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A brief history of RF and microwave power measurement
From the beginning of the RF and microwave systems, it was necessary to determine the power level in different systems plans (input power, output power, power level in-between the stages, etc.). The power measurement principles were quite primitive compared to nowadays technologies. In the late 1930s, the klystron microwave power tube was used in the early experimental stages of klystron cavity to give a gross indication of power level [24]. Whereas the diode-based detection of the day was not capable to work at such microwave frequencies as the klystron tube. For the high power systems, set of terminals were being arranged to absorb the power, then, the built-up heat versus time was being measured. With the launch of the crystal technology in the period of the world war II, new types of detectors were initiated based on this technology. Consequently, the detectors became faster, more rugged and performed at higher frequencies. One of the earliest sensing element built in crystal technology had a positive temperature coefficient (PTC); this type of element uses the power substitution methods to produce the readout voltage. The thermistors which have negative temperature coefficient (NTC) were much more rugged, for this reason, they became more dominant compared to PTC elements. The calorimeters were also being used with the thermistors in the early measurements. In the 1960’s, the 434A power meter was an oil-flow calorimeter, where the maximum measurable power using this meter was about 10 watt [25]. On the other hand, water flow calorimeters were being used for medium and high power levels. Finally, it is worth to mention that some of the early power sensors are still used nowadays (such as thermistors, calorimeters, diodes …). However, more decent technologies and complex instruments are employed to improve the detection performances.
Measuring or improving of system efficiency
Efficiency is a measure of how well a device (or system) converts one energy source to another. In microwave engineering, we are interested in converting DC to RF power or the opposite. With the rapid development of wireless communication systems, the demand of higher data rate and larger frequency bandwidth is more and more increased. This can only be achieved by consuming more energy [27]. Therefore, increasing the efficiency of the devices is necessary.
In mobile radio networks, the amplifiers in both cell phones and base stations consume the highest amount of energy comparing to other system parts. (50-80) % of the consumed power in the base station is drained in power amplifier [28]. Moreover, these amplifiers suffer from low efficiencies. Hence, increasing their efficiencies will significantly increase the overall system efficiency and the battery life.
Diode detector parameters
To establish the RF power measurement, the detector parameters have to be carefully chosen (or designed). In practice, we cannot obtain an ideal power detector with the best performances in all parameters. Therefore, some detector parameters are usually 40 sacrificed (or degraded) in order to improve (or make the trade-off with) others. In the following, we explain the theory of those parameters, and the relations between each other.
Bandwidth of interest (Δf)
The bandwidth of interest represents the desired frequency band (of RF signal) which can be measured by the detector. The bandwidth is probably the first parameter to be considered when choosing (or designing) a power detector. To maximize the absorbed power at the input, a matching network (corresponding to the bandwidth of interest) can be added (or integrated) to the detector. This network also rejects the undesired frequencies which can be injected in the detector. A bulky matching network can cause significant losses in the input power (especially at high frequencies), thus, small networks sizes are recommended.
2.3.2 Power consumption ( )
As discussed in the paragraph 2.2, some diodes need to be biased in order to operate at a certain DC point (Q). This helps to decrease their high impedances (since high impedance can block the input signal), and enhance their non-linearity of I-V curve (which is poor around 0). Figure 2.4 shows the different regions of I-V diode characteristic, and the static operating point Q. For the detection purpose, the diode has to be biased so the Q point is kept in the nonlinear region. The following equation provides the I-V relation of a diode [57]: I IS .(exp(V / n.VT ) 1) (2.1) A*.A.T 2 q. B And I S exp (2.2) K.T.
Table of contents :
List of Tables
List of Figures
General introduction
Chapter 1 Power Measurement Applications & Power Sensors
1.1 A brief history of RF and microwave power measurement
1.2 Why measuring power ?
1.3 Power measurements applications
1.3.1 Proof of design
1.3.2 Component protection
1.3.3 Power regulation
1.3.4 Measuring or improving of system efficiency
1.3.4.1 Envelope tracking technique (ET)
1.3.5 THz power detection
1.4 Power sensors
1.4.1 Power definition
1.4.2 Types of power measurement
1.4.3 Some backgrounds of power detectors
1.4.4 Heat based power detectors
1.4.4.1 Bolometers
1.4.4.2 Thermocouple sensors
1.5 Conclusion
Chapter 2 Diode Based Detectors : Theory & Parameters
2.1 Introduction
2.2 Diode detector principles
2.3 Diode detector parameters
2.3.1 Bandwidth of interest (Δf)
2.3.2 Power consumption (𝑃𝐷)
2.3.3 Voltage or current sensitivity (𝛾)
2.3.4 The detector noise floor
2.3.4.1 Thermal (Johnson) noise
2.3.4.2 Flicker (1/f) noise
2.3.4.3 Avalanche noise
2.3.4.4 Shot noise
2.3.4.5 Estimation of noise equivalent power (NEP)
2.3.5 Video resistance (𝑅𝑉)
2.3.6 Video bandwidth (BW)
2.3.7 Dynamic range (Dy)
2.3.8 Figure of merit (FOM)
2.4 Conclusion
Chapter 3 PN Diode Detectors : Design & Characterization
3.1 Introduction
3.3 Extraction of the diode parameters
3.4 Design of adjustable power detector based on PN diode
3.4.1 N-load circuit
3.4.2 PN diode
3.4.3 Matching network
3.4.4 Detection simulation in ADS
3.4.5 Measurement results
3.4.6 Theoretical analysis
3.5 The thermal behavior of the PN diode
3.5.1 The deviation of the PN model with temperature
3.5.2 The deviation of the sensitivity with temperature
3.5.3 Simulation / measurement of sensitivity with temperature
3.6 State of the art
3.7 Conclusion
Chapter 4 Zero Bias Detectors : Design & Characterization
4.1 Introduction
4.2 Zero bias detectors for 5G applications
4.2.1 Overview of MOSFET operation regions
4.2.2 Zero bias detector based on single NMOS
4.2.2.1 Detector design
4.2.2.2 Measurement results
4.2.3 Zero bias detector using stack of 6 NMOS
4.2.3.1 Theoretical background
4.2.3.2 Detector design
4.2.3.3 Measurement results
4.2.4 Linearizing the detector response
4.2.5 Temperature compensated zero bias detector
4.2.5.1 Theoretical background
4.2.5.2 Detector design
4.2.5.3 Measurement results
4.2.6 State of the art
4.3 Frequency compensated power detector in G-band
4.3.1 Theoretical background
4.3.2 Detector design
4.3.3 Measurement results
4.3.4 State of the art
4.4 THz power detector
4.5 Conclusion
General conclusions and future works
References
