  In this letter, we study the wireless point-to-point communication from a
transmitter (Tx) to a receiver (Rx), which is jointly aided by an active
intelligent reflecting surface (AIRS) and a passive IRS (PIRS). We consider two
practical transmission schemes by deploying the two IRSs in different orders,
namely, Tx$\rightarrow$PIRS$\rightarrow$AIRS$\rightarrow$Rx (TPAR) and
Tx$\rightarrow$AIRS$\rightarrow$PIRS$\rightarrow$Rx (TAPR). Assuming
line-of-sight channels, we derive the achievable rates for the two schemes by
optimizing the placement of the AIRS with the location of the PIRS fixed. Our
analysis shows that when the number of PIRS elements and/or the AIRS
amplification power is small, the AIRS should be deployed closer to the Rx in
both schemes, and TAPR outperforms TPAR with their respective optimized
AIRS/PIRS placement. Simulation results validate our analysis and show the
considerable performance gain achieved by the jointly optimized AIRS/PIRS
deployment over the baseline double-PIRS system under the same power and IRS
element budgets.
