Abstract: Active high density multi-element antenna system [DS] for radiolocation of RF target radiation has a processor-controlled antenna array [CAA] having rings [R1, R2, R3] concentric about a central axis to define arcuate sectors Sn about the central axis, each ring having adjacent p.c. boards [PC1, PC2, PC3] with PIN diode-switched antenna elements within sectors. The rings provide three rings [E1, E2, E3] of discrete dipolar elements, defining electrically isolated antenna units [ASm], each radial to the central axis, of quasi-log-periodic configuration. Antenna units are switched in rotational sequence about the central axis to provide narrow beam signal selectivity, directionally rotatable about the central axis. An array control system [ACS] is operated, as under microprocessor control [34], by a host system [HS] to cause RF scanning. PIN diode switching is used on printed circuit boards within the array.