Microwave Physics
and Quasioptics:
Passive and Active
RF-Components
Microwave Physics and Quasioptics:
Introduction
Passive and Active Microwave Components
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Axel Murk
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Institute of Applied Physics
University of Bern
13.10.2009
1
Microwave Physics
and Quasioptics:
Objective
Passive and Active
RF-Components
Introduction
Passive
I
Termination
Attenuator
Filter
Coupler
Ferrites
Basic overview of the microwave hardware that is used
at our institute (and in all modern communication and
navigation equipment).
I
Practical introduction to fundamental test equipment,
with an invitation to a hands on experience for those
who are interested.
I
Discussion of problems and possible error sources in
microwave remote sensing instruments.
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
2
Microwave Physics
and Quasioptics:
Example of a 22 GHz Receiver
Passive and Active
RF-Components
IAP Radiometer Praktikum
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Atmosphere
H2O
Coupler
Antenna
Amplifier
Mixer
Filter
Amplifier
RF = 22.2
+/− 0.5 GHz
Detector
Multiplier
Mixer
Amplifier
Oscillator
DC
Attenuator
IF =0 to 0.5 GHz
Local Oscillator
IF = |RF +/− LO|
LSB
Noise
Diode
USB
LO
LO =22 GHz
Power
Black Body
Calibration
Target
Active
Detector
Frequency
3
Microwave Physics
and Quasioptics:
Outline
Passive and Active
RF-Components
Introduction
Introduction
Passive Microwave Components
Termination
Attenuator
Filter
Coupler
Ferrite Devices
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Active Components
Detector
Multiplier
Mixer
Amplifier
Oscillator
4
Microwave Physics
and Quasioptics:
Background Knowledge
Passive and Active
RF-Components
I
Electromagnetic waves and their complex representation
x
E = E0 e jω(t± c )
I
Decibel scale for power ratios: 10 · log10 (P1 /P2 ) [dB]
I
Transmission lines: waveguides, cables, micro-strip lines
⇒ theory later in this lecture
I
Impedance, matching and standing waves
4 Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
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5
Microwave Physics
and Quasioptics:
Scattering Parameters
Passive and Active
RF-Components
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Passive
7
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7
!
Introduction
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Termination
Attenuator
Filter
Coupler
Ferrites
(
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4 Active
I
Relation between incident (a) and reflected or
transmitted waves (b) of a Device Under Test (DUT)
b1 = S11 a1 + S12 a2
b2 = S21 a1 + S22 a2
b1
S11 S12
a1
Matrix notation:
=
b2
S21 S22
a2
Easily measured with a Vector Network Analyzer
I
Expandable to devices with N ports
I
I
Detector
Multiplier
Mixer
Amplifier
Oscillator
6
Microwave Physics
and Quasioptics:
Cascaded S-Parameters
Passive and Active
RF-Components
Total Network T
Port 1
I
I
I
aA1
EA1
A
Network
B
Network
aB2
EB2
Introduction
Port 2
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Cascading two 2-port devices A and B: ST 6= SA SB
Multiplying the S-parameter matrices does not work!
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Definition
(T-Matrix)
of transmission
parameters
b1
T11 T12
a2
=
a1
T21 T22
b2
TT = TA TB
Conversion between S and T
− det(S) S11
T12 det(T )
1
1
T = S21
S = T22
−S22
1
1
−T21
.
determinat: det(S) = S11 S22 − S12 SS21
I
7
Microwave Physics
and Quasioptics:
Passive Microwave Components
Passive and Active
RF-Components
Definitions
Introduction
I
Linear transfer characteristic
– S-parameters do not depend on the power
– A continuous wave signal does not get distorted
Passive
I
Most passive components are reciprocal Sij = Sji
Ferrite isolators and circulators are an exception
Active
I
For lossless two-port devices:
– Reflections at both ports are identical S11 = S22
– Energy conservation |S11 |2 + |S21 |2 = 1
Termination
Attenuator
Filter
Coupler
Ferrites
Detector
Multiplier
Mixer
Amplifier
Oscillator
Design depends on the frequency range, the required
performance and other aspects (e.g. costs, size, mass, power
handling).
8
Microwave Physics
and Quasioptics:
Lumped Element Devices
I
Discrete network of individual components, e.g. coils,
capacitors, resistors.
I
Dimensions < λ, phase differences from the assembly
can be neglected.
I
Passive and Active
RF-Components
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Usable up to ∼3GHz (and above), but parasitic effects
and radiation losses increase with frequency.
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Example for a lumped element 100MHz bandpass filter of a
radio amateur receiver.
9
Microwave Physics
and Quasioptics:
Distributed Devices
I
All components are connected by transmission lines
with dimensions in the order of λ.
I
The connections are an integral part of the circuit, e.g.
for tuning or impedance matching.
I
Usable up to ∼100 GHz (and above).
I
Dielectric and ohmic losses increase with frequency, and
manufacturing becomes very demanding.
Example of an integrated 24 GHz receiver module.
Passive and Active
RF-Components
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
10
Microwave Physics
and Quasioptics:
Quasi-Optics
I
At Millimeter and submillimeter wavelengths free space
propagation provides lowest losses.
I
Quasi-optical components with dimensions > λ are used
to guide, split or combine the beams.
Passive and Active
RF-Components
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
FSP Sideband Filter
to Cryostat
Active
300 mm
Detector
Multiplier
Mixer
Amplifier
Oscillator
Local Oscillator
Image BBH
to Cold Sky
Signal BBH
to Antenna
Quasi-optical module characterized at IAP for the 660 GHz
receiver SMILES, a Japanese remote sensing instrument for
the International Space Station.
11
Microwave Physics
and Quasioptics:
Termination
Passive and Active
RF-Components
I
Terminates a transmission line (ideally S11= −∞ dB ).
I
Tapered absorbing dielectrics in waveguides (a),
resistive films in planar or coaxial devices (b).
I
I
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Standard coaxial 0-18 GHz terminations specified with
return loss < -26dB (VSWR<1.1), expensive matched
termination for VNA calibration have ≥ -36 dB.
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Free space terminations for anechoic chambers or
radiometric calibration targets. Often made of lossy
foams with a pyramidal surface to improve the
matching.
12
Microwave Physics
and Quasioptics:
Attenuator
Passive and Active
RF-Components
I
Lossy two-port device to reduce the signal level by -xx
dB
Introduction
I
Ideally well matched and frequency independent.
Passive
I
Resistive networks in coaxial (a) and planar devices,
absorbing vane in waveguides.
I
Often used to reduce standing waves caused by
components with a bad matching.
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
13
Microwave Physics
and Quasioptics:
Filter
Passive and Active
RF-Components
I
Used to reject certain frequency bands
I
Realized as low-, high or bandpass filter (and also
band-reject)
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Bandpass Filter for a L−Band Radiometer
10
Insertion Loss −0.39 dB
0
FWHM
Amplitude [dB]
−10
S11
S12
S21
S22
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
−20
−30
−40
Center
Frequency
Out−of−band
Rejection
−50
−60
−70
−80
1.32
1.34
1.36
1.38
1.4
1.42
1.44
Frequency GHz
1.46
1.48
1.5
Measurement example of a cavity filter with four sections.
14
Microwave Physics
and Quasioptics:
Cavity Filter Example
Passive and Active
RF-Components
7.8 GHz high pass filter made out a series of iris coupled
waveguide resonators. Mesh of the finite element model and
simulation results.
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Simulated E-fields in the rejection and transmission band.
15
Microwave Physics
and Quasioptics:
Software for Cavity Filter Design at IAP
Passive and Active
RF-Components
I
Finite Elements: COMSOL Multphysics, Agilent EMDS
I
Mode Matching: S&P (written by P. Füholz)
MICIAN ”Microwave Wizard”
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
16
Microwave Physics
and Quasioptics:
Planar Filter
Passive and Active
RF-Components
Steps to get from a lumped element lowpass filter (a) to an
equivalent microstrip design (d).
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Inductors and capacitors are replaced by microstrip ”stubs”.
Easy to integrate in a circuit, but degraded out of band
performance.
17
Microwave Physics
and Quasioptics:
Power Splitter
Passive and Active
RF-Components
Used to distribute an input signal at port 1 equally and in
phase between the two output ports 2 and 3. An example is
a simple waveguide or microstrip T-junction.
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
It can be shown, however, that it is not possible to match all
ports of a symmetric, reciprocal and lossless device, i.e. the
Sii parameters cannot be zero.
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
18
Microwave Physics
and Quasioptics:
Resistive Power Splitter
Passive and Active
RF-Components
I
I
A simple resistive power splitter is matched at all ports
and has a wide bandwidth, but it has additional -3dB
loss and ports 2 and 3 are not isolated.
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
The Wilkinson power divider has a limited bandwidth,
but it is lossless for S21 and S31, and 
ports 2 and 3 are
0 1 1
−j 
1 0 0 
isolated. For an ideal device [S] = √
2
1 0 0
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
19
Microwave Physics
and Quasioptics:
Directional Coupler
Passive and Active
RF-Components
I
4-port device, input port 1 is isolated from port 4.
I
Splits the power coming from port 1 equally or with a
different coupling ratio between ports 2 and 3.
I
Most important characteristics:
Directivity, bandwidth, phase and amplitude balance
I
Very usefull to measure the return loss of a device.
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Reflectometer setup with a directional coupler to measure
the return loss ρL of a device. which corresponds to the
power ration P4 /P3 .
20
Microwave Physics
and Quasioptics:
Hybrid Coupler
I
I
Passive and Active
RF-Components
Input power is split equally between port 2 and 3.
For a matched and lossless device the phase difference
has to be either 90 or 180 degrees.
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
180 degree ”rat-race” coupler

0
 1
1
[S] = √2 
 1
0
1
0
0
−1

1 0
0 −1 

0 1 
1 0
90 degree ”quadrature” coupler


0 1 j 0
 1 0 0 j 

[S] = √12 
 j 0 0 1 
0 j 1 0
21
Microwave Physics
and Quasioptics:
Multihole Waveguide Coupler
Passive and Active
RF-Components
I
Coupling holes connect two parallel waveguides.
I
Bandwidth increases with number of holes.
Introduction
Passive
1
2
4
3
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Submm devices tested at IAP:
micromachined 350 GHz hybrid
and etched 600 GHz hybrid
22
Microwave Physics
and Quasioptics:
Ferrites
Passive and Active
RF-Components
I
Ferromagnetic ceramic (Fe2 O3 +impurities) with
high resistivity, µr > 1000, εr < 10.
I
Can be magnetized permanently by an external
magnetic field.
I
Electromagnetic waves interact with the magnetic
dipoles.
→
−
Propagation parallel to H results
in different effective permeability
−
µ+
r and µr for left- and righthanded circular polarization, and
thus in different propagation constants (Faraday
rotation):
γµ0 MS
±
µ = µ0 1 + ω0 ±ω
I
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Larmor frequency ω0 = γB0
23
Microwave Physics
and Quasioptics:
Faraday Isolator
I
Non-reciprocal two-port device to reduce standing
waves (ideally S21 = 1 and S12 = 0)
I
Resistive vanes at both ports of a circular waveguide are
oriented at an angle of 45◦ to each other and absorb
energy when they are parallel to the E field.
I
Passive and Active
RF-Components
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Ferrite rod in the center rotates the polarization by
±45◦ , depending on the propagation direction.
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
24
Microwave Physics
and Quasioptics:
Circulator
Passive and Active
RF-Components
I
I
Non-reciprocal three-port device with a ferrite post at
the junction.
Introduction
Passive
Allows to use the same antenna for transmission and
reception (radar, communications).
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Circulator example simulated with COMSOL Multiphysics
25
Microwave Physics
and Quasioptics:
Isolator Example
I
I
Passive and Active
RF-Components
Measured performance of a high quality 1.4 GHz
isolator, which will be used in an L-band radiometer for
SMOS validation
Good performance only over a very narrow bandwidth
Isolation, loss and matching degrade outside of the
specified frequency band
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Measurement of a 1.4 GHz narrow−band isolator
−0.07 dB
0
−10
Amplitude [dB]
I
−20
−30
−40
S11
S12
S21
S22
−50
−60
1
1.2
1.4
1.6
1.8
2
2.2
Frequency GHz
2.4
2.6
2.8
3
26
Microwave Physics
and Quasioptics:
Other Ferrite Devices
Passive and Active
RF-Components
Introduction
Passive
I
Waveguide switch by reversing the magnetic field
of a circulator.
I
Variable phase shifters for electronic beam steering:
Fast change of the pointing of a phased-array antenna
without any moving parts
I
Absorbers for low frequencies.
I
Electrically tunable filters and oscillators
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
27
Microwave Physics
and Quasioptics:
Common Symbols for Passive Devices
Passive and Active
RF-Components
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
28
Microwave Physics
and Quasioptics:
Active Components
Passive and Active
RF-Components
I
I
Nonlinear transfer characteristic leads to signal
distortions and frequency conversion (b), which is not
the case on a linear curve (a).
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Nonlinear devices can still have an almost linear
behavior for small scale signals (c)
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
29
Microwave Physics
and Quasioptics:
Power Measurements
Passive and Active
RF-Components
I
DC
AC to ∼ GHz
AC to ∼ 0.1 THz
AC to > THz
I
Introduction
Different ways to measure electric power,
depending on the frequency range:
−→
−→
−→
−→
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
voltmeter + ampèremeter
oscilloscope
diode detector
bolometer
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Other selection criteria:
I
I
I
I
Power range (nW or kW?)
Accuracy (absolute or relative?)
Linearity (required dynamic range?)
Time constant (continuous wave or modulated?)
30
Microwave Physics
and Quasioptics:
Bolometric Detection
Passive and Active
RF-Components
I
Microwave energy is absorbed and heats the device, the
temperature change ∆T = R · P is measured with a
thermometer.
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Absorber T(P)
P
Active
Thermometer
Radiation
Detector
Multiplier
Mixer
Amplifier
Oscillator
Thermal conductance R
Heat sink
T0 = const
I
Advantages: good power handling, no fundamental
frequency limit, possibility for absolute calibration.
I
Disadvantages (which can be overcome):
relative slow, not very sensitive, thermal drift.
31
Microwave Physics
and Quasioptics:
Cryogenic Bolometers
Passive and Active
RF-Components
Most sensitive detectors used in radio astronomy:
I Cooled below 0.5 K
I ”Spiderweb” geometry to minimize mass, heat capacity
and thermal conductivity
I Used in many cosmic background experiments
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Complete bolometer array and close-up
views of the spiderweb bolometers.
32
Microwave Physics
and Quasioptics:
Diode Detector
Passive and Active
RF-Components
I
I
Junction betwee semiconductors with different doping
(p-n diode) or metal-semiconductor (Schottky diode).
Non-linear I/V curve rectifies the RF signal.
For small signals it can be approximated by a quadratic
curve, and the DC output signal is linear with the input
power.
reverse bias
n
I
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
forward bias
I = I0 [exp(V/V0)−1]
p
_ _ _
+ + +
⟨ I(t)⟩ > 0
V
breakdown voltage
Forward direction
Introduction
Passive
reverse current I0
V(t)
33
Microwave Physics
and Quasioptics:
Characteristics of Diode Detectors
I
Advantages:
I
I
Passive and Active
RF-Components
Very fast (rise times < ns), relative sensitive
Introduction
Passive
Disadvantages:
I
I
I
Termination
Attenuator
Filter
Coupler
Ferrites
Easily destroyed by ESD (electrostatic discharge)
Moderate linearity and temperature stability
Upper frequency cut-off given by the parasitic capacity
of the junction
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Response of a typical diode detector. Only in the square-law
region the output signal is proportional to the input power.
34
Microwave Physics
and Quasioptics:
Diode Layout
Passive and Active
RF-Components
To use diodes at THz frequencies the junction area needs
to be as small as possible,
which is achieved by point-like
whisker contacts or very small
planar devices.
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
F
i
g
.
1
.
S
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i
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g
e
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e
c
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e
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i
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.
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a
p
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r
o
x
i
m
a
t
e
l
y
1
8
0
x
8
0
x
4
0
m
.
35
Microwave Physics
and Quasioptics:
Frequency Multiplication
Passive and Active
RF-Components
A nonlinear device generates harmonics of an input signal
with the fundamental frequency f0 .
Introduction
Passive
V(t)
|V(t)|
Termination
Attenuator
Filter
Coupler
Ferrites
Active
0
f0
−10
−20
−30
−40
Time
Amplitude [dB]
Amplitude [dB]
Time
Frequency
Detector
Multiplier
Mixer
Amplifier
Oscillator
0 0
−10
−20
−30
−40
2f0
4f0
6f
0
8f0
Frequency
36
Microwave Physics
and Quasioptics:
Examples of Frequency Multipliers
Passive and Active
RF-Components
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
37
Microwave Physics
and Quasioptics:
Heterodyne Principle
Passive and Active
RF-Components
I
I
Superposition of a strong local oscillator (LO) signal
with a weaker radio frequency (RF ) signal on nonlinear
device generates an intermediate frequency
IF = |LO ± RF |
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Normal double sideband mixers (DSB) convert both
sidebands, single sideband conversion (SSB) requires a
RF filter or a special mixer.
Mixer
RF
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
IF
LO
RF−LO
RF + LO
LO
Power
2 LO
USB
LSB
IF
LO−RF
down−conversion
up−conversion
Frequency
38
Microwave Physics
and Quasioptics:
Mixers Designs
I
Single ended mixer (a): Common for mm wavelengths.
No isolation between RF and LO.
I
Balanced mixer (b): Two mixing elements, 3dB hybrid
combines LO and RF. Good LO to RF isolation, LO
noise and spurious harmonics are rejected.
I
Passive and Active
RF-Components
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Double balanced mixer (c): Also IF port is isolated,
dynamic range is improved.
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
39
Microwave Physics
and Quasioptics:
Subharmonic Mixer
I
I
I
Passive and Active
RF-Components
Antiparallel diode pair down-converts with the second
LO harmonic IF = |RF − 2LO|
Advantages:
Lower LO frequency and good LO/RF isolation.
Disadvantages:
Higher conversion loss and LO power requirement.
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
RF
diode pair
RF filter
LO
IF Filter
IF
40
Microwave Physics
and Quasioptics:
SIS Mixer
Passive and Active
RF-Components
Superconductor-Isolator-Superconductor tunnel junction:
I
I
Two Niobium layers at 4K (ρΩ = 0),
separated a 2 nm thick Al2 O3 barrier
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Cooper-pairs (2e − ) tunnel through the barrier,
resulting in a sharp bend in the I/V curve
Active
superconductor
V0
insulator
superconductor
I0
bias current I0 [µA]
400
a)
Detector
Multiplier
Mixer
Amplifier
Oscillator
b)
300
200
100
0
0
2
4
6
bias voltage V
U00 [mV]
41
Microwave Physics
and Quasioptics:
SIS Mixer
Passive and Active
RF-Components
Band structure and photoassisted tunneling in a SIS junction.
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
S
I
S
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
unfilled energy states
energy
superconductor
"bandgap"
photon
2e
filled energy states
42
Microwave Physics
and Quasioptics:
SIS Mixer Characteristics
Passive and Active
RF-Components
I
Very low noise, close to the quantum limit hν/kB
I
Upper frequency limit from the bandgap voltage
Niobium: 1.4 THz
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
65 µm
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
junction
1µm2
(1)
O
(2)
48 µm
Nb top-wiring
(3)
NbTiN
SiO2 ground
dielectric plane
feed point
O
Example
of an SIS mixer for
the HIFI instrument. The
junction has an area of only
1µm2 , most parts in the image are tuning elements for
the impedance matching.
43
Microwave Physics
and Quasioptics:
HEB Mixer
I
I
I
I
Passive and Active
RF-Components
Hot Electron Bolometers (HEB) are extremely fast
bolometers, which can be used as mixing element.
Superconducting microbridge (d <10 nm) close to the
transition temperature.
No fundamental RF frequency limit (>2THz)
Limited IF bandwidth (∼ 5 GHz) given by cooling rate
of the electrons.
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
44
Microwave Physics
and Quasioptics:
Amplifier
bias
I
Increase signal amplitude
I
Made with bipolar or FET
transistors
Passive and Active
RF-Components
out
in
Introduction
C
B
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
E
I
Tradeoff between low noise
and high power
Active
emitter
n
p
base
source
gate
Detector
Multiplier
Mixer
Amplifier
Oscillator
drain
n AlGaAs
n+
quantum−well
with 2DEG
GaAs
bipolar transistor
collector
undoped GaAs
HEMT−FET transistor
Schematic of a bipolar npn transistor and a High Electron
Mobility (HEMT) field effect transistor, which works with a
2D electron gas in a quantum well.
45
Microwave Physics
and Quasioptics:
Amplifier Specifications
Passive and Active
RF-Components
I
Gain (amplification in dB)
I
Frequency range and gain flatness
Introduction
I
Noise figure (how much noise is added)
Passive
I
Maximum output power and 1dB compression point
Termination
Attenuator
Filter
Coupler
Ferrites
Examples:
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
Power amplifier
G=45dB (±2dB), NF=8dB
f=0.8-2 GHz, 1dB Gc = +36dBm
VSWR = 1.7dB Bias supply 24V, 2A
Lownoise amplifier
G=15dB (±1dB), NF=0.4dB
f=1-1.4 GHz, 1dB Gc = +12.5dBm
VSWR = 1.7dB
Bias supply 12V, 40mA
46
Microwave Physics
and Quasioptics:
Oscillator
Passive and Active
RF-Components
Active element (1) with a resonant feedback (2)
Introduction
(1) Transistor, electrons in a vacuum tube (for high power),
Gunn diode (semiconductor with negative resistance), ...
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
(2) LC-circuit, microstrip and dielectric resonator,
waveguide cavity, quartz crystal, ...
Active
L
Detector
Multiplier
Mixer
Amplifier
Oscillator
C
Schematic of a LC oscillator with ω0 = √1LC and
example of a dielectric oscillator in stripline technology.
47
Microwave Physics
and Quasioptics:
Magnetron
I
Microwave generator for high output power (>1MW)
with good efficiency (>80%)
I
A high electric field accelerates electrons in a circular
cavity, a magnetic field forces them on a spiral path
which excites microwave resonances.
I
Passive and Active
RF-Components
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Standard for microwave ovens and radar systems
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
48
Microwave Physics
and Quasioptics:
Oscillator Specifications
Passive and Active
RF-Components
I
Frequency accuracy and stability
I
Phase noise (specified in dB below carrier [dBc])
I
Harmonic and spurious signals
I
Phase noise and short term accuracy depends on the
quality of the resonator (Q-factor).
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Active
●
●
●
Phase Noise
Residual FM
Spurious
Detector
Multiplier
Mixer
Amplifier
Oscillator
CW output
Residual FM is the integrated
phase noise over 300 Hz - 3
kHz BW
phase
noise
harmonic spur
~30dBc
non-harmonic spur
~65dBc
sub-harmonics
0.5 f0
f0
2f0
49
Microwave Physics
and Quasioptics:
Oscillator Types
I
Atomic clocks (Cs or Rb) for absolute time standards
with ∆f /f < 10−15 (e.g. at METAS, UniNE, NIST)
I
Quartz oscillators as reference signals up to 100 MHz
reach ∆f /f = 10−6 to 10−9 , depending on temperature
compensation or temperature stabilization.
I
Passive and Active
RF-Components
Introduction
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
All higher frequencies are usually synchronized to a
quartz crystal with a phase-locked loop (PLL).
Active
Detector
Multiplier
Mixer
Amplifier
Oscillator
free running
phase locked
Example of a 6 GHz cavity oscillator
50
Microwave Physics
and Quasioptics:
Modulation Analog
Passive and Active
RF-Components
I
Amplitude modulation (AM): VAM = A(t) sin(f0 · t)
Introduction
Passive
Carrier
Termination
Attenuator
Filter
Coupler
Ferrites
Voltage
Time
Active
Modulation
Frequency modulation (FM): VFM = A0 sin(f (t) · t)
Phase Modulation (PM): VPM = A0 sin(f0 · t + φ(t))
Voltage
I
Detector
Multiplier
Mixer
Amplifier
Oscillator
Time
51
Microwave Physics
and Quasioptics:
Modulation Digital
Passive and Active
RF-Components
Introduction
Amplitude
Passive
Termination
Attenuator
Filter
Coupler
Ferrites
Frequency
Active
Phase
Detector
Multiplier
Mixer
Amplifier
Oscillator
Quadrature
Digital Modulation phase-shift keying (QPSK):
Polar Display: Magnitude & Phase Represented Together
QPSK IQ Diagram
Q
01
00
g
Ma
Phase
0 deg
I
●
●
Magnitude is an absolute value
Phase is relative to a reference signal
11
10
52