Understanding and optimizing microstrip patch antenna cross polarization radiation on element level for demanding phased array antennas in weather radar applications

摘要

The antenna cross polarization suppression (CPS) is of significant importance for the accuratecalculation of polarimetric weather radar moments. State-of-the-artreflector antennas fulfill these requirements, but phased array antennas arechanging their CPS during the main beam shift, off-broadside direction.Since the cross polarization (x-pol) of the array pattern is affected by thex-pol element factor, the single antenna element should be designed formaximum CPS, not only at broadside, but also for the complete angularelectronic scan (e-scan) range of the phased array antenna main beampositions.Different methods for reducing the x-pol radiation from microstrip patchantenna elements, available from literature sources, are discussed andsummarized. The potential x-pol sources from probe fed microstrip patchantennas are investigated. Due to the lack of literature references,circular and square shaped X-Band radiators are compared in their x-polperformance and the microstrip patch antenna size variation was analyzed forimproved x-pol pattern.Furthermore, the most promising technique for the reduction of x-polradiation, namely "differential feeding with two RF signals 180°out of phase", is compared to single fed patch antennas and thoroughlyinvestigated for phased array applications with simulation results from CSTMICROWAVE STUDIO (CST MWS). A new explanation for the excellent portisolation of dual linear polarized and differential fed patch antennas isgiven graphically. The antenna radiation pattern from single fed anddifferential fed microstrip patch antennas are analyzed and the shapes ofthe x-pol patterns are discussed with the well-known cavity model. Moreover,two new visual based electromagnetic approaches for the explanation of thex-pol generation will be given: the field line approach and the surfacecurrent distribution approach provide new insight in understanding thegeneration of x-pol component in microstrip patch antenna radiationpatterns.