Development of an Actively Steered Phased Array Antenna for Doppler Reflectometry

Transcription

1 Technische Universität München IRW 12 FZ Jülich Development of an Actively Steered Phased Array Antenna for Doppler Reflectometry C. Koenen 1, U. Siart 1, T. F. Eibert 1, T. Happel 2, G. D. Conway 2, and U. Stroth 2 1 Lehrstuhl für Hochfrequenztechnik TU München 2 Max-Planck-Institut für Plasmaphysik Garching Helmholtz Virtual Institute: Advanced Microwave Diagnostics for Plasma Dynamical Processes & Turbulence Studies

2 Geometrical configuration H-plane ( B ) E-plane ( B ) 2

3 Content Gaussian beam-shaping & expected spectral resolution Feed structure Broadband coupling structure Piezo controlled phase shifter Array design and simulation results Focussing elements Reflector horn antennas 3

4 Gaussian beam shaping Desired Gaussian beam parameters: - beam waist of w 0 = 7λ - focal point in F = mm distance from the array - side lobes below 35 db / best as possible 4

5 Achievable Gaussian beams Design frequency: 75 GHz Focal distance: 100 mm - amplitudes are fixed at array aperture (z = 0) - beam waist dependent on frequency (w 0 = 7λ) focal point must be shifted away from aperture 5

6 Achievable Gaussian beams Design frequency: 75 GHz Focal distance: 100 mm - frequency dependent radius of curvature at array aperture frequency dependent phase distribution at array aperture 6

7 Expected spectral resolution on AUG Δk = 2 2 w 1 + w2 k 0 ρ ρ = R plasmsa R beam R plasmsa + R beam (Hirsch, Holzhauer 2004) 7

8 Series fed array antenna Principle structure: Required components: - radiating elements (H-plane reflector horns) - phase shifter / delay lines - broadband coupling structure - compensation lines + focusing 8

9 Ideal model of the coupling structure a = 2.54 mm b = 1.27 mm main feed line radiating element λ w 4 waveguide with reduced & variable height 9

10 S-Parameter of the ideal coupling structure λ w 4 waveguide height max. reflection mean coupling variation from mean coupling mm -22 db db ± 0.80 db mm -25 db db ± 0.65 db mm -30 db db ± 0.79 db 10

11 Difficulties using the ideal coupling structure main feed line radiating elements - slots too small for milling >> laser-cut apertures - long waveguide in-between elements for beam steering 11

12 Adapted model of the coupling structure - λ w 4 waveguide realized by laser-cut aperture - main feed line bent >> fix aperture & longer waveguide main feed line radiating element exchangeable metal plate λ realizes w 4 waveguide 12

13 Details of the adapted coupling structure 4 mm λ mm (element spacing) 13

14 Coupling structure prototype 14

15 Coupling structure prototype 15

16 Coupling structure prototype 60 µm 400 µm 16

17 Phase shifter piezo actuator Image: piezosystem Jena branch guide coupler non-contacting short Graphics: Clemens Moroder 17

18 Phase shifter prototype Image: Clemens Moroder 18

19 Series fed array antenna Principle structure: Required components: - radiating elements (H-plane horns) - phase shifter / delay lines - broadband coupling structure - compensation lines + focusing 19

20 Array structure of frequency scanned version TOP-view: input FRONT-view: SIDE-view: 2 mm spacing cutting planes 20

21 Required coupling values db loss between coupling structures (from simulation) 21

22 S-Parameter simulation results CST MWS f-solver: 780k Tetrahedrons ~12mins per frequency sample, 3XX samples 200h total solver time 22

23 Amplitude distribution 23

24 Required dispersion characteristics j kz + πr2 E = E 0 r, z e λr f,z Φ f,z (frequency dependent radius of curvature at array aperture) r = 0 mm (center element) r = 16 mm r = 32 mm 24

25 Focusing the array with a waveguide sections Fundamental waveguide with reduced width: - individual focusing section for each radiating element - a determines the dispersion characteristic of the waveguide - length d is element wise individually adjusted a d to reflector horn a approx. 18 mm from feed 25

26 Theoretical achievable dispersion characteristics a = 2.20 mm ( TE10 cut-off = 68.1 GHz ) r = 0 mm (center element) d = d 0 r = 16 mm d = d mm r = 32 mm d = d mm 26

27 Theoretical achievable dispersion characteristics a = 2.10 mm ( TE10 cut-off = 71.4 GHz ) r = 0 mm (center element) d = d 0 r = 16 mm d = d mm r = 32 mm d = d mm 27

28 Theoretical attenuation of fundamental waveguide nearer to cut-off frequency attenuation higher effect negligible as 2d 0 < 1 mm and max. attenuation a max < 0.01 db 28

29 Design of the reflector horn reflector Gaussian beam feed horn from focusing element Design: Patrick Kolesa 29

30 Simulation results 75 GHz amplitudes normalized to maximum of each column artifacts in reflector horn 30

31 Simulation results 92 GHz amplitudes normalized to maximum of each column artifacts in reflector horn 31

32 Simulation results 110 GHz amplitudes normalized to maximum of each column artifacts in reflector horn 32

33 Conclusion - Procedure to emit Gaussian beam from linear antenna array - Broadband coupling structure for W-band - Piezo controlled phase shifters - Array structure - Focusing by means of waveguides with reduced width - Reflector horns Prototypes available 33