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2.4GHz quad double quad

A simple quad double quad design that gives low SWR and high gain.

Written by: G4RFR ( FRARS ) Wednesday, 7 August 2002

Click for full size imageThe G6NLC duad double quad antenna was inspired by designs for the 23cm and 13cm Amateur TV allocations. This design has been scaled, built, and then analysed with a network analyser to ensure the performance is optimum. The design is basically 4 double quad antennas phased together such that the signal from each antenna is added. The overall gain of this antenna is approaching 16dB, just under four times that of a single double quad.

To construct this antenna, start with a piece of double sided PCB 260mm by 230mm. Mark the center points in both the horizontal and verticle planes. Using the two diagrams, mark and drill the holes that will have the UT141 coax pushed through for connection to the double quad elements.

In this design, I left 10mm of coax on the back of the antenna to provide adjustment if required. On the front of the antenna, the double quad elements are spaced 14mm from the ground plane, and they are made from copper wire 1.8mm thick. When soldering the double quad elements in position, ensure they are all facing the same way. i.e. ground connection on the left, inner connection on the right. This will eliminate any phasing problems.

Next, cut four pieces of UT141 coax 80mm long, and strip 1.5mm of outer from each end, leaving a total outside length of 77mm. These will form part of the phasing assembly. Follow the diagram as to the connection of these pieces of coax. Connection of two double quads in parallel will result in an impedance of 25ohms.

Next for the 25ohm to 100ohm matching sections, cut two pieces of 61mm UT141, again strip the outer back 1.5mm from each end to leave a outside length of 58mm. Of course 2 100ohm coax's in parallel will result in an impedance of 50 ohms. Connect each piece to the joined 77mm lengths as per the diagram. Under the connector, both centre conductors from the 58mm lengths are connected to the centre pin of the SMA socket. Solder the outer of these lengths to the SMA socket body to ensure a good earth connection.

If you have followed this design carefully, your antenna will perform very well and have an excellent match to 50ohms resulting in a low SWR.

This antenna has been sucessfully used in an obstructed path link over a few kilometers. The beamwidth is fairly narrow and the antenna is low profile. To waterproof, simply find an old plastic container that will go over the front and back parts and use silicon sealent to fix them onto the double sided PCB.

Thanks go to Jan - SM3JJI for spotting the obvious mistake!

Links:

  • More FRARS Wireless LAN articles [Click here]
  • 2.4GHz double quad antenna [Click here]
  • 23cm version of this antenna [Click here]

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