Planar elliptical dipole
Image of the Planar elliptical dipole.

The elliptical dipole antenna may find application for use in the FCC (or ETSI) defined ultra-wideband (UWB) radio band of 3.1 - 10.6 GHz. While it may not be the optimal structure to serve as a Gaussian impulse shaping filter required for UWB radio, it is a relatively simple, widely used antenna which finds application in a number of devices.

The elliptical dipole consists of 2 elliptical discs excited at their closest point. Achieving a practically realizable implementation of this excitation without impacting on the radiation pattern requires some care. Since the antenna pattern displays nulls in the axial direction, a microstrip-to-balanced stripline (also known as parallel strips line) feed is used, as shown below.

Practical implementation with microstrip-to-balanced stripline feed

The antenna achieves a good match (S11 < -10 dB) over a > 6:1 bandwidth for a 100 Ohm input impedance. In this band, the radiation pattern changes from an omnidirectional pattern at low frequencies, to a more erratic multipath shape at higher frequencies.

While various ratios of ellipse width-to-length are possible, a 1:1 ratio is also common.

Typical reflection coefficient of an elliptical dipole
Radiation pattern of the elliptical dipole at various frequencies in the operating band