# Compact Planar Super-Wideband Monopole Antenna with Four Notched Bands
## 1 Introduction  
Recently, ultra-wideband (UWB) systems have attracted the attention of researchers, due to their high data transmission rate and low power consumption [1, 2]. According to the regulations defined by the Federal Communications Commission (FCC), a frequency range of 3.1-10.6 GHz was allocated for UWB systems [3]. Though UWB antennas cover a wide frequency range, still, they cannot be used for high-speed long-range applications. UWB antennas are mainly preferred for indoor communications, due to their limited transmission power [4, 5]. The limitations of the UWB antennas can be overcome by super-wideband (SWB) antennas, which work well even with single device communication systems. The SWB antennas are characterized by a bandwidth ratio of 10:1 or higher [6]. The SWB antenna supports both short-range and long-range communication systems, and therefore serves as a potential candidate for wireless personal area networks (WPANs). SWB could be used for screening, sensing, and to provide high-resolution images required by the modern sensors. It can also be useful for radar imaging and real-time monitoring systems. SWB provides the advantage of high-speed audio/video transmission with enhanced channel capacity [7, 8]. In the literature, several antenna structures have been reported for SWB applications [9, 10, 11, 12, 13, 14, 15, 16]. In [9], the authors proposed a microstrip line-fed modified rectangular-shaped SWB antenna with an elliptical ground surface, where two stubs were used to obtain a bandwidth ratio of 14.6:1. A crescent-shaped radiating patch SWB antenna was reported with a bandwidth ratio of 11.6:1 [10]. In [11], a triangular Sierpinski geometry with a truncated ground plane and semi-circular patches on either side of the radiator was proposed, where a bandwidth ratio of 15.5:1 and maximum gain of 5.5 dBi were achieved. A microstrip line-fed star-shaped fractal antenna design with the semi-elliptical ground surface was presented [12], where the bandwidth ratio of 11.3:1 was obtained. In Reference [13], a truncated circular-shaped monopole antenna, loaded with an elliptical slot in its center, was proposed to obtain a bandwidth ratio of 11:1. A coplanar waveguide (CPW)-fed square-shaped antenna loaded with two stubs on either side of the radiator was presented [14] with a bandwidth ratio of 14.5:1. An S-shaped SWB monopole antenna with defected ground structure (DGS) and bandwidth ratio of 13.3:1 was proposed [15]. In Reference [16], a microstrip line-fed asymmetrical rectangular patch antenna loaded with U-slots and triangular slits was reported with a bandwidth ratio of 13.5:1. The above-reported antennas suffer from the disadvantage of large size, which limits their applications into portable RF devices. The compact size antennas can be easily incorporated into miniaturized wireless systems and RF devices used for commercial and defense applications [17]. Furthermore, due to the super-wide frequency bandwidth of the SWB antennas, they may cause interference with the surrounding wireless equipment working in the licensed frequency bands such as wireless local area network (WLAN), worldwide interoperability for microwave access (Wi-MAX), amateur radio bands, and so forth [18; 19]. The notch bands introduced in the wideband spectra can alleviate this interference issue. Recently, a few SWB antennas with band-notched features have been reported [20; 21; 22; 23; 24; 25; 26]. In Reference [20], a microstrip line-fed octagonal ring-shaped SWB antenna with WLAN band-notched behavior was presented. A tapered microstrip line-fed SWB monopole antenna was designed in Reference [21], where a rectangular slit was introduced in the patch to reject the WLAN band. In Reference [22], a microstrip line-fed rectangular-shaped SWB antenna was proposed, where two U-shaped slots were etched in the radiator and the feed line to notch WLAN and X-band, respectively.