Abstract
This chapter will treat firstly a summary of the filters synthesis by using Butterworth and chebyshev techniques. After that, a second part will be devoted to the design of planar filters using different techniques; this section will present some examples in bibliography. The aim of this part is to understand the different methods and steps followed to design planar filters, in the same time to discover and to define the different parameters which characterize a filter structure. Therefore, we have chosen some new research studies on low pass filers. The last part will present our contribution in designing planar filter. The first filter structure is a dual bandpass microstrip filter operating for DCS and Wimax applications, this section will introduce the different steps followed to achieve such filter. The second circuit is a novel design low cost microstrip lowpass filter with a cutoff frequency of 2.3 GHz. At the end, we will present a transformation of the microstrip filter to a CPW lowpass filter making it easy for integration with passive and active microwave components.
TopIntroduction
Microwave system consists of a number of components including filters; they are capable of passing a specific frequency band and suppressing the undesired signals. Recent research on microwave filters is very active because of continuous demands of high-performances circuits for modern wireless communication and electronic systems.
In recent years, filters have become important components for wireless communication products for microwave frequency bands. For example, global systems for mobile communications, wireless local area network (LAN) and the unlicensed industrial-scientific-medical (ISM) (Miyake, Kitazawa, Ishizaki,Ymanda, & Nagatomi,1997; Kuo, Yeh, & Yeh, 2005; Zhang, Chen, & Xue, 2007; Hong, 2011; Ishii, 1995).
To design such circuits, many techniques and steps are followed (Pozar, 1998; Zverev, 1967; Hong & Lancaster, 2001; Borazjani & Rezaee, 2010; Martin, et al., 2003; Sor, Qian, & Itoh, 2001; Hayati, Sheikhi, & Lotfi, 2010; Xu Ji, Wu, & Miao, 2013; Velidi & Sanyal, 2011; Ma & Yeo, 2011; Wang, Xu, Zhao, Guo, & Wu, 2010; Chen, 2014;Wang, Lin, & Chen, 2004; Kuo, Hsu, & Huang, 2002; Velázquez-Ahumada, Martel, & Medina, 2004). Let’s start with the conventional design procedure for microstrip lowpass filters (LPF) which consists mainly of two steps, the lowpass prototype circuit and after that looking for a microstrip achievement that will give nearly the lumped-element filter response (Chen, Sung, & Su, 2015). Generally, passing from lumped elements to microstrip configuration is often simple to reach. Microstrip filters have many adavantages as compact size, sharp roll-off, and wide stopband which are the current trends in the design of microstrip LPFs (Karimi, Lalbakhsh, & Siahkamari, 2013;Wang, Xu, Zhao, Guo, & Wu, 2010). Due to the inherent characteristics of a microstrip line, conventional designs of microstrip LPFs fail to satisfy the requirements of compact size and wide stopband (Hong, 2011). To meet the requirements, recent studies mainly resort to specially designed resonators for realizing their respective equivalent circuit models (Karimi, Lalbakhsh, & Siahkamari, 2013; Wang, Xu, Zhao, Guo, & Wu, 2010). In some studies the two-steps procedure is discarded and each filter structure design is based on many methods and techniques of tuning or optimization. All that make these kind of filters so harder to be designed and fabricated by designers in comparison with the conventional microstrip filters like stepped-impedance LPFs and open-stub LPFs (Hong, 2011). Among the challenge for designing LPFs, we find many studies looking for achieving these kind of filters with wide stopband (Lui, Xu, & Xu, 2015).
Key Terms in this Chapter
Butterworth Filter: The Butterworth filter is a type of signal processing filter designed to have as flat a frequency response as possible in the passband. It is also referred to as a maximally flat magnitude filter.
DGS: Defected Ground Structure is a technique that means that a “defect” has been placed in the ground plane, which changes the behavior of perfect ground. Although the additional perturbations of DGS alter the uniformity of the ground plane.
Stepped-Impedance: Is to use alternating sections of very high and very low characteristic impedance lines for lowpass filters. Such filters are usually referred to as stepped-impedance, or hi-Z, low-Z filters, and are popular because they are easier to design and take up less space than a similar low-pass filter using stubs.
Chebyshev Filter: Chebyshev filters are analog or digital filters having a steeper roll-off and more passband ripple or stopband ripple.
CPW: Coplanar waveguide is a type of electrical transmission line which can be fabricated using printed circuit board technology, and is used to convey microwave-frequency signals. On a smaller scale, coplanar waveguide transmission lines are also built into monolithic microwave integrated circuits.
EBG: Electromagnetic Band-Gap materials (EBMs), are a class of periodic metallic, dielectric, or composite structures that exhibit a forbidden band, or bandgap, of frequencies in which waves incident at various directions destructively interfere and thus are unable to propagate.
WiMAX: Worldwide Interoperability for Microwave Access is a family of wireless communications standards initially designed to provide 30 to 40 megabit-per-second data rates, with the 2011 update providing up to 1 Gbit/s for fixes stations.
DCS: Digital Communication System also known as “GSM 1800”, DCS is a radio frequency band used in Europe, Africa, Asia, and South America for GSM mobile phones. DCS bands are 1710-1785 MHz and 1805-1880 MHz. There are at least five licensed sub-bands within that range in most countries that have DCS. In the context of WCDMA and LTE networks, the DCS band is also known as band 3.