microwave satellite telecommunications: · pdf filemicrowave e. m. field measurements,...

“SAPIENZA, UNIVERSITÀ DI ROMA”

FACULTY OF INFORMATION ENGINEERING, COMPUTER SCIENCE AND STATISTICS

Master Degree in Electronic Engineering

MICROWAVE SATELLITE TELECOMMUNICATIONS:

CHARACTERIZATION OF THE ALPHASAT RECEIVING SYSTEM AND 90-GHz RADIOMETER

Graduant Supervisor Pasquale Salemme Prof. Frank S. Marzano Assistant Supervisors

Elio Restuccia (ISCTI) Fernando Consalvi (FUB)

Rome, 11 October 2011

Summary • Introduction

• Receiving station architecture

Receiving station diagram block

• Laboratory Measurements

Conical Horn Antenna

Low Noise Amplifier Block

First Conversion Block

Second Conversion Block

Satellite Beacon Receiver SBR

Total receiver noise figure

• Link Budget for the Rome site

Numerical-statistical and Hardware analysis

• 90-GHz Radiometer

Diagram block

RF Characterization

• Conclusions

Pasquale Salemme

“Microwave Satellite Telecommunications: characterization of the AlphaSat receiving system and 90-GHz Radiometer“

• The current need for an increasingly wider bandwidth in satellite radio communications pushes to exploit higher frequency ranges

• Higher frequency propagation suffers much more atmospheric components effects that reduce drastically connection availability in unfavourable weather conditions

• In order to analyze and quantify degradation of transmission channel performance at Ka-band (20 GHz) and Q-band (40 GHz), European Space Agency scheduled, in 2012, to launch AlphaSat satellite for conducting radio propagation studies by a “Technology demonstrator Payload”, denominated TDP5

Introduction

Pasquale Salemme

“Microwave Satellite Telecommunications: characterization of the Alphasat receiving system and 90-GHz Radiometer“

• Microwave Laboratory of Communications and Information Technology Institute (ISCTI, Economic Development Ministry - Communications Department - Rome) is developing a Q-band receiving station in Rome, designed in collaboration with Electronic and Telecommunications Engineering Department (DIET) of Rome University “Sapienza” and Ugo Bordoni Foundation (FUB)

• Components recovered inside an unused receiving station, dedicated to previous propagation experiments, have been used with a great advantage from economic point of view

Introduction

Pasquale Salemme


Receiving station architecture

Receiver station diagram block

Pasquale Salemme



LNA block and first conversion

Pasquale Salemme



Second conversion and IF2 amplifier block

Pasquale Salemme


Laboratory Measurements


• Receiver has a conical horn antenna, with operating bandwidth from 40,5 to 42,5 GHz, slightly higher than required but still suitable for the design, as confirmed by results

• Antenna has been equipped with a rectangular waveguide feeder that discriminates linear polarization of received e.m. field

• Measurements have been performed in an indoor environment, intended for microwave e. m. field measurements, provided with anechoic panels disposed on ceiling, antenna back wall and three carriages, free to be placed within the environment, in order to optimize measure eliminating most undesired e. m. echoes

Pasquale Salemme




Pasquale Salemme


• Conical horn antenna has been placed on an azimuth turntable plane, provided with degrees scale, in order to appreciate up to 10/60 of a degree measurements values (± 11 degrees in steps of 10/60 of a degree) have been interpolated and results normalized to maximum received power


Maximum antenna gain measurement

“Comparison method with a calibrated antenna” The method consists in comparing under test antenna with a calibrated antenna

ut dBi ant ref dBi R dB

G G P

Pasquale Salemme


ut R dB Rant ref dBm Rant dBmP P P

• Measurement distance was about 4 m, lower than foreseen for the far-field zone (2D2/ = ~16 m)

• Small correction has been done according to current methodology [R. C. Hansen]

• Maximum aperture efficiency:


Maximum antenna gain measurement

“Comparison method with a calibrated antenna” The method consists in comparing under test antenna with a calibrated antenna

Pasquale Salemme


2

0,64

1a LIN

g

e

g

AG

A A


Co-polar antenna radiation patterns (± 11 degrees in steps of 10/60 of a degree)

<- Azimuth co-polar radiation pattern

Zenith co-polar radiation pattern ->

Pasquale Salemme



Cross-polar antenna radiation patterns (± 2 degrees in steps of 10/60 of a degree)

Pasquale Salemme


Azimuth co-polar and cross-polar radiation patterns

Zenith co-polar and cross-polar radiation patterns

This antenna minimizes received power level variations, due to

satellite apparent movement (2 dB for about ± 1 degree).

Antenna tracking hasn’t been implemented.



Device Under Test (DUT) consists of:

- an isolator (placed next to antenna)

- an RF filter (which eliminates possible

undesired signals, in particular image

frequency ones at 32,590 GHz)

- an LNA

- its output isolator

Isolator - RF filter frequency response forward and reverse

Pasquale Salemme


First Conversion Image Frequency



Pasquale Salemme


DUT gain has been evaluated with a network analyzer, measuring scattering parameter s21 module in the 32-47 GHz frequency range. At the working frequency (39,402 GHz) DUT gain is about 17,3 dB.


Block LNA Noise Figure

• Using a noise source having two working conditions (powered and not), two noise powers at two different noise equivalent temperatures are available

• ENR (Excess Noise Ratio) is the characteristic parameter of noise source previously calibrated by the manufacturer as a function of frequency

• “Y” ratio is defined as:

where Non and Noff are noise powers relative to the two-state noise source

• Noise source has been driven by a noise figure meter that automatically performs measurement steps and returns DUT noise figure value

“Y” method

h c

LIN

c

T TENR

T

on

off

NY

N

Pasquale Salemme




LNA operating frequency (39,402 GHz) is higher than the maximum noise figure meter working frequency (2,047 GHz), measurement system needs a down converter, constituted by a mixer and a generator as LO. Whole measurement system noise is taken into account by calibration step.

Pasquale Salemme




Pasquale Salemme


The measurement takes place in two steps:

calibration step: noise source has been connected directly to mixer input. Noise source ENRdB (11,19 dB at 39,402 GHz) has been set in noise figure meter and then calibration process activated

measurement step: DUT has been connected between noise source and measuring system



• It has been assembled using a waveguide mixer and a local oscillator operating at 35,996 GHz. LNA output signal (39,402 GHz) therefore has been shifted to IF1 (3,406 GHz). The block also includes isolators connected to the three mixer ports

• Block conversion loss has been measured by a power meter with a power sensor:

Pasquale Salemme




• It has been assembled using a waveguide mixer and a local oscillator operating at 35,996 GHz. LNA output signal (39,402 GHz) therefore has been shifted to IF1 (3,406 GHz). The block also includes isolators connected to the three mixer ports

Pasquale Salemme


• DUT output frequency is higher than noise figure meter input range and so the second IF converter block, present in the receiving chain (described afterwards), has been used in measurement system, converting IF1 3,406 GHz in IF2 70 MHz

• Measurement is in single sideband (SSB) because contribution due to image frequency has been attenuated strongly by the RF filter

• Its attenuation (0,5 dB) can be taken into account



• Second converter looks like a single unit and translates IF1 3,406 GHz to 70 MHz using its own inside local oscillator (3,336 GHz) (-> 10 MHz caesium-beam primary frequency standard available in ISCTI)

• Conversion gain IF1-IF2 test bench is very simple and uses a RF generator and a spectrum analyzer

• Measurement has been done injecting a 3,406 GHz frequency signal in IF1 converter input port and the input-output difference has been measured

The IF1-IF2 conversion gain is about 32 dB.

Pasquale Salemme




Pasquale Salemme


• For noise figure measurement the scheme is similar to the previous

Frequency Response starting 10 to 130 MHz and starting 67 to 73 MHz


Second Conversion Block – 2nd Image Frequency Rejection

• RF filter, which attenuates first conversion image (32,590 GHz) more than 60 dB, cannot eliminate second conversion image (3,266 GHz) corresponding to RF input (39,262 GHz) due to its large bandwidth (about 3 GHz)

• However, thanks to second converter input filter, there is a satisfactory second conversion image rejection, approximately 48 dB

PIF2 level measurement at 70 MHz with input at 39,402 GHz (left)

and at 39,262 GHz (right)

Pasquale Salemme


• Second conversion output, after an amplification stage at IF2, has been connected to the Satellite Beacon Receiver (SBR)

• SBR is a double frequency conversion receiver which provides an output voltage Vdc , whose amplitude is related to the input level signal

• SBR automatically looks for and locks an input signal whose frequency is within its bandwidth research (70 MHz ± 200 kHz)

• It is possible to select search time (one minute minimum, eight minutes maximum) in a limited frequency range around the last position. After this period, SBR will scan entire band (± 200 kHz)

• Output voltage Vdc is the receiving station output information to be recorded by data logger-computer group

Pasquale Salemme



Satellite Beacon Receiver SBR

Locked and unlocked states

• The various receiving system components have been assembled and then total noise figure has been measured, using methodology described above, from RF 39,402 GHz input to IF2 70 MHz down converter output

• LNA block noise figure (4,46 dB) essentially determines the total RF-IF2 noise figure value

• Measure can be compared to the theoretical result, using cascade components noise figure formula:

2 3

1

1 1 2 1 2 1

1 1 1... 4,67

..

n

tot

n

F F FF F dB

G G G G G G

• Theoretical value is 0,36 dB lower than one measured at test bench, difference presumably due to measurement uncertainties composition

Pasquale Salemme



Total receiver noise figure

Link Budget for the Rome site

Numerical-statistical analysis

Satellite-receiver link budget at Q band will be described in terms of: total additional attenuation (according to ITU-R recommendation), received power, antenna temperature, system noise temperature, G/T and C/N ratios, all as function of the probability p that value has been exceeded or not, depending by considered parameter.

AlphaSat TDP5 characteristics Working frequency f =39,402 GHz Maximum gain antenna GPL = 26,7 dBi Antenna aperture diameter DPL = 0,6 m Half power beam width Θ3dB = 9 ° Transmitted power PPL = 2,7 dBW

Receiving station characteristics (Roma – ISCTI): Lat 41° 49’ 53,18’’ N Long 12° 27’ 58,56’’ E Antenna aperture diameter DR = 0,245 m Half power beam width Θ3dB = 2,17 ° Opening efficiency ηa = 0,6 Maximum gain antenna GR = 37,9 dBi Receiver noise figure NFR = 5,03 dB Receiver noise temperature TR = 633,41 K Waveguide losses Lfr = 0,1 dB Antenna depointing losses Lr=1 dB Receiver physical temperature T0 = 290 K Ground noise collected by receiver antenna Tgr = 30 K Atmospheric mean radiating temperature Tm = 280 K at 0,1% time PLL bandwidth B = 100 Hz (20 dBHz)

Pasquale Salemme


Prob

[%]

AT

[dB]

PR

[dBm]

Tant

[K]

Tsys

[K]

G/T

[dB/K]

C/N0

[dBHz]

C/N

[dB]

0,05 32,9 -151,0 309,8 942,9 7,0 16,7 -3,3

0,1 24,7 -142,9 309,1 942,0 7,0 24,9 4,9

0,5 11,4 -129,6 289,8 923,2 7,1 38,2 18,2

10 2,0 -120,2 136,9 773,7 7,9 48,3 28,3

50 0,9 -119,0 85,6 723,6 8,2 49,8 29,8

90 0,6 -118,8 68,0 706,5 8,3 50,2 30,2

( ) ( )R PL PL R fs TP p P G G L A p

20log 4 /fsL d

( ( )/10) ( ( )/10)10 (1 10 )T TA p A p

ant c m grT T T T

where: AT(p) is total additional attenuation in dB

Lfs is free space attenuation in dB ->

/( / ) 10log( )R fr r sysdB KG T G L L T

0 _

( / / 10log( ))R ISO BdBHzC N P G T k

0

( / ) /dBC N C N B

Pasquale Salemme


0,1% annual time (~ 9 hours)



Received Power [dBm]:

R

LL

antsys TTTT frfr

)101(10)10/(

0

)10/(

Total additional attenuation and rain contribution [dB] Isotropic antenna received and effective powers [dBW]

Expected C/N and C/N0 ratios [dB and dBHz] Expected G/T ratio [dB/K]

Pasquale Salemme




• To compensate partially the deterioration caused by use of an antenna with gain lower than one recommended by ESA, PLL bandwidth B has been reduced from 1 kHz to 100 Hz, improving C/N ratio of 10 dB

• An RF generator set at 39,402 GHz, followed by appropriate attenuation, simulates satellite signal

• Second conversion block output signal at IF2 (70 MHz) has been applied to a signals analyzer, able to measure C/N ratio (B = 100 Hz)

• MatLab® results are very near to measured C/N values, as shown in the graph below

Pasquale Salemme



Hardware analysis- C/N values measurements of RF-IF2 receiver chain

• Output voltage vs. received power graph has been obtained using the whole system, including the SBR with PLL bandwidth B equal to 30 Hz, in this case, to check frequency locking stability

For a stable frequency locking the

lowest power received level PRF is about -136 dBm, corresponding to a off-duty probability lower than 0,2%. Frequency locking becomes unstable with a lower received power level. Signal loss occurs for power level lower than -140 dBm

Pasquale Salemme



Hardware analysis - Output voltage vs. received power graph

Pasquale Salemme


90-GHz Radiometer

Diagram Block

• In progress at ISCTI Microwave Laboratory, designed in collaboration with Ugo Bordoni Foundation (FUB)

• Two reference temperatures radiometer

• Designed to perform, in parallel with the 40-GHz AlphaSat receiver, additional estimates of attenuation, obtained from brightness temperature observations of the same propagation atmosphere zone by suitable algorithms

Pasquale Salemme


90-GHz Radiometer

Diagram Block

• Antenna Orthogonal Mode Transducer OMT (Orthogonal Polarization Selector)

• RF Network Selector: four circulator cascade at switching field inversion

• Hot load: Diode Noise Generator+Isolator – Cold load: termination at room temperature

• Gunn diode local oscillator and mixer conversion

• Quadratic Detector type: Diode Tunnel + Post integrator

• ADC Conversion

• Data acquisition unit (RS-232) and control

Pasquale Salemme


90-GHz Radiometer

RF Characterization

• Vector Network Analyzer with bandwidth extension from 75 to 110 GHz by WR10 waveguide

• Magnitude and phase of the four scattering parameters

• Instrument calibration with "gold" calibration kit, useful for high precision measurements at high frequency

Pasquale Salemme


90-GHz Radiometer

RF Characterization – RF Network Selector • Switches controlled by a network control unit that connect periodically gate mixer

with the other four

Pasquale Salemme


90-GHz Radiometer


with the other four

s11 s22

Pasquale Salemme


90-GHz Radiometer


with the other four

s12 s21

Pasquale Salemme


90-GHz Radiometer


with the other four

All measures and graphs of Alphasat TDP5 receiver characterization and of 90-GHz radiometer are shown in attached CD-ROM

Conclusions • The activity devoted to the study and realization of a Q-band (40 GHz) receiving

station for AlphaSat satellite and a 90-GHz Radiometer, located in Rome (Italy), has been illustrated.

• Components recovered inside an unused receiving station, dedicated to previous propagation experiments, have been used with a great advantage from economic point of view.

• On the other hand this has exacted constraints in design choices that led to the described system configuration.

• Obviously receiver performances, even if they demonstrate proposed solution validity, can be improved by nowadays available technology, in particular for the antenna and the low noise amplifier, which largely imply overall system receiver efficiency.

• Final check will be possible after satellite AlphaSat launch and, after a reasonable data registration time period, it will be possible to assess performances described in this presentation.

• Short-term future developments will deal with:

Implementation and boxing of the Q-band receiver outdoor and indoor sections and of 90-GHz Radiometer

Procurement of motorized dual-feed reflector antenna (TEMIX? Proposal under evaluation) -> aperture diameter of 120 cm (against current 24 cm) -> C/N increase of about 14 dB

Pasquale Salemme


Pasquale Salemme


This work has been presented at COST Action IC0802 “Propagation tools and data for integrates Telecommunication, Navigation and Earth Observation systems” (28-30 September 2011, Institute of Atmospheric Physics, Prague, Czech Republic) and will be submitted at EuCAP 2012 “6th European Conference on Antennas and Propagation” (26-30 March 2012, Congress Centre, Prague)

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