1) The document discusses deconstructing magnetrons from microwave ovens to use their resonant cavities and tap wires as antennas for experimentation. 2) Connecting the tap wire to an SMA connector was difficult due to material incompatibilities between the copper cavity and stainless steel panel mount. 3) Simulating the magnetron output in EM Pro software proved too complex, so plane wave simulations were used instead. Reducing the magnetron's 900-1000W output power was also explored through circuit designs.

1. Magnetron Deconstruction and Antenna Adaptation
After extensively researching magnetrons I was able to find a number of resources in
which detailed the governing equations but was unable to find anyone that had converted one
into an antenna. Our application of a magnetron was certainly atypical and thus we had to
adopt some unconventional methods. Several microwaves were purchased for <$20 a piece
from various people from Craigslist so that we would have some disposable "learning"
materials. One magnetron was used primarily for the temperature testing (see weekly journal:
week 1) and the others were taken apart to retrieve the magnetrons.
A magnetron works by supplying high voltage to a central cathode (typically Tungsten
Thorium) which causes it to emit electrons. Permanent magnets are placed on either side of the
cathode so that the electrons around a central axis. The outer shell, called the anode, has small
cavities which act as a resonant chamber for the electrons. As the newly emitted electrons pass
by the open chambers the trapped electrons vibrate at a frequency around 2.45 GHz (typ).
However, as the magnetron heats up, the size of the cavities expands and the resonant
frequency can drift. For heating applications this doesn't matter: any frequency in that range
with 900 W of power will certainly heat food rather quickly.
Hitachi 2M121A Microwave Oven Magnetron

2. (note: resonant cavity was vice clamped during deconstruction and deformed from its original circular
shape )

4. After taking apart a magnetron we realized that the central tap wire connects the oscillating
electric field from the resonant chamber to the distribution antenna. The antenna is simply a
quarter wave monopole made of a pinched copper tube that was presumably used to draw and
seal the vacuum within the resonant chamber. Therefore we determined that if we could slice a
magnetron exactly where the tap wire connects to the chamber we could convert it into an
antenna.
[NOTE DANGEROUS STEP: The white ceramic insulators that surround the antenna and power
leads are made of Beryllium Oxide. This ceramic is VERY TOXIC if broken into an inhalable
powder.]
After precisely slicing the magnetron cavity with a band saw, the tap wire was exposed. Now
we needed only to attach the SMA conductor the tap wire and the SMA panel mount to the
outer cavity. Unfortunately the panel mount was made of stainless steel and the cavity was
entirely copper. Thus, our first attempt to connect the two resulted in a very messy connection
that was fragile and inconsistent.

5. Later, Mr. Estevez helped us use the oxygen acetyl welder to firmly attach the SMA panel to the
outer copper cavity. Although this was vastly better than our first attempt, it still demonstrated
inconsistent results (see VNA Analyses). In the end this antenna was easily surpassed by the
professionally made antenna lent to us by Mr. Gerling (a $2500 precisely tuned and
manufactured antenna).

6. During this deconstruction/antenna creation process we thought it necessary to be able to
simulate the output of the magnetron in EM Pro. We had already developed simulations using a
plane wave assumption but a monopole output is significantly different that a plane wave. After
hours of measuring and molding we were able to make a reasonably accurate magnetron in
Solid Works. However we later realized that EM Pro was not suited to handle this level of
complexity nor would our computers have the processing capabilities necessary for this level of
accuracy. This avenue was quickly abandoned and all future EM Pro simulations were
performed using plane wave excitations.

7. We also were under the impression that 900~1000 W might be too much power for our setup.
Because we are delivering a significant amount of power outside the resonant frequency, (see
output spectrum courtesy of NASA Eagleworks) we started searching for methods to reduce the
output power.
We eventually found a circuit from an random website with all sorts of magnetron experiments,
[NOTE: These experiments are VERY DANGEROUS: http://danyk.cz/magn2_en.html]

8. At the time we were unable to verify the schematic due to our lack of electrical engineering
experience, however Scott Vollmer, an EE undergraduate, joined the project during the middle
of Fall 2015 and did verify the circuit and the components were purchased.
Figure 1: 50 Watt Magnetron Circuit

9. Figure 2. Normal magnetron circuit from manufacturer
A lot was learned about magnetrons through research and deconstruction, however we do not
believe they are an appropriate power source for an EM Drive. Due to their large and unstable
output bandwidth as well as the significant amount of heat generation they are not easy to
work into a theoretical 'low thrust' device. Ideally an EM Drive would use a very high power
source with a phase lock loop (PLL) in order to track the reflection coefficient of the cavity and
adapt the signal to match the resonance. Although we foresaw this near the beginning, we

10. were never able to become familiar enough with the components necessary to create a
frequency tracking power source. A high power RF source would also cost us the entire budget
of the project and we would need a host of other components to make the system work
(isolator, waveguide to coax, high power attenuator, see proposal for future experimentation).
If one were to adapt a magnetron for an EM Drive application, it would most likely only be
feasible if a circulator was used. This device uses ferrous materials to create a one-way round-
about for the EM radiation. Attaching a magnetron to a waveguide with a circulator could be
done with the S12 port toward the resonant cavity and the S23 port toward a broadband
matched load. This would result in all reflections from the cavity being absorbed in some sort of
load and no reflections traveling back to damage the magnetron.