Some Great Thoughts

"Go ahead and do your best" | "It is the simple things in life that build brilliance in creativity..simplicity cannot be taught, it is not tamper with it" | "All men dream but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find that it was vanity; but the dreamers of the day are dangerous men, for they may act their dream with open eyes to make it possible" | "इच्छा हमेशा योग्यता को हरा देती है" | "If you think you can do a thing or think you can't do a thing, you're right. -Henry Ford" | "Failure is success if we learn from it. -Malcolm S. Forbes" | "The future belongs to those who believe in the beauty of their dreams. -Eleanor Roosevelt" | "The great men and women of history are remembered, not because they never made mistakes or never failed, but because they didn't let their failures stop them. They kept on until they succeeded" | "असफलता हमें सिखाती है कि सफलता का प्रयत्न पूरे मन से नहीं किया गया"

Wednesday, June 5, 2013

Design of Dualpassband Microwave Filter for 6/4 GHz Band (Satellite Communication)

In satellite communication 6/4 GHz band used in many countries. Commercial communication satellites use a frequency band of 500 MHz bandwidth near 6 GHz for uplink transmission and another 500 MHz bandwidth near near 4 GHz for down link transmission. While an uplink of 5.725 to 7.075 GHz and a downlink of 3.4 to 4.8 GHz is used. For both uplink and downlink band a single dual bandpass filter can be used instead of two band-pass filters.
To design microwave filter well known classical methods like Butterworth, Chebyshev are used but these methods are applicable on single band filters. To design the multipassband filter some limited analytical techniques have been proposed. These all techniques are based on optimization method. Apart from these techniques another technique to design of microwave filter with arbitrary frequency response also proposed which is based on iterative quasi-Newton algorithm. The methodology proposed in this paper  follow this technique and rests on the translation of analog specification of both bands of 6/4 GHz band into digital specification since in digital domain the design is little bit easy. A designer can also take advantage of these sophisticated and continuously developing digital techniques in digital domain.

Following program can be used to design a dualpassband filter for satellite communication:

%% clear the command window & workspace
clear all
%% define the besic perameter related to filter
% order of numerator % denominator
% frequency range of passbands & stopbands
f5=[.9715:1/1000:1 1];
f=[f1 f2 f3 f4 f5];
edges=[0 f(1278:1280)];
% magnitiude to define passbands & stopbands
m1=[repmat(-40,1,900) -40:1:0];
m3=[0:-1:-32 -33:1:0];
m5=[0:-1:-27 -28.5 -30];
m=[m1 m2 m3 m4 m5];
%% desigining of filter
% conversion of magnitude from dB to normal value
% define the weight of error
% numerator & denominator of digital filter
% frequency responce of digital filter
% transfer function of digital filter
% pole zero plot of designed digital filter
% conversion of digital filter from digital to analog
% bode plot of analog filter
% numerator & denominator of analog filter
% conversion of negative coefficent of numerator & denominator to make
% filter stable
if NUM<0
if DEN<0
% transfer function of analog filter with new coefficents
% bode plot of analog filter with new coefficents

%% end of designing program

The frequency response for designed filter will be: