Performance and modeling of 700 GHz SIS finline mixers

Paul Grimes, G. Yassin, S. Withington, Karl Jacobs

Published Jan 1, 2007• 0 citations

Abstract

Fig. 1. (Top) A 700 GHz finline mixer chip. The finline taper runs from the left to center of the chip, and the mixer tuning circuit, RF block and bond pads are on the right (Bottom) Cross-sections through the finline taper, showing the metallization and the E-field lines. The finline taper gradually transforms the waveguide mode at A through unilateral finline (B) to antipodal finline (C), before transitioning from antipodal finline to microstrip (D-F). Abstract—SIS mixers using finline waveguide to microstrip transitions show a number of advantageous features, particularly in providing a broadband, fixed impedance feed to the SIS mixer tuning circuit. The large chip area and insensitivity to mixer block machining tolerances simplifies the assembly of the mixer, as well as allowing more advanced mixer designs to be fabricated on a single chip. Finline SIS mixers have shown good performance in the 230 and 350 GHz bands[1][2], and we have also previously reported results from two finline SIS mixers in the 600-720 GHz band[3][4], obtaining best receiver noise temperatures of ~250 K. In this paper we present results from several finline mixers in the 600-720 GHz band, using both variants of our original 3-stage Chebyshev filter tuned single junction mixers and new Belitsky tuned mixers. These dual junction tuned mixers show significantly better performance than our previously reported results, with receiver noise temperatures below 200 K. We present detailed SuperMix simulations of the receiver performance and compare these with measured results. We find good agreement between simulations and measured performance can be achieved by introducing a small amount of attenuation in the RF circuit of the mixer. We also present simulations of the IF bandwidth of finline mixers, and suggest a method by which this can be greatly improved.

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