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Published byImogene Singleton Modified over 9 years ago
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Aperture Antennas INEL 5305 Prof. Sandra Cruz-Pol ECE, UPRM Ref. Balanis Chpt. 12, Kraus Ch15
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Aperture Antennas Most common at microwave frequencies Can be flushed-mounted We will analyze radiation characteristics at far field – Rectangular aperture – Circular aperture
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Find Radiation Pattern in 2-D E-plane ( =0), H-plane ( =90 o )
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Far field is the F of the near field Fourier Transform for 1-D For two-dimensions, x and y; f t
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Properties of Fourier Transform
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Taking the Fourier transform of the 2 equations above:
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Now, we define, And we obtain, Which has a solution of Then we take the inverse transform
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If z=0, then, we are at the aperture Which looks like: Which is the inverse of F…
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This is the Fourier transform for 2 dimensions, so: Therefore, if we know the field distribution at the aperture, we can used these equations to find E(r) @ff =>First, we’ll look at the case when the illumination at the rectangular aperture it’s uniform. It can be shown that,
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Uniformly illuminated rectangular aperture *Note: in Balanis book, the aperture is a x b, so no 4 factor on the eq. above.
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TE 10 illuminated rectangular aperture
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How does this pattern looks…
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Near-field distrb. and far- field patterns with HPBW and SLL. Principle used in UPRM anechoic chamber.
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Comparison of uniform vs. cosine-tappered aperture
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Rectangular Aperture: Directivity For TE 10 illuminated Rectangular Aperture the aperture efficiency is around 81%. For the uniform illumination, is 100% but in practice difficult to implement uniform illumination.
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AF
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Circular Aperture (Uniform illumination) In this case we use cylindrical coordinates
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Circular Aperture w/ uniform illumination For TE 11 illuminated Circular Aperture the aperture efficiency is around 84%. For the uniform illumination, is 100% but in practice difficult to implement uniformity
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