A double-double balanced HBT Schottky diode broadband mixer at X-band

A Schottky diode double-double balanced mixer with 10 dB conversion loss and >60 dB LO-IF isolation has been achieved using AlGaAs/GaAs HBTs. The HBT Schottky mixer converts a 6-10 GHz RF signal down to a 2-6 GHz IF band with a fixed LO of 10 dBm at 12 GHz. The IP3 is as high as 11 dBm at this LO drive level. An up-conversion loss of <10 dB was also measured with an IP3 of as much as 12 dBm at midband. The Schottky diodes were constructed by making a Schottky contact to the HBT MBE N/sup -/ collector layer. The resulting Schottky diodes obtain a cut-off frequency of 1 THz and an ideality factor=1.05. The same HBT process yields an f/sub T/ and f/sub max/ of 23 GHz and 50 GHz, respectively, for a 2 /spl mu/m emitter width Self-Aligned Base Ohmic Metal HBT. The work in this paper represents the first double-double balanced HBT Schottky diode mixer demonstration and achieves superior performance to a previously published double-double balanced X-band MESFET Schottky mixer.