Microwaves

Phase balance

Is a measure of how well the phase difference tracks over the frequency range of operation.

Input-matching circuit

Matches the diode impedance to the characteristic impedance of the system (usually 50Ω).

Input Coupling Network

This combines the RF and LO signals

Diode circuit

This takes the RF and LO signals and mix them together to form new signals.

Insertion loss

The internal loss through the filter within the passband.

rejection

This tells how much an undesired frequency is attenuated on the skirts of the filter

Side-coupled half-wave resonator filter
Short-circuited quarter-wave stub filter
Inter digital filter

What are the Types of bandpass filter?

1. To attenuate low-frequency signals that cause problems in a system and help the system operate properly.
2. It also may help when a test generator has a high degree of low-frequency signals.
3. To reduce the low-frequency gain that some high-frequency transistors have.

Applications of High Pass FILTER?

Duplexer

used when a transmitter and a receiver have to use the same antenna. It is used with a tunnel diode to produce an amplifier.

Isolators

This application to keep the high level of an LO in a mixer circuit in the mixer itself and not have it radiate out through the incoming antenna. It is designed to supply a constant load to an oscillator circuit.

Low-level linear amplifier

- It is sometimes called the intermediate amplifier
- The currents that these amplifiers draw are higher than the low-noise amplifiers.

DC voltage
Gain
Positive
Feedback
Frequency-determining components

What is the components of an Oscillator?

Most conventional diodes and transistors do not
operate at microwave frequencies.

The lengths of the diodes and transistor leads
present a significant amount of inductance at
microwave frequencies.

The internal capacitances of the diodes and
transistors are very high and will prevent operation
at microwave frequencies.

The transit time of the carriers in a diode or
transistor is sufficiently high to prevent normal
operation.

Why Microwave solid state devices?

Microwave Diodes

In the RF spectrum, diodes can amplify, oscillate, mix, detect, attenuate, and switch a high frequency signal in the appropriate circuit.

Point Contact Diode

Oldest microwave semiconductor device
Ideal for low-signal applications and are widely used in microwave mixers
and detectors.
They are extremely delicate and cannot withstand high power.
They are easily damaged, and , therefore must be used in such a way as
to avoid shock and vibration.

Basic Transistor

The input to a transistor (bipolar for now) is the base lead. This is the control element in the transistor where the ac signal or, possibly, a dc voltage is applied to control operations in the device.

Planar and Epitaxial

The types of microwave transistors that evolved from the junction transistor are _____ and ______ transistors

epitaxial device

is similar to the planar transistor, with the exception of an additional thin layer of low conductivity material in the collector region

LOW-NOISE TRANSISTOR

The emitter and the base of the transistor are split into a series of "fingers." That splitting of the paths for current is helpful in getting low-noise characteristics, because the best noise source you can get is a resistance with current flowing through it.
Thus, if we can reduce the resistance of a device or decrease the current flowing through it, we can reduce the noise and create a low-noise device, such as a transistor.
The total current at the input to the interdigital structure is divided among all the sections of the structure. That results in each individual section carrying much less current than if a single section for the junction is used

HETEROJUNCTION BIPOLAR TRANSISTOR (HBT)

A variation in the bipolar transistor.
The ______ utilizes two different types of junctions. The term heterojunction is described as the interface between two regions of dissimilar semiconductor materials. It has the property of accelerating the electrons so they can switch at very high speeds.
it provides a bipolar transistor that can go through the entire microwave range and into the millimeter range (60, 70, and 80 GHz).

HIGH ELECTRON MOBILITY TRANSISTORS (HEMTS)

The HEMT looks similar to the low-noise FET. Their gate-source-drain structures are almost identical.
HEMTs use a doped GaAs/AlGaAs structure in which the motion of the charge carriers is confined to a thin sheet within the GaAs buffer layer. The type of structure results a higher mobility for the electrons
Some applications require the low-noise figure, while others do not need that as a critical parameter. On the other hand, some applications need as much gain as possible.
The choice of HEMT or FET depends entirely on the application

Vacuum tubes

Are devices used for controlling a large current with a certain voltage to produce amplification, oscillation, switching, and other operations. Are used in microwave transmitters requiring high output power

klystron

A microwave vacuum tube using cavity resonators (buncher cavity and catcher cavity) to produce velocity modulation of an electron beam that produces amplification.

MAGNETRONS

a combination of a simple diode vacuum tube with built-in cavity resonators and an extremely powerful permanent magnet. Are capable of developing extremely high levels of microwave power. It is most resonant at a single frequency.

Ring-Bar TWT

The _______ has got characteristics likely the Ring-Loop TWT. The slow wave structure can be made easier by cut-out the structure of a copper tube.

Waveguides

Most microwave energy transmission above 6 GHz is handled by_____. Are hollow metal conducting pipes designed to carry and constrain the electromagnetic waves of a microwave signal.

Signal Injection and Extraction

Probes and loops can be used to extract a signal from a waveguide.
When the signal strikes a probe or a loop, a signal is induced which can then be fed to other circuitry through a short coaxial cable.

Imagine you have a long, flexible hose that you can bend and twist in any shape you want. The hose is like the waveguide, and the water flowing through it is like the microwave signal.

> When you turn on the faucet very high (high frequency), the water flows very fast through the hose. It hits the walls of the hose at a big angle, making the hose bend and twist. The water travels a long distance between the walls before it hits them again.
> When you turn down the faucet a bit (lower frequency), the water flows slower through the hose. It hits the walls of the hose at a smaller angle, making the hose less bent and twisted. The water travels a shorter distance between the walls before it hits them again.
> When you turn off the faucet completely (cutoff frequency), there is no water flowing through the hose. The hose is straight and flat. There is no signal in the waveguide.

How does waveguides work? (Simple Explanation from net)

Transverse magnetic (TM) field.

When the magnetic field is transverse to the direction of propagation. It permits sections of waveguide to be interconnected with minimum loss and radiation.

T section or T junction

is used to split or combine two or more sources of microwave power.

Coaxial transmission lines

A transmission line in which one conductor completely surrounds the other, the two being coaxial and separated by a continuous solid dielectric or by dielectric spacers.

A. Flexible
B. Semi-rigid

Types of Coaxial Transmission Lines

BNC CONNECTOR

A coaxial connector for low power RF signal below 3 MHz; 50 TO 75 ohms impedance

SMA- Sub Miniature Version A

From DC to 18 GHz; 50 ohms impedance

N CONNECTOR

Carries RF signals up to 18 GHz; 50 to 75 ohms impedance 50 ohms (bottom)
75 ohms (top) (Mas malaki to tapos may red)

Ground-Plane Spacing (GPS)

It is the spacing between the ground planes, or copper on the circuit boards.

Coplanar waveguide

It is a modification of the microstrip circuitry
In a coplanar waveguide, there is still a circuit trace on the top of the board that is a certain width and thickness, but there are also ground planes on both sides of the circuit trace and there is no ground plane on the bottom of the circuit board. A conductor surrounded by ground "guides" the electromagnetic wave down the transmission line.

They do not waste the radiated energy and because they provide an increase in gain, which helps offset noise at microwave frequencies

Why is highly directive antennas are preferred in line-of-sight transmission of microwave signals?

Sectoral Horn Antenna

Flaring the rectangular waveguide in only one dimension.

PARABOLIC REFLECTOR ANTENNAS

Consists of a parabolic reflector which is a large dish shaped structure made of metal or screen mesh, combined with a horn antenna. Beam widths of only a few degrees are typical with parabolic reflectors.

Center-feed (front side) Feed Method

The energy radiated by the horn (antenna) is pointed at the parabolic dish (reflector,) which focuses the radiated energy into a narrow beam and reflects it toward its destination.

From directrix, signals are parallel and in phase w/ each other = maximum radiation within a narrow beam from the parabolic dish

WHY PARABOLIC?

CASSEGRAIN FEED METHOD

• The horn antenna is positioned at the center of the parabolic reflector ( back side).
• At the focal point is another small reflector with either a parabolic or a hyperbolic shape.

HELICAL ANTENNAS

• is a wire helix.
• A center insulating support is used to hold heavy wire or tubing formed into a circular coil or helix.

Gain = 12 to 20 dB range
Beam Width = Approx. 12 to 45 degrees

What are the gains and beam widths of a helical antenna?

SLOT ANTENNAS

is a radiator made by cutting a one half wavelength slot in a conducting sheet of metal or into the side or top of a waveguide.

Dielectric or lens antennas

A device that serves as a lens for microwaves just as glass can serve as lens for light waves. Use a special dielectric material to collimate or focus the microwaves from a source into a narrow beam

polystyrene or some other plastic

What does lens antenna made of?

Millimeter range above 40 GHz.

The main use of Lens Antenna?

PATCH ANTENNAS

- are made with microstrip on PCBs.
- The antenna is a circular or rectangular area of copper separated from the ground plane on the bottom of the board by the PCB's insulating material.

Bandwidth Increases, bandwidth is directly related to the thickness of the PCB

If the PCB is thick on a patch antenna, what happens?

PHASED ARRAYS

is an antenna system made up of a large group of similar antennas on a common plane.

improve gain and directivity

What is the main purpose of Phased Arrays?

ROUND LOOP ANTENNA FOR 868MHZ

• It is just a closed loop of pc-board copper connected to the transmitter's or receiver's antenna terminals.
• The larger the loop, the more efficient it is, and the better it works.

INVERTED - F ANTENNA

Is a type of antenna used in wireless communication. It consists of a monopole antenna running parallel to a ground plane and grounded at one end.

Switched beam arrays and Adaptive arrays.

What are the kinds of adaptive beam forming antennas?

MICROWAVE MATERIALS

These are special types of materials that are an integral part of the circuits they support, for which they are the base.

Dielectric

an insulator, that is, a device or material that does not allow current to pass through it.

Dissipation factor

is the loss in the material to RF and microwave energy. As the f increases, so does the DF.

Dielectric thickness

is a dimension of the material itself, not of the copper attached to it. It must be low so that the calculated dimensions for a specific material would remain within an acceptable frequency range.

Peel strength

is the amount of force required to separate the copper from the dielectric material

Coefficient of thermal expansion (CTE)

Is the amount that the material changes mechanically with temperature.

Electrodeposition

is the process of depositing a substance on an electrode by electrolysis

Rolled copper

is usually a special order used for more critical RF and microwave applications. The Cu block to be fabricated is sent thru a roller combination. The force applied determines the final thickness of the Cu.

◆ Dielectric constant: 4.0 to 4.6;
◆ Dissipation factor: 0.018 to 0.025;
◆ Thickness tolerance: 0.031 inch ±0.004 inch; 0.062 inch ±0.006 inch.

SPECIFICATIONS OF TYPICAL EPOXY PRINTED CIRCUIT BOARD USED FOR RADIO AND TELEVISION CIRCUIT BOARDS:

◆ Dielectric constant: 2.50 ±0.05;
◆ Dissipation factor: 0.0015;
◆ Thickness tolerance: 0.031 in ±0.0015 inch; 0.062 inch ±0.002 inch.(10-12%)

SPECIFICATIONS FOR A TYPICAL RF AND MICROWAVE MATERIAL:

1. Teflon fiberglass materials
2. Non-PTFE materials
3. Thermoset polymer composites

TYPES OF MICROWAVE MATERIALS:

Teflon fiberglass materials

This material is usually referred to as PTFE-glass material. (PTFE is the abbreviation for polytetrafluorethylene, the chemical name for Teflon.)

Used to reinforce the teflon and make it more structurally rigid. It also increases the dielectric constant of the material, but it also increases the losses.

What does adding fiber glass in PTFE-glass materials do?

Woven type

This method of placing fiberglass in a a teflon material looks like magnified cloth fabric.A base of Teflon has fiberglass strands woven throughout the material

Non-woven

In this Teflon-based material, the fiberglass particles are added in a random fashion and not the woven structure.

THERMOSET POLYMER COMPOSITES

Is defined as a material that becomes permanently hard and unmoldable when once subjected to heat.

Polymer

Is a material that consists of many parts, either natural or synthetic

Composite

Defined as a material made up of many distinct parts.

1. Dielectric constant and frequency
2. Dissipation factor
3. Peel Strength
4. Coefficient of thermal expansion
5. Dielectric Thickness

PARAMETERS TO CONSIDER IN THE CHOICE OF MATERIALS

Matched detector

Is designed to take an RF signal at the input and use the matched diodes to convert it, very efficiently, to a video or dc signal, as needed.

Combining amplifiers

This employs back-to-back quadrature hybrids. The outputs of the amplifiers similarly are applied to the two input ports of the output quadrature hybrid. If we apply two signals to the input, the hybrid combines the signals at the output port. As a result, we have a small input power to the entire component and an output that is the result of the two amplifiers being used

Switch

When the diodes are forward biased, the energy goes from the input port, through the hybrid combination, and out the output 1 port with a very low loss. When the diodes are reverse biased, the energy coming into the device will be reflected back toward the input. But because a hybrid junction is present, the energy does not get back to the input but is sent to the other port, output 2.

Amplitude balance

Tells how closely the output ports track one another.

continuously variable attenuator

Continuously varies the attenuation to any value within the range of the attenuator.

Bandpass Filter

This passes a specific band of frequencies and rejects frequencies below and above that band.

ripple

A result of the of sections (or poles) used to construct the finished filter.

Short-circuited quarter-wave stub filter

In this type of filter, all the elements are a quarter- wavelength long. The ends of the extended resonators are shorted to ground, which results in the proper bandpass response.

Inter digital filter

This type of filter has a series of quarter-wave resonators grounded at alternate ends to form the required bandpass response.

1. To provide the difference between the RF and LO inputs at the output of a mixer.
2. To remove the spurious signals and harmonics from generators or systems in which too many signals may be present.

Applications of lowpass FILTER?

Amplifiers

A device that increases the level of a signal to produce the required amount (voltage or power) at the output .

Power amplifier

- It is an amplifier that produces much higher amounts of output power.
- It is not a linear device. There has to be a certain amount of power at the input to produce an output power.

Oscillator

An oscillator is a device that provides a sustained unstable signal that can be used as a frequency reference in a testing system or communications system or to provide a certain frequency to produce a required tone.

Barkhausen criterion

1.The total Gain must be equal to 1
2.The total phase shift must be equal to 0 or 360 degrees.

To sustain oscillation: ?

Colpitts oscillator
Clapp oscillator
Hartley oscillator

Types of Lc oscillators?

Colpitts oscillator

An LC oscillator which has the capacitance portion of the LC tank circuit split into two capacitors with one in the feedback path

Clapp oscillator

An LC oscillator which is very similar to the Colpitts except that the Clapp has an additional capacitor in the inductance side of the circuit that is used as a fine adjustment for the frequency of the oscillator

Hartley oscillator

An LC oscillator which is an LC oscillator with the inductance portion split instead of the capacitance

Vacuum Tube

An electron tube containing a near-vacuum that allows the free passage of electric current.

1. Schottky (which mix or detect)
2. PIN (which attenuate or switch)
3. Tunnel(which amplify or oscillate)
4. Gunn (which also oscillate)
5. Varactor diodes (multipliers)

What are the types of microwave diodes

Schottky Diodes

Consists of a semiconductor (usually N-type) and a metal that comes in contact with the semiconductor. It is a general-purpose diode that usually is used for mixer and detector applications at those higher frequencies.

F - The unipolar action makes the Schottky diode ideal for RF and microwave applications, because the diode can respond to high frequencies without distorting the output or causing other problems.

T/F. The unipolar action makes the Schottky diode ideal for RF applications, because the diode can respond to low frequencies without distorting the output or causing other problems.

READ ADVANTAGE and APPLICATIONS of Schottkey Diode

READ ADVANTAGE and APPLICATIONS of Schottkey Diode

Pin Diodes

This consists of two narrow, but highly doped semiconductor regions separated by a thicker but lightly doped intrinsic material.

F - When the PIN diode is operated at frequencies below about 100 MHz, it acts just like any other PN junction device and rectifies the signals that are applied to its input.

T/F. When the PIN diode is operated at frequencies below about 200 MHz, it acts just like any other PN junction device and rectifies the signals that are applied to its input.