Okay so toady we will discuss about umm millimetre
wave passive components like filters resonators there basic properties And couplers power dividers and finally different
types of transitions so passive components like band pass filter or coupler it is very
popular in any wireless communication system For example if we design any trans receiver
system so in trance receiver system then the first component will be the antenna and then
we have to use a band pass filter So band pass filter it not only eliminate the noise
it will also eliminate undesired bands So after band pass filter if we use a single
antenna for both transmission and reception So in that case we have to use one isolator
or some SPDT switch or umm may be orthomode transducer so after that we can use different
types of receiver architecture If we use homodyne architecture it does not involve many passive
components but if we use super hit train receiver technology it involves many passive components
particularly band pass filter So here I am going to show you one more umm
receiver architecture its known as mixer less receiver architecture or six port architecture
which use many passive components So this the schematic circuit of the six port
receiver so here you can see the RF incoming signal it is fade to one branch line coupler
BLC so this is one type of coupler which will divide the power into two ports when we face
difference of ninety degree so this architecture its using three branch line coupler so not
only that one power divider usuallypower divider and local oxilator signal it is fed to this
power divider So all of this are passive components right
side you can see the micro strip line footprint or layout so this is the PCB part PCB layout
of the umm six port receiver and umm the only RF active device is used detector basically
detector diode at millimetre wave frequencies they are connected to this first branch line
couplers output port Prt three port four and bottom one port five and port six So we need basically for RF detectors and
with this we can demodulate any signal and it works as a receiver so you can see so many
different types of passive components are being used in this particular receiver architecture
so the size of this receiver architecture in terms of lambda its quiet big thats why
its not popular at lower microwave frequencies but its very popular at millimetre wave frequencies
because the accuracy of this receiver is much higher compare to super heterodyne or homodyne
receiver technology I will give you one more example so this is
a typical antenna array with accessories used for synthetic aperture radar system so this
orange colour umm patches you can see they form one arrays antenna it is being used for
both transmission and reception So it is followed by TR module so inside TR module we have isolator
on passive component and also bandpass filter that is again passive components and just
before it we have a pin diode paste for the phase shifter So this is for scanning purpose and you can
see there are many Wilkinson power divider so this a two way one is to one Wilkinson
power divider this is one more so there are so many passive components import any radar
architecture or any actual wireless system So before going to the coupler and filter
let us discuss about a basic resonator which is dielectric resonator At millimetre wave frequencies metal loss
is very high so we usually try to avoid any metallic structure at millimetre wave frequencies
and if we can make some resonator based on dielectric wave guide in that case we can
avoid metal loss to some extend and the only loss will be facing is dielectric loss so
thats how we can minimize loss from in structure and resonators Where are they used They used in filter design as well as they
used in antenna design So when we will be using in antenna design then in that case
we expect radiation from the resonator or the quality factor due to radiation QR should
be smaller and when we use similar resonator in filter design So what we expect that all of the electromagnetic
energy it should be confined inside the resonator or quality factor should be as high as possible
there are different shapes of dielectric resonator like cylindrical resonator rectangular resonator
hemispherical resonator so most popular design is cylindrical resonator and let me discuss
quickly the some basic properties of a cylindrical dielectric resonator Usually different types of dielectric materials
are used to make this dielectric resonator So epsilon R is high usually typically its
more than ten and the only thing we have to keep in mind that the loss tangent value or
dielectric loss should be as small as possible Because we are using dielectric resonator
to minimize losses so lets start with the dielectric cylindrical dielectric resonator As you can see in this figure we have a cylindrical
dielectric resonator let us consider it is isolated from rest of in space and Z axis
represent the axis of the cylinder and typical materials we use with epsilon R ten to hundred
so it is of compact size but only problem we face is that it is sensitive to temperature
to temperature variation and mechanical vibration so thats why it is not very popular in space
application Where we may have to deal with large temperature
variation now since we have dielectric air boundary so we will be having hybrid modes
so typically it supports hybrid mode HEM suffix NML NML is the mode no and if you recall image
guide so almost similar analysis we can follow here and HEM NML in addition to this we have
TE or TM to Z so almost transverse electric or transverse magnetic with respect to Z axis It also supports hybrid modes HE when EZ dominates
over HZ and EH when HZ dominates over EZ now how we fix the mode designation so N it represents
no of extrima maxima or minima along circumference so phi direction M it denotes very umm the
number of extrima in along radius and L it denotes along exis axis so if N equal to zero
that means there is no extrima along phi or no variation along phi So we will call this mode as axis symmetric
mode for example TM zero ML mode or TE zero ML mode this modes are axis symmetric mode
and in some cases we will see L or along Z we will be facing less than half wavelength
but there would be one maxima or minima so thats why sometimes L is replaced by delta
to represent that its length is less than Lambda g by two and we call it then TE zero
one delta mode for the fundamental mode So for TE zero one delta mode then it is axis
symmetric mode we don’t have any variation along phi we have only one extrima along radius
and along Z the dimension is less than lambda g by two so characteristics of TE zero one
delta modes its written here so we don’t have any del del phi radiation and less than
a half cycle variation along Z and not only that on the dielectric air interface electric
field is parallel So that means we can replace this dielectric
air boundary by on magnetic L or magnetic wall so the non zero feed components mainly
we have E phi components and both the radial components and Z direction component of magnetic
field vector H So let me show you the field plots so remember
the axis its in Z direction then right hand top right figure it shows the electric field
variation it clearly shows that we have only five components of electric field and not
only that at centre electric field component is zero so this bottom figure it shows the
electric field strength variation along radius starting from centre So you can see that at centre it is zero then
its increasing having a maximum inside the dielectric and R equal to A represents air
dielectric boundary so above A that means in air it decays exponentially And we don’t
have any EZ component or ER component of the electric field you can compare this electric
field variation with the TE zero one mode in a circular wave guide this is also a axis
symmetric mode in circular wave guide So almost similar field variation but only
difference is that in circular waveguide all this electric field is confined within the
structure but for the dielectric resonator in air it decays exponentially so we have
some fencing fields and the amount of fencing field it depends on the dielectric constant
of this material and now if I want to use this resonator as umm an antenna in that case
we will have radiation due to the fencing field And we will expect that the electric field
and magnetic field they should be in same phase otherwise we will not have any radiation
and for feeder application the whatever electric field or magnetic field we have in air they
should be in phase quadrega so that almost there is negligible radiation and now look
at the magnetic field variation so magnetic fields they forms loop and we have both the
radial component and the Z component So on the central plane of this dielectric resonator
magnetic field is maximum Some there are many closed form expressions
available in literature so this is one of them it is accurate within plus minus five
percent you can say if the resonator dimension is given that means the resonator height D
its diameter twice a dielectric material epsilon R then we can calculate its resonance wave
no K not So we have two closed form expression of two
different cases two different as aspect ratios when D by two A it is within point five to
one you can use this fist formula to calculate resonance frequency So you recall that K not
this is equal to two pi by lambda not so from that you can calculate then what is F not
and the second one when D by two A is within point two to point five Now the quality factor this is one of the
important parameters will frequently use to represent loss Q in general this is equal
to omega not into W by PL where omega not represents the resonance frequency w is the
maximum stored energy inside resonator and Pl is the total power loss so if loss is minimum
in that case quality factor will be much higher now what are the sources of losses for any
structure passive struct component The losses it can be due to conductor loss
it can be due to dielectric loss or it can be because of radiation so then we can define
three quality factors which will represent this three different losses and then the overall
quality factor Q they are related to this quality factors like this expression as can
be given one by Q equal to one by QC plus one by QD plus one by QR so where QC represents
conductor quality factor QD this is dielectric quality factor and QR
this is radiation quality factor So if we want higher radiation QR should be small if
we want to use dielectric resonator in filter application this overall quality factor should
be as high as possible so that we can umm we can say that the loss inside the structure
is minimum and it stores almost all of the given energy inside the structure now whatever
resonator we are considering here we did not consider any conductor So QC that means it is infinite we don’t
have any conductor loss equal to zero And QD it depends on loss tangent of the material
this is equal to one by tan delta so its a property of the material and now choosing
a dielectric material which has very low dielectric loss it can be made very high and QR it is
approximately twice omega not into WE by PR so it is lowest among this three so mainly
the loss term will be facing is due to radiation We have a closed form expression to calculate
QR its given here Q so its a function of D height of the resonator epsilon R dielectric
constant whatever being used inside the material and also the diameter twice A So let me show you one graph how the resonance
frequency it varies with aspect ratio D by two A and the dielectric constant So in this
particular graph we are expecting three different values of epsilon R two zero forty and eighty
X axis represents the aspect ratio D by twice A so an Y axis represent normalized resonant
wave number K not A is twice by lambda not and epsilon R this is the dielectric constant
of the material so it becomes as a whole it becomes a frequency parameter We can see then if we increased the aspect
ratio D by two A then this resonance umm this resonant wave number it decreases or in other
words you can say resonance frequency of the dielectric resonator it decreases So K not
and omega not it vary inversely with root epsilon R it also depends on epsilon R if
we increased epsilon R then umm for given dimension obviously resonance frequency will
increase but change in resonance frequency due to epsilon R its very small Now since QR is minimum among the three different
quality factors so lets see QR depends on which parameters again we are considering
three different aspect ratios D by twice A equal to point three for this blue line D
by twice A equal to point five for this black one and one this is for this red one We are
plotting K not A that normalised wave number versus epsilon R so epsilon R we are considering
twenty to ninety And you see when we increased epsilon R then
this normalised wave number it decreases and also it varies with D by twice A what we expected
from the previous graph and the interesting thing is that QR which is shown on right side
it also increases with increasing epsilon R approximately QR is proportional to epsilon
R to the power three by two so if we increased epsilon R then QR will increase in other words
there will be less radiation And radiation bandwidth will decrease and
if I we have now three curves for three different aspect ratios so we see that smaller aspect
ratio this point three one it provides lower QR that means higher bandwidth so If I want
to design one antenna using cylindrical dielectric resonator we have to use then lower epsilon
R and lower aspect ratio Some properties of dielectric resonators in
general HEM one one delta mode this is the umm lowest order hybrid mode Higher order
mode next to TE zero one delta is HE one one delta Now single mode operation bandwidth
is maximum for D by twice A equal to point four so actually it can be shown that umm
the mono mode bandwidth it depends on aspect ratio And when we used any guiding structure or
even a resonator we expect that it should be excited only in single mode and then the
bandwidth is limited by the cut off frequency of next higher order mode so we have to increase
the cut off separation of this two cut off frequencies to increase the effective monomer
bandwidth of any given resonator or of any guiding structure and it can be shown that
approximately for TE zero one delta mode it is maximum When D by twice A equal to point four it can
be further increased by using a ring resonator So what is ring resonator If we simply drill
one air via inside this dielectric resonator we call it a ring resonator Now how it increases
the mono mode bandwidth Let us concentrate on the electric field plot so the next higher
order mode HEM one one delta mode the electric field plots for this mode is shown here You can see electric fields its having maximum
on centre on axis of this cylinder so if I drill one air via it is going to affect this
HEM one one delta mode most You compare this with the electric field configuration of TE
zero one delta mode Lets go back to the previous slides so for
TE zero one delta mode we have electric field minima so if we drill one AR via inside it
will not affect this TE zero one delta mode as much or in other words we can say the cut
off frequency it is less affected by AR via place at the centre of this dielectric resonator
but cut off frequency for the next higher order mode Which is HEM one one delta mode it will increase
if I place one AR via on along the axis of this dielectric resonator so thats how mono
mode bandwidth of the resonator can be increased Now if I choose aspect ratio D by two A equal
to point four then according to resonance frequencies the fundamental mode is TE zero
one delta mode so next higher order mode will be HE one one delta mode then EH one one delta
mode will appear then the TM zero one delta mode Now this field pattern for this TM zero one
delta mode it is very similar to TE zero one delta mode so only thing is that we have to
repress electric field by magnetic field lines simply we have to interchange that Otherwise
it looks very similar TM zero one delta mode it has been use to design dual mode filter
and dielectric cavity antennas So we have many applications in filter we can use resonators
in oscillators design for the tank circuit we can use dielectric resonator Dielectric
resonator also used for antennas and frequency is selective limiters So since its also popular in antenna design
umm let me discuss Some basic properties when we use it as an
antenna Again when we use as an antenna different shapes are popular it can be rectangular shape
it can be hemi spherical it can be cylindrical also But if I compare the QR or compare the
bandwidth in impedance matching bandwidth of the antenna it is observed that the bandwidth
is maximum for rectangular dielectric resonator so here in this picture I am showing one rectangular
dielectric resonator and the fundamental mode is TE one one one and it is the most used
mode for DRA Rectangular DRA and so it actually shows half
of a full resonator it is placed on a ground plane you can see it is being fed by one SMA
connector and the inner conductor of SMA connectors it is drilled inside this DRA and you can
see also one umm slot edged in the ground plane this is to couple power from SMA cable
to DRA now if I consider a full resonator so ground place is ground plane is placed
in middle So for this full resonator look at the electric
field plot it looks like one loop Z is the top direction and this DRA it is placed in
the XY plane so magnetic field it is perpendicular and it forms loop in XY plane you can look
at the field plots in XY plane umm the electric field it is perpendicular and magnetic fields
they are parallel so again if I go back to this XZ plane so on this mid line shown by
X axis And blue line here electric field this is
exactly perpendicular or you can say we have one we can place one PEC here umm or you can
simply cut this resonator and use half of this resonator backed by a metal or ground
plane So if I place a ground plane here at the mid plane then we are having this DRA
dielectric resonator antenna shown at the left side now its radiates mainly the X component
due to the X component of electric field So electric field in space it will be parallel
to X mostly in Z direction and this is the radiation pattern E plane radiation pattern
and H plane radiation pattern so E plane this is the XZ plane and we have highest cane in
both side both in XZ plane or E plane and YZ plane or H plane So you can see how this
DRA is being excited by using SMA I will show you another example Here DRA is
being excited by using a micro strip line the inner conductor of this SMA is connected
to strip of the micro strip line and here we have a printed circuit board on substrate
so the micro strip is placed bot at bottom most layer and top layer is the ground plane
of the substrate and slot is edged in the ground plane You can see it looks like on
plus sign and then DRA it is placed on that So thats how we can excite DRA by using micro
strip line This right figure it shows uses of DRA in filter application this is a rectangular
ca rectangular wave guide cavity filter and inside one cavity so here you can see we have
actually eight cavities and coupling between two cavities controlled by Irises It is the
cutview and umm this dielectric resonator basically its a ring resonator Where we have AR via at the centre of this
resonator it is placed inside the cavity because of this dielectric resonator the overall dimension
of the filter it decreases at the same time quality factor increases or in other words
you can say lossloss it decreases So this is the use of dielectric resonators cylindrical
dielectric resonator in filter applications So we will take a break after that we will
start filter Thank you

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