Multiband Balanced Filters With Controllable Bandwidths Based on Slotline Coupling Feed

Novel multiband balanced bandpass filters with controllable bandwidths are presented in this letter. Slotline coupled-feed structure (SLCFS) is employed to suppress the common mode (CM), due to its intrinsic CM rejection. For differential mode, the tri-band/quad-band performance is realized by three/four pairsofhalf-wavelength resonators, which are designed for different passbands, respectively. Since the load effects between different resonators are very slight, the passband frequencies and bandwidths can be independently tuned and designed. Moreover, quasi-elliptical bandpass responses could be achieved to enhance the selectivity. Finally, two multiband balanced filters are designed and fabricated to validate the design method. To the best of authors' knowledge, the quad-band balanced filter may be the first ever reported.