# 868 MHz planar antenna design

#### Tibor10

Joined Jan 22, 2020
2
Hi everyone,

I am struggling with antenna design for my PCB. This is how my PCB looks like.

I have started just by copy designs which have already exist and want to modify them but I am not even copy and simulate antenna from TI.

I try to simulate the exact copy of this antenna using HFSS but I have no results. Ground on bottom side, antenna on top side and lumped port between them. I do not have matching circuit but even without it I should get any results, return loss is less than 0.5 dB and frequency is shifted.

Could you please anybody help me with this? What am I doing wrong?

Thank you very much in advance.

#### Janis59

Joined Aug 21, 2017
1,057
In the NRF24L datasheet are given a high accuracy drawing of 2,4 GHz antenna of Your proposed. Just if to magnify it proportionally, seems all the problems may be solved in firsts approximation. At least, You be capable to etch the first sample and stick it to N1201SA or other VNA. Then You shall see which places must be corrected longer or shorter. My advice - choose very very carefully the material of pcb. 99% of all FR4 materials will have a 0,015 loss factor what is detrimental, but Rogers Duroid 6630 is bit expensivish but having LF=0,0003 (Q-factor=2400). Dont forget the thickness of pcb plays the role as well.

At 868 I had adjusted only one sort of antennas, its 7 element Yagi-Uda for maximum beat-through distance. May search here year ago for accurate data of element sizes. But it is 70 cm long and 120 mm wide.

Other construction I like very much is the J-pole, There You may find my grieveful story about it was adjusted its enough to change so minor as 0,1 mm wider of narrower the distance between both parallel parts, and antenna parameters drifts with a factor up to the very ten. So, first must be solved how to fix it well. And pcb may happen to be one of such methods I havent tested. J-poles most unique thing is the sharply narrow lobe by horizontal axis (it dont illuminate the Cosmos unneedly) and omni lobe around vertical axis. Thus, at identical (or slightly higher) G-factor as halfwave vibrator, it gives (as radio-hamsters acclaim) much larger beat-through distance of communication.

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#### Tibor10

Joined Jan 22, 2020
2
Thanks for answer but in fact I need 868 MHz antenna which fits on my board which has to be FR4 board. I thought that I just take existing antennas (from TI DN024, DN023 or DN031) and put it there but it seems that it does not worked properly or maybe I have problem to simulate it by HFSS. Or I just have bad knowledge about antennas and that is my biggest problem

Thank you anyway for your time.

In the NRF24L datasheet are given a high accuracy drawing of 2,4 GHz antenna of Your proposed. Just if to magnify it proportionally, seems all the problems may be solved in firsts approximation. At least, You be capable to etch the first sample and stick it to N1201SA or other VNA. Then You shall see which places must be corrected longer or shorter. My advice - choose very very carefully the material of pcb. 99% of all FR4 materials will have a 0,015 loss factor what is detrimental, but Rogers Duroid 6630 is bit expensivish but having LF=0,0003 (Q-factor=2400). Dont forget the thickness of pcb plays the role as well.

At 868 I had adjusted only one sort of antennas, its 7 element Yagi-Uda for maximum beat-through distance. May search here year ago for accurate data of element sizes. But it is 70 cm long and 120 mm wide.

Other construction I like very much is the J-pole, There You may find my grieveful story about it was adjusted its enough to change so minor as 0,1 mm wider of narrower the distance between both parallel parts, and antenna parameters drifts with a factor up to the very ten. So, first must be solved how to fix it well. And pcb may happen to be one of such methods I havent tested. J-poles most unique thing is the sharply narrow lobe by horizontal axis (it dont illuminate the Cosmos unneedly) and omni lobe around vertical axis. Thus, at identical (or slightly higher) G-factor as halfwave vibrator, it gives (as radio-hamsters acclaim) much larger beat-through distance of communication.