Passive sonar system forms the various beams in any desired directions to obtain the improvement in Signal-to-Noise(S/N) ratio, bearing detection and localization of targets, and the attenuation of interferences from other directions. Detection of modern underwater targets is becoming increasingly difficult as noise reduction technology leads to considerably low-level acoustic emissions. Therefore, the improvement of beamforming is very important to detect modern underwater targets at the long range in the complex environmental sea. Also, to react to the fast attack mobiles such as torpedoes, port and starboard discrimination is required to be performed very quickly. In this paper, we proposed the implementation of omnidirectional target bearing detector without port and starboard ambiguity to detect effectively the low-level underwater targets. The port and starboard discrimination is performed by cardioid processing and the improvement of beamforming utilizes the cross correlation matrix of individual hydrophone pairs of linear array sensors. The sea test result shows that the system implemented is good for the detection of the low-level underwater targets.