Reseach On Millimeter Wave Front-end Of E-band LFMCW Radar

With fast popularity of vehicle, more and more traffic accidents are occurred, so that there is an urgent demand for driving security. Research shows automotive collision avoidance radar as a significant assistive tool can improve the traffic safety effectively. Based on this background, automotive collision avoidance radar develops rapidly.E-band frequency is pure and rich in spectrum resources and less electromagnetic interference to environment, which has become an important band automotive radar system. Usually, automotive collision avoidance radar includes pulsed radar and linear Frequency-Modulated Continuous Wave(LFMCW). But LFMCW radar has been applied more widely for its merits such as high measuring accuracy, simple structure, low transmitting power and no blind areas.Millimeter-wave front-end is an important component of radar system. This thesis’ research mainly focuses on millimeter-wave transceiver front-end and its key component of an E-band LFMCW radar system. According to the requirements, transmitter and receiver of system which is asked to have the function of ranging, velocity measurement and direction-finding use the same antenna. Through the study of related theories of millimeter wave and radar system, this thesis proposed a double transmitters and receivers scenario of hybrid integration. To maintain the consistency between transmitting signal and local oscillator(LO) signal as much as possible, they share an input signal of X-band frequency. After the input signal is doubled to Ka-band, it is split into two signals, one for transmitter, the other one for LO. They are all obtained by 8 times multiplier. Receivers adopts zero-intermediate frequency(IF) structure. The structure greatly reduces the circuit complexity and is easy to integrate the circuit and miniaturize circuit size.According to the millimeter-wave front-end design scheme, the main work of this thesis is described as follows:1. Chose single device that satisfies the requirement of design and analyzed each of them in detail.2. Designed a six-port coupler which connects the front-end transmitting port, two receiving ports and two antenna ports. The coupler consists of two cascaded directional couplers that are based on branch-line hybrid.3. E-plane probe transition was chosen as conversion structure of microstrip line and waveguide. Designed a waveguide for the connection of microstrip-line coupler and antenna. Designed a two-port testing structure of waveguide to debug the transmitting port of front-end and antenna.4. Simulated the gold model connecting the die and microstrip circuit and Analyzed its impact to the front-end system performance. The simulated model had been used in the practical circuit.5. Designed a power of front-end system whose power supply is controlled and implement that power up gate first and then drain. Designed a cavity which assembly all parts of the front-end system. It is good air tightness and prevents leakage of signal and self-excitation.After debugging, the key indicators of system are as follows:Without regarding the loss of test piece, transmitting 6 dBm. Receiver gain exceeds 60 d B. Testing distance is about 46 m.The experimental results shown the front-end system accomplish preliminary target, but it still needs to be improved.