Dual mode microstrip ring resonator with composite-right/left-handed line

Microwave and RF filters play an important role in various electronic systems, including cellular radio, satellite communications and radar. Filters are used in these systems in order to discriminate between wanted and unwanted signal frequencies. High performance filters are desirable for good signal reception and therefore for a better system performance. The demands for high performance filters are mainly due to the stringent frequency spectrum requirements following the emerging of new applications for modern communication systems. High performance filters are filters with low insertion loss, high frequency selectivity, phase linearity and potentially no harmonic response. Following the advancement of modern technologies, design considerations have been extended to achieve compact size and light-weight, making the filter design a more challenging task. Although enormous amount of literature on various filter theories is available, new filters are continually developed and reported in major journal and conference publications, to suit severe design specifications. In general, microwave filters are divided into two broad classes, they are distributed type and lumped-element type. At microwave frequencies the use of distributed circuit elements in implementing passive microwave devices is widespread. They differ from lumped circuits as one or more dimensions are a significant fraction of the operating wavelength. Design formulae are available in many texts. Distributed filters can take the form of planar structures or waveguide cavity and they are preferable for high Q filter design. However, the latter has the advantage of low or no spurious harmonic responses. In this chapter, we will give a new design perspective for a potentially high performance filter namely a dual-mode microstrip ring resonator with composite-right/left-handed (CRLH) line, for suppression of first harmonic.