# A Compact Printed Monopole Antenna for WiMAX/WLAN and UWB Applications
## 1 Introduction  
With the rapid development of radio technology, some systems require more than a single working frequency; thus, integrating several communication standards into a single system has become a recent trend. To meet the operating frequency band requirements of IEEE 802.11 WLAN in the operating band of 2.4 GHz (2400-2484 MHz), 5.2 GHz (5150-5350 MHz), and 5.8 GHz (5725-5825 MHz), as well as the Worldwide Interoperability for Microwave Access (WiMAX) band of 2.5/3.5 GHz, the development of a multi-band antenna of 5.5 GHz (2500-2690/3400-3690/5250-5850 MHz) [1] with low cost, small size, easy manufacture, and good performance has attracted increasing attention. Recently, different architectures of multi-band antennas have been designed, including the use of microstrip feed technology to implement multi-band antennas such as an H-shaped slot antenna [2], a Y-shaped dual broadband microstrip antenna [3], a diamond-shaped slot with two U-shaped antennas [4], and an E-shaped radiation patch antenna [5], to achieve dual-band WLAN characteristics. Coplanar waveguide feed concepts have also been applied to microstrip antennas, such as the use of narrow rectangular slots with meandering asymmetric slot antennas for dual-band antennas [6], compact wide-slot antennas [7], compact asymmetric-coplanar-strip-fed tri-band meander-line antennas [8], and rectangular slot antennas [9]. Asymmetric coplanar branches have also been used for WLAN applications [10]. In addition, the use of planar inverted F antennas combined with parasitic elementshas been proposed for WLAN operation [11], an inverted L-slot triple-band antenna [12] and a CPW-fed tri-band printed antenna has been developed [13]. The antennas discussed above are suitable for WLAN communication and ground acquisition units such as the WTU-508 [14], but they are not applicable to our own developed cable-less seismograph nodes. Their practical application for cable-less seismograph nodes would contradict with their miniaturization and high-bandwidth broadband applications. Therefore, we designed an antenna that can satisfy the needs of miniaturized (<500 mm\({}^{2}\)) and high-frequency bands (relative bandwidth >60%). The working scene of our self-developed seismograph is shown in Figure 1. A frequency of 2.4 GHz is used for communication between the seismograph and the AP (Access Port) relay, a frequency of 5.8 GHz is used for communication between the central control unit and the AP (Access Port) relay, and a frequency of 4.95 GHz is used for the remote seismograph information exchange with the portable hard drive. The ideas presented in this paper were inspired by previous structures described in the literature. The idea of a triangular structure was motivated by a previous design [15]. The meandering technique has also been previously discussed [16] and has enlightened the idea of constructing an M-type radiation patch and optimizing the structural size parameters using HFSS software. The inverted F structure was also inspired by previous work [17]. Finally, the antenna design of the present study is an extension of previous works. This paper presents a printed monopole antenna design for WiMAX/WLAN applications for cable-free self-positioning seismograph nodes. Great improvements have been achieved in miniaturizing the antenna and in widening the bandwidth of the high-frequency band. The innovation of this design is the effective enhancement of the working bandwidth of the antenna, which was achieved by using a five-pronged feed band and a tapered impedance transformer. The feeder strip connected the triangle and two branches to form an upper-surface radiating patch. This structure was able to effectively shunt the current to generate three resonant frequencies. The M and F elements mainly served as the meandering technology to increase the current path of the antenna surface, to reduce the resonant frequency of the antenna, and to improve the bandwidth of the antenna.