Everyone knows “classical” quad antenna. Its perimeter
is equal to wavelength. Each side of the quad is 1/4 wavelength.
Amplification of the “classical” quad antenna is 3-dBi,
input impedance (in a free space) is close to 120-Ohm (Figure 1).
Good antenna but the size!
It is possible to reduce its size by folding it in
a “cage” shape. The simplest cage in which the antenna may be
transformed is a cage of 10 sections 0.11 wavelength each. The
Compact Cage Antenna (CCA) gain is 1.5-dBi and input impedance
is close to 50-Ohm. Figure 2 shows the CCA grabbed
from MMANA. There are shown antenna currents and the source. MMANA
file for the antenna (named Trihat- quad) may be found at MMANA
“Antenna Library“ (References 1)
or loaded by the link below.
3 shows free space radiation patterns for Compact Cage
4 shows Compact Cage Antenna
radiation patterns at 1/3 wavelength height above the ground,
shows Compact Cage Antenna radiation
patterns at 1.0 wavelength height above the ground.
Compact Cage Antenna may be fed at the low corner with
the twin line (see Figure 6). The antenna may be fed with coaxial
cable through a balun as well.