A new planar spiral antenna with integrated impedance transformer is presented which needs no external balun and can be fed by a coplanar waveguide. The proposed structure has a return loss of <À10 dB over a broad bandwidth of 0.5-5 GHz that is suitable for cognitive radio applications. The effects of different spiral and transformer parameters are investigated through various simulations. A case of the proposed antenna is fabricated, and measurement results are presented including return loss, gain, and radiation patterns.ABSTRACT: A novel printed microstrip reconfigurable antenna with three switchable frequencies is proposed. The proposed microstrip-fed Figure 6 Current distribution of the proposed antenna at (a) 0.7 GHz and (b) 2 GHz. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com]

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SUMMARYThe transmission-line matrix (TLM) method enables simulation of interior electromagnetic field propagation problems. With the use of absorbent walls, we can simulate exterior problems such as the radiaition of a microstrip antenna. The input impedance is deduced from the standing wave observed in the feedline. The radiation pattern is determined from the field over a plane located in the immediate vicinity of the antenna, using the theory of radiating apertures. However, the CPU time and memory space involved are excessive.Since the radiating structure has several resonant frequencies, it is convenient to apply classical digital signal processing techniques such as finite impulse response filtering associated with a linear prediction method. The present paper focuses on a Prony-Pisarenko method to improve on the TLM method in terms of both computation time and precision of the frequency-domain analysis of the results. In this case, overall CPU time is reduced by a factor of 2 to 3. The paper discusses the results obtained for radiation patterns. This represents a new field of application for the TLM method whose drawbacks are reduced by using appropriate signal processing methods.

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