1402 Tx Leakage Cancellers for 24 GHz and 77 GHz Vehicular Radar Applications Choul-Young Kim', Jeong Geun Kim', Joon Ho Oum', Jong Ryul Yang', Dong-Kyun Kim2, Jung Han Choi2, Sang-Wook Kwon2, Sang-Hoon Jeon3, Jae-Woo Park3, Songcheol Hong' Dept. of EECS, Korea Advanced Institute of Science and Technology (KAIST), 373-1, Guseong-dong, Yuseong-gu, Daejeon, 305-701, Republic of Korea 2Samsung Advanced Institute of Technology (SAIT), Mt. 14-1, Nongseo-ri, Giheung-eup, Yongin, Republic of Korea 3Knowledge*on Inc., 513-37, Eoyang-dong, Iksan, 570-210, Republic of Korea Abstract -Tx leakage cancellers for 24 and 77 GHz vehicular radar systems are presented. These have high Tx-to-Rx isolation and wideband characteristics. Tx leakage cancellers are composed of four Lange couplers, a 900 delay line, and a Wilkinson combiner. Tx leakage cancellers are implemented on GaAs substrate. A 24 GHz Tx leakage canceller shows the transmitting loss of 5.7 dB and Tx leakage cancellation of 28.1 dB. Also a 77 GHz Tx leakage canceller shows the transmitting loss of 3.6 dB and Tx leakage cancellation of 28.2 dB. Isolations due to Lange coupler are 15.1 dB in 24 GHz Tx leakage cancellers and 13.1 dB in 77 GHz Tx leakage cancellers, respectively. The isolations due to the topology of the Tx leakage canceller are expected to be 13 dB and 15.1 dB, respectively. These compact Tx leakage cancellers show wideband characteristics of bandwidth beyond 4 GHz. Index Terms -Automotive, radar. I. INTRODUCTION Vehicular radar systems in 77 GHz have been introduced in the car market. The main applications for those radars were the ACC (Adaptive Cruise Control) function. ACC radar systems have a maximum range of 100-200m. Those long range applications in the 77GHz band are suitable because of the small antenna apertures. In short range radar applications, 24 GHz band technology is suitable because small beam antenna do not need. The FMCW radar configuration is generally used in automotive collision avoidance radar [1]. In CW (Continuous Wave) radar systems such as FMCW radars, the high Tx-to-Rx isolation is required to improve the sensitivity. CW radars use two separate antennas to improve Tx-to-Rx isolation [2]. However, the size of radar system becomes to be doubled because two antennas are used. To reduce the size of radar, CW radars with a single antenna can be implemented using a circulator or a coupler. A circulator or a coupler is usually used to separate transmitting signal and receiving signal in the radar systems with a single antenna. However, the circulator shows low isolation characteristics, especially at mm-wave frequency. Therefore, the large Tx leakage signal from transmitter due to the low isolation of circulator or the reflection from the antenna can degrade the sensitivity of the receiver, and even saturate the receiver components, so that the dynamic range of the receiver is reduced. Besides it is difficult to be integrated with other MMICs. To achieve a good Tx-to-Rx isolation performance in the radar system with a single antenna, the reflected power canceller (RPC) has been proposed [3]-[4]. Recently, the RPC which is based on DSP has been reported [5]. It shows a good Tx-to-Rx isolation performance up to K-band frequencies. However, it is complicated to implement the RPC in mm- wave frequency because it needs a high performance vector modulator and complex control circuits. Another approach to reduce the Tx leakage is proposed that is the balanced radar topology by author [6]. However, when it transmits the signal, half of transmitting signal is dissipated at the terminating resistor at the coupler. Also, half of the receiving signal is dissipated at the resistor of the Wilkinson combiner. As a result, 6 dB power losses are occurred in the balanced radar topology. In mm-wave systems, the power efficient systems are required because it is difficult to generate a high output power. A small size transistor has to be used to achieve a high gain, whereas a large size transistor has to be used to achieve a high output power. Therefore, the trade-off between the gain and the power performance is required. This paper presents the Tx leakage cancellers for the 24 GHz and 77 GHz vehicular radar applications which have a high Tx-to-Rx isolation and wideband characteristics, and also can improve the power losses of the transmitting and receiving signal. II. OPERATION OF TX LEAKAGE CANCELLER Fig. 1 shows the block diagram of the radar system with the proposed Tx leakage cancellers. Tx leakage cancellers are composed of four Lange couplers, a 900 delay line, and a Wilkinson combiner. The output signal from the signal source is transferred to the antenna through the Tx leakage canceller and radiated through the antenna. The radiated signal is reflected from the target object and captured with the same antenna. 0-7803-9542-5/06/$20.00 ©2006 IEEE