Rectangular shown at Figure 1 has good parameters and
not so sensitive to height (that is very important for low amateurs
HF-ranges) compare with dipole. Upper horizon wire is broken by
a nut insulator at it's center. Due to
a small height the antenna is suitable for 80- and 40-meters Band.
However, it should not be any high objects near the antenna (that
do "shadow" to the antenna). Distance between low wire
and roof or ground may be several tens centimeters.
Input impedance of the antenna may depend
on installation conditions. Matching of the antenna with the feeder
provides by choice of a feeding point at low horizon wire. At
corner feeding the antenna has input impedance near 30-40-Ohms.
The more far the feeding point from the corner is- the more input
impedance (up to several thousands Ohms) would be. Feeder is going
along antenna wires then from the middle of a vertical side the
feeder is going aside (to any direction). For good symmetrical
it is desirable to connect the braid of the coaxial with antenna.
Radiation parts at the antenna are the
vertical sides. For increasing of the efficiency of the Rectangular
the sides should be made from aluminum tubes in diameter 10- 20-mm.
Horizon sides of the antenna provide very low radiation (because
the currents distribution at the antenna), so, they could be made
from antenna wire in diameter of 1-2 mm. Figure 2
shows the currents distribution at the Rectangular (made by MMANA).
antenna has gain near 2- 3 dBi, pass-
band (at SWR 1.5:1.0) near 2% from the center frequency.