  As the number of qubits in nascent quantum processing units increases, the
connectorized RF (radio frequency) analog circuits used in first generation
experiments become exceedingly complex. The physical size, cost and electrical
failure rate all become limiting factors in the extensibility of control
systems. We have developed a series of compact RF mixing boards to address this
challenge by integrating I/Q quadrature mixing, IF(intermediate
frequency)/LO(local oscillator)/RF power level adjustments, and DC (direct
current) bias fine tuning on a 40 mm $\times $ 80 mm 4-layer PCB (printed
circuit board) board with EMI (electromagnetic interference) shielding. The RF
mixing module is designed to work with RF and LO frequencies between 2.5 and
8.5 GHz. The typical image rejection and adjacent channel isolation are
measured to be $\sim$27 dBc and $\sim$50 dB. By scanning the drive phase in a
loopback test, the module short-term amplitude and phase linearity are
typically measured to be 5$\times$10$^{-4}$
(V$_{\mathrm{pp}}$/V$_{\mathrm{mean}}$) and 1$\times$10$^{-3}$ radian (pk-pk).
The operation of RF mixing board was validated by integrating it into the room
temperature control system of a superconducting quantum processor and executing
randomized benchmarking characterization of single and two qubit gates. We
measured a single-qubit process infidelity of $9.3(3) \times 10^{-4}$ and a
two-qubit process infidelity of $2.7(1) \times 10^{-2}$.
