Moxon-Yagi for LEO Satellites

| April 30, 2026 | Amateur Radio (Ham Radio) | No Comments

A Moxon-Yagi is a highly effective, compact choice for LEO (Low Earth Orbit) satellite operations, particularly for handheld use. By combining the wide beamwidth and excellent front-to-back (F/B) ratio of a Moxon rectangle with the high gain of Yagi directors, you get an antenna that is easier to point at a moving satellite than a high-gain, narrow-beam traditional Yagi.

Why Use a Moxon-Yagi for Satellites?

Most LEO satellite work happens on the 2m (VHF) and 70cm (UHF) bands. A traditional Yagi for 2m can be quite long and unwieldy for handheld operation. The Moxon-Yagi solves several practical problems:

  • Size: The Moxon rectangle “folds” the elements, reducing the 2m wingspan by about 25–30% compared to a standard dipole or Yagi.
  • Directivity: It offers a very clean radiation pattern with a deep null behind the antenna, which helps eliminate local terrestrial interference (QRM) during weak-signal satellite passes.
  • Beamwidth: It has a wider “sweet spot” than a multi-element Yagi, making it much more forgiving if your tracking isn’t 100% precise.
  • 50-Ohm Match: A well-designed Moxon has a native impedance very close to 50 ohms, allowing for a direct coax feed without complex gamma matches or hairpins.

Popular Design: The Dual-Band Hybrid

A common configuration is to use a 2m Moxon as the driven element and mount several 70cm Yagi elements on the same boom.

1. The Single Feedline Trick

Many builders use inductive coupling to avoid using a diplexer. In this setup, the coax is connected only to the 2m Moxon. A 70cm “slave” driven element is placed very close to the 2m element. Through mutual induction, the 70cm energy is transferred to the UHF portion of the antenna.

2. Dimensions and Geometry

For a 2m (145 MHz) / 70cm (435 MHz) build, a typical design (like the well-known M1GEO or LY3LP designs) looks like this:

  • VHF Section: A 2-element Moxon (one driven element, one reflector).
  • UHF Section: 3 to 5 Yagi elements (director and/or reflector) optimized for 435–438 MHz.
  • Boom: Usually made from 20mm or 25mm PVC pipe or a wooden dowel.

Homebrewing Tips

If you are building this from scratch using materials like aluminum welding rods or 10-12 AWG copper wire:

  • Software Simulation: Use MMANA-GAL or EZNEC to fine-tune the element spacing. Because the 70cm elements are “nested” within the 2m footprint, they can interact and shift the resonance of the 2m section.
  • Element Mounting: For a lightweight handheld version, 3.2mm aluminum welding rods are ideal. You can secure them to a PVC boom by drilling holes through the pipe and using hot glue or small cable ties.
  • The “Gap” is Critical: In a Moxon, the distance between the tips of the driven element and the reflector (the “tails” that point at each other) is the most sensitive dimension for achieving a good SWR and F/B ratio. Use an insulator like a small piece of plastic tubing to keep this gap consistent.
  • RF Choke: Always include a small “Ugly Balun” (4–5 turns of the coax around the boom) right at the feedpoint to prevent the shield from becoming part of the antenna and skewing the pattern.

Operating Considerations

  • Polarization: Satellites tumble as they pass over. Since the Moxon-Yagi is linearly polarized, you will need to rotate the antenna on its axis (wrist-twist) during the pass to maintain the strongest signal as the satellite’s orientation changes relative to you.
  • Full Duplex: If you plan to transmit and receive simultaneously (standard for linear transponder satellites), ensure your coax is high quality (like RG-58 or LMR-240) to minimize loss on 70cm, where cable attenuation is much higher.