Technical Interests on the SKA

Noriyuki Kawaguchi

National Astronomical Observatory of Japan

SKA WorkshopNovember 5, 2010

SKA Overview

HIGH SENSITIVITYAttractive to all radio astronomers

WIDEBAND DETECTION OF A RADIO SIGNAL

Technical Challenging

Wideband Receiver

• Octave band (4-8 GHz) is now common in mm- and submm- SIS receivers in their IF.

• Decade band (1-10 GHz or 2.5-25GHz) is attractive not only for the SKA but also for radio spectroscopy searching molecular line forest.

• Century band (200MHz-20GHz) is prospective in the next decade.

Octave to Decade Band

• Radiator (antenna)– Reflectors are independent from the operating

frequency except for the surface accuracy.– Technically difficulties on the radio launcher.

• Receiver– Decade band LNA is commercial available.

• Digital Signal Processing– A high speed sampler makes possible to detect a radio

signal without making frequency down conversion.

Self-Complementary AntennaMushiake’s Principle Z0=188.4 Ω

Input impedance is constant over a wide frequency range.

The “Self-complementary antenna” was originated and its constant-impedance property was discovered in 1948 by Y. Mushiake. Several years later, Professor V. H. Rumsey in the USA studied the antenna with log-periodic shape for the purpose of developing “Frequency-independent antenna” by making use of such a property of self-complementary antenna. For this reason, his antenna was actually “log-periodic self-complementary antenna”. In the meantime, his coworkers developed an extremely broadband practical antenna by modifying his original structure, and it advanced further to the log-periodic dipole array. These antennas which are derived from the original log-periodic self-complementary antenna structure are generally called “Log-periodic antenna” or “LP antenna”. It is well-known that these so-called “Log-periodic antennas” have extremely broadband property.

Please recall memories

Kildal Feed

Constant Directivity

Quad Ridge Radiator

ETS/LINDGREN, 2GHz – 18GHz Double Ridge Horn

Bruns, IEEE EMC,45, 1, p.55, 2003

Taper Slot Radiator

After Saito, Ricoh Technical Report, No.24, Nov. 1998

10GHz – 60GHz

Trial Test on the Taper Slot Antenna

Kagoshima University

UWB Low Noise Receiver

Overview of Semiconductor Devices

４ Gsps,2bit（ Matsumoto, Kawaguchi, １９９５）

HBT

FET/HEMT

A/D Converter

Low Noise Amplifier

Memory,DSP

(Area Density)

Hig

h Sp

eed,

Low

Noi

se

InP HEMT for LNA

Open

Short

HEMT

Source

Source

Drain

Gate

Active elements was evaluated on the test fabrication chips.

The passive elementsThe passive elements for resistance, inductance and capacitance are evaluated at the cooled environment.

Test Equipments

Vacuum Dewar

manipulator

Magnifier

Probe20K Stage

Test devices are mounted on a cooled stage to measure the electric performances.

MMIC designThe active and the passive elements are assembled onto an InP substrate to form a MMIC of a 2-stage amplifier to be cooled down at 30 K or lower temperature.Two MMIC chips will be built into a 43-GHz LNA module.The MMIC chip is now under fabrication and become available soon in March 2008.

The coplanar wave-guide is expected to be low in the transmission loss.

Amplifier Module

Waveguide-to-Microstrip-line conversion

Waveguide-to-Coplanar transition is requested for the new 43-GHz MMIC amplifier.

A GaAs MMIC amplifier currently used for VERA telescopes

Trx ~ 60K

InP HBT technology

High speed A/D converter,

The highest sampling rate is 50GHz.

3-bit 50-GHz AD chip

(3 mm × 3mm ）

Comparator Encoder

Hope to free from frequency conversion with a high speed AD converter.

LNA outputs of 22-GHz and 43-GHz signal are to be digitized directly.

A noise spectrum over 20-24GHzdetected with a 50-GHz sampler

20GHz 25GHz

Red Dots: RF Direct Digital SpectrumGreen Dots: Analog Spectrum

The first successful result in the world.

W49N on NRO 45m detected without frequency conversion

Spectrum after frequency conversion Direct detection (20.480-24.576GHz)

LO=(16.85+3)-GHz signal converts a 22-GHz Signal to a 2.2-2.4GHz signal. The IF signal Is digitized at a speed of 8.192-GHz (over sampling), then Fourier transformed with 512K spectrum.

A 20.480-24.576GHz (BW=4.096GHz)signal is directly digitized at a sampling rate of 8.192GHz, then Fourier trans-formed with 512K spectrum. The spectrumorder is inverted.

Ultra High Speed SamplerSampling jitter was evaluated.

0.2-psec jitter is observed.

Trans.

Reflection

50 GHz

InP HBT AD Module

Frequency ConversionThe Heterodyne Technology was established in 1918.

Direct Detection(1887)

Amplifier

Mixer, LO

Vacuum Tube Amp.(1906)Heterodyne Detection(1918)

Amplifier

A/D

Semiconductor Amplifier(1947)Digital Processing(1970 ～ )

Mixer, LO

Direct Heterodyne(+Analog)

Heterodyne(+Digital)

A/D

DirectDigital

InP HBTFull DigitalReceiver(2007?)

Amplifier

Concluding Remarks

• Possible Japanese contributions– Low noise amplifier (InP HEMT MMIC)– High speed AD converter (InP HBT)

• No frequency conversion gives great merits to the SKA, simplifying the receiver.

– High speed computation (Massive Computing)

• Industry engagement in Japan– Preparing a proposal for the advance

instrumentation program by 2016