Conceptual design of a dual-band circularly polarized square loop antenna under even-mode resonance

A dual-frequency, circularly polarized (CP) square loop antenna under even-mode resonance is presented. The square loop antenna is diagonally fed by a fork-like dipole launcher. Four tuning stubs are symmetrically introduced near the current distribution nulls of the second odd-order resonant even-mode. In this way, the second odd-order even-mode is excited and dual-band circularly polarized characteristic can be realized. The dual-band behavior of the antenna is numerically studied and a closed-form formula is deduced. The preliminary result in this work is expected to be useful in future dual-band CP loop antenna designs.