C/X-Band sub-harmonic mixer using single oscillator and its design flow

This article describes the concept of designing a dual-band subharmonic mixer for C-band (4.3-5.3 GHz) and X-band (9.8-11.2 GHz) applications. This mixer exploits a single local oscillator (LO) (with a frequency of 2.6GHz) with two harmonics (second and fourth), in contrast to the two LOs, utilized in a conventional dual-band mixer. This configuration results in reduced system complexity and noise. The proposed mixer utilizes two signal interference technique (SIT)-based bandstop filters at the LO port, and a dual bandstop stub at the IF port to get good isolation. A prototype of the proposed configuration is fabricated on flexible Rogers' substrate RO5880B with 0.8 mm thickness. The total implementation area of the circuit is 43 mm x 32 mm. Circuit performance is validated by measurement. Based on the measured result, the mixer performs equally well in both bands with the conversion loss (CL) in the range of 6.1-10.9 dB. The measured LO-to-IF and LO-to-RF isolations are better than 25 dB, whereas the measured RF-to-IF isolation for both bands is better than 15 dB. Further, the measured value of 1 dB compression point is found to be - 8 dBm and - 7 dBm at 5.3 and 11.2GHz, respectively.