A method of moments formulation for the current on arbitrarily shaped planar conductors in layered media is utilized to study the characteristics of printed spiral antennas. This algorithm permits the use of distributed and lumped impedance loads on the conductor. Also, it takes advantage of the discrete rotational symmetry exhibited by certain structures, thus reducing the matrix storage requirements. Numerical results are presented for two-arm and four-arm spiral antennas. Resistive loading along the outer portions of the spiral is used to eliminate reflected current contributions. For conductor-backed printed spirals, the presence of the ground plane reduces the amount of mode 1 radiation, allowing for the radiation of higher order spiral modes. Increasing the number of the spiral arms is shown to alleviate this problem by increasing the order of the first contributing higher order mode.