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Example 10: Eggbeater LEO Satellite Antenna for 432 MHz (70cm)

This omnidirectional circularly polarized antenna is designed for up-facing coverage of Low Earth Orbit Satellites. It is model EB-432/RK70CM from M2 Antenna Systems. Their website description is:

” The EB-432 EGGBEATER offers exciting new performance characteristics for both fixed and mobile operations. The EGGBEATER produces smooth Omni directional HORIZONTAL polarity at the horizon. Above the horizon, the pattern transforms to RIGHT HAND CIRCULAR, making it a natural for OSCAR satellite use. By spacing the EGGBEATER 1/8 wave above a metal surface or the RK-70CMfor base installations, the circular lobe increases by 6 dB, producing a hemispherical pattern. “

Since circularly polarized can be hard to feed (or properly phased) in real hardware, we were skeptical of some of these claims. This antenna was vector-gain 3D patterned with 10 degree spherical resolution from 400 to 470 MHz in 1 MHz steps. A sample 3D total gain plot at 432 MHz can be seen below. By downloading the desktop plotting software and the plotfile below, you may render 3D plots at any frequency on your PC. 

When plotting the peak gain (from any direction) we can see that it is about 3 to 5 dBi over the operating range. The upwards (towards the sky) gain is about 1 to 2 dBi, and the antenna is indeed RHCP (although the axial ratio is only modest at 4 to 6 dB, Z-Axis). Gain towards the horizon is plotted in the four cardinal directions and varies significantly with direction and frequency, coming in at about -1 to +3 dBi. The sideways gain in the Y (and -Y) axis is about 3 dB higher than the X (and -X) direction. This can be seen in the graphs below and is obvious in the 3D spherical gain plot.

While it may be overly optimistic to consider this a “+6 dBi gain” omnidirectional antenna, it does have some gain close to this, and generally meets the design goals of being a RHCP satellite antenna with useable gain at the horizon.  

We plan to permanently install it outside with an LNA and SDR receiver, and hook it into the SatNOGS network and see how well it works. 

The Excel dataset with graphs may be downloaded HERE

The 3D plot-file may be downloaded HERE

 

 

Date 17 Jul, 2018

Categories 3D Spherical Patterns, ALL Antennas, Circularly Polarized

Photo Measured Antenna Gain for LEO Satellite RHCP Circularly Polarized 70 cm

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