Aperture efficiency of reflectarray antenna
I saw most of the IEEE papers on reflectarray design had included the value for aperture efficiency.
How can we calculate the aperture efficiency of a reflectarray antenna?
How much percent of aperture efficiency is consider good?
Thanks.
are you asking about the antennas in which aperture coupled feeding is used?
I'm interested about the aperture efficiency value of reflectarray antenna which is spatially feed by a horn antenna.
Is the aperture efficiency same as the radiation efficiency of common antenna?
My guess is no. I would expect the overall efficiency to be lower, since there are other losses in the system. But check the IEEE standard for the definitions.
APERTURE EFFICIENCY, 0
The Antenna Efficiency, 0, is a factor which includes all reductions from the maximum gain. 0 can be expressed as a
percentage, or in dB. Several types of "loss" must be accounted for in the efficiency, 0:
(1) Illumination efficiency which is the ratio of the directivity of the antenna to the directivity of a uniformly
illuminated antenna of the same aperture size,
(2) Phase error loss or loss due to the fact that the aperture is not a uniform phase surface,
(3) Spillover loss (Reflector Antennas) which reflects the energy spilling beyond the edge of the reflector into
the back lobes of the antenna,
(4) Mismatch (VSWR) loss, derived from the reflection at the feed port due to impedance mismatch
(especially important for low frequency antennas), and
(5) RF losses between the antenna and the antenna feed port or measurement point.
The aperture efficiency, 0a, is also known as the illumination factor, and includes items (1) and (2) above; it does not result
in any loss of power radiated but affects the gain and pattern. It is nominally 0.6-0.8 for a planer array and 0.13 to 0.8 with
a nominal value of 0.5 for a parabolic antenna, however 0 can vary significantly. Other antennas include the spiral
(.002-.5), the horn (.002-.8), the double ridge horn (.005-.93), and the conical log spiral (.0017-1.0).
Items (3), (4), and (5) above represent RF or power losses which can be measured. The efficiency varies and generally gets
lower with wider bandwidths. Also note that the gain equation is optimized for small angles - see derivation of wavelength
portion of equation of equation [7]. This explains why efficiency also gets lower for wider beamwidth antennas.
check the following link:
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