Study On The Analysis And Control Of Radar Cross Section Of Antennas

Today, due to the rapidly development of stealing technology, the RCS levels of many weapons such as aircraft and warship is decreased for 1 or 2 quantities. Meanwhile, the RCS of platform themselves become very small by using the Frequency Selective Surfaces (FSS), Radar Absorbing materials, High Impedance Surfaces (HIS), etc. Then the main factor that impacts the RCS of platform is the antennas on the platform. So it is important to analyzing and reducing the RCS of antennas for the design of stealth platform. The analysis and reduction of the RCS of antennas are the two main research objects of this thesis. The main contributions and innovation of the thesis are outlined as follows:1. Inspired by the multiplication principle of radiation pattern, we present scattering pattern of array antennas can also be decomposed into the multiplication of array scattering factor and element scattering. Base on the basic theory of antenna scattering, the formula of array scattering factor is derived.Some important properties of array scattering is obtained through analyzing the array scattering factor, then some important conclusion are drawn: first, the scattering pattern of array antennas is affected by the structure of array configuration, and there are no relationship between the scattering pattern of array antennas and elements; Second, the amounts and angles related to the peak scattering of array antennas is determined by the interelement spacing. Meanwhile, the angle related to the peak scattering is varied with the interelement spacing in a special rule. Third, it can be seen that the scattering properties of array antennas is mainly determined by the configuration of array, rather than antenna elements.2. A new method to synthesize the scattering pattern of array antennas is presented in the thesis. The scattering peaks of array antennas are restrained by the spatial arrangement of array elements which is obtained by optimizing the array scattering factor. In order to validate the proposed method, the scattering patterns of a planar Half-dipole array, a bow-tie antenna array, and a waveguide slots array are optimized, respectively. The simulated and calculated results validated the proposed method. Through the optimization of the scattering pattern of array antennas, it was found that the proposed method can help to restrain the peak scattering when the antenna elements are connected any loads. For the waveguide slot array, the optimized positions of the slots are affected the scattering pattern in different ways, when the incident wave excited the slot or not. When the incident wave excited the slots, the optimized positions of antenna elements can restrain the peak scattering. Otherwise, when the incident wave can not excited the slots, the optimized positions of antenna elements have little impact on the scattering pattern.3. A new FSS structure which has high frequency selectivity is presented utilizing the equivalent circuit model. The proposed FSS is a transformation form of conventional square-loop FSS. Besides, four narrow branches are added to each element, and connect to other neighboring elements to decrease the bandwidth of the proposed FSS. After analyzing the amplitude and phase of reflection coefficient, it can be concluded that the FSS acts as perfect conductor surface when it reflects the incident wave whose frequency is in the stop-band of the FSS. Consequently, in order to reduce the RCS of a microstrip dipole antenna, the metallic ground of the antenna is replaced by the proposed FSS ground. The simulated and measured results show that the RCS of the antenna is reduced considerably when replacing the metallic ground with FSS ground.4. For the normal incident plane wave, the reflection phase of High Impedance Surface (HIS) is 00, and the reflection phase of metallic surface is 1800. Hence, a new method that reduces the RCS of objects is proposed. In this method, the scattering from HIS and PEC surface is canceled out due to the different reflection phase when combining the HIS and the PEC surface. In order to validated the proposed method, the HIS is added surround the two microstrip antennas to cancel the reflected field from the metallic surface of antennas. The simulated and measured results proved that the proposed method can effectively reduce the in- band RCS of micrstrip antennas.