**1. Introduction**

236 Ultra Wideband – Current Status and Future Trends

[63] Najam A.I., Duroc Y., Tedjini, S. UWB-MIMO antenna with novel stub structure.

*Progress In Electromagnetics Research J. C* 2011; 19 245-257.

In 2002, the FCC in the US authorized the unlicensed use of the ultrawideband (UWB) frequency spectrum for commercial applications in the range from 3.1 to 10.6 GHz with an emission limit of -41.3 dBm/MHz which is near to the thermal noise floor [1]. UWB communication systems operating in such a wide frequency band and low power emission level could easily be interfered by the existing nearby communication systems such as the Wireless Local Area Networks (WLANs) operating in the frequency bands of 2.45-GHz (2.4– 2.484 GHz), 5.25-GHz (5.15–5.35 GHz) and 5.75-GHz (5.725–5.825 GHz) [2] and the Worldwide Interoperability for Microwave Access (WiMAX) systems operating in the 2.35- GHz (2.3-2.4 GHz), 2.6-GHz (2.5–2.69 GHz), 3.35-GHz (3.3-3.4 GHz), 3.5-GHz (3.4–3.6 GHz), 3.7-GHz (3.6-3.8 GHz) and 5.8-GHz (5.725–5.85 GHz) bands[3]. Many countries such as the UK, Canada, France, Germany, Argentina and India etc. will allow at least four of these bands in operations [3]. In such cases, the UWB systems could be affected by several interference signals. These interference signal could be suppressed by using RF filtering.

Traditional filtering is implemented using lumped elements, which however increases the cost and system complexity and occupies more space in the wireless devices. Another feasible solution is to design the UWB antennas with band-notched characteristics to suppress the interference signals [4, 5]. Figure 1 shows a general design concept for a bandnotched UWB antenna. An UWB antenna, as shown in Figure 1(a), has an impedance bandwidth from *fL* to *fH*, which are the lowest and highest -10-dB cut-off frequencies, respectively, of the S11. A bandstop resonant structure, as shown in Figure 1(b), also has a bandwidth from *fL* to *fH*, but with a resonant frequency at *fN* to stop the undesired signal passing through. Combining the UWB antenna with the resonant structure as shown in Figure 1(c), a band-notched antenna is formed. The band-notched antenna will not interfere with other communication systems nearby using the same frequency band at *fN*.

© 2012 Weng et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Weng et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Creating Band-Notched Characteristics for Compact UWB Monopole Antennas 239

ellipse with a minor-radius-to-major-radius ratio of 0.5 to reduce the beam tilt of the antenna

**Figure 2.** (a) Layout and (b) side view of CPW antenna with two CPW resonators, and (c) layout of

*a*

**Figure 3.** Simulated return losses of reference UWB antenna for different values of (a) *R1* and (b) *R2*

 *5.3* 

*b 9* 

**Parameter Value (mm) Parameter Value (mm)** 

*L 35 Ld 0.3 Wg 32 W1 0.3 Lg 20 W2 0.3 Rr 15 W3 0.3 R1 4 S 3 R2 4.5 W 0.3* 

*t 0.0035 Lc*

*H 0.762 Lc*

**Table 1.** Antenna dimensions for dual-band notch

CPW resonator

(a) Notched band at 5.5GHz (b)Notched band at 3.5GHz

[12]. Detail dimensions of the dual band-notched antenna are listed in Table 1.

**Figure 1.** Basic design concept for band-notched UWB antenna

In general, the design procedure for a band-notched antenna can be described as follows. An UWB antenna without band-notched function is designed to have good impedance matching over the UWB, which is used as a reference antenna. Proposed resonant structures are added to the reference antenna to create notches at some specific frequencies. The dimensions of the resonant structures can be used to control the center frequencies and bandwidths of the notches. Different designs have been proposed to realize the bandnotched characteristic for UWB planar monopole antennas [5-18]. These include using parasitic elements [6], folded strips [7], split-ring resonators (SRRs) [8], quarter-wavelength tuning stubs [9], meander-ground structures [10, 11], resonated cells on the coplanarwaveguide (CPW) [12], fractal tuning stub [13], slots on the radiator [14-16] or ground [17], and slots or folded-striplines along the antenna feed line [18]. However, most of these designs targeted at creating a single-notched band and only one design targeted at a triplenotched band using meander lines [11].

In this chapter, we study the applications of CPW resonators, λ/4-resonators and MLs to design single, dual, triple and quadruple band-notched characteristics for compact UWB monopole antennas. The studies are carried out using computer simulations and the simulated results are verified using the antenna measurement system, Satimo Starlab. The simulated and measured results on the return loss, radiation pattern, peak gain and efficiency agree well. The pulse responses and fidelities of the single, dual, triple and quadruple band-notched antennas are also measured and compared with those of the reference antenna.
