  In this research, a 2.4 GHz planar array antenna 2X2 combined with frequency
selective surface (FSS) is proposed to obtain a high gain and high efficiency
for improving the performance of vital sign monitoring through the wall using
Self-injection-locked radar systems. The FSS is designed on a double-layer with
unit cells of 9X7 for each layer. Modified Jerusalem cross-shaped of FSS is
proposed to enhance the gain. The antenna array and additional FSS can obtain a
gain of 15.2 dB and 82% of efficiency. the vital sign monitoring of the subject
behind the wall has been successfully carried out.
