# Pcb as antenna track

Discussion in 'Radio and Wireless' started by Rajinder, Mar 1, 2018.

1. ### Rajinder

443
7
Jan 30, 2016
Hi all
I am looking at doing a project with 433MHz radio modules.

I think that 3x10 (power8)/433MHz is 0ne wavelength.
If i divide this again by a quarter to get a 1/4 wavelength.

Just say this came to 7cm as an example.
I want to know how i can make a PCB track to act as an antenna. Say it needs to go i to a 50 vonnector. Is it essy maths?
Can anyone help?

2. ### duke37

5,364
769
Jan 9, 2011
70mm would be the length in free space. If the trace is placed on a PCB it becomes a transmision line which will have characteristics dependant on the dielectric constant and thickness of the board. Remember that you will need another quarter wave or ground plane to drive the element from.

3. ### Rajinder

443
7
Jan 30, 2016
I worked it out like 3x10 (power 8)/433MHz=0.70cm
Then dont i need to divide be 4 to get 1/4 wavelength?
Is there anywhere or some info available to explain when this track is placed on the PCB. Some simple examples?

4. ### davennModerator

13,671
1,892
Sep 5, 2009
no 0.70 m not cm (so it's 70cm)

the formula for wavelength is ....
300 / freq(in MHz) = length ( in metres)

yes
then you would have to multiply by the Vf (velocity factor) of the copper track. as a rough guide (and for your use, it would be close enough)
x.88

so 300 / 433 = 0.69m /4 = 0.1725m x 0.88 = 0.1518m = 15.18cm for an electrical 1/4 wave
normally it would be run around the outer edge of the pcb

NOTE: at 433MHz you wont get a 1/4 antenna on a pcb unless the pcb is large
most antennas for this purpose (remote controls etc) are smaller than a 1/4 wave and very inefficient

Dave

Last edited: Mar 3, 2018
5. ### Rajinder

443
7
Jan 30, 2016
Hi
Thanks for the help much appreciated.
Am i wrong in thinking the track should be 15.18cm in length (as per your calculations)?

I have a few more questions
1. How would i work out the width of the track
2. If i wanted to match it to say a 50 ohm impedance. What would i need to do? Is it a case of adding matching components or adjusting track width to get the correct impedance?
3. If i decide to use a antenna rather than pcb track as a antenna i.e. wound coil antenna. Is there any simple guidelines for the number of turns, length and type of wire i need to use?

Sorry for all the questions.

5,164
1,081
Dec 18, 2013
What radio module are you using, most of the application notes will have details about connecting an antenna and any filtering / matching components that are needed.

7. ### Rajinder

443
7
Jan 30, 2016
Hi
I am looking to use a HT12E/D with 433MHz RF modules. I have played around with these before. But what I need is the antenna design i.e. the number of turns, type of wire, length etc to get maximum range.
Thanks.

8. ### davennModerator

13,671
1,892
Sep 5, 2009
how big is the PCB and how big is the enclosure ?

as I said up the page ... just about anything you use in a small confinement is going to have very poor efficiency

Dave

5,164
1,081
Dec 18, 2013
As Dave mentioned above. You will be limited by the size of the PCB ground plane you are using. Getting the first part of the dipole is easy. You need 1/4 wavelength of 1 mm (approx.) solid core wire. The second part of the dipole or image antenna or counterpoise, what ever you want to call it will depend on the size of the ground plane you are using on your PCB design.
Thanks

10. ### Rajinder

443
7
Jan 30, 2016
Hi
Many thanks for the information.
I have a couple of more questions:
1. Please could you explain, what you mean by 'limited by the size of the PCB ground plane you are using'?
2. I am using the whole of layer 2 as a ground plane. What do I need to consider regarding this?
3. My thinking was that you make a PCB track with length as 15.82cm and then put a ground plane underneath it and use the appropriate filter matching components to get the 50 ohm matching. Is that not correct?
4. Is there a simple step by step guide that I can follow?
I am a novice but really would like to understand this area a little better.