Tham khảo tài liệu 'microstrip antennas part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Circularly Polarized Microstrip Antennas with Proximity Coupled Feed for Circularly Polarized Synthetic Aperture Radar 319 B bandwidth Hz This bandwidth requirement must be compatible with a low axial ratio AR below 3 dB for ensuring transmitting receiving circularly polarized waves. To satisfy the matching of input impedance the return loss must be smaller than 10 dB in this bandwidth range. The primary considerations in the design and subsequent fabrication processes are low cost light weight and ease of manufacturing. One antenna aperture will be used for both transmitting and receiving CP-SAR signals with a circulator to control the direction of signal flow into out from the CP-SAR sensor circuit Chan 2004 . The CP-SAR antenna consists of an array of single antenna elements each being a microstrip antenna for circular polarization. Even though it is also possible to obtain a CP array comprising of linearly-polarized elements the electrical performance of a CP-elements array is generally better than that of an LP-elements array Bhattacharyya 2008 namely 1 bandwidth of a CP-elements array is significantly wider about twice than that of LP-elements array and 2 gain of a CP-elements array is significantly higher than that of LP- elements array for large element spacing. The single element patches which have been optimized are then spatially arranged to form a planar array. A better control of the beam shape and position in space can be achieved by correctly arranging the elements along a rectangular grid to form a planar array. The beam pattern for optimum ground mapping function is cosecant-squared beam in the elevation plane E-plane which can correct the range gain variation and pencil beam in the azimuth plane H-plane Vetharatnam et al. 2006 . The antenna side lobe levels in the azimuth plane must be suppressed in order to avoid the azimuth ambiguity. To deal with reflection the antenna side lobes and back lobes also must be suppressed. The antenna gain is .
