Wideband matching an electrically short bowtie antenna; 50 ohm, 434 MHz

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kellogs

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This is the technique applied so as to obtain a wideband matching + balun for a bowtie antenna.

I have run a simulation:


The two 43.3 nH inductors are there to cancel each -j*118 antenna arm reactance. Does it make sense ?

I have remeasured the antenna + caps / inductors populated with my nanoVNA and have found R - j*20 ohm. R was in the 10 - 20 ohm range, can't remember, anyway, less than 50. i have made approximations for all of the matching network's elements, i.e. precise values were used for only 8 pF, 24 pF and 7.5 nH. What should I do next to at least get that reactance closer to zero ? The antenna is very deaf currently.

Thank you
 
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You say wideband but list a single frequency?
It you mean signal bandwidth, that will be small compare to the carrier frequency and antenna matching range. The entire ISM band is less than 2MHz wide.

A bowtie is presumably cable fed? I'd stick with a stub match, half wave cable balun or just common mode choke. Those are all effective and well proven methods.
One example:

Look in the ARRL handbook or similar for others.
 
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The antenna + matching network all live on a PCB. It is electrically small for the frequency and its measure impedanced in one spot was 14 -j*236 ohm.

It will to get detuned when placed in other spots, i.e. impedance variation of +/- 5%, so I wanted at least the matching network to be forgiving of that.
 
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A 'bowtie', usually stacked in multiples as a 'short back fire' array, are renowned for being wideband and low gain - but with having good anti-ghosting properties - they were one of the TV aerial types we commonly used in certain areas, where ghosting was a problem.

From it's construction it's essentially a variant of a folded dipole, so presumably has something like 300 ohms impedance, and is balanced - hence you need a balun to connect it to coaxial cable.
 
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kellogs said:
It will to get detuned when placed in other spots, i.e. impedance variation of +/- 5%, so I wanted at least the matching network to be forgiving of that.
Click to expand...
You are over-complicating things; the matching / detuning is not that critical as the capacitive loading inherent to a PCB antenna mostly swamps the effects of proximity loading.

See the 434 MHz PCB antenna designs in this document:
 
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rjenkinsgb said:
capacitive loading inherent to a PCB antenna mostly swamps the effects of proximity loading.
Click to expand...
Capacitive hats on dipoles come to mind.
There is no GND pour underneath the bowtie... I do not understand how the PCB bowtie is ineherently loaded.
Also, proximity loading is a big concern, so.. I *guess* sticking to balanced structures far away enough from at least the enclosure is the way forward.
 
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