RECONFIGURABLE AND ELECTRICALLY TUNABLE FILTERS WITH MULTIPLE SPLIT-RING RESONATORS

摘要

Reconfigurable filters with electronic change of the number and position of passbands consist of three or four concentric split-ring resonators (1, 2, 3 or 8, 9, 10, 11) which are excited with feeding lines (4, 4' or 12, 12') respectively. Electronic change of the passbands is accomplished by means of the de-tuning of individual split-ring resonators which become nonfunctional in the filter structure due to significant change of their resonant frequency. In that way different filter configurations can be obtained with reduced number of passbands in respect to the initial filter structure. De-tuning technique is applied using switching devices like PIN diodes, which either ground the certain split-ring resonators or interconnect two adjacent resonators, thus forming a new one. Four different topologies are achieved: three with discrete passband tuning and one which uses the combination of discrete and continuous tuning. Filters with discrete passband tuning which consist of three or four resonators use six or eight PIN diodes respectively. Depending of the applied de-tuning technique and PIN diode positions in the filter with three resonators, it is possible to obtain seven or five different configurations. In the filter consisting of four resonators eleven different configurations can be obtained. Combination of discrete and continuous control of the position and number of passbands is employed in the filter with three split-ring resonators by means of PIN and varicap diodes. Using varicap diodes enables continuous and independent tuning of the first and the third passband, while the second passband is fixed. PIN diodes are used to reconfigure the triple-band filter into the dual-band filter in which both passbands can be tuned independently, using the same varicap diodes which are employed for tuning of the triple-band filter. Multi-state operation in all proposed filter configurations are performed using microcontroller and corresponding electronic circuits which provide required bias voltages.