ProLogic Inc., Fairmont, WV, solved a tough antenna design challenge by simulating the design with MicroStripes electromagnetic simulation software from Flomerics. The initial antenna design had back sidelobes that put significant energy into the face of a radar array that was co-located. Electromagnetic simulation enabled ProLogic engineers to evaluate the performance of more than 20 possible alternative designs in a fraction of the time and at a much lower cost than would have been required to build and test prototypes. “The simulation process delivered a design that eliminated the problem,” said Larry Fry, principal RF systems engineer for ProLogic Inc. “When this design was built and tested it performed as the simulation predicted.”

ProLogic Inc. provides information technology (IT) solutions to government agencies and has more than 200 employees. Recently, ProLogic was tasked with co-locating a fast hopping digital communications system with a radar in the same radome. The radar operates from approximately 1250 to 1350 MHz. The communications system operates from 960 to 1215 MHz. The original antenna design had sidelobes that were at -16 dBi at 960 MHz and -6 dBi at 1215 MHz, which would put significant energy into the face of the radar. The antenna was located directly above the radar antenna array midline (39 dB directive phased array) by approximately 60 inches with a 42 inch high IFF antenna located between the two.

MicroStripes was used to model the original antenna to establish a baseline. MicroStripes differs from other electromagnetic simulation software in that it uses the Transmission Line Matrix (TLM) method for solving Maxwell's equations that solves for all frequencies of interest in a single calculation and therefore captures the full broadband response of the system in one simulation cycle. A further advantage is that the TLM method creates a matrix of equivalent transmission lines and solves for voltage and current on these lines directly. This uses less memory and CPU time than solving for E and H fields on a conventional computational grid.

“Several different antenna designs were considered to try and get the sidelobes down to minimum,” Fry said. “MicroStripes enabled us to model each solution and eliminate those that did not do the job. Without MicroStripes it would have been impossible to achieve the goals we established for the antenna system in the time and cost allocated. We did not have to go to the range until we had an antenna that we felt would work satisfactorily. The modeling indicated that we would see fields on the order of 105 to 115 mV/m at a distance of one to two meters below the antenna. Later, we put d-dot probes on the face of the radar and measured the fields from the communication system on the probes. The fields and the measured data agreed to within 5 percent of the predicted value.”

“ProLogic has been using MicroStripes for over three years,” Fry added. “This tool has saved us time and money with simulations that would have taken many months of time and many dollars spent on range time. When we have had problems learning how to set up specific calculations and models for MicroStripes to perform, the folks at the support facility made sure that we always felt we were their priority. The thing that really impresses me about this program is its accuracy. The results we have seen on this project and many others are amazing for electromagnetic simulation.”