Research On The Radiating And Scattering Characteristics Of Low Profile Antennas And Their Arrays

In recent years, with the development of mobile communication, satellite communication and radar technology, development trend of antenna technology is towards directions of low profile, broadband and high gain, and many new types of antennas are put forward. However, theoretical and experimental results show that the contribution of antenna to the complete RCS is very large within a certain scope of observation angle. This destroys stealth property of object. Therefore, radiating and scattering characteristics of low profile antennas and their arrays are studied together in this dissertation. It is hope by the work of this dissertation that some new kinds of miniaturized, wideband and high gain antennas for mobile communication and direct satellite broadcasting can be found, meanwhile, ways for reducing scattering of antennas can be found by analyzing of scattering mechanism.The main work and innovations of this dissertation are following:1. Base on magnetic frill feeding model of coaxial cable, a new coaxial cable feeding model of magnetic frill that contains an internal resistance is proposed. A voltage source with internal resistance is placed in the gap between inner conductor of caxial cable and ground plane. The effect of inner conductor diameter of the coaxial cable is considered by technology of thin wire simulation. Using this model, computing time is saved and efficiency is improved.2. The parallel FDTD method based on MPI is studied on high-performance computer cluster. A code of parallel FDTD for descrization space with N×M×P(N,M,P≥3) subdomains is written, and the correctness and efficiency are verified. This part of work provides computation platform for further simulation of electrically large objects.3. A novel planar monopole is proposed, whose bandwidth is improved by placing parasitic element close to the monopole element, the frequency range of this antenna can cover frequency bands of DCS, PCS, UMTS, and 2.4G WLAN. Another novel microstrip-fed folded wideband planar monopole antenna is also proposed, by folded approach, height of antenna is reduced. Simulation results and experimental results of these two kinds of antennas are in agreement.4. Using parallel FDTD method, a 2×2 array composed of wideband double H-shaped aperture-coupled microstrip antennas, and a 4×4 array composed of inset-fed patch antennas are studied. They can operate in Ku band within 11.4GHz-13.4GHz and 11.4GHz-12.8GHz respectively. The effect of the structure parameters on the element impedance and return loss of the whole array is analyzed. Simulation results are in agreement with experimental results.5. Characteristics of RCS of microstrip antennas with finite ground plate are studied. Methods of loading with lumped impedance and with slots cut in the patch for reducing RCS of microstrip antenna are studied. The results show that lumped impedance loading can reduce RCS at resonant frequencies, while cutting slots in patch properly can reduce RCS in a relatively wider frequency band, but radiation property of the antenna changes little.6. A separation method is put forward, which can be used to study the contributions of patch, substrate, and ground plate of microstrip antenna individually. By this method, it is found that the RCS charateristics of the microstrip antenna array are similar to that of metallic plate within the large amount of frequency band. The patch only contributes to the total RCS when operating frequency is approaching the resonant frequency of patch. In addition, the effect of cutting slots in ground plate, loading between patch and ground plate, and distributed loading on ground plate on reduction of RCS is studied. Part of the simulation results are verfied, and the computation results are in agreement with measured results.7. Scattering characteristics of planar dipole arrays with and without reflectors are studied. The influence of loading in dipole centers by loads, such as inductance, capacitance, resistance, parallel connetion of capacitance and resistance, open circuit, and short circuit, on scattering characteristics of antenna array is analyzed. The results show that RCS of dipole array without reflector can be minimized by loading inductance in dipole centers, but for dipole array with reflector, loading resistance in dipole center can minimize the RCS.