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 are coupled to a differential signal. An isolated port is connected to ground through a matched resistance. An output port 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 to the output port. A f₂ rejection filter on the PCB is wrapped around the balun and includes a first folded element with a transmission length of λ₂/4 and connected to the output port. A second folded element has a transmission length of λ₂/4 and connected to the tap point. A third folded element connects the tap point to the output port and has a transmission length of λ₂/4.