Abstract: A surveillance apparatus (100) is provided, said apparatus including a linear sub-array (101) of N omnidirectional transmitter elements (103) and a planar sub-array (102) of M receiver elements (104). A plurality of the transient elements (105) are generated by separating out at each of the receivers (104) the signals transmitted from the antenna elements (103) of the transmitter sub-array (101). This allows the geometry of each path (from each transmitter antenna element, to the point being imaged and back to the receiver antenna elements) to be converted to a delay or phase shift to focus on the particular point being imaged. The transient elements (105) form a cylindrical array (106) at the mid points between transmitter and receiver sub-arrays. Such a configuration enables a full 360 degrees of cover in azimuth and typically +/?60 degrees in elevation.

Abstract: A microstrip side-coupled directional coupler (20) uses inductive loading to achieve improved directivity. In one embodiment, short-circuited inductive stubs (26, 27) are connected to the coupled line (22) of the coupler (20). In a second embodiment, pairs of short circuited inductive stubs (34, 35) are connected respectively to the coupled line (32) and the primary transmission line (35) of a directional coupler (30). In a third embodiment, the primary transmission line (41) and the coupled line (42) of a coupler (40) are both centre loaded with short-circuited inductive stubs (43, 44) respectively.