Department of Electronics & Communication Engineering
BLOOMS TAXONOMY
UNIT NO: -5 SUBJECT: - Antennas and Microwave Engineering
FACULTY: - V.SANTHOSH KUMAR BRANCH/SEM/YEAR: - ECE/ IV-I
1.List the WAVE GUIDE TEE JUNCTIONS [L1] [CO5]
A waveguide Tee is formed when three waveguides are interconnected in the form of English
alphabet T and thus waveguide tee is 3-port junction. The waveguide tees are used to
connects a branch or section of waveguide in series or parallel with the main waveguide
transmission line either for splitting or combining power in a waveguide system.
There are basically 2 types of tees namely
1.H- plane Tee junction
2.E-plane Tee junction
A combination of these two tee junctions is called a hybrid tee or “ Magic Tee”.
E-plane Tee(series tee):
1. An E-plane tee is a waveguide tee in which the axis of its side arm is parallel to the E
field of the main guide. if the collinear arms are symmetric about the side arm.
2. If the E-plane tee is perfectly matched with the aid of screw tuners at the junction, the
diagonal components of the scattering matrix are zero because there will be no reflection.
3. When the waves are fed into side arm, the waves appearing at port 1 and port 2 of the
collinear arm will be in opposite phase and in same magnitude.
H-plane tee: (shunt 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.
If two input waves are fed into port 1 and port 2 of the collinear arm, the output wave at
port 3 will be in phase and additive.
If the input is fed into port 3, the wave will split equally into port 1 and port 2 in phase
and in same magnitude.
Magic Tee ( Hybrid Tees )
A magic tee is a combination of E-plane and H-plane tee. The characteristics of magic tee are:
1. If two waves of equal magnitude and same phase are fed into port 1 and port 2 the
output will be zero at port 3 and additive at port 4.
2.If a wave is fed into port 4 it will be divided equally between port 1 and port 2 of the
collinear arms and will not appear at port 3.
3.If a wave is fed into port 3 , it will produce an output of equal magnitude and opposite
phase at port 1 and port 2. the output at port 4 is zero.
4.If a wave is fed into one of the collinear arms at port 1 and port 2, it will not appear in
the other collinear arm at port 2 or 1 because the E-arm causes a phase delay while H arm
causes a phase advance.
2.Discuss about Gunn oscillation modes. [L2] [CO5]
A gunn diode can operate in four modes:
1. Gunn oscillation mode
2. stable amplification mode
3. LSA oscillation mode
4. Bias circuit oscillation mode
Gunn oscillation mode: This mode is defined in the region where the product of frequency
multiplied by length is about 107 cm/s and the product of doping multiplied by length is greater than
1012/cm2.In this region the device is unstable because of the cyclic formation of either the
accumulation layer or the high field domain.
When the device is operated is a relatively high Q cavity and coupled properly to the load, the
domain I quenched or delayed before nucleating.
2.Stable amplification mode: This mode is defined in the region where the product of frequency
times length is about 107 cmls and the product of doping times length is between l0 11and
1O12/cm2
3. LSA oscillation mode: This mode is defined in the region where the product of frequency times
length is above 107 cmls and the quotient of doping divided by frequency is between 2 x 104 and 2 x
105.
4. Bias-circuit oscillation mode: This mode occurs only when there is either Gunn or LSA
oscillation. and it is usually at the region where the product of frequency times length is too small to
appear in the figure. When a bulk diode is biased to threshold. the average current suddenly drops as
Gunn oscillation begins.
3.Demonstrate about Circulators and Isolators [L3] [CO5]
Both microwave circulators and isolators are non-reciprocal transmission devices that use the property
of Faraday rotation in the ferrite material. A non-reciprocal phase shifter consists of thin slab of ferrite
placed in a rectangular waveguide at a point where the dc magnetic field of the incident wave mode is
circularly polarized. When a piece of ferrite is affected by a dc magnetic field the ferrite exhibits
Faraday rotation. It does so because the ferrite is nonlinear material and its permeability is an
asymmetric tensor.
MICROWAVE CIRCULATORS:
A microwave circulator is a multiport waveguide junction in which the wave can flow only from the nth
port to the (n + I)th port in one direction Although there is no restriction on the number of ports, the
four-port microwave circulator is the most common. One type of four-port microwave circulator is a
combination of two 3-dB side hole directional couplers and a rectangular waveguide with two non
reciprocal phase shifters.
A perfectly matched, lossless, and nonreciprocal four-port circulator has an S matrix of the form
Using the properties of S parameters the S-matrix is
MICROWAVE ISOLATORS:
An isolator is a nonreciprocal transmission device that is used to isolate one component from
reflections of other components in the transmission line. An ideal isolator completely absorbs the
power for propagation in one direction and provides lossless transmission in the opposite
direction. Thus the isolator is usually called uniline.
Isolators are generally used to improve the frequency stability of microwave generators, such as
klystrons and magnetrons, in which the reflection from the load affects the generating frequency. In
such cases, the isolator placed between the generator and load prevents the reflected power from the
unmatched load from returning to the generator. As a result, the isolator maintains the frequency
stability of the generator.
The isolator here is a Faraday-rotation isolator. Its operating principle can be explained as follows.
The input resistive card is in the y-z plane, and the output resistive card is displaced 45° with respect
to the input card. The dc magnetic field, which is applied longitudinally to the ferrite rod, rotates the
wave plane of polarization by 45°. The degrees of rotation depend on the length and diameter of the
rod and on the applied de magnetic field. An input TEIO dominant mode is incident to the left end of
the isolator. Since the TEIO mode wave is perpendicular to the input resistive card, the wave passes
through the ferrite rod without attenuation. The wave in the ferrite rod section is rotated clockwise by
45° and is normal to the output resistive card. As a result of rotation, the wave arrives at the output.
4.Explain about RWH Theory in detail [L4] [CO5]
Kroemer proposed a negative mass microwave amplifier in 1958 and 1959. According to the energy
band theory of the n -type GaAs, a high-mobility lower valley is separated by an energy of 0.36 eV
from a low- mobility upper valley.
Electron densities in the lower and upper valleys remain the same under an Equilibrium condition.
When the applied electric field is lower than the electric field of the lower valley (E < Ee), no electrons
will transfer to the upper valley.
When the applied electric field is higher than that of the lower valley and lower than that of the
upper valley (Ee < E < Eu)), electrons will begin to transfer to the upper valley.
when the applied electric field is higher than that of the upper valley (Eu < E), all electrons will
transfer to the upper valley.
When a sufficiently high field E is applied to the specimen, electrons are accelerated and their
effective
temperature rises above the lattice temperature also increases. Thus, electron density/I and are both
functions of electric field E.
5. Analyze VSWR Measurement using microwave testbench. [L5] [CO5]
In a microwave network, if load impedance and line impedance are not matched, signal fed
from the source is reflected again towards source causing standing wave pattern in the network.
Voltage
Standing Wave Ratio is a measure used for finding the magnitude of ration of reflected signals
maximum
and minimum
amplitudes.
S V max
V min
Procedure:
1. Microwave Source is energized with 1 KHz square wave signal as carrier.
2. Tunable passive components are so adjusted to get reading across the VSWR meter in 30 dB scale.
3. Detector (Tunable probe detector) is adjusted to get maximum power across the VSWR meter.
4. Slotted line carriage is moved from the load towards source to find the standing wave minimum position.
5. By adjusting the gain control knob of VSWR meter and attenuator the reading across the VSWR meter is
made as 1 or 0 dB known as normalization.
6.Again the slotted carriage is moved towards source to find the next minimum position. The reading shown at
this point in the VSWR meter is the ratio of magnitude of reflected signals minimum and maximum voltages.
7. VSWR meter has three different scales with different ranges as specified below.
If the device under test (DUT) is having the range of VSWR 1 – 4, reading is taken from the first scale from the
top (NORMAL SWR Scale 1 – 1 – 4).
9. If the device under test (DUT) is having the range of VSWR 3.2 – 10, reading is taken from the second scale
from the top (NORMAL SWR Scale 2 (3.2 – 10).
10. If the device under test (DUT) is having the range of VSWR 1 – 1.33, reading is taken from the third scale from
the top (EXPANDED SWR Scale 3 (1 – 1.33).
11. If the device under test (DUT) is having the range of VSWR 10 – 40, a 20 dB range is selected in the VSWR
meter and reading is taken from the first scale from the top (NORMAL SWR Scale 1 – 1 – 4) which is then
multiplied by for getting the actual reading.
