GPR antenna bandwidth


Courtesy of Geoscanners AB

I was really surprised and somehow confused the first time I heard about a half wave dipole with bandwidths in excess of 100%. Two things didn’t quite fit my previous knowledge about antennas; first, for any bandwidth exceeding 60% I was used to talk in terms of ratios. Secondly, I had never heard of any half wave dipole antenna with bandwidth greater than 10% and that only for a well manufactured and tuned device. It was of course all a big misunderstanding; we were using the same words but meaning different things. This tutorial tries to explain what do GPR (ground penetrating radar) people mean when they talk about bandwidths in excess of 100%.

Bandwidth definition of terms

There are different definitions for antenna bandwidth and it all depends on whom are you talking to or about which device the definition is valid. For instance, I was used to think of bandwidth as a measure of how much frequency variation is available while still obtaining an acceptable VSWR (2:1 or less) and minimizing losses in unwanted directions.

So, what is it after all, the bandwidth? Balanis [1] gives a better definition for bandwidth: “The bandwidth of an antenna is defined as: the range of frequencies within which the performance of the antenna, with respect to some characteristics, conforms to a specified standard”. In other words, there is no unique characterization of the bandwidth and the specifications are set to meet the needs of each particular application.

All in all, that means different field of antenna applications can define their very own bandwidth specifications as long as is understood among all professionals within that specific field.

What is then called antenna bandwidth in ground penetrating radar? I haven’t found anywhere a clear, in terms of exact figures, definition of antenna bandwidth for GPR antennas. It seems to be, and often quoted as: “industry standard”, “commonly accepted”, etc, that antenna bandwidth in ground penetrating radar is defined as follows.

Antenna Bandwidth (GPR): Is the ratio of the difference of the upper and lower frequencies of acceptable operation to the center frequency of that band multiplied by 100.

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