an automatic antenna matching method for monostatic fmcw...

An automatic antenna matching method for monostatic FMCW

radars

Professor: Prof. Dr.-Ing. Klaus SolbachSupervisor: Dipl. -Ing. Michael ThielStudent: Yan Shen

Outline

• Introduction • System Development and Design• Impedance Tuner Design• Test Results• Controller Algorithm• Conclusions and Further Work

IntroductionHardware Realization of the FMCW Monostatic Radar

)]2cos()[cos(2

21)]cos()[cos(21)]cos(2)][cos(1[ 1212121 ωωωωωωωωω +Δ+Δ=++−==×AAAAAARXTX

RXRXnTXRXRXnTXRX ××+×=×+× )(

If RX and TX are not well decoupled:DC offset

Reduced performance of the mixer due to changed DC operation.

fd Δ≈ /1

if Zimage(V1,V2) = Zantenna, RX and TX are well decoupled.

Impedance tuner

Decoupling Diplexers

Antenna impedance changes

Rat-race coupler

Temperatures, radiation environments

• Rat-race Coupler• Wilkinson Power Divider• Gilbert Cell Mixer• Patch Antenna• System Modelling and Development

System Design and Development

Rat-race CouplerADS layout Schematic VS Momentum

P1

P2 P3

P4

Wilkinson Power DividerADS layout

P1

P2

P3

Schematic VS Momentum

Gilbert Cell Mixer

y1

y2

IF output

LO input

RF input

V_DCSRC4Vdc=5.6 V

RR7R=1200 Ohm

RR9R=0.6 kOhm

RR10R=0.6 kOhm

CC5C=1 pF

OpAmpAMP1

VCC=5 VVEE=-5 VZero1=Pole1=BW=500 MHzVOS=200 uVIOS=0.2 uASlewRate=5e+8CCom=1 pFRCom=1 MOhmCDiff=1 pFRDiff=15 kOhmRout=100 OhmCMR=75 dBGain=60 dB

PortP3Num=3

RR8R=1200 Ohm

PortP2Num=2

V_DCSRC2Vdc=1.9 V

RR1R=10 Ohm

I_DCSRC3Idc=0.06 mA

V_DCSRC1Vdc=2.9 V

RR2R=10 Ohm

npnH3shp4Q5Icmax=8 mA

rpndR5

Imax=0.24 mAl=5.72 umw=0.48 umR=3 kOhm


rpndR4


PortP1Num=1

rpndR6



rpndR3


cmimC4

l=54.71 umw=54.71 umc=3 pF

cmimC3

l=54.71 umw=54.71 umc=3 pF

cmimC2

l=54.71 umw=54.71 umc=3 pF

cmimC1

l=54.71 umw=54.71 umc=3 pF





Mixer schematic Power level test

Single inset-fed patch antenna

Twin inset-fed patch antenna

Quad inset-fed patch antenna

larger bandwidth

Patch Antenna

largest bandwidth

System Modelling

Case 1 Case 2 IF_gain=20log(1.015/0.066)=24dB!

Case 1:R_image=50 Ohm, E_image=0Case 2:R_image=25 Ohm, E_image=80

@10.00G

-21.10dBm

1.34dBm

@10.01G

-26.23dBm

-40.97dBm

DC�0.486V10 MHz�1.613V

System Matching

Reflection Tuner

The traditional transmission tuner: Additional induced losses on thefeed line due to multiple reflections and losses in the ATU itself:

The reflection tuner:Losses on the tuner has no influence to the system.

Tuner Design

Transmission Tuner

Principle of our tuner

C1: 0~90°tune the phase

Simulation result:

TLINTL1

F=10 GHzE=C1Z=50.0 Ohm

RR1R=RX Ohm

TermTerm1

Z=50 OhmNum=1

RX: 33.3~75 Ohmtune the amplitude

Tuner schematic:

Phase shifterVariable resistor

FET as Voltage-controlled Resistorsnonlinear Triquint MGF1402 package.

Ugs:-0.5913 ~ -0.5101 V

MGF1402

Rds~Ugs

Phase Shifter Design

Variable reactance reflection phase shifter

Lange coupler

Branch-line coupler

90°hybrid coupler:

Phase shifter schematic:Branch-line coupler and Silicon tunning Varactor SMV 2019-108

Phase shift: 218°

Simulation result:P1 P2

Udiode: 0~20 V

Tuner Schematic:

Udiode: 0~20V

Ufet: -0.6~0V

Simulation result: PCB:

PCB of the Final Radar System

Test ResultsRat-race coupler Power divider

PCB VS Momentum

Branch-line coupler

NWA

Antenna Tuner

Phase shift is not enough;FET works good.

Two ways to improve

Too high series inductance

PCB VS Momentum

(a)

(b)

(c)

Controller SystemReal control system

),( UdiodeUfetfUdc =

Original data set Interpolation

in Matlab

Udc=Interp(Udiode, Ufet)

Minisearch function in Matlab

Starting points

Udcmin

Udiode, Ufet

HP 4142BModularDC

Source

SMU0

SMU1

Udiode

Ufet

Radar system

Udc

OptimizerDAQInstrument

Control algorithm

Simulated control system

Optimizer ADS model

Aim: Minimize Udc

Three dimentional plotted graph Original data set, Column 1 is Udiode and Column 2 is Ufet. Column 3 is Udc.

1. [x, fval, history, DC] = func2 ([1, 0]) Result: x = 4.7380 -0.0219

fval = 2.5215e-005

2. [x,fval,history,DC]=func2([3,-0.4])Result: x = 4.9778 -0.2191

fval = 5.0413e-010

Examples

3. [x,fval,history,DC]=func2([2,-0.5])Result: x = 2.0001 -0.7000

fval = 2.0723

ConclusionsThis master thesis developed a dynamic method to minimize the DC offset at the output of the mixer. A demonstrator was built on an RF grade circuit board (PCB) working at an RF of 10 GHz and consisting of a voltage controlled oscillator (VCO), a Rat- race coupler, a power divider, a tunable impedance network, a Gilbert cell mixer. The hardware is shown below.

• There is a large space for the optimization of the tuner. Some methods can be found out to reduce the series inductance in order to increase the phase shift, which will lead to a larger range of realizable impedance values as shown in the ADS simulation.

• The performance of the dynamic method to minimize the DC offset can be improved by using an I/Q mixer. An IQ-mixer consists of two balanced mixers and two hybrids. It provides two IF signals with equal amplitudes which are in phase quadrature. Two outputs provide two DC values which can be used better to control the two control voltages for the tuner.

• In the future, this work can be transferred into an integrated circuit solution working at much higher frequencies (e.g. 77) based on CMOS or BICMOS technology, where resistors, capacitors, diodes, transistors and multi level metals conductorsare available.

Further Work

A 10-bit data multiplexor manufactured in a SiGe BiCMOS process.

Patch Antenna

• Let the substrate dielectric constant, thickness, patch length, patch width, be denoted by , h, L, W respectively.

• In this experiment the patch will be fed by a microstrip transmission line, which usually has a 50 Ohm impedance. The antenna is usually fed at the radiating edge along the width (W) as it gives good polarisation, however the disadvantages are the spurious radiation and the need for impedance matching.

• Here, an inset feed is used to match the antenna, because the resistance varies as a cosine squared function along the length of the patch. A 50 Ohm can be found in a distance from the edge of the patch. This distance is called the inset distance.

rε

Appendix A

1) Width of the patch

Where c = the velocity of light= operating frequency

2) Because the electric field lines reside in the substrate and parts of some lines in air. This transmission line cannot support pure transverse-electric-magnetic (TEM) mode of transmission, since the phase velocities would be different in the air and the substrate, an effective dielectric constant must be obtained in order to account for the fringing and the wave propagation in the line.Effective dielectric constant:

212 0

+=

rf

cWε

0f

21

)121(2

12

1 −+

−+

+=

Whrr

reffεεε

3) The length may also be specified by calculating the half-wavelength value and then subtracting a small length to take into account the fringing fields as:

LLL eff Δ−= 2

)8.0)(258.0(

)264.0)(3.0(412.0

+−

++=Δ

hW

hW

hLreff

reff

ε

ε

4) For a given resonance frequency, the effective length is given as:

We get:W=9.945mm, L=7.801mm

reffeff f

cLε02

=

We use the curve fit formula to find the exact inset length to achieve 50 Ohm input impedance for the commonly used thin dielectric substrates.

2669740439.2561

69.682187.931783.61376.0001669.010

2

345674

0Ly

rr

rrrr r ×⎪⎭

⎪⎬⎫

⎪⎩

⎪⎨⎧

+−+

−+−+= −

εε

εεεεε

we get:=2.220y

Rat-race Coupler

TLINTL6

F=10 GHzE=90Z=50 Ohm

PortP4Num=4

TLINTL5


PortP1Num=1

TLINTL4

F=10 GHzE=90Z=70.7 Ohm

TLINTL3


TLINTL2


TLINTL1

F=10 GHzE=270Z=70.7 Ohm

PortP3Num=3

PortP2Num=2

RR1R=R_image Ohm

VARVAR1

_width=1.07circle_width=0.62_radius=4.36

EqnVar

PortP2Num=2

MSUBMSub1

Rough=20 umTanD=0.0027T=0.070 mmHu=20 mmCond=4.1e7Mur=1Er=3.55H=0.508 mm

MSub

MLINTL4

L=0.44 mmW=_width mmSubst="MSub1"

PortP1Num=1

PortP3Num=3

PortP4Num=4

MLINTL2


MCURVECurve3

Radius=_radius mmAngle=60W=circle_width mmSubst="MSub1"

MCURVECurve2


MCURVECurve4


MCURVECurve1


MLINTL3


MLINTL1


Principle

Real circuit schematic ADS Layout

Basic circuit

Wilkinson power divider

TLINTL7


TLINTL4


TLINTL3


PortP1Num=1

RR1R=100 Ohm

TLINTL1


TLINTL2


PortP3Num=3

PortP2Num=2

VARVAR1

_length2=1.04503 {o}_length1=2.13804 {o}_length=_radius-circle_width/2+0.26_radius=2.3_width=0.533843 {o}_width2=0.400138 {o}circle_width=0.70009 {o}

EqnVar

MLINTL8

L=0.5 mmW=1.07 mmSubst="MSub1"

MLINTL9

L=0.5 mmW=1.07 mmSubst="MSub1"

MSUBMSub1

Rough=20 umTanD=0.0027T=0.070 mmHu=20 mmCond=4.1e7Mur=1Er=3.55H=0.508 mm

MSub

MTEE_ADSTee1

W3=1.07 mmW2=circle_width mmW1=circle_width mmSubst="MSub1"

MSTEPStep1

W2=_width2 mmW1=1.07 mmSubst="MSub1"

MSTEPStep2

W2=_width2 mmW1=1.07 mmSubst="MSub1"

MLINTL7

L=1 mmW=1.07 mmSubst="MSub1"

MTEE_ADSTee3

W3=_width mmW2=_width2 mmW1=circle_width mmSubst="MSub1"

MTEE_ADSTee2

W3=_width mmW2=_width2 mmW1=circle_width mmSubst="MSub1"

MLINTL6

L=_length2 mmW=_width2 mmSubst="MSub1"

MLINTL5

L=_length2 mmW=_width2 mmSubst="MSub1"

MLINTL3

L=_length1 mmW=circle_width mmSubst="MSub1"

MLINTL4

L=_length1 mmW=circle_width mmSubst="MSub1"

PortP3Num=3

PortP2Num=2

PortP1Num=1

MLINTL2

L=_length mmW=_width mmSubst="MSub1"

R_Pad1R1

L1=0.5 mmS=0.15 mmW=0.4 mmR=100 Ohm

MLINTL1

L=_length mmW=_width mmSubst="MSub1"

MCURVECurve1


MCURVECurve2


Principle Basic circuit

Real circuit schematic ADS Layout

rein UUU +=

WuZUu

L

== ][; WiZIi L =×= ][;

Lrein ZUUI /)( −=

L

re

L

in

ZUb

ZUa == ,

baibau −=+= ; 2/)(2

)(L

L

ZIZUiua ×+=

+= 2/)(

2)(

LL

ZIZUiub ×−=

−=

22

21;

21 bPaP rein ==

Relative voltage and current:

Wave variables:

So

Power:

wave variable

Appendix B

Tuner with Branchline coupler and SMV 2019-108

Tuner with Branchline coupler and SMV 1245-011

Mixer testing circuit board

System circuit board

Appendix CTuner test results

Appendix DInterpolation

• function v3=interpolation(v1,v2)• userdata = importdata('final.txt');• data = userdata.data;• Ufet=-0.7:0.05:0;• Udiode=0:1:6;• Udc1=data(1:15,3)';• Udc2=data(16:30,3)';• Udc3=data(31:45,3)';• Udc4=data(46:60,3)';• Udc5=data(61:75,3)';• Udc6=data(76:90,3)';• Udc7=data(91:105,3)';• Udc=[Udc1;Udc2;Udc3;Udc4;Udc5;Udc6;Udc7];• v3=interp2(Ufet,Udiode,Udc,v2,v1);• v3=abs(v3);

Optimization

• function [x fval history DC] = func2(x0)• history = [];• options = optimset('OutputFcn', @myoutput);• [x fval] = fminsearch(@(x)

interpolation(x(1),x(2)),x0,options); • function stop = myoutput(x,optimvalues,state);• stop = false;• if state == 'iter'• history = [history; x];• end• end• DC=interpolation(history(:,1),history(:,2));• plot3(history(:,1),history(:,2),DC,'-*')• xlabel('Udiode'),ylabel('Ufet'),zlabel('Udc');• grid on• axis ([0 6 -0.8 0 -2 6])• end

an automatic antenna matching method for monostatic fmcw...

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