具廣角回波特行之平面陣列微波回應器的設計

Abstract

在本文中，我們設計、製作並量測了一個具廣角回波特性之平 面 陣列微波回應器。這樣的回應器是由四組孔徑耦合的微帶天線 (Microstrip line fed aperture coupled patch antenna) 所組成， 並 且使用 Van Atta 的設計來排列每個天線組其天線單元的位置。 其中 ，每個天線組均包含了一個接收天線、微波放大器、與發射天 線。來 自於詢問器的訊號會被接收天線接收，經由放大器放大之後， 再由發射 天線發射。經由 Van Atta 這樣的設計，使得所有發射天 線所發射出 來的場，會在入射波入射進來的方向上相結合，而在其 他的方向上相 互抵消。因此，這個回應器只會對在線上的詢問器方 向做回應。在 10.025 GHz 這個設計頻率上，每一個天線的反射係數 均低於 -19 dB， 而且每個放大器均具有10 dB 的增益與 -28 dB 的反 射係數。為了未來 的運用，我們也設計了一個18.45 GHz 的三級放 大器。這個三級放大 器的量測結果為 27.6 dB 的增益與 –12.6 dB 的反射係數。這個設計 出來的回應器的在10 GHz 的量測結果，其 下降 10 dB (5 dB) 的回 應角為106 degree (80 degree)。這個結果 與一個只有一組天線的回應 器的理論值相當的近似。而它在有偏壓 與無偏壓的 RCS 圖形，在此 也被量測並比較它們的差異。在這兩個狀 態間，有超過 20 dB的差異。 最後，我們還量測了在 30 degree 的入 射訊號下，回應的回波圖形。其 量測的結果與理論的結果相當接近。 In this thesis, a new planar array transponder with a broad responding was designed, fabricated, and measured. The transponder was composed of four pairs of aperture-coupled microstrip antennas, arranged by using the Van Atta design. Each antenna pair contained a receiving antenna, a microwave amplifier, and a transmitting antenna. The signal coming froman interrogator is received by the receiving antennas directly enlargedby the amplifiers, and then reradiated by the transmitting antennas. Nolocal oscillators were needed in the design. By the Van Atta array arrangement, the reradiated fields from all the transmitting antennas combine in the wave incident direction and cancel with each other in other directions, thus the transponder can respond the signal only tothe on-line interrogator. At the design frequency of 10.025 GHz, themeasured return loss for the aperture-coupled microstrip antenna was lessthan -19 dB, and the return loss and gain of the amplifier were -28 dB and 10 dB, respectively.For future applications, a three-stage amplifier at 18.45 GHz was also designed, with the gain and return loss measured to be 27.6 dB and -12.6 dB. The measured 10 dB (5 dB) responding beamwidth for the 10 GHz array transponder was 106□(80□, which was aproximately the same as that of a transponder with a single antenna pair. The RCS patternsfor the transponder at the on state (with bias) and off state (without bias)were also measured and compared. More than 20 dB difference between the patterns of these two states has been observed. Finally, the responding pattern for an obliquely incident wave (30□away from the normal direction)was measured. The measured result agreed very well with the theoretical one.