What does LHCP/RHCP gain mean here? The axial ratio is important, you should check the axial ratio again.

If an antenna is linearly polarized and has a gain of 18 dB, then it will have a gain of 15 dB for RHCP and the same for LHCP. Any linearly polarized antenna will pick up either circular polarization 3 dB down.

Thank you Sir Malcolm White .

Is it compulsory that the difference between Absolute gain and CP gain should be 3 dB? If the difference is less than 3 dB then it will be acceptable or not?

Kindly reply Sir.

Dear Sir Yunjing Zhang,

The axial ratio of the array is of1.03 dB. So it is circularly polarized. But at the same time the gain of RHCP and LHCP (as per Ludwig-3 scale) is also find out and these are 15.1 and 15.2 dBic respectively. So the array is dual-circularly polarized or Linearly polarized as the magnitude is almost same in both direction of polarization?

Kindly draw your attention and try to provide some relative papers for the same Sir.

You need to learn about polarization. Read a chapter from a textbook or a lecture or tutorial on polarization from the internet. Your questions show that you do not understand the basic theory. Any linearly polarized antenna will always receive circular polarization 3 dB down (exactly half the power). A perfect circularly polarized antenna will always pick up linear polarization 3 dB down (exactly half the power). If the antenna or polarization is not perfect, then these ratios will be different. Any linear, circular or elliptical polarization can be made from two orthogonal linear polarizations of different size and relative phase, or from LHCP and RHCP of different size and relative phase, or any two orthogonal polarizations (on opposite sides of the Poincare sphere).

Your array is still linearly polarized neither circular nor dual.

The question is little bit confusing. Are you asking for dual polarization or circular polarization. A CP always consist of LHCP and RHCP. Hence the term dual CP may not be correct in true sense. Dual Polarization (DP) is different and Circular Polarization (CP) is different. Please, give more information of your query.

Sudipta Maity Sir,

Thanks for your kind attention.

I had design an antenna which gives the linear polarization (axial ratio>3 dB). Then I go for design an eight-element array with single port excitation using CST. This array gives the LHCP gain as 15.2 dBic and RHCP gain as 15.1 dBic (as per Ludwig-3 scale). The absolute gain of the array obtained as 18.1 dB.

As the LHCP and RHCP magnitude is almost same, so the array will called as what? Is it Dual-circularly polarized or Linear Polarized?

Please add your answer Sir.

Kalyan Sundar Kola you can very well relate what u asked Sudipta Maity and what Malcolm White suggested. I guess Sudipta will also agree with what Malcolm said. This is straight forward answer.

If you are telling, it is LHCP and RHCP, then, why are you asking for linear polarization. It is simply Circular Polarization (CP). I have doubt about the term 'Dual CP'. Recent articles are using this, but they are giving results only LHCP, RHCP and AR (Axial Ratio). The use of 'dual' terms may not be justified. I never seen such term in 1950's-1990's paper.

In my design the AR is 0.95 dB, so the array is circularly polarized. But when I am going to check the magnitude using Ludwig-3 scale in CST it gives the LHCP gain as 14.96 dBic and RHCP gain as 14.84 dBic. Almost same magnitude.

So is it so called Dual-circularly polarized or Linearly polarized?

Entire design done by CST with single Port of excitation.

If the axial ratio is 0.95 dB then LHCP and RHCP cannot be only 0.12 dB different. There must be a mistake in your prediction or the CST results or in your understanding of what they mean. I think that 1 dB axial ratio means that there should be 12 dB difference between RHCP and LHCP. If RHCP and LHCP are the same then the polarization is linear. With only 0.12 dB between them it is very close to linear with about -40dB circular component (I think - i would need to spend more time to be sure). The results you describe cannot all be correct.

Sorry Sir, It was my mistake.

Actually the AR is obtained as 1.26 dB. The LHCP gain is 15.2 dBic and RHCP gain is 15.1 dBic (Obtained from CST Microwave Studio). So what is will be called? Linear polarization or circular polarization or Dual-circular polarization?

Kalyan Sundar Kola

I am not sure about the term dual CP.

You have mentioned that AR is 1.26 dB. If the co-polarized component is LHCP, as per the mentioned AR, cross-polarized component (RHCP) should be less than nearly 23 dB compared to LHCP gain.

Vikas Khairnar Sir,

Thank you for your attention and reply.

Sir is there any relation between AR with CP gain. You said that if AR is 1.26 dB so the difference between LHCP and RHCP should be 23 dB or LHCP should be 23 dB less compare to LHCP.

If is there any relation please share with me sir.

Kalyan Sundar Kola

Please find this link. In this link Malcolm White sir has nicely explained fundamentals of polarization, especially circular polarization and axial ratio measurement.

https://www.researchgate.net/post/How_do_I_measure_axial_ratio_of_the_antenna

For more theoretical background please refer these links

https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1220729

http://www.satsig.net/axial.htm

Kalyan Sundar Kola

Yes, there is a relation between AR and XPD (Cross Polarization Discrimination, which is the difference between LHCP and RHCP in dB).

You can use the simple program in the attachments to know it by introducing any AR value (or range) and see what is the expected XPD and vice versa.

Kerlos Atia Abdalmalak Sir,

I cant access the attached file. If you dont mind, can you mailed ([email protected]) me the file. It will be be great helpful for me.

Thanking you.

Vikas Khairnar

Sir ,is there any particular book is available to you which having those relationship between AR or gain all those things. If you have then please share with me sir. Kindly attached me on [email protected]

Thanking you.

for dual CP-antenna, you should have RHCP and LHCP simultaneously

Naser Ojaroudi Parchin

Thank you for your kind attention.

In this case I have to use two different port or any other technique is there? If possible then please kindly share some papers regarding the same.

Thank you once again.