Devices, systems, and methods for radar-based artificial reality tracking

1. A radar system comprising:

a radar mechanism comprising at least one transmitter and at least one receiver;

a signal generator that generates a frequency-modulated radar signal;

a delay mechanism that:

receives the frequency-modulated radar signal from the signal generator; and

after a certain period of delay, passes the frequency-modulated radar signal to the transmitter to be transmitted to at least one transponder located on a wearable artificial reality device; and

at least one processing device communicatively coupled to the receiver, wherein the processing device:

receives the frequency-modulated radar signal from the signal generator;

detects a signal returned to the receiver from the transponder in response to the frequency-modulated radar signal;

calculates a beat frequency that:

corresponds to a difference between an instantaneous frequency of the frequency-modulated radar signal received at the processing device and an instantaneous frequency of the signal returned from the transponder; and

is proportional to an apparent distance between the transponder and the receiver; and

calculates a distance between the transponder and the receiver based at least in part on:

an analysis of the signal returned from the transponder and the frequency-modulated radar signal received from the signal generator; and

the beat frequency.

2. The radar system of claim 1 , further comprising an additional wearable artificial reality device that secures at least:

the transponder;

the receiver;

the signal generator; and

the delay mechanism.

3. The radar system of claim 2 , wherein the receiver comprises a plurality of receivers that are secured to the additional wearable artificial reality device such that each of the plurality of receivers are separated by at least a certain distance.

4. The radar system of claim 1 , wherein:

the frequency-modulated radar signal follows a modulation cycle that comprises an approximately linear sweep between a first frequency and a second frequency; and

the certain period of delay generated by the delay mechanism causes:

the transmitter to receive the frequency-modulated radar signal at a different point in the modulation cycle than the processing device; and

the instantaneous frequency of the frequency-modulated radar signal received by the processing device to be offset by a certain amount relative to an instantaneous frequency of the frequency-modulated radar signal transmitted by the transmitter.

5. The radar system of claim 4 , wherein offsetting the instantaneous frequency of the frequency-modulated radar signal transmitted by the transmitter increases the beat frequency by a certain value such that the apparent distance between the transponder and the receiver exceeds the distance between the transponder and the receiver by a certain length.

6. The radar system of claim 5 , wherein the processing device accounts for the increase in the beat frequency by the certain amount while calculating the distance between the transponder and the receiver.

7. The radar system of claim 1 , wherein the delay mechanism comprises a fiber optic cable that transmits the frequency-modulated radar signal from the signal generator to the transmitter.

8. The radar system of claim 7 , wherein a length of the fiber optic cable is selected such that the frequency-modulated radar signal traverses along the fiber optic cable for an amount of time corresponding to the certain period of delay.

9. The radar system of claim 1 , wherein the delay mechanism comprises at least one of:

a coaxial cable;

delay line; or

light-emitting diode.

10. The radar system of claim 1 , further comprising a frequency multiplier positioned between the delay mechanism and the transmitter.

11. The radar system of claim 10 , wherein the frequency multiplier:

receives the frequency-modulated radar signal from the delay mechanism; and

passes the frequency-modulated radar signal to the transmitter after multiplying a frequency of the frequency-modulated radar signal by a certain factor.

12. The radar system of claim 1 , wherein the processing device further determines, based at least in part on the distance between the transponder and the receiver, a current three-dimensional location of at least a portion of a user wearing the wearable artificial reality device.

13. The radar system of claim 12 , wherein:

the processing device further passes the current three-dimensional location of the portion of the user to an artificial reality system that provides virtual content to the user; and

the artificial reality system modifies at least one virtual component of the artificial reality system to account for the current three-dimensional location of the portion of the user.

14. An artificial reality system comprising:

a radar mechanism comprising at least one transmitter and at least one receiver;

a signal generator that generates a frequency-modulated radar signal;

a delay mechanism that:

receives the frequency-modulated radar signal from the signal generator; and

after a certain period of delay, passes the frequency-modulated radar signal to the transmitter to be transmitted to at least one transponder located on a wearable artificial reality device; and

at least one processing device communicatively coupled to the receiver, wherein the processing device:

receives the frequency-modulated radar signal from the signal generator;

detects a signal returned to the receiver from the transponder in response to the frequency-modulated radar signal;

calculates a beat frequency that:

corresponds to a difference between an instantaneous frequency of the frequency-modulated radar signal received at the processing device and an instantaneous frequency of the signal returned from the transponder; and

is proportional to an apparent distance between the transponder and the receiver; and

calculates a distance between the transponder and the receiver based at least in part on:

an analysis of the signal returned from the transponder and the frequency-modulated radar signal received from the signal generator; and

the beat frequency.

15. The artificial reality system of claim 14 , further comprising an additional wearable artificial reality device that secures at least:

the transponder;

the receiver;

the signal generator; and

the delay mechanism.

16. The artificial reality system of claim 15 , wherein the receiver comprises a plurality of receivers that are secured to the additional wearable artificial reality device such that each of the plurality of receivers are separated by at least a certain distance.

17. The artificial reality system of claim 14 , wherein:

the frequency-modulated radar signal follows a modulation cycle that comprises sweeping linearly between a first frequency and a second frequency; and

the certain period of delay generated by the delay mechanism causes:

the transmitter to receive the frequency-modulated radar signal at a different point in the modulation cycle than the processing device; and

the instantaneous frequency of the frequency-modulated radar signal received by the processing device to be offset by a certain amount relative to an instantaneous frequency of the frequency-modulated radar signal transmitted by the transmitter.

18. A method comprising:

generating a frequency-modulated radar signal;

passing the frequency-modulated radar signal to:

a processing device communicatively coupled to a receiver; and

a delay mechanism that, after a certain period of delay, passes the frequency-modulated radar signal to a transmitter to be transmitted to at least one transponder located on a wearable artificial reality device;

detecting a signal returned to the receiver from the transponder in response to the frequency-modulated radar signal; and

calculating a beat frequency that:

corresponds to a difference between an instantaneous frequency of the frequency-modulated radar signal received at the processing device and an instantaneous frequency of the signal returned from the transponder; and

is proportional to an apparent distance between the transponder and the receiver;

calculating a distance between the transponder and the receiver based at least in part on:

an analysis of the signal returned from the transponder and the frequency-modulated radar signal received at the processing device; and

the beat frequency.