Measures of power
Standard
1) Standard for the power measure:
to) Standard primario used exclusively in the metrologici laboratories
b) Standard sostituzionale carries out comparisons between powers to various frequencies
c) Standard secondario
2) primary Standard:
to) Electric power meter to cancellation pressure
A metallic plate to the inside of a waveguide is placed, the plate is connected through a thread to the advanced horizontal side of the guide, the deflection of the plate is function of the cancellation on it incident but in order to find it with exactitude is necessary that there are environmental conditions them (temperature, pressure, humidities) constant and the same deflection must be measured by means of interferometry between direct and reflected wave of a laser.
b) Electric power meter to Hall effect
Measure the potential difference generated them from the field e.m. the heads of a semiconductor.
3) sostituzionale Standard:
to) termostatato Calorimeter
In a calorimeter I have a two vaschette containing ciascuna resistance adapted to the source which it is connected that for one it is the continuous one while for the other is marks them RF of which we want to measure the power, between the two vaschette are had of the thermocouples in series which produce a potential difference them proporziona them to the temperature difference, varied the continuous one sin when I do not find that the temperature difference is 0, to that point the two sources will have produced the same effect and therefore power RF is equal to the power in continuous that per² is easy measurable. The problem of this outline is in the thermal estate.
b) Calorimeter to flow of liquids
In this case we have a single resistance dipped in a calorimeter where of the fluid it enters and it exits, and termopila a measure the difference of temperature between the two flows, is possible the two following modalities of measure:
b1) I apply to the resistance marks them RF of which to measure the power and I measure the difference of temperature between the flows, after which I apply continuous and the varied one sin when I do not obtain the same difference of temperature.
b2) I apply before the continuous one, I add to it marks them RF therefore I diminish the continuous one sin when I do not obtain the same difference of temperature that I had with the single one continues, this concurs me to polarize the system in the zone of optimal job for the operation of the termopila.
c) Dispositive sensitive to the temperature
I can use is the metals which are PTC (…their resistività increase growing of the temperature) that the semiconductors which are NTC (…the resistività diminish to growing of the temperature in how much are greater the electron number that gives the valence band is moved towards the conduction band). They are used also measuring to thread which are much similar to fuses.
4) secondary Standard:
to) diode valves to splice that gives straightening proporziona they to power RF that crosses them
b) thermocouples that measure the difference of temperature between irradiated and not irradiated zone
c) termistori
Methods of measure of the power
5) Factor of calibration of the sensor:
it holds account of two typical characteristics of the
sensor that is the coefficient of 
reflection,
that it is the prevailing source of the error and varies is in
function of the power incident that of the frequency, and the
effective efficiency of the 
sensor that account
of the fact holds that the power can be dissipated in various points
of the sensor. The value of the calibration factor is
approximately 0.9 that it wants to say that measure one inferior power
of 10% regarding the power really incident.
6) Sensor to termistore:
A termistore is a semiconductor in which the elevation of the temperature provoked for Joule effect from the power incident determines a lessening of the resistività, however the curves that express the resistance in function of the dissipated power are not linear and strongly vary with the temperature therefore all the practical circuits preview a feedback to us of the termistore that ago that it is always found in the same point of job on the characteristics. In particular the termistore comes polarized in continuous, when the power incident of it diminishes the resistività then the Power Meter arranges a lessening of the continuous one that filler the resistività to the previous value.
A typical coaxial assembly previews 4 termistori, two that carry out the measure of the power 50 incident and that therefore they introduceW towards the 200 ending andW towards the Power Meter while others 2 termistori supply to the thermal compensation.
7) Power Meter to double bridge:
A Power Meter to double bridge is constituted from a bridge for the RF and a bridge for the thermal compensation maintained in equilibrium through of the amplifiers differentiates them. The tensions in escape from the amplifiers differentiate them come sent to a chopper that in short the sum and modulate with a wave quadrant, in such a way can be concurred at a distance with the Power Meter of being placed from the sensor. To the escape of the Chopper we have is marks them sum which frequency that marks them difference which it comes amplified and subsequently multiplied for that one in escape from the converter, in total comes applied to a converter Tension/has the difference of the squares of the tensions in escape from the amplifiers differentiates them which is proporziona them to the dissipated power. A zero circuit is moreover present.
They are possible measures beginning from â?"50dBm.
8) Sensor to thermocouple:
Draft of a brace of joined various metallic materials to an extremity, the following physical effects are had:
to) if scaldiamo a barretta of metal on one side, they are carried of electrons in conduction band, they for via of the temperature gradient are moved towards the other extremity leaving of the Ionian ones positi to you, after all therefore a potential difference will be had them, this effect is called Thomson.
b) if we put to contact two metals characterizes from different functions to you job, so that they splinter-bar will create a potential difference them, this effect is called Peltier.
The total effect is called Seebeck effect and substantially it associates a potential difference them to one temperature difference. So that it is possible to measure low powers, it is necessary that the dimensions of the element dissipated are contained and that represents an ending for marks them RF to such aim comes true thermocouples to thin film. In practical the every sensor it contains two thermocouples in series to form a termopila, they introduce 50W towards ending RF and 200W towards the voltmetro.
9) main Characteristic of the thermocouples:
The main characteristic of a supplied thermocouple is sensibility that is im V in escape for every mW of power in income, it is the product of the thermoelectrial power (… the tension in escape for degree of difference of temperature between the two splices, is worth approximately 250nV/°C) and of the thermal resistance (… the temperature variation due to the power incident, it is worth approximately 0,4°C/W) therefore the sensibility of a thermocouple it is worth approximately 100nV/mW and it diminishes because of the thermal connection in the case if they place two in series. The maximum measurable power is 300mW.
Inasmuch as the thermocouple supplies tensions many lowlands, of the order of the nV, a chopper becomes necessary to 220 Hz integrated in the same sensor which it amplifies marks them and of the transmission concurs with the Power Meter.
10) Outline of a Power using Meter thermocouples:
The sensor as seen it is constituted from the thermocouple, chopper and an amplifier that it sendes marks them to an analogous amplifier place in the Power Meter, subsequently there is a block that contains amplifiers and suppressors that concur to vary the over the entire scale of the instrument, then a diode valve peak detector and an amplifier that account of the calibration factor holds, marks them in escape from it comes sent to a voltmetro. They are moreover also present a autozero circuit that acts to goes them of the thermocouple and an oscillator of reference to 50MHz that instead it acts to mount and it concurs the calibration of the instrument.
11) Measure of power with diode valve detector:
The characteristic of the 
diode valve
can be developed in series of powers in around of the 
origin where considering that the terms that origin gives
the continuous one are those of equal order and that then for V small
we can ourselves be arrested 2° to the order, we have that the
continuous one is proporziona them to the square of the tension and
therefore to the power. To the aim to finish the source, in
parallel to the income a resistance from 50 is hadW while the diode valve is placed
passing and is of Schottky type (…possesses giunzione a
metal-semiconductor) so as to to have one small barrier of
upgrades them. The rivelabili powers go from â?"70dBm
(…in correspondence of which are had approximately 50nV in
escape) to â?"20dBm for frequencies until to 40GHz.
Measures of power and errors for maladjustment
12) Power yielded to the cargo from a generator:
We consider the case of a generatore
(…characterized from a coefficient of reflection GG) connected to a
cargo (…characterized from a coefficient of reflection GL) by
means of one line without losses. The power yielded to the line
is 
having replaced 
and
subsequently 
before where bG is the wave emitted from the generator in the
adapted cargo case. Such power incident P1 will coincide with the that available from the
generator 
in the case of conjugated adaptation
G G= G 1* power P Lyielded to the cargo is only instead 
…in how much the line is without
2 losses and thereforeto 1 =b … 
.
13) Losses for maladjustment:
It is the relationship between the power available from the generator and that effectively yielded to the cargo
where the length of the line of transmission therefore G can be made to stretch to zero 1 = GL .
One then has the loss for maladjustment from Z0 that is 
and
that one for 
maladjustment.
14) Observations on conjugated and loaded adaptation adapted:
In the case of conjugated adaptation all the power available from the generator comes supplied to the cargo however is of the waves reflected that they could damage the same generator, in the case instead of simply adapted cargo, the power supplied to the cargo is not maximum but not are reflected waves.
15) Objective of the power measures:
To measure the power that the device to characterize would distribute on one adapted ending.
16) Uncertainty for maladjustment:
It holds account of the fact that GG and GL is famous with precision for that it regards the module, only follows some that Mconj and MZ0 can only be estimate to you by means of the uncertainty for maladjustment
variable between the maximum value and the minimal value in function of the back of the carriers of which the module is famous solo.
Errors and uncertainty total in the power measures
17) Typology of errors and uncertainties in the power measures:
The prevailing errors are associate you to the loss for maladjustment and to the maladjustment uncertainty, there is then the not perfect efficiency of conversion of the sensor and the errors it associates you to the electronics of the Power Meter.
18) Errors of the measure associate you to the electronics of the Power Meter:
to) uncertainty in the power emitted from the calibration oscillator
b) uncertainty for maladjustment of the reference oscillator
c) uncertainty due to the amplifiers and the changes of scale
d) noise
and) loss of the reference of zero in the case of one measure of along period
19) Equation of the power measure:
For via of the maladjustment the power dissipated on the
cargo the revealed 
P is moreover must in particular hold
account of the errors introduced from the Power Meter, indicating with
m those due to calibration and scalatura while indicating with t those
due to the reference of zero 
is had from which
extracting revealedP
and replacing the equation of the power measure is obtained 
.
20) Esteem of the uncertainty total of the measure:
There are two strategies of esteem of the uncertainty total of the measure:
to) Uncertainty total of the case worse
All the sources of errors come calculated to the their maximum value so that they are added in constructive way, obtain therefore an esteem for excess of the possible errors
b) Uncertainty total like medium quadratic value
The sum of the squares of the single uncertainties is estimated and if of ago the square root, the hypothesis in this case is that the error sources are between incorrelate they
21) Comparison between the sensors of power measure:
to) Accuracy
A same Power Meter pu² to use is a sensor to thermocouple that to LBSD obtaining a range that it goes from â?"75dBm to 30dBm while the sensors to termistori come uses you in the range between â?"30dBm and 10dBm.
b) Range of frequency
The sensors cover the same range of frequency to the inside of which but the reflection coefficient varies and therefore also the uncertainty. The smaller coefficients of reflection are had for the sensors to thermocouple and the LBSD.
c) Speed of answer
The measures of mark them many small make bands many grips but these imply long times of answer, are gone from the 35ms of the termistore to the 100ms of the thermocouple.
d) Maximum applicable power
22) Configurations for the measure of powers:
A protection device is had (…a circolatore or an insulator or a suppressor) frapposto between the source and the DUT that in kind is an amplifier whose exited if greater of 10mW it comes sended is to the cargo that to the Power Meter by means of a directional coupler. For lower powers the cargo is represented directly from the sensor. In case moreover the dispositive one you introduce a remarkable distortion is preferred to carry out the measure with a phantom analyzer.
Measures of attenuation
23) Methods for the attenuation measure:
to) methods to relationship of powers
b) comparison with a suppressor of precision to RF
c) comparison with a suppressor of precision to IF
d) comparison with a suppressor of precision to AF
and) methods without standard of substitution
f) methods base to you on the measure of reflection coefficients
24) Methods to relationship of powers:
It marks them coming from from the generator comes attenuated and leaked they are then present, before and after the DUT of which measuring the attenuation, she is of the insulators that of the Tuner which supply to make that the DUT sees a good adaptation is towards the source that towards the Power Meter. The attenuation obtains like relationship between the found power when the two Tuner adapts to you is directly connected between they and the found power when instead the DUT comes frapposto.
This method is strongly sensitive to variations of the power supplied from the source between the two measures, therefore alternatively the same one can be sended marks them through a coupler to 3dB is to the circuit of previous measure that to according to Power Meter, a divisor Kelvin Varley comes then fixed so as to to have zero on the detector in both logons, the attenuation can therefore be obtained from the values of attenuation in the two cases of the divisor.
25) Methods to comparison of powers:
Coming from from the source marksthem to frequency f 0 comes modulated from switch to diode valves PIN piloted from a wave a having quadrant equal frequency to 1kHz, a directional coupler sendes the same one marks them is to the reference branch that to the measure branch which meet then on an amplifier differentiates them whose exited from 1kHz it is brought back to the continuous one through a P.S.D. endured after which the meter is had.
The reference branch is constituted from two insulators and a variable suppressor that has the task to make to work the being followed diode valve in the region of the characteristic with quadratic law IDC µ V2 . On the measure branch an insulator is had and then two tuner between which it is frapposto a suppressor of precision to RF, to follow a suppressor is still had and others two tuner between which to insert the device of which it agrees to measure the attenuation, to follow then is a diode valve.
The measure is carried out connecting between they the two tuner and putting the variable suppressor of precision to a high value of attenuation after which the DUT becomes part and the variable suppressor varies sin when the same power is not had incident on the detector. The attenuation is equal to the difference between the attenuations settate in the variable suppressor.