Python 3, 123 101 98 bytes

for i in range(1,52):r=[chr(j+65)for j in range(abs(26*(i//26)-i%26))];print(''.join(r+r[-2::-1]))

lol I am really bad at this

thanks @Leaky Nun for the r[-1::-1] == r[:-1][::-1] tip (:

Alternative solution, with help from @Leaky Nun (88 bytes)

for i in range(1,52):r=list(map(chr,range(65,91-abs(i-26))));print(''.join(r+r[-2::-1]))