Microwave Components Passive Termination Attenuator Filter Coupler Ferrites Active Passive and Active Microwave Components Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 8.4.2007 www.iapmw.unibe.ch Microwave Physics Institute of Applied Physics Universitat Bern Objective Switzerland = Swiss Confedration CH (Confoederatio Helvetic) Population = 8.5 million GDP (PPP) = $65,000 1 Microwave Components Passive Termination Attenuator Filter Coupler Ferrites I Basic overview of the microwave hardware that is used in our group (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 MW Instruments Spectrum Analyzer 2 Microwave Components Outline 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 MW Instruments Spectrum Analyzer Microwave Instrumentation Spectrum Analyzer 3 Microwave Components Topics already covered in WS2007 Lecture ”Introduction to Applied Electromagnetism” Passive Termination Attenuator Filter Coupler Ferrites Active I Electromagnetic waves I Decibel scale for power ratios: 10 · log 10 (P1 /P2 ) [dB] I Transmission lines: waveguides, cables, micro-strip lines I Impedance, matching and standing waves I Vector Network Analyzer Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 4 Microwave Components Introduction Passive Components in the 22 GHz receiver of the IAP Radiometer Praktikum: Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator Atmosphere H2O Coupler Antenna Amplifier Mixer Filter Amplifier Detector MW Instruments RF = 22.2 +/− 0.5 GHz 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 Spectrum Analyzer Frequency 5 Microwave Components Passive Microwave Components Passive Definitions I I Termination Attenuator Filter Coupler Ferrites Linear transfer characteristic – S-parameters do not depend on the power – A continuous wave signal does not get distorted Active Detector Multiplier Mixer Amplifier Oscillator Most passive components are reciprocal |S21|2 = |S12|2 Ferrite isolators and circulators are an exception MW Instruments Spectrum Analyzer I For lossless two-port devices: – Reflections at both ports are identical |S11|2 = |S22|2 – Energy conservation |S11|2 + |S21|2 = 1 Design depends on the frequency range, the required performance and other aspects (e.g. costs, size, mass, power handling). 6 Microwave Components Lumped Element Devices I I I Discrete network of individual components, e.g. coils, capacitors, resistors. Passive Termination Attenuator Filter Coupler Ferrites Dimensions < λ, phase differences from the assembly can be neglected. Active Usable up to ∼3GHz (and above), but parasitic effects and radiation losses increase with frequency. Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer Example for a lumped element 100MHz bandpass filter of a radio amateur receiver. 7 Microwave Components 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. Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer Example of an integrated 24 GHz receiver module. 8 Microwave Components Quasi-Optics I I At Millimeter and submillimeter wavelengths free space propagation provides lowest losses. Passive Termination Attenuator Filter Coupler Ferrites Quasi-optical components with dimensions > λ are used to guide, split or combine the beams. Active Detector Multiplier Mixer Amplifier Oscillator FSP Sideband Filter to Cryostat 300 mm MW Instruments Spectrum Analyzer 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. 9 Microwave Components Termination Passive I Terminates a transmission line (ideally S11= −∞ dB ). I Tapered absorbing dielectrics in waveguides (a), resistive films in planar or coaxial devices (b). I Standard coaxial 0-18 GHz terminations specified with return loss < -26dB (VSWR<1.1), expensive matched termination for VNA calibration have ≥ -36 dB. Active I Free space terminations for anechoic chambers or radiometric calibration targets. Often made of lossy foams with a pyramidal surface to improve the matching. MW Instruments Termination Attenuator Filter Coupler Ferrites Detector Multiplier Mixer Amplifier Oscillator Spectrum Analyzer 10 Microwave Components Attenuator I Lossy two-port device to reduce the signal level by -xx dB I Ideally well matched and frequency independent. I Resistive networks in coaxial (a) and planar devices, absorbing vane in waveguides. I Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator Often used to reduce standing waves caused by components with a bad matching. MW Instruments Spectrum Analyzer 11 Microwave Components Filter Passive I Used to reject certain frequency bands I Realized as low-, high or bandpass filter (and also band-reject) Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator Bandpass Filter for a L−Band Radiometer 10 Insertion Loss −0.39 dB 0 FWHM Amplitude [dB] −10 S11 S12 S21 S22 MW Instruments Spectrum Analyzer −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. FWHM (full width at half maximum) 12 Microwave Components Filter Types and Specifications Passive Termination Attenuator Filter Coupler Ferrites Selection depends on frequency and relative bandwidth. Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer Online tool of the manufacturer K&L http://www.klfilterwizard.com 13 Microwave Components Cavity Filter Example 7.8 GHz high pass filter made out a series of iris coupled waveguide resonators. Mesh of the finite element model and simulation results. Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer Simulated E-fields in the rejection and transmission band. 14 Microwave Components Software for Cavity Filter Design at IAP I I Finite Elements: COMSOL Multphysics, Agilent EMDS Passive Termination Attenuator Filter Coupler Ferrites Mode Matching: S&P (written by P. Füholz) MICIAN ”Microwave Wizard” Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 15 Microwave Components Planar Filter Passive Steps to get from a lumped element lowpass filter (a) to an equivalent microstrip design (d). Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer Inductors and capacitors are replaced by microstrip ”stubs”. Easy to integrate in a circuit, but degraded out of band performance. 16 Microwave Components Planar Filter Design using ADS Passive Agilent Advanced Design System (ADS) is a powerful electronic design automation software, which includes libraries and optimizers for planar filters. Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator Design flow for a bandpass filter from the schematic to the layout and simulation result. MW Instruments Spectrum Analyzer 17 Microwave Components Power Splitter Passive Termination Attenuator Filter Coupler Ferrites 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. Active Detector Multiplier Mixer Amplifier Oscillator 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. MW Instruments Spectrum Analyzer 18 Microwave Components Resistive Power Splitter 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. Passive I 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 isolated. For an ideal device [S] = √2 1 0 0 1 0 0 Active Termination Attenuator Filter Coupler Ferrites Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 19 Microwave Components Directional Coupler 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 Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator Very usefull to measure the return loss of a device. MW Instruments Spectrum Analyzer Reflectometer setup with a directional coupler to measure the return loss ρL of a device. which corresponds to the power ration P4 /P3 . 20 Directional Coupler 10-dB 1.7-2.2 dB directional coupler. From left to right: input, coupled, isoated, and transmitted port Coupling = - 10 log(P3/P1) Insertion loss = - 10 log (P2/P1) Coupling loss = -10 log (1-P3/P1) Isolation = - 10 log (P4/P1) Directivity = - 10 log (P4/P3) Microwave Components Hybrid Coupler I I 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. Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 180 degree ”rat-race” coupler 0 1 1 0 [S] = √12 1 0 0 −1 1 0 0 −1 0 1 1 0 90 degree ”quadrature” coupler 0 1 [S] = √12 j 0 1 j 0 0 0 j 0 0 1 j 1 0 21 Microwave Components Multihole Waveguide Coupler I Coupling holes connect two parallel waveguides. I Bandwidth increases with number of holes. 1 2 4 3 Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer Submm devices tested at IAP: micromachined 350 GHz hybrid and etched 600 GHz hybrid 22 Microwave Components Examples of Microstrip Couplers Passive 40 Termination Attenuator Filter Coupler Ferrites 30 directivity 20 [dB] 10 insertion loss 0 Active coupling -10 Detector Multiplier Mixer Amplifier Oscillator -20 return loss -30 0 20 40 60 frequency [GHz] 80 100 120 Simple proximity coupler with wide bandwidth MW Instruments Spectrum Analyzer Optimized step-design with λ/4 matching sections. 23 Microwave Components Ferrites I Ferromagnetic ceramic (Fe2 O3 +impurities) with high resistivity, µr > 1000, εr < 10. I Can be magnetized permanently by an external magnetic field. I I Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator 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 MW Instruments Spectrum Analyzer Larmor frequency ω0 = γB0 24 Microwave Components Faraday Isolator I I I Non-reciprocal two-port device to reduce standing waves (ideally S21 = 1 and S12 = 0) Passive Termination Attenuator Filter Coupler Ferrites 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. Active Detector Multiplier Mixer Amplifier Oscillator Ferrite rod in the center rotates the polarization by ±45◦ , depending on the propagation direction. MW Instruments Spectrum Analyzer 25 Microwave Components Circulator I I I Non-reciprocal three-port device with a ferrite post at the junction. Passive Termination Attenuator Filter Coupler Ferrites Allows to use the same antenna for transmission and reception (radar, communications). Active Detector Multiplier Mixer Amplifier Oscillator Absorbers for low frequencies. MW Instruments Spectrum Analyzer Circulator example simulated with COMSOL Multiphysics 26 Microwave Components Isolator Example I I I 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 Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator Measurement of a 1.4 GHz narrow−band isolator MW Instruments Spectrum Analyzer −0.07 dB 0 Amplitude [dB] −10 −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 27 Microwave Components Other Ferrite Devices Passive Termination Attenuator Filter Coupler Ferrites Active I Waveguide switch by reversing the magnetic field of a circulator. I Variable phase shifters for electronic beam steering I Attenuator for low frequencies I Tunable filters and oscillators Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 28 Microwave Components Common Symbols for Passive Devices Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 29 Microwave Components Active Components I Nonlinear transfer characteristic leads to signal distortions and frequency conversion (b), which is not the case on a linear curve (a). I Nonlinear devices can still have an almost linear behavior for small scale signals (c) Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 30 Microwave Components Power Measurements Passive I Different ways to measure electric power, depending on the frequency range: DC AC to ∼ GHz AC to ∼ 0.1 THz AC to > THz I Termination Attenuator Filter Coupler Ferrites −→ −→ −→ −→ Active voltmeter + ampèremeter oscilloscope diode detector bolometer Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 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?) 31 Microwave Components Bolometric Detection I Microwave energy is absorbed and heats the device, the temperature change ∆T = R · P is measured with a thermometer. Passive Termination Attenuator Filter Coupler Ferrites Active Absorber T(P) Detector Multiplier Mixer Amplifier Oscillator P Thermometer Radiation MW Instruments Thermal conductance R Spectrum Analyzer 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. 32 Microwave Components Cryogenic Bolometers 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 Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer Complete bolometer array and close-up views of the spiderweb bolometers. 33 Microwave Components Diode Detector I Junction betwee semiconductors with different doping (p-n diode) or metal-semiconductor (Schottky diode). I 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. Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments n Spectrum Analyzer I forward bias I = I0 [exp(V/V0)−1] p _ _ _ + + + ⟨ I(t)⟩ > 0 V breakdown voltage Forward direction reverse bias reverse current I0 V(t) 34 Microwave Components Characteristics of Diode Detectors Advantages: I Passive Termination Attenuator Filter Coupler Ferrites Very fast (rise times < ns), relative sensitive I Disadvantages: I Active Easily destroyed by ESD (electrostatic discharge) Moderate linearity and temperature stability Upper frequency cut-off given by the parasitic capacity of the junction I I I Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer Response of a typical diode detector. Only in the square-law region the output signal is proportional to the input power. 35 Microwave Components Diode Layout Passive Termination Attenuator Filter Coupler Ferrites 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. Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments F i g . 1 . S c a n n i n g e l e c t e n Spectrum Analyzer r o n m i c r o g r a p h o f a p l a n a r S c h o t t k y b a r r i e r d i o d e . C h i p d i m s i o n s a p p r o x i m a t e l y 1 8 0 x 8 0 x 4 0 m . 36 Microwave Components Frequency Multiplication A nonlinear device generates harmonics of an input signal with the fundamental frequency f0 . Passive Termination Attenuator Filter Coupler Ferrites Active V(t) |V(t)| Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 0 f0 −10 −20 −30 −40 Time Amplitude [dB] Amplitude [dB] Time Frequency 0 0 −10 −20 −30 −40 2f0 4f0 6f0 8f0 Frequency 37 Microwave Components Examples of Frequency Multipliers Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 38 Microwave Components Heterodyne Principle 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 | Passive Termination Attenuator Filter Coupler Ferrites Active Normal double sideband mixers (DSB) convert both sidebands, single sideband conversion (SSB) requires a RF filter or a special mixer. Mixer RF Detector Multiplier Mixer Amplifier Oscillator MW Instruments IF Spectrum Analyzer LO RF−LO RF + LO LO Power 2 LO USB LSB IF LO−RF down−conversion up−conversion Frequency 39 Microwave Components Mixers Designs I I I Single ended mixer (a): Common for mm wavelengths. No isolation between RF and LO. Passive Termination Attenuator Filter Coupler Ferrites Balanced mixer (b): Two mixing elements, 3dB hybrid combines LO and RF. Good LO to RF isolation, LO noise and spurious harmonics are rejected. Active Detector Multiplier Mixer Amplifier Oscillator Double balanced mixer (c): Also IF port is isolated, dynamic range is improved. MW Instruments Spectrum Analyzer 40 Microwave Components Subharmonic Mixer I I I 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. Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments RF Spectrum Analyzer diode pair RF filter LO IF Filter IF 41 Microwave Components SIS Mixer Superconductor-Isolator-Superconductor tunnel junction: I Two Niobium layers at 4K (ρΩ = 0), separated a 2 nm thick Al2 O3 barrier I Cooper-pairs (2e − ) tunnel through the barrier, resulting in a sharp bend in the I/V curve Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments a) superconductor V0 insulator superconductor I0 bias current I0 [µA] 400 Spectrum Analyzer b) 300 200 100 0 0 2 4 6 bias voltage V U00 [mV] 42 Microwave Components SIS Mixer Passive Band structure and photoassisted tunneling in a SIS junction. Termination Attenuator Filter Coupler Ferrites Active S I Detector Multiplier Mixer Amplifier Oscillator S unfilled energy states energy MW Instruments Spectrum Analyzer superconductor "bandgap" 2e photon filled energy states 43 Microwave Components SIS Mixer Characteristics I Very low noise, close to the quantum limit hν/kB I Upper frequency limit from the bandgap voltage Niobium: 1.4 THz Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator 65 µm junction 1µm2 MW Instruments Spectrum Analyzer (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. 44 Microwave Components HEB Mixer I I I I 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. Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer 45 Microwave Components Amplifier bias I I out Passive Increase signal amplitude Made with bipolar or FET transistors Termination Attenuator Filter Coupler Ferrites in C B E I Active Tradeoff between low noise and high power emitter n p base Detector Multiplier Mixer Amplifier Oscillator source gate drain MW Instruments Spectrum Analyzer 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. 46 Microwave Components Amplifier Specifications I Gain (amplification in dB) I Frequency range and gain flatness I Noise figure (how much noise is added) I Maximum output power and 1dB compression point Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator Examples: MW Instruments Power amplifier G=45dB (±2dB), NF=8dB f=0.8-2 GHz, 1dB Gc = +36dBm VSWR = 1.7dB Bias supply 24V, 2A Spectrum Analyzer Lownoise amplifier G=15dB (±1dB), NF=0.4dB f=1-1.4 GHz, 1dB Gc = +12.5dBm VSWR = 1.7dB Bias supply 12V, 40mA 47 Microwave Components Oscillator Passive Active element (1) with a resonant feedback (2) Termination Attenuator Filter Coupler Ferrites (1) Transistor, electrons in a vacuum tube (for high power), Gunn diode (semiconductor with negative resistance), ... Active (2) LC-circuit, microstrip and dielectric resonator, waveguide cavity, quartz crystal, ... Detector Multiplier Mixer Amplifier Oscillator MW Instruments L Spectrum Analyzer C Schematic of a LC oscillator with ω0 = √1LC and example of a dielectric oscillator in stripline technology. 48 Microwave Components Magnetron I I I Microwave generator for high output power (>1MW) with good efficiency (>80%) Passive Termination Attenuator Filter Coupler Ferrites A high electric field accelerates electrons in a circular cavity, a magnetic field forces them on a spiral path which excites microwave resonances. Active Detector Multiplier Mixer Amplifier Oscillator Standard for microwave ovens and radar systems MW Instruments Spectrum Analyzer 49 Microwave Components Oscillator Specifications 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). ● ● ● Phase Noise Residual FM Spurious Passive Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments CW output Residual FM is the integrated phase noise over 300 Hz - 3 kHz BW phase noise Spectrum Analyzer harmonic spur ~30dBc non-harmonic spur ~65dBc sub-harmonics 0.5 f0 f0 2f0 50 Microwave Components Oscillator Types I I I Atomic clocks (Cs or Rb) for absolute time standards with ∆f /f < 10−15 (e.g. at METAS, UniNE, NIST) Passive Termination Attenuator Filter Coupler Ferrites Quartz oscillators as reference signals up to 100 MHz reach ∆f /f = 10−6 to 10−9 , depending on temperature compensation or temperature stabilization. Active Detector Multiplier Mixer Amplifier Oscillator All higher frequencies are usually synchronized to a quartz crystal with a phase-locked loop (PLL). MW Instruments Spectrum Analyzer free running phase locked Example of a 6 GHz cavity oscillator 51 Microwave Components Modulation Analog I Passive Amplitude modulation (AM): VAM = A(t) sin(f0 · t) Termination Attenuator Filter Coupler Ferrites Carrier Active Detector Multiplier Mixer Amplifier Oscillator Voltage Time Modulation MW Instruments Spectrum Analyzer Frequency modulation (FM): VFM = A0 sin(f (t) · t) Phase Modulation (PM): VPM = A0 sin(f0 · t + φ(t)) Voltage I Time 52 Microwave Components Modulation Digital Passive Termination Attenuator Filter Coupler Ferrites Amplitude Frequency Active Detector Multiplier Mixer Amplifier Oscillator Phase MW Instruments Spectrum Analyzer Quadrature Digital Modulation phase-shift keying (QPSK): Polar Display: Magnitude & Phase Represented Together QPSK IQ Diagram Q 01 M 00 ag Phase 0 deg I ● ● Magnitude is an absolute value Phase is relative to a reference signal 11 10 53 Microwave Components Spectrum Analysis: From Time- to Frequency Domain Passive : ; 4 Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator MW Instruments 8 Spectrum Analyzer & 4 8 To increase the frequency resolution a longer time series has to be analyzed. 54 Microwave Components Spectrum Analyzer Passive I Realtime analyzer measures all channels simultaneously ⇒ best signal-to-noise ratio for a given integration time I Swept spectrum analyzer moves a filter over the spectrum ⇒ flexible standard instrument for most measurement tasks Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator " # & 1 Spectrum Analyzer 1 " )= )= MW Instruments 55 Microwave Components Realtime Spectrum Analyzer Passive I I Termination Attenuator Filter Coupler Ferrites Filterbank spectrometer Size, cost and power consumption increase linear with number of channels. Active Detector Multiplier Mixer Amplifier Oscillator Acousto Optical Spectrometer (AOS) Bandwidth up to 1 GHz, typically 1-2k channels. MW Instruments Spectrum Analyzer I Digital autocorrelation and FFT spectrometer 1 GHz bandwidth with 16k channels in a small unit. Cost effective and rapidly evolving because of the huge marked for digital technology. 56 Microwave Components Acousto Optical Spectrometer (AOS) I I I IF signal is converted to an acoustic wave in a crystal (Bragg-cell), which modulates its refractive index. Passive Termination Attenuator Filter Coupler Ferrites A collimated laser beam is diffracted by the resulting phase grating. Active Detector Multiplier Mixer Amplifier Oscillator A linear CCD array detects the image, which represents the IF spectrum. MW Instruments Spectrum Analyzer 57 Microwave Components Digital FFT Spectrometer Passive I IF signal is sampled with a fast Analog/Digital Converter (ADC) with sampling rate fs . I Time record of N samples is Fourier transformed in realtime in a fast FPGA processor. I Termination Attenuator Filter Coupler Ferrites Active Detector Multiplier Mixer Amplifier Oscillator The averaged power spectra cover a bandwidth of fs /2 with a frequency resolution of fs /N. MW Instruments Spectrum Analyzer Time records 1 2 ...n Time record Sampling ADC fs fs = Sampling frequency (sampling rate) t = 1/fs = Sample time Spectrum display Time record . ∆ t . .. .. ... . . . .. .. ... .. . 0 0 Samples T ∆f Window N N/fs FFT 0 0 Lines Frequency range N = Number of sample points (*powers of 2) n = Number of lines (or bins) = (N/2) + 1 T = Time record length = N x t = 1/ f f = Frequency step = 1/T = fs/N (N/2) (fs/2) 58 Microwave Components Swept Spectrum Analyzer I I LO of a heterodyne receiver is swept over the frequency range of interest Passive Termination Attenuator Filter Coupler Ferrites Resolution bandwidth (RBW) can be adjusted by changing the IF filter Active Detector Multiplier Mixer Amplifier Oscillator & & & MW Instruments 5 Spectrum Analyzer ) 2' + ) & " = = 59 Microwave Components Effect of RBW and VBW RBW determines the frequency resolution. Smaller RBW reduces the noise floor, but increases sweep time: Passive Termination Attenuator Filter Coupler Ferrites 0" " Active FF$/!.% 0' 53 6 * " F. F$/!.% F. $/!.% Detector Multiplier Mixer Amplifier Oscillator MW Instruments Spectrum Analyzer Video Bandwidth (VBW) determines smoothing of the spectrum: 60 Microwave Components Spectrum Analyzer: Filters and Detectors Digital filters and FFT processing improve speed and channel selectivity at narrow bandwidths. 0' ' 8A" Passive *0'' ** Termination Attenuator Filter Coupler Ferrites '' Active >:='0: 23 " @'' ); *; *:" Detector Multiplier Mixer Amplifier Oscillator *0=0 :'0: 23 <'.%FF/! ' (,$/! MW Instruments Different ways to analyze the detector output, depending on the measurement task (e.g. RMS for noise measurements): G G Spectrum Analyzer " 9 " (" 9 " ' 9" + 9( : ;# " :8' ; 61
