Waveguide flange or more generally a waveguide-to-coax adapter or feedhorn base

The wider bit at the bottom of a feedhorn for a radio dish is typically called a waveguide flange or more generally a waveguide-to-coax adapter or feedhorn base—depending on its function.

Here are some terms for different purposes:

1. Waveguide Flange
   – A flat, widened end used to mechanically and electrically connect the feedhorn to a waveguide or other components (e.g., a low-noise block downconverter or LNA).
   – Common types include UG flanges, such as UG-515/U for WR-650 waveguides.
2. Waveguide-to-Coax Adapter
   – If the wider section includes a transition from rectangular waveguide to a coaxial connector (e.g., N-type or SMA), it’s called this.
   – It often appears larger to accommodate the mode transition and to reduce return loss.
3. Feedhorn Base
   – Informal term used when referring to the broader mechanical portion that allows the horn to be mounted or joined to other parts of the feed assembly.
4. Backshort Cavity (if applicable)
   – Some designs include a cavity or wider section that functions as a tunable resonator (or backshort) to improve impedance matching at the feed point.

To make a simple, functional flange or base for your 1420 MHz cantenna to mount it at the focus of a 1.5 m dish, you need to ensure:

• Mechanical stability (secure attachment to dish or feed support).
• RF integrity (low reflections, good transition if connecting to waveguide or coax).

Here’s a simple DIY approach using common materials, assuming your cantenna is a tin or copper cylinder open at one end and fed with coax (like an N-connector probe inside):

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📡 Goal: Build a simple bottom flange or mounting base for your 1420 MHz cantenna

📏 1. Determine your waveguide diameter

For 1420 MHz (21 cm), the standard waveguide is WR-650:

• Inside dimensions: 165.1 mm × 82.55 mm
• Cutoff frequency (TE10 mode): ~900 MHz

Your cantenna (a short section of waveguide) should be roughly:

• Diameter: ~150–160 mm (if circular)
• Length: ~1/2 wavelength or longer (~10–15 cm is common)

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🛠️ 2. Simple flange / mounting base options

Option A: Flat metal plate (DIY flange)

Materials:

• Flat aluminum or brass plate (~2–3 mm thick)
• Drill
• Screws/bolts
• Metal shears or jigsaw

Steps:

1. Cut a square plate ~25 cm × 25 cm (or large enough to bolt to a bracket or LNA).
2. Drill a hole in the center to fit your cantenna snugly.
3. Insert the cantenna into the hole so the open end sticks out, and seal/glue it in place.
4. Drill holes around the plate’s corners for mounting it to the dish support arms or bracket.

This becomes your mechanical mount and acts as a ground plane for better coupling.

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Option B: PVC cap with metal foil or mesh

If you’re feeding the cantenna directly with coax and want a non-metallic base:

• Use a PVC end cap (e.g., for 6-inch pipe).
• Line the inside with adhesive copper foil or conductive tape.
• Drill for the coax cable and glue the cap onto the cantenna.
• Add a bracket or screws to mount the cap to the dish struts.

This gives RF shielding and mechanical strength.

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Option C: 3D-printed mount with foil lining

• 3D print a circular or square base with mounting ears.
• Line the inside with copper tape or aluminum foil for RF continuity.
• Connect to cantenna body and dish mount.

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🔌 3. Connect to feed system

• Use an N-type connector (female panel-mount) with the probe going into the cantenna.
• Ensure the probe length and placement is tuned (~1/4 wavelength from closed end).

For 1420 MHz:

• Probe length: ~3.75 cm (for copper wire)
• Distance from can bottom: ~4.8 cm

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📐 4. Position at dish focus

• For a 1.5 m paraboloid, the focal length f≈D2/(16d)f \approx D^2 / (16d), where:
  • D=1.5 mD = 1.5 m (diameter)
  • dd = dish depth (measure this!)
• Mount your cantenna so its phase center (near probe) is at this focal point.

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