以新型90度耦合器電路設計之汽車防撞警示雷達及短距無線通訊前端電路

Abstract

本論文提出利用90度耦合器組成的新型微波電路架構，用於開發汽車防撞警示雷達系統及短距無線通訊系統前端電路，提出利用新型電路設計之雷達及無線收發機架構，達成雷達及無線通訊系統前端電路精簡化。 本論文的第一部分提出三種90度耦合器構成的新型電路，一個新型LO穿透式混頻器，此混頻器由一個90度枝狀耦合器及兩個蕭基特二極體組成，此混頻器有將本地振盪信號傳輸至天線埠之特性。接著提出LO穿透式IQ混頻器架構，此IQ混頻器由兩個穿透式混頻器加上45度延遲線及兩個90度枝狀耦合器構成。如同一般IQ混頻器，所提出的LO穿透式IQ混頻器除了可同時接收信號的振福及相位外，也具備將本地振盪信號傳輸至天線埠的特性，應用於雷達收發機中接收時並不會有額外的接收功率損耗在功率分配網路上，可提高整體的功率使用效率。接著提出一個創新的全雙工雙向放大器，此雙向放大器由一個90度耦合器及兩個反射式放大器組成，所提出的放大器具有將傳輸及接收信號同時放大的特性；具備此特性，將此放大器應用在無線收發機前端電路中可省去信號切換器的使用。 本論文的第二部分提出一個10.5 GHz的都普勒雷達收發機。傳統單一天線架構的雷達收發機有本地振盪器信號使用效率不佳的問題，在此本文提出一個利用穿透式IQ混頻器設計的新型雷達收發機架構，用以改善本地振盪信號使用效率並將雷達前端電路精簡化。文中將實現一個利用LO穿透式IQ混頻器構成的10.5 GHz都普勒雷達收發機，此收發機採用一個DGS (Defected-Ground-Structure)結構設計的本地振盪器，結合鎖相迴路構成的頻率產生器當作本地信號源，設計出來的雷達收發機可以操作在10.36 至10.74 GH，其輸出功率為6 dBm。與傳統架構相比，在相同輸入功率10 dBm下利用LO穿透式IQ混頻器設計之收發機可提供多出3.3 dB的接收功率；當輸入功率只有0 dBm時，所提出之接收機可提供多出16.2 dB的接收信號強度。所設計之雷達收發機可用於偵測速度及移動方向並提供0.25 km/hr的速度解晰度。 本論文的第三部分提出兩個FMCW 24 GHz車用防撞雷達系統，一個側視雷達系統及一個前視雷達系統。此雷達系統由一個6 GHz的壓控振盪器驅動，信號經過兩個倍頻器倍頻後產生所需的24 GHz信號；一個12 GHz的放大器用來提供接收機所需的功率；使用一個次階混頻器來將雷達回波信號降頻至基頻直接處理。針對側視雷達的應用設計一個由微帶天線饋入的號角天線作為收發天線，所有的射頻電路、天線、及基頻控制信號處理板全部整合至一個尺寸為60 × 45 × 30 mm3的模組中，此尺寸使雷達可以裝置在小型車的後照鏡下方。從實驗的結果顯示，此雷達模組當偵測對象是人時可以偵測到8公尺的距離，當對象是一台小型汽車時可以偵測至15公尺遠。接著提出一個24 GHz的前視雷達系統，提出一個9x8的串聯饋入式的天線陣列設計。此天線在E-平面及H-平面上功率分布都採用中央較高旁邊較低的設計，使的此天線有較好的旁波束能階(SLL)，此天線量測結果可達到18.5 dBi的增益，同時在E-及H-平面上的半功率波束角度分別為10.5及11.2度。此雷達系統的等效輻射輸出功率為23 dBm，整個調變頻寬內只有0.7 dB的功率誤差。此論文中也提出一個線性頻率調整機制，此線性頻率調整器能將頻率調變的線性度從9%的誤差調整至只有0.3%調變誤差，並且實現2D(二維)快速傅利業轉換(FFT)演算法來處理回波信號，此演算法可以同時解出待測物的相對距離及速度。從實驗結果，此前視雷達系統可偵測位於15公尺外的人，且提供0.7 km/hr的相對速度解析度。 最後，本論文將提出一個利用全雙工雙向放大器設計的無線通訊系統前端電路架構，設計一個10 GHz雙向放大器，此放大器的傳輸與接收增益分別為14與13 dB。此收發機採用一個八木(Yagi)天線當作收發天線，此天線有12 dBi的天線增益，其半功率波束寬度為40度。一個典型的環型混頻器用來將基頻信號調變至射頻，且同時將接收到的射頻信號降頻至基頻。整合起來的收發機可提供15.5 dBm的等效輻射輸出功率，其整體升降頻的增益皆為17 dB.

This dissertation discusses the development of vehicle collision warning radars and short-range communication RF front-end with new quadrature hybrid composed circuits. A new radar and a communication RF front-end architectures using the proposed circuits are presented with simplified circuit complexity. In the first part of this dissertation, three new quadrature hybrid composed circuits are presented. A new LO transparent hybrid mixer is proposed, which is composed of a branch-line coupler and two Schottky diodes. The new hybrid mixer can transmit the LO power to the antenna. Then, a LO transmissive quadrature hybrid mixer is proposed. The quadrature hybrid mixer is composed of two hybrid mixer, 45° delay lines, and branch-line couplers. The proposed quadrature hybrid mixer can receive signal with phase. Moreover, the proposed mixer shows high transmission efficiency to pass LO power to antenna and no received power wasted in the oscillator port. A novel full-duplex bi-directional amplifier is then presented. The bi-directional amplifier is composed of a quadrature hybrid and two reflection type amplifiers. The proposed amplifier can enhance the signals in both transmitting and receiving directions, which can be used in a transceiver front-end without using the signal switches. In the second part, a 10.5 GHz Doppler radar using the proposed LO transmissive quadrature hybrid mixer is presented. The proposed architecture offers higher local power usage efficiency than the conventional ones and simplifies the front-end complexity. A defected-ground-structure local oscillator along with the phase-lock-loop frequency synthesizer is used in the system to provide better phase noise and good frequency stability. The designed transceiver can be operated from 10.36 to 10.74 GHz with output power level of 6 dBm. Compare to the conventional quadrature radar, the proposed one offers 3.3 dB received power more when the LO power is 10 dBm, and 16.2 dB more when the LO power is 0 dBm. The implemented radar can measure the speed and moving direction with 0.25 km/hr resolution. In the third part, two complete FMCW 24 GHz collision warning radars are presented. The 24 GHz radars are designed for sideway-looking and the forward-looking applications. In the 24GHz radar systems, a 6 GHz VCO, two frequency doublers, a 12 GHz gain block, and a sub-harmonic mixer are developed. In the sideway-looking application, a patch-fed horn antenna is designed. All the RF circuits, antenna, and base-band signal processor are integrated into a dimension of 60 × 45 × 30 mm3. This size is ready to be installed under the back-mirror of a small car. The developed radar shows a capability to detect a human in 8 meters and a small car located in 15 meters away. In 24 GHz forward-looking radar, a planar 9x8 series-fed patch antenna array is developed. The antenna has an antenna gain of 18.5 dBi, and the half power beam widths are 10.5 and 11.2 degrees, in E- and H-plane respectively. The radar transceiver shows an output EIRP of 23 dBm with only 0.7 dB power deviation within the whole modulation bandwidth. A frequency linearizer mechanism is presented. The frequency linearizer improves the modulation frequency deviation from 9 % to 0.3 %. A 2D-FFT signal processing algorithm is implemented to estimate the object speed and distance, simultaneously. From the experiment, the radar can detect a human up to 15 meters away and measure the relative speed with 0.7 km/h resolution. In the end of this dissertation, a full-duplex communication RF front-end using the new bi-directional amplifier is presented. A 10 GHz bi-directional amplifier is developed, which has transmission gains of 14 and 13 dB in two directions. A planar Yagi-antenna is adopted. The antenna shows a gain of 12 dBi and half-power beam width 40 degrees. A ring mixer is used as the up / down converter to convert the signal between RF and base-band. The integrated transceiver shows the overall up / down conversion gain of 17 dB and output EIRP 15.5 dBm.