How does this radar detector horn antenna is fed?

[randsl]

I saw this radar detector tear-down post : https://www.allaboutcircuits.com/news/teardown-tuesday-whats-inside-a-radar-detector/

It seems the horn used in this detector is using none of the conventional wave-guide excitation techniques shown below.
 




How the small piece of PCB track at the end of the RF PCB is receiving the signals/exciting the wave-guide? It sits in parallel with the wave-guide axis. 

Could anyone explain a bit about the excitation operation of the waveguide with this small PCB track?

cheers,

[rfeecs]

Here's an example:
http://www.google.com.pg/patents/US6639486

Try googling "tapered ridge to microstrip waveguide transition" and you will find other similar transitions.

[randsl]

It's very interesting and very clever method to couple RF signals into a wave-guide...
Also I guess it's a very cheap method as well specially if you want to use in inexpensive products... so you can avoid expensive connectors assembly etc.

What are the cons of this method?
Does the performance of the antenna degrade if the aluminum ridge is covered with oxides? or it doesn't matter?

Is this method only available for rectangular waveguides? or can we use this technique for circular waveguides as well...?

cheers,

[rfeecs]

I wouldn't think oxides would be a problem, as long as there was still a good contact to the microstrip.

Attached is an example of a different type of transition for circular waveguide, but equally economical.  This one is from a DBS satellite tv LNB.  It looks like they coupled off two different channels for each waveguide.

[zl2wrw]

[SNIP] Attached is an example of a different type of transition for circular waveguide, but equally economical.  This one is from a DBS satellite tv LNB.  It looks like they coupled off two different channels for each waveguide.

Two probes per waveguide in a satellite LNB is so that the LNB can electronically switch RF polarisation.
Given the presence of a "septum" (or something like that) in each waveguide (the metal thing between the probes in the middle of each waveguide) I'd say that your LNB is probably designed for circularly polarised signals.

You might find this interesting:
http://www.attplus.cz/hamradio/projekty/article/Prime_focus_circular_waveguide_feed.pdf

[rfeecs]

[Two probes per waveguide in a satellite LNB is so that the LNB can electronically switch RF polarisation.
Given the presence of a "septum" (or something like that) in each waveguide (the metal thing between the probes in the middle of each waveguide) I'd say that your LNB is probably designed for circularly polarised signals.

You might find this interesting:
http://www.attplus.cz/hamradio/projekty/article/Prime_focus_circular_waveguide_feed.pdf

Yes, that article seems to explain exactly what is going on here.  There is that stepped septum in each waveguide.  It comes in from the same side on both.  So one polarization goes to the top two probes and the other goes to the bottom two.

I was thinking two channels because based on the size of the dielectric pucks, the two LO's are at two different frequencies.  I've been searching around trying to find out why.  Apparently this is a DishPro LNB which "stacks" the two different polarization signals down the same wire by converting them to two different frequencies.  Interesting.