Directional GPS‐IR Observations Using a Linearly Polarized Double‐Ridged Horn Antenna

Most GPS interferometric reflectometry (GPS‐IR) studies use geodetic RHCP antennas with near‐hemispherical coverage and select the reflection zone through elevation and azimuth masks during processing. Direction‐ and polarization‐selective antennas are established in GNSS reflectometry, and tilted or linearly polarized antennas have also been used for SNR‐based retrieval, but a fixed‐beam horn antenna has not been evaluated for this purpose. This study investigates directional GPS‐IR observations using a linearly polarized double‐ridged horn antenna (DRHA), which constrains the observation geometry at the acquisition stage. Field experiments over four observation periods, compared with a conventional RHCP configuration, show spectral widths of 390.5–393 frequency bins for RHCP and 183–284 bins for the DRHA, corresponding to a reduction of 28%–53% depending on antenna orientation and observation geometry. The results highlight a trade‐off between signal availability and angular selectivity. The RHCP configuration collects more observations, but a large fraction is removed during filtering, whereas the DRHA produces fewer observations of which a higher proportion is retained. A filtering strategy based on a minimum elevation angle (10°), 3× median absolute deviation (MAD), and azimuth constraints (applied only to RHCP) was used to ensure robust estimation. Sub‐decimeter accuracy (< 10 cm RMSE) was achieved under favorable conditions, whereas less favorable observation geometries resulted in RMSE values exceeding 40 cm. These findings show that a directional, linearly polarized horn antenna produces more concentrated spectra than an RHCP antenna and can be used with standard GNSS‐IR processing where controlling the reflection geometry is important.