Lesson 8 Microwave Components

Coupler

A device consisting of two transmission lines with no direct connection, allowing a portion of energy from one line to be present in the second line.

Isolation

The measure of how well a directional coupler prevents energy from passing in the reverse direction.

Quadrature Hybrid

A specialized coupler that takes an input signal and equally divides it between two outputs which are 90° out of phase.

Amplitude Balance

A comparison of the power levels at the two output ports of a quadrature hybrid.

Power Divider

A device that splits an input signal into two or more output signals while maintaining the same input power.

Detector

A component that converts RF signals to video or DC signals, commonly using matched diodes.

Matched Detector

A detector designed to efficiently convert RF signal into a usable DC or video output.

Low Pass Filter

A filter that passes frequencies below a certain cutoff frequency and attenuates higher frequencies.

High Pass Filter

A filter that passes frequencies above a certain cutoff frequency and attenuates lower frequencies.

Bandpass Filter

A filter that passes a specific range of frequencies and attenuates frequencies outside that range.

Amplifier

A device that increases the level of a signal to produce the desired voltage or power at the output.

Oscillator

A device that generates a sustained oscillating signal, used as a frequency reference.

Insertion Loss

The loss of signal power resulting from the insertion of a device in a transmission line.

Breakdown Voltage

The minimum voltage that causes a diode to conduct significantly.

Reflectometer

A device used to measure the reflection of signals in transmission lines and to analyze impedance.

Circulator

A non-reciprocal device that directs signal flow in only one direction through its ports.

directional

means, basically, that energy is passed in one direction only. Any energy from a reverse direction will not pass or allow the component to operate properly.

phase balance

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

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.

image-rejection mixer.

One application in which both quadrature hybrids and power dividers are used is

input power and the output voltage

Two factors affect sensitivity of detectors

Sensitivity r

inimum input signal level required to make the detector operate and the amount of output voltage obtained for a certain amount of input power.

input coupling network:

combines the RF and LO signals in the mixer

diode circuit

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

step attenuator

series of fixed attenuators that are switched in and out as needed to give the selected value of attenuation

continuously variable attenuator

continuously varies the attenuation to any value within the range of the attenuator

Filter skirts

on either side of the passband. This is where the signal is greatly attenuated

Insertion loss

the internal loss through the filter within the passband

ripple

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

rejection

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

Side-coupled half-wave resonator filter-

has a series of resonators side by side with designed gaps between them for coupling purposes to obtain the final response

Short-circuited quarter-wave stub filter.

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.

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

Duplexer

Used when a transmitter and a receiver have to use the same antenna

circulator

It is used with a tunnel diode to produce an amplifier

isolator

It is designed to supply a constant load to an oscillator circuit.

Low noise amplifier

It used many times at the “front end” of a receiver - It provides sufficient gain to allow it to be the controlling factor in determining the noise

Low-level linear amplifier

intermediate amplifier

Low-level linear amplifier

The currents that these amplifiers draw are higher than the low-noise amplifiers.

power amp

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

1

TO sustain oscillation The total Gain must be equal to ?

0/360

.TO sustain oscillation The total phase shift must be equal to ?

Barkhausen Criterion

requirements to sustain oscillation

growing oscillations

total gain greater than 1

Damped oscillations

total gain lesser than 1

Colpitts oscillator w

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

Clapp oscillator,

has an additional capacitor in the inductance side of the circuit that is used as a fine adjustment for the frequency of the oscillato

Hartley oscillator,

hich is an LC oscillator with the inductance portion split instead of the capacitance.