Tham khảo tài liệu 'microstrip antennas part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Design of Low-Cost Probe-Fed Microstrip Antennas 19 and a 75-mm square ground plane was designed using the HFSS software for operation at GHz. The optimized antenna dimensions are shown in Fig. 28 a the simulated input impedance and axial ratio results are presented in Fig. 28 b and the reflection coefficient magnitude in Fig. 29. As expected the microstrip antenna with the new geometry exhibits very good AR dB and reflection coefficient magnitude -48 dB characteristics at GHz without the need for any external matching network. Fig. 29. CP truncated-corner patch axial ratio and reflection coefficient magnitude. Globalstar Antenna Moderately thick microstrip antennas can also be used for bandwidth improvement. To exemplify such application a prototype of a Globalstar antenna was manufactured using a low-loss substrate fir tan 5 and h mm . Left-handed CP Globalstar mobile-terminals require two radiators. The first is designed for uplink frequencies Tx to GHz while the other receives the downlink ones Rx - to GHz Nascimento et al. 2007a . The antenna geometry and a photo of the prototype are shown in Figs. 30 a and b respectively. The optimized antenna dimensions using the HFSS software are presented on Table 2 for the radiators designed on finite ground plane and dielectric L 140 mm W 85 mm . Tx Rx Lt1 mm Lr1 mm Lt2 mm Lr2 mm Ct mm Cr mm Pt mm Pr mm Dt mm Dr mm Table 2. Globalstar antenna dimensions. 20 Microstrip Antennas a b Fig. 30. Globalstar antenna a geometry - b photo of the prototype. The axial ratio and reflection coefficient magnitude are presented in Figs. 31 and 32 for the Tx and Rx antennas respectively. Fig. 31. Globalstar antenna axial ratio and reflection coefficient magnitude Tx radiator. Design of Low-Cost Probe-Fed Microstrip Antennas 21 Fig. 32. Globalstar antenna axial ratio and reflection coefficient magnitude Rx .
