PERALATAN AKTIF GELOMBANG MIKRO

PERALATAN AKTIF GELOMBANG MIKRO

• Peralatan aktif tersebut berasal dari solidstate yang digunakan untuk menjalankan fungsi peralatan seperti : suitsing, penguat, mixer, filtering, dsb

• Beberapa solidstate tsb a.l. : Bipolar junction transistor (BJT), silicon metal-oxide semi conductor field effect transistor (MOSFET), GaAs metal semi-conductor field effect transistor (MESFET), high electron mobility transistor (HEMT), hetero junction bipolar transistor (HBT),dsb

BEBERAPA DEVICES GELOMBANG MIKRO

• BIPOLAR TRANSISTORS

• GaAsFETs

• HEMT – High Electron Mobility Transistors

• Impatt Diodes

• PIN Diodes

• Varactor Diodes

• YIG Devices (Yttrium-Iron Garnet)

Bipolar Microwave Transistors

• Conventional bipolar transistors are not suitable for microwave frequencies.

• Electrons move faster than holes.

• Component leads introduce elevated reactance.

• XL increases and XC decreases therefore collector feedback becomes worse as frequency increases.

• Transit time and mobility of carriers. As transit time approaches signal period phase shifts occur.

PERBAIKAN TERHADAP BIPOLAR TRANSISTOR

REMEDIES (1): Interdigital design of emitter and

base minimizes capacitances. Gallium arsenide. Faster than

silicon. N type GaAsFET. Why N type? Flat component leads.

REMEDIES (2).: Low noise design considerations:

* Planar and epitaxial methods of construction use diffusion and surface passivation to protect surfaces from contamination as opposed to diffusion method of mesa structure implementing acid etching.

* Shot noise is proportional to the square of current therefore operate at moderate Ic.

* Thermal noise is reduced at lower power levels. With interdigital base design Rb is low therefore lower voltage drop and less power.

FET Microwave Transistors

• Designed to minimize capacitances and transit time

• NPN bipolar and N channel FETs preferred because free electrons move faster than holes

• Gallium Arsenide has greater electron mobility than silicon

Monolithic Microwave Integrated Circuit (MMIC)

Photograph of a monolithic integrated X-band power amplifier. This circuit uses eight heterojunction bipolar transistors with power dividers/combiners at the input and output to produce 5 watts.

Gunn Device (TED)

• Slab of N-type GaAs (gallium arsenide)

• Sometimes called Gunn diode but has no junctions

• Has a negative-resistance region where drift velocity decreases with increased voltage

• This causes a concentration of free electrons called a domain

• Ditemukan oleh thn 1963,Mr.Gunn

IMPATT Diode

• IMPATT stands for Impact Avalanche And Transit Time

• Operates in reverse-breakdown (avalanche) region

• Applied voltage causes momentary breakdown once per cycle

• This starts a pulse of current moving through the device

• Frequency depends on device thickness

• Ditemukan thn 1965,Mr Johnson

PIN Diode

• P-type --- Intrinsic --- N-type

• Used as switch and attenuator

• Reverse biased - off

• Forward biased - partly on to on depending on the bias

Varactor Diode

• Lower frequencies: used as voltage-variable capacitor

• Microwaves: used as frequency multiplier

– this takes advantage of the nonlinear V-I curve of diodes

YIG Devices

• YIG stands for Yttrium - Iron - Garnet

– YIG is a ferrite

• YIG sphere in a dc magnetic field is used as resonant cavity

• Changing the magnetic field strength changes the resonant frequency