چكيده به لاتين
Abstract:
Nowadays, war equipments are required to be camouflaged from the enemy radars and antennas are necessary part of theses equipments. Microstrip antennas are proper choices to be installed on military platforms due to their lightweight and easy fabrication. Most of the time, gain of theses antennas is not sufficient and they are used in array configuration with large ground plane which can reflect electromagnetic waves and make high radar cross section (RCS).
Lots of methods are presented to reduce the RCS of patch antennas. One of them is using frequency selective surfaces (FSS) in which antenna propagation characteristics are preserved. In this thesis, RCS reduction is realized using FSS in ground plane, substrate and superstrate of patch array antenna. First, ground plane of the antenna is substituted with band stop FSS. Array antennas have limited space for FSS cells and therefore, miniaturized FSSs are employed to make wide band RCS reduction. Because stop band FSSs are transparent to incident waves in RCS reduction frequency range, wide band absorbers are needed beneath the antenna to avoid back scattering from the other objects behind the antenna. For patch antenna with microstrip feed, some designs are studied to use commercial and plasma absorbers and new plasma absorber is introduced with combination of plasma and lossy FSS to reduce the RCS of the antenna.
Transmission line analysis is a fast and useful method for 2-D and planar structures. However, circuit model of many FSSs are not available. For example when some FSSs with different shapes are combined to make a new FSS or when FSS is placed in a complex medium, transmission line method cannot be applied because of lack of circuit model. In this thesis a new approach is introduced to find the circuit model of a complicated FSS. Also an equivalent circuit model is presented for lossless and lossy FSS embedded in plasma layer which can be employed for transmission line analysis of the plasma absorber.
FSSs can also be used above the antenna for RCS reduction. For instance, an absorptive and partially reflective FSS as a superstrate of patch array antenna is investigated. Also using a mantel cloak for monostatic and bistatic RCS reduction of patch antenna on a cylindrical perfect electric conductor is studied.
Keywords: Radar Cross Section Reduction, Patch array antenna, Frequency Selective Surface (FSS)