The Corner Reflector Antenna
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To increase the
directivity
of an antenna, a fairly intuitive solution is to use a reflector. For example, if we start
with a wire antenna (lets say a
half-wave dipole antenna),
we could place a conductive sheet behind it to direct radiation in the forward direction.
To further increase the directivity, a corner reflector may be used, as shown
in Figure 1. The angle between the plates will be 90 degrees.
 Figure 1. Geometry of Corner Reflector.
 Figure 2. Equivalent sources in free space.
Assume that the original antenna has an omnidirectional pattern given by
 The above directly follows from Figure 2 and array theory (k is the wave number. The resulting pattern will have the same polarization as the original vertically polarized antenna. The directivity will be increased by 9-12 dB. The above equation gives the radiated fields in the region in front of the plates. Since we assumed the plates were infinite, the fields behind the plates are zero.
The directivity will be the highest when d is a half-wavelength. Assuming
the radiating element of Figure 1 is a
short dipole with
a pattern given by
 Figure 3. Polar and azimuth patterns of normalized radiation pattern.  . The height of the plates
should be taller than the radiating element; however since linear antennas do not radiate well along the
z-axis, this parameter is not critically important.
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. Then the radiation pattern (R) of the
"equivalent set of radiators" of Figure 2
can be written as:
, the fields
for this case are shown in Figure 3.