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

Abstract

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 × 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.