

Power Delivered to Antennae  RF Cafe Forums

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(I1I2),imag(I1I2)); mag
sprintf('VOLTAGE RATING FOR C9') [mag,theta]=cart2pol(real((I2I3)*XC9),imag((I2I3)*XC9));
mag
sprintf('CURRENT RATING FOR L1') [mag,theta]=cart2pol(real(I3),imag(I3));
mag
sprintf('VOLTAGE RATING FOR C10') [mag,theta]=cart2pol(real((I3I4)*XC10),imag((I3I4)*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



