RFID and NFC are two of the most widely-used technologies today, but their
potential is constantly deprived by mistakes and skipped development steps, resulting
in poor working devices.
When designing systems that include radio transceiver with antenna, we have to
pay attention to proper network matching. We strive to achieve target impedance,
which is the same as source impedance, and has only the real part. In this case, most
of the energy of the excitation signal will result in electromagnetic radiation.
Additionally, we want to prevent signal reflection and losses along transmission lines.
Impedance matching is a challenging iterative process that requires an
understanding of RF systems. We can use equations to calculate values for matching
components, however, calculation does not consider PCB design, operating
environment, parasitic values of PCB and electric components, etc. Therefore, we
cannot rely only on calculations, as they are applicable to a limited extent.
The content of this thesis is the development of a concept and design tool that
can automate some steps in the matching network design process of connected RFID
antenna. It consists of three parts: PCB with adjustable impedance matching circuitry
and logics (AMSB), Vector network analyzer (VNA), and a PC application that
controls, acquires and display the results (AMS).
The AMS app controls the VNA and AMSB and automates some steps of the
process. The user enters input data required to calculate matching components values,
which are fed into the AMSB to display the results acquired by VNA. The AMS app
has interactive settings of adjustable capacitors that allows user to adjust matching to
reach desired target impedance.
The developed tool accelerates and automates steps in the development of RFID
or NFC systems. The tool’s output helps us to quickly achieve matching on another
circuit. However, the values represented by the tool do require corrections when
implemented on another PCB, since the layout is usually not identical. When the
correction is known, the tool makes sense and is effective.
The tool has some limitations when the results are applied to the PCB with large
differences in layout of the signal paths. Additionally, variable capacitors in shunt
configuration have high capacitance offset, which prevents us from performing
matching on antennas with higher inductance.
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