Design Of Multiple Band-Notched UWB Antennas And Broadband Planar Microstrip Reflectarrays

As a key component of the promising ultra-wideband (UWB) systems, themultiple-band-notched UWB antenna has been found to be very useful in wirelesscommunication systems. As a combination of the reflector antenna and the planar arrayantenna, the microstrip planar reflectarray is a kind of new antennas, which combinesthe advantages of these two kinds of antennas. The microstrip planar reflectarray hasinherent advantages over parabolic reflector antennas and planar array antennas, forexample, simple structure, easy fabrication and low cost. Therefore, in recent yearsmicrostrip reflectarrays have become a hot research topic in this field. This dissertationmainly makes insight to the design of multiple-band-notched UWB antennas andbroadband microstrip planar reflectarrays.First, an antenna with dual band-notched characteristics is designed. By embeddingtwo different resonating structures at the proper region on the reference UWB antenna,the dual notched frequency bands are achieved. The surface current distributions on theresonating structures are also used to further analyze the band-notched characteristics.The measured impedance bandwidth defined by VSWR<2of7.8GHz (3-10.8GHz),with the dual notched bands of3.3-3.7GHz and5.0-6.0GHz, is obtained.A novel fork-shaped UWB antenna with triple band-notched characteristics isproposed. By loading three different resonating structures at the proper region on thereference UWB antenna, the triple notched frequency bands are realized. The measuredimpedance bandwidth defined by VSWR<2of7.8GHz (3-10.8GHz), with the triplenotched bands of3.3-3.7GHz,5.15-5.4GHz and5.7-5.9GHz, is obtained.A reflectarray antenna composed of a combination of double-petal loops ofvariable size is presented. To evaluate the performance of the designed element, aparametric study is carried out using Ansoft HFSS. For the optimal parametrics, theproposed structure shows an almost linear behavior, while the phase range is in excessof500°, the phase curves are approximately parallel in8.5-11.5GHz band. Then, aprime-focus77-element reflectarray with this type of element has been designed andimplemented. The measured results show that the obtained1-dB gain bandwidth of thereflectarray with double-petal loop elements reaches as large as25%.At last, a dual-layer T-shaped element is presented for designing a circularlypolarized (CP) reflectarray that converts the linearly polarized incident field of the feedinto an outgoing circularly polarized field. CP reflectarray with a linearly polarized (LP) feed can perform the polarization transformation, such as LP-orthogonal LP,LP-left-hand CP (LHCP), and LP-right-hand CP (RHCP), by means of simply rotatingthe array or its LP feed, respectively. Compared to the microstrip rectangle patch, theT-shaped one shows an almost linear behavior and a much larger phase variation range.Then, a prime-focus81-element reflectarray with this type of element has been designedand implemented. The measured results show that the obtained1-dB gain bandwidthand3-dB axial-ratio bandwidth of the reflectarray with the T-shaped elements reach aslarge as20%and28%, respectively.