need help about microstrip line antenna

[riyadhe]

He decided to go for rectangular and has no access to (large volume) of good dielectric, so with this in mind he has limited or no options to reduce the size of the patch.

To get reasonable antenna efficiency he can only use air (or foam) as dielectric. So he can only reduce the resonant frequency (given certain size) by cutting into the rectangular patch and/or adding vertical sections to increase the capacitance to ground (of the edges of the patch).

Riyadhe: A standard patch antenna you can see as a transmission line with a half wave electrical length. Due to radiation there are losses in that line. If you know the voltage and current distribution of the standing wave pattern (similar to that of a half wave dipole), you may know that if you move the feed to one end, the impedance at resonance increases.

There is some induction in the vertical part of the probe feed, this results in a difference in the free resonant frequency of the patch and "measured" resonant frequency. If you like, you can counteract that inductance with a series capacitor. That capacitor can be a small patch at the bottom side of the FR4, or a small isolated patch in your large patch. both techniques are used in many wide band patch antenna designs with air as dielectric.

The Wilkinson divider (and if required the diplexer), you can make on a separate PCB that is at the ground plane below the radiating patch. What is the maximum thickness of the complete antenna structure?

I assume your antenna will look at the sky (so received noise is low). To get the most out of it (in combination with a good LNA), you should optimize for good radiation efficiency as the losses in the antenna are at ambient temperature and will add thermal noise.

You may try "Compact & Broadband Microstrip Antennas" (Wong) to get design ideas.

thax for your advise, but i have tried air substrate yet...
i knew that book it's very use full book for me i think...

in my project, the thickness of my substrate no limitation but not so thick. my limitation is on length n width, is about 45x45 cm..

 

[ferdows]

hi
i try many time to made u antenna send me to the useful kind and i want say some point and advise to u i try send u u file tomorrow sorry about postpone
1- that antenna u find in wong book and u try to use for u application is too large for u application look to the book which written that antenna which i think design for 1.5GHz and upper is 75mm*75mm so for u antenna normally u should increase it then time
2- i never seen FR4 epoxy with thickness of 2 mm u should define the standard size like 1.6mm
3- pls use mm as unit and dont simulated u antenna with terminal simulation and u wave port should be on u ground and i seen u dont penetrated u substrate an u should penetrated ground also
4- for the frequency u chosen i think that kind model antenna u send for me never response and i think u should increase the effective length of antenna by method link meandered structure and other new technique
5 if u amateur in antenna i never suggest Wong's book and i suggest this book:
Broadband Planar Antennas Design and Applications Zhi Ning Chen and Michael Y. W. Chia