# The Development of a Spaceborne SAR Based on a Reflector Antenna
## 2 Principles and Classification of Reflector Antennas
### Types and Characteristics of Reflector Antennas
#### 2.2.6 Summary of Reflector Antenna Types and Characteristics  
Different reflector antenna types offer distinct advantages tailored to specific applications. Parabolic reflectors are widely used in satellite communications and radio astronomy for their high gain and simple design, while offset reflectors eliminates feed blockage, enhancing gain and efficiency in radar and satellite systems. Parabolic cylindrical reflectors provide high-resolution imaging and are effective in scanning radar systems. Elliptical reflectors, with dual foci, enable flexible beam shaping for multi-beam and pattern-specific radars. Dual-reflector designs, such as Cassegrain antennas, improve aperture efficiency and reduce feedline loss. Spherical reflectors support wide-angle and multi-beam coverage, making them suitable for radio astronomy and multi-target tracking. Table 1 summarizes the main characteristics of these five types of reflector antennas and their representative application examples in existing spaceborne SAR systems.  
From a comparative perspective, each reflector antenna type presents distinct trade-offs between electromagnetic performance, structural complexity, and system-level applicability. Parabolic reflector antennas offer high gain and are widely used in conventional SAR systems, but suffer from feed blockage, especially at larger apertures. Offset designs mitigate this issue at the expense of increased structural asymmetry. Parabolic cylindrical reflector antennas, while structurally simple and effective for wide-area scanning, lack focusing capability in the orthogonal direction, making them unsuitable for high-resolution spotlight imaging. Elliptical reflector antennas enable dual-focus beam shaping and multi-beam operations but introduce challenges in manufacturing precision and mechanical deployment. Dual-reflector antenna configurations enhance aperture efficiency and beam symmetry while reducing feed blockage and cross-polarization, though their mechanical complexity increases deployment risk. Spherical reflector antennas are advantageous  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Reflector Antenna Types** & **Characteristics** & \begin{tabular}{c} **Representative** \\ **Spaceborne SAR Systems** \\ \end{tabular} \\ \hline Parabolic Reflector Antenna & \begin{tabular}{c} High gain, narrow beam, strong \\ directivity, simple structure \\ \end{tabular} & \begin{tabular}{c} Lackrose, Magellan, \\ SAR-Lupe, HJ-1-C, Qilu-1, \\ Acadia, Neptune-01, \\ TecSAR, RISAT-2 \\ \end{tabular} \\ Parabolic Cylindrical Reflector Antenna & \begin{tabular}{c} Line source feed, suitable for \\ wide-angle scanning \\ Dual-focus design, flexible \\ beam control \\ \end{tabular} & \begin{tabular}{c} HJ-2-E/F \\ \end{tabular} \\ Dual-Reflector Antenna & \begin{tabular}{c} Two-reflector system, compact \\ feed placement, low feedline loss \\ \end{tabular} & \
\begin{tabular}{c} QPS-SAR \\ \end{tabular} \\ Spherical Reflector Antenna &
\begin{tabular}{c} Spherical surface, suitable for \\ wide-angle coverage \\ \end{tabular} & - \\ \hline \hline \end{tabular}
\end{table}
Table 1: Basic classification and spaceborne SAR applications of reflector antennas.  
in wide-angle and multi-beam scenarios but require correction techniques to overcome inherent aberrations and reduced gain.  
Ultimately, the selection of the reflector antenna type in spaceborne SAR systems must balance resolution, swath width, weight, deployability, polarization performance, and cost. Scientific missions may prioritize imaging quality and flexibility, favoring complex dual-reflector or elliptical systems, whereas commercial platforms often favor robustness and compactness, leaning toward traditional or offset parabolic reflector antennas. This classification not only supports structural taxonomy but also serves as a design guideline in aligning antenna architecture with mission-specific SAR imaging requirements.