Compact balun with rejection filter for 802.11a and 802.11b simultaneous operation

摘要

A balancing/unbalancing (balun) structure for operating at frequency f1 includes a microstrip printed circuit board (PCB). A balun on the PCB includes two input ports (P2,P3) coupled to a differential signal. An isolated port (P4) is connected to ground through a matched resistance. An output port (P1) is coupled to a single-ended signal corresponding to the differential signal. A plurality of traces on the PCB connect the two input ports, the load connection port and a tap point (209) to the output port. A f2 rejection filter on the PCB is wrapped around the balun and includes a first folded element (210-216) with a transmission length of λ2/4 and connected to the output port. A second folded element (217-221) has a transmission length of λ2/4 and connected to the tap point. A third folded element (204-208) connects the tap point to the output port and has a transmission length of λ2/4.