I found that website recently too. Article go from the most basic to very advance but all information are explained in an easy to understand way, and he has a reference list as well. Needless to say it is the best source of unbiased information that i have seen to date.It such a shame that this website isn’t nearly as popular as these BS blog from Picard and the like.

and you will have your answer on polarization there.

https://basicsaboutaerodynamicsandavionics.wordpress.com/2016/08/11/radar-fundamentals-part-ii/

Guys ,related question: why polarization is important for radar ? iam not talking about specific kind but logically speaking , wouldn’t the polarization filter reduce the output of the radar and reduce the minimum level of echo that it can receive ? and if radar can only transmit/receive wave polarizated in one plane ,what will happen if there is a 45 degree wire mess on target ? ( since it change the polarize plane of the reflection)

By how many Db’s ? That is the most important concept. It is true that mismatched polarization can reduce the signal level received But. As long as it’s not cross polarized. You will only lose 3 Db’s. In other hand if the wave is cross polarized.. you will lost quite amount of 25Db. One type of radar, the 5N63 for S-300 took advantage of it by actually transmit and receive different polarization.

related to wire mesh.. do you seriously think that it will be a form of stealth just because it can help change polarization ? Note that the mesh also need to be quarter wavelength thick. Plus that wire mesh is used to convert linearly polarized wave (vertical or horizontal) into circular polarization. Thus the reflected wave would be in circular pol and you will lose signal.. but 3Db.

This look like it is polarized in horizontal plane

and this one is vertical

[ATTACH=CONFIG]246878[/ATTACH]

and so is An/APG-81.

and yeah i make mistake. It’s not the most common polarization for fighter aircraft application but.. it does handle vegetation absorption better than other polarization.

Iam quite sure the one in pictures is offset parabolic design rather than offset cassegrain type, there is no secondary reflector in front of the feed

Inverse cassegrain antenna’s secondary reflector does not have to move. The secondary reflector on Sapfir 23 is the antenna’s shroud itself.

[ATTACH=CONFIG]246869[/ATTACH]

sholdnt the value for slotted array lower than value for Phased array ? ( AFAIK , Phased array can prodce smaller beamwidth )

There’s more than narrow beamwidth to an antenna. Note that smaller beamwidth means more Sidelobe. I do not know how i could explain but.. you need an antenna pattern visualization.

And no. Being an ESA does not mean you can circumvent the physics of how narrow beamwidth is generated. Instead you can make it larger by applying some weighting factor to tradeoff angular resolution for lower sidelobe.

The following is some common weighting factor used in ESA radar. You can use it as K factor in the beamwidth equation i provided before.

[ATTACH=CONFIG]246856[/ATTACH]

And btw do anyone have a formula to estimate gain for different kind of radar ( parabolic vs slotted array vs AESA …etc ) based on their aperture size and frequency ?, i seen it before but cant find it anymore

Well the simplest formula one can find is :

G=30000/Hb*Vb

Where Hb is Horizontal beamwidth and Vb is Vertical Beamwidth. In Degrees.

Other books may give different constant like 26000 (Skolnik) or 23750 (Ingo Harre’s website) The beamwidth should be given in radians if these values are used.

To find beamwidth. You can use following formula :

Bw=K*Lambda/Ad

Where K is factor to account antenna illumination tapering factor.
0.886 is for parabolic antenna with no illumination tapering.
1.25 is typical for fighter aircraft antenna with Taylor -40Db. slotted planar array and may also apply on Phased array.

The value is in Radians so multiply it by 57.3 to convert it to degrees.

Usage example as follows :

We have an antenna with diameter of 90 cm (0.9m) works in X-band (3 cm or 0.03m) Find the beamwidth and gain.

First we have to estimate the beamwidth. Assume it’s a typical fighter aircraft radar with slotted planar array or ESA.

Bw=1.25*(0.03)/(0.9)

Bw=0,041 rad or 2.3 degrees.

Since the antenna is circular.. no need find the horizontal beamwidth as it would be the same.

We can find the antenna gain :

Gain=30000/(2.3*2.3)
Gain=5671 in non dimensional format. In log10 (decibel) format it would be 37 Db.

The reason for that..

Parabolic is simple to manufacture, high performance (high gain, easy to get narrow beamwidth) Plus it just can take any polarization (only depend on feed)

A downside of parabolic antenna in radar is that it has no control upon radiation pattern, making it bit susceptible to ground clutter for airborne application. Thus for requirements that does not need extensive clutter application or where low cost is needed. Parabolic is preferred.

The next generation slotted planar array antenna as one in AWG-9 and APG-66 address the radiation pattern control issues. Since it made out of smaller antenna that forms array. one can realize lower sidelobe than Parabolic antenna. Problem however it’s more expensive as it demands precision manufacturing to mass produce the antenna element. And circular polarization, if desired is difficult to achieve. Notice that most if not all slotted planar array antenna are either in vertical or Horizontal polarization. Vertical polarization is more common for fighter aircraft application as it can handle vegetation absorption of radar signal better than horizontal polarization.

we need weapon test footaaaage naaaaw.

yeah. would love to see PAKFA clip.. launching missiles or drop bombs.