| Continuous wave(CW) radar has been widely used in military and civilian areas, but the main problem of CW radar is TX leakage which will affect the sensitivity of the receiver. Based on microstrip passive structures, this paper will propose two kinds of balanced radar front-end leakage cancellation structures. Deep study will be carried out as follows:1. Research of balanced Radar RF front-end which is based on passive cancellation structure will be carried out. Leakage cancellation of some kinds of balanced structures will be analyzed and their advantages and disadvantages will be summarized too.2. Based on the existing balanced structure, a circularly polarized balanced radar RF front-end will be proposed. Cross knot and phaser will be introduced into the original network, so that the whole network can realize leakage cancellation including TX leakage, antenna reflection signal and antenna mutual coupling signal while achieve circularly polarized radiation. Ultimately the circular polarized balanced radar front-end can achieve transceiver isolation of about 50dB and axial ratio will be less than 3dB.3. The problems of the antenna pattern deformation and axial ratio deterioration will be researched, and then some measures will be taken to make axial ratio less than 3dB and the antenna pattern regularity.4. A polarization variation balanced feeding network will be proposed. This structure can achieve leakage cancellation including TX leakage, antenna reflection signal and part of antenna mutual coupling signal, but can also achieve LHCP and RHCP by controlling the emission signal. Slot coupled feeding high-isolation dual polarized antenna will be designed to compensate for some antenna mutual coupling and achieves isolation of about 45dB. Eventually the entire balanced network is designed and simulated and achieve transceiver isolation of about 40dB. Meanwhile, by controlling two emission signals, left or right circular polarization or linear polarization will be realized. |
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