Doktoranden Vortrag, Bistatic Radar

8/14/2019 Doktoranden Vortrag, Bistatic Radar

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Doktorandenvortrag

Slide 1--------

Gentlemen,

I welcome you to my first presentationof a series of presentations to followabout a special type or radar.

It is a combination of two main featuresthe bistatic and polarimetric Radar.

In short terms bistatic simply meansthat transmitter and receiver arephysically separated.

Polarimetric means that the oscilationplane of a propagating electromagnetic

wave is used for gaing informationform an object to be detected.

Today, in this presentationwe will concentrate on the systemand realisation principles.

In the foregoing and preparations ofthis presentation, I made a patent searchto investigate the state of the art atthe german patent office in Munich.

For the term 'bistatic radar',

I found a total of 58 applications, whichis a rather moderate number.

For the combination of polarimetricbistatic radar there was no application found.

In the communication area, theacivitiy in radio networks and bluetoothbecame apparent.

Especially for today, I have selected twoapplications, one which has been latelydisclosed from German Space center and a

more sophisticated applicationfrom l'etat francais, which is quiterecent and very attractive.

Interesstingly, there are only a fewpatent families, and applications lack toshow a specific stragedy or featureslike net patents which used in other areas.

Furthermore, I found that the applicationsin this technological field appear to be


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very intuitive on the one hand andhave a high informational and educationalvalue on the other.

Also, it seems that scientists are notused to write patent disclosures, althoughin some aspect they have to be more clearly.

So, if anybody has some questionsabout this field, I might be ableto answer them.

Slide 2-------Now, lets take a look on the overviewon this presentation.

%First, note that these slides are%made or should be made%selfexplanatory and illustrative

%so

Starting the circle from History,we will first regard a conventionalmonostatic radar, its measurementsequence and polarimetric capabilites.

Next, a bistatic arrangement willbe considered in view of the scattering matrix.

Then, considerations towardsfull polarimetric measurment will closethe circle.

Slide 3-------

From the evolution there are some anmials whichare a good example for the radar conceptrealized in nature, in the sense of echo-locationor even using polarimetric information from sunlight.

In the nasciturus days (a nasciturus is an unbornchild) of radar, experiments, especially reflexionmeasurments from solid objects where conductedusing spark gaps in the last quarter of the 19th

century following the forcast of electromagnetic waves.

As a pioneer, Tesla formulated the bistatic ideafor detection of objects.

In the 1930, the bistatic concept was developedand in the preparation of world war II, propagationeffects and its influene in performance werediscovered, and the interaction of chargedparticles.


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Slide 4-------

During and after the war, bistatic systemsvanished, partly due to technical advancement

Now, what is most interesting in the bistatic quarter,is the socalled revival which is a revival

every twenty years.

Today, radar has entered commercial applicationsand might play an important role in the anti-terrorcampain. Also, base station of wireless communicationnetworks can be used as illuminators.

On the right hand, you see an application usingtwo monostatic radars which track the trajectoryof an helicopter.

Slide 5

-------

In the upper portion of the figure,you see a transmit branch andin the lower portion, you see the receivebranch.

The signal to be used is generated by an intelligentsynthesizer which consists of a DSP with wave tableand is capable of generating several kinds ofsynthesis, like pulse code modulation, pulswidthmodulation, two state phase shifted keying, apseudo noise sequence or any numerical oscillation

from a function table.

The signal is made complex, filtered, the quadratureis formed, it is summed and than shifted into theoperation frequency range by using a ring modulatormixing a signal from a local oscillator as carrier.

After final filtering and signal conditionthe signal is amplified by a high power amplifier,and than, the antenna is fed to radiate the signaland illuminate the target.

When the scattered signal is received, it passed

through a limiter, is amplified, conditioned anddown-shifted into the intermediate frequency range.

After some sample/hold blocks, the scatteredsignal can be processed and displayed.

Slide 6-------

In this conventional


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monostatic arrangements wehave to adress three componentswhich may limit system performance.

The first problem isthat we have only onechannel and one antenna,where we can only transmit and

receive in a time divisonmultiplex manner.

The second problemis the circulator which hasvery essential impact on thesystem behaviour

And the third problemthat is the protectioncircuit which has toprevent the reception circuitfrom blowing, because

we have extremelydifferent power levels

In consequence polarimetricoperation is possible butvery limited.

An advantage of the monostaticsystem is that the transmissionand the reception angle

are equal, and geometry iseasier to understand.

Slide 7-------

Now, let's take a look on an operationcycle.

In this example I have dividedthe complete cycle in roughly ten parts.

We start with a transmission burst whichmay be a chirp or the like.

After some settling time for the systemthere is a receiving window.

And next, there is a dead time.

In this pulse repetition cycle,

the effictive reception time is about 60 %


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of an operation cycle.

Thus, for fast moving objects the measurmentmight be still sufficient,but for polarimetric measurments,it takes quite a lot time to stepseveral polarisations.

Thus, there must be a buffer memory and so on.

Slide 8-------For improving the latter arrangment to becapable for polarimetric measurments

we can provide a two antenna system whichis alternatively switched.

For a complete cycle, the total duration

of 1000 T was assumed, because the systemstanding behind the arrangment, e.g. asignal processor has around 1000 clock cyclesfor computation.

The sequence is horizontal sendingreceiving horizontal and then verticaland the same for vertical sending.

Because of the settling and switching times,there is approximately 600 T free time,

which can be used for computation,

but the effective polarization activesensing time is only 0,4 per cycle.

slide 10--------

Thus, a bistatic system could be takeninto account to overcome this limitations.

This arrangent differs from the monostaticone before in that we have

two antennas, no circulator, no limiter.

These antennas may be also differently designed.

Now our intelligent waveform syntesizercan be used more advantageously,

and on the receiver side I


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alternatively provided a digitaldemodulation circuit, which does allthe demodulation in the intermediate frequencyrange by using a band with samplingand no anti aliasing filter.

Note that we can now transmit and receivewith high power or low noise, respectively.

Slide 11--------

Now, we come to one of the centralaspects of a bistatic system,the so called bistatic triangle.

In the upper figure we have thebaseline, the transmitter on theleft and the receiver on the right.

The spacing or distance is L

Now we have the object elevatedin the sky which moves on a socalledisorange contour.

This is a path or trajectory followingan ellipse.

An ellipse is an elongated circle,a sliced cylinder.Remeber lisajous' figures

using an oscilloscope withhorizontal and vertical input,

where we input a parametercurve using

to orthogonal signals withdifferent amplitude.

The ellipse is the geometricallocation for which the sumof the distances from the twofixed points is constant

and equal to the majoraxis of the ellipse.

In this recursive definitionwe have the fixed pointsas our transmitter andreceiver.

Therefore, as long ourtarget moves on this isorangecontour, the distance


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characteristics of the objectare equal.

When moving along said contourthe bistatic angle, which isan very important propertyis changing.

Now, for the operation.

The transmitter illuminatesthe object and the interactionof the object with the radiationis received.

Therefore the timeto travel can be differently,and is the sum of thetransmitter-to-objectand the object-to-receiver distance.

Although the presentation has beendescribed with reference to preferred examples

workers skilled in the art will recognize that changesmay be made in form and detail without departing fromthe scope of the patents.

For example, all of the various functions andcircuitry described hereincan be implemented in any appropriate circuitryincluding software, ASICs, special logic techniques, oreven analog implementations.


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Doktoranden Vortrag, Bistatic Radar

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