利用915MHz螺旋天線以及2.4GHz蜿蜒線天線實現無線功率傳輸系統接收天線之微小化

Abstract

本論文主要研究於無線功率傳輸系統中接收天線微小化設計。為解決目前無線功率傳輸系統當中之接收天線尺寸偏大，不合適使用於生物體如蜜蜂身上的困難。本論文主要提出兩種天線微小化設計方式。 首先提出915MHz天線微小化的方式為利用FR4雙層版製作螺旋天線，這一設計採用的是接地共平面波導饋入。此螺旋天線共設計兩款，具有相似的架構，差異的目的是希望有兩款不同的匹配電路。螺旋天線尺寸分別為10×25mm及10×26mm，以高頻3D結構電磁場模擬軟體Ansys HFSS (high frequency structure simulator)模擬天線本身特性，對線圈數、線圈間距以及螺旋線圈截面積進行參數優化，第一款天線實際量測最大增益為-7.19dBi，第二款則為-7.06dBi，並且有保持著偶極天線的場型，量測上垂直於螺旋天線的平面上有等值大小的增益。 第二種則為2.4GHz天線微小化設計，方式是採用蜿蜒線式天線，基板是使用RO4003雙層板，尺寸為10×15mm，蜿蜒線式天線設計方式則是採用微帶線饋入，利用耦合的方式，並且利用末端折線次數的優化，達成天線面積縮小，實際量測最大增益為-4.45dBi，並且也保持著偶極天線的場型，垂直於螺旋天線的平面上有等大小的增益。 因為天線皆是經過微小化設計，天線本身無法完成匹配，考量到微小化天線對匹配的敏感性，以及兼顧面積尺寸下，使用SMD電感及電容元件作外部匹配，均可達-10dB以下匹配。在915MHz及2.4GHz接收天線也有配合整流電路進行量測，以比較其與單獨天線2D場型量測之間的差異。

This thesis focuses on the miniaturized design of receiving antennas in wireless power transfer (WPT) systems. The study aims to address the issue of large receiving antenna sizes in current WPT systems, which are unsuitable for applications on biological entities such as bees. Two miniaturization approaches for antenna design are proposed in this thesis. The first approach targets the miniaturization of a 915 MHz antenna by utilizing a spiral antenna fabricated on a dual-layer FR4 substrate with a grounded coplanar waveguide (GCPW) feeding structure. Two variants of the 915 MHz spiral antenna are designed, featuring similar architectures but differing in their matching circuits. The spiral antenna dimensions are 10×25 mm and 10×26 mm, respectively. Two antenna are simulated using the high-frequency 3D electromagnetic field simulation software Ansys HFSS (High-Frequency Structure Simulator). Key parameters, including the number of turns, spacing between turns, and cross-sectional area of the spiral, were optimized. The measured maximum gain of the first antenna is -7.19 dBi, and the second antenna achieves -7.06 dBi. while maintaining a dipole-like radiation pattern, with uniform gain observed in the plane perpendicular to the spiral antenna. The second approach involves the miniaturization of a 2.4 GHz antenna using a meandered-line design. This antenna was fabricated on a dual-layer RO4003 substrate with dimensions of 10×15 mm. The meandered-line antenna design employed a microstrip feed and coupling mechanism, with further size reduction achieved by optimizing the number of bends at the end sections. The measured maximum gain was -4.45 dBi, also maintaining a dipole-like radiation pattern with uniform gain in the plane perpendicular to the antenna. Due to the miniaturized nature of both antennas, good intrinsic impedance matching could not be achieved. Considering the sensitivity of miniaturized antennas to matching and the need to balance size and performance, external matching circuits using SMD components are implemented. Both antennas can achieve better than 10dB return loss. Measurements were conducted on both the 915 MHz and 2.4 GHz receiving antennas integrated with rectifier circuits, and the results were compared with those obtained from standalone antenna 2D radiation pattern measurements.