please it is a midterm exam question

any one plesae has an idea about the following question related to microwave oven


1-does a microwave excite a signal mode or multiple mode, and why is this prefered?


2-explain mode stirring and how it is implemented in microwave ovens?

note that the microwave oven excited at 25 GHZ

It can be shown that the number of modes dN in a frequency range df for a cavity
resonator is
dN/df = (8*pi *V *fo^2) / c^3
V= volume, f0=2.45GHz for ovens (etc, the ISM band)
Example: 4x3x2dm3,V=24 liters, df is assumed to be 100MHz (the allowed ISM band 2.4-2.5GHz, in some countries 60MHz, the actual bandwidth of a magnetron is just a few MHz but with a larger drift range)
=> dN=13 modes can exist in df,

therefore you can calculate existing modes can be
n=3 m=3 l=2 fres=2.40
n=2 m=1 l=3 fres=2.42
n=0 m=2 l=3 2.46
n=4 m=4 l=0 2.50
n=0 m=4 l=2 2.50

Compare three of the simplest modes in terms of the field distribution from the table above: TE023 , TM440 and TE042 (which all have resonant frequencies close to 2.5GHz and) which all have fields that are easily found by comparison with TE101. The orientations of the coordinate systems are chosen in the figures so that we are in all cases looking in the direction of the electric field, and the dashed lines show the positions of the nodes where the field is always =0.