基於半模態基板集成波導之頻率相依與固定頻率之波束掃描圓極化漏波天線

Abstract

在本論文中，我們提出了一款基於半模態基板集成波導結構的新型圓極化漏波天線。該天線結合了週期性擺放的寬的橫向開槽和一條縱向延伸的狹縫，其單元結構並使用兩個集總電容，透過選擇適當的電容值可實現從後向（-42°）、邊側（0°）到前向（35°）的頻率掃描波束，同時模擬結果顯示其主波束方向之軸比均保持在3 dB以下。 此外，吾人發現，透過調整電容值，可以改變波導結構中的傳播常數，顯示此天線可藉由改變電容值來實現固定頻率的圓極化波束掃描。基於此原理，將電容替換為變容二極體，並將偏壓電路整合到原天線結構中；經過適當設計，包括射頻與直流訊號隔離元件等，可將主波束方向之軸比維持在3 dB以下。該天線在維持頻率相依波束掃描特性的同時，透過對變容二極體施加反向電壓，亦可在固定頻率下實現圓極化波束掃描。 該天線由14個單元結構組成，並經過製作與測試，實測結果與模擬結果高度一致。樣品天線實現了從-30°到32°的固定頻率圓極化波束掃描範圍，主波束方向之軸比皆小於3 dB，且在所有波束方向的操作條件下|S11|均低於-10 dB。樣品天線在邊側方向達到10.4 dBic的峰值增益，測得的效率為 65%，並在波束掃描過程中保持小於2.6 dB的增益變化。其緊湊的尺寸和穩定的性能使其適用於需要固定頻率圓極化波束掃描的雷達系統。

In this thesis, a novel circularly polarized (CP) leaky-wave antenna (LWA) based on a half-mode substrate-integrated waveguide (HMSIW) structure is proposed. The unit cell of the proposed antenna, incorporating a transverse wide slot and a longitudinal slit, integrates two lumped capacitors with capacitances selected to enable frequency CP beam scanning from backward (-42°) to forward (35°), including broadside (0°), while maintaining an axial ratio (AR) below 3 dB, as confirmed by simulation results. Additionally, we found that by adjusting the capacitance values, the propagation constant within the guided structure could be modified, indicating that the antenna can achieve fixed-frequency CP beam scanning through capacitance variation. Based on this principle, the capacitors were replaced by varactor diodes, and a biasing circuit was integrated into the original LWA structure. With an appropriate design that includes RF and DC signal isolation components, the AR was maintained below 3 dB. The designed antenna, while supporting frequency beam scanning, can also achieve CP beam scanning at a fixed frequency by applying a proper reverse bias voltage to the varactors. The proposed antenna, consisting of 14 unit cells, was designed, fabricated, and tested, with measured results closely matching the simulations. The antenna achieved a fixed-frequency CP beam scanning range from -30° to 32°, including broadside, with an AR below 3 dB and |S11| below -10 dB across all beam directions. The prototype achieved a peak gain of 10.4 dBic and a measured efficiency of 65% at broadside, with gain variation of less than 2.6 dB during beam scanning. Its compact size and stable performance make it suitable for radar systems requiring CP beam scanning at fixed frequencies.