Design method for multiband antenna device

The invention provides a design method for a multiband antenna device which can design a multiband antenna device having expected characteristics in a short time. The method comprises the following steps: in a first step, for earth conductors, determining configuration of using radiating elements for a low-frequency band and using radiating elements for a high-frequency band, and electrical length of each part including a radiating element branch circuit; in a second step, respectively specifying first electrical length between a branch point and the radiating element used for the low-frequency band, second electrical length between a branch point and the radiating element used for the high-frequency band, and third electrical length between a branch point and a power supply point, so as to determine resonant frequency of the low-frequency band, resonant frequency of the high-frequency band, and anti-resonant frequency; and in a third step, specifying an impedance transmission component used for improving VSWR between a power supply circuit and the power supply point.