A novel thoretical treatment of antireflection-structured surfaces possessing general one-dimensional continuous profiles is presented. Closed-form solutions for the field reflection coefficients of these antireflection-structured surfaces are obtained through the use of effective medium theory and tapered transmission-line theory. Two specific surface profiles (sinusoidal and triangular) are analyzed in detail. Both the sinusoidal and triangular profiles are found to exhibit low reflectances over a broad range of angles and wavelengths. Results obtained with effective medium theory and transmission-line theory are compared with results obtained through the application of rigorous coupled-wave analysis.