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
Geometrical configuration H-plane ( B ) E-plane ( B ) 2
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
Gaussian beam shaping Desired Gaussian beam parameters: - beam waist of w 0 = 7λ - focal point in F = 200 400 mm distance from the array - side lobes below 35 db / best as possible 4
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
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
Expected spectral resolution on AUG Δk = 2 2 w 1 + w2 k 0 ρ 2 1 2 ρ = R plasmsa R beam R plasmsa + R beam (Hirsch, Holzhauer 2004) 7
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
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
S-Parameter of the ideal coupling structure λ w 4 waveguide height max. reflection mean coupling variation from mean coupling 0.300 mm -22 db -12.8 db ± 0.80 db 0.200 mm -25 db -16.1 db ± 0.65 db 0.100 mm -30 db -21.9 db ± 0.79 db 10
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
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
Details of the adapted coupling structure 4 mm λ 0 4 2 mm (element spacing) 13
Coupling structure prototype 14
Coupling structure prototype 15
Coupling structure prototype 60 µm 400 µm 16
Phase shifter piezo actuator Image: piezosystem Jena branch guide coupler non-contacting short Graphics: Clemens Moroder 17
Phase shifter prototype Image: Clemens Moroder 18
Series fed array antenna Principle structure: Required components: - radiating elements (H-plane horns) - phase shifter / delay lines - broadband coupling structure - compensation lines + focusing 19
Array structure of frequency scanned version TOP-view: input FRONT-view: SIDE-view: 2 mm spacing cutting planes 20
Required coupling values 0.335 db loss between coupling structures (from simulation) 21
S-Parameter simulation results CST MWS f-solver: 780k Tetrahedrons ~12mins per frequency sample, 3XX samples 200h total solver time 22
Amplitude distribution 23
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
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
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 0 0.092 mm r = 32 mm d = d 0 0.369 mm 26
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 0 0.099 mm r = 32 mm d = d 0 0.396 mm 27
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
Design of the reflector horn reflector Gaussian beam feed horn from focusing element Design: Patrick Kolesa 29
Simulation results 75 GHz amplitudes normalized to maximum of each column artifacts in reflector horn 30
Simulation results 92 GHz amplitudes normalized to maximum of each column artifacts in reflector horn 31
Simulation results 110 GHz amplitudes normalized to maximum of each column artifacts in reflector horn 32
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