WR90 to SMA transition

One of the completed horns ready for testing

I needed a couple of transitions, so decided to try to make a very simple narrowband design, optimised for 10368 MHz with low loss and a good match over a few hundred MHz. I ran up a design with rounded corners to the cavity to make it simple to machine using an 8 mm slot drill. I chose aluminium for the body as it performs well, although without anodising, it is going to need protection from the elements. I used some good quality Radiall SMA four-hole flange-mount sockets.

Although this looks a simple part, the instructions I make for myself show the level of detail.

I’ll publish the measured performance soon. So far, I can get around -23dB across ±100MHz. Once optimised, I will have some of these for sale to bona-fide experimenters. Email neil@g4dbn.uk for details

CAD model in Fusion360
Modelled through loss and return loss from OpenEMS

2 thoughts on “WR90 to SMA transition”

  1. bonjour j ais realiser des transition guide / sma pour diferente bandes du 24 GHz /10 gHz , mon expérience montre que il faut absolument un fond réglable si on veut une adaptation correcte, , j ais aussi utiliser des SMA dont j ais retirer le téflon pour passer en ligne a air en recalculant le diamètre de façon a respecter la valeur d impédance de 50 ohms mes transition sont réaliser toute usiner dans la masse le mesures ont été faite par marcel F5DQK , qui a un blog , j ais obtenus un RL a -32 dB d’adaptation et en large bande sur les 24 GHZ , je vois que tout vos usinages sont très professionnel , et magnifique
    73s philippeF8BTP

    1. Merci Philippe, quelle bonne idée. L’utilisation d’une section de ligne à air d’environ 2,90 mm de diamètre extérieur permettra une détermination précise de la longueur de la sonde.

      For folks who don’t read French, Philippe explains that he removes more of the PTFE insulation than I do, and machines a smaller hole of the right diameter to make a 50 ohm air-spaced coaxial line where the probe of the pin passes through the wall of the guide. That will make a much better definition of where the end of the waveguide probe ends. It would also look MUCH neater. Brilliant idea. Philippe also points out that to get the best possible return loss, it helps to have a moveable backshort. I am hoping to avoid that by careful measurement, optimisation and precise machining of the probe position. I made several models with the pin at different spacings from the backshort and made fine adjustments to the pin length. To make manufacture simpler, I might fit a tuning screw in future models. Commercial transitions are often designed for very wide bandwidth, but I want a near-perfect match at a reasonable Q-factor, aiming for the absolute minimum insertion loss.
      73 Neil G4DBN

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