Amplitude deltas are derived as a function of Standing-Wave slope excursion
caused by target motion, i.e., the greater the motion the larger the excursion.
Excessive motion causing excursions greater than 90° results in
Note the weak amplitudes at
and the frequency doubling (folding) at D.
Optimum responses are shown by A
Far-field Diverse Wavelength,
Ratiometric Differential Interferometry
Doppler has become the generic
term used to describe these families of devices.
It is important to note that in
this application, of the two properties at play--Constructive and Destructive
Interference; and the Doppler Effect--Interference, not Doppler
is the First Order Effect.
Dual Frequency Differential Approach This Differential approach is an effort to overcome the variations
in signal strength due to SWR nulls. These variations are caused by target
position verses WL of the incident µwave energy--as represented in
the above plots.
Dual Standing Waves due to frequency shifting of the Gunn oscillator,
e.g., ~10 GHz and ~20 GHz
The Measurement is the Differential of the amplitude deltas of the
two wavelengths, measured from standing-wave slope to standing-wave slope.
The system is pulse "Doppler" and received signals are sampeled. This
is done to reduce RF exposure to the subject; resulting in nW/C2
instead of mW/C2.
Beat intervals related to WL ratios note: 100% and 75% have the longest continuos interval between beat
Remote Heart Rate Measurement System Block Diagram
FSK Gunn Osc, Detector & pre-amp
Dual Sample & Hold
for channel separation
VGAs for gain balancing,
for common artifact rejection
In order for this Differential system to work properly, It is important
that both channel's gains be equal.
Spatial Diversity Detector Array Waveguide mounted diode array with spacing between diode
mounts < 45 degrees of WL (for ease of construction, spacing can be
delta + 1 WL, i.e., 0’ + 360’ = 0’, 40’ + 360 = 40’, 80’ + 360’ =
80’, etc.). see diagram
LO injection from Transmitter to receiver is by waveguide coupling with
Separate Transmitter and Receiver Antennas
Small Pyramidal Horn antennas with beam forming dielectric "lens" (low
sidelobes) at exit/entrance. Overall size of structure to be dictated by
customer requirements. However, to aid in development, antenna should
off larger than finial version.
Potential problem areas and possible
1)_ Clutter due to motions of intervening foliage,
e.g., grasses, etc.
a. "Pulse Doppler" modulation with Range Gating
of Received signals.
b. Range Coding with secondary modulation.
2)_ Variation in system sensitivity due to target/device
distance verses WL nulls.
a. Use of dual modulation for range discrimination.
By selection of one modulation frequency, device is most sensitive in that
range cell: sensitivity increases in a linear fashion, similar to pulsed
Spatial Diversity Diode
Detector Array, using effective fractional
WL spacing (S < 45°)
Waveguide mounted diode array with spacing between diode mounts <
45 degrees of WL (for ease of construction, spacing can be delta + 1 WL,
i.e., 0’ + 360’ = 0’, 40’ + 360 = 40’, 80’ + 360’ = 80’, etc.). see
Separate Transmitter & Receiver with beam forming dielectric "lens" (low sidelobes)
Separate Transmitter & Receiver
using LO Spill-over Injection