Effect of Power Divider Phase in Power Distribution Networks

For the CCAT Heterodyne Array Instrument (CHAI) we studied the basic components for the local oscillator (LO) distribution in the 4-pixel block, of which 16 units will constitute the 64 pixels in the 455–495$\,$GHz band. A single LO signal is divided by a cascade of on-chip 3 dB power dividers based on superconducting planar transmission lines, implemented in multipixel waveguide mixer blocks. In this article, we present two different types of power dividers, namely, a microstrip Wilkinson and a coplanar waveguide (CPW) 90$^{\circ }$ hybrid, which are designed, simulated, and fabricated. Upon integrating them in a two-pixel block with the intended mixers, we observe an unexpected difference in terms of equal power distribution to both mixers. The 90$^{\circ }$ phase difference between the outputs of the hybrid, in the presence of standing waves due to an imperfectly terminated isolated port, causes an imbalance between the LO-power transmitted to both mixers. This inequality is frequency-dependent and alternates considerably across the band. The Wilkinson due to its in-phase power division is immune to this effect and therewith demonstrates a significantly more even power transmission to the mixers.