Radiation characteristics of an electrically small MF broadcast antenna-by simulation

MF broadcast stations typically employ tall towers, heights 0.2 to 0.625 wavelength (/spl lambda/), mounted over extensive radial wire ground systems (120 radials, 0.25 to 0.4 /spl lambda/ long, buried 20 cm below the surface of the ground). In spite of the fact that MF radio broadcast services are to some extent (at least in Canada) moving to the VHF band, there is a continuing world wide interest in MF (even LF) antennas, particularly electrically short antennas, perhaps a growing interest as frequencies are vacated by some broadcasters. This paper reports on a detailed computational electromagnetic analysis of an electrically small MF umbrella antenna system, with electrically short insulated elevated radials. While an acceptable antenna radiation efficiency can be obtained, for electrically small antennas, the greater the efficiency the narrower the bandwidth of the antenna. For antenna heights less than about 0.1 /spl lambda/ the antenna bandwidth can be small, too small to meet the requirements for a MF broadcast station. The antenna system described has an acceptable operational bandwidth, as well a number of unique features.