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Power delivered to antennae - RF Cafe Forums
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darcyrandall2004
Post subject: Power delivered to antennae Posted:
Fri Mar 09, 2007 11:32 pm
Colonel
Joined: Tue Feb
27, 2007 6:16 am
Posts: 46
Hello. I am designing a UHF transmitter.
I wish to be able to determine the requirements of components on the
output stage, after the amplifier and the power delivered to the antennae.
To begin with I am analyzing the application note designed for 380MHz.
My final design will be for 450MHz
The RF2175 datasheet claims
that the amp delivers 31.8dBm Linear Output Power.
The figure
below shows the output stage and where I have attempted to calculate
the current in the branches.
BELOW IS THE MATLAB
CODE I USED TO CALCULATE THE CURRENTS IN THE BRANCHES, COMPONENT RATINGS
AND THE MAXIMUM POWER DELIVERED TO THE ANTENNAE.
format long
clear
f=380000000;
wo=2*pi*f*i;
%DETERMINE THE RF2175
AMP'S OUTPUT POWER IN WATTS
pout=(10^(31.8/10))*10^-3;
%THE
CALCULATED RF2175 OUTPUT IMPEDANCE (THE CONJUGATE OF THE LOAD)
rf2175_z=1.83712875712576
+ 7.16437870763534i
%CALCULATE THE THEVENIN VOLTAGE, P=v^2/r,
pout=v^2/(2*real(rf2175_z))
v=sqrt(pout*2*real(rf2175_z))
%CALCULATE THE IMPEDANCES OF COMPONENTS AT 380MHZ
XC9=1/(wo*56*10^-12);
XL1=wo*3.6*10^-9;
XC10=1/(wo*12*10^-12);
XC11=1/(10^-9*wo);
XL6=wo*12.55*10^-9;
%CALCULATE THE BRANCH CURRENTS
I(1,:)=[rf2175_z+XL6,-XL6,0,0,-v];
I(2,:)=[-XL6,XL6+XC9,-XC9,0,0];
I(3,:)=[0,-XC9,XC9+XL1+XC10,-XC10,0];
I(4,:)=[0,0,-XC10,XC10+XC11+50,0];
I=rref(I);
I1=I(1,5);
I2=I(2,5);
I3=I(3,5);
I4=I(4,5);
sprintf('CURRENT RATING
FOR L6')
[mag,theta]=cart2pol(real(I1-I2),imag(I1-I2));
mag
sprintf('VOLTAGE RATING FOR C9')
[mag,theta]=cart2pol(real((I2-I3)*XC9),imag((I2-I3)*XC9));
mag
sprintf('CURRENT RATING FOR L1')
[mag,theta]=cart2pol(real(I3),imag(I3));
mag
sprintf('VOLTAGE RATING FOR C10')
[mag,theta]=cart2pol(real((I3-I4)*XC10),imag((I3-I4)*XC10));
mag
sprintf('VOLTAGE RATING FOR C11')
[mag,theta]=cart2pol(real(I4*XC11),imag(I4*XC11));
mag
sprintf('POWER DELIVERED TO 50 OHM ANTENNAE')
real(I4*I4*50)
BELOW IS THE RESULTS PRODUCED
rf2175_z =
1.83712875712576
+ 7.16437870763534i
v =
2.35822259134855
ans =
CURRENT RATING FOR L6
mag =
0.25101690661180
Amps
ans =
VOLTAGE RATING FOR C9
mag =
1.82181323340670 Volts
ans =
CURRENT RATING FOR
L1
mag =
2.56132106649834 Amps
ans =
VOLTAGE RATING FOR C10
mag =
1.59717311590861
Volts
ans =
VOLTAGE RATING FOR C11
mag
=
0.03475316915436 Volts
ans =
POWER DELIVERED
TO 50 OHM ANTENNAE
ans =
-0.75495330687175 Watts
»
I understand that the current rating for L6 would be determined
by the dc bias current it supplies.
Do these other calculations
look correct?
When the data sheet states that the amp has 31.8dBm
output power, does this mean that if the load is a conjugate of the
output impedance, 31.8dbm will be delieverd to the load? Or is half
of this value disspiated in the output impedance of the amp?
Thankyou
Cheers
Top
darcyrandall2004
Post subject: Posted: Mon Mar 12, 2007 11:19 pm
Colonel
Joined: Tue Feb 27, 2007 6:16 am
Posts: 46
Not
sure why your image isn't appearing. Let's try this:
(Kirt Blattenberger
3/13/2007)
Posted
11/12/2012
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