end sem ppt

Under the guidance of

Prof. Subratra Sanyal & Dr Arijit De by

Bhaskar Ray Karmakar

10EC63R05

DEPARTMENT OF ELECTRONICS & ELECTRICAL COMMUNICATION ENGINEERING

INDIAN INSTITUTE OF TECHNOLOGY

KHARAGPUR – 721 302

DESIGN OF NARROWBANDPASS SHARP REJECTION STRIPLINE FILTER FOR SPACE APPLICATION

The bandpass filter is suppose to be designed with following characteristics.

Sharp rejection,narrow bandpass with out of band rejection of 50MHz. Maximum insertion loss of 2dB & return loss better than 15dB Having centre frequency 2GHz & bandwidth of 100MHz. Compact Size.

OBJECTIVE

A microwave filter can be manufactured out of

MOTIVATION

A dielectric resonator filter Waveguide filter. Transmission line filter.

Fig:1Type of microwave filter

Waveguide Filter Microstrip Filter Stripline FilterWaveguide filters are manufactured by placing irish or slits.

It is made by etching one side of a dielectric substrate.

Here a piece of transmission line is inserted in a pool of dielectric substrate.

The mode of propagation is either TE or TM

Here mode of propagation is quasi TEM, since its half lying in dielectric & half in air.

Pure TEM propagation is found in stripline circuit as it is completely inside the dielectric substrate.

Since discontinuities are introduced which aid in working of a waveguide filter, it is difficult to construct.

It is easiest to construct. Some discontinuities are necessary to etch the resonating structure. Discontinuities like bend , open ended & closed end are often seen. Proper treatment like chamfering is essential for the optimum performance of the circuit

Discontinuities of same types are find here, but a better performance is observed due to pure TEM mode of propagation.

It is heaviest of all the three types of available options

It is lightest of three. It is much lighter than waveguide filter but little heavier than microstrip filter due to requirement of two dielectric slabs .

It offer the low loss with highest Q among the three substrate

They offer low Q ,while insertion loss is low & return loss is acceptable for good performance.

Unloaded quality factor is stripline is quite close to that of microstripline, but here the insertion loss and return loss in this case is better than microstrip configuration.

COMPERATIVE STUDY DIFFERENT KIND OFWAVEGUIDE,MICROSTRIP & STRIPLINE FILTER

Depending on the configuration bandpass filter can be designed on the following circuits.

Stepped Impedance. Parallel Coupled Line. End Coupled Line. Interdigital. Comb Line. Hairpin. Irregular line.

DIFFERENT AVAILABLE CIRCUITS FOR CONSIDERATION

HairpinLadder Network

Fig 2: A CAD layout of ladder and hairpin structure

COMPARASION OF AVAILABLE CIRCUITSParallel coupled line

End Coupled Line.

Interdigital Combline Hairpin

Cascade of parallel coupled half wavelength line

It’s a series of half wavelength long strip resonator

Its an array of quarter wave length long line with alternating short & open circuits.

Its same as parallel coupled line except that each resonator is short circuited at one end & grounded at other end through capacitor

The half wavelength resonators are folded into a U shaped.

Small in size and easy to fabricate due to absence of short circuit

It become extremely large at low frequency and length is two times greater than paralled coupled filter.

Dimension of these filters are one quarter of physical wavelength at operating frequency building such filter at low frequency is tedious job.

They are more compact than interdigital filter and particularly suitable for narrowband pass application.

Since it much more compact it finds it application in MIC or MMIC.

No ground connection is required.

No ground connection is required.

They need to be grounded through grounding

They are short circuited at one end and connected to the ground with a capacitor.

Since grounding is not required mass production on single substrate is possible with low cost.

Suitable for wideband application

Narrowband width is hard to achieve since finding a optimum spacing between the resonators is hard to achieve.

With a high unloaded Q a deep skirt can be obtained but sharp rejection is almost impossible task.

It is ideal for narrow band pass application where sharp rejection is not desired.

They will look for quite large resonator spacing if narrowband pass is desired.But as they are more suitable for MIC’s they are not employed for narrowband circuit.

M14

M12

M45 M58Mn-3,n

M23 M67 Mn-2,n-1

M34 M56 M78 Mn-3,n-2 Mn-1,n

CASCADED QUADRIPLET

Fig:3 Typical Coupling structure for CQ filters

A CQ bandpass filter consists of cascade sections of four resonators each with one cross coupling.The cross coupled can be arranged in such a way that improves the selectivity.

ORIENTATION TYPES OF COUPLING

Three different types of coupling are

1. Magnetic Coupling 2. Electric Coupling 3.Mixed Coupling

The coupling in all these structure is proximity coupling.

The coupling co efficient of the mixed coupling decrease with the increase of the spacing.

Electric coupling is dominant for a small spacing and magnetic coupling is dominant for a large spacing.

Fig 4: Different types of coupling

The coupling co efficient ‘k’ is defined as ratio of coupled energy to stored energy.A general expression is given by

Where E & H electric & magnetic field vectors & ‘k’ is coupling coefficient.

For extraction of ‘k’ a more generalized formula is given by

For a synchronously tuned structure the expression reduce to

COUPLING COEFFICIENT

1 2 1 2

2 2 2 2

1 2 1 2

. .

* *

E E dv H Hk

E dv E dv H dv H dv

2 2 2 22 102 01 02 02

2 2 2 201 02 2 1 02 01

1

2p p

p p

f ff f f fk

f f f f f f

2 22 1

2 22 1

p p

p p

f fk

f f

EXTRACTION OF ‘k’

For example in deriving the value of ‘k’ the following structure is considered with spacing between the two resonator is .5mm and length of each arm is 9mm. The relative dielectric constant is 10.8.The arm gap is 1.5 mm and ports are located at equal distance from the end.

From the graph the two peaks are located at 2420MHz and 2950MHz.So the calculated value of ‘k’ is .1954.

Following are the inference from the simulated structure Stronger Coupling will result in separation of two peaks.

The port location with respect to the coupled resonators must be same.

Fig 5: Electric Coupling & response

A numerous types of coupling scheme are available.

They are

TYPES OF COUPLING

Loose Coupling.

Direct CouplingSide Coupling

Enhanced Coupling.

Matched Loose Coupling

Fig 6: Different types of coupling

ALTERNATIVE PORT ARRANGEMENT

Fig:7CAD layout and response due to change of the port distance

S21=4.6dBS11=23dB

0.25mm

S21=4.53dBS11=6dB

0.5mm

S21=4.9dBS11=5.2dB

.35mm

DESIGN EXAMPLE & RESULT

Fig: 8a CAD layout with an increased gap area

Fig 8b:Square resonator with interdigital structure

S21=3.2dBS11=6.68dB

PORT POSITION

The tap point can be calculated from

2

0

( ) 4sin ( )2

QR lZ L

l1

l2

l2

l2

Input

Centred

dCenter

output

Fig:9 Different port location & its response

SRRs WITH INTER PARTICLE

Fig 10:Different orientation of inner particle & its response

EFFECT OF THE ORIENTATIONS & INTER PARTICLE SPACING OF THE SRRs

Fig11a: Multiple inner resonators corresponding response

Fig 11b:Increased Coupling area & associated response

C2

C1

C3

Fig 12c:Equivalent diagram in term of circuit element

Fig 12a:End coupled Structure Fig 12b:Side Coupled Structure

1 '0

ln{coth( . )}2

D Sb

D

2 '0

2ln{coth( . )}

2

D Sb

D

Where b1 & b2 is the suceptance ,S is the spacing between two adjacent strip

CALCULATION OF GAP SPACING FOR END SIDE & BROADSIDE COUPLING

Fig 13a: Endside coupling

The normalized susceptance of (i+1)th gap is given as an end coupled filter with "n" stages is bi,i+1 and can be expressed as

On rearranging first equation we get

Fig 13b:Broadside coupling

S1 Sn

, 1, 1 2

, 1

0,1 , 10 1

1

2 1 0

(1 )

2

, 12

( ) /

i ii i

i i

n n

i i

b

where

g g

i ig g

f f f

'1 01

ln{coth }2

bS

D D

20, 1 , 1

0

, 1 1ei i i i

Zi i

Z

20, 1 , 1

0

, 1 1oi i i i

Zi i

Z

The relation between Z0e & Zoe in terms of W/D,S/D is

0

94.15 /

ln 2 1ln 1 tanh( .

2

reZ

W S

D D

0

94.15 /

ln 2 1ln 1 coth( .

2

roZ

W SD D

2

6

0

1 188.3 (1 )ln tanh( . )

2 (1 )r

S

D Z

2

6

0

1 94.15 (1 )ln coth

(1 )r

S

D Z

02

1ln coth .

12 r

S

D D

CO M PARISI O N BETWEEN TH E TWO TYPES O F CO UPLING

DESIG N ALG O RITH M FO R M ICRO WAVE CIRCUITS

Fig 14: An Algorithm for designing microwave circuits

FABRICATION & RESULTS

The width of dielectric in this case is.635mm while the length of each arm of resonator is 7.9 mm and width is 1.11483mm.The port width is .5 mm.

S21=6.43dBS11=15.06dB

Fig 15: CAD layout & response due to simulation on TMM 10

CHOICE OF CQ STRUCTURE

Fig 16:Different orientation of CQ and corresponding response

CIRCUIT DESIGNS & RESULTS

Fig 17:CAD layout for different structures

COMPERASION TABLEDesign Return Loss

(S11) dBInsertion Loss(S21)dB

Out of band rejection at 60dB (MHz)

Stub Length(mm)

Dimension mm*mm

1 15.87 3.79 25.23 No stub 65.87*46.55

2 36.2692 1.30914 28.21 5 66.05*46.55

3 37.11 1.3843 26.3372 5 & 5 mm away from port end

66.05*46.55

4 47.71 1.2562 29.34 2.5 & .5 mm away from port end

65.33517*60.361

CIRCUIT DESIGN & DIMENSION

Fig 18a:Fabrication on TFG Woven Fig18b: Dimension of the fabricated structure.

MEASUREMENT & RESULTS

Fig19: Measured & Simulated response of the designed circuit

The simulated and measured results quite close.

DISCUSSION

Response Central Frequency

Insertion loss

Return Loss Bandwidth Rejection Bandwidth

Simulated 37.71 1.2562 2 180 29.34

Measured 25.21 1.94 1.97 182.2 29.51

All the enclosures were fabricated in house.The etching technique used for the fabrication is quite old.Etching can be improved by doing the same in LPKF machine.The two dielectric structure was attached using a very crude process.

Fig20: Measurement of Insertion loss and return loss on two occasion

MEASUREMENT IN ISAC BANGALORE

Reduction in bandwidth: Though the designed circuit offered desired response in term of insertion loss & return loss, more work is need to reduce the bandwidth. This can be done selecting a proper dielectric substrate and also properly choosing the orientation of the resonators .

Suppression of leaky modes: It can be achieved by using structure like suspended striplines or using suitable bonding structure.

Design of fractal resonators: It can increase the Q of the structure and alo the size is

reduced.

FUTURE SCOPE

[1] George L.Matthaei, Leo Young,E.M.T. Jones(1980),Microwave Filters, Impedance-Matching Networks, And Coupling Structures,” Artech House,INC .

[2] Jia-shen G.hong and M.J.Lancaster (2001),Microwave filter for RF/Microwave Applications, A Wiley Interscience Publication,

[3] J. S. Hong and M. J. Lancaster, “Couplings of microstrip square open loop resonators for cross-coupled planar microwave filters,” IEEE Trans. Microwave Theory Tech., vol. 44, pp. 2099–2109, Nov. 1996

[4] Richardson, J.K,”Gap spacing for End Coupled & Side Coupled Strip-Line Filter,” IEEE Trans. Microwave Theory Tech, vol-15,no-6,June 1967 .

[5] Richardson, J.K,”Gap Spacing for Narrow Bandwidth End Coupled Symmetric Stripline Filter”, IEEE Trans. Microwave Theory Tech., vol-16,no-8, August 1968 .

[6] Bharathi Bhat,Shiban K Koul (2007),Stripline-like Transmission lines for Microwave Integreated Structure, New Age International Publisher,New Delhi,pp 22-456 .

[7] G.K. Gopalakrishnan and K. Chang,”Novel excitation schemes for the microstrip ring resonator with lower insertion loss,” Electronics Letters ,Vol. 30 No. 2, 20th January 1994.

[8]Kai Chang (1996), Microwave ring circuit and antennas,Wiley Series in Microwave and Optical Engineering, pp 261.

[9] L.Hsieh and Kai Chang,”Compact dual mode elliptic function bandpass filter using a single ring resonator with one coupling gap,” Electron.Letter., Vol.36,No 19,pp.1626-1627,September 2000.

REFERENCE