A Dual-Mode Monoblock Dielectric Bandpass Filter Using Dissimilar Fundamental Modes

In this article, a novel dual-mode monoblock dielectric resonator (MDR) for compact monoblock dielectric bandpass filters is presented and put into practical use for the first time. In the dual-mode resonator, two dissimilar TEM modes are generated by forming two perpendicular metalized blind holes in a silver-coated cuboid-shapes dielectric block. The resonator can maximize the space utilization with up to 50% volume reduction while maintaining a wide spurious-free frequency band. The coupling of the two modes in such a resonator can be effectively controlled by one or more partial-height metalized posts. A convenient input/output (I/O) coupling scheme for surface-mount applications is introduced, and versatile coupling arrangements for realizing various filter characteristics are presented. To demonstrate the proposed filter miniaturization technique, a six-pole inline bandpass filter with one pure imaginary transmission zero (TZ) in a 3.5-GHz band is electromagnetic (EM) designed, and a ten-pole symmetric bandpass filter with two pure imaginary TZs in a 2.6-GHz band of fifth-generation (5G) new radio (NR) frequency band is designed, prototyped, and tuned. Experimental results show that the proposed dual-mode MDR filter can obtain an acceptable RF performance for 5G applications with a significant volume reduction compared to existing single-mode solutions.