Direct Synthesis of Continuously Tunable Wideband Bandpass Filtering Attenuator With Multiple Transmission Zeros

In this brief, a direct synthesis design method of a continuously tunable wideband bandpass filtering attenuator is proposed. By adjusting the adjustable resistors, the attenuation amount that is inversely proportional to its resistance value can be obtained. In order to improve frequency selectivity, a half wavelength open-circuited stub and a parallel coupled line were loaded to achieve three pairs of transmission zeros (TZs). For the problem of low efficiency of traditional attenuators, a synthesis design method that can improve design efficiency was adopted, and a filtering attenuator with working frequency of 2.21-4.65 GHz, fractional bandwidth of 71.14%, and tunable attenuation range of 1.58-18.98 dB was simulated to verify the reliability of the method. The synthesis design outcomes correspond well with the simulation results.