We investigate the reduction of mutual coupling between the radiating elements of a compact antenna array using a periodic structure. The periodic structure is designed such that it exhibits an electromagnetic bandgap for in-plane transmission over a specified frequency band around the operational frequency of 2.40 GHz. The experimental setup consists of a two-element dipole antenna array. For a spatial separation of /6, significant improvement of the radiation efficiency was observed
Opportunistic use of White Spaces (WS) has opened up a whole new paradigm in research on cognitive radio (CR). One of the issues addressed by the QoSMOS project is the design of a flexible and efficient physical layer (PHY) for CR systems. To this aim, different modulation techniques are being investigated and are presented in this paper. They fulfill the low out of band leakage and spectral efficiency requirements of a CR operating in fragmented WS. The design of reconfigurable and flexible radio-frequency (RF) front-end is also introduced, since its performance is tightly linked to these parameters and to the implementation feasibility and constraints. Emphasis is put on benchmarking the performance of the proposed schemes over classical approaches.
A lumped-element tunable pre-selection bandpass is presented that consists of three coupled resonators. The bandpass employs a digitally tunable capacitor (DTC) and allows for tuning of the centre frequency with a resolution of 5 bit. It covers the frequency range from 450 MHz to 940 MHz, including the DVB-T band, the TV white space (TVWS) band, and the LTE-800 frequency band. The insertion-loss variation amounts to 0.3 dB. The filter measures 20 mm by 20 mm, it can therefore be easily integrated into analog RF front-ends. The filter's application to cognitive-radio platforms is discussed.Index Terms-cognitive radio, digitally tunable capacitor (DTC), tunable bandpass filter
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