同軸過孔間距縮小化及隔離度優化於毫米波雷達板之應用

Abstract

將傳統雷達板的IC晶片和天線放置於印刷電路板（PCB）的不同側，並利用同軸過孔進行連接，可以減少兩者之間的耦合干擾，然而50歐姆同軸過孔在毫米波雷達應用上間距過大。為減少間距，本文研發低阻抗同軸過孔來改善，並在不連續性處做設計來補償阻抗不匹配的問題。設計後同軸過孔的間距降低了23%，從原先的1.3毫米降至1毫米，降低了一倍不連續區域之厚度，約為天線操作頻率62 GHz對應之1/10波長。同時，在不連續區域採用了蕈狀電磁能隙設計，可解決天線發射端和接收端之間的隔離問題。止帶出現在50-90 GHz，頻寬約57%。

在量測同軸過孔時，受到探針物理尺寸的限制，需要在同軸過孔旁引入一段傳輸線，並透過校正的方式去扣除傳輸線效應。然而校正方式如TRL，需要大量的校正件來計算傳輸線的效應並進行扣除。本論文提出了一種基於多重反射概念的校正方式，只需要一個校正件就可以計算出同軸過孔的電氣特性。模擬結果顯示在待測物後方接上一段約14.5mm的傳輸線，並利用此種校正方式推估之待測物特性與直接模擬待測物獲得之電氣特性一致。此外在量測結果對於反射大於 -20 dB的頻段，該方法與 UTRL 校正後之結果趨勢一致，可有效計算出同軸過孔的電氣特性，驗證該方法的有效性。

Placing IC chips and antennas on separate sides of a PCB and connecting them with coaxial vias reduces interference. In millimeter-wave radar applications, however, the spacing between 50-ohm coaxial vias can become problematic. To address this, we developed low-impedance coaxial vias and incorporated discontinuities to handle impedance mismatches. These adjustments reduced via spacing by 23%, from 1.3 mm to 1 mm, and halved the thickness of the discontinuity region, roughly 1/10 wavelength at 62 GHz. Additionally, a mushroom-shaped electromagnetic bandgap in the discontinuity improved isolation between transmit and receive ends of the antenna, creating a stopband from 50 to 90 GHz with a 57% bandwidth.

During measurements, physical probe size limitations required a transmission line segment next to the coaxial via, with corrections made for its effects using calibration methods like TRL. We propose a new calibration method based on multiple reflections, using just one standard to determine coaxial via characteristics. Simulation showed this method accurately estimates characteristics with a 14.5 mm transmission line segment, consistent with direct electrical simulations. For bands where reflections exceeded -20 dB, results aligned with those corrected by UTRL, confirming the coaxial via's electrical properties and validating our approach.