Abstract: An airport-surveillance system for determining the position and identification of aircraft (4) on the airfield which utilizes secondary radar and includes an interrogation station (1) installed on the airfield (3) and from which the interrogation signal is transmitted by way of a narrow sharply forcused beam of an antenna which scans the airfield and further includes transponding stations installed in the aircraft (4). The present invention provides accurate identification and location of the aircraft by utilizing a receiver which has a sharply focused antenna beam and which is geographically located a distance away from the interrogation antenna and wherein the replies from the transponder of the aircraft are received by the receiving antenna only when the interrogation and receiving antenna beams (2, 22) intersect. By scanning all locations of the airport, the position and identification of all aircraft on the airport can be determined.

Abstract: A circuit for the comparative vector measurement of keyed radio signal pulses, in particular DME pulses which arrive virtually simultaneously in a plurality of receivers and which can exhibit large level differences is utilized where, in each receiver, the pulses are fed to a switching amplifier which has an amplification which is adjustable in discrete stages and the reduction of which is effected automatically with the rise in the leading edge of the relevant signal pulse, and where, when the relevant switching amplifier of the receivers has been traversed, at a specific measuring time which is common to all receivers, the instantaneous amplitudes and instantaneous phases of the measuring signals are measured, the circuit providing that the pulses are fed to the switching amplifier by way of a delay device and, that for the setting of the amplification of the switching amplifier, a control circuit is provided which is directly fed with the radio pulses and which comprises a logarithmic amplifier and a subse

Abstract: An amplifier circuit for the unadulterated transmission of phase information of a supplied ac voltage signal over a large dynamic range includes a series connection of a series of similar amplifier stages each of which is followed by a symmetrical limiter. The amplifier operates as a logarithmic amplifier for maintaining the amplitude information of the supplied ac signal. Each of the amplifier stages comprise an emitter-base transistor amplifier circuit having negative feedback and an output circuit which contains a resonant circuit which is strongly damped by an attenuating resistor and whose capacitance is formed by a trimmer capacitor connected in parallel to a pair of diodes. The diodes are connected in anti-parallel relation to one another and represent the limiter. The capacitance is adjustable for purpose of impedance adjustment and is set in such a manner that the resultant resonant circuit impedance is capacitive.

Abstract: A method for the comparative vector measurement of keyed radio signal pulses arriving nearly simultaneously at several radio receivers, particularly DME pulses, which can exhibit great level differences. The pulses at each receiver are individually fed to an amplifier or attenuator having an amplification or attenuation, respectively, which can be adjusted in distinct steps, whose reduction or increase, respectively, takes place automatically with the rise of the leading edge of the respective signal pulse. After passing through the respective amplifier or attenuator of the receivers, the instantaneous amplitudes of the measuring signals are measured at a specific measured time which is common to all receivers.