Experiment-1

AIM: Familiarization with the Microwave Laboratory Equipment.

Instruments Used :- Circulator, Isolator, Attenuator, Directional Coupĺer, Horn Antenna, E-Plane Tee, H-Plane Tee,
Magic-Tee, PIN Modulator, Gunn Diode Oscillator, Frequency Meter, Power Meter, VSWR Meter

Theory:
Circulator

A circulator is a device that transports radio frequency or microwave signals from one
port to another. They typically have three ports. They are made of magnets and ferrite
materials with magnetic properties. Circulators can be made to circulate clockwise or
counterclockwise. So the name "circulator" makes sense in that it transmits the signal
around to the three ports. This allows a receiver and a transmitter to share the same
antenna. This is the most common use for a circulator. When the transmitter sends a
signal, the device directs the signal to the antenna port. So in summary, a circulator is a
device that is designed to direct radio frequencies or microwave signals from Port 1 to
Port 2 with a minimum loss.

Isolator

An isolator is a two-port device that transmits microwave or radio frequency power in one
direction only. Due to internal behavior, the propagation in one direction is allowed while the
other direction is blocked. The non-reciprocity observed in these devices usually comes from the
interaction between the propagating wave and the material, which can be different with respect
to the direction of propagation. It is used to shield equipment on its input side, from the effects of
conditions on its output side; for example, to prevent a microwave source from being detuned by
a mismatched load.

Attenuator

The attenuators are basically passive devices which control power levels in a microwave
system by absorption of the signal. An attenuator which attenuates the RF signal in a
waveguide system is referred to as a waveguide attenuator. A waveguide attenuator works
exactly opposite of an amplifier, which increases the power of the signal without altering the
waveform. They are achieved by the insertion of resistive films.

Types of Waveguide Attenuators:

• Fixed Low Power Attenuator: Signal loss is constant and cannot be changed.
 • Fixed Low Power Precision Attenuator: Signal loss is fixed and high precision elements are used.

• Fixed High Power Precision Attenuator: Precision elements yield optimum electrical performance at high
power.

• Continuously Variable Attenuator: Also known as CVA, where the signal loss can be changed using a
mechanical adjustment screw, knob or dial.

Directional Coupler

Directional couplers are passive devices used mostly in the field of radio technology. They couple a defined amount
of the electromagnetic power in a transmission line to a port, enabling the signal to be used in another circuit. An
essential feature of directional couplers is that they only couple power flowing in one direction. Power entering the
output port is coupled to the isolated port but not to the coupled port.
A directional coupler designed to split power equally between two
ports is called a hybrid coupler. Directional couplers are most
frequently constructed from two coupled transmission lines set close
enough together such that energy passing through one is coupled to the other. This technique is favoured at
microwave frequencies where transmission line designs are commonly used to implement many circuit elements.

Horn Antenna

A horn antenna or microwave horn is an antenna that consists of a flaring

metal waveguide shaped like a horn to direct radio waves in a beam. Horns
are widely used as antennas at UHF and microwave frequencies, above 300
MHz. They are used as feed antennas (called feed horns) for larger antenna
structures such as parabolic antennas, as standard calibration antennas to
measure the gain of other antennas, and as directive antennas for such
devices as radar guns, automatic door openers, and microwave radiometers.
Their advantages are moderate directivity, low standing wave ratio (SWR),
broad bandwidth, and simple construction and adjustment.

E-Plane Tee

An E-plane Tee is a waveguide tee in which the axis of the side arm is parallel to the E-field
of the main guide. If the collinear arms are symmetric about the side arm, there are two arm
characteristics. When waves are fed into the side arm, the waves that appear in the collinear
arms will be in opposite phase and have the same magnitude.
H-Plane Tee

An H-Plane Tee is a waveguide Tee in which the axis of its side arm is shunting the E-field
or parallel to the H-field of the main guide and attaching another waveguide.

Magic-Tee

A magic tee (or magic T or hybrid tee) is a hybrid or 3 dB coupler used in microwave
systems. It is an alternative to the rat-race coupler. In contrast to the rat-race, the
three-dimensional structure of the magic tee makes it less readily constructed in
planar technologies such as microstrip or stripline. The "magic" comes from the way
it prevents signals from propagating between certain ports under specific conditions.
This allows it to be used as a duplexer; for instance, it can be used to isolate the
transmitter and receiver in a radar system while sharing the antenna. In practical
examples, it is used to both isolate circuits and mix signals, for instance in a COHO
radar. It is a 4-port waveguide tee that is a combination of an E-Plane and H-Plane
Waveguide Tee.

Frequency Meter

It is constructed from a cylindrical cavity resonator with a variable short-circuit termination.

The shorting plunger is used to change the resonance frequency of the cavity by changing
the cavity length. DRF (Direct Reading Frequency meter) measures the frequency directly.
It is particularly useful when measuring frequency differences or small changes.

PIN Modulator

PIN Diode modulators offer an ideal way for amplitude and pulse modulation
of a microwave signal through a wide range of frequencies. These modulators
utilize a PIN Diode which is mounted across the waveguide line with an R.F.
isolated DC bias lead passing to an external TNC (F) Connector. The PIN diode
comprises a semiconductor diode having three layers: the P-type layer, the
Intrinsic layer, and the N-type layer. Between the P and N regions is the
intrinsic material, where the doping level is very low. The P and N-type
regions are known to be heavily doped.
Gunn Diode Oscillator

A Gunn Diode Oscillator (also known as a Gunn oscillator or transferred

electron device oscillator) is an inexpensive source of microwave power
and comprises a Gunn diode or Transferred Electron Device (TED) as its
major component. It performs a similar function to Reflex Klystron
Oscillators. In Gunn oscillators, the Gunn diode is placed in a resonant
cavity. A diode is a semiconductor-based component that allows current to
flow in only one direction. It has two terminals: anode and cathode. It acts
as an electronic switch, exhibiting very low resistance in forward bias and
very high resistance in reverse bias.

Power Meter

It is used to measure the power of electromagnetic signals, particularly in the

microwave frequency range (typically from 100 MHz to 40 GHz). Typically, a
microwave power meter consists of a measuring head containing the power
sensing element, connected via a cable to the meter itself, which displays the
power reading. The head may also be referred to as a power sensor or mount.
Different power sensors can be used for varying frequencies or power levels.
Historically, in most power sensor and meter combinations, the sensor converted
microwave power into an analog voltage, which the meter then read. Modern
power sensor heads often include electronics to produce a digital output and can
connect via USB to a PC, which functions as the power meter.

VSWR Meter

A VSWR meter basically consists of a high gain, high Q, low noise voltage
amplifier normally tuned at a fixed frequency at which the microwave signal
is modulated. The VSWR meter uses the detector signal out of the microwave
detector as its input, amplifies it, and provides the output on the calibrated
voltmeter. The meter itself can be calibrated in terms of VSWR.

Observation-
The experiment involved studying various components of the microwave laboratory. The isolator allowed forward
transmission only, while the circulator directed input power sequentially to adjacent ports. The movable short
generated standing waves inside the waveguide, and the slotted section with the tunable probe enabled field
sampling and VSWR measurement. The H-plane Tee split power equally with in phase outputs, whereas the E-plane
Tee split power equally with 180° out-of-phase outputs. The Magic Tee produced both sum and difference outputs,
and the Twister rotated polarization successfully. Horn antennas radiated directional microwave energy, the
attenuator reduced signal power without changing the waveform, and the filter allowed only selected frequencies to
pass.
Result:

• All microwave components used in the experiment were examined and analyzed.

• The purpose and operation of each device in signal measurement, isolation, coupling, power division, and wave
guidance were understood.

• Observations emphasized practical applications in satellite communications, and microwave link technologies

Conclusion:-
The experiment gave practical insight into various microwave laboratory components. Each component was
examined for its design, operation, and role in signal control. This understanding is important for designing and
implementing microwave systems .