The minimum range capability of a radar is determined primarily by the pulse length. It is equal to half the pulse length of the radar (164 yards per microsecond of pulse length). Electronic considerations such as the recovery time of the receiver and the duplexer (TR and anti-TR tubes assembly) extend the minimum range at which a target can be detected beyond the range determined by the pulse length.
Sea return or echoes received from waves may clutter the indicator within and beyond the minimum range established by the pulse length and recovery time.
Targets detected by the side-lobes of the antenna beam pattern are called side-lobe echoes. When operating near land or large targets, side-lobe echoes may clutter the indicator and prevent detection of close targets, without regard to the direction in which the antenna is trained.
VERTICAL BEAM WIDTH
Small surface targets may escape the lower edge of the vertical beam when close.