機載 X-Band之合成孔徑雷達主動射頻相控陣列天線系統

Abstract

本研究為機載X-Band之合成孔徑雷達主動射頻相控陣列天線系統（SAR）系統進行設計與效能驗證，旨在提升動態環境下的目標偵測能力及高精度成像表現。SAR 系統廣泛應用於遙感探測、軍事監測及地表觀測等領域，為了滿足不同應用場景的需求，本研究是一種基於單極化通道DPCA-SAR架構，結合 X 頻段高頻率特性，針對載波頻率、天線設計及發射功率等關鍵參數進行了優化。

本研究選定 9.65 GHz 作為載波中心頻率，以輸入端的反射係數（Reflection Coefficient）S11-15dB為標準，最終模擬結果操作頻率為9.4GHZ到10.1GHz，對應於 X 頻段應用，以提供更佳的穿透能力與高解析度成像效果。針對系統性能進行參數分析後，本研究提出了一種經過優化的天線陣列設計方案。天線尺寸設計為 400 mm x 200 mm x 1.5 mm。採用 6x4 雷達子陣列 PCB 板，與 PMIC 共構進行測試。

此設計考量了天線單元間距與旁瓣抑制效果，在天線尺寸以及天線單元間距耦合中的多方考量，最終使用了單元間距為0.42波長的天線設計，最終實現了 16.32 dBi 的增益，滿足長距離偵測的需求。

本研究最終的整體雷達系統的規劃架構為 32x16 陣列。在不考慮 PMIC 共板設計的情況下，系統尺寸可預估為 423 mm x 182.5 mm x 149 mm，增益估算可達到 28.84 dBi。因此，系統在高度設計上仍具有一定的 PMIC 板置入的容忍度，可進一步提升設計靈活性與整體性能。

為了進一步提升 SAR 系統的效能，本研究採用了 Qorvo 的高效氮化鎵（GaN）功率放大器 QPA0001\cite{qpa0001}，其具備 2 瓦的飽和輸出功率及 50\% 的功率附加效率（PAE），能在高頻環境下保持穩定的增益與低噪聲特性。該功率放大器的選擇，結合低噪聲放大器（LNA）與高性能射頻切換開關(RF SWITCH)，構成了一個完整的射頻前端系統，能支援高效能天線陣列應用。

同時，本研究針對射頻系統的電源需求，設計了一套整合的 PMIC 電源管理方案。PMIC 採用了多階段電壓調節，包括 28V 到 16V 以及 28V 到 5V 的降壓轉換，並且使用 MAX17577\cite{max17577_17578} 和 LT3094 \cite{lt3094}等元件進行精確的電壓控制，提供穩定的 -5V 和 3.3V 偏壓。此設計有效降低了功率損耗，提高了整體系統的效率和穩定性，能支援多通道 ADAR1000 模組和天線陣列的穩定工作。

本研究還針對中科院提供的射頻前端系統進行了詳細的鏈路預算分析，包括傳輸系統、自由空間損耗（FSPL）、接收系統等三大模組。結果顯示，在 20 公里距離下，傳輸系統可達到 85.7 dBm 的有效輻射功率（EIRP），並在增益補償及損耗控制方面表現良好，有效支援長距離的高分辨率成像需求。

總結，本研究提出了一種創新的雷達架構，其中包含了複雜的PMIC整合，以及用於測試ADAR1000(BFIC)的SDP-S（System Demonstration Platform Serial）評估板，成功整合了相位中心位移技術、氮化鎵功率放大器(QPA0001)、PMIC 電源管理方案及鏈路預算分析方法，提升了系統的成像解析度與目標辨識能力。此系統具備高度靈活性與擴展性，未來可廣泛應用於軍事偵察、災害監測等多種領域。

This research focuses on the design and performance validation of an airborne X-band active phased-array antenna system for synthetic aperture radar (SAR), capable of achieving phase center displacement.The goal is to enhance target detection capabilities in dynamic environments and improve high-precision imaging performance. SAR systems are widely used in remote sensing, military surveillance, and surface observation. To meet the requirements of various application scenarios, this study proposes a solution based on a single-polarization channel architecture (DPCA-SAR), incorporating the high-frequency characteristics of the X-band and optimizing key parameters such as carrier frequency, antenna design, and transmission power.

The study selects 9.65 GHz as the carrier center frequency, with a reflection coefficient (S11) of -15 dB as the standard. The operating frequency range is from 9.4 GHz to 10.1 GHz, corresponding to X-band applications, providing better penetration capability and high-resolution imaging performance. After analyzing system performance parameters, an optimized antenna array design is proposed. The antenna system includes a power management subsystem and an SPI control interface. The PCB measures 400 mm × 200 mm × 1.5 mm and implements a 6 × 4 radar sub-array for testing with PMIC integration.

This design considers the spacing between antenna elements and the sidelobe suppression effect. After evaluating multiple factors related to element spacing and coupling, the final design uses an element spacing of 0.42 wavelengths, achieving a gain of 16.32 dBi, meeting the requirements for long-distance detection.

The final radar system architecture is planned as a 32x16 array. Without considering PMIC integration into the same board, the system size is estimated to be 423 mm x 182.5 mm x 149 mm, with an estimated gain of 28.84 dBi. This leaves room for PMIC board integration, enhancing design flexibility and overall performance.

To further improve SAR system performance, this study employs Qorvo's high-efficiency Gallium Nitride (GaN) power amplifier QPA0001, which offers 2 watts of saturated output power and 50\% power-added efficiency (PAE). It ensures stable gain and low noise characteristics in high-frequency environments. The power amplifier is combined with a low-noise amplifier (LNA) and high-performance RF switch, forming a complete RF front-end system to support high-performance antenna array applications.

Additionally, the study designs an integrated PMIC power management solution to address the RF system's power requirements. The PMIC employs multi-stage voltage regulation, including step-down conversions from 28V to 16V and 28V to 5V. Components such as the MAX17577 and LT3094 are used for precise voltage control, providing stable -5V and 3.3V bias voltages. This design effectively reduces power loss and improves overall system efficiency and stability, supporting the reliable operation of multi-channel ADAR1000 modules and antenna arrays.

The research also conducts a detailed link budget analysis for the RF front-end system provided by the National Chung-Shan Institute of Science and Technology, including transmission systems, free-space path loss (FSPL), and reception systems. The results show that at a 20 km distance, the transmission system achieves an effective isotropic radiated power (EIRP) of 85.7 dBm. It demonstrates excellent gain compensation and loss control, effectively supporting high-resolution imaging needs for long distances.

In summary, this research proposes an innovative radar architecture that integrates complex PMIC designs, the SDP-S (System Demonstration Platform Serial) evaluation board for testing the ADAR1000 (BFIC), phase center displacement technology, Gallium Nitride power amplifier (QPA0001), PMIC power management solutions, and link budget analysis methods. The system enhances imaging resolution and target recognition capabilities while offering high flexibility and scalability. This system has the potential for wide applications in military reconnaissance, disaster monitoring.