A low-cost direct conversion transmitter suitable for multi-OFDM ultra wide band

In this paper a low-cost direct-conversion UWB transmitter, based on single balanced sub-harmonic mixers, is described. The UWB transmitter prototype is implemented by a laboratory set-up composed of subsystems designed and fabricated in hybrid technology. The key subsystems are represented by the IQ up-converters, each of them consisting of two couple of anti-parallel diodes connected by a wideband balun. The measurements highlight a conversion loss ranging from 12 dB to 15 dB, and a minimum isolation, related to second order LO harmonic, of 53 dB. Due to the diodes characteristic no DC supply is needed and the optimum functionality is achieved with a LO power of 7 dBm. The transmitter includes power splitter for the LO distribution to the IQ mixers, the power combiner and a band-pass output filter. All the subsystems are optimized in the 3.1-4.8 GHz band. Finally, in order to assess the transmitter performances in a realistic environment, system level simulations have been performed compliant with MBOA specifications.