IEEE Microwave Magazine - October 2016 - 73

Gain (dB) or Return Loss (dB)

substrate was selected (31 mil)
in conjunction with a few more
Simulations with Lifted Ground
35
grounding substrate vias un30
derneath the SMT part, which
25
proved stabilize the part in
20
the simulator.
Additional Via Inductance
15
Another interesting but
2.506
GHz
10
common issue we encountered
1.665 dB
5
was the effect that power sup0
plies can have on total RF radar
-5
system performance. Figure 20
-10
shows the transmit spectrum
of the RF chain when a hobby-15
ist power supply was used for
-20
the RF core. When compared
-25
1
1.5
2
2.5
3
3.5
4
to Figure 17(a), the sideband
Frequency (GHz)
skirts of the transmit tone can
be seen coming up with draGain Manufacturer's Output Return Loss
Gain Lifted
Output Return Loss
matic shoulders due to the
Data
Manufacturer's Data
Ground
Lifted Ground
additional noise produced by
the inexpensive power supply.
These sideband noise skirts Figure 19. The schematic and simulation of the PA on a thicker RF-4 substrate.
cause very serious degradation
in the radar sensitivity (which
is why military and aerospace companies spend significant design effort in creating spectrally pure and lownoise power supplies and oscillators for their systems).
The original OCW system used batteries, which avoids
this issue totally and produces purer tones, such as the
one in Figure 17.

Conclusions
An entire FMCW radar system was fully designed in
an EDA tool from system concept to layout so as to
facilitate the creation of a new radar RF core having
better performance, lower cost, and a smaller footprint and that is more easily mass-produced than the
original MIT OCW coffee-can radar. An EDA system
simulator provided the ability to easily compare the
system performance between the original coffee-can
design and the new re-caffeinated system for both
RF link and time-domain simulations, as shown in
the various figures and in Table 2. Built-in radar
library elements facilitated the building of the target
model and also the baseband processing.
A full radar PCB RF core was created, including EM
analysis of the planar antennas, and the entire system
was built and assembled. A system, circuit, and EM
cosimulation encompassed the entire radar, including
antennas, board coupler, attenuator, LPF, and amplifiers and mixer. This cosimulation was used to verify
the FMCW radar performance with various target configurations in a time-domain simulator with baseband
processing performed using both MATLAB cosimulation and built-in baseband processing blocks.
For more detail, this design project will be included in
a future release of the NI AWR Design Environment, and

October 2016

Figure 20. The effect of a cheap power supply on a
transmit signal.
readers are invited to open it up, play with it, redesign
it, and improve the system design. A video of the initial
version of this application, as presented a 2015 International Microwave Symposium's MicroApps session, is
available at https://youtu.be/DB5TkXgpaW4.

Acknowledgements
We thank John Carroll for assisting with the measurements and Debra Gomez for helping prepare the
graphics in this article.

References
[1] D. Schneider. (2012, Nov. 1). Coffee-can radar: How to build a synthetic aperture imaging system with tin cans and AA batteries.
IEEE Spectr., vol. 49, no. 11. pp. 24-25 [Online]. Available: http://
spectrum.ieee.org/geek-life/hands-on/coffeecan-radar

https://www.youtu.be/DB5TkXgpaW4 http://http:// http://spectrum.ieee.org/geek-life/hands-on/coffeecan-radar

Table of Contents for the Digital Edition of IEEE Microwave Magazine - October 2016