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.

News

September 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:
IMG_20160927_122325.jpg

Good news is that new photos will come in better quality, as i repaired my old phone, which contains OV5640 autofocus camera module.


September 19, 2016:  Some news on VCO project.

Here 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 of half 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.
 
IMG_20160919_104923.jpg IMG_20160919_113733.jpg

Laminating machine fix.
My 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 turned 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.

IMG_20160918_125716.jpg


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.

Email: tmtlib@gmail.com