Distinctive propagation characteristics of millimeter wave (mmWave) bands require channel sounding for link management. Reported mmWave channel-sounder setups support only simplex operation while depending on bulky and expensive lab equipment; especially for frequency domain channel sounding (FCS), which can be performed with simple hardware. This work presents a solution in the form of a 60 GHz modular front-end designed using off-the-shelf components with tailor-made passive circuits and high-frequency interconnections, all compatible with printed circuit technology. An FCS setup is developed using two units of the designed transceiver front-ends, which can sweep 6 GHz bandwidth with 1 MHz resolution. An antenna duplexing circuitry is also presented, which enables each front-end unit to use a single transmit-receive antenna ensuring a high correlation between the round-trip channels. To the best of the authors’ knowledge, this work reports the first FCS setup, which preserves channel reciprocity in round-trip sounding. The application of the designed system is showcased through a channel reciprocity key generation (CRKG) algorithm, which exploits the high correlation between the forward and receive channels to demonstrate a physical layer security system functional at 60 GHz.