Development - Simulation - Consulting |
Dish
Antenna |
S-Band Parabolic Antenna An
in-house project of emPhys
Physical Technology. Project task Develop
a small dish antenna for applications in satellite communication. Here are
the specifications: · Patch feed for 2.3 GHz · Circular left-hand
polarization ·
Optimal
illumination of parabolic dish with f/D = 0.4 · Low losses · Transmission power up to 1000 W · System impedance 50 Ω Project Execution The
geometry model comprises the 1 m parabolic dish and the patch feed. Due to
the high power requirement the patch cannot be realized as a PCB or ceramic
patch. A low loss design with air dielectric is required. The model avoids
reflections at the outer boundary by surrounding it with a perfectly matched absorption
layer.
Parameter study Frequency response 2.1 -
2.5 GHz Patch and reflector
geometry Power feed and impedance
match Focal position Adjustment of circular
polarization Results
Radiation pattern
Assessment of radiation pattern by 3D-visualization and
polar diagram in H and V plane. The main lobe achieves a directivity (gain)
of 24 dBi. This results in illumination efficiency
of 50 %.
Impedance match
S11 and reactances
of the patch feed in the frequency range 2.1 to 2.5 GHz. Coaxial feeder and
focal position of the patch feed are optimized. Please find the details
below.
Focal position of patch feed
Below we show the impact of the patch feed's
focal position to the impedance match at the nominal frequency of 2.3 GHz.
The patch was shifted by ±50 mm from its theoretical focal
position. The left diagram shows S11, the right shows the reactances.
These datasets are available for the frequency range 2.1 to 2.5 Ghz.
Feed position on patch radiator
The study parameter is here the distance of
the connection of the coaxial feed on the patch radiator disc and the disc's center.
A center distance of 11.0 - 11.5 mm results in an excellent impedance match
to the 50 Ω system
impedance. The diagrams below show the parameter results at 2.3 GHz. These
datasets are available from 2.1 to 2.5 GHz.
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The left diagram show the S11
curve as measured with a Rohde & Schwarz ZVL3 network analyzer, the right
diagram shows the COMSOL result. For the measurement the patch feed was not mounted
on the dish but radiated into the laboratory. Also for the calculation in
COMSOL the dish was removed from the model. Measurement and model show excellent
agreement in resonance frequency with a realistic S11 = - 15 dB. The model
value S11 = -27 dB seems to be 'too good to be true'. This is probably due to
the idealized conditions of the model. The model's perfectly matched layer
(PML) avoids reflections very well. The measurement were carried out in
normal, not reflection-free chamber. Furthermore the model avoids error
sources like cables, connectors and calibration error of the analyzer. Summary
A model for the optimization of a patch feed
for a small parabolic dish antenna was developed with COMSOL Multiphysics.
The model ids fully parameterized regarding all geometrical dimensions of the
antenna. The patch feed could be specified regarding
frequency, impedance match, focal position and dish illumination. The
illumination efficiency of now 50 % may still be improved to some degree. The study is going on. We will be trying to
improve the bandwidth and we will introduce circular polarization into the
model. We will investigate two strategies to achieve circular polarization
and we will report about results here. This model takes some 15 minutes for one
parameter set on a 4 core i7 CPU at 3.6 GHz. It needs about 40 GBytes memory with direct solver. A comparably comprehensive prototype study
would require manufacturing many prototype variants and a plentitude of
measurements in a reflection free chamber. We plan to bring this patch antenna to the
market in linear and circular polarized versions. As the model is
parameterized it can easily be adapted to other operation frequencies. The
rage from L band at 1.2 GHz up to Ku band at 12 GHz seems realistic. Please contact us if you are
interested in this development! |