A Balanced Sub-Harmonic Mixer for multi-OFDM Ultra Wide Band Direct Conversion Transmitters

In this paper a single balanced sub-harmonic mixer, suitable for direct-conversion IEEE 802.15.3a ultra wide band transmitter, is introduced, fabricated and tested. The circuit, which consists of two pairs of anti-parallel diodes connected by a wideband balun and proper frequency terminations, is optimized for direct up-conversion in the 3.1-4.8 GHz band. The prototype was realized by means of hybrid technology, surface mount packaged Schottky diodes and passive components. The measurements highlight a conversion loss ranging from 12 dB to 15 dB and an in-band second LO harmonics in the range of 48 dB to 57 dB. The proposed passive mixer optimum functionality is achieved with a LO power of 7 dBm. Finally, the prototype response was shaped by a microstrip multisections coupled-lines band pass filter, designed to operate as output spectrum shaping. The system level considerations demonstrated the suitability of the proposed circuit topology for UWB MBOA applications