# Small Aperture Antenna Arrays for Direction of Arrival Estimation

## TL;DR

This paper shows how to design small antenna arrays for better direction finding by using non-uniform spacing and accounting for mutual coupling.

## Contribution

The paper introduces a new design criterion for small aperture antenna arrays using spatial covariance and mutual coupling for improved DOA estimation.

## Key findings

- Small aperture arrays with non-uniform spacing and dissimilar elements improve DOA estimation.
- Mutual coupling should be included in DOA estimation rather than being mitigated.
- The spatial covariance matrix is critical for optimal DOA performance in small arrays.

## Abstract

In this paper, we establish criteria for the design of small aperture antenna arrays for Direction of Arrival (DOA) estimation. We define a small aperture antenna array as one consisting of a few elements with an average interelement spacing less than or equal to half a wavelength. We use the spatial covariance matrix of the antenna array to derive the design criterion. It is well known that the DOA estimation performance of an antenna array is strongly related to the amount of information in this matrix. Also, the Cramer-Rao Bound of the estimated DOA is closely related to this matrix. We establish and demonstrate that, for optimal DOA estimation performance, a small aperture antenna array should have non-uniformly spaced and dissimilar antenna elements. Since mutual coupling between antenna elements makes their in situ responses dissimilar, instead of mitigating mutual coupling, one should include mutual coupling in the DOA estimation process to enhance the DOA estimation performance of antenna arrays.