Study On Printed Ultra-wideband Antenna With Reconfigurable Band-notched Characteristics

As the decent solution and practical application environment of high-speed wireless communications within short distance, ultra-wideband (UWB) technique has drawn more and more attention attributable to its merits of high date rate, large space capacity and low percent of intercept and capture. The structure and far field radiating characteristic of the antennas for UWB are peculiar due to the special characteristic and application of ultra-wideband technique. So the study of UWB antenna is of great valuable.In this dissertation, the design process of UWB antennas and the method of band-notched characteristic have given respective, according to the two types of common UWB antennas. The printed monopole antenna and printed broad slot antenna are proposed. Then the reconfiguration trait of the notched bands is shown. The major achievements are listed as follows:1. Three methods for the design of UWB antennas have been summarized. Introducing these methods, the UWB antennas with the structure of printed monopole antenna also printed broad slot antenna have figured out, based on the common rectangle metal patch and rectangle slot antenna. The entire size of UWB monopole antenna is0.28λ×0.17λ, which is less by 30% compared with the uniform kind of antenna, with the bandwidth covered 2.75-10.9GHz ( VSWR≤2). While whole size of UWB slot antenna is0.35λ×0.3λ, with well far field radiating characteristics and the bandwidth covered 2.75-10.9GHz.2. Analyzing the distribution of the surface current, the UWB antennas with 3.5GHz and 5.5GHz dual notched bands have devised. With two half wavelength U-shaped stubs embedded in printed monopole antenna, two quarter-wavelength I-shaped stubs and one half wavelength W-shaped stubs embedded in printed broad slot antenna, the radiation of the current is restrained at the frequencies of notched bands in the two UWB antennas. The equivalent electro circuits of the band-notched antennas have given qualitative. The measured results show that the bandwidths of the two UWB antennas both cover 3.1-10.6GHz; the notched bands cover 3.3-3.6GHz and 5.15-5.875GHz. The gain within the notched band is lower by 10dB compared to the gain with crossing band, realizing the purpose of band rejection.3. The reconfiguration of the band-notched characteristics can be studied after the switches embedded into the patch. The RF MEMS switches are selected as the controlling elements, which test to have high isolation and low insertion loss. From the theory of the band-notched characteristics created, the location of the switches can be worked out. The two UWB antennas both have several switches in the special positions. The influence from the states of the switches changed has been analyzed according to equivalent circuit evolving from the transition-line theory.The measured results show that the UWB antennas have the ability to transition within the four working states which comprise no notched band, 3.5GHz single notched band, 5.5GHz single notched band and both notched bands. The isolation among within the four working states proved well, which provide clear evidence for the achievement of the band-notched characteristics reconfiguration.