Spatial power amplifier using a passive and active TEM waveguide concept

A new spatial power amplifier is presented in which power is spatially combined within a TEM waveguide using a low-loss transition array of E-plane integrated finlines to microstrip lines. The TEM-mode waveguide is implemented using a periodically patterned surface called a uniplanar compact electromagnetic bandgap (UC-EBG) structure. Our designed Ku-band back-to-back transition array demonstrates a maximum return loss of 17.5 dB and a maximum insertion loss of 0.65 dB. The TEM waveguide is found to have a 1-GHz bandwidth centered at 14.5 GHz. Tuning of the center frequency may be accomplished via an active UC-EBG structure that incorporates varactor diodes. The use of the UC-EBG surface allows more power cards to be inserted within the TEM waveguide since the amplifier cells saturate uniformly. The spatial power combiner is used to combine the output powers of 12 20-mW monolithic-microwave integrated-circuit amplifier chips. The designed power module yields an output power of 23.15 dBm and a combining efficiency of 86%. A comparison between the passive and active UC-EGB surfaces is experimentally demonstrated.