Radiation pattern for a dual band microstrip patch antenna

[mnhtapu]

I designed a dual band microstrip patch antenna resonating freq 3.5 and 5.5 Ghz. I attached the two radiation patterns simulated in CST. The radiation pattern at 5.5 Ghz is different from that of 3.5 GHz. But if you look at S11 graph, return loss is almost same for both frequencies.
I'm afraid that due to the radiation pattern at 5.5 Ghz, the antenna can't be called dual band. Is it mandatory that the radiation pattern at those 2 frequencies should be of same shape?
Any comment is highly appreciable.
Thanks.
Nazmul

 

[zorro]

Hi mnhtapu,

Matching is good at both frequencies. But at 5.5 GHz, it seems to have a radiation notch along the z-axis. If it is intended to radiate in that direction (I suppose it is), then this is a problem.
Otherwise, the radiation patterns don't need to be too similar. Enough gain should be provided in the directions if interest, and good matching and efficiency at the frequences of interest.
Regards

Z

 

[mnhtapu]

Thanks for your reply.
Regarding to radiation efficiencies at 5.5 GHz it's -0.107 dB and at 3.5 GHz it's -0.89 dB, are these values in acceptable range?
10 log(Power radiated/ input power to antenna) = radiation efficiency in dB
That's how we express radiation efficiency in dB? Plz correct me if I'm wrong.

 

[zorro]

10 log(Power radiated/ input power to antenna) = radiation efficiency in dB

According to the usual definition, as of "input power to the antenna" you should consider "power accepted by the antenna", i.e., reflected power should not be included. It is considered in total efficiency.

Regarding to radiation efficiencies at 5.5 GHz it's -0.107 dB and at 3.5 GHz it's -0.89 dB, are these values in acceptable range?

At 5.5 GHz is very good. I'm a bit surprised for the increase of losses at the lower frequency. Defining conductor and dielectric as lossless, you could see what is the origin if that inefficiency.

Regards

Z