ENVELOP Antenna: A Class of Very Low Profile UWB Directive Antennas for Radar and Communication Diversity Applications

In this paper we present the concept of new electrically narrow very low profile (ENVELOP) directive antennas for low frequency radars and diversity communication applications. The basic structure consists of a short TEM horn combined with an inductive loop antenna. The proposed antenna height is 0.063λ_0whereλ_0is the minimum operating wavelength and has good matching and radiation characteristics over more than an octave. It is based on the principle of crossed electric and magnetic dipoles with a TEM horn as the electric dipole and a sheet loop as the magnetic dipole. However, unlike the standard structures, the proposed structure is designed to enhance the radiation in a direction perpendicular to the TEM horn axis. This limits the maximum pattern bandwidth to about one octave but allows the antenna height along the direction of maximum radiation to be very small which is very important for airborne radars and in low frequency military communications that require conformal antennas. Three different variations of the basic structure are also presented which offer improved pattern characteristics and/or pattern and polarization diversity. Two antennas were fabricated and measured. The measured results agreed well with the simulation results and both showed that the antenna can operate over 1–2 GHz with consistent radiation pattern, low dispersion and input impedance matching performance.