antenna q factor

Patch antenna on thin air substrate has narrow bandwidth and high Q-factor.

That's right, patch antenna has drawback of its narrw band with so i suggest to design path antenna with diffrent substrat to see which is the best design...

Mouloud

Any resonant type of antenna on high quality substrate can be fine tune and have a bandwidth defined by the loaded Q. Are you sure you need very narrow band antenna? Often it is easier to limit bandwidth with RF filter and simplify antenna design.

Br,
RF-OM

Something electrically small would meet your condition. Why are you looking for this type of antenna?

What center frequency and bandwidth? Other characteristics?

try small loop antena (if HF) , you can try even if is a microwave band (I know someone that tried for 2.4GHz, but the connector was greather than antenna!)

if not, try adding tunning reactances or narrow band filters, or patch antenna posted before

Small loop antenna will work at higher frequencies too. The actual Q-factor will depends on loading and substrate material and can be done very high when optimized with special technology. But Q-factors more then several hundreds become unusable due to external effects like operators hand, humidity changes and so on. I used such antenna with gamma matching on 915 MHz and 2.4 GHz ISM bands and results were good.

Best regards,
RF-OM

Thanks for the answers.
The centre frequency should be 868 MHz. The antenna itself should have the narrow bandwidth. Bandwidth limiting with filter is not possible.

You should consider, that resonant antennas usually have poor performance (high losses) due to low radiation resistance. But basically, any microstrip resonator is also a high Q resonant antenna, operating without external tuning elements, as requested.