Theory And Design Of The Miniaturized Broadband And Wide Beamwidth Circularly Polarizedantennas

The purpose of communication is transmitting and exchanging information. With therapid development of modern wireless technologies, people can communicate with eachother almost everywhere and anytime. Antenna, which is a transfer device to transmit andreceive electromagnetic wave, plays an indispensable role in the wireless communicationsystems. To meet the strigent miniaturization requirement of the entire system, it becomesmore and more important to reduce the size of the related antennas.To this end, the focus of this dissertation is on the theories and technologies forminiaturization of a class of resonant circularly polarized antennas, without muchcompromise of the electromagnetic performance of the original antennas. The maincontents of this dissertation include the theory and design methodologies of the antennaminiaturization, with the emphases on the design of the small-size broadband, widebeamwidth, and specific-platform-mounted circularly polarized antennas.Firstly, combined with the existing antenna miniaturization technologies, a novelwideband circularly polarized antenna with small size at L band is proposed. By using adielectric substrate with high dielectric constant to reduce the antenna size and a flexiblefeeding mechanism to broaden the bandwidth, a dual-feed wideband U-slot microstripantenna structure is designed. The small antenna has a more than20%overlappeedbandwidth (voltage standing wave ratio less than2and axial ratio less than3dB), andshows stable radiation characteristics in the entire working frequency band. As animprovement, we combine the proposed U-shaped slot patch antenna with the foldedconducting wall to further reduce the size of antenna. In the design, we modify the structureof ordinary folded conducting wall to simplify the construction process and reduce themanufacturing cost as well. The antenna shows a very wide circular polarizationbeamwidth and its3dB axial ratio beam covers the entire upper hemisphere.Secondly, an experience-based integrated design procedure for antennas working onspecific platform with strigent environmental requirements is presented to guide the designof the platform-mounted antennas. According to this guideline, we successfully design atwo-element omnidirectional circularly polarized antenna array for inter-missilecommunication at S band, and an endfire microstrip antena with wide circular polarization beamwidth at C band for missile-borne system. In the former design, we use the foldedslots to reduce the size of cavity backed slot antenna, broaden the radiation beamwith usingtwo cross slot with unequal arm length, and optimize the coaxial feeding position toimprove the impedance matching and the axial ratio of the proposed antenna. Two similarantennas are installed on the missile symmetrically in circumferential direction, whichresults in an almost three-diemensionally omnidirectional radiation. While in the latterdesign, to avoid using the scanning antenna array that often requires a complex feedingnetwork, we propose a novel wideband circularly polarized microstrip Yagi antenna withend-fire radiation. The designed antenna has enough high gain in the endfire direction, andthe circular polarization beamwidth exceeds80oin both the vertical and horizontal planes.Finally, in order to overcome the limitation of the conventional design methods forantenna miniaturization, the meta-surface based antenna structures are investigated in detail.A stacked circularly polarized microstrip antenna loaded with partially reflective surfaces(PRS) is designed to improve the gain of the original antenna. The PRS reduces the antennatransverse dimensions significantly when compared with the conventional antenna arrayingtechnology. Therefore, this method is suited to decrease the number of array elements andconsequently the fabrication cost for a large antenna array. In addition, another meta-surface based antenna structure, reactive impedance surface based antenna (RIS-antenna),is also studied in depth to achieve further miniaturization of the antenna. The author usesthe capacitive region of the RIS to minimize the antenna dimension for the first time. It isfound that the capacitively loaded antenna owns lower working frequency if compared withthe inductively loaded RIS-antennas proposed by other researchers in the exisging literature.At last, the author uses a hybrid miniaturization method that combines the modified foldedconducting wall and RIS together to present a very compact CP antenna design which onlyhas the lateral dimension of1/5wavelength.