Exploring the Beam Squint Effects on Reflectarray Performance: A Comprehensive Analysis of the Specular and Scattered Reflection of the Unit Cell

Abstract

In this article, the phenomena of beam deviation in reflectarray is discussed. The radiation pattern of the unit cell, which plays a vital role in shaping the beam of the reflectarray, is analyzed by considering undesired specular and scattered reflections. These unwanted reflections adversely affect the pattern of the single unit cell, thereby reducing the overall performance of the reflectarray. To conduct our investigations, three cases of reflectarray-i.e., (i) a center-fed with broadside beam (Case-I), (ii) a center-fed with the beam at 30° (Case-II), and (iii) off-center-fed with the beam at 30° reciprocal to feed position with reference to the broadside direction (Case-III)-are simulated. Different degrees of beam deviation are analyzed in each reflectarray by assessing the radiation pattern of a single element. The simulation results shows that maximum of 0°, 3.4°, and 0.54° beam squint across the bandwidth found in Case-I, Case-II, and Case-III, respectively; this leads to aperture efficiencies of 31.2%, 11.9%, and 31.2%, respectively. The significance of specular reflections is further confirmed by half (left half and right half) aperture analysis of Case-II. This involves simulating the half-plane aperture illuminated by horn antenna, resulting in a distinct beam angle at the same frequency. However, deviations of -4.71 to +4.1 for the left half aperture and -1.82 to +1.1 for the right half aperture are noticed. Although the analysis specifically focuses on the three cases of the reflectarray, the proposed methodology is applicable to any type of reflectarray. The study presented in this work provides an important insight into the practical aspects of reflectarray operation, particularly in terms of quantifying undesirable effects that are normally overlooked in the design of this class of arrays. To achieve a good performance, a new design of the dielectric loaded horn feed is proposed. This design approach is both simple and applicable to any reflectarray, with the added benefit of maintaining a low profile for the RA. Moreover, this work holds significant potential for remote sensing satellite systems as beam deviation can adversely impact data collection accuracy and compromise observation precision, resulting in distorted images, reduced data quality, and overall hindrance to the system's performance in capturing reliable information.

Keywords: beam squint; reflectarray; scattered reflection; specular reflection.

Figure 1

Schematic diagram of RA with beam oriented at 30°. (a) ${\theta }_f$° = 0°. (b) ${\theta }_f$° = 30°.

Figure 2

Schematic representation of RA and coordinate system.

Figure 3

Simulated radiation patterns of the center-fed RA at (a) 25°. (b) 30°. (c) 35°.

Figure 4

Simulated radiation patterns of the off-centered RA at (a) 25°. (b) 30°. (c) 35°.

Figure 5

Normalized radiation patterns of the UC of size D = 4.632 mm at (a) various oblique incidence at 11.725 GHz; (b) normal incidence at 10.7 GHz, 11.725 GHz, and 12.75 GHz; (c) incidence at 30° at 10.7 GHz, 11.725 GHz, and 12.75 GHz.

Figure 6

(a) Incident and reflected field of uniform plane wave at oblique angle on the unit cell; schematic diagram of the incident and reflected wave on the surface of the UC. (b) Normal incidence and reflection from the UC at the center of the center-fed RA with broadside beam. (c) Oblique incidence on the UC in LHA of the center-fed RA with beam oriented at 30°. (d) Oblique incidence on the UC in RHA of the center-fed RA with beam oriented at 30°.

Figure 7

Schematic diagram of the RA along with the pattern of the UC: (a) center-fed RA with broadside beam; (b) center-fed RA with beam oriented at ${\theta }_b$ = 30°; (c) RA with feed oriented towards the mirror angle of the beam at ${\theta }_b$ = 30°.

Figure 8

Simulation of Case-II RA: (a) with LHA; (b) with RHA; (c) normalized patterns of the main lobe for the half apertures RA at 10.7 GHz, 11.725 GHz, and 12.75 GHz.

Figure 9

Farfield realized gain of Case-I, Case-II, and Case-III.

Figure 10

Phase range of unit cell: (a) single layer; (b) double layer.

Figure 11

Phase distribution on the RA aperture with (a) F/D = 1, (b) F/D = 0.5, and patch distribution on the RA aperture with F/D = 0.5 for (c) UC with phase range of 360°, (d) UC with phase range of 500°.

Figure 12

Schematic diagrams of (a) a simple horn-fed RA; (b) a Cassegrain RA; (c) a dielectric-loaded horn-fed RA.

Figure 13

Geometry and comparison of the RA’s in Case-I and proposed design in terms of farfield realized gain.