Development of phase inverter for performance improvement of FM-CW radar

In this paper, development of a phase inverter module for FM-CW (frequency modulated continuous wave) Radar is presented. The development is performed in the form of a design and simulation based on the theory of Samuel Y. Liao [2] and Tamasi Moyra et.al's research for J mode phase inverter [6]. In a FM-CW Radar, two parallel separate antennas are used for transmitting and receiving signals simultaneously. Side lobes from both antennas are interfering with each other. This creates false detection at the receiver. To overcome this problem, a phase inverter is needed to remove interfering signals from the transmit antenna's side lobes at the receiver. The phase inversion is performed for 180 degree phase shift (λ / 2) between the TX and RX signals. Experiments were conducted for developing phase inverter based on J, T, Y and # junction methods. Based on the calculations and simulations for the J-junction method, S11 of -22.2 dB and S14 of -43.475 dB (return loss), S12 of -4 dB and S13 of -3.34 dB (insertion loss output) were obtained, while phases S12 of 147° and S1 of -123°. For T-junction, S11 of -24.86 dB and S14 of -23 dB (return loss), S12 of -2.8 dB and S13 of -4.7 dB (insertion loss output) were obtained with phases S12 of 133° and S1 of -133°. Y-junction produces S11 of -25.86 dB and S14 of -25.989 dB (return loss), S12 of -3 dB and S13 of -5 dB (insertion loss output) with phases S12 of 65° and S1 of -23°. The #-junction creates S11 of -17.08 dB and S14 of -25.81 dB (return loss), S12 of -4.17 dB and S13 of -3.5 dB (insertion loss output) with phases S12 of 128° and S1 of -143°. Based on the results of designs and simulations, the phase inverting of 180° can be obtained more precisely by using the T- junction. The phase inverting using this T-junction achieves the best performance and will be implemented for our Radar antennas.