bandwidth of a simple pin feed square patch antenna

[amntt]

i want to know how much bandwidth is acceptable for a patch antenna? for example is 200 mhz an acceptable bandwidth for a patch antenna or i made a mistake somewhere in my design:roll:

 

[WimRFP]

Required minimum bandwidth depends on your application, so you should first ask yourself what bandwidth do I need.

Relative bandwidth depends strongly on the substrate heigth / wavelength ratio, and the dielectric constant.

The bandwidth increases when using lossy dielectric, but this is because of the power is converted into heat instead of radiation. Especially for thin substrate layers, check the radiation efficiency.

 

[amntt]

many thanks it realy help.how i can check the radiation efficiency using simulator such as cst?

 

[WimRFP]

i don't know CST, but it is a standard feature in all antenna simulation programs. Pleas don't confuse it with antenna efficiency. Only radiation efficiency shows the ratio between radiated power and electrical input power. When it is 25%, it means 75% of the net input power is converted into heat (in copper and or dielectric material).

If you are going to simulate your antenna using infinite size dielectric, the radiation pattern under low elevation does not match real world measurement. Also the radiation efficiency may be pessimistic.

 

[amntt]

i find it in far field simulation of cst .total rad efficiency=-16.83db, rad efficiency -16.82 => it means that my design antenna is not good and it is too lossy to radiate???

 

[WimRFP]

Very likely your conclusion is right. What is your dielectric thickness/lambda ratio and the loss tangent (or tan(d) )?

 

[amntt]

its return loss is -20 db and it is matched , dielectric epsilon is 4.3 width 0.3cm but it is metamaterial loaded substrate,frequancy=1.72 ghz ,

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its radiation pattern is good its gain is 3 db and bandwidth 200MHZ

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:-? what can i do :-(

 

[WimRFP]

What is the radiation efficiency? The bandwidth (assuming VSWR=2) seems very wide for a 0.3 cm distance between patch and ground plane. A square patch should have better gain, so maybe the radiation efficiency is poor.

Regarding: what can I do:
This all depends on the actual application for your antenna, so I don't know..

 

[amntt]

the antenna is loaded with metamaterial structure inorder to get wider bandwidth. band width is important for me . what do u mean by "what is the radiation efficiency?"

 

[WimRFP]

Radiation efficiency: (radiated power) / (net electrical input power) So when you have radiation efficiency = 40%, 60% is converted to heat instead of radiation. net electrical input = Pfwd - Prefl


Small volume or size, high efficiency and large relative bandwidth don't come together, you can only have two at the same time. I doubt whether or not metamaterials can change this. This is the reason for asking the radiation efficiency.