Pharos matches a dynamic directional (beam shaping) radio on the air with another on the ground, with the two tracking each other for multi-mile range for video and telemetry. Coming to Kickstarter in 2-3 weeks.
The Pharos is a newly-developed smart antenna. Unlike conventional omni-directional antennas that waste energy in all directions, the Pharos concentrates the available power where you need it most. Working in conjunction with the Pixhawk autopilot (a version with its own autopilot is being also developed), the antenna activates the side facing your UAV, boosting reception and range. A second Pharos can also be used on the aircraft, quadrocopter or UAV, keeping ground control in aim at all times. The Pharos is also circular-polarized, granting immunity to polarization losses and multipathing signals, an optimum choice for challenging environments.
Air:
Ground:
Comments
Antenna size is an issue, lower the frequency and your antenna gets bigger. However a slot antenna might work? Radio is all about the antenna and much less about the radio.
MCX
@ Hugo, Yes, you’re right. The physical 360 yaw maneuver to determine the highest RSSI I mentioned above can be replaced with a digital cycling of the antennas every x seconds. This way you get a match faster heading determination towards HOME without needing to maneuver the frame a.k.a. smoother trajectory.
Right Hugo!
The pharos could also scan all antennas and compare their RSSI value. With the RSSI of the 3 best antennas, the direction of the GS can be triangulated. The drone then start moving in that direction and re-scan every few seconds to re-adjust trajectory.
-Hugo
@ Monroe King, That’s interesting. Like you said the multielement antenna was not build for this purpose but with some hacking (firmware related) I guess it’s possible. Let’s see:
If for example, you lose GPS, the GPS failsafe will put the drone in AltHold mode by default. Then a preprogramed 360 yaw turn can be programed as part of the GPS failsafe to determine the highest RSSI (towards the ground station). The highest RSSI will occur when one of the corresponding antennas faces the GS and it will determine a specific compass heading (not bearing as the bearing requires GPS location of the drone).
At that point, the FC (still in Alt Holt) issues this heading so the drone flies towards the generic location of the HOME point. This “modified RTL” is prone to wind drift as GPS location is not available but subsequent 360 yaw maneuvers can be preprogrammed to determine the highest RSSI every x seconds and refine the heading to HOME.
At the final stage when the drone is visible, the pilot can either take manual control or issue a LAND command as soon as the drone is close enough.
The process above is the fundamental direction finding principle based on RSSI. I never thought of this possibility and my thought process might have flaws but I think it’s doable. In our current set up we get readings of both the drone and GC RSSI. See the video on page 3. The RSSI readings are just below the artificial horizon.
Here is a thought! With this type of antenna you might be able to get a vector you could use for navigation in case of LOS of GPS or compass? I understand right now it does not work that way but it could be made to do so?
@ Andy Little, Thanks. We think we just touched the surface of the solid state antenna trackers. These circuits can be found on sophisticated equipment so far i.e. airborne radar antennas, so our goal was to bring this technology to the consumer level and especially the drones. The small size and low power consumption of the solid state antenna trackers makes it possible to equip drones with tracking antennas as this was a privilege of only the Ground Station units up until now.
About your consideration of the antenna size Vs your smaller airframe:
You can try to disassemble the antenna enclosure (4 screws) and take the antenna elements apart. Then place each antenna element at the 4 cardinal points of your airframe i.e. nose, tail, left wing, right wing and the antenna controller at the middle of the airframe, connected with your radio. You will need 4 extension coaxial cables to do so. With this hack you can save some space (and weight) and have a more customized solution that will boost your 5.8GHz range.
Some of our drones are modified as described above so the antennas and controller are integral part of the airframe.
@Magnet Systems
It certainly looks interesting. I can see a use for the solid state ground Antenna tracker part, though a traditional higher gain antenna should give better range, but is more bulky and fragile. For the airborne part, at least for the size of aircraft I fly, it is a little bulky, but for larger aircraft I am sure it will be very useful.
I think you have an interesting product!
@ Andy Little The total losses are low (0.8dB) as we have been using a 4-layer PCB with Rogers material for the antenna controller circuitry, ideal for this specific design.
We thought of Phased array but this wouldn’t solve the problem of 360 coverage as you would still need 4 antennas. So we end up to the switching technique which is simpler but when combined with the X-air antenna (perfect axial ratio) does not leave any blind regions a.k.a. the RHCP is retained in the whole BW of the antenna. Combining this with the rapid antenna switching time (5 microsec) you get a 360 coverage with the gain of the X-air (10 dBi). You can call that Hybrid-omni as this is what it actually is.
For example, look at the previous page video on sec 4:52. At that point we issue a “point camera here” command to the right of the drone and the whole drone yaws 90 degrees to the right (we use a 2-axis gimbal so the drone needs to yaw). This is the point when the antenna switching happens. You will see no fluctuations on the video streaming or telemetry quality. This is a result of the rapid switching time.
The antenna dimensions are 7x7x7 cm which is actually a cube with a side equal to the surface of an X-air antenna.
Yes, we considered the mechanical gimbal and we have been using a mechanical tracking antenna unit for quite some time integrated to our Ground Station. Take a look here: http://www.adcormagnetsystems.com/gcs.html But this is not the optimal set up especially for the drone due to weight, complexity and power requirements. The Pharos antenna is a motorized antenna replacement with no moving parts, 65 gr of weight and only 20mA of current draw. At the picture below, you can see the Pharos antenna attached to the tablet GS tablet (White Pharos with blue LED) and on the drone a black Pharos is attached underneath. Actually the one attached to the drone is a modified Pharos that includes a camera producing the spherical vision that you can see on the big screen at the back.
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