Multifunction Radio Frequency System Design Using Nonlinear Models

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McRae, John
Electrical Engineering , RF , System Design , X-Parameters , Polynomial Modeling , Frequency Planning , Multifunction Systems , Software Defined Radar
Multifunction radio frequency (RF) systems provide a general-purpose hardware platform for designers to implement arbitrary waveform transmission and reception. In this thesis, a multifunction RF transceiver is designed, simulated and tested. The transceiver was designed for radar applications operating at X-band (8 to 12 GHz) and is wideband, thereby providing the designer with a wide wireless window through which they can simultaneously transmit and receive multiple signals. The system is constructed entirely using commercial off-the-shelf components; the design therefore consists of frequency planning, specifying a system architecture and selecting appropriate components. The final transceiver design was constructed using a homodyne architecture, which contains a mixer in the transmitter and the receiver in order to perform frequency translation between baseband and X-band. Using a mixer in the system design requires that a frequency plan be developed in order to ensure that image and sideband overlaps do not occur at the mixer outputs. Frequency planning rules were therefore developed for wideband applications and were used to specify an instantaneous bandwidth of 1.1 GHz, the largest for a multifunction system. A new criterion, called the radar metric, was then developed to quantify the design specifications of the RF system. The frequency plan and radar metric were used to specify the final system design, which could then be simulated. In order to acquire accurate simulation results, each component was individually measured and characterized. The amplifiers in the system were characterized using nonlinear models so that their harmonic behaviour could be accounted for. Wideband systems are particularly susceptible to harmonic interference since it is possible for harmonics to enter the large frequency window provided by the system, hence the need for accurate nonlinear modeling. Finally, a prototype was constructed which showed that the system was able to generate a maximum transmit power of 13.56 dBm, with a receiver noise figure of 2.33 dB. Moreover, simultaneous signals were transmitted and received through the system, thereby verifying the multifunctional capabilities of the transceiver.
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