**6. References**

[1] Liu L, Cheung SW, TI Yuk (2011) Bandwidth Improvements Using Ground Slots for Compact UWB Microstrip-fed Antennas. Progress In Electromagnetics Research Symposium (PIERS) 2011. Suzhou, China.

[2] Cheung SW, Liu L, Azim R, Islam MT (2011) A Compact Circular-Ring Antenna for Ultra-Wideband Applications. Microwave and Optical Technology Letters. 53: 2283– 2288.

292 Ultra Wideband – Current Status and Future Trends

**5. Conclusions** 

low frequencies.

**Author details** 

**6. References** 

L. Liu, S.W. Cheung, Y.F. Weng and T.I. Yuk

Symposium (PIERS) 2011. Suzhou, China.

**Figure 18.** Surface current distribution of antenna using cable B at (a) 3 GHz and (b) 11 GHz

The effects of small ground-plane sizes of planar UWB monopole antennas and feeding cable on measurements have been described and studied using computer simulation and measurement. A group of nine UWB antennas with the same radiator but different ground-plane sizes have been used for studies. Results have shown that the widths of the ground planes have more effects on the measured efficiencies. There are large discrepancies between the simulation and measured performances of these antennas at

(b)

(a)

The models of two practical feeding cables have been developed for studying the cable effects using computer simulation. Measurement results have verified the accuracies the two simulation models. Both the simulation and measured results have shown the feeding cable

*Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong* 

[1] Liu L, Cheung SW, TI Yuk (2011) Bandwidth Improvements Using Ground Slots for Compact UWB Microstrip-fed Antennas. Progress In Electromagnetics Research

without EMI suppressant tubing has significant effects on measurements.

	- [20] Liu L, Weng YF, Cheung SW, Yuk TI Foged LJ (2011) Modeling of cable for measurements of small monopole antennas. Loughborough Antennas & Propagation Conference (LAPC) 2011, Loughborough, UK.

**Chapter 13** 

© 2012 Meeloon 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 Meeloon 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.

**UWB-Bandpass Filters with Improved** 

Mongkol Meeloon, Sarawuth Chaimool and Prayoot Akkaraekthalin

In wireless communication systems, microwave planar bandpass filters are employed in most applications. The broadband and multiband applications are renewing the interest in the design of planar broadband filters with low loss, compact size, high suppression of spurious responses, and improved stopband performances. However, since the ultrawideband (UWB) system covers very wide frequency range of 3.1 to 10.6 GHz and then may be interfered with the existing undesired narrow band from the 5.2 GHz or 5.8 GHz wireless local area network (WLAN) radio signals. Moreover, the WiMAX (3.5 GHz) and RFID (6.8 GHz) communications may interfere with the UWB system within the range defined by the FCC. Therefore, UWB bandpass filters with single- and multi-narrow notched bands are needed to avoid being interfered by the exiting RF signals. In order to obtain operations, several techniques have been reported in literatures based on UWB-bandpass filters with slotted resonators (Meeloon et al., 2007, 2008, 2009), UWB-bandpass filters with slotted resonators and embedded slotted feed (Meeloon et al., 2009, 2011), and UWB-bandpass filters with slotted resonators and embedded fold-slot feed (Meeloon et al., 2010, 2011).

In this chapter, many advanced UWB-bandpass filters are presented based on slotted linear tapered-line resonator (SLTR) and slotted step-impedance resonator (SSIR) structures for size reduction and improved stopband performances. A comprehensive treatment of slotted resonators and both ends of the resonator with interdigital coupled lines is described. The design concept is demonstrated using two filter examples including one with an SLTR and another one with an SSIR. These filters have not only compact size but also a wider upper stopband resulting from resonator bandstop characteristics. Single-SLTR and single-SSIR filters are designed and constructed and their performances are extensively investigated in simulation and measurement. The proposed filters demonstrate their capabilities in suppression of spurious responses. Also, two-SLTR and two-SSIR filters are designed and

**Stopband Performance** 

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/48736

**1. Introduction** 
