Relative Level (dB) -15-14-13-12-11-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 Primary Illumination Feed Excitation large scan angles. The antenna pattern degradation is gradual, increasing with the distance of the feed element from the focal point of the parabolic reflector; this can be seen from the secondary radiation pattern plots (bottom), which also show the antenna patterns of all individual feed row excitations. Comparing Figure 9 to Figure 10(a) and (b), there is no significant difference in the illumination (amplitude) for the different activated rows. However, the position of the illumination maximum changes depending on the activated row and is not always fixed at the reflector's center. This is an indication that the mechanical feed elements' boresight direction is not pointed toward the reflector center and is understood as an unwanted side effect from using a planar feed array. 40 30 20 10 -15 -10 Secondary Elevation Pattern Gain: 41.9 dBi TRANSMIT REFLECTOR ANTENNA PATTERN A somewhat unusual approach for a reflector feed system is used on transmit to illuminate the wide swath. On transmit, all feed rows are activated to generate a narrow primary beam, which illuminates a small portion of the reflector resulting in a wide secondary beam. Figure 11 demonstrates that this approach works as expected. -5 05 10 Angle (°) (a) Relative Level (dB) -15-14-13-12-11-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 Primary Illumination Feed Excitation 15 Relative Level (dB) -15-14-13-12-11-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 Primary Illumination Feed Excitation (a) Secondary Elevation Pattern 40 30 20 10 Gain: 38.9 dBi 40 30 20 10 -15 -10 -5 05 10 15 Angle (°) (b) FIGURE 10. The reflector excitation and radiation patterns for the case that different rows of feed elements are activated. (a) The first feed row is active. (b) The last feed row is active. DECEMBER 2022 IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE Secondary Elevation Pattern Gain: 32.9 dBi -15 -10 -5 05 10 15 Angle (°) (b) FIGURE 11. The (a) reflector excitation and (b) radiation patterns for the transmit case where all feed elements are activated. 19 Gain Pattern (dBi) Gain Pattern (dBi) Gain Pattern (dBi)