Hello,
im designing normal circular microstrip patch antenna with coaxial probe feed. my design is built over FR-4 substrate . every time i got about 60% radiation efficiency ? why
thank you
1- check impedance matching (50 ohm)
2- efficiency= Gain/Directivity, so the values of G and D should be near to each other
In addition to M. K. Abdulhameed 's response about impedance matching, FR-4 has a relatively high (and frequency-dependent) loss profile. These losses will definitely contribute to a drop in radiation efficiency, such that I would not recommend it for patch antenna use above 1 GHz if you need higher gain values.
i agree with Dr. Stuart Barth and in additional i prefer to use Roger with low dielectric constant.
Thank you M. K. Abdulhameed and Stuart Barth . yes it is true to use roger 5880 RT. but roger increase patch size incurably. what can i do in your opinions ?
Alaa Imran Al-Muttairi Rogers (among others) manufactures several other good microwave substrates with higher permittivities. Generally, the relative permittivity of FR-4 is between 4 and 4.5; I would suggest looking at RO-3035 or RO-3006.
Of course, the maximum possible gain of the antenna will scale inversely to the dielectric constant, so you don't want to go too high, either (e.g., RO-3010).
Generally, Microstrip patch antennas are mostly known for their poor gain, the antenna efficiency is a function of gain and directivity according to G=e*D. Also, the FR-4 dielectric has a higher relative permittivity, where the antenna gain's inversely proportional with relative permittivity and directly proportional to substrate height. Many approaches were used to enhance the antenna gain, for more information refer to this paper " Design and optimization of rectangular microstrip patch array antenna using frequency selective surfaces for 60 GHz ".
Regards
Ali Adnan Hamzah M. Marhoon Stuart Barth thank you for your answers.
some of the above solutions mentioned improving the impedance matching. But, impedance matching is not related to radiation efficiency. the definition of radiation efficiency is Rad_efficiency=radiated power/accepted power. In this definition, the reflection due to impedance mismatch is not considered.
What do you think about this?
In a strict sense, Radiation Efficiency is defined as
Radiation Efficiency = Radiated Power/Accepted Power
Accepted Power = Incident Power - Reflected Power
Here reflected power is due to Impedance Mismatch
The Accepted Power is radiated or dissipated by loss in dielectric and conductor.
On the contrary, Total Efficiency is defined as
Total Efficiency = Radiation Power/Incident Power
Therefore the following is hold:
Total efficiency
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