UWB Transciever Design

[ali_cmi]

Hello all,
Its Ali here. I am a Electrical (Telecom) Engineering student and my Final Year Project (FYP) is Portable GPR in which I am designing UWB transceiver. Currently I am working on the transmitter part.

Here are a few specs of the design:
-Simulation Software: NI Multisim 12.0.1
-Its an Impulse Radar with Bandwidth of 1 GHz centered at 500 MHz (currently)
-I used the logic of NORing a clock with its inverted delayed version, giving an approximate Gaussian Pulse of duration 1 ns. Clock decides Pulse Repetition Frequency (PRF). Its frequency is set to 100 MHz currently. (Idea from the Paper I am following)
-I generated the ref using AD 8009-ARZ, a high speed Op-Amp and generated the inverted version of it using the same op-amp.
-I made the NOR gate by generic transistors (FETs). (Please guide about practical transistors I should use)
-I haven't designed the pulse amplifier yet (current output voltage)

First of all, please comment on the approach I am using i.e., is it okay to generate clock using Op-amps? Is there

any other better way? etc.

The problem(s) are as follows:

-Antenna Design (Vivaldi etc.) on frequency of 0-1 GHz yields an impractical design. I thought of designing an active modulator to ease off the antenna design but have no idea on how to do it. Please help me in this matter.
-Choice of transistors for NOR gate.

What, in your opinion is the best approach to tackle this project?

If anything I wrote above isn't clear, please say so that I can elaborate it/provide visual aid.

P.S: Please don't quote number of results of google by just typing 'frequency multipliers' or anything else like that. I have done my homework on this.

Also, the more you elaborate, the more I can understand as I am quite an amateur in this matter.

Thank you in advance.

[Davor]

Regarding the fast logic, seek ECL circuitry, or if you insist on FETs try SCFL. There are MESFET logic families dedicated for 10Gbps optical communications.

Good luck with 500MHz as a centre frequency.

[ali_cmi]

Regarding the fast logic, seek ECL circuitry, or if you insist on FETs try SCFL. There are MESFET logic families dedicated for 10Gbps optical communications.

Good luck with 500MHz as a centre frequency.

Hey Davor, thank you for replying.

By your way of saying, I guess 500 MHz is a wrong choice, right?

I'll try what you mentioned here and post here.

This band 0-1 GHz is causing antenna design problems as i said. Any views about that?

[Davor]

Yes, it contradicts the purpose and the means. A serious wideband antenna has 1:2 frequency coverage. It also has negligible gain, which is of not much consequence for you.
If you pick some of the Satellite TV bands for your purpose, you'll find off the shelf LNAs dirt cheap, fitted in a handy housing that comprises a wideband antenna and supplying signal ready for detection. If you place a Gunn diode in such illuminator you'll have RF part ready.

[ali_cmi]

Yes, it contradicts the purpose and the means. A serious wideband antenna has 1:2 frequency coverage. It also has negligible gain, which is of not much consequence for you.
If you pick some of the Satellite TV bands for your purpose, you'll find off the shelf LNAs dirt cheap, fitted in a handy housing that comprises a wideband antenna and supplying signal ready for detection. If you place a Gunn diode in such illuminator you'll have RF part ready.

Your views mean a lot. Would you be kind enough to elaborate this 1:2 frequency coverage thing. (I am an amateur, as I said)

What frequency band would you suggest so that I may shift my design to that frequency?

[Davor]

It is your FYP so you better see what you can scavenge on a scrapyard first.
Check the literature for TEM horn wideband microwave antenna. You'll find that 3GHz and up are favourable regarding the antenna construction. Maybe the best thing you can do is just walk to the microwave lab in your faculty/university and ask for a quick tour. Some of these constructions can be incredibly simple to build. WiFi cantena is a nice example of a microwave antenna in disguise.
Otherwise, use whatever off the shelf or scrapyard devices you can fix.

[ali_cmi]

It is your FYP so you better see what you can scavenge on a scrapyard first.
Check the literature for TEM horn wideband microwave antenna. You'll find that 3GHz and up are favourable regarding the antenna construction. Maybe the best thing you can do is just walk to the microwave lab in your faculty/university and ask for a quick tour. Some of these constructions can be incredibly simple to build. WiFi cantena is a nice example of a microwave antenna in disguise.
Otherwise, use whatever off the shelf or scrapyard devices you can fix.

I am on it. We have a 2.4 GHz Pyramidal Horn Antenna available in Lab.

I wanted to use it but generating that high frequency and pico-second pulse is a daunting task in itself. That's why I moved to 0-1 GHz. Now when I saw antenna design results being monumentally impractical, I am down to zero and struck badly.

The real problem is generating a band of 1 GHz around 3 GHz.

About the scrap yard, the region where I live is third-world. We rarely see the items you stated. But, I am going for it now.

[pelanj]

I think Davor meant he university scrap yard - I have found a lot of useful things there Anyway, I imagine having a 2.4 GHz oscillator, amplifier, etc. is quite easy, as there s WiFi, Bluetooth etc. in the band. Even the satellite receiver tech (GHz) is like 20 years old. What exactly are you trying to achieve? I am by no means an expert on this topic - but I think that the operational frequency is not that much important (in a range), it is more about how to extract the information.

Are you trying to replicate a GPR or are you taking a different approach?

[Davor]

The real problem is generating a band of 1 GHz around 3 GHz.

No it is not. If you apply a Dirac to a filter, it will respond by it's full frequency response. What you thought of was a baseband from 0 to 1GHz. Now just translate it to, say, 2.4GHz. The pulse envelope should remain the same. From the Tx source point of view, antenna is yet another filter. You should really check the TEM horn.

BTW, why don't you simply check the existing GPR project and build your thing from there. I'm sure you'll find lots of horn antennas laying around the microwave lab, and with some guidance it will not be that complicated. At my faculty everyone is just crazy about meta materials, and those boring horns are just using up the space

[ali_cmi]

Let me clear about the previous GPR project thing i stated.

Last batch in my institute developed GPR prototype. They used VNA as a source. It was first of its kind here. As VNA is a bulky device (not talking about the handy ones), I chose to replace that VNA (just the UWB transceiver module of it) by designing my own one.

Being an undergrad, I have next to none experience in this kind of work but my interest drove me to do it. I have been at it since june of this year and to be honest, for people who want to see results, I have done nothing (but research which has no credit)

This is the first of its kind project here.

[ali_cmi]

Hello Pelanj,

I believe the above post cleared my objective.

I am basically trying to replicate a GPR source. And of course the frequency range should be such that I should be able to see something hidden in ground upto (0.5m).

So, please share your valuable experience.

[ali_cmi]

No it is not. If you apply a Dirac to a filter, it will respond by it's full frequency response. What you thought of was a baseband from 0 to 1GHz. Now just translate it to, say, 2.4GHz. The pulse envelope should remain the same. From the Tx source point of view, antenna is yet another filter. You should really check the TEM horn.

BTW, why don't you simply check the existing GPR project and build your thing from there. I'm sure you'll find lots of horn antennas laying around the microwave lab, and with some guidance it will not be that complicated. At my faculty everyone is just crazy about meta materials, and those boring horns are just using up the space

Yes, I told you that 2.4 GHz horn is available in lab and now I plan to use it.

The point of my post is what you stated, I have an idea that I need to shift the baseband signal I have generated to 2.4 GHz but the actual question is how to do it practically.

The antenna design, thankfully, opened my eyes to the fact that I need to do the modulation-thingy to use the already available antenna.

The fun part is me playing with HFSS Antenna Design kit. The antennae corresponding to my current frequency range have parameters in several meters. and its worrying as well.

[ali_cmi]

One more thing, I have to use something 'active' in my design now as power levels are monumentally low. I need at least 4-5 Watts of power.

[Davor]

5W in pulses, I guess. A Dirac is a nice pulse - thing, so if you just filter it a bit prior to feeding the antenna, you'll get a nice pulse packet in the air. Ask someone in a microwave lab to point you to the right direction with microwave filters.
Check if they have any spare Gunn diodes, and see about power rating. Those can be easily gated by short pulses too. Prior to PSK and QPSK the microwave links were pulse gated Gunn diodes. Pulse bandwidth is nicely reverse proportional to it's duration, and here you go.