Measurements of dipole, bow-tie, log-periodic and log-spiral antennas on a dielectric-filled parabola

The power patterns and input impedances of four types of planar antennas on a dielectric-filled parabola are presented. The measurements were made on a microwave scale model of a proposed submillimeter-wave receiver front end. The dipoles have the lowest input impedance (generally preferred for matching to most nonlinear elements used in low noise receivers), while the log spiral has the broadest bandwidth and the most circularly symmetric patterns. If cross polarization is a consideration, the log-periodic antennas are likely to give less satisfactory performance. The bow-tie has the most compact impedance locus but its H-plane patterns vary widely with frequency. All of the antennas slightly underilluminate the dielectric-filled parabola. The input impedances of the antenna on the dielectric-filled parabola differ from those of the same antennas in free space and in general the real part decreases.<>