Design Of Reconfigurable Antennas And Research On Direct Antenna Modulation Technology

Reconfigurable antennas have a great number of advantages and can be widely used in the multi-functional and multi-band communication. High-security communication technology is also of great importance to the wireless communication. In this thesis, the research on reconfigurable antennas and the high-security communication of direct antenna modulation technology is carried out. The contexts of the research can be widely used in the fields of multi-functional, multi-band and high-security wireless communication. The main work in this thesis is mainly reflected in the following aspects:Firstly, a novel microstrip patch antenna with both frequency and circular polarization diversities is presented in this thesis. The proposed antenna consists of two parts, a patch with two orthogonal slots on the upper substrate and a 3 d B hybrid coupler fed structure which printed on the lower substrate. Two groups of diodes placed across the orthogonal slots are utilized to achieve frequency reconfiguration. Another two diodes, placed between the input port of the antenna and the 3 d B hybrid coupler, are utilized to switch between left-hand circular polarization(LHCP) and right-hand circular polarization(RHCP). The simulation and measured results verify the reconfigurable characteristics of the antenna.Then, a single-fed reconfigurable antenna with multi-band and multi-polarization functions is presented. The proposed antenna consists of a square patch fed along its diagonal line with four parasitic stubs added around its four sides connected by four PIN diodes. The center of edges of two stubs far away from the feed point is connected to ground via another two diodes, while those of the other two stubs are connected to ground via capacitors. By turning these diodes on and off, the antenna has five different operating states. It is capable of switching between right hand circular polarization(RHCP) and left hand circular polarization(LHCP) in the single frequency band, or operates at two frequency bands with reversed linear polarization. In addition, it can radiate 45 o linear polarization as a traditional patch antenna fed along its diagonal line. The measured results verify the reconfigurable characteristics of the antenna.Finally, the multi-directional secure communication based on direct phase modulation array is discussed. The mechanism of the direct phase modulation and its advantages in the communication are introduced. Then, the technology is applied to a one-dimension array. Its multi-directional communication and secrecy are analyzed in detail. The bit error rate(BER) calculation formula for the traditional communication and the direct antenna modulation is discussed. The differential evolution(DE) algorithm is used to optimize the phase offset of each element. The BER of traditional phased array is compared with that of direct phase modulation array in every direction. The simulation results of BER show the high security of the multi-directional transmission based on the direct phase modulation array.