Slotted Waveguide Build

• Cut the 100x50mm (3mm thick) rectangular hollow box section aluminum to 5 waveguide wavelengths, with an additional 100mm added for mounting (About 910mm. see double sided waveguide calculator or Single sided Waeguide calculator).
• Mark (with a square and metal scribe) the horizontal center line of each slot and from this, the top and bottom lines of each slot. (Nb. These are all offset 3mm from the top to allow for the insertion of the top reflector.) I used the square to run these lines right around all faces. This ensured the front and rear slots line up.
• Mark the horizontal center line for the N-Socket hole.
• Mark a horizontal line at the top of the bottom reflector.
• Mark the vertical center line of each slot. Nb.They alternate left and right of the center.
• Mark the centers for drilling holes at either end of the slot, 3.25mm in from the top and bottom line.
• Punch each of these marks to help guide the drill.
• Punch the center marks for the N-Socket

• Use a small drill bit to drill a guide hole at each punch point. This helps when drilling the larger holes.

• Drill a 6.5mm hole (slot width), widening each of the guide holes.

• Drill a 10mm hole for the N-Socket, then use a 16mm drill to widen the mouth. The N-Sockets have a conical end. Use an N-Socket to ensure it fits.
• Placing the N-Socket in the hole, mark out the location of the mounting holes.
• Punch the centers of these holes
• I drilled mine to 3mm diameter, so I could thread the holes. I used 4mm nylon bolts, so there is no metal sticking into the cavity.

• Use a router (with a tungsten tipped tool) to join the top and bottom hole of each slot. I only had a 1/4inch cutting tool. This is slightly less than 6.5mm, so I did this in two runs. Nb. Do this slowly so the tool doesn't have to cut too quickly. Also be careful to file away sharp edges at the end of each slot cut.

• Use a file to square the ends.
• Also use the file to clean up the edges. The inside shouldn't be rough.
• We are aiming at 1mm maximum error in length for each slot. Having marked the top and bottom line, it is easy to see where we need file to.

• Using a 44mm wide off cut of the box section, cut an L piece for the bottom reflector and a flat plate for the top reflector.

• Measure half way down the small side of the L section, mark out and drill two mounting holes.
• Using the marked position of the top of the bottom reflector as a reference, do exactly the same to one of the short sides of the main antenna.
• The top reflector is mounted by drilling small holes and using pins to hold it in place (I used small nails).

• The bottom reflector can be riveted in place. It doesn't have to be a perfect fit. Small gaps around the edges will let moisture out.

  Nb.The top pictures are from a single sided version, which is mounted top and bottom.
  The bottom two are the double sided one. It is mounted on the bottom only, having two brackets for stability.

• The top reflector of the Single Sided one was riveted. I used an L shape, the same as the bottom reflector, cutting the mounting side across the diagonal to fit the cut off top (done to stop water buildup).

  For the Double sided version, the Top Reflector was held in place with small panel pins. I drilled 1mm holes through the front and back of the waveguide and into the edge of the top plate and hammered in the panel pins.

  I siliconed the edges to ensure the antenna didn't fill up with water.

• The slots were covered by thin polyester tape (microwave friendly and only a micron thick). This stops water getting in and spiders and other insects making the antenna their home. The tape I used is sometimes called "yellow thermoset tape". Test the tape in a microwave oven. It shouldn't heat up (don't blame me if it melts down, catches fire and sticks to the insdes of the oven).

• N-Socket has a 2mm diameter copper wire soldered to it, and is cut so that this is 30.7mm long (including the small bit of the N-Connector it is soldered to).

• A conical feed is a much better probe than the straight wire 1/4 wavelength dipole. It is made from a 20mm x 40mm piece of copper and rolled into a cone. It is slightly harder to make, but it is worthwhile.

  Cut the red area from the copper and roll into a cone. Solder along the joint and solder onto an N-Connector so that the cones base will be exactly half way across the cavity. In my case, this was 22mm (including the bit of the Nconnector it was soldered to). I had to cut down the center of the Nconnector slightly.

  Nb.The 10mm hole in the waveguide for the Nconnector will be too small for a cone probe. You will need to drill it out to 16mm. Do this in small increments, widening the hole one or two drill bit sizes at a time. It will make a much neater hole.