RF 433 or 315Mhz module antenna problem

[nikhil arora]

I have attached the schematic diagarm with little explanation on it.
the main part we have to see is the Antenna ouput of the RF module.

We have to connect this ouput to the antenna for this we use tracks to the antenna connector on PCB.
Now for short distances we can use this track(if made long) as anttena and for long distance we can connect external antenna.
now my questions are

1>
Just by having a 50ohm track at antenna ouput can behave as good antenna for short distance.

2>
The losses in the bend of the track are significant at these frequencies can we ignore that losses. or I have to make bend in other way.

3>
for calculating the width of the pcb for 50ohm line we need only the dielectric constant of pcb and thickness of pcb only.
I am using glass epoxy or similar pcb without any ground plane so we cannot use microstip line formula.


I will answer all your queries
thank you for each reply

 

[Russlk]

If you don't have a ground plane, the line cannot be 50 ohms and it will radiate. If you make the line 1/4 wavelength, the driving point impedance will be about 75 ohms and it should be a good radiator. I don't think the width of the line is important at all.

 

[nikhil arora]

Thanks I got your point and i totally agree that line without ground plane cannot be 50 ohms.
Now my doubt is
Do i have to resonant it for better efficiency or leave it as it is.

 

[Russlk]

For best efficiency, you should adjust the length to be resoant.

 

[nikhil arora]

resonant lenght comes around 17cm and I may not have that much of space on pcb

thats why have bend it like this even then I may not have complete quarter wavelenght.

is loop antenna more effecient than this one

 

[Russlk]

The loop antenna is more directional but I don't know how it compares for efficiency. You can zig-zag the antenna to make it resonant in a shorter distance, but I don't know how to calculate it.

 

[nikhil arora]

I think we cannot introduce much of zigzag. What problem do we face when we introduce much zigzag in our antenna.

 

[i_build_stuff]

You probably won't get good results by just bending (or "zigzagging") the antenna track. That completely changes the fields around the antenna.

If you don't want to play with Maxwell's equations, then I'd suggest using some known antenna type, like a loop antenna, folded dipole, whatever. That way, you can just use the formulas for that type and know that it will work.

Otherwise, there are really tiny RF connectors that you can place right next to the antenna pin on your chip / module, and run a proper line out to an external antenna. MCX connectors, for example, are 75-ohm and take up about 1/4 of a square cm. MMCX are 50-ohm, and take up about a 2.5mm square.

 

[Russlk]

Yageo makes a 433 mHz antenna that is about 3cm long. Using a parabolic reflector, I got a range of 300 meters. I don't know where to buy it now, Mouser has stopped carrying it in the catalog. Try a Google search.

 

[nikhil arora]

If you don't want to play with Maxwell's equations, then I'd suggest using some known antenna type, like a loop antenna, folded dipole, whatever. That way, you can just use the formulas for that type and know that it will work.

on pcb we can have loop antenna only.

Otherwise, there are really tiny RF connectors that you can place right next to the antenna pin on your chip / module, and run a proper line out to an external antenna. MCX connectors, for example, are 75-ohm and take up about 1/4 of a square cm. MMCX are 50-ohm, and take up about a 2.5mm square.

These connectors are having more cost then RF module itself.

 

[DirtyLude]

Nice links on embedded rf antenna design:

**broken link removed**
**broken link removed**
**broken link removed**

 

[nikhil arora]

I have gone through
https://www.electro-tech-online.com/custompdfs/2006/03/00831b.pdf
and few other files of microchip appnotes

and files sugessted by you but I didnot find what i was looking.

I think I will jumper for having two antennas.