Microstrip-Fed Dielectric Resonator Circuits Without Shielding

The classic dielectric resonator (DR) circuits require additional metal cavities for the electromagnetic shielding, which leads to a bulky size and difficulty in integration inevitably. To deal with this issue, several approaches have been proposed with the expense of high insertion loss (IL) or poor out-of-band rejection. Inspired by the transmission characteristic theory of DR proposed recently, new low-loss resonant modes are found and further excited by microstrip directly to implement a filter and a filtering power divider in this article. The detailed theoretical analysis and verification have been conducted. For demonstration, two prototypes operating at 3.6 GHz are simulated, fabricated, and measured. The minimum measured IL of the proposed DR filter and filtering power divider is 0.93 and 3.92/3.86 dB, respectively. Comparison between the circuit without and with a metal cavity shows that the low-loss characteristic can be maintained without additional shielding.