Non-galvanic PCB feeding method of cavity filters

In this paper, a novel low-cost method for coupling into Radio Frequency (RF) cavity filters is presented. The method is based on a non-galvanic and connector-free connection from the output of the power amplifier (PA) to the first resonator of the filter. This is achieved by means of capacitive coupling of the microstrip line from the output of the PA to the feeding pin of the first resonator of a filter. A significant reduction of the overall base station cost is achieved, since no extra connectors, blind-mate bullets or screws are required. The absence of the galvanic connection also leads to improved Passive Inter Modulation (PIM) performance. As a demonstrator, a 3-pole, 1800 MHz filter is designed, fabricated and tested. The measured results show a good agreement with simulations.