A photonic radar decoy (50) is provided which simulates an aircraft to a radar having an interrogating signal. A plurality of receiving antenna (52, 54, 56, 58, 60) are attached to the decoy (50) with each of the receiving antenna (52, 54, 56, 58, 60) independently capable of receiving the interrogating signal from the interrogating radar system. Each signal received by an antenna (52, 54, 56, 58, 60) is transmitted to a signal combiner and amplifier (82) by delay lines (72, 74, 76, 78, 80). The combiner and amplifier (82) coherently adds the transmitted signals, thereby producing a coherent signal which is amplified and subsequently emitted by a non-directional transmission antenna 106, simulating a dynamic and complex radar signature of an aircraft.

An object detecting apparatus uses a radar system 24 which employes a directional antenna 6. A transmission parameter of the system 24 is calibrated for each transmission direction such that, at a boundary 22 of a detection area 20, there is a maximum signal intensity and a minimum sensitivity. The calibration is effected using reflectors of known reflective response which are positioned around the boundary 22 during calibration.

The present invention relates to a radar apparatus that uses a plurality of transmitting/receiving antennas A1-A4 and receives a reflected wave, of a transmitted wave, reflected from a target. By utilizing the property that the path of the transmitted wave from an antenna A1 and its reflected wave and the path of the transmitted wave from the next selected antenna A2 and its reflected wave share the same spatial system, and therefore that both received signals have the same characteristics in terms of frequency and phase, a judgment is made as to whether there exists any difference between the receiving characteristics of the antennas, and the received signal is corrected in accordance with the result of the judgment. It is also possible to judge the presence or absence of a change in the characteristic of each antenna, and apply a correction accordingly, even during the normal operation of the apparatus.

An improved omnidirectional radar retroreflector and marine personal locator incorporating same. One embodiment of the radar retroreflector includes first and second collapsible radar reflective disc portions biased in a substantially perpendicular open position with a plurality of radar reflecting web sections extending substantially perpendicularly therebetween creating eight sets of three mutually-perpendicular radar reflective surfaces forming an omnidirectional radar retroreflector. In a collapsed position, the first and second disc portions bend around a common axis of intersection in a non-destructive manner folding the web sections. A second embodiment of the radar retroreflector consists of a balloon having, when inflated, two intersecting disc-shaped portions oriented substantially perpendicularly and a plurality of radar reflecting web sections extending substantially perpendicularly therebetween creating eight sets of three mutually-perpendicular radar reflective surfaces and forming an omnidirectional radar retroreflector. A marine personal locator, prior to activation, restrains the radar retroreflector in a collapsed position. The radar retroreflector opens upon activation and is suspended on a tether by a balloon. The marine personal locator can also include a light source and a radio transmitter. Prior to activation of the marine personal locator, all components can be contained within a housing.