antenna microstrip

Hello Guys,

I am making a 434MHz transmitter module placement . Please see the attached pic below,

I wanna ask as the microstrip on the Right Hand side o f the board doesnt has a GND plane is the placement OK ? . The antenna is a small ducky right angle to the plane of the PCB .


Thanks in Adv

TrIsHooL

Probably this line with out gnd is used as inductor to match the antenna.
TO judge it do the EM simulation of this structure

I think this is a mistake. Under the SMA connector you should place a gnd plane (the body of the connector is floating?)
You can take as example the reference design of TI CC1101, you'll find it in TI web pages.

I hope this can help.

Mazz

kspalla,

I do not have an access to these simulation programs unfortunately , I am only calculation and testing driven .

Mazz ,
The Ti application notes or any other never says to place a 50Ohm microstrip without a bottom GND plane . I have an application where I place a helical antenna right angle to pcb (space constraint and directionality) . It is a property of these antenna not to place a GND plane beneath them to save it from getting detuned . I cange the schematic with some compromising and placing a GND below the connector as suggested . I would like to know is this enough reason to not alow microstrip work as a radiator (the small GND strip placed below) and OK to do so.

Thanks
-Ts

OK, now I have understood better the issue.
I think that the second solution is good for the uStrip.
Maybe the best approach for you is to make 2 different protos and test which one works better.
Mazz

What you are proposing, a line without the groundplane is not good practice. That being said, 400 MHz is a relatively low frequency with a wavelength over two feet and you might get lucky and things will work well enough for your application.

If it does happen to work I would caution you about thinking that you have found something that is generally acceptable.

The "small rubber duck" is probably intended to be a flexible ? wave monopole and I suspect that there is no groundplane for the antenna either. Groundplanes play an important part in antenna performance (and transmission lines). Eliminate them at your peril.

Azulykit , thanks will not try to remove the GND plane , can you please help me with what width of GND plane trace beneath the Microstrip (50Ohm) should be necessary . That is equal to or somewhat wider than the top feed line ? the moment the microstrip leaves the main GND plane and moves towards the antenna.

-Ts

there is no canned answer for how small you can truncate the groundplanes. Under the microstrip I would consider something around 3 to 5 times the trace width as a minimum. Under the monopole for decent performance I would like to see something in the vicinity of a wavelength. It really depends on your requirements. Smaller dimensions could be acceptable.