基植於智慧型天線技術之頻率調變連續波船舶相位陣列雷達系統實現

Abstract

本論文利用頻率調變波(Frequency-Modulated Continuous Wave, FMCW)與智慧型陣列天線技術的概念，設計與實現一新型態之X頻段波船舶雷達系統，其關鍵之特點乃是利用頻率調變波的概念偵測船舶距離，並且藉由智慧型相位陣列天線技術進行全電子式波束掃描進行辨識船舶之方向，與機械式雷達系統相較，能有效提升整體雷達系統之運作功效，如縮短船舶的距離與方位辨識時間與提供即時完整之訊息。本論文所提出之雷達系統在發射鏈路中包含了八支線性子陣列天線，每一子陣列天線涵蓋了一維的串聯饋入貼片天線，每相鄰之單一貼片天線之間距為半波長做週期性的排列，此子陣列天線位於垂直平面上可產生高指向性與窄主波束之特性。此外，本論文亦提出混合式類比-數位波束合成之架構，特別設計了相位本地震盪電路(Phased Local Oscillator, Phased LO)架構而非透過昂貴的X頻段相移器調整相位，即可達到即時波束合成的目標，藉此提高訊號雜訊比。另外，我們亦可藉由直接數位合成器(Direct Digital Synthesis, DDS)產生與控制頻率調變波之振幅與相位，達到波束合成之效。在相位陣列天線技術中，相位校正乃為重要之課題，故本雷達系統位於每一發射鏈路之末端耦合X頻段之訊號，藉由混波器將高頻訊號降至基頻，以供基頻數位訊號處理其相位權重，適時地回授與修正相位本地震盪電路所產生之相位，可精準控制波束合成之方向，實現智慧型天線技術來辨別船舶之距離與方位。在此雷達系統之接收端部分，將運用了由32個方形貼片所組成之陣列天線作為接收端天線，並且實現了由X頻段降頻至正交基頻之降頻電路與基頻數位訊號處理。本論亦提供距離、方位與智慧型天線系統中的波束合成技術達到波束掃描之量測結果進行討論與分析。 本論文所提出之雷達系統之中心頻率操作於9410 MHz、操作頻寬為50 MHz與掃頻時間為250 μs之規格下運作，具有多目標距離與方位偵測之能力。為了達到良好的頻率調變訊號之線性度，我們將採用直接數位合成器(AD9958)產生線性之頻率調變訊號，使此雷達系統達到較佳的FMCW頻率差之資訊。本雷達系統在發射端部分所設計之相位陣列天線增益為22 dBi，其位於垂直與水平平面之半功率波束寬度分別為15度與20度。此外，本系統亦使用雷達目標模擬器測試，此模擬器將動態改變傳送FMCW訊號之延遲時間，回送至接收端進而解析出距離之資訊，本系統之距離解析度約略為三公尺，與理論值相符。最後，我們將呈現在水平面的位置平面顯示器(PPI)於本論文中。

This dissertation presents the development, fabrication, and measurement of an X-band marine phased-array frequency-modulated continuous-wave (FMCW) radar system based on the smart antenna technology. The proposed FMCW radar system incorporating the electrically beam-forming technique is presented in this dissertation. Such a system is composed of eight subarray antennas arranged linearly in the transmitter chain, each of which consists of ten 1-D series-fed patch array antennas with half-wavelength separation period generating a directionally narrow pattern along the vertical plane. The hybrid analog-digital beam-forming scheme was implemented; specifically, the phased local oscillator was developed for manipulating the phase angle over the local oscillator rather than over the output X-band signal for transmission. Slightly continuous beam steering in around one degree increments can be achieved by dynamically altering the progressive phase delay angle among the subarrays. Alternatively, by dynamically adjusting the amplitude and phase of the FMCW signals generated by direct digital synthesis (DDS) device (Analog Device-AD9958), we can also achieve the function of beam-forming. Phase angle calibration was implemented by coupling each transmitter output and down-converter into the baseband to calculate the correction factor to the weight. Additionally, the targets with their positions and ranges are estimated by using the smart antenna technology. The receiver in the radar system, which includes the hardware for down-converting the X-band signals to I/Q baseband, the array antenna composed of 32 identical square patches, and the software for implementation, has been deployed. The measurements for range detection, positioning determination, and beam-forming techniques at X band frequencies have been carried out in this research work. The proposed radar system is operated at the center frequency of 9410 MHz with bandwidth 50 MHz and a sweep time of 250 μs. To obtain good linearity, the linear FM signal is generated by DDS (Analog Device-AD9958). The phased array antenna gain in the transmitter is around 22 dBi. The 3-dB beamwidths after beam-forming are 15 degrees and 20 degrees along the vertical and horizontal planes, respectively. Furthermore, the performance of this radar system has been evaluated using the radar target simulator by dynamically manipulating the transmitted FMCW signal and processing by the receiver to solve the distance accordingly. The measured results indicate that the range resolution is approximately 3 meters, which agrees with theoretical value. Finally, the plan position indicator (PPI) display is also shown along the horizontal plane in the dissertation.