antennas_feb14

antennas_feb14 - Antennas Greg Taylor University of New...

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Astronomy 423 at UNM Radio Astronomy Antennas Greg Taylor University of New Mexico Spring 2011
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2 G. Taylor, Astr 423 at UNM Radio Window spans a wide range of λ and ν from λ ~ 0.33 mm to ~ 20 m! ( ν = 1300 GHz to 15 MHz )
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3 G. Taylor, Astr 423 at UNM Outline • Fourier Transforms • Interferometer block diagram • Antenna fundamentals • Types of antennas • Antenna performance parameters • Receivers • Dipole Antennas
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Fourier Transforms 4 G. Taylor, Astr 423 at UNM
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Fourier Transforms 5 G. Taylor, Astr 423 at UNM
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6 G. Taylor, Astr 423 at UNM Mixer Software Square law detector Bandpass filter, IF amplifier
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7 G. Taylor, Astr 423 at UNM E.g., VLA observing at 4.8 GHz (C band) Interferometer Block Diagram Antenna Front End IF Back End Correlator
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8 G. Taylor, Astr 423 at UNM Antenna amplitude pattern causes amplitude to vary across the source. Antenna phase pattern causes phase to vary across the source. Polarization properties of the antenna modify the apparent polarization of the source. Antenna pointing errors can cause time varying amplitude and phase errors. Variation in noise pickup from the ground can cause time variable amplitude errors. Deformations of the antenna surface can cause amplitude and phase errors, especially at short wavelengths. Importance of the Antenna Elements
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9 G. Taylor, Astr 423 at UNM Wavelength > 1 m (approx) Wire Antennas D i p o l e A e = G λ 2 /4 π Y a g i Helix or arrays of these Wavelength < 1 m (approx) Reflector antennas Wavelength = 1 m (approx) Hybrid antennas (wire reflectors or feeds) Feed General Antenna Types
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10 G. Taylor, Astr 423 at UNM Effective collecting area A( ν , θ , φ ) m 2 On-axis response A e = η A η = aperture efficiency Normalized pattern
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antennas_feb14 - Antennas Greg Taylor University of New...

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