Any ideas of the 1: 1.5 to 1: 1 to 1: 1.5 bandwidth ?
Clearly there must be a problem with the antenna if it causes you to specify the
SWR backwards. SWR is always a ratio of a number greater than or equal to one
number to one. So 1.5 : 1 is a valid SWR, but 1 : 1.5 is not. Getting it backwards
is often a sign that someone learned their antenna from dodgy webpages and is
likely to be misinformed in other areas as well.
Besides, there is no reason that the antenna necessarily reaches a 1.00 : 1 SWR
at resonance, so we'd just talk about the 1.5 : 1 SWR bandwidth.
What is the gain (if any) in dbd, NOT dbi.
The antenna is slightly shorter than a dipole. Presuming the feedline is effectively
decoupled from the antenna, the gain will be slightly lower than that of a dipole
with the top at the same height.
The actual gain in dBi will depend on the vertical angle it is measured at, the height
above ground, ground conductivity, etc. But basically it will work the same as a
vertical dipole, or as a quarter wave ground plane with sloping radials. The current
distribution on all such antennas is pretty much the same, so the differences in
gain and patter will be minor.