I. Introduction
With the blooming and boosting of wireless communication (WC) technologies, many new techniques, methods and devices are going to be tiny and highly integrated [1]-[2]. Additionally, antenna is also moving to low frequency like 700MHz, which is also an important component for signal trans-receiving in a WC system. For MHz-band, antenna size is large, making it difficult for MIMO application in a small smart iPhone. Antenna miniaturization for MHz band designs is an interesting and meaningful work [3]-[5]. Especially, for rapid developing marine WC systems, low-frequency (LF) is very commonly used because of its strong penetrability for water, sea and underground environments. As we know, the conventional LF antenna based on 1/4 λ theory is large, making it impossible for mobile devices [6].