Compact Balanced Dual-Band Bandpass Filter With Tunable Upper Band Using Hybrid Structure

In this paper, a reconfigurable balanced dual-band filter based on microstrip and SIW hybrid structure is proposed. The upper passband and lower passband are determined by SIW and microstrip line respectively. The two parts don't interfere with each other, so the two passbands can be designed independently. By slotting in the symmetry line of the middle metal layer, the structure maintains excellent common mode rejection. On this basis, the varactors are loaded in the SIW part to make the center frequency of the upper passband tunable. The measured results show that the center frequency of the upper passband can change from 4.9GHz to 5.38GHz, while the lower passband remains unchanged basically, which verifies the feasibility of the design.