Direction Finding in Systems Constrained for Size, Weight and Power

Considerations and Our Approach
By Dr. Joseph Kunze

Direction finding (DF), or the ability to measure the direction from which a received signal was transmitted, has a variety of applications including navigation, search and rescue, tracking, and signal intelligence. For our military, direction finding on incoming RF energy plays a critical part in current electronic support (ES) systems. While improved angle-of-arrival (AOA) accuracy is always desired, increasing the pool of candidate signals which the system can direction find will improve ES capabilities to cover a wider variety of threats.  More flexible DF systems are desired that possess increased bandwidth, a wider field of view (FOV), two-dimensional scanning, and dual polarization apertures.

When it comes to applications that involve installation on military platforms constrained for size, weight, and power (SWAP) of the system pose a significant challenge.

In many cases, the required baseline at the upper end of the frequency band cannot be met due to the physical size of elements, which are sized according to the lower end of the frequency band. For this reason, many interferometers used today break the operating band into sub-bands with multiple apertures per sub-band. This creates a few challenges when installing the DF aperture on a military platform. Multiple apertures on multiple baselines require a large amount of real estate to operate effectively. In addition, the DF receiver behind the aperture now has risen in complexity to handle all the different apertures at the various bands.

Given the limitations of traditional interferometric approaches, this challenge requires technical solutions that provide improvements to the aperture to increase bandwidth coverage while maintaining a compact form factor. This overall goal will allow for expansion of the platforms that can support direction finding missions that may currently be too small for a typical interferometer suite.

Evolving electronic threats faced by our warfighters require direction-finding platforms that are able to detect over a broad frequency range and with polarization diversity. Key to achieving this performance is the development of antenna technology that provides ultra-wideband, dual-polarization performance over a wide field of view, in a form factor that is appropriate across military platforms constrained for SWAP.

There is a demonstrated demand among our military forces for a compact, low-profile, ultra-wideband direction-finding system. As an example, US Navy submarine direction-finding ability is currently limited due to lack of space for upgraded platforms that would require larger antennas. Military operations requiring covert or low-observable operation (such as SOCOM) could also benefit from enhanced direction-finding ability in a small package. Other examples include numerous unmanned vehicles, which are highly constrained for SWAP.

The solution is to develop an ultra-wideband, conformal, dual-polarized antenna aperture. An extremely low-profile antenna that provides an expanded field of view while maintaining angle-of-arrival accuracy across a wide instantaneous bandwidth to support evolving software-defined direction-finding systems.

SI2’s innovative ultra-wideband structurally integrated aperture technology is a key enabling technology for addressing this next generation of RF threats.

Our approach to solving this problem includes

  • Understanding the specific constraints and their impact on performance requirements
  • Employing our proven wideband antenna architecture and novel antenna miniaturization techniques
  • Simulating and optimizing aperture performance
  • Testing the Concept – refines and optimizes performance that can then be integrated into next generation direction-finding electronics to develop a full system solution.


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