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reduction of antenna size in satellite communication

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egliu

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Does anyboby have any ideas to reduce antenna size and keep similar performance as a biger one
 

yingyang

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antenna reduction

Precisely, what performance would you like to retain??? bandwidth, efficiency, gain, polarisation????

You cannot maintain all the good properties without sacrificing some common characteristics such as gain & efficiency....

Worst still, you may have bad cross-polarisation....
 

flatulent

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laws of physics

It all depends. The volume of the antenna is related to the gain. If you want less diameter you will have to increase thickness by using an array of yagis. This is very difficult at higher gains and frequencies. The famous antenna book by Kraus describes this constant volume effect.
 

g579

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It is very simple. You should use an LNA or LNB with a better noise figure.
 

flatulent

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noise figure

I suspect that the receiving system in question alread has a 1 or 2 dB noise figure as these are relatively cheap these days. This means that even using liquid nitrogen cooling only 0.6-1.3 dB of SNR could be gained.

Your only other choice if you want to reduce the antenna gain is to switch to a lower data bit rate if this is possible.
 

hr

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i agree with flatulent;it is impossible to reduce the nf more;
 

g579

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flatulent,
I do not agree with you. For low noise systems the important thing does not the noise figure itself, gut the G/T for the antenna system (where G is the antenna gain and T is the noise temperature of the system). So using 0.5 dB noise fig. amp. instead of 2 dB means much more than the 1.5 dB difference !
 

flatulent

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noise figure definition

The definition of noise figure is the amount that the signal to noise ratio is reduced by the given amplifier compared to a ideal noisless amplifier. The T you used is for the entire system and what the antenna is pointing at including side lobes pointing to earth.
 

egliu

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thanks but the problem is ....

dear all

thanks for your kindly dvices

as a receiving antenna, it is possible to reduce antenna size using lower antenna temperture techniques. But when we want to transmit, the antenna pattern must meet ITU requirements. As you know, the sidelobe and cross polarization can be suppreased by changing aperture field distribution, but how to narrow antenna beamwidth is a big problem. does anybody have ideas on it?

thanks and regards
 

flatulent

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laws of physics

You are constrained by the laws of physics. Gain, antenna size, and beamwidth are all related. You can control the beamwidth in the two (vertical and horizontal) planes independently. This can either be done with reflector dimensions or by number of radiating elements in a phased array being different in each direction. Another factor you have control of is the taper of dish illumination or the weighting of the phased array elements. These control the sidelobe level and the main beam width. Again, the laws of physics pretty much hold you in.
 

egliu

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hi flatulent

thanks a lot, I know this well. My custom want to have a smaller antenna for mobile communication, so I have to help find a solution. any other ideas on this.

regards
 

flatulent

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serious problems

You also have the problem of keeping the antenna pointed as the mobile vehicle moves about. One very expensive solution is to have a phased array that has nulls in the direction of the adjacent satellites. This requires extra receivers to monitor the signals from these satellites and adjust the null in their direction. What makes this worse is if the TX and RX frequencies are different. Could you give me more details. Either in public or by PM? Your customer may be trying to use the wrong satellite service. One designed for mobile users will have antenna requirements more usable on vehicles.
 

egliu

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hi flatulent

it is no problem on tracking system, we can use beacon signal and mechnical system to track the satellite. the problem is focusing on too big antenna at C band.

regards
 

flatulent

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Your only choice

It looks like your only choice is a phased array with nulls in the directions of the adjacent satellites. This will require a two dimensional array of possibly printed antennas with different lengths of transmission line to each one. If the TX frequency is different from the RX frequency, the nulls should be positioned at the TX frequency and you will take your chances on RX with your desired signal being high enough commpared to the other ones that you can demodulate it properly. If this will not work, you will have to have two sets of antenna elements that may be able to be on the same plane (different spacing than the TX array) with their own set of phasing transmission lines to null out the other satellites on RX as well.
 

egliu

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phase array can not reduce antenna aperture size, am i right? So we are thinking to use coformal array, is it possible? any suggestion on software?

thank you again
 

flatulent

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create nulls

The phased array may be able to pass the required specifications by putting nulls at the other satellite angles instead of the minimum radiation at all angles usually specified in the regulations. I am not sure if the rules you have to meet will allow this. This meets the spirit of the law, but not the letter. If you can make the array part of some surface that already exists, you have extra degrees of freedom to play with.
 

Lupin

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Size reduction

For what concerns patch antenna array, I can say that you can use slotted patch antennas inspite of standard configurations such as rectangular, squared circular patches.
I've obtained wider bandwidth(!!), shift of working frequency (size reduction), similar Ellipticity Bandwidth but lower Gain.

Hope it can be useful to you.

Regards
Lupin
 

edf

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You might investigate the 4 Square Antenna.
 

egliu

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Re

4 Square Antenna for satellite communication? would you mind tell me more about your idea?

regards
 

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