mobile antenna as a rectenna

Rather than a diode voltage multiplier which is lossy, I would try a RF tuned transformer (autotransformer) before a simple rectifier.

ok.and can the antenna be used as a rectenna.i mean its already tested and had high gain?

For best results, use a non-resonant antenna so it can pick up all wavelengths and use super fast rectifiers, preferably ones with low capacitance and switching speeds faster than 1nS. You will get more voltage if you use diodes with Vf lower than 1mV. Mount them to a good heat sink if you are going to draw more than a few Amps.

Good luck!

Brian.

ok i will for sure
tomorrow i am going to get the components
and i will be taking your guidance here in this thread if i have some problem

Oh no......

Brian.

oh no for what?

Before rushing out to buy components, tell us what you are expecting from the rectenna. You will not find the parts I stated although the specifications are what you would need to do anything useful with the power you would harvest.

We get lots of messages posted here from people who expect to power a city from electricity harvested from an old telescopic antenna, salavged from an old radio. If this is what you want to do, stop right now! The amount of energy you will be in the micro-Watts range and of no practical use for anything. For example, in experiments I did here some years ago, with a 50m long wire, antenna tuner and properly matched tuned circuit I could *just* get a glow from an LED when viewed in total darkness. That is from a 50KW transmitter about 5Km away. I consider myself lucky to get that much, even after many hours of trying.

Brian.

i want to run a temperature sensor placed at a distance of a maximum of 10 feet from the mobile transmission tower (BTS)

What are the feed specifications of your "temperature sensor"?
If such device needs several milliwatts DC input, use a rechargeable battery and a programmable timed operation, say once per minute or once per hour. Then use the rectenna to continually recharge the battery.
If the rectenna is located close to the BTS, you have a good chance to succeed. Using a monopole quarter-wave antenna with a Schottky-diode rectifier (use a RF mixer diode) can generate 2...3 V and 1-2 mA into the battery. You will need to experiment with positioning the antenna so the diode will not burn and deliver a reasonable powe into the load (battery). You can add a reflector or use a dipole tuned to BTS frequency band.

I would also add a tuned circuit after the tuned antenna or you may find the rectifier is generating and radiating harmonics of the BTS signal. Also be careful working only 10 feet from the transmitter antenna, the RF field intensity will be quite high. Also consider that in some countries it would be considered theft! A small PV panel would really be more appropriate in this application.

Brian.

can i use antenna of a smart phone as it is already tested and will save alot of time

You said a BTS not a cell site. You need an antenna tuned to the freq of the BTS transmitter

Dave

ok my mistake but here in pakistan we call cell sites BTS
ok cell site ..if i use it near a cell site then can i use the antenna of a mobile phone?

You can but I think you underestimate the need for microwave style of construction. If this is only 10 feet away from a mast, wouldn't it be easier to connect to the masts power supply?

I have a remote temperature sender here, a DS18B20, a PIC12F1822 and a tiny 433.92MHz transmitter module. It runs night and day from a solar PV panel, and only draws 5mA in a 200mS burst about once per minute, the remainder of the time it draws less than 10uA. The rechargeable battery keep it going all night until it can recharge the next day. All built in a small 'cigarette packet' sized plastic box with the PV glued to it's lid. It is much easier than the rectenna system you propose.

Brian.

from mast do you mean mobile site?
the thing is that i have chosen it as my final year project and i will have to do it via this mode all i need is some guidance in antenna design so that atleast i can receive a minimum voltage of i mV



the thing is i am not underestimating the MW.
its just that i want to do it in a new way.

having a pickup antenna at / near the base of a cell tower is going to be next to useless. The RF field there will be extremely low
The antenna arrays of a cell tower are designed to project the RF field out at a particular angle ( radiation pattern) to achieve the desired coverage from that tower
RF being angled directly down towards the base area of a tower is a waste of energy and it wont be done

You are seriously underestimating the possible received power levels,as cell towers don't have an overly high ERP for a start, probably average less than ~ 500W

That's why we wanted the BTS clarification because Broadcast Transmitter Sites are up in the 10's to 100's of kiloWatts and RF fields around the towers is quite high

cheers
Dave

so what should i do?

solar energy is a god solution, it's not easy as your final project.

but now i have picked it and i will have to do it so please guide me in designing an antenna which can receive a minimum 1mV at a distance of minimum of 40 meters.