[SOLVED] Diode for rectenna @ 2.45GHz

[lab-lab]

Hi,
I have to realize a rectenna @2.45GHz. Can you tell me which diode should work best?
I have found this family HSMS-286X (which is zero-bias)..... has anybody tried to use these diode at such a frequency?

Do you have any further/alternative suggestions?
thanks

 

[jiripolivka]

You are right, I tested those diodes connected in a dipole. They are good as detectors or rectifiers. I would estimate they can achieve ~40% efficiency with up to ~10 mW output power.
An alternative solution I found with BAR-12 from Siemens, it is also a Schottky but of a larger size (glass envelope), so it can rectify up to ~13 dBm or more with a good efficiency.
For power transmission, a rectenna matrix may be used, comprising many dipoles with diodes, connected in series and parallel as needed. But to transmit a reasonable power like >1 Watt, I do not see a suitable rectifying element for 2.45 GHz.

 

[lab-lab]

Thanks a lot for the info..... do you happen to know which should be the lowest detectable power @2.45GHz...and also @860MHz?
Thanks!!

 

[jiripolivka]

This detector parameter is called TSS, "tangential sensitivity". It is determined by ~1 kHz modulated signal, distinguishable on an oscilloscope screen from noise. With a good detector, TSS typically is ~ -35 dBm; by using a narrow-band selective amplifier for 1 kHz, you may get even better.
At 860 MHz, detectors with Schottky diodes can be a bit better than at 2.45 GHz.
But at both frequencies you can use a low-noise preamplifier, and for the extreme demands, a radiometer is suitable. Then we do not speak about the lowest detectable power but our measure is noise temperature ( T = P/[k.B]) and temperature resolution.

 

[lab-lab]

Thanks a lot for the useful tips!... being a newbie of this kind of circuitry, I still have some doubts on which precise diode model should be more convenient?
And in which configuration? series, common cathode....)

Thanks a lot again for sharing your experience!

 

[tony_lth]

Through simulation, you will know better these diode.

 

[lab-lab]

I read on a datasheet that the HSMS-286X family should be used with an external bias @2.45GHz, in small signal detector applications.
Can anybody suggest an alternative that works at zero-bias, @2.45 GHz for low power (<-20dBm)?

As of now, I came up with these possibilities: HSMS2852, HSMS2860, and HSMS 285C.
Any other suggestion?

thanks

 

[jiripolivka]

Dear lab-lab:

I cannot offer you the details: I made a rectenna test setup for the JH university, to test various diodes of HSMS 286 series. In a dipole I made a holder to clip in such diode; some HSMS diodes have different arrangement in plastic enclosure. Testing a single diode I think is best but you can try to connect diodes in parallel or in series, to see what happens.
To detect the low power like -20 dBm, DC-biasing the diode may be good for sensitivity. The difference between making a sensitive detector and making a power rectifier is quite big. Be ready for experiments.
I am not used to modeling; I prefer to make experiments with simple setups, to see the real world.

 

[lab-lab]

As a matter of fact, I have to implement a power rectifier... however, the in-coming power is very low (approx. -30dBm).
In your opinion, and without giving away confidential details, is there a diode that can function without bias at 2.45GHz?
RIght now, I do not have limitation regarding the output power ..... obviously, the higher the better
Thanks for any help you may give

 

[jiripolivka]

As I wrote, there is a big difference between a "sensitive" detector, for the RF input levels like -20..-30 dBm, and a "power" rectifier, with RF input levels > 1 mW.

A good RF Schottky diode like the mentioned HSMS from Agilent or BAR-12 from Siemens can be good with the low levels as those are zero-bias diodes. Using a DC bias with a forward current of several uA may be good, but the RF signal should be preferably AM modulated, so you can retrieve the modulating signal by a selective video amplifier after detector.

Detectors like those using ZBS Schottky diodes have a "quadratic" response up to ~-20 dBm but a "linear" response up to 0 dBm, then they rather are limiting. Also video load resistance should be adjusted, from 1...10 MOhm for low-level operation, to <1 kOhm for high-power rectification.