Abstract: A nonlinear radar system includes a handheld unit including a display screen, a first antenna configured to generate and emit an incident signal having a first frequency, and a second antenna configured to receive a reflected return harmonic signal having a second frequency, as well as a transponder tag is attached to an existing golf ball. Such a transponder tag is in communication with and responsive to the handheld unit, and includes an electromagnetic nonlinear element configured to be detected by the incident signal without the need for a line of sight. Upon being detected by the incident signal, the transponder tag is configured to transmit the reflected return harmonic signal having the second frequency different from the first frequency. The transponder tag is passive and does not require a power source other than incident radiation.