Implementation of Transmitter and Receiver for GPR

[ali_cmi]

Hello,
I am a final year student of BEE Telecom. I chose my Final Year Project to design a Transmitter and Receiver for GPR. GPR has already been developed in my institute. It uses VNA (Vector Network Analyzer) as its source.

Some features of that project are:
-> Double-Ridged Horn Antenna
-> Synthetic Aperture Radar (SAR) with UWB source (VNA) in Mono-synthetic mode
-> Only s11 (first parameter of s-parameters) was measured by VNA
-> 2.4 GHz center frequency with 1 GHz Bandwidth---a pulse with 1 ns duration transmitted by a Stepped-freqeuncy transmitter
-> Tx and Rx are in VNA
-> Only Return Loss measurements are observed
-> Data from VNA is processed in Matlab to create a rough image of observed reflections

I hope the data above is enough for you to get the idea. I have just started working in the project

Since VNA is a multipurpose device and the already-implemented project used it to find S11 only, I chose this project to introduce portability in GPR. (VNA available in my institute is bulky)

In short, my goal is to develop a Tx and Rx which function as the VNA does; thus introducing portability.

The problem is that I have no idea where to begin. I need a head start. I need to develop complete understanding of how the Stepped-Frequency Transmitter (used in already-developed project) and compatible receiver works and I have to develop the whole system without changing other features like antenna, codes etc.

Please guide me and point me in the right direction.

Also, any low-cost/medium-cost idea from you will be appreciated.

Regards.

 

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[woof!]

Ali, this kind of highly technical question will get a lot more traction on Carl Moreland's Geotech forum where more electronics geeks hang out. But you do deserve a decent response here since that's possible.

I suppose that you already know that going up in frequency improves portability but degrades depth capability. Going down in frequency improves penetration, but increases the size of the antenna array needed to do the job thus impairing portability.

It sounds like your real-life problem where you're at right now, is how to take a system that already exists at your Institute and in a few months make it do something interesting that it hasn't already done. I don't know enough about GPR to be of much help on the details. However, I can offer a few suggestions that you might want to pursue longer term if GPR is something you're really interested in. And, these suggestions might lead you in a direction that your Institute's existing system can be adapted to taking a step in the right direction.

Here are what I perceive to be the biggest problems in current GPR technology.

1. High cost.

2. Physically large and inconvenient to use, typically "lawnmower" mechanicals.

3. Signal processing results in data which requires too much human interpretation by someone who really understands what they're doing.

4. Too many soils in which penetration is so poor as to make the apparatus useless.

5. The technical things you wish you could do, half of those are forbidden by FCC & CE due to regulations written with communication systems in mind, regulations which ought to exempt GPR but don't.

I rather doubt that any one "fix" will cure all those ills. However, you may be able to make progress on one item without degrading the others, and that will be progress.

Some ideas that may be worth considering:

1. Consumer wireless communication is driving big advances in antenna designs which incorporate things like ferrites to alter wave impedance. Their big obsession is with compactness, which is a worthwhile objective for GPR as well. .......They are often trying to minimize directionality, but the same techniques can be used to increase directionality.

2. Consumer wireless communication apparatus often pays attention to the issue of diversity. Those techniques can be used creatively (for different objectives) in GPR.

3. If you're imagining a commercial GPR, it's easy to get bogged down in the problem of how to do the signal processing in the end product. Don't get stuck on that, forget what you want the end product to consist of and concentrate on what you want it to do. Prototype around a slow and mechanically cumbersome PC-based commercial (e.g. Matlab) software based system. The hard part is to make a particular antenna system and signal processing approach to deliver good results, so that's where the focus of effort should be. After you've achieved good results with that monster kluge, whittle down what you really want from it down to the bare essentials and drag additional engineers into it (if necessary) to achieve those bare essentials in economical hardware and custom software.

4. If in real life you get more than halfway through #3, you'll probably be wanting to talk with a company that's involved in underground detection. I wish you well, and when that day comes, remember who responded first to your post here and please send ol' Woof! a PM inviting discussion over the potential for commercialization.

--Dave J. (alias "Woof!")
Chief Designer, FTP-Fisher