The spectrum of the intensity of dispersed waves obeying cyclostationary statistics is studied. The formalism is based on an exact formula by Marshall and Yariv [IEEE Photon. Technol. Lett. 12, 302 (2000)] relating the intensity spectrum after first-order dispersion to the Fourier transform of a certain restriction of the time-averaged fourth-order correlation of the optical wave $e\left(t\right)$ before dispersion. The formalism permits a simple computation of the spectrum of composite models defined by the independent addition or multiplication of a stationary and a cyclostationary field. The computations are simplified by introducing the auxiliary field $z_{\tau }\left(t\right)=e{\left(t\right)}_{}^{*}e(t+\tau )$ , whose power spectral density represents the basic building block for solving the spectrum of composite models. The results are illustrated by a number of examples, including the intensity spectrum after dispersion of analog-modulated, partially coherent carriers, or the complete spectrum of intensity fluctuations of multiwavelength dispersion-based microwave photonic filters.