Santa Struggles with Radio Frequency Interference – Could Hinder Gift Delivery

Santa Calling about Radio Frequency InterferenceWhen my caller ID lit up showing an incoming call from “The North Pole” I scratched my head wondering who it could be. Only one person I know of lives at The North Pole. Yup, it was Santa. In the past, Santa has worked with ANSYS engineers to improve the structural and aerodynamic properties of his sleigh. This year, Santa had another concern that he was calling me about. It seems that on some test flights in preparation for this year’s Christmas Eve deliveries, Santa noticed that the sleigh’s on-board GPS radio that he and his elves rely on for accurate tracking information wasn’t always working properly. Santa noticed that the problem usually occurred when he flew near cell phone base station towers. We assured Santa that we could help and we set about modeling the installed radio frequency (RF) systems on his sleigh in order to understand what was happening.

In addition to the GPS radio, Santa’s sleigh also has a radio that transmits live video from the sleigh to tracking stations on the ground so that Santa’s helpers can keep an eye on his sleigh while he is climbs down chimneys and delivers goodies. He also has a two-way radio that provides direct communication back to the North Pole. All of these radios have to work together flawlessly on Christmas Eve even when Santa flies close to other sources of radio frequency signals, and the entire RF suite must be considered when tracking down pesky interference problems. Fortunately, ANSYS has a powerful arsenal of tools available for modeling the performance of antennas and radio interference in complex environments.

My colleague, Prasanna Padmanabhan, and I were able to quickly create simulation models to predict the antenna and radio performance on Santa’s sleigh when he flies in proximity to a tower-mounted cellular base station antenna.

image001

Santa’s sleigh flying too close to tower-mounted cellular base station antennas caused problems with the on-board GPS receiver (CAD model of Santa’s sleigh courtesy of D. Pope Jr.)

ANSYS HFSS and Savant were used to examine the field intensities close to the tower-mounted antennas. Not surprisingly, the field strengths can be quite high close to the tower’s antennas when they are transmitting as seen by the red areas in the field plot below.

The radiation produced by the base station antennas on the tower can be quite intense (red areas) and can cause interference problems is Santa gets too close.

The radiation produced by the base station antennas on the tower can be quite intense (red areas) and can cause interference problems is Santa gets too close.

We also investigated how the sleigh mounted antennas are impacted by flying close to the tower, as this can have an adverse effect on the performance of Santa’s radios. The picture below shows that significant distortion to the GPS antenna’s radiation pattern can occur when Santa flies close to the tower as he often must to minimize the distance between stops. If Santa is to complete all of his deliveries in one night, then he has to take every short cut he can even if that means flying precariously close to active cell towers.

The GPS antenna radiation pattern sees significant distortion due to interactions with the tower and cellular base station antennas. On the left is the pattern without the tower present and on the right when Santa flies by the tower

The GPS antenna radiation pattern sees significant distortion due to interactions with the tower and cellular base station antennas. On the left is the pattern without the tower present and on the right when Santa flies by the tower

In order to assess the interference to Santa’s radios, we used ANSYS EMIT with its built-in radio models to simulate the performance of all the systems. This allowed us to assess all of the possible types of interference that could occur between all of the radios. What we found was that the cellular base station did indeed interfere with the GPS radio. The powerful diagnostic tools in EMIT immediately identified the mechanisms causing the interference and suggested that one potential solution is for Santa to use a higher performance GPS radio with better front-end selectivity to block out-of-band signals if he is going to be flying so close to towers. Of course, this means a more expensive GPS radio but Santa exclaimed,

“Do whatever it takes! No cost is too big to insure that good girls and boys aren’t disappointed on Christmas day!”

 

EMIT shows all of the information necessary to quickly identify the cause of radio frequency interference (RFI). The red square in the upper right indicates interference to the GPS radio on the sleigh, and the other diagnostic views show the exact cause.

EMIT shows all of the information necessary to quickly identify the cause of radio frequency interference (RFI). The red square in the upper right indicates interference to the GPS radio on the sleigh, and the other diagnostic views show the exact cause.

We used EMIT to determine the required GPS performance needed to prevent the interference and had a suitable radio installed in Santa’s sleigh. The new simulations indicated that the updated equipment would solve the problem and Santa’s elves verified that this was the case on test flights.

image009

All green squares in the matrix from EMIT indicates that no RFI is present. Santa is ready to go!

Needless to say, Santa was quite relieved to resolve this pesky interference problem in advance of the most important night of the year for him, and ANSYS is proud to have been able to help. Santa is already thinking ahead to next year when he plans to install a microwave satellite communications system on his sleigh, and ANSYS will be right there with the RF simulation software needed to insure optimum interference-free performance.

From all of us here at ANSYS, we wish you HAPPY HOLIDAYS!!!