Patent GB-1403997-A (GB)
Title: Waveform communication system
IPC: H04B7/00
Filed: 1972-10-27
Abstract: 1403997 Aerials; radio signalling INTERNATIONAL BUSINESS MACHINES CORP 27 Oct 1972 49538/72 Headings H4A and H4L A communication system comprises first and second aerial means both having arrays of aerial elements which are distributed over respective geometrically similar three-dimensional surfaces. Each aerial element of the first aerial means is connected to a respective aerial element of the second aerial means by an electrical link of the same electrical length. Said links provide means whereby radiant wave signals received by the first aerial means are transferred to the second aerial means, for re-transmission. The invention also covers a communication system in which two retrodirective terminals are disposed within each others field of view for transferring waves therebetween, one of said terminals being of the kind described above. Also, means at one of said terminals provides an electrical wave for determining the frequencies of the received and transmitted waves and means for stabilizing said received and transmitted waves against Doppler frequency shifts and drift of the means for providing an electrical wave. In a first embodiment, a plurality of crossed dipoles 20, Fig. 1A, are uniformly distributed over a spherical surface 12A, and another plurality of crossed dipoles 22 are uniformly distributed over a spherical surface 14A. Respective reflecting spheres 24, 26 are disposed inside the surfaces 12A, 14A and are connected by a tubular member 16A. One array is used for reception and the other is used for transmission, and each element 20 is coupled to a respective element 22 by circuitry which is housed in the member 16A and which has the same electrical length in all cases. The crossed dipoles are designed for circular polarization. The diameters of the spherical surfaces 12A, 14A are sealed in proportion to the respective wavelengths at the received and transmitted carrier frequencies. Said surfaces are each nominally a quarter-wavelength above the associated reflecting sphere, with the dipoles distributed upon it at half-wavelength intervals. Where used as a space station, spin stabilization about the axis of symmetry may be applied. In a second embodiment, the spherical surfaces and reflecting spheres are replaced by coaxial cylindrical surfaces, and reflecting cylinders (Fig. 1B, not shown). The aerial elements are simple dipoles, arranged in co-linear arrays, parallel to the common axis (Fig. 1C, not shown). Either embodiment may be used to provide a terminal or terminals for a retrodirective oscillating loop communication system as described in Specification 1,403,998. Referring to Fig. 2A, a carrier frequency f ab  is used for radio signals sent from a terminal A to a terminal B, and a lower carrier frequency f ba  for signals sent in the opposite direction. At each terminal the received signals are converted to intermediate frequencies by a mixer 104 or 154, and are amplified by an amplifier 110 or 158. Information signals are made available on a line 112 or 160 and the carrier signal is extracted by means of a filter 116 or 168. After passing through a limiter 119 or 172 the I.F. carrier may be modulated in a modulator 128 or 178 by information signals on a line 126 or 174. The output from the modulator is converted up in frequency by a mixer 136 or 182, and is transmitted to the other terminal. The intermediate carrier frequencies at both terminals are nominally the same (f i ), as are the local oscillator frequencies (f l ). The transmitted carrier frequencies are offset from the frequency f l  in opposite senses, i.e. f ab =f l +f i , and f ba =f l -f i . A fixed frequency local oscillator 186 is provided at the terminal B, but at the terminal A a variable frequency local oscillator 108 is controlled by output voltage from a frequency discriminator 122, which is connected to the output side of the limiter 119. This enables the retrodirective loop to be stabilized against Doppler shifts &c.