Research On Several Issues In Ultra-wideband Antenna And Array

With the rapid development of modern wireless communication technology, the electronic communication equipment is becoming more and more functional and integrated, the demand for antenna is also becoming more and more challengeable at the same time. Due to the advantages of high-speed date rate, good concealment and high resolution, the ultra-wideband(UWB) signal is widely used in indoor wireless communication, modern radar, electronic countermeasure and other fields. In consideration of research subjects and practical requirements of ultra-wideband wireless communication technology in commercial and military fields, this dissertation is mainly concerned with the ultra-wideband planar antenna along with its band-stop implementation methods, ultra-wideband differentially fed antenna and ultra-wideband tightly coupled phased array. The author’s major works and contributions are as following:1. In order to effectively mitigate the undesirable interferences generated from other narrow-band systems within the range of bandwidth of UWB wireless communication systems, the author investigates the methods of realizing the rejected bands for several conventional UWB planar monopole antenna. a). To improve the frequency selectivity of the rejected bands for the antenna, thus completely filtering the narrow-band interference, a compact dual band-notched UWB antenna with high stop-band-edge selectivity using an arcshaped stub on the backside, an arc-shaped slot on the patch and a parasitic resonator near the feed line is proposed. b). On the basis of the capacitively-loaded loop(CLL) resonator, three kinds of modified CLL resonators with multiple resonant frequencies are designed, and then, by employing the resonators along the feed line, the corresponding multiple rejected bands of the UWB monopole antenna are obtained. c). Two dual band-notched UWB antennas are designed by employing parasitic branches. The operating mechanism with the band-stop characteristic is also studied though thorough analysis and discussion.2. Differential circuits has important research significance for UWB communication system, which is due to the super performance of common-mode rejection, low noise, low interference, harmonic suppression, and high linearity. The differential-fed antenna is analyzed and studied in this thesis. Firstly, the basic theory of the differentially driven technique is analyzed and discussed. By introducing the mixed-mode S-parameter matrix, some key parameters of the differential-fed antenna are deduced and analyzed, such as input impedance, differential-mode/common mode reflection coefficient, equivalent reflection coefficient, and so on. Secondly, due to the distorted radiation pattern of the planar monopole antenna at high frequencies, a novel planar UWB antenna loaded with a pair of symmetrical open-circuited stubs is proposed to overcome the radiation pattern sinking. Based on this, a planar UWB differential-fed antenna is designed to improve polarization purity of the radiation pattern, thus obtaining favorable radiation property. Thirdly, a low profile antenna with a unidirectional radiation pattern is proposed. A novel differential feeding scheme is designed to provide an ultra-wideband impedance matching. A parasitic bilayer rectangular ring is adopted to improve radiation directionality, especially in the high frequency band, thus enhancing the gain in the normal direction. At last, taking the differential-fed antenna aforementioned as element, a double-element array is designed to further improve the antenna gain. An ultra-wideband four-way out-of-phase slot-line power divider is employed as the feeding network for the double-element array.3. Combined with project technical specification of low profile, ultrawideband and wide-angle scan, the author designed an ultra-wideband tightly couple phased array(TCPA). First of all, with the guidance of the equivalent circuit model, a TCPA unit cell is designed for infinitely periodic array. The operation bandwidth and radiation property about the unit cell is also analyzed and discussed based on the commercial simulator. Then, the truncation effects for the finite size array is studied and analyzed. The resistive termination and short-/open-circuit termination of edge elements are used to overcome the truncation effects. Cooperated with a finite 4 by 4 array, the numerical analysis of the two termination techniques are analyzed and compared, which validates that short-/open-circuit termination can provide higher efficiency. At last, two wide angle impedance matching(WAIM) layers is adopted to further improve the impedance matching of unit cell. To reduce the calculation time, two semi-infinite arrays(8 by infinite & infinite by 8) can be used to not only study and analyze the edge termination, but also predict the normalized array patterns for scanning in principle planes. Based on the semi-infinite arrays, a finite TCPA with size of 8 by 8 elements is designed and analyzed. The operation frequency bandwidth, the unit active VSWR, the scanning property, and the measurement methods are also analyzed and discussed for the array.