Ground radiation antenna utilizing characteristic mode theory

This article presents two ground radiation antennas with simple feeding structures for mobile applications. Characteristic mode theory is exploited to design the proposed antennas. For antenna 1, a small loop without any lumped elements is used as the feeding structure. And the total length of the feeding loop is only 20.2 mm (0.06 λ0.9GHz). The operating band of the proposed antenna 1 is 834‐1020 MHz. Across the whole operating band, the measured efficiencies of antenna 1 are higher than 72%. In addition, a new method to generate an extra resonant frequency is proposed, which has little effect on the existed resonant modes at the lower band. The dual‐mode antenna 2 without loading any lumped elements is obtained by implementing this method, which covers 812‐940 MHz and 1543‐1576 MHz bands. Furthermore, the new resonant frequency can be controlled independently. Namely, the higher frequency band of antenna 2 can be adjusted freely without changing the lower band. To validate the design strategy, two ground radiation antennas are fabricated and measured. The measured results indicate that the proposed antennas are suitable for mobile terminals.