PRECISION PHASE SHIFTER:

• The rotary type of precision phase shifter consists of

-A circular waveguide containing a lossless dielectric plate of
length 2l called halfwave section. 2l=lg/2
-A section of rectangular-to-circular transition containing a
lossless dielectric plate of length l, called "quarter-wave
section“ oriented at an angle of 45° to the broader wall of the
rectangular waveguide.
- A circular-to-rectangular transition again containing a
lossless dielectric plate of length l (quarter wave section)
oriented at an angle 45°.
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• The incident TE10 mode becomes TEll mode in circular waveguide
section.
• The half-wave section produces a phase shift equal to twice that
produced by the quarter wave section. The dielectric plates are tapered
at both ends to reduce reflections.
• Let Ei be the maximum electric field strength of input. This is resolved
into components, E1 parallel to the plate and E2 perpendicular to the
plate.
• After propagation through the plate these components are given by

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• After propagation through the plate the field components can be
written as

• Thus, quarter wave section converts the linearly polarized TE11 wave
to a circularly polarised wave or vice versa.
• The field components parallel and perpendicular to the half wave
sections are,

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• At the output end, the field components parallel and perpendicular to
the quarter wave plate are given by

• These two components are identical. Therefore the resultant field is

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Ferrite Phase shifters:
• The propagation constant in the ferrite media changes with
permeability.

• Most of the ferrite materials have relative dielectric constants in the

range 9 to 16.
• The phase shift in a ferrite device is generated by magnetizing the
ferrite inside the wave guide by RF current.
• The phase constant in the propagating line varies due to change in
permeability with magnetization.

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• Ferrite phase shifters may be latching or non-latching, depending
upon whether continuous holding current must be supplied to
sustain the magnetic bias field.

Schematic diagram
of a twin toroid
phase shifter -->

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• The twin toroid is a latching, nonreciprocal device.
• It uses either a closed magnetic circuit or a magnetic circuit with very
Small air gaps. The relative permeability of the ferrite is controlled by
adjusting the magnetic flux level existing in the closed magnetic
circuit.
• The dielectric spacer is used to concentrate the rf energy in the center
of the waveguide. The walls of the ferrite toroid are located in those
regions of the waveguide which support a circularly polarized
magnetic field.
• If b+ is the propagation constant when a positive bias field saturates
the ferrite and b- be the propagation constant for negative bias field,
the maximum amount of phase shift per unit length is (b+- b- ).
• The variable phase shift less than this can be achieved by reducing
the bias field level. When the direction of propagation changes, the
values of b- and b+ interchange.
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• The conductive and dielectric losses are directly proportional to the
length or inversely proportional to the saturation magnetization. The
magnetic loss varies approximately directly with the saturation
magnetization.
• The sum of these losses shows a minimum value in the frequency
range given by

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MIC Ferrite Phase Shifter:
• Passive MIC phase shifters are constructed with ferrite substrate using
the property that the propagation constant of microwaves along the
microstrip line on ferrite substrate can be changed by varying the
magnitude and/or the direction of the static magnetic field Ho.
• Thus, the phase shift for a fixed length of the microstrip line can be
controlled electrically. This leads to low cost, small and highly reliable
components.

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• Types of ferrite MIC phase-shifters—analog and digital.

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• Analog Control:
- In analog phase shifter, the phase is controlled by varying either the
magnitude or the direction of the magnetization vector M using
applied static magnetic field Ho.
• Digital Control:
- In digital phase shifter, the phase is controlled by using high
remanence ferrite materials and latching the substrate by a current
pulse to change direction of dc magnetic field.
- A pulse current of sufficient amplitude, through a single turn wire
threading the ferrite is used to magnetize the ferrite substrate.
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• The remanence of magnetic materials is defined in terms of its
residual magnetic induction when an externally applied magnetizing
current is reduced to zero as shown in the B-H curve.

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• For a n bit digital phase shifter, the least significant bit will have a
phase shift of 3600/2n
• A digital phase shifter of n-bits will consist of n separately actuated
sections giving

• A series of different = 180deg, 90deg and 45 deg can be cascaded

in a single housing to form a 3-bit digital phase shifter.

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Reciprocal Phase Shifters:
• When a ferrite substrate is magnetized to saturation in a direction
perpendicular to the microstrip line, there is a very small interaction
between the ferrite and the RF magnetic field. As a result, the
effective RF relative permeability is approximately unity.

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• When the ferrite sample is magnetized to saturation in its plane
parallel to the strip line, maximum interaction is obtained between
the ferrite substrate and the RF magnetic field.
• Then the RF effective permeability becomes,

• u and K are the component of the permeability tensor. M=Magnetic

dipole moment/unit volume.

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• The propagation constant of the TEM mode on the ferrite substrate is
given by

• Writing in terms of a filling factor q,

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• When ferrite magnetization direction changed between two states,
the fractional change in phase constant is

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• Both analog and digital controlled reciprocal phase shifters can be
constructed using a loosely meander line microstrip conductor to
minimize size.
• Adjacent lines of the meander scheme are spaced by distance > 5
times substrate height to minimize RF coupling and to avoid non-
reciprocal effects.
• DC current through perpendicular wires penetrating holes 1-1' and 2-
2' generates magnetic fields for magnetization and also the direction
can be changed as per requirement of phase change.
• In digital phase shifter two states of magnetization corresponding to
two values of phase shifts are obtained by sending dc currents
through 1-1' and 2-2', respectively (2-2' for parallel and 1-1' for
perpendicular magnetizations).
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Non-reciprocal Phase Shifter:
• In a non-reciprocal phase shifters, a circularly polarized magnetic field
region is obtained by using a meander microstrip configuration with
coupling between the lines.
• This is achieved by closely spacing the lines of length l/4 at the
center frequency.
• Because of coupling, the two magnetic field components at a center
point P between two adjacent lines become spatially orthogonal.
• Since lines are l/4 long, the RF current flowing at the center of line 2
is delayed by 900 relative to the current flowing at the center of line 1.
Thus, the resulting RF magnetic field at P is circularly polarized.

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Non-reciprocal Phase Shifter: a) Top view of the strip, b) Side view from
the plane of the strip 22
• By magnetizing the ferrite along the direction of lines and reversing
the direction of the magnetization, a non-reciprocal differential phase
shift is generated.
• Digital/latching phase shifter can be obtained by using sufficiently
thin ferrite and small wires through holes in the substrate for dc
current I1 and I2.
• The magnitude and direction of magnetization can be altered by
current pulses.
• Parameters for such a phase shifter are:
Phase shift= 1bit(3600+100)

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