Implementation of Doppler Radar

Transcription

1 Implementatin f Dppler Radar Applicatin Nte Justin Erskine ECE 480 Design Team 5 Executive Summary Dppler radar is an easy and effective way t measure relative speed. With the ability t make smaller antennas, Dppler can be used in multiple mbile ways. Data btained can be used fr just raw data r in ther mre integrated ways.

2 Table f Cntents INTRODUCTION... 3 BACKGROUND... 3 IMPLEMENTATION... 4 CONCLUSION... 6 REFERENCES... 7

3 Intrductin The Dppler Effect has been characterized fr a lng time nw, when it was first bserved fr sund waves. This effect has been used fr very practical purpses by applying it t electrmagnetic waves. It is a very useful way t determine speed alng with ther applicatins in a system. This applicatin nte will g ver several ways t implement Dppler radar in a way that is useful fr a particular system. Backgrund Dppler radar uses the same principles discvered by Christian Dppler when bserving sund and applies them t electrmagnetic waves. In general, the Dppler Effect is a shift in frequency perceived by a receiver frm a signal surce due t relative mvement f the surce and/r receiver. The mst bvius way t see hw this can affect electrmagnetic waves is hw astrnmers use the clr shift frm light waves travelling frm astral bdies t identify the speed these bjects are mving away r tward the Earth. Fr a Dppler radar system, a knwn frequency signal is transmitted frm an antenna which is pinted at a reference bject. A separate antenna is used t receive the signal that is reflected back frm the reference t measure the Dppler shift f the signal. The basic frmulas used frm here are as fllws: f r = v± v f v± vs Heref r is the received frequency, f the surce, v s relative speed f the surce, v the bserver speed, and v the speed f the waves in the medium. Fr practical purpses the difference in frequency is used fr calculatins. f = f r f Figure 1 belw shws an example f a basic blck diagram fr a Dppler mdule:

4 Figure 1: Dppler Mdule Blck Diagram Implementatin A simple Dppler mdule, als called a micrwave mtin sensr, can be easily integrated int multiple types f systems fr varius purpses. Dppler mdules have an internal scillatr used t prduce the signal frequency transmitted as the surce. The received signal is then mixed with this set signal, which prduces an utput that is a sinusid cntaining the frequency difference between the utput and receiver signals. In mst systems, these values need t be recrded r read in a tangible way and this is usually dne with sme srt f micrcntrller. The easiest way fr a micrcntrller t read data frm an analg device is if it utputs a DC level vltage. Sme mdules have this feature built int them. Fr thse that dn t, like the HB100 used in the ECE 480 Design Team 5 prject, utput just the AC signal. Fr these mdules a frequency-tvltage circuit must be implemented. An IC, such as the LM2907N, can be used fr this specific purpse r any ther discrete cmpnent circuit. This circuit can be used t calibrate the utput data fr a specific set f expected frequencies cming frm the mdule t cntain it in reference vltage range.

5 Sampling f this data and the manipulatin f it thrugh cde is needed t take this raw data and make it useful fr the system. T find speed frm the utput signal f the mdule the equatin f = 2 * v λ λ = c f is used, where c is the speed f light, f is the signal frequency, and v is the speed f value t the applicatin. This can easily be implemented int cde since we wuld knw what frequencies crrespnd t what DC vltage level frm designing and testing the frequency-t-vltage circuit. When the micrcntrller cnverts this analg signal t a digital ne, it btains a hexadecimal number. This hexadecimal number needs t be adjusted t the reference vltage and bit reslutin f the ADC prt. An example f this cde, written in C, can be fund in Figure 2 belw with a 5 vlt reference. CnvertADC(); //perfrm ADC cnversin while(busyadc()); //wait fr result adc_result = ReadADC(); //get ADC result data = (adc_result/1024)*5; Figure 2: Sample C Cde The value btained frm this can then be manipulated using Dppler equatins t find the speed f the target bject. The HB100 uses a surce signal with a frequency f arund 10 GHz and sme cmmn speeds crrespnding t the difference can be seen belw in Figure 3.

6 10.5 GHz Surce F Speed (mph) Figure 3: Speed Values The values fund in Figure 3 are nly true with the surce bject r target bject being statinary. Mst systems implement Dppler radar in this way. If a mving target s speed is what is necessary then the surce is statinary and pinted tward the mving target bject, like in the case f a plice radar gun. If the speed f the mving bject which cntains the surce f the signal wave is required then signal needs t be emitted tward an bject that always desn t mve. As an example, airplanes use a Dppler system that reflects a signal ff the physical grund t keep track f the plane s speed. This is als the case fr ECE 480 Design Team 5 s prject. When the Dppler measurement system is mbile the grund is the mst practical reference. Cnclusin Using the Dppler Effect is a great way t measure relative speed. This can have many types f applicatins, frm just recrded the raw speed t mtin sensing in security equipment. Design Team 5 is using Dppler radar t effectively measure a skier r snwbarders tp and average speed using the principles cntained in this dcument.

7 References Russell, Daniel A. The Dppler Effect and Snic Bms Kettering University Crci, Renat. Radar Basics Miniature Micrwave Mtin Sensr HB100 Data sheet