4G MIMO ANTENNA DESIGN & Verification

Transcription

1 4G MIMO ANTENNA DESIGN & Verification Using Genesys And Momentum GX To Develop MIMO Antennas

2 Agenda 4G Wireless Technology Review Of Patch Technology Review Of Antenna Terminology Design Procedure In Genesys Verifying Antenna Performance Using Genesys To Determine Multi-Element Patterns Verifying Method With Momentum GX Conclusion

3 4G Wireless: LTE, WiMAX, Mobile WiMAX, n Fourth Generation Wireless Infrastructure: Higher Data Rates Up to 150 Mbs downlink, 50Mbs uplink Multi-Data Formats Edge, GSM, FTE, UMTS etc. Speedy Mobiles 100 km/hr

4 Antenna Parameters Selection criteria for antenna type: Beam pattern Gain Power handling capability Directivity Bandwidth Manufacturability Cost

5 Patch Antenna Characteristics Patch antenna topologies: Advantages Ease of manufacture Form complicated antenna patterns Flexible substrates Variety of shapes and structures Weight Cost Disadvantages Substrate material limits efficiency Lossy, lower radiation efficiency means increased transmit power Power limited

6 Patch Antenna Shapes There is an almost endless number of antenna feed topologies: Rectangular, Circular, Arrays Shapes affect bandwidth, radiation patterns and polarization Spacing and phase affect directivity, gain and radiation pattern Patch Patterns Series Feed Parallel Feed

7 Radiation Patterns Fields defined by E-theta and E-phi E total is the vector sum of both components E theta sweeps from the North Pole 0 o to 90 o E phi sweeps from 0 o to 180 o around the North Pole E θ E φ Note relationship of the field to the X and Y axis of the circuit board

8 Orientation In Antenna Patterns Patch antennas Rarely Have Symmetrical Pattern Due to current distribution on patch(s) Phi=0 o Phi=90 o

9 Antenna Design Procedure Use linear analysis to evaluate physical dimensions Verify design with Momentum GX Determine additional matching circuitry using MATCH Examine prototype with far field analysis Design and verify a steer-able beam array Develop a mathematical model of the far field pattern Apply procedure to dual antenna pattern Verify multi-element pattern with Momentum

10 Patch Design Start with a rectangular design Resonance is determined by length along the feed axis Length is approximately λ 2 Width is loosely equal to length, however maximum efficiency is given for width by (1) ν0 2 ε r + 1 ε r 1 h W = εeff = + 2 ε W f r r L h = ( ε + 0.3) eff W h W ( ε 0.258) eff Fringe Effect h ν0 L = 2 L 2 f ε r eff L L L W

11 Patch Design Frequency requirements for LTE band II Approximately 7.5% bandwidth Transmit band is 60 MHz wide, MHz Receive band is 60 MHz wide, MHz The design will then center at 1920 MHz Start a patch Length =1440 mils, with a Width =1860 mils Substrate is FR4 Er=4.5, height =.059 inches

12 Using Linear Modeling Start with simple transmission line model to verify the length

13 Using Momentum GX First simulation establishes resonant frequency Of course transmission line does not model radiation Markers show band edges for the transmit and receive bands

14 Reducing Patch Width And Optimizing Length Reducing patch width has small effect on response but reduces footprint Width =1200 mils Length = mils

15 Evaluating Matching Structures Using Genesys MATCH we can determine the optimum matching structure Start with settings dialog we set the frequency band of match The settings represent the full band MHz with 50 pts

16 Using Antenna Data For Match In Sections Tab We Point MATCH To The Momentum Data Set As The Terminating Impedance The Type Of Matching Structure Is Selected Next We will try to use distributed matching for incorporation into the layout

17 Stepped Impedance Network Stepped impedance provides a good match at band center but the band edges are not improved

18 Quarter Wave Matching Line A simple quarter wave provides improvement at band center but again the band edges are not improved

19 Match For Transmit Band The patch antenna chosen is inherently narrow band Focus on matching for the transmit frequencies since a poor match can result in watts of power loss Re-center resonant frequency for transmit band center 1880 Mhz Slight increase in antenna length decreases center frequency

20 Synthesize Matching Network Using MATCH Again To Find Best Structure In this case a simple quarter wave transmission provides an adequate match at band center and edges Length = mils

21 Final Momentum Analysis Final analysis places center frequency at ~1880 MHz Quarter wave matching line gives us -36 db return loss at ~1880 Transmit band edges provide ~-10 db return loss Receive band has the worst match of > -3 db, possible second antenna

22 Plotting Field Patterns We must have performed a Momentum simulation first!

23 E total Compared To Phi Select antenna graph measurement then select phi cut Radiation pattern is dependent upon rotation around phi axis

24 Antenna Patterns Field pattern is a function of φ φ = 0 φ = 90 θ θ 0 φ = 0 0 φ = 90

25 MIMO Networks Require Agile Antennas Standards affect antennas for base stations and mobiles devices Base stations need to provide data to multiple users while compensating for multi-path and delay Mobiles also need to compensate for multi-path and fading

26 Networks Require Agile Antennas Variety of antenna function and types Omni Directional Diversity Steer-able Array Switched or Multi-Beam Patch Antenna Types

27 MIMO- Steerable Antenna Use Genesys to develop MIMO Antennas Design and evaluation of steerable MIMO Antennas We use the results of our antenna design to predict the contributions from an array If the patch antennas are reasonably isolated S mn ~ 0, then linear superposition can be used to plot the far field contributions (2)

28 Determining Far Fields Far Field value is the superposition of each radiator FAR FIELD FAR FIELD Fp 2 1 = ( R *sin( θ )) + ( R *cos( θ ) d ) 2 Fp1 Fp2 Fp = θ θ ( R *sin( )) + ( R*cos( ) d ) 2 R R R* sin( θ ) θ A α θ B β d = λ / 4 R * cos( θ ) + d R * cos( θ ) d

29 Mathematically Generated Pattern Superposition of Fields k := λ := 1 θ k := k π 180 n := 1 R := 100 λ A :=.5 K := n λ 4 B :=.5 D := 2 K α := 0deg β := 0deg ( ( ) ) 1.0 ( ) Ant :=.5 cos θ k k π.5cos θ k π π E := R cos θ k k 2 + K π R sin θ k 2 π F := R cos θ k k 2 K π R sin θ k 2 γ k := α 2π E k δ k := β 2π F k ( ( ) + ( ) i) v1 := Ant A cos γ k k k ( ( ) + ( ) i) v2 := Ant B cos δ k k k A sin γ k B sin δ k V := v1 + v2 k k k Ant k V k θ k θ k

30 Superposition Of A Two Element Array Far Field plot of two omni-directional antennas Driven with equal amplitude and in phase Note the new directionality Ant k V k θ k θ k Single Antenna Pattern Result Of Far Field Superposition

31 Antenna Interference An intuitive look at interference vs. spacing Like colors or phases add while unlike colors or phases subtract A + B + + +

32 Front Sided Antenna Little or no backward radiation Pattern becomes narrower with little side lobe radiation Typical of patch antenna Ant k V k θ k θ k

33 Changing The Feed Phase Varying the phase and amplitude of the elements Results in controlling the tilt or angle of maximum radiation V k V k β := 60deg θ k V k β := 90deg β := 180deg θ k θ k

34 Pattern Array Field patterns for an array of antenna elements can be analyzed or synthesized by*. 1) Knowing the single element radiation pattern 2) The amplitude and phase of the sources driving each element 3) Knowing the spacing or separation between elements Method may be extended to multiple elements d d d A α B β C χ D δ *Interference or coupling between elements is zero or nearly zero

35 Array Design In Genesys Applying the same trigonometry within Genesys We start with the single patch antenna from before Using Momentum far field data we obtain the element pattern Genesys rich set of math functions allows us to project far field data from the captured single element pattern This method may be extended to two or more element arrays The ability to tune parameters such as feed amplitude and phase as well as antenna distance gives full control over the far field When applied to a large number of elements, optimization reduces the time and effort

36 Extracting The Element Pattern Run a Momentum GX analysis of the proposed antenna Extract Momentum E-field dataset values for single element New Data Vector With Field Values

37 Using Genesys Math Functions Trigonometric equations relating far-field value to element pattern characteristics SUPER POSITION OF FIELDS k := θ k := k π 180 ( ( ) ) 1.0 ( ) Ant :=.5 cos θ k k π.5cos θ k π A :=.5 λ := 1 B :=.5 n := 1 D := 2 K K := n λ 4 α := 0deg R := 100 λ β := 0deg π E := R cos θ k k π + K + R sin θ k 2 π F := R cos θ k k π K + R sin θ k 2 γ k := α 2π E k δ k := β 2π F k ( ( ) + ( ) i) v1 := Ant A cos γ k k k ( ( ) + ( ) i) v2 := Ant B cos δ k k k A sin γ k B sin δ k V := v1 + v2 k k k

38 Tuning For Phase And Levels Antenna parameters are made tunable Instant visualization on far field pattern Antenna A level 0 o Phase Phase Difference Antenna B level Antenna spacing in half wavelengths

39 Result Of Phase Offsets Antenna beam steers, side-lobes and beam width change ~28 o ~42 o 60 o Phase 90 o Phase

40 Additional Degrees Of Freedom Pattern is influenced by drive levels and element separation Added elements offer improved control over beam Element spacing 1.3 half wavelengths Element spacing 3 half wavelengths

41 Verifying Predicted Pattern Layout two element patch antenna modeled after single element previously designed and simulated Use Momentum to generate the combined far-field with appropriate voltages and phase Review the far-field pattern to verify the predicted performance

42 Verifying Isolation At band center, 1880 MHz isolation is -43 db -43 db=50 millionths

43 Setting Source Values Under Momentum s far-field options The source levels and relative phase Note that the phase is set at 180 o Why?

44 More Features For Momentum GX 3D Field Viewer

45 Comparing Predicted Field Comparison of far-field predicted and Momentum GX Both show a half power beam width of 29 0 PREDICTED Momentum Momentum 3D View Single Element Pattern

46 Adding Phase Shift At Ports Result of 28 o difference in phase between sources Note identical beam values at -3dB of 38 O from beam center PREDICTED 28 Degrees Momentum Note: The current version of Momentum plots half beam

47 Using Two Evaluations Plotting both halves of Momentum field requires two phase evaluations Note values are equal between predicted and Momentum! PREDICTED Momentum 60 Degrees

48 Elements Driven Opposite The extreme for two element antenna is 180 phase difference Difference in magnitude due to re-normalizing in Momentum PREDICTED 180 Degrees Momentum

49 Orientation Of Beam Relative To Board Major cut was through phi = 0 Swept pattern steers along X-axis 0 φ = 0

50 Field Pattern In Genesys Extending the equations to four elements a narrow beam is achieved

51 Optimization Of Beam Pattern Beyond two elements selecting the correct feed-phase is burdening We use the optimization features of Genesys to aide in finding the best set of feed amplitude and phases Goal = 30 deg

52 Beam Amplitude Optimization Additionally we optimize the feed amplitudes to compensate for beam power as a result of steering a = b = c = d = Angles in radians

53 Other Sources Of Antenna Data Single antenna element information can be measured and imported via TestLink

54 Conclusion An antenna design procedure was presented A rectangular patch was designed and verified with Momentum 3D-Planar EM Field Simulator A modified antenna was optimized for a LTE band and matching network incorporated The single patch field pattern was then used to model or predict the effect of an array of two or more elements Verification of this technique was established with Momentum field solver Optimization aides in extending this procedure to larger arrays

55 Agilent Genesys product bundles start at about $4K USD The modules used to complete the synthesis, design and verification of MIMO antenna system presented in this paper can be found in the Genesys Non-Linear Pro GX (W1426L) for about $16.6K USD

56 References Antenna Theory Analysis and Design, Constantine Balanis, Wiley, second edition, Pgs Ibid, Pgs Fundamentals of Applied Electromagnetics, Fawwaz Ulaby, Prentice Hall,1997, Pgs Agilent AN note 3GPP Long Term Evolution, doc EN Agilent AN Mobile WiMAX PHY Layer Operation and Measurement, doc EN Agilent AN MIMO Channel Modeling and Emulation Test Challenges, doc EN Agilent AN MIMO Wireless LAN PHY Layer RF Operation & Measurement, doc EN