FPGA-controlled Outphasing Modulator Using A Power Combining Antenna
Publicerad
Författare
Typ
Examensarbete på kandidatnivå
Bachelor Thesis
Bachelor Thesis
Program
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Coupling between antenna elements is often an undesired characteristic in antenna
arrays, due to its distortion of radiation patterns and degradation of beamforming
accuracy. However, if this coupling could be exploited in outphasing through
load modulation, it has the potential to improve total system efficiency. This project
aimed to design a high-efficiency outphasing system for communication applications,
consisting of two power amplifiers (PAs) and a power combining antenna array.
To evaluate how different load impedances affect PA performance, a custom active
vector-receiver load-pull setup was constructed and calibrated using an FPGA
board. This setup enabled precise control over the presented load impedance to the
PAs and was critical for measuring power added efficiency and output power under
dynamic loading conditions. The resulting load-pull data informed the selection of
ideal 2-port S-parameters for the power combiner. Based on these, a two-element
patch antenna array was designed to serve as the combiner. Separate matching networks
were implemented to match the antenna ports to the desired S-parameters.
Two types of matching networks were considered: using lumped components and
using microstrip lines. Using lumped components, the desired S-parameters were
able to be matched quite well, yielding an error of around 9% whereas the microstrip
line network was unable to provide sufficient matching in its current configuration.
Using the PA load-pull data and the S-parameters of the designed antenna, the
performance of the outphasing system was tested through simulations in both MATLAB
and CST. The results confirmed that outphasing was achievable with this setup,
where amplitude modulation was realized by steering the antenna beam away from
the receiver. Additionally, the simulations indicated that implementing an appropriate
matching network could enhance the overall system efficiency.
Beskrivning
Ämne/nyckelord
antenna, load modulation, antenna array, outphasing, power amplifiers, load-pull, FPGA, matching network