This is a multi-loop antenna with vertical polarization. It is quite short - only 4.25 m, but it covers 14 - 29.7 MHz range. I have built and measured a test version of this antenna. The antenna requires a mast. I used a fishing pole but for a permanent location, I would rather suggest using aluminum tubes.
As you can see in the photograph above, you need some space on both sides of the mast to stretch its wire loops. Because the Manta Ray is flat, its azimuthal radiation pattern is slightly oval.
The Manta Ray I have built did not correspond to the model exactly. My antenna had only 2 radials 3 m long and 2 radials 5 m long. 4 radials altogether were enough to ensure a good impedance match, but you better use 16 or more radials to keep ground losses low. The test antenna was fed via 35 meters of RG-58 coax, what decreased its SWR below 2:1 for any frequency within 14 - 29.7 MHz range when measured near the transmitter. See the antenna analyzer screenshot below.
Click here to download this antenna models. Please note that the MMANA-GAL model does not have radials over the ground but a direct connection to the Mininec ground.