This paper presents a coupled half-width leaky-wave antenna driven differentially. The guided-wave structure of coupled half-width microstrip lines are proposed and investigated, showing two leaky modes in the form of even- and odd-symmetry, respectively. Rigorous studies show that the odd-leaky-mode outperforms the even-mode approach in radiation patterns and bandwidth. Following the rigorous investigation of the modal characteristics of the coupled half-width EH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> mode guided structure, this paper reports a differentially fed, coupled, odd-leaky-mode, half-width, antenna of size 1λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> by 3.6λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> (including the feed), showing measured maximum antenna gain of 11.6 dBi, 15% fractional bandwidth, gain flatness of 2.4-dB variation, and input return loss greater than 10 dB. (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free space wavelength at the maximum gain frequency of 10.1 GHz). Both full-wave simulated results and measured data show good agreements for the proposed antenna structure. The measured leaky-wave antenna performance is compared to the recently published results, demonstrating a good compromise among all major performance metrics.