Why my rectenna does not work correctly ?

[vlinh96]

Hello everyone,

I'm an EE student and I'm having a project about the rectenna at 2.45 GHz and -10 dBm.

My rectifier uses SMS 7630-079 LF from Skyworks as the diode for the circuit and the load of rectifier is fixed at 10 kOhm. I measured its S-parameters and the circuit is well-adapted at 2.45 GHz. However, when I measured the DC rectified voltage, I had nothing at all. Meanwhile, in ADS simulation, I could get 0.7 V for DC voltage.

Could you tell me why my circuit didn't work ? Do we have some problem with the ground or not ?

Thank you for your help.

P/S : I'm a newbie in this section.

 

[vfone]

Seems that is not much DC voltage to measure at -10dBm input power.

 

[vlinh96]

Seems that is not much DC voltage to measure at -10dBm input power.

Thank you for your reply, vfone.

In some papiers, they can rectify some voltage. Is that strange ?

I increased the input power of my rectifier (up to 10 dBm), however, I still got nothing.

A question : To measure the DC rectified voltage, we use Vdc measurement of multimeter ?

 

[vfone]

The detected DC output level depends also by the configuration of the diode detector, but if you don't get any DC voltage at +10dBm, you may have a damaged diode in the circuit. Even a single Schottky diode and a resistor (or a choke) for DC return, should get some DC voltage output at +10dBm RF input.
A DVM (digital voltmeter) which is able to measure DC down to tens of mV should be fine for measurements.

 

[dick_freebird]

How are you determining the input power?
Feeding the "rectenna" from free space and
incident radiation, I'd think tough to quantify
believably.

Applying -10dBm from a 50-ohm signal generator
I'd think defeats the rectenna-as-an-object
paradigm?

If crest voltage at -10dBm equates to 0.15V P-P
(as I make out the chart in this,

Measurement and Control of RF Power (Part I) | Analog Devices

Fig. 1. shows a typical modern communications signal chain. The signal to be transmitted is generated at baseband by a digital-to-analog converter (DAC.) This signal is then mixed up to an intermediate frequency (IF) where it is filtered before being mixed up to the final radio frequency (RF.)...

www.analog.com

then there's little reason to expect a Schottky
with ~0.3V Vf, to push any current on the positive
half-cycle (0.065V?) and especially not enough
to push a 10Kohm load around.

Check out Fig. 4 in that web page and tell us
why you think your results should be any
different than the ~1mV shown for 25C operation.

I struggled with a similar thing over a decade ago,
in the RFID-tag application space, and was glad
we lost that bid.

 

[vlinh96]

The detected DC output level depends also by the configuration of the diode detector, but if you don't get any DC voltage at +10dBm, you may have a damaged diode in the circuit. Even a single Schottky diode and a resistor (or a choke) for DC return, should get some DC voltage output at +10dBm RF input.
A DVM (digital voltmeter) which is able to measure DC down to tens of mV should be fine for measurements.

Thank you for your reply.

The diode was always alive during the measurements - I checked with the S-parameters and the multimeter before and after each measurement.

I used a multimeter whose limit is around 200mV for my measurements.

 

[vlinh96]

How are you determining the input power?
Feeding the "rectenna" from free space and
incident radiation, I'd think tough to quantify
believably.

Applying -10dBm from a 50-ohm signal generator
I'd think defeats the rectenna-as-an-object
paradigm?

If crest voltage at -10dBm equates to 0.15V P-P
(as I make out the chart in this,

Measurement and Control of RF Power (Part I) | Analog Devices

Fig. 1. shows a typical modern communications signal chain. The signal to be transmitted is generated at baseband by a digital-to-analog converter (DAC.) This signal is then mixed up to an intermediate frequency (IF) where it is filtered before being mixed up to the final radio frequency (RF.)...

www.analog.com

then there's little reason to expect a Schottky
with ~0.3V Vf, to push any current on the positive
half-cycle (0.065V?) and especially not enough
to push a 10Kohm load around.

Check out Fig. 4 in that web page and tell us
why you think your results should be any
different than the ~1mV shown for 25C operation.

I struggled with a similar thing over a decade ago,
in the RFID-tag application space, and was glad
we lost that bid.

Thank you for your reply and your article.

I connected my rectifier directly to a RF signal generator from Keysight Technologies.

"Applying -10dBm from a 50-ohm signal generator I'd think defeats the rectenna-as-an-object paradigm?" -- I don't understand this sentence. Sorry for my bad English. Do you mean that the generator can harm the final result? According to me, a signal generator is just a perfect antenna whose impedance is 50 Ohm.

Concerning the diode, I chose SMS7630-079LF because of its very low forward voltage (around 0.12 V). At -10 dBm (around 0.1 V peak), the diode can start to rectify the voltage.
However, the problem of this diode is its low reverse bias (around -2V). I'm not sure that the diode can 100% "eliminate" the negative part of signal.