Study On The Broadband And Conformal Printed Antennas

Rapid development in communication systems has led to the prosperity of antennas, among which two important types of antennas are promising and valuable for applications and have been the international research frontiers. One is broadband printed antennas, which can cover multi communication bands, thus the number of antennas used in the communication systems can be reduced greatly. As a result, the costs, weight, and problems with electromagnetic compatibility and safety aspects in the systems will be decreased. The other is conformal printed antennas, which can satisfy aerodynamic constraints of high speed aircrafts and vehicles and are reliable, durable and aesthetical. In this dissertation, several novel designs of broadband printed antennas are presented, in addition, the characteristics of conformal printed antennas are studied and the experimental verifications are given. The dissertation will include the following contents.Firstly, a survey on the broadband printed antenna and conformal microstrip antenna is presented. Then, the numerical methods such as Finite-Difference Time-Domain Method (FDTD), Method of Moments (MoM) and Finite Element Method (FEM) are introduced in details, which are used to analysis the novel antennas. Further more, the above three methods are compared.Secondly, based on the study of coplanar waveguide (CPW), by linearly tapering the connection area between the CPW feed line and the radiation slots, we get two new designs of broadband printed slot antennas. The impedance characteristics and radiation patterns of the slot antennas with different size of tapers are presented and discussed. For their test antennas, simulated results agree well with the measured ones, and the impedance bandwidth of -10 dB return loss reaches 37% and 40% respectively.Thirdly, a CPW-CPW transition is presented, which changes the size of CPW while keeping the characteristics impedance of CPW unchanged and can be used to connect the printed antenna above or other CPW feed line to a given size coax. Then, the influence of different tapered angles on the propagation characteristics of the transition is analyzed, and the reasonable range of the tapered angle for application is given. Moreover, the performances of broadband printed slot antennas with CPW-CPW transitions are analyzed.Lastly, bow-tie microstrip antennas (BMA) conformal to cylinders with small radius are studied.In order to simulate this complicated antenna accurately, how to set up the antenna analysis model and the solving details are presented. Then, both the radiation patterns and the return loss of the antenna with different cylinder curvature radius and length are calculated. The one-element BMA and two-element BMA array conformal to cylinders with small radius and finite length are fabricated and measured. Theoretical results are compared with experimental results, showing good agreement. It is observed that not only the radiation patterns are changed, but also the resonant frequency is lowered and the impedance bandwidth is reduced significantly when cylinder radius decreased. Therefore, the planar microstrip antenna should be modified when to be mounted on the surface of a cylinder with small curvature radius.