Contents I. Introduction
It has been reported that, by loading a slot in microstrip patches of various shapes [1]–[3], microstrip patch antennas can be operated at two different frequencies. One resonant frequency is due to the fundamental mode of the main patch; the other is due to the fact that the currents along the edges of the slot introduce an additional resonance [2]. Moreover, if the frequency ratio of the two frequencies is adjusted to be close, a wide-band operation is obtained. Such a design is also applicable for a planar inverted-F antenna (PIFA), which has an advantage of size reduction. A rectangular PIFA with a U-shaped slot has been proposed to perform the dual-frequency operation for the wireless local-area network (WLAN) applications [4], [5]. However, the impedance bandwidth of higher frequency band cannot satisfy the wideband requirement (4.9–5.9 GHz, 19%) and few experimental results are given. To enhance the impedance bandwidth, the U-shaped slot with unequal arms has been used to obtain a bandwidth of more than 20% [6], [7]. In this paper, we demonstrate that a triangular PIFA with a V-shaped slot also has dual-frequency characteristic, and a bandwidth of more than 30% in higher operating frequency can be obtained by selecting a proper shorting-wall width. Details of the obtained dual-frequency and wide-band performance are presented and discussed. Geometry of the proposed antenna. mm, mm, mm, mm, mm, mm, mm, mm. Simulated and measured return loss for the antenna shown in Fig. 1. mm, mm. Measured return loss for the proposed antenna with different shorted plane widths.
