My NVIS antenna is a 40 meter folded dipole 8 feet above the ground. It uses 450 ohm ladder line, and is fed with RG8x. Below it, and every 4' out from the antenna is slightly buried electric fence wire 70 ft each for a total of 9 reflectors. each added reflector reduced the reluctance, and the resistance a little bit. The lowest SWR is 1.6 to 1 on 7,245, and 2;1 on 7.3,and 7.165 where the reluctance equals 0. My usual operating frequency is 7.279.
BTW; the antenna is very low noise, and is a great receiving antenna to the north and south on 20, and nearly all directions on 15.
I get S9+30 reports on 40 meters when the F0F2 Austin AFB report is at least 6.5 Mhz.