Master Thesis. Mobile Phone Antenna Modelling. Umut Bulus. Supervised by Prof. Dr.-Ing. K. Solbach

Transcription

1 Master Thesis Mobile Phone Antenna Modelling Umut Bulus Supervised by Prof. Dr.-Ing. K. Solbach

2 Contents Introduction Theoretical Background Antenna Measurements on Different PCB Variations Investigation of the Chassis Investigation of Coupling between the Antenna Element and Chassis Modelling and Optimizing the Structure (Antenna Chassis Combination) Conclusion Umut Bulus, Page 2

3 Introduction Integrated Antenna element couples strongly with the PCB PCB acts as a second radiator Increase efficiency Integrated Antenna element couples strongly with the PCB PCB acts as a second radiator More Efficiency More Antenna Bandwidth Bandwidth of the antenna Umut Bulus, Page 3

4 Introduction The thesis task Design and test of Monopole and PIFA antennas on a large ground plane Reflection coefficient measurement of antennas mounted on PCB at Different Positions Orientations PCB Length Variations Test of the PCB as a dipole antenna via a balun and coaxial cable Investigation of the coupling between the antenna element and PCB by 2 port measurements at different antenna element Positions Orientations Developing an equivalent circuit representation of the antenna element, the coupled PCB and the coupling mechanism Umut Bulus, Page 4

5 Theoretical Background Potential Bandwidth: The bandwidth for the best matching case The impedance of the center frequency is selected as the characteristic impedance. The reflection coefficient is approximately zero for the center frequency So, the potential bandwidth could be found between the -1 db frequency points. Umut Bulus, Page 5

6 Antenna Measurements on Different PCB Variations Antenna Designs on Large Ground Plane (42.5 cm Χ 5 cm) No Simulation Tool Monopole Antenna Center Frequency: 1.47 GHz Bandwidth: 12.3 % Gain Maximum at 1 GHz: Db PIFA Antenna Center Frequency: 1.48 GHz Bandwidth: 7.86 % Gain Maximum at 1 GHz: Db C-Patch Antenna Center Frequency: 1.66 GHz Bandwidth: 3.48 % Gain Maximum at 1 GHz: Db Umut Bulus, Page 6

7 Antenna Measurements on Different PCB Variations Orientation F = - f oriented fl arg e ground Orientation Number 1 Orientation Number 2 Orientation Number 3 PBW [%] Orientation Number F / [GHz],15,1,5 -,5 -, Orientation Number C Patch PIFA C Patch PIFA Umut Bulus, Page 7

8 Antenna Measurements on Different PCB Variations Antenna Position Change on the PCB Antennas at Orientation Number 3 The dots indicate the Feed Points f F = position - fl arg e ground PBW [%] Position Number F / [GHz],15,1,5 -,5 -, Position Number C Patch PIFA Monopole C Patch PIFA Monopole Umut Bulus, Page 8

9 Antenna Measurements on Different PCB Variations Variation of PCB Length Antennas at Orientation Number 3 The dots indicate the Feed Points PCB is cut in every 3 mm between 3 mm to 9 mm F = f PCB length - fl arg e ground BW [%] PCB Length / [mm] F / [GHz],15,1,5 -,5 -, PCB Length / [mm] At the edge In the middle At the edge In the middle Umut Bulus, Page 9 Monopole Antenna

10 Antenna Measurements on Different PCB Variations 35,15 BW [%] PCB Length / [mm] F / [GHz],1,5 -,5 -, PCB Length / [mm] Most Bandwidth Orientation Number 3 Antenna located at the top edge of the PCB At the edge In the middle At the edge In the middle Around 13 mm PCB Length PIFA Antenna 35,15 BW [%] F / [GHz],1,5 -,5 -, PCB Length / [mm] PCB Length / [mm] At the edge In the middle At the edge In the middle C-Patch Antenna Umut Bulus, Page 1

11 Investigation of the Chassis The chassis is cut into two arms and measured as a dipole antenna 2 baluns and 4 different methods Providing Symmetric excitation using an unbalanced coaxial feeding cable Umut Bulus, Page 11

12 Investigation of the Chassis First, measuring the chassis as a monopole Monopole is conversion of Dipole Antenna The possibility to use the unbalanced coaxial feed 15 degree dipole antenna measurement in the frequency range of 8-2 MHz S11 of the Monopole Antenna Resonance Impedance 19 ohm, so for dipole, it should be around 38 ohm Resonance frequency 646 MHz Umut Bulus, Page 12

13 Investigation of the Chassis Second, Dipole Simulations of the Chassis at different angles in the frequency range of 5-2 MHz S11 of 45 degree chassis S11 of 3 degree chassis S11 of 3 degree with straight part S11 of 15 degree chassis Center Frequency PBW 45 degree 62 MHz 2 % 3 degree 717 MHz 38 % 3 degree with straight 785 MHz 55 % 15 degree 762 MHz 67 % Straight 86 MHz 82 % S11 of straight chassis Umut Bulus, Page 13

14 Investigation of the Chassis Finally, 1:1 RF Transformer Method (35-15 MHz) S11 of 1 ohm The tests of open, short terminals and 1, 56, 22 ohm resistors are done. Finally, the reference plane is selected as primary port of the transformer and the balun is excluded by the formula; S11 of 56 ohm S21S12ΓL Γin = S S22ΓL Γ in is the reflection coefficient of the dipole Improved by zeroizing S11and S22 and by using a ferrite core to suppress the current flow on the outer part of the coaxial cable Error percentage of the method [%] = 1 Z Measured Umut Bulus, Page 14

15 Investigation of the Chassis The reason of the spreads in the 1, 56, 22 ohm tests is analyzed as non-linear phase variation with frequency of the RF Transformer which is not correctly compensated by the electrical delay. S11 of 22 ohm 15 degree of non-linear insertion phase In the simulation of 3 degree dipole; Impedance value changes between 34.5 to ohm Average impedance is 84 ohm Very high error percentage at 1 ohm More accurate than 1 ohm at 22 Acceptable error percentage closer to 56 ohm MHz interval is found as acceptable Umut Bulus, Page 15

16 Investigation of the Chassis Reflection Coefficient of 3 degree dipole antenna measured in the frequency range of MHz The center frequency is 747 MHz and the resonance impedance is 27 ohm PBW is 42 % S11 of 3 degree chassis Comparable with the simulations Umut Bulus, Page 16

17 Investigation of the Chassis The gain of the 3 degree dipole antenna measured at 1 GHz E-Plane 5 Db maximum gain 7 degree HPBW Dynamic range 32 Db H-Plane GAIN/[dB] E-Plane ANGLE / [Degree] GAIN/[dB] ANGLE / [Degree] H-Plane 6.44 Db maximum gain 87 degree HPBW Dynamic range 6.5 Db Difference is because of the error in the measurement construction Umut Bulus, Page 17

18 Investigation of Coupling between the Antenna Element and Chassis Coupling between 3 degree Chassis and 1 GHz Antennas 2 port measurements to measure and S 21 S 12 RF Balun externalization S 12 Coupling = S S 12 Measured 12 Transform er Position 1 and 2 Position 3 and 4 Position 5 Antenna elements located at 5 different positions at 3 different orientations on the dipole antenna Umut Bulus, Page 18

19 Investigation of Coupling between the Antenna Element and Chassis S12 S12 /[db] f / [MHz] Monopole at position 1 S12 S12 /[db] f / [MHz] Monopole at position 2 Umut Bulus, Page 19

20 Investigation of Coupling between the Antenna Element and Chassis S12 S12 /[db] f / [MHz] Monopole at position 3-5 S12-1 S12 /[db] f / [MHz] Monopole at position 4 Umut Bulus, Page 2

21 Investigation of Coupling between the Antenna Element and Chassis S12 S12 /[db] f / [MHz] PIFA at position 1 S12 S12 /[db] f / [MHz] PIFA at position 2 Umut Bulus, Page 21

22 Investigation of Coupling between the Antenna Element and Chassis S12 S12 /[db] f / [MHz] PIFA at position 3 S12 S12 /[db] f / [MHz] PIFA at position 4 Umut Bulus, Page 22

23 Investigation of Coupling between the Antenna Element and Chassis S12 S12 /[db] PIFA at position f / [MHz] The bandwidth of the antenna-chassis system is related to the amount of coupling A part of the antenna element is not over the dipole at the first position At position 2, it is totally over the dipole, this is because position 2 has more coupling Two radiators at 747 and 1 MHz frequencies Umut Bulus, Page 23

24 Investigation of Coupling between the Antenna Element and Chassis The coupling of 2 antennas at the same frequency 747 MHz 1 GHz 1. Realization at 747 MHz Monopole antenna at 747 MHz is tested on 747 MHz chassis The coupling is more if they are at the same frequency as expected. So, more BW is achieved S11 /[db] f / [MHz] 747 MHz 1GHz Umut Bulus, Page 24

25 Investigation of Coupling between the Antenna Element and Chassis 2-port Simulations of Monopole-Dipole and Monopole-PIFA structures at position 2 Frequency range of MHz S12 Simulated S12 Simulated Very close results Simulation approves the measurement S12 Measured S12 Measured Umut Bulus, Page 25

26 Modeling and Optimizing the Structure Monopole Antenna Model Series characterization at the first resonance Term Term2 Num=2 Z=5 Ohm R R1 C R=34.5 Ohm C2 C= pf L L1 L= nh R= C C1 C= pf Resonance impedance is 34.5 ohm 1 ω = corresponds to LC L1 C1 = nh pf where the frequency is 1 GHz S(2,2) S(1,1) db(s(2,2)) db(s(1,1)) freq (54.MHz to 1.5GHz) freq, GHz A parallel capacity to match the measured results better Umut Bulus, Page 26

27 Modeling and Optimizing the Structure PIFA Antenna Model Parallel characterization at the first resonance Term Term2 Num=2 Z=5 Ohm TLIN TL1 Z=5. Ohm E=2.69 F=1 GHz L L2 L=16.6 nh R= R R1 R=275 Ohm L L1 L=4.32 nh R= C C1 C=6.45 pf A very short transmission line λ at 1 GHz and a parallel inductance S(2,2) S(1,1) db(s(2,2)) db(s(1,1)) Near to the inductance formula.75 nh per mm of the probe freq (54.MHz to 1.5GHz) freq, GHz Umut Bulus, Page 27

28 Modeling and Optimizing the Structure Improved Chassis Model (at 1.9 GHz) 3 degree dipole antenna Series characterization at the first resonance Term Term2 Num=2 Z=5 Ohm R R1 R=27.5 L L1 L=12 nh R= C C2 C= pf C C1 C=2.2 pf Same resistor value -2-4 Series Capacitance and Inductance are tuned proportionally S(2,2) S(1,1) db(s(2,2)) db(s(1,1)) freq (351.2MHz to 1.2GHz) freq, GHz Umut Bulus, Page 28

29 Modeling and Optimizing the Structure Modeling of Coupling Two modeling parameters for the coupling; Matching to the Transmission Parameters of the Measurements 1-Port measurement from the antenna side when the dipole is shorted (chassis) must give more BW than the antenna alone Antenna Positions at position 2 are used Monopole-Dipole Improved Model Term Term2 Num=2 Z=5 Ohm R R2 C R=34.5 Ohm C3 C= pf L L2 L= nh R= C C4 C= pf TLIN TL1 Z=5 Ohm E=4 F=1 GHz C C5 C=3 pf R R1 R=27 Ohm L L1 L=12 nh R= C C2 C= pf C C1 C=2.2 pf Term Term4 Num=4 Z=5 Ohm Monopole Antenna Dipole Antenna Umut Bulus, Page 29

30 Modeling and Optimizing the Structure 2 port coupling results; -6-8 S(2,4) S(1,3) db(s(2,4)) db(s(1,3)) freq (54.8MHz to 1.21GHz) freq, GHz 1-port measurement from the monopole side when the dipole (chassis) is shorted; -1 S(2,2) db(s(2,2)) -2-3 freq (54.8MHz to 1.21GHz) freq, GHz Umut Bulus, Page 3

31 Modeling and Optimizing the Structure PIFA-Dipole Improved Model TLIN TL1 Term Z=5. Ohm Term2 E=2.69 Num=2 F=1 GHz Z=5 Ohm L L4 L=16.6 nh R= R R2 R=275 Ohm L L5 L=4.32 nh R= C C6 C=6.45 pf TLIN TL2 Z=5. Ohm E=-65 F=1 GHz C C8 C=4 pf R R1 R=27.5 L L1 L=12 nh R= C C2 C= pf C C1 C=2.2 pf Term Term4 Num=4 Z=5 Ohm PIFA Antenna Dipole Antenna 2-port coupling results; -4-6 S(2,4) S(1,3) db(s(2,4)) db(s(1,3)) freq (54.8MHz to 1.21GHz) freq, GHz Umut Bulus, Page 31

32 Modeling and Optimizing the Structure 1-port measurement from the PIFA side when the dipole (chassis) is shorted; -2 S(2,2) db(s(2,2)) freq (54.8MHz to 1.21GHz) Comparison of the Model and Realization freq, GHz Monopole PIFA C-Patch Antenna Element Alone Antenna- Chassis Model 12.3 % 16 % 23 % 7.86 % 29 % 25 % 3.48 % 17 % 1 % Antenna- Chassis Realization Umut Bulus, Page 32

33 Conclusion The antennas are tested on large and small ground plane variations The chassis is investigated as a dipole The couplings between the antenna element and chassis are measured. It is seen that the bandwidth is related to the coupling. The equivalent networks of antenna elements, coupled chassis and the coupling mechanism in between are designed The chassis and coupling equivalents are improved after tuning the chassis center frequency to 1.9 GHz Umut Bulus, Page 33

34 Thank you for your attention Umut Bulus, Page 34