Antenna Measurement using Vector Network Analyzer. Jong-hwan Keum Agilent Technologies

Transcription

1 Antenna Measurement using Vector Network Analyzer Jong-hwan Keum Agilent Technologies

2 Agenda Overview Antenna Measurement System Configuration(Examples) Antenna Measurement System Design Considerations Transmit Site Configuration A U T Receive Site Configuration Receiver Speed Time Domain Analysis Positioner controller Summary Provide by System Integrators 2

3 Antenna Characterization System Solution Antenna Characterization System includes: 1. RF Subsystem : Receiver, Sources and Convertor/Mixers A U T Positioner controller 2. Mechanical Subsystem : Positioned or Scanner, Anechoic Chamber and Absorber Material 3. Measurement & Data Analysis Software Provide by System Integrators Agilent primary provides RF Subsystem only. We need to involve channel partners such as Orbit/FR-Satimo, NSI and SPS for complete solution. 3

4 Far-filed Antenna Range Antenna Under Test (Boeing 747 weather radar antenna) Rotation axis (azimuth axis) Antenna positioner (Rotates antenna through all angular positions) Microwave source and source antenna (on top of 20 meter tower) Range distance = 600 m (Between source tower and test antenna) Test tower ( 20 meters high) 4 Slide 4

5 Near-field Antenna Measurements Vertical motion Sampling antenna (open ended waveguide) Antenna Under Test < 1 meter Mechanical scanner (robotically moves the sampling antenna) Horizontal motion 5

6 What is Vector Network Analyzer? Vector network analyzers (VNAs) Are stimulus-response test systems Characterize forward and reverse reflection and transmission responses (S-parameters) of RF and microwave components Quantify linear magnitude and phase Are very fast for swept measurements Provide the highest level of measurement accuracy Reflection Transmission DUT RF Source S 21 S 11 S 22 S 12 Magnitude Phase R1 LO R2 Test port 1 A B Test port 2 6

7 Agilent VNA Portfolio Test Accessories FieldFox RF Analyzer & RF VNA 5 Hz to 4/6/9/14/18/26.5 GHz ENA-L Low cost VNA 300 khz to 1.5/3.0 GHz LF VNA 5 Hz to 3 GHz ENA World s most popular economy VNA 100 khz to 4.5, 6.5, khz to 14, 20.0 GHz PNA-L World s most capable value VNA 300 khz to 6, 13.5, 20 GHz 10 MHz to 40, 50 GHz PNA-X, NVNA Industry-leading performance 10 MHz to 13.5, 26.5, 43.5, 50, 67, & 110 GHz Banded mm-wave to 2 THz PNA Performance VNA 10 MHz to 20, 40, 50, 67, 110 GHz Banded mm-wave to 2 THz PNA-X Receiver 8530A Antenna Replacement Mm-Wave Solutions Up to 2 THz 7

8 Agenda Overview Antenna Measurement System Configuration(Examples) Antenna Measurement System Design Considerations Transmit Site Configuration A U T Receive Site Configuration Receiver Speed Time Domain Analysis Positioner controller Summary Provide by System Integrators 8

9 Typical PNA-X Far Field Configuration 9

10 Far Field Outdoor Configuration (Measurement Receiver, Hardware TTL or Software trigger) Optional amplifier Source antenna 85320A Test mixer AUT PSG Synthesized source PSG or MXG 85320B Reference mixer Trigger out Trigger in LAN Measurement automation software LO in LO out (Opt/ 108) 85309A MHz Positioner Power Supply Positioner controller LAN LAN Router/Hub LAN PNA trigger out GPS sync 10 MHz in/out PNA trigger in N5264A opt. 108 PNA-X and PSG 10

11 A IF B IF C IF D IF LO AUX LO IN 0 db Gain Nominal IF IF IF IF RF LO RF LO RF LO RF LO 0 dbm to 18 GHz + 6 dbm to GHz ( prefer + 8 dbm ) + 18 dbm Max +/ - 10 Volts DC +/ - 9 Volts DC + 15 Volts DC A RF B RF C RF D RF Far Field Outdoor Configuration (Measurement Receiver & N5280A, HW TTL or SW Trigger) Optional amplifier Source antenna AUT Radiated Ref Signal PSG or MXG N5280A Positioner Power Supply LO in Power Supply 10 MHz Out LAN Measurement automation software MXG U 3022 AY 11 Positioner controller 10 MHz in Trigger In/Out Router/Hub MHz IF Trigger in/out 20meters LAN LAN Trigger In/Out 20 meters 10MHz In 10MHz out N5264A option

12 Far Field Configuration (New) (PNA-X & U3020A Y03/Y04 ) Source antenna AUT Radiated Ref Signal Optional amplifier U3020AY04-1TX Remote Optical Converter U3020AY04-1RX Remote Optical Converter AU T Positioner Power Supply Measurement automation software PNA-X(26.5/50GHz) Positioner controller LAN Optical Signal (B) Optical Signal (Source, R, A) U3020AY03 Optical Test Set 12

13 Far Field Configuration (New) (PNA-X, U3020A Y03 & Optical Tx/Rx/ Test port Module) RF 83020A (optional) RF Multiport Switch RF SGH AUT 1 Mile Antenna Farm H-Pol V-Pol Multiport Switch RF M9403A Optical Tx Optical Fiber RF M9403A Optical Tx M9404A Optical Rx M9408A Test Port AUT 11713C Switch Driver Meas Positioner Power Supply Measurement automation software Ref Signal Positioner controller Control U3020AY03 Optical Fiber 11713C Switch Driver GPIB See Fiber Optic Detail GPIB Signal Ref

14 Typical near-field Configuration (using a PNA-X)

15 Large Scale Remote Mixing Near Field Probe

16 Typical PNA-X for Compact Far-Field (TTL or Software Trigger) 16

17 PNA-X Pulsed Antenna Configuration Measurements: -Average, point-in-pulse, and Pulse profiling 17

18 Typical RCS measurement configuration (using a PNA with option 014) Rx Tx PIN Switch PIN Switch Control PNA series network analyzer RF Source LAN Receiver #1 Receiver #2 18

19 Millimeter Wave Configuration (Example) 19

20 Millimeter Wave Configuration (examples) 20

21 Millimeter Wave Configuration(Example) Using external source & harmonic mixer 21

22 Agenda Overview Antenna Measurement System Configuration(Examples) Antenna Measurement System Design Considerations Transmit Site Configuration A U T Receive Site Configuration Receiver Speed Time Domain Analysis Positioner controller Summary Provide by System Integrators 22

23 Design Considerations Designing an antenna system is an iterative process: First design the transmit site Next design the receive site Then, return to the transmit site to make equipment adjustments required by the receive site Finally, confirm power levels are adequate for entire system 23

24 Transmit Site Configuration Typical transmit site configuration. Optional amplifier L 2 Transmit antenna E RP Considerations in selecting a transmit source: Frequency range of AUT Distance to transmit antenna Source power PNA/PNA-X internal source typically used for near-field and compact ranges. External sources typically required for large outdoor ranges. Speed requirements L 1 G amp PSG or MXG Synthesized source or Internal PNA source Reliable power with faster switching at a lower price 24

25 Calculate the effective radiated power Effective Radiated Power (E RP ): Power level at the output of the transmit antenna. E RP = P source (L 1 + L 2 ) + G amp + G t Optional amplifier L 2 Transmit antenna E RP G amp Where: P source L 1 & L 2 G AMP G t = Power out of the source (dbm) = Loss from cable(s) between source and antenna (db) = Gain of the amplifier (if used) (dbi) = Gain of transmit antenna (dbi) L 1 PSG or MXG Synthesized source or Internal PNA source Reliable power with faster switching at a lower price Make power calculations first without an amplifier, add one only if required to achieve the desired transmit power 25

26 Calculate the free-space loss (power dissipation) Free-space loss (power dissipation, P D ): difference in power levels between the output of the transmit antenna and the output of an isotropic (0dBi) antenna located at the receive site. P D = *log(R) + 20*log(F) Where: R = Range length (meters) F = Test frequency (GHz) This equation does not account for atmospheric attenuation, which can be a significant factor in certain millimeter-wave frequency ranges. A calculator which will derive this number for you can be found at: 26

27 Calculate the maximum power level at the output of the AUT P(AUT): power level present at the output of the antenna-under-test (AUT). P(AUT) = E RP P D + G(AUT) Where: E RP = Effective Radiated Power (dbm) P D = Free-space loss (db, at the maximum test frequency) G(AUT) = Expected maximum gain of AUT (dbi) 27

28 Dynamic Range, Accuracy & Signal-to-Noise Ratio Required dynamic range is the difference between maximum bore site level and minimum AUT level that must be measured. Examples of measurements made are: Side-lobe levels, null depth and cross-polarization levels. Measurement accuracy is directly affected by the signal-to-noise ratio as shown in this figure. 28

29 Receiving Site: Direct Connection to VNA Test Ports ( without External mixing) Sensitivity = P(AUT) DR S/N L Reference Where: P(AUT) (dbm) DR = Power at the output of the AUT = Required dynamic range (db) Test P(AUT) S/N = Signal-to-noise ratio (db) PNA-X opt. 200, 020 L L = Cable loss (db) from AUT to PNA input Example: P(AUT) = 0dBm, DR = 60dB, S/N = 30dB and L = 5dB Sensitivity = -95dBm Receiver #1 Receiver #2 29

30 Choosing an analyzer Agilent has developed options for the PNA series specifically for antenna measurements. However, the PNA-L and ENA analyzers can also be used in less complex applications. Family Model/Option Frequency range Sensitivity at test port with 1 khz Fmax E5071C Opt kHz/100KHz to 4.5 GHz < -92 dbm Sensitivity at direct receiver input with 1kHz Fmax Power Fmax +10 dbm E5071C Opt kHz/100KHz to 8.5 GHz < -80 dbm Option not available +5 dbm ENA E5071C Opt. 2K5 300 khz to 20 GHz < -76 dbm +0 dbm E5072A Opt khz to 4.5 GHz < -91 dbm < -125dBm +18 dbm E5072A Opt khz to 8.5 GHz < - 87 dbm < -125dBm +12 dbm PNA-L (new) PNA (new) PNA-X N5239A 300 khz to 8.5 GHz < -104 dbm < -120 dbm +15 dbm N5231/2A 300 khz to 13.5/20 GHz < -104/ -95 dbm <-120/ -111 dbm +12 dbm N5234/5A 10 MHz to 43.5/50 GHz <-95/ -84 dbm <-104/ -95 dbm -4 dbm N5221/2A 10 MHz to 13.5/26.5 GHz < -99 / -96 dbm < -114/ -111 dbm +12 dbm N5224/5A 10 MHz to 43.5/50 GHz < -94 / -96 dbm < -105/ -107 dbm +4 dbm N5227A 10 MHz to 67 GHz < -88 dbm < -98 dbm 13 dbm N5241/2A 10 MHz to 13.5/26.5 GHz < -97/ -93 dbm < -109/ -99 dbm +17 / +11 dbm N5244/5A 10 MHz to 43.5/50 GHz < -93 dbm < -103 dbm +13 / -1 dbm N5247A 10 MHz to 67 GHz < -87 dbm < -95 dbm +12 dbm 30

31 Choosing an analyzer Agilent has developed options for the PNA series specifically for antenna measurements. However, the PNA-L and ENA analyzers can also be used in less complex applications. Family Model/Option Frequency range Frequency stepping speed (10 MHz/pt at max IFBW with no band crossings Sensitivity at test port with 1 khz Fmax Sensitivity at direct receiver input with 1 khz Fmax Power Fmax N5230C Opt. 020/ khz to 6 GHz 100 us < -99 dbm < -108 dbm +10 dbm PNA-L N5230C Opt. 120/ khz to 13.5 GHz 110 us < -94 dbm < -108 dbm +2 dbm N5230C Opt. 220/ MHz to 20 GHz 160 us < -85 dbm < -97 dbm +10 dbm N5230C Opt. 420/ MHz to 40 GHz 160 us < -75 dbm < -86 dbm -5 dbm N5230C Opt. 520/ MHz to 50 GHz 160 us < -70 dbm < -78 dbm -9 dbm E8362C 10 MHz to 20 GHz 278 us < -100 dbm < -114 dbm +3 dbm PNA E8363C 10 MHz to 40 GHz 278 us < -94 dbm < -105 dbm -4 dbm E8364C 10 MHz to 50 GHz 278 us < -94 dbm < -103 dbm -10 dbm E8361C 10 MHz to 67 GHz 278 us < -79 dbm < -88 dbm -5 dbm 31

32 Receiving Site: External(remote) mixing Configuration When do you need external mixing? When the AUT is located far from the analyzer which requires long cables. The long cables reduce accuracy and dynamic range often to unacceptable levels A Test mixer Benefit of remote mixers Down converts signal to an IF signal Reduces RF cable losses Maximizes accuracy and dynamic range LO in Amplifier LO out 85320B Reference mixer 85309A IF Freq. 32

33 Receive Site Configuration This figure shows a typical receive site configuration. The following slides show how to calculate the various levels indicated MHz Test port +8 dbm +30 dbm MHz -10 dbm +10 dbm 33

34 Select the LO Source Frequency Range Required: 0.3 to 18 GHz Power Required at 85309A LO Input: 0-6 dbm Sources Available: PSG/ESG/MXG Internal LO Source of PNA-X (or PNA opt. H11 with amplifier) Determine 85309A to LO source distance: P s = Cable length (meters) X cable loss MHz Where (db/meter) + P in P s = Power out of the LO source P in = Required power into 85309A (0 to 6 dbm) 34

35 Reference Signal Level & Cable length 85309A to Mixers Requirement: Signal must be high enough to achieve the desire accuracy Reference mixer provides: A phase reference & a reference signal for a ratioed measurement (test/reference) Ratios out any variations in signal levels from system Cable length must be calculated to assure adequate power from the 85309A Cable length (meters) = (P out (85309A) P in (mixer)) / (cable loss/meter@frequency) MHz High quality, low loss, phase stable cables are recommended 35

36 Power at Reference/Test Mixer P TM = E RP P D + G(TEST) L2 P RM = E RP P D + G(REF) L1 Where: P RM = Power level at the reference mixer (dbm) P TM = Power level at the reference mixer (dbm) E RP = Effective radiated power (dbm) P D = Free space loss (power dissipation) (db) G(REF) = Gain of reference antenna (dbi) MHz G(REF) = Gain of reference antenna (dbi) L1 or L2= cable loss between ref. or Test antenna and ref. mixer (db) 36

37 Power at the Inputs and Receiver Sensitivity IF power level at the receiver can be calculated by the following: P REF = P RM conversion loss of mixers + conversion gain of 85309A (L 3 +L 5 ) P TEST = P TM conversion loss of mixers + conversion gain of 85309A (L 4 +L 6 ) Where L = Cable losses as shown in the figure. Conversion gain of 85309A = 23 db (typical). Sensitivity required of the PNA can be calculated by the following: Sensitivity = P REF DR S/N Where DR = Required dynamic range S/N = Signal-to-noise ratio determined earlier as required of measurement uncertainty Now, with this sensitivity number, select an analyzer MHz 37

38 Measurement Speed Measurement speed is made up of many components. The speed displayed on the analyzer is only one part of the actual speed. Total measurement speed you can either measure it directly, or get an estimate from an equation. Calculating Approximate Speed The approximate speed of the PNA can be calculated: Total Measurement time = data taking + pre-sweep time + band crossing + retrace Where: Data taking ~ 1/IFBW (PNA IFBW) + Description Old PNA Old PNA-L new PNA/PNA-L & PNA-X Pre-sweep(swept ~ 222 us ~ 56 us ~ 30 us mode) Band crossings ~ 4 8 ms ~ 2 ms ~ 800 us Retrace ~ ms (display on), 5-8 ms (display off) 38

39 Measurement Speed Example (Old PNA) Configuration: PNA with 201 points, 1 GHz span, 10 khz BW sweep 1. Determine if step or swept. (IF BW <= 1kHz or time/point > 1 ms, then stepped otherwise swept.) 2. Data taking: 1/IFBW=1/10 khz = 100 us(swept mode) So 201 points * 100 us/point = 20.1 ms 3. Pre-sweep time: 222 us 4. Band crossings: None 5. Retrace time: 10 to 15 ms Total measurement time = 20.1 ms us + 10 to 15 ms = 30 to 35 ms (Nominal) 39

40 Agenda Overview Antenna Measurement System Configuration(Examples) Antenna Measurement System Design Considerations Transmit Site Configuration A U T Receive Site Configuration Receiver Speed Time Domain Analysis Positioner controller Summary Provide by System Integrators 40

41 TDR Time Domain Reflectometry O SCOPE 2 t Trigger Chan 1 t STEP / SNAP GENERATOR DIRECTIONAL COUPLER UNKNOWN 41

42 Relationship between time domain & frequency dom ain, TDR, and VNA. DUT is stimulated by one harmonic at a time Reflections are measured at each harmonic Results are integrated by the inverse Fourier transform 42

43 Time Domain Modes with a VNA Reflection responses of a cable in frequency domain. Reflection responses of the same cable in time domain. 43

44 General Time Domain Procedure Set-up the VNA per the general measurement procedure - Give additional consideration to the frequency span* Calibrate and Verify Confirm DUT operation in the frequency domain Turn-on the frequency to time transformation - Adjust parameters; bandpass/lowpass, windowing Select S-parameter and format (linear to start) Orient yourself to where things are in time - Spend some time finding things by breaking connections and causing reflections Set start / stop or center / span time Use markers and delta markers for measurement Consider using time gating 44

45 Time-Domain Transform Mode Summary Step Response Impulse Response Reflection Transmission Low-pass Simulates traditional TDR DC value extrapolated Start frequency harmonically related throughout span Higher(twice) resolution than bandpass Ideal for identifying discontinuities (location & type) in devices that pass low frequencies. Impulse Ideal for seeing excitation responses in devices that devices that pass low frequencies, such as cables. Horizontal axis shows 2-way travel time Bandpass Horizontal axis shows 1-way(actual) travel time Any arbitrary frequency range Ideal for measuring band limeted devices such as filters. Also useful for fault location (but not type) especially when system can not pass low frequencies. 45

46 Time Domain Range Time Span with No Response Repetition (aliasing) Range[sec] 1 F Points 1 Frequency Span[Hz] Test for Aliasing - Increase Time Span and Look for Obvious Repetitions - Re-measure with a Slightly Smaller Frequency Span and See if the Response Moves To increase range : Increase NOP, Decrease Frequency Span Depends on the Electrical Length of the Device Must be 2x for Reflection Measurements Change Alias-Free Range by Changing f 46

47 Resolution the Time Domain Response Resolution -The Ability to Resolve Closely Spaced Responses -Dependent Upon Step Rise Time and Impulse Width -Frequency Span Window = Impulse Width 50% = Step Rise Time 10% - 90% Range Resolution : The Ability to Locate a Single Response in Time Time Span Points-1 47

48 Agilent E5071C ENA Option TDR 48

49 ENA TDR Spec. 49

50 Time/ Frequency Domain Transform Gating out unwanted responses Real-time viewing of data Main Path Response Ground Path Response t Main Path AUT 50

51 Time Domain Gating Removing effects of ground path reflections Antenna Response Time Domain Frequency Domain 51

52 Agenda Overview Antenna Measurement System Configuration(Examples) Antenna Measurement System Design Considerations Transmit Site Configuration A U T Receive Site Configuration Receiver Speed Time Domain Analysis Positioner controller Summary Provide by System Integrators 52

53 Agilent s RF Subsystem components Model # N5264A N5280/1A 85309A 85310A 85320A 85320B 85331B 85332B Description PNA-X Measurement receiver Frequency converter LO/IF distribution unit Distributed frequency converter Test mixer module Reference mixer module SP2T absorptive PIN switch, GHz SP4T absorptive PIN switch, GHz Non-Agilent Components A UT N5280/1A N5264A RF sources (ESG, PSG or MXG) Positioner controller PNA-X 2 or 4-port PNA 53

54 Summary Designing Antenna Measurement Systems requires attention to many details Agilent has the components to meet your Antenna measurement needs Agilent s and channel partners can provide a complete antenna test solution AU T Positioner controller Provide by System Integrators 54