New monolithic crystal filter with side tabs

Wide tab electrodes are utilized for waveguiding the energy of anharmonic modes to lossy mounting at plate edges of monolithic crystal filters (MCFs). The effect of Z´-tabs on dual-resonator MCFs operating in the third-overtone thickness-twist mode is examined. The theoretical and experimental results show that while the unwanted mode suppression achievable with the Z´-waveguides is limited by the occurrence of untrapped modes, it is possible to attenuate both the strong (3, 1, 3) and newly excited modes below -20 dB. Experimental results for MCFs having wide Z´- and X-tabs are also presented