Communications: radio wave antennas – Antennas – Balanced doublet - centerfed
Patent
1981-01-23
1984-06-12
Wilbur, Maynard R.
Communications: radio wave antennas
Antennas
Balanced doublet - centerfed
G01S 1384
Patent
active
044545126
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to secondary radar systems, that is to say systems in which distances are measured by means of radiating a signal from a measuring station, which receives a return signal from an active target or reflecting station.
It is known to employ a pulse radar to interrogate an active target which, on reception of a pulse from the measuring station, transmits a pulse or, more usually, a coded reply after a predetermined time. Usually the measuring station is arranged to compute or display the range of the target. The present invention, however, employs continuous wave transmission and an indication of range is obtained by comparison of the phase of modulation of the reflected wave with the phase of similar modulation of the transmitted wave. The time of propagation of a wave retransmitted from a different reflecting object is, approximately, 1 ms per 150 Km and accordingly unambiguous measurement of the distance of the reflective object can be made by a comparison of the phases of the respective modulations provided that the frequency of transmission in kHz is less than 150 divided by the distance in kilometers. It is intended that the present invention should be used in combination with radio telephones or other forms of mobile transceivers. Accordingly, it is intended that a receiving station as described hereinafter should be part of a mobile transceiver and is operative to transmit or receive according to the state of the transmit/receive switch in the mobile transceiver. The modulation which is preferably employed in this invention is at an audio frequency and accordingly the various modulating, demodulating and amplifying circuits that would be present in a mobile receiver may be employed for the performance of the present invention. The measuring station may be similarly adapted for use in or as part of a mobile receiver, it being thereby possible for the operators of two portable or mobile transceivers to measure the distance separating them.
SUMMARY OF THE INVENTION
In one embodiment of the invention, a primary carrier wave is radiated from the measuring station and carries modulation which may be at an audio frequency. The modulation is recovered at the receiving station and is used to modulate a secondary carrier wave which is transmitted by that station for reception by the measuring station. It is desirable to ensure that the modulation is retransmitted in the same phase as it is received. The secondary carrier wave may be at the same as or at a different frequency to that of the primary carrier wave.
In order to derive, at the receiving station, a signal suitable for retransmission, the primary carrier wave may be used to derive timing pulses at the receiving station. The timing pulses may define an interval in which high frequency clock pulses can be accumulated in a counter. That interval may be reproduced for obtaining a modulating signal for the secondary carrier waves by repetitive accumulation of pulses or decrementing of pulses to the same total as is accumulated during timing intervals. A signal which is produced each time the said total is reached may constitute the modulation of the secondary wave.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a schematic diagram of one embodiment of a measuring station;
FIG. 2 is a schematic diagram of one embodiment of a receiving station;
FIG. 3 indicates one form of phase comparator for use at a measuring station; and
FIG. 4 is an arrangement for indicating the phase synchronism of transmitted and received signals.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the measuring station illustrated by FIG. 1 of the drawings, an oscillator 1 produces an audio frequency tone signal which is preamplified by an amplifier 2 and then modulated by a modulator 3 with a radio frequency signal obtained from an oscillator 4. The modulated carrier signal is amplified by an amplifier 5 and, when a switch 6 is in a "transmit" position, is radiated from an antenna 7. When the switch 6 is
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Burk Robert C.
Wilbur Maynard R.
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