Abstract
Abstract. The antenna cross polarization suppression (CPS) is of significant importance for the accurate calculation of polarimetric weather radar moments. State-of-the-art reflector antennas fulfill these requirements, but phased array antennas are changing their CPS during the main beam shift, off-broadside direction. Since the cross polarization (x-pol) of the array pattern is affected by the x-pol element factor, the single antenna element should be designed for maximum CPS, not only at broadside, but also for the complete angular electronic scan (e-scan) range of the phased array antenna main beam positions. Different methods for reducing the x-pol radiation from microstrip patch antenna elements, available from literature sources, are discussed and summarized. The potential x-pol sources from probe fed microstrip patch antennas are investigated. Due to the lack of literature references, circular and square shaped X-Band radiators are compared in their x-pol performance and the microstrip patch antenna size variation was analyzed for improved x-pol pattern. Furthermore, the most promising technique for the reduction of x-pol radiation, namely "differential feeding with two RF signals 180° out of phase", is compared to single fed patch antennas and thoroughly investigated for phased array applications with simulation results from CST MICROWAVE STUDIO (CST MWS). A new explanation for the excellent port isolation of dual linear polarized and differential fed patch antennas is given graphically. The antenna radiation pattern from single fed and differential fed microstrip patch antennas are analyzed and the shapes of the x-pol patterns are discussed with the well-known cavity model. Moreover, two new visual based electromagnetic approaches for the explanation of the x-pol generation will be given: the field line approach and the surface current distribution approach provide new insight in understanding the generation of x-pol component in microstrip patch antenna radiation patterns.
Highlights
Dual polarized phased array antennas for weather radar application in dense radar networks are currently under discussion (Vollbracht, 2014)
The differential feeding method was verified as a valuable x-pol reduction solution from literature research for phased array weather radar applications
Numerous feeding methods were discussed for phased array applications
Summary
Dual polarized phased array antennas for weather radar application in dense radar networks are currently under discussion (Vollbracht, 2014). Such antennas promise even faster three dimensional volume scanning compared to state-of-theart high power radar systems with reflector antennas and their twin axis mechanical drives. The change from parabolic reflector antennas with fixed beamwidth and gain values to phased array antennas with inherent scan angle dependent co/x-pol patterns is highly challenging. High-quality reflector antennas provide CPS values of up to −30 dB in S- C- X- Band, within the half power beamwidth. A new phased array weather radar antenna should provide the same CPS on broadside, and even more challenging, the same CPS over the complete e-scan range.
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