# A Rectangular Notch-Band UWB Antenna with Controllable Notched Bandwidth and Centre Frequency
## 1 Introduction  
During the last two decades, ultra-wideband (UWB) technology has attracted the attention of both academics and industries. UWB is a technology that uses a very low energy level for short-range, high-information spread over a large bandwidth, usually more than 500 MHz. Due to the short duration of UWB pulses, it is easier to engineer high data rates with low latency. This encourages the usage of UWB in sensor networks, wireless positioning systems, biomedical imaging, and high data short-range communications [1]. Antennas have a major effect on the performance of UWB communication systems, therefore, the design of an antenna must meet its typical requirements, such as impedance matching, radiation stability, compact size, and low cost, which is quite challenging to achieve. The patch antennas are good candidates for UWB applications because of their lightweight, planar geometry, and ease of integration with other electronic components [2; 3]. The main challenge in UWB communication is to avoid existing licensed and unlicensed wireless communication bands within the UWB spectrum, such as local area networks (WLAN) (IEEE802.11a,HIPERLAN/2,) operating in the 5.15-5.825 GHz band, WiMax (3.3-3.6 GHz), and X-band satellite communication (7.25-8.395 GHz). Filters are usually used to reject unwanted bands to improve communication quality. However, the use of filters increases the cost and volume of the system as well as insertion losses [4; 5]. Therefore, much research has been focused on the design of UWB antennas that have band rejection features to avoid potential interference from existing bands. Previous studies have developed many notched band UWB antennas using different approaches to avoid interference problems. These band rejection techniques include etching slots on patch [6; 7; 8], split-ring resonators [9; 10; 11], electromagnetic bandgap (EBG) structures [12; 13; 14], and inserting a resonant cell in a microstrip line [15; 16]. Some researchers achieved notched band capabilities by coupling parasitic elements to the radiator [17; 18]. These techniques facilitate the design of notch-band antennas. However, References [6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18] designs had the common disadvantage of a conventional notch with poor selectivity. The conventional notch is only capable of rejecting interference in the central frequency of a targeted band. To notch the unwanted bands in practical applications, a rectangular notch with high selectivity is required. Figure 1 shows a typical conventional notch and rectangular notch bands. In recent years, few rectangular notched antennas have been reported, because of their potential to reject the unwanted bands [19; 20; 21; 22; 23; 24]. In [19], using a large antenna, two conventional notch bands were attained at 5.2 and 5.8 GHz to reject the wireless local area network WLAN (5-6 GHz) without filtering the bandwidth between two bands. In [20], a rectangular notch-band antenna is presented at the WLAN band; however, the size of the antenna is too large to be used in modern compact electronic devices. In [21], several slots and split-ring resonators were coupled to a Coplanar Waveguide (CPW) line to achieve a wideband notch; however, because of its complicated geometry, the antenna does not offer frequency shifting of the notch band. In [22], to achieve a sharp-selectivity notch band, multiple quarter-wavelength slits were etched on the ground, and half-wavelength stubs were coupled to a microstrip; however, the geometry of the antenna was too complicated and required two-port excitations for its operation. In [23], folded strips and two pairs of inductively coupled resonators were employed for band-rejection with the advantage of controllable bandwidth. However, the geometry of the antenna was complex, and the overall size of the antenna is large.