The antenna feed point impedance is 12.5 ohms. Overall dimensions: 250 x 137 x 137 cm. Longest spreader (half-diagonal): 97 cm. If need be, it should not be difficult to hide this antenna in the attic.
When I tried to add more bands, I observed strong interaction between different band dipoles. I think it would be difficult to tune a 4-band or 5-band version in the real world. Also, bandwidth decreased. Moreover, the AGT was going up, and an extra effort would be required to improve the NEC-2 models.
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5-band mini dipole with triangle cap-hats
Finally, I managed to design a 5-band mini dipole with quite acceptable bandwidth and gain. I took the mini dipole version with Triangle No. 1 hats and created something that looked like a crab to me.