Abstract: Conventional secondary radar systems use mechanically rotating antennas to radiate a concentrated beam that rotates in a horizontal plane. Data exchange between ground stations and airborne transponders can only take place if the aircraft is struck by the antenna lobe. The distance from the aircraft to the ground station is determined from the signal transit time. Directional information is derived from the antenna position. The secondary radar system according to the invention uses an omnidirectional antenna, so that data can be exchanged between ground station and aircraft at any time. To determine the position of the aircraft, interrogation signals are transmitted by a single active ground station such that the reply signal from a transponder falls within the common system time frame of the ground station. The times of arrival of the reply signals at different ground stations are then directly proportional to the distances from the aircraft to these ground stations.

Abstract: A two-way ranging system in which deviations of transmit times of interrogation signals from a nominal transit time are determined at a transponder. These deviations are dependent upon the propagation conditions for interrogation and reply signals in the medium of propagation. A normally fixed delay is developed in the transponder. This fixed delay occurs between the reception of an interrogation signal and the transmission of a reply signal. This fixed delay is so shortened as to compensate for transit time deviations of the interrogation and reply signals.

Abstract: Several satellites serving as reference stations (S.sub.j) for a user revolve about the earth in different orbits. At least four reference stations must be within sight of a user station (N) at the same time. The user station measures the ranges to at least four reference stations by one-way ranging. From these ranges and the positions of the reference stations, which are transmitted as data words, the user station determines its position.To determine the positions of the reference stations, the ranges from the respective reference station to at least three ground stations (B.sub.i) are measured by two-way ranging. From these ranges and the known positions of the ground stations, the position of the reference station is obtained. The interrogation signals of all reference stations contain the same basic signal (K.sub.s), which represents a pseudorandom code. The reply signals of the ground stations contain differently coded signals (K.sub.

Abstract: The DME pulse pair is followed by a third, steep-edge pulse. The time marks are divided from the third pulse. To ensure that no random pulses are evaluated as the third pulse, the pulse pairs are still evaluated for decoding and to control tracking, while the third pulse can be evaluated only during a given time after the reception of the pulse pair. The novel interrogators and transponders can also cooperate with existing interrogators and transponders, in which case only the improvement in accuracy is lost.

Abstract: Located adjacent to runways, taxiways, and approach ramps are secondary radar interrogators which radiate the P1 and P3 pulses and the P2 pulse via different directional patterns into sectors to be monitored which are individually assigned to each interrogator. Direction finders at different locations determine the directions of arrival of SSR reply signals radiated by an airborne SSR transponder in a sector to be monitored. From the directions of arrival and the locations of the direction finders, the respective transponder position is determined. The interrogators require no central control. Alternatively, the arrival times of the SSR reply signals are measured at several points; an evaluating device forms the differences in arrival time, and the intersection of the hyperbolic lines of position determined in the evaluating device is the position of the transponder.

Abstract: Monitoring apparatus for a time reference scanning-beam microwave landing system which supplies directional information throughout a 40.degree. to 60.degree. landing approach sector. Several transponders are provided within the radiation field of the directional antenna of the landing system, these being directionally separated. Each transponder retransmits a part of the beam passing by it back to the directional antenna of the microwave landing system. The retransmitted signals are in converted form and are processed by the MLS system similar to radar echo signals, but are modulated at different discreet frequencies for identification. Errors are detected by comparing received transponder signals with locally generated reference signals at the MLS equipment.

Abstract: This relates to a reference station for distance-measuring systems wherein the distance between aircraft and the reference station can be measured. The station comprises an antenna and at least one receiver and/or transmitter. The antenna consists of a plurality of spatially distributed elements.

Abstract: An electronic navigation system ground station, which may be either an omni-range beacon (such as VOR) or a passive direction finder. A circular array of antenna elements has a feed arrangement which includes switched programming of at least one discrete set of phase shifters to effect successively changed phase-rotation fields for minimizing the adverse effects of multipath signals between the ground station and a remote station, aboard an aircraft for example.

Abstract: A ground station for VOR navigation systems with at least one transmitter and several radiators, which ground station radiates azimuth-dependent and azimuth-independent information. The azimuth-dependent information consists of the wave amplitude-modulated with 30 Hz in the field and generated by the superposition of the nondirectionally radiated VHF carrier on a VHF figure-8 directional pattern rotating at 30 Hz. The azimuth-independent reference wave consists of a 30-Hz wave which is contained as frequency modulated in a 9,960-Hz subcarrier wave amplitude-modulated on the VHF carrier.

Abstract: An ILS (Instrument Landing System) having at least one of the Glide-slope and Localizer functions, each of said functions comprising course and clearance signals. For the course and clearance signals of either function, a single transmitter is supplied, the necessary frequency difference between those signals being obtained by dividing the transmitter output into two signals, one of which is uniquely phase modulated to produce a predetermined frequency offset with respect to the other.

Abstract: A facility for monitoring in the near field, the carrier-frequency and sideband signals radiated by a DVOR ground station is provided. In a first embodiment the monitor antenna is located outside the circle in the near field, and a controllable phase shifter compensates for the phase shifts caused by the different path lengths between the radiators of the circular array and the monitor antenna. In a second embodiment, the central radiator is used as the monitor antenna. The sideband signals received by this monitor antenna are modulated in a controllable phase shifter whose control is synchronized with the switching sequence of the commutator.