Wideband Loop-type Antenna by Controlling Resonance Frequencies

In recent years, many small internal antennas have been designed for mobile handsets in [1, 2]. Many monopole-type antennas have been investigated because they operate at the lowest resonant mode which is helps to reduce their size. A loop-type antenna, on the other hand, has rarely been applied to small antenna design because the lowest resonant mode is a parallel resonance (anti-resonance). Certain types of monopole antennas can be designed to operate on a low frequency band [3], but the overall size of the monopole antenna sets a rough limit of the bandwidth,. In [4], multi-resonant elements were utilized to widen the bandwidth, but this technique makes antenna rather than large. To extend the operation bandwidth without changing the size of the antenna, this paper proposes a wideband loop-type antenna that is tuned from a conventional loop-type antenna by simply adding a spiral inductance and a gap capacitance. This method provides an ability to effectively control resonance frequencies. It differs from conventional antenna design methods in utilizing the concept of a resonant perturbation. This design mechanism is analyzed in this paper by observing voltage and current distribution as a function of resonant modes at a transmission line. The design goal in this paper is to present a dual band for a wide global system for mobile communications (GSM) and Bluetooth.