Study On Broadband Antenna Feeding Networks

Broadband antenna system has found more extensive applications in wireless communication system due to its rapid development as well as the update of the microwave technology.And the feeding network's quality of the broadband antenna is the key to the performance of the entire broadband antenna system.Therefore,it becomes an urgent problem for scholars to achieve a broadband feeding network for an antenna,which also puts forward higher requirements for devices such as power dividers,filters and duplexers that are often used in feeding networks.Miniaturization,wideband,high performance and low cost are the development directions of modern microwave devices.In response to this practical demand,this paper devises a broadband Wilkinson power divider to widen the bandwidth by loading multi-section impedance transformers;a wide-band bandpass filter with compact structure,wide upper-stopband and excellent performance which is designed by the branch-loaded resonator and the split-ring resonator;and a lumped diplexer which is based on low-pass filter prototype and composed by a low-pass filter and a high-pass filter that use one common port forming a parallel connection.This dissertation is organized in following frames:1.The researching background and status at home and abroad of broadband powerdivider,broadband filter and diplexer are introduced.The principle of widening the working bandwidth of multi-section impedance transformer and the calculation formulas of isolation resistance are introduced.The working principle of common resonator and the prototype function of the lumped low-pass filters are introduced.2.A broadband Wilkinson divider with a bandwidth of 0.5-3 GHz is designed,of which the overall size is 50mm*60mm,it uses a five-stage stepped impedance converter to achieve six multiplier operating bandwidths,the voltage standing wave ratio?VSWR?of the input port is less than 1.3 in the whole working band,the transmission coefficient of the two output ports is less than 3.3dB,and the isolation resistor is loaded at the transformation node of the impedance converter such that the overall passband isolation is greater than 20 dB.3.A wideband bandpass filter with open stubs loaded consists of three paths is designed.The coupling between the paths can generate resonance points in the passband and broaden the passband bandwidth of the filter.To further optimize the performance of the filter,the wideband bandpass filter which replaces the loaded open stubs with the split-ring resonators to reduce the size,increase the rectangular coefficient of the filter,and suppress the high order harmonics,a bandpass filter with a wide upper stop band and a bandwidth from 0.27to 1.4 GHz has been designed,with in-band insertion loss less than 0.5 dB,and the upper stop band rejection greater than 20 dB?up to 6.4f₀?.4.A broadband lumped duplexer with compact structure is studied.The common port of LPF and HPFare connected in parallel to form a duplexer,and the high-pass filter circuit is adjusted to achieve high isolation.In the operating band of 30-500MHz,with 125MHz as the dividing frequency,the insertion loss in the two passbands is better than 0.3dB,and the isolation between the passbands is better than 30dB,which guarantees that it works well at the overlap frequency.