ARINC Solves Army Chinook Antenna Problem Using 3-D Graphics Modeling and Analysis

First, ARINC created a wire mesh model of the Chinook and "placed" the problem antenna on the model, near the front-side of the aircraft.

ARINC then used its proprietary software and 3-D graphics technology to generate the antenna's radiation "bubble" to accurately see the problem: a large antenna gain "dip" almost directly over the front of the helicopter.

The magnitude of the dip reached -50 dBi, almost precisely what the Chinook was experiencing in the field. The reason for the problem: At high frequencies, the antenna energizes large portions of the Chinook helicopter. The fuselage itself becomes an extension of the antenna, helping to radiate energy in undesired directions. ARINC then generated the induced skin current distribution.

The current is concentrated on the forward portion of the fuselage on the side around the antenna (red and green segments represent highest skin current), degrading performance in the near-vertical incident skywave (NVIS) region. ARINC then evaluated different antenna locations and configurations, and determined the optimum design (as shown below in yellow centered on top of the fuselage).

Now, the skin current is concentrated on the top-front of the helicopter, where it can radiate toward the NVIS area—just what's needed.

The new bubble shows that the relocated antenna totally eliminates the low-gain problem and improves overall NVIS performance by a factor of 100. The highest antenna gain in the NVIS region is increased from -30 dBi (magenta segments) to -10 dBi (green segments).