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Recently, the Dynamic Spectrum Access (DSA) techniques are proposed to solve the problem of spectrum scarcity and help to use the limited spectrum resource as effectively as possible. The current ongoing spectrum reform opens up the possibilities to exploit the DSA techniques. This paper aims to provide a critical review on the various ongoing efforts towards the use of DSA concept for the frequency management of future wireless communications systems, especially from the Cognitive Radio (CR) perspective. The CR aims for an efficient and dynamic access to the spectrum, and provides a new method of spectrum management. This paper also highlights the various challenges associated with CR in order to realize the concept of DSA.

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A novel compact coplanar waveguide (CPW)‐fed zeroth‐order resonator (ZOR) is reported in this article. The zeroth‐order mode is required to reduce the resonator's size. The composite right/left handed transmission line (CRLH TL) structure is designed on a single layer via‐less CPW‐fed, which reduces the fabrication complexity and makes the structure more feasible. The resonator has a compact size of 21.6 × 5.2 mm2. The measured insertion loss and return loss of the resonator are −0.72 dB and −21.3 dB, respectively at the resonant frequency, 2.80 GHz. The performance of the proposed ZOR is compared with the previously reported ZORs. All the performance parameters of the resonator are evaluated by full‐wave electromagnetic simulator IE3D, based on the method of moments (MoM) and all the results are verified by measurement. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2576–2580, 2015

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