In 1995, two American scholars used a radio telescope with a diameter of 26 meters to look for unknown signals emitted from the depths of the vast universe. However, so far, no radio source with the characteristics of received signals has been found, and there are no special stars in the direction of these radio waves.
The sentence 'no radio source with the characteristics of received signals' means that it is not certain that the source of the radio wave has received the signal.