The QO-100 satellite gained popularity among many radio amateurs and made intercontinental communication available. The designers of the QO-100 satellite transponder have ingeniously set the frequencies and bands in such a way that it is possible to use many commonly available components to build a reception and transmission setup. Downlink is in the 3 cm band, uplink in the 13 cm band.
For broadcasting, it is advisable to use circular polarization, which can be achieved as easily as possible with a parabola and an irradiator with circular polarization. The choice of a suitable irradiator depends primarily on the f/D ratio of the parabolic reflector.
Helix and patch type irradiators are most often used, respectively. by modifying it as SWEAT by feed. The patch irradiator is suitable for dishes with f/D around 0.4. Regular TV dishes have a higher f/D. When using an unsuitable irradiator, the signal from the irradiator goes beyond the edges of the dish or does not use its surface.
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Dimensions of patch feed for QO-100
It is best to start from the original drawing of the dimensions of the patch feed. The critical dimension is the emitter-reflector distance, which must be 3 mm. The experience of the designers of this feed confirms that even a small deviation will cause degradation of properties.
Production of patch feed
We will need an N- or SMA connector, a reflector plate and an emitter. Cut or cut out the plates and drill holes for the connector and soldering of the radiator. Determining the distance between the emitter and the reflector using a drill proved to be useful for me. After soldering, we can easily pull it out.
I used high-quality cuprextite as a reflector. After the circle was cut out, the edges were smoothed by hand. A tin plate from a box was used for the radiator preamplifier.
Patch feed tuning
For the correct functioning of the patch feed, it is necessary that one resonant frequency is above and the other below the band, i.e. approx. 2400 MHz. Without this setting, correct circular polarization will not be achieved.
Precise adjustment can be made by pressing or pushing the corners of the radiator. If you have a measuring technique, the possible process is as follows (uncalibrated meter):
If we assume that the reflection is -27 dB, or -29 dB, so these are not bad parameters for an irradiator made "on the knee" (PSV < 1.1). Patch feed is one of the easy-to-implement feeds for the QO-100. Practical tests also confirmed that the patch feed works very well.