A compact bandpass filter has been investigated in this paper, the filter has four stepped impedance resonators, six open stubs are loaded on the two inner resonators, by adjusting sizes of six open stubs, a wide passband can be obtained. This proposed filter contributes respectively one transmission zero on either side of the wide passband. The proposed topology is demonstrated with a design operating at 5.205 GHz with 20.2% bandwidth, and more than 20dB of spurious suppression from 0 to 4.26 GHz and from 6.27 to 8.85 GHz is demonstrated in experimental results, which match well with the simulated results.

To obtain an adjustable passband filter, one open stub with three branches is loaded on an open loop resonator. The first and the third passband frequencies of the tri-band filter can be flexibly controlled by tuning lengths of three branches, whereas the second passband frequency is fixed. The fabricated filter has good tri-passband performance at 2.19, 4.26, 6.30 GHz. Measured results agree well with the simulated ones.

Both underlay spectrum sharing radios and overlay spectrum sharing radios have their advantages and disadvantages. Ultra wide band (UWB) and cognitive radio (CR) are important underlay and overlay technology respectively used as secondary radio systems. In this paper, a cognitive impulse ultra wide band (CIUWB) spectrum sharing radio technology is presented based on impulse UWB and CR.