Distance measurement using EHF signals

A system comprising:

• a first transmit communication unit mounted on a first surface for transmitting a receive EHF signal toward a second surface spaced from the first surface;
• a first receive communication unit mounted on the first surface adjacent the first transmit communication unit for receiving a receive EHF signal transmitted from the second surface;
• a detecting circuit coupled to the first transmit communication unit and the first receive communication unit for determining an indicator representative of a distance between the first and second surfaces based on the propagation of the transmit and receive EHF signals between the first transmit communication unit and the first receive communication unit;
• wherein a second transmit communication unit and a second receive communication unit mounted on the second surface;
• wherein the first transmit communication unit transmits the transmit EHF signal to the second receive communication unit, the second receive communication unit is coupled to the second transmit communication unit and communicates a communication signal representative of the transmit EHF signal received by the second receive communication unit to the second transmit communication unit, and the second transmit communication unit transmits to the first receive communication unit the receive EHF signal representative of the communication signal;
• and
• wherein the first receive communication unit is coupled to the first transmit communication unit, with the first and second transmit communication units and first and second receive communication units forming in combination a ring oscillator.