Antennas for Ground Penetrating Radar
Antennas for Radar Projects
I’ve seen 700-26000 MHz UWB antennas used in the effort to develop dedicated ground radar for agricultural use, though their effectiveness left much to be desired. Vivaldi antennas have been tried for this application with some success, while quad patch antennas are sometimes used for radar projects, working but not as well as they could. But what type of antennas is best for ground penetrating radar applications?
The Right Antenna for Your Ground Penetrating Radar Project
Ground Penetrating Radar or GPR is always a difficult environment. Simulations suggest that circular patch, bowtie and Vivaldi antennas work for ground penetrating radar. All of these antennas can be found for the 500 MHz to 1.5 GHz range that can be used for GPR.
You will never get enough bandwidth out of a patch antenna for ground penetrating radar. A Vivaldi antenna will work for ground penetrating radar, but for the 500 MHz frequency, it's big enough to be unwieldy. It would be difficult to put in a shielded housing at that size. You have to put it in a shielded housing or you will get lots of signal interference from TV stations. Most of the GPR's in the 500 MHz frequency range use a fat Bow Tie with some extra capacitance between the elements to improve the impedance match. Now your choices are between large UWB antennas and something else … a log periodic antenna.
Log periodic antennas have the advantage of working over a very wide frequency range. A 400-1000 MHz Log Periodic antenna works up to 1150 MHz, and the LP antenna is more compact than a Vivaldi antenna that works over the same range. The phase error for these log periodics is quite small. And log periodic antennas are directional like police radar antennas while operating over a wider frequency range, letting you shift to a frequency that works better for tracking the target or penetrating the material you’re analyzing.
What Simulations Say Versus Reality
Ansys HFSS or High Frequency Electromagnetic Field Simulation is often used to model antennas, and many simulations suggest you can use bowtie antennas for ground penetrating radar. According to Kent Britain of Kent Electronics, there are three whole families of antennas HFSS cannot model, though they can simulate bowtie antennas.
These simulations tend to be overly optimistic for bowtie antennas for use in GPR, suggesting that a bowtie antenna in shielded housing and using a load resistor for impedance matching allowed for a bandwidth from 500 MHz to 2 GHz. However, it is difficult to get good isolation between the transmitting (TX) and receiving (RX) antennas. Most of your receiving energy is in that resistor, so performance will actually be very poor if you try to use a bowtie antenna for GPR.
What Antenna Should You Use for Ground Penetrating Radar?
The best solution is to go with a durable log periodic antenna instead for ground penetrating radar projects. Bowtie antennas don’t have enough isolation between the sending and receiving antennas. Patch antennas lack the bandwidth. Ultra-wideband antennas have too much bandwidth. Log periodic antennas offer the best balance between the two designs, and their directional nature makes them quite efficient. Printed circuit board log periodic antennas are ideal, because of their durability in the field and low cost.