Task: Path loss modelling
Target frequency: 433 MHz;
Laboratory environment: in a basement where there were other equipment and metal shelves. A few acoustic absorbers were placed around the setup.
- TX antenna sealed in a small bottle (diameter 3 cm, length 10 cm)
- TX antenna moving inside 50 L of a tissue-simulating liquid (held in a basin);
- RX antenna fixed outside of the basin;
- Both are connected to a Network Analyzer (very old, but calibrated before each measurement) that recorded the S parameters of different TX-RX distances;
- Addition: The coaxial cables seemed to be very sensitive. A gentle twist could result in big changes in the S-parameters' curves in the frequency domain.
TX antenna integrated to an electronic system (MCU+RF module+battery)
The whole electronic system was sealed in the small bottle (diameter 3 cm, length 10 cm), placed inside the aforementioned basin, and moved along the same trail as in Scenario 1;
RX antenna fixed outside of the basin and connected to a Spectrum Analyzer that recorded the received signal level at the same TX-RX separation distances as in Scenario 1;
S21 is regarded as Tranmitter power level - Received signal level - cable loss;
Illustration of the setup
S21 increases (generally) as TX-RX distance increases
S11 against frequency and S22 against frequency were normal reflection curves, and the values were reasonable.
What could be the causes then? Is that because the network analyzer is too sensitive to the noises in the environment?
(The network analyzer was supposed to work well as other people were using it for measurement as well. )