A Spiral Antenna Backed by a Conducting Plane Reflector

An Archimedean planar spiral antenna is numerically analyzed in the presence of a conducting plane reflector. The analysis shows that the spiral antenna backed by the plane reflector has two distinct regions in the current distribution, which explain the radiation of a circularly polarized wave for the outer circumferenceCranging over about1.3 lambda 2.9 lambda, wherelambdais a free-space wavelength. Further consideration is given to a truncated spiral antenna whose outer circumference is on the order of1.4 lambda. The truncated spiral antenna maintains a decaying current distribution and radiates a circularly polarized wave over a 1:1.2 frequency bandwidth. It is also demonstrated that a power gain on the order of 8.5 dB is realized over the same frequency rang