Frequency switchable microstrip filter for microwave frequencies

This paper presents a frequency agile parallel-coupled microstrip filter. The centre frequency of the device may be switched very rapidly between two discrete values by applying optical illumination to a pair of silicon dice, which are mounted on the printed side of the board. Measurement results indicate that one may achieve a shift of 359MHz in the centre frequency by illuminating both dice with only 30mW of optical power. The optical power was measured at the end of the light delivery system. Increasing the level of optical power to 200mW reduces the passband insertion loss (measured at the centre frequency) from 3.614dB to 2.037dB. The minimum return loss values when both dice are illuminated with 30mW and 200mW are 10.10dB and 14.82dB respectively. The percentage bandwidth in the off-state differs from that in the on-state by only 1.86%. The maximum frequency switching range is approximately 380MHz. The measured and simulated results for the filter are in good agreement.