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Structure for preventing intermodulation interference in satellite transmission

  • US 20040082298A1
  • Filed: 10/28/2002
  • Published: 04/29/2004
  • Est. Priority Date: 10/28/2002
  • Status: Active Grant
First Claim
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1. A structure for preventing intermodulation interference in satellite transmission, comprising:

  • a receiving antenna for receiving vertical and horizontal polarized signal sent from a satellite;

    an RF amplifying system for down-converting and amplifying the received vertical and horizontal signals;

    a first and a second band-pass filter for filtering signals output from said RF amplifying system;

    a first mixer for receiving a signal output from said first band-pass filter and executing a frequency subtraction operation;

    a local oscillator, from an oscillating frequency of which a frequency of said signal output from said first band-pass filter is subtracted in the frequency subtraction operation at said first mixer to generate a first mid-band;

    a high-pass filter for filtering and isolating a signal within said first mid-band and output from said first mixer, and outputting the filtered and isolated signal;

    a second mixer for receiving the signal filtered at and output from said second band-pass filter and executing a frequency subtraction operation;

    a first-stage local oscillator, from an oscillating frequency of which a frequency of said signal output from said second band-pass filter is subtracted in the frequency subtraction operation executed at said second mixer to obtain a reverse-phase signal of said signal output from said second band-pass filter;

    a third band-pass filter for filtering and isolating said reverse-phase signal output from said second mixer;

    a third mixer for receiving the signal output from said third band-pass filter and executing a frequency addition operation;

    a second-stage local oscillator, to an oscillating frequency of which a frequency of said signal output from said third band-pass filter is added in the frequency addition operation executed at said third mixer to obtain a second mid-band;

    a low-pass filter for filtering and isolating a signal within said second mid-band and output from said third mixer, and outputting the filtered and isolated signal; and

    a multiplex adder for receiving and combining said signals separately output from said high-pass filter and said low-pass filter;

    whereby second and third harmonic differences between a frequency obtained by subtracting the oscillating frequency of said second-stage local oscillator from the oscillating frequency of said first-stage local oscillator and the oscillating frequency of said local oscillators do not fall in said first and said second mid-bands, respectively, and an intermodulation interference can therefore be prevented.

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