High selectivity and common‐mode suppression wideband balanced bandpass filter using slotline resonator

Abstract

Novel wideband balanced bandpass filter with high selectivity and common‐mode (CM) suppression is constructed with slotline resonator. When the intersection points of the microstrip feedline and slotline resonator are close to the midpoint of the slotline resonator, the coupling between the fundamental mode of the slotline resonator and microstrip feedline can be maximised, whereas the second mode can be suppressed. Making use of this feature, the third‐order wideband filter with low insertion loss, wide upper‐stopband and flat group delay is designed by using the slotline resonator and two quarter‐wavelength microstrip resonators paralleled to the slotline resonator with tapped‐line coupling at their short‐circuited ends. Based on the third‐order single‐ended filter structure, a novel balanced filter with a 1 dB fractional bandwidth up to 72% is designed with low insertion loss and enhanced CM suppression. To improve the selectivity, the fifth‐order wideband balanced filter with wide upper‐stopband is designed with parallel coupling structure between two slotline resonators. The corresponding CM suppression is better than 42 dB within the whole differential mode passband. The wideband balanced filter is designed and fabricated, and good agreement between measurements and simulations is obtained.

High CM suppression balanced SIW BPF and HMSIW directional coupler utilising perfect electric conductor/perfect magnetic conductor characteristic

“…The initial sizes of SIW resonator can be obtained by (3). The relation M 12 with the width w 1 of coupling window in Fig.…”

“…The CM and differential-mode (DM) equivalent half circuits are separately built and the design method is simple in the way that the CM suppression can be made independent of DM response. Afterwards, many novel structures and design methods of balanced filter have been developed using a variety of transmission-line structures [2][3][4][5].…”

Differential SIW slot antenna array with intrinsic common‐mode rejection

“…Thus, the differential antenna can also be directly connected to the differential circuit without introducing a balun, making it easier to be integrated without additional radio frequency (RF) energy losses. Furthermore, the CM suppression is an important indicator for the differential circuit to reduce the signal-to-noise ratio in the differential circuit [1,2]. Meanwhile, the CM signal should not be radiated or received by antenna [3].…”

High selectivity and common‐mode suppression balanced bandpass filter with TM dual‐mode SIW cavity

“…Balanced circuits are attractive for the advantage of suppressing common-mode (CM) noise [1,2]. Ideally, balanced BPFs should exhibit good performances, including low insertion loss, high selectivity, broad stopband for differential-mode (DM) signal, and high CM suppression [3].…”