Microstrip Circuit Leakage Signal Canceling Technology Based Research

The wireless communications or radar systems working in single-antenna mode is increasingly used in various civil and military fields for its size and cost advantages. When the isolation between the transmitter and receiver link is not enough in duplex wireless communication systems and continuous wave radar systems, the power of transmitted signal leaking into the receiver link from the transmitter link may be too high. It will reduce the sensitivity of the receiver, even will block the receiver. How to solve this problem has become one of the key factors of improving the system performance. In this dissertation, several kinds of leakage signal canceller structures based on microstrip circuit are proposed. These solved the leakage signal problem to some extent. Meanwhile, those structures have advantages of small size, low cost, easy to use compared to the active RF leakage signal canceller.First of all, this dissertation analyzed the impact of transmitted signal leaking into receiver link from transmitter link is too high in single antenna wireless transceiver systems, described several kinds of suppressing methods, analyzed the advantage of the leakage signal canceller based on microstrip circuit. Secondly, a kind of parallel line coupler adding a mismatch load using micostrip circuit in free port is designed in this paper. This structure is simple and low cost, test shows it can achieve the isolation below-68dB in2.4GHz frequency. Thirdly, a kind of branch line coupler adding a mismatch load using electric adjust circuit in free port is designed.This structure is flexible and can easily regulate the frequency and isolation, test shows it can achieve the isolation below-65dB between2.3to2.4GHz frequency. Fourthly, a kind of branch line coupler hybrid structure is designed. This structure can provide good isolation in K-band, test shows it can achieve the isolation below-63dB in24GHz frequency. Finally, a kind of symmetrical branch line coupler hybrid structure is designed, this structure can achieve high isolation bandwidth in K-band, test shows it can achieve the-40dB isolation bandwidth higher than1.1GHz near24GHz frequency.