在粗糙且多反射點的地表環境下具多天線米波雷達之高解析度低空仰角估測

High-Resolution-Low-Elevation-Angle Estimation for Meter-Wave Radar with Multiple Antennas in the Rough and Multiple-Reflections Ground

洪晟祐(CHENG-YOU HONG)

指導教授 ： 鍾日龍

中原大學/電機資訊學院/電子工程學系/碩士(2022年)

https://doi.org/10.6840/cycu202201533

摘要

近年來，米波雷達因其頻段正好避開了戰機的匿蹤波段，反而成為一種有效的反匿踨的雷達技術而獲取高度關注。然而，傳統米波雷達並無採用數位陣列天線技術，因此並無波束成形的設計，故容易受到多路徑鏡面反射地形效應的影響，導致其低空偵測能力弱化、覆蓋空域破碎以及抗干擾能力不佳等缺點。再者，米波雷達系統受到多路徑傳播的地形效應影響，致使低仰角時產生波束上翹造成偵測盲區，危及空防安全。
首先，本論文在典型單一鏡面反射之多路徑模型下，考慮利用數位陣列天線搭配超高分辨率陣列訊號處理技術以及可適性波束成形技術來得到高精確度的低仰角度估測值。上述的方法適用在單一鏡面反射的平坦的陣地，然而，若是陣地地面粗糙，則典型單一鏡面反射之多路徑模型則不再適用。為解決此問題，本論文提出了並建立四種米波雷達匹配粗糙且具多反射點之多路徑地形效應的米波雷達陣列天線接收訊號模型。第一種模型，吾人考慮在鏡面反射波之外有多個具有相同波程差的反射點，每個反射點的角度由多路徑模型的幾何關係確定。再來，第二種模型，吾人考慮除了鏡面反射波之外，其餘的反射角度以均勻對稱於鏡面反射角度的方式來呈現，並假設此時的所有反射角度的波程差皆為相等。接著，第三種模型，吾人考慮反射點成隨機分布並隨機搭配均勻對稱於鏡面反射角度，且考慮每一反射波經歷不同波程差的情況。再來，第四種模型，吾人考慮反射點成均勻分布，並分別假設每個反射點對應的擴散角度為隨機選取擴散角度，且考慮不同波程差的情況。
最後，吾人設定了一些參數及環境且利用電腦進行大量模擬來評估在不同環境中米波雷達採用陣列訊號處理技術呈現的效果以及效能。首先陣列訊號處理技術方面，研究中吾人做了關於多重信號分類(MUltiple SIgnal Classification, MUSIC)、空域平均式MUSIC (Spatial-Smoothing MUSIC, SS-MUSIC)、根值空域平均式多訊號分類(root-SS-MUSIC)、可適性波束成型(Adaptive Beamforming)和零值展寬(Null broadening)的電腦模擬，透過電腦模擬來觀察對於各個不同的環境、仰角及訊號模型，這些方法是否能提供漸近無偏且有效的高分辨率仰角估計。

關鍵字

可適性波束成型 ； 角度估測 ； 陣列訊號處理技術 ； 多重信號分類 ； 零值展寬 ； 根值空域平均式多訊號分類 ； 空域平均式多訊號分類

並列摘要

Recently, the meter wave radar had re-attracted by lots of researchers because its operating band can avoid the stealth band of modern stealth fighters and it becomes anti-stealth radar technique. However, the conventional meter radar does not utilize the digital antenna-array technique to make good use of the advantage of beamforming, and thus it is vulnerable to be influenced by the terrain effect of multipath propagation, resulting in weak low-altitude detection capabilities, broken coverage of the airspace, inferior anti-jamming capabilities. However, in the metric wave radar system, the influence of the terrain effect of multipath propagation will cause the lifted-up beam at low elevation angles, resulting in detection blind zone and endangering the safety of air defense.
First, in the thesis we consider, in the classical multipath model with only one specular reflection, using digital antenna array together with super-resolution array signal processing technique and adaptive beamforming technique to obtain the precise estimation of low elevation angles. The above methods can be well suited to the flat ground; however, a classical multipath model cannot be suited to the rough and multiple-reflections ground. To solve the above problem, in the thesis we try to propose four multipath model with rough and multiple-reflections ground for the meter radar with antenna arrays. In the first model, we consider, except a classical specular reflection, the other reflections are assumed to have no round-trip difference between the specular reflection. Each angle of reflections is determined by the geometrical relation of the multipath model. Then, in the second model, we consider, except a classical specular reflection, the other reflections are symmetrically with the specular reflection, the angles of them are uniformly distributed centered with the angle of the specular reflection. In the model, the assumption of no round-trip difference between all of multipath is made. Next, in the third model, we consider random reflections in the effective reflection region where the angle of each of the random reflection is randomly chosen from the permissible set of angles. Besides, in the model, the difference between round-trip of all of multipath is taken into account. Then, in the fourth model, we consider multiple reflections which are uniformly distributed in the permissible region. Each of the angle of the uniform reflection is randomly chosen from the permissible set of angles. In the model, the difference between round-trip of all of multipath is also considered.
Finally, in the computer simulation part, we build up the received signal model of a meter wave radar array antenna with multipath terrain effect, and set up some simulation parameters and environments. Then, we conduct a large number of computer simulations to evaluate detection probability and minimum mean squared error of the meter wave radar by using signal processing technology in different environments. We have conducted experiments on MUltiple SIgnal Classification (MUSIC), spatial-smoothing MUSIC (SS-MUSIC), root SS-MUSIC, adaptive beamforming and null broadening. From the simulation results, we can observe that whether these methods can provide asymptotically unbiased and efficient high-resolution elevation-angle estimates for various environments in the classical and proposed multipath signal model.

並列關鍵字

adaptive beamforming ； angle estimation ； array signal processing technology ； MUltiple SIgnal Classification (MUSIC) ； null broadening ； root Spatial-Smoothing MUSIC (root-SS-MUSIC) ； Spatial-Smoothing MUSIC (SS-MUSIC)

參考文獻

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