近毫米波汽車防撞主動廣角回波器之研發

Abstract

在本文中，我們成功地研發一個具有廣角回波特性的近毫米波主動式平面陣列回應器。這個回應器包含二個天線子陣列，每列由四對微帶天線組所組成(所以在設計中共有八對微帶天線組)，其排列採用Van Atta設計方式。其中，每個天線組均包含一個接收天線，一個微波放大器，與一個發射天線。該放大器位於連接收發天線之傳輸線的中間以增強再輻射場的功率準位。藉由Van Atta排列方式，整個回應器可以接收任一入射角度的訊號，而在該入射角度，輻射最大的回應訊號。在24.27GHz頻率，每一天線反射係數低於-20dB，其頻寬為2.73%(23.9-24.6GHz)。而每一放大器在24GHz具有10dB的增益及-19dB的輸入反射係數，其頻寬為13%(22.2-25.3GHz)。整個回應器在設計頻率(24.27GHz)具有120°(80°)的10dB(5dB)回應波束寬。在入射角範圍-40<θ0<40中，此回應器的RCS比同尺寸大小金屬板的RCS平均大了約10dB。而回應器本身有偏壓(on state)及無偏壓(off state)的RCS量測圖形也被做了比較，平均有10dB的差異。此回應器可以在天線頻寬(23.9-24.6GHz)內正常工作。另外，對於此次放大器的設計，我們在網路分析儀上使用TRL de-embedding校準方法量測一個埋藏於微帶電路中的電晶體NE42484C HEMT。對於近毫米波放大器的設計，所量測到的電晶體S參數可提供較準確的設計資訊。

In the thesis, a near millimeter-wave active planar array transponder with a broad responding beam was developed and measured. The transponder contains two antenna sub-arrays. Each sub-array is composed of four pairs of microstrip antennas, arranged by using the Van Atta approach. Each antenna pair contains a receiving antenna, a microwave amplifier, and a transmitting antenna. The amplifiers are incorporated in the midways of the transmission lines of each pair to enhance the level of the reradiated field. By the Van Atta array arrangement, the reradiated fields from all the transmitting antennas combine in the wave-incidence direction and cancel with each other in other directions, thus the transponder respond the signal only to the on-line interrogator. At 24.27 GHz, the measured return loss for the microstrip antenna is less than -20 dB and the measured bandwidth is 2.73% (23.9 to 24.6 GHz). The measured return loss and the gain of the designed amplifier are respectively -19 dB, and 10 dB at 24 GHz and the measured bandwidth is 13% (22.2 to 25.3 GHz). The measured 10 dB (5 dB) responding beamwidth of the transponder for the design frequency 24.27GHz is about 120°(80°). In the range -40°< θ0 < 40°of the incidence angles, the RCS's of the transponder are, in average, 10 dB higher than those of a metal plate with the same size. The RCS patterns for the transponder at the on state (with bias on) and off state (with bias off) have also been measured and compared. About 10dB difference between the patterns of the two states can be observed. The transponder works well over the -10dB bandwidth (23.9-24.6GHz) of the antennas. For the amplifier design, NE42484C HEMTs were measured by using TRL de-embedding method with a network analyzer. The measured s-parameters of the HEMTs provide a more accurate design information in near millimeter-wave amplifier design.