{HEAD ~ The grid electrode} is curved along {TAIL ~ a short side direction} thereof and includes portions having different thicknesses, the portions being arranged in the short side direction 
is curved along
{ HEAD ~ The grid electrode } is curved along { TAIL ~ a short side direction } thereof and includes portions having different thicknesses , the portions being arranged in the short side direction
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH