a plastic support ring 38 using tie wraps 30 this assembly is further attached to antenna 23 it is of critical importance that the modulating diode 36 is positioned within the path of the reflected radar beam however it should be appreciated that the modulating diode 36 can be placed anywhere within the radar beam for example an alternate embodiment is where the diode 36 is placed a distance away from the edge of antenna 23 by attachment directly to enclosure 15 the self test circuit signal generator 32 in the preferred embodiment is a 16 08 khz crystal oscillator used to generate the required reference signal the signal is next divided by the counter 33 such as by thirty two using a cd4060b cmos ripple counter in the preferred embodiment to provide the resulting reference signal s7 a 502 5 hz pulse train reference signal s7 is delivered to the modulating diode 36 by line 37 in the preferred embodiment the modulating diode 36 is a 1n34b germanium signal diode in an alternate embodiment of the present invention as shown in fig5 the required reference signal may be generated remotely by signal generator 32 39 and transmitted to the radar systems 10 10 n through lines that feed into each system through its multi pin connector 16 see fig2 for example in the expanded industrial control application utilizing several systems as described above one signal generator 32 39 could be utilized to generate the required reference signal for all of the radar systems 10 10 n in the preferred embodiment the reset pin of ripple counter 33 is pulled to ground to initiate the self test operation upon.