Gary,
There are several ways to achieve electronic oscillations: some that require an LC circuit and some that don't.
Typically, these oscillations are divided into 4 general "shape" categories, as indicated.
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A
n LC circuit is required to produce an analog Sine Wave (digitally produced sine waves do not). As the frequency desired is increased, the actual physical size of the "L" (inductor) and the "C" (capacitor) decreases (as a rule). At GHz ranges of oscillations, the L component is quite small and may even appear as no bigger that a single conductor trace (on PCBs), as JimB noted above. And the C component is, of course, equally small.
I
n this case of cell phone usage, less transmission power is required for successful communication because transmission distances are quite short (nearest "tower", i.e., generally "line-of-sight comms). This also allows for significant reductions in component sizing, particularly with capacitors.
As for the other wave shapes, you can google them for the various methods for producing those shapes, if you choose. They are not, as a rule, used as a carrier wave in radio transmission(s).
<<EDIT>>
Just saw your last post ; '
Ah, but it is! A magnetron's cavity creates both the L and C needed for oscillation. The cavity's dimensions determine the resonant frequency of the magnetron.