forming the conformal antennas or antenna arrays. Conformal antenna has many excellent electromagnetic merits, such as good electromagnetic compatibility, insusceptible to electronic interference, and small radar cross section (RCS), etc. Consequently, it becomes one of the most concerned development directions in modern antenna technology. Usually, conformal antenna arrays are also required to have low/ultra-low sidelobe levels (SLLs). However, if conventional conformal antenna arrays based on amplitude weighting are used the dynamic range ratios of the amplitude excitations are generally rather high, resulting in stringent requirements on precision of the feeding network which even cannot be realized in practice.On the other hand, if an additional degree of design freedom-time-is introduced into conventional conformal arrays and thus forming the conformal four-dimensional (4D) antenna arrays, the low/ultra-low sidelobes can be realized with lower dynamic range ratios of amplitude excitations by the time modulation. This thesis is just to focus on both of the advantages of4D antenna arrays and conformal antenna arrays, studing on the relevant techniques of conformal antenna arrays based on the theory of4D antenna arrays. The thesis is mainly divided into following three parts:Firstly, the relevant basic principles and the key technical problems to be resolved for the conformal antenna arrays are introduced in this thesis, mainly focused on the study of beam forming and pattern synthesis of the conformal array antenna’s fundamental forms such as the circular arrays or spherical arrays. Meanwhile, optimal design for microstrip antennas suitable for conformal array design are investigated. A relatively broadband conformal parasitic patch antenna with low-profile is proposed and designed, and the experimental results show the excellent radiation performance of the element that is suitable for being mounted on the conformal carrier. Secondly, the4D antenna array theory is applied to the design of conformal antenna arrays. Some technical requirements are studied on the conformal4D antenna arrays in order to achieve high quality conformal arrays with low price and simplify the feed network to reduce the complexity, which are difficult to realize in the conventional conformal arrays. The time sequences of the conformal4D antenna arrays are optimized using the differential evolution (DE) algorithm. The results show that it can be used to synthesize the desired low/ultra-low sidelobe patterns and realize shaped beam with lower dynamic range ratios of amplitude excitations.Finally, the fundamental experiment has been carried out to verify the conformal4D antenna array theory. A full-wave simulation was conducted in frequency domain using the commercial software HFSS to obtain the patterns at the center frequency and other sideband frequencies. The mutual coupling effect of the antenna elements in the practical conformal arrays can be solved by the optimization approach combining the DE and HFSS or by synthesizing patterns with practical testing element pattern. The simulated and some measured results validated the method of pattern synthesis in conformal4D antenna arrays, which have better performance in practical antenna system as compared to conventional antenna arrays.