Ultra-wideband Antenna Miniaturization Technology And Its Application In Broadband Planar Reflect Array Antenna

With the rapid development of wireless communication technology,there is a rising demand in miniaturized,planar and wideband antennas.The ultra-wideband(UWB)communication technology has many advantages such as high transmission rate,large system capacity,low power consumption,low cost,and capability against the multipath interference.Therefore,UWB antennas and their miniaturization techniques have become a hot and also a challenging topic in both academia and industries.On the other hand,for long distance communication systems,high gain and directional antennas are needed,therefore the microstrip antenna array and the parabolic dish antenna are good options.However,the microstrip antenna array usually requires complicated feeding networks,which leads to a reduced antenna gain and efficiency,while the parabolic dish antenna suffers from its bulky size and lack of mobility.The reflectarray antenna is a good solution to tackle the above-mentioned drawbacks of microstrip antenna array and parabolic dish antenna,which features advantages such as light weight,low cost,high efficiency,and conformal structure.In this dissertation,various methods to design miniaturized UWB antennas are firstly studied and a miniaturized UWB dipole antenna is then designed and analyzed.Two miniaturization techniques are thereafter employed for reflectarray element designs and it is shown that the bandwidth of reflectarray antennas has been broadened effectively.The main contents of this dissertation are arranged as follows:1.The miniaturization of a printed planar UWB dipole antenna is presented.By introducing a concave arm besides the dipole,an electromagnetically coupled region is observed on the one half of the antenna.This results in a lower cutoff operating frequency and the other half of the antenna is responsible for a UWB performance,which leads to both the miniaturization and UWB operation of the antenna.The measured results show that the proposed antenna achieves a bandwidth of 133% covering 2 GHz-9.9 GHz and features a size of 0.28?×0.28?(? is the free space wavelength at 2 GHz).2.Based on a slotted rectangular patch unit cell,the concave arms are introduced to broaden the bandwidth of a reflectarray antenna.By placing a pair of concave arms alongside the slotted rectangular patch,extra resonance is introduced and the element is optimized for a wider phase range and a more linear phase slope.The measured results show that the proposed antenna achieves a gain of 25.7 d Bi at 10 GHz,an aperture efficiency of 65%,and a 1-d B gain bandwidth of 32%.3.The half-cut approach which is used in UWB antenna miniaturization,is employed to design a reflectarray unit cell.Using the half-cut method on a slotted rectangular patch structure,the unit cell size is halved and the structure can be optimized to achieve satisfactory reflection characteristics.This results in more elements arranged in a given aperture and therefore an improved performance can be achieved.The simulated results show that the proposed antenna exhibits a 1-d B gain bandwidth of 43.2% and a maximum aperture efficiency of 64.5% at 10 GHz.