Research On Novel Feed Networks And Applications

Feed network plays an important role in phase-array antenna and radar systems. Antenna array with good performance needs not only favouable radiating elements but also matching feed networks. Power dividers, phase shifters, couplers, and filters are the basic components of common feed networks which can realize impedance matching, amplitude and phase control, harmonic suppression etc. With the development of multi-band/multi-standard wireless communication, current and future mobile terminals become increasingly complex because they have to deal with a variety of frequency bands and communication standards. So the weight, volume and multi-band/multi-mode functionality are the key factors to be considered in antenna design and manufacture. As a part of an antenna, feed network should achieve small size, light weight, multi-band/multi-mode functionality. In recent years, microsrip line has attracted serious attention in microwave components because its advantages of low profile, conformability to a shaped surface, ease of fabrication, and compatibility with integrated circuit technology. Based on the theory of microstrip line, this dissertation is devoted to creating novel dual-band power divider, phase shifter, wide band coupler and dual-band band stop filter structure. The main innovations of this dissertation are listed below:(1) On the basic of power divider, three novel dual-band power divider structures are proposed. One is a small-size coupled-line Wilkinson powe divider for dual-band applications. The analytical design theory is given and the electrical parameter analysis is provided. Several numerical examples are presented to demonstrate the flexible dual-band applications. The second is a novel coupled-line Gysel power divider for dual-band and high-power applications. Because of using coupled-line sections, additional design parameters make the proposed structure more design freedom and more simple. Based on the even-and odd-mode analysis, rigorous design equations and available constraint condition are derived. Numerical examples with different frequency ratios and an EM full-wave simulated example are given to verify the provided scheme. The third is a novel high-power dual-band coupled-line Gysel power dinvider with impedance-transforming functions. Different from the above coupled-line Gysel power divider, this structure gives exact closed-form analytical design equations and inherent impedance-transforming functions. This novel Gysel power divider which has arbitrary different terminated impedances of the source and the load ports presents a wider frequency-ratio range and more design freedom. A practical microstrip power divider is designed, fabricated, and measured to verify the proposed circuit structure and analytical design approach. This part of research work has been published in The Scientific World Jounal.(2) On the basic of phase shifter, a novel compact plannar phase shifter with a microstrip radial stub is proposed. The parameters which influence the input impedances of the radial stub and the frequency band of the phase shifter are analyzed. The design parameters of typical examples for phase shifters are illustrated. Two phase shifters are designed, fabricated and measured to verify the designed structure and the analysis. The proposed structure offers an alternative where simple and planar phase shifters are required.(3) On the basic of wide-band coupler, a novel three-port hybrid coupler is presented. The coupler provides both wide bandwidth and simple structure. The total circuit configuration is flexible and does not require complex multi-layer layout and complicated computations. The circuit calculation, microstrip fabrication, and measurement of a prototype wide-band coupler finally verify this proposed method. (4) On the basic of dual-band bandstop filter, a small-size high-selectivity bandstop filter with coupled-line stubs for dual-band applications is proposed. This kind of coupled-line dual-band bandstop features compact and simple structure, flexible frequency-ratio adjustment, and high selectivity. The frequency ratio of the dual-band BSF can be adjusted flexibility by using analytical approach. Good agreement between the simulated and measured results shows that the proposed dual-band BSF can work with low insertion loss, shape rejection and high selectivity. This part of research work has been published in Electronics Letters.(5) On the basic of the feedwork applications, a dual-band circularly polarized antenna and an antenna array are realized with the presented feedworks. The circularly polarized antenna with the proposed three-port hybrid coupler as its feedwork works well at2.1GHz (UMTS, Universal Mobile Telecommunication Systems) and2.45GHz (WLAN, Wireless Local Area Network). The frequency ratio is1.167. A feedwork composed of three dual-band Gysel power dividers presented above is use to realize the antenna array. The array includes four dual-band circularly polarized antenna units. The simulated and measured results show the dual-band circularly polarized antenna and antenna array work well which verifies the availability of the novel feedworks presented in this dissertation.