The RF portion is now complete. The component on the left hand side of the image below is a Analog Devices ADC4360 synthesizer running at 870 MHz and serves as the local oscillator to jump down to our first intermediate frequency.

One leg of the output is used to drive the transmitter and the other leg is amplified and split four ways for each of the receivers. The traces for the receivers are laid out such that they’re all the exact same length and thus have the same phase shift. This is critical because our system measures the phase differences between antennas to determine the location of a neighbor and layout differences would produce large offsets in phase.

The ‘X’s there surrounding the traces form a via shield tying the surface ground plane to the internal ground planes and serve to isolate the signal from its surroundings.