On Friday, February 14, 2014 1:09:58 PM UTC-6, Kafkaësque wrote:
It seems that nobody has pointed out the third advantage of capacity
hats; that they reduce the Q of the antenna, and therefore broaden the
bandwidth.

If we define bandwidth in terms of 3:1 SWR(50), a capacitive hat tends to decrease the bandwidth since it reduces the feedpoint impedance. For instance, the 3:1 SWR(50) bandwidth of a 1/4WL vertical is about 1.2 MHz while the 3:1 SWR(50) bandwidth of a 1/8WL vertical with horizontal top hat is about 0.5 MHz according to EZNEC.
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73, Cecil, w5dxp.com