RF signal synthesis

Abstract: Apparatus for generating complex composite RF signals comprising a source of unmodulated RF carrier signal (11), means for splitting the RF carrier signal output of the source into equal components (12), separate modulating means (13, 14) to which respective carrier signal components are applied, signal combining means (15) to which the outputs of the modulating means are applied. and separate baseband control signal generating means (21₁,... 22 N ) the outputs of which are applied to respective modulating means to effect in-phase and quadrature modulation of the respective carrier signal components.

Description: This invention relates to apparatus and method for gener-ating complex composite RF signals, such as spread spectrum signals. Spread spectrum signals are used in satellite navigation systems such as Global Positioning System (GPS) or Glonass. For development and evaluation purposes it is desirable to simulate locally such signals in laboratory equipment EP-A-139033 (A N T Nachrichtentechnik) provides a digital direct modulator which results in clock-edged transitions. Synchronous 1 Mega-bit signals are employed. Thus in the I/Q domain, the signal consists of a sequence of signals chosen from an NxN constellation. US-A-4308617 (Bendix) provides a noiselike amplitude and phase modulation coding for split spectrum transmissions. PN generators produce a binary sequence for each modular two added to the datastream, which results, for each pair, in only four points being used in a QPSK modulator. As is known there is provided apparatus for generating complex composite RF signals, the apparatus comprising: an unmodulated RF carrier signal source; a splitter coupled to the RF carrier signal source for splitting the output of said source into I & Q quadrature components; a modulator coupled to receive in-phase components from the splitter and a baseband control signal generator operable to generate control signals representing the in-phase components of the complex composite signal; and a modulator coupled to receive quadrature components from the splitter and a baseband control signal generator operable to generate control signals representing the quadrature components of the complex composite signal. In accordance with the present invention the baseband control signals are analogue signals generated from a plurality of signal generators and are summed in respective summers. In a preferred embodiment the modulating means each comprise a biphase linear attenuator. An embodiment of the invention will now be described with reference to the accompanying drawing which is a block schematic diagram of an apparatus for generating complex composite RF signals. In the arrangement illustrated an oscillator 11 or other form of generator provides an unmodulated carrier signal which is fed, via splitter 12, to two modulators 13, 14. The equal carrier signal inputs to the modulators form the basis for subsequent I & Q quadrature components of a complex composite RF signal output. The outputs of modulators 13 and 14 are then summed in network 15 to provide the RF output. The modulation control signals applied to modulators 13, 14 are derived from, for example, pluralities of computerised signal generators 21₁, 21₂... 21 N and 22₁, 22₂... 22 N . These are arranged to generate control signals representing sets of amplitude, frequency and phase parameters for the respective I & Q components of the complex composite RF signal. Such parameters can be used for generating, for example, spread spectrum signals as are used in global positioning systems (GPS) to simulate signals received from a number of satellites. The sets of control signals from each plurality of signal generators are summed in respective summing networks 16, 17 and, after any necessary amplifications, applied to the respective modulators 13, 14. Preferably the modulators 13, 14 are biphase linear attenuators such as are manufactured by Olektron Corporation.

Claims: Apparatus for generating complex composite RF signals, the apparatus comprising: an unmodulated RF carrier signal source (11); a splitter (12) coupled to the RF carrier signal source (11) for splitting the output of said source into I & Q quadrature components; a modulator (13) coupled to receive in-phase components from the splitter and a baseband control signal generator operable to generate control signals representing the in-phase components of the complex composite signal; and a modulator (14) coupled to receive quadrature components from the splitter and a baseband control signal generator operable to generate control signals representing the quadrature components of the complex composite signal; characterised in that the baseband control signals are analogue signals, the apparatus containing a plurality of signal generators (21 1-N ; 22 1-N ) and respective summers (16, 17) for summing the outputs of said signal generators, to generate said control signals. An apparatus according to claim 1 further including amplification means provided between respective summers and modulators from the baseband control signal generators A method of generating complex composite RF signals comprising the steps of generating an unmodulated RF carrier signal splitting the unmodulated RF carrier signal into I & Q components, modulating each component separately with respective baseband control signals representing parameters of I & Q components of the complex composite RF signal and summing the modulated components to form the complex composite RF signal; characterised in that the baseband control signals are analogue signals generated from a plurality of signal generators (21 1-N ); 22 1-N ) and are summed in respective summers (16, 17).

Inventors: READ ARNOLD GEORGE, READ, ARNOLD GEORGE
Applicants: NORTHERN TELECOM LTD, NORTHERN TELECOM LIMITED
Application year: 1991
Main classification: H04L27
IPC codes: H04L27