AWR Software for the Design of MIMO and Phased Array Antenna Systems
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In this final example, the power amplifiers (PAs) are nonlinear, designed to operate at their 1db compression point (P 1dB)
for maximum ef ficiency. They are, therefore, sensitive to the changing load impedances presented by the array. The
beam of a 16-element array is steered by controlling the relative phasing and attenuation to the various transmit
modules (Figure 13). In practice, the AWR Microwave Of fice harmonic balance simulation used to characterize the power
amplifiers takes substantial time to run with 16 PAs. Therefore, the beam is steered with the amplifiers turned of f. The
designer then turns on the individual PA for specific points of interest once the load impedance from the directed
antenna has been obtained.
Figure 13: Changing antenna feed impedance as a function of beam steering using the variable phase and attenuator settings
At this point the designer can directly explores the PA's nonlinear behavior as a function of the load (antenna) impedance.
With the load-pull capability in AWR Microwave Office software, PA designers can investigate output power, compression, and
any other number of nonlinear metrics defining the amplifier's behavior, as shown in Figure 14.
Figure 14: Simulated antenna feed impedance vs. frequency, superimposed over power load-pull contours for a broadband an MMIC PA (inset)
With a detailed characterization of the RF links for each individual element, the overall system simulation is able to
indicate trouble areas that would have previously gone undetected until expensive prototypes were made and tested in
the lab (Figure 15).
Figure 15: Phased array simulations with RF link effects, including the impact of impedance mismatch between PA and steered antenna array
