+ Post New Thread
Results 1 to 6 of 6
  1. #1
    Member level 5
    Points: 1,249, Level: 7

    Join Date
    Nov 2014
    Posts
    92
    Helped
    0 / 0
    Points
    1,249
    Level
    7

    C band SATCOM question

    Hello,

    I’m reading the article “Satellite Basics” at http://www.idirect.net/Company/Resou...e%20Basics.pdf. The following can be read for C band:

    Because of its weaker power it requires a larger antenna …

    Question: why weaker power? Does it relate to C band?

    Senmeis

    •   AltAdvertisement

        
       

  2. #2
    Member level 4
    Points: 761, Level: 6

    Join Date
    Feb 2017
    Posts
    73
    Helped
    9 / 9
    Points
    761
    Level
    6

    Re: C band SATCOM question

    It is not weaker it is about the wavelength of the C band. For parabolic reflectors the directivity equation is G=10*log_10(k*((pi*D)/lambda)^2)) where k= efficiency factor generally between 0.5-0.8, D= diameter of the reflector, lambda=speed of light/frequency.
    Now you can get the idea that when the frequency goes up wavelength goes down, because lambda is in denumerator of the equation when lambda goes down gain increases. So for the same reflector size, C band has the lowest gain.
    So lets say you want to get a 30 dBi gain from your antenna at C band and Ka band.Assuming both of your antennas have %70 efficiency(k=0.7) you would need 1.25m antenna for Ka band transmission at 29GHz , for the same gain you would need a 6.3 meter antenna for C band transmission at 5750 MHz.
    Last edited by jesuschrist; 9th November 2018 at 12:07.



    •   AltAdvertisement

        
       

  3. #3
    Member level 5
    Points: 1,249, Level: 7

    Join Date
    Nov 2014
    Posts
    92
    Helped
    0 / 0
    Points
    1,249
    Level
    7

    Re: C band SATCOM question

    Click image for larger version. 

Name:	Pages from SATCOM 101 Webinar 1 1112.jpg 
Views:	11 
Size:	209.2 KB 
ID:	150038
    On the attached slide you’ll find this description:

    (C band ) Requires larger antennas than L-, Ku-, or Ka- band

    According to your theory, L band should be weaker than C band, but on this KVH slide L band comes with Ku and Ka bands together.

    Senmeis



    •   AltAdvertisement

        
       

  4. #4
    Advanced Member level 4
    Points: 10,162, Level: 24
    Achievements:
    7 years registered

    Join Date
    Feb 2007
    Location
    All over the Map.
    Posts
    1,097
    Helped
    219 / 219
    Points
    10,162
    Level
    24

    Re: C band SATCOM question

    This is a subject that causes a great deal of confusion. The presence of a frequency variable in the space loss calculation just adds further confusion. The power received by an antenna is related to the power density over the antenna and the antenna surface or aperture area. It is true that gain increases with frequency. That is an opportunity to add more confusion. Neither power density nor antenna aperture are frequency dependant.

    ETS-Lindgren Inc. provides a discussion in their technical notes that goes a long way at explaining the issue you raise (lower frequency results in weaker signals). Run it down and study the couple of pages discussing the issue.

    I like to remind myself that spherical spreading of a signal does not depend on frequency. More confusion results if one fixes gain. Now the physical size of an antenna decreases with increasing gain.

    It would be helpful to get a firm grasp of effective radiated power (sometimes described as effective isotropic radiated power).

    Look up the reference and watch the fun as I expect these comments to excite a discussion.

    Regards,

    Azulykit



  5. #5
    Member level 5
    Points: 1,249, Level: 7

    Join Date
    Nov 2014
    Posts
    92
    Helped
    0 / 0
    Points
    1,249
    Level
    7

    Re: C band SATCOM question

    Could you please provide the link to this reference? There is a big archive. In fact I agree with all your description in the last posting. Right now L band in the second slide seems to generate the biggest confusion.

    Senmeis



    •   AltAdvertisement

        
       

  6. #6
    Full Member level 2
    Points: 831, Level: 6

    Join Date
    Jun 2018
    Posts
    131
    Helped
    12 / 12
    Points
    831
    Level
    6

    Re: C band SATCOM question

    Waiting for the link about the topic. Interesting discussion.

    ETS-Lindgren Inc. provides a discussion in their technical notes that goes a long way at explaining the issue you raise (lower frequency results in weaker signals). Run it down and study the couple of pages discussing the issue.
    Last edited by ktr; 3rd December 2018 at 17:01. Reason: forgot qutoe



--[[ ]]--