"To what extent does the atmospheric density on earth influence the energy loss of microwave transmission?". Michael Krebs, a young student from Wettingen (CH), asked himself this question and - in order to answer it - made an experiment.
In this experiment, the focus lies on the advantages and disadvantages of energy transmission from the station to the earth’s surface using microwaves by conducting a simplified experiment with a sender and receiver at three locations differentiated by their altitude.
Theory
The concept of microwave transmission has been around since World War II, when the need for data transmission and radar became more prominent. Many countries have invested time and money into researching the characteristics of microwave-based data links, which is one of the main applications nowadays.
By cutting the complexity of the system down to a minimum, the ultimate idea revolves around a microwave transmitter and a microwave receiver.
Sender
The heart of the experiment was a microwave oven (MWO 2088 from ohmexSwitzerland, 700W). The device was being taken apart and all its components were laid out on a table.
Figure 1: Components of the microwave laid out
The components were then ready to be assembled. The metal framing of the oven served as a shielding and the magnetron sits in the middle. The lamp got attached to the outside of the metal frame in oder to send a physical signal to identify if the apparatus is running or not.
To guide the emitted microwaves, a horn was created, using cardboard, aluminium foil and a thick aluminium tube.
Figure 2: Finished apparatus with horn attached
Receiver
The receiver consisted of two main components, both provided by Computer Controls.
The first component is a wideband antenna, wich captures the microwaves. This antenna detects frequencies between 680MHz and 10GHz. The second component is a spectrum analyser, which displays the converted waves from the antenna into power intensity in dBm.
Keysight - Basic Sprectrum Analyzer N9322C
Keysight - X-Series Signal Analyzers
Figure 3: Setup of the sender and receiver
Measurement
To measure the loss of power during transmission in different densities of the atmosphere, measurements in different altitudes had to be conducted. Schlatt, Andermatt and the Gotthard pass fulfilled all the criteria and were chosen to be the locations for measurements. Per location, 10 measurements were taken.
The sender and receiver were placed at a distance of four meters from each other. The measurements lasted 10 seconds at 700W of output power from the sender.
The intensity data displayed by the spectrum analyser, were then noted for the frequency emitted by the microwave, which is 2.45GHz.
Data Interpretation
The diagram below shows the average of the 30 measurements at the three locations, including the elevation and average atmospheric pressure data during the time of the experiment.
The chart allows to analyse the dependence of microwave transmission on atmospheric density, which is being looked at here as pressure.
At lower atmospheric densities, the amount of power (W) received by the instrument is higher than at higher densities.
Figure 4: Power output comparison chart with pressure data
Conclusion
The conclusion is based on the correlation between pressure and power received at different altitudes.
In that sense, the experiment was a success. First of all, it has been proven that the power intensity of microwaves with a frequency of 2.45GHz decreases radially the greater the distance between sender and receiver is. Furthermore, when defining the independent variable as atmospheric pressure, the density of atoms changes. Even though the effects of atmospheric scattering and diffraction in the upper layers of the atmos-phere is still unclear, the self-made apparatus was able to provide sustainable data for partially an-swering the research question.
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