Antiambiguity Direction Finding by Harmonics' Amplitudes With Two-Element Time-Modulated Array

A novel antiambiguity method is proposed to eliminate the mirror-image ambiguity generated in direction finding (DF) with the two-element time-modulated array based simply on harmonic amplitude. When the time delay of the two modulation sequences and the array element spacing satisfy a specific relationship, the amplitude difference between the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ +\text{1}\text{st}$</tex-math></inline-formula> and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ -\text{1}\text{st}$</tex-math></inline-formula> harmonics shows monotonicity with the variation of the incident angle. Consequently, the incident angle can be estimated without the interference of mirror-image ambiguity, solely based on the amplitude–frequency measurement result. This method can be easily implemented by frequency sweeping devices. Therefore, the proposed method is beneficial to develop DF systems with low complexity and cost. Numeric simulations and experiment have been conducted to verify its effectiveness.