My RF/DSP projects and publications
July 25, 2016
I have created this page to share my knowledge related to electronics and
computer programming. Materials provided here might be
useful for students, engineers and other researchers. My intent is to organize my knowledge, get some
feedback, show my capabilities to potential employers.
NewsSeptember 27, 2016: HMC363 prescaler burnt out.
Few days ago my prescaler stopped to work. HMC363 IC burnt out while
doing frequency measurements using small wire probe. It seems that too
much power was coupled to prescaler board through the probe. No more
readings on frequency meter. Here is the photo of my prescaler board:
Good news is that new photos will come in better quality, as i
repaired my old phone, which contains OV5640 autofocus camera
September 19, 2016:
Some news on VCO project.
is prototype of 5GHz VCO on generic
1.0mm FR4 substrate. Main build blocks are FET transistor, microstrip
hairpin resonator and varactor diodes. Few hairpin resonators was
manufactured on a PCB without ground plane, so they could be cut out
and positioned to match phase oscillation conditions. My idea was to
use 5GHz first harmonic to build X-Band VCO which can be used for FMCW
sensor. After prototype is done several problems are found. One of the
problems is temperature frequency drift. Heating PCB from 25°C to ≈
80°C leads to ≈ 160 MHz frequency drift at 5GHz, so useful tuning
bandwidth is reduced. Varactor diodes must compensate temperature
frequency drift and still provide some margin for FMCW modulation.
HMC363 divide by 8 prescaler and 2.7GHz frequency
counter was used to measure oscillator frequency at 5 and 10GHz.
Currently I do not have
other measuring equipment. As prescaler was connected
through 20dB microstrip coupler, i conclude that 10GHz microstrip
band-pass filter performance is acceptable. SIW slot antenna
performance is good at 10GHz, more measurements will be
performed. Relative dielectric constant at 10GHz of used FR4 material
is Er = 4.2. It is confirmed by using 10GHz dielectric resonator
positioning. 5200MHz hairpin resonator was replaced by 10500MHz
dielectric resonator. The same frequency is obtained each ≈ 7.8mm. It
is approximately half wavelength 50Ohm microstrip line at 10500MHz on a
1.0mm FR4 substrate. In parallel feedback configuration DR displacement
wavelength results in 180 degree shift in both microstrip "arms", which
gives total phase shift of one wavelength. I conclude that microstrip
resonator oscillator is better to build on Rogers substrate, while
dielectric resonator oscillator can be build on generic FR4 substrate.
Using Rogers substrate requires to minimize board area, because it
affects cost very much. Prototyping on Rogers substrate is also much
more expensive compared to FR4 substrate.
Laminating machine fix.
laminating machine control circuit board was broken, resulting in
random LED blinking and constant heating. In my opinion schematic is
unnecessary complicated, moreover PCB have two cracked traces and DIP
soldering points which peeled off. Thermocouple is potentially exposed
to electrostatic discharge from laminating sheet, and it seems that
control IC is not protected from such discharge. Mechanical part is
pretty good. Motor and heater work directly from 220V AC. I cut out
control circuit board. To temporarily fix laminating machine, I
connected motor and heater directly to power line. Heating element
connected to power line through "on/off" switch. Thermocouple is
connected to multimeter. Around three thin A4 sheets could be laminated
while multimeter shows resistance of R ≈ 15 KOhm. Then heater must be
on for around 10 seconds to heat up laminating rollers a bit. At power
on around two minutes are required to heat up laminating rollers.
This is an A3 laminating machine, so it has pretty large rollers, which
cools down slowly.
August 16, 2016
Currently I am working on proof of concept project of cost-effective
microwave sensor system. It must be not only cost-effective, but easy
to assemble and require minimal or no tuning. Main parts are VCO,
mixer, antenna and DSP circuit. Preliminary layout design of VCO is
done already and prototypes performance will be evaluated this month.
Experiments on substrate integrated waveguide slotted array antenna
(SIW) and patch array antenna will be performed. Another important
application of SIW in this project is to realize effective inter-pcb
transition of microwave signal, which will allow to use single layer
PCB without coaxial interconnections between boards.