Research On The Wideband Techniques For Efficient And Miniaturized Antennas

As the key components for transmitting and receiving electromagnetic waves,antennas play a crucial role in wireless communication systems.In the trend of light weight,high volume,high velocity of the wireless communication systems,antennas are in highly demand of efficient radiation,miniaturization,and broadband characteristics.(In this dissertation,the term “efficient” represents high radiation efficiency of an antenna,which is the ratio of output radiate power and input radiate power of the antenna).Considering that the bandwidth is theoretically restricted by the antenna’s size,it is highly desirable to realize wideband compact antennas with resort to new techniques.Owing to the high radiation efficiency characteristics of the near-field resonant parasitic(NFRP)elements in miniaturized antennas designs,in this dissertation,several efficient,wideband,compact antennas are proposed following the methods of introducing more NFRP elements,adapting NFRP elements,and combining intelligent algorithms.The main contents and innovations are:In Chapter 2,a method for enhancing the bandwidth of the low profile,compact,circularly polarized(CP)patch antenna is analyzed.In detail,one NFRP patch,which sets between the radiating patch and the ground,is introduced to tune the perturbations of this CP patch antenna.The corresponding axial ratio(AR)modes of the CP antenna are also tuned to expand the operational bandwidth.The measured results showed that the antenna has stable radiation patterns and wide AR beamwidth over the band.Its fractional impedance and AR bandwidths are 4.6% and 2.33%,respectively.Compared with the traditional CP patch antenna at the same low profile,the AR bandwidth of the reported antenna is 2 times larger.In Chapter 3,several wideband small compact monopole/dipole antennas enabled with interdigitated NFRP element are presented respectively.Inspired by metasurface antennas(MSAs)which utilize several discrete subwavelength patches to enhance bandwidth,the NFRP element was firstly designed in an interdigitated version.With resort to the monopole/dipole excitation,it is investigated that the fundamental mode and first higher mode of the interdigitated NFRP element can be overlapped to realize a wide impedance bandwidth.The wideband electrically small dipole antenna,linearly polarized(LP)and CP magnetic-based compact antennas are proposed and experimentally validated,respectively.All the measured results demonstrated that these antennas hold the advantages of wideband,stable radiation patterns and high radiation efficiency(>88%).Compared with the antennas utilizing intact NFRP element,the bandwidth is significantly enhanced.In Chapter 4,a wideband,flexible electrically small dipole filtenna is presented.Firstly,the operating mechanism and tuning method of the inherent radiation null of the dipole-driven NFRP antenna is presented and analyzed.Then,by implementing multiple NFRP elements and properly allocating their relative physical positions,an electrically small NFRP filtenna with two adjustable radiation nulls is attained.This antenna exhibits good bandpass characteristics at an electrically small size: ka ～ 0.924(the corresponding frequency point is 1.96GHz).Finally,the flexibility of this antenna was validated under different bending conditions and the results confirmed that its performance characteristics are substantially maintained.The radiation efficiency is higher than 82% at all bending conditions.Compared with the referenced dipole antenna at the same electric size,the bandwidth is enhanced by 37% and the frequency selectivity at two edges are also enhanced respectively.In Chapter 5,an intelligent algorithm based,small compact wideband antenna design concept is proposed.To take full advantage of wideband characteristics of spherical antenna,a three-dimensional(3-D)-printed,wideband,compact hemispherical-shaped antenna is presented,which is based on the particle swarm optimization(PSO)algorithm.With resort to the near-field capacitive couplings between the NFRP elements and the driven monopole,the bandwidth is enhanced under the optimization process of PSO algorithm.The antenna was fabricated using the low-cost 3D printing technology.The measured results show that this antenna has a wide fractional bandwidth of 17.97% and high radiation efficiency of 85% at an electrically small size,ka=0.837 corresponding to the frequency point 666 MHz.Compared with the single monopole antenna,the bandwidth of the reported antenna is ～1.7 times larger.