Design and Development of Quadrature Hybrid Coupler at 18-40 GHz External Guide : Internal Guide : Presented by : Mr. Syed Sadullah Hussaini Mrs.K.Ch.Sri Kavya Mr. B.V.Raj Gopala Rao Scientist ‘C’ Associate Professor M.Tech ( C&R) DLRL-Hyderabad K.L.University 10102157
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Design and Development of Quadrature Hybrid Coupler At
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Design and Development of Quadrature Hybrid Coupler at
18-40 GHz
External Guide : Internal Guide : Presented by :
Mr. Syed Sadullah Hussaini Mrs.K.Ch.Sri Kavya Mr. B.V.Raj Gopala Rao
Scientist ‘C’ Associate Professor M.Tech ( C&R)
DLRL-Hyderabad K.L.University 10102157
Objective
• The aim of the project is to design and develop hybrid coupler with differentconfigurations at 26.0 – 40.0 GHz and 18.0 – 40.0 GHz.
• Following configurations have been investigated and the effectof DGS has been studied (As DGS makes the design compact and sharpens the cutoff).
Single section Branch line coupler
Cascaded Branch line coupler .
5 – Section branch line coupler.
5 – Section branch line coupler with DGS effect.
Re – entrant mode Coupler or Hopfer Coupler.
• Microwave Tools used :
Advanced Design system (ADS)
ANSOFT Designer
Microwave Components• Microwave components can be categorized by the type of circuit elements
which are used: discrete (or lumped) versus distributed
• Lumped elements in generic electronic circuit such as inductors andcapacitors are generally available only for a limited range of values and aredifficult to implement at microwave frequencies
• Distributed elements are formed using sections of transmission line.Depending on the layout (line width, geometry, etc.) sections of line canbehave very much like capacitors, inductors, or a combination of both
• Advantages of distributed components:» At high frequencies high performance discrete elements must be very small
and can be difficult to manufacture and assemble» Designs using distributed elements can often be made more cheaply, and may
perform better at high frequencies
Continued…..• The key difference between circuit theory and transmission line theory lies in
electrical size.
• A very general distinction between lumped and distributed is:» Lumped elements have a physical size <<<<<<λ» Distributed elements have a physical size comparable to λ
• Thus we can say that a transmission line is a distributed-parameter network where voltages and currents can vary in magnitude and phase over the length of the network.
• Here we will focus on microstrip Transmission line microwave circuits
• One drawback to distributed elements is that the characteristics are highly frequency-dependent
• Another disadvantage of using distributed elements at lower frequencies is larger sizes(because of larger wavelengths at lower freq.'s)
Transmission Line Review
Transmission Line Terminated with Zo
High-Frequency Device Characterization
Reflection Parameters
Transmission Parameters
Low-Frequency Network Characterization
Why use S-parameters??
Measuring S-parameters
Microstrip Transmission line
Its an inhomogeneous Transmission Line structure
Employs a high dielectric substrate, the EM field is concentrated very tightly near the conductor in the free-space region, avoiding excessive radiation loss.
Advantages:» Suitable for etching» ease of mounting components» Accessibility for circuit tuning
Electric E and Magnetic H field lines for fundamental Quasi-TEM in Microstrip
1 ,
)/444.1( ln667.0393.1)(120
1 ),4
8ln(60
eff
0
hw
hwhw
hw
hw
wh
Z eff
Synthesis procedure: Give Z0 to find w / h.
rrrrr
rrr
ZBZA
hwBBB
hw
hw
0
0
2A
A
2377 ),11.023.0(
11
21
60 where
2 ,61.039.0)1( ln2
1)12( ln12
2 2e
8e
Analysis procedure: Give w / h to find eeff and Z0.
)/( 12121
21
whrr
eff
Formulas for Quasi-TEM Design Calculations
Hybrid Coupler
A Hybrid is a passive device which couples part of the transmission power using two transmission lines.Difference between Directional coupler and Hybrid coupler.Applications
To design a Hybrid coupler: Planar Microstrip ConfigurationWide band of 26.0 – 40 GHz and 18.0-40.0GHzTight coupling of -3dBReturn loss > 20dBIsolation >20dB
Applications of Hybrid Couplers :
• Balanced Amplifiers
• Balanced Mixers
• Image rejection mixers
• Phase shifters
• Attenuators
• Beam forming Networks
Direction of Arrival (DOA)Image Rejection Mixer
Balanced Amplifier
Design of -3dB Coupler at 26 – 40 GHz
Z1 , Z2 Series and branch line impedances.
Even and Odd mode Analysis.
Conventional BLC has a limited bandwidth of 15%.
Bandwidth can be enhanced by cascading multiple sections.
Single Section Branch-line Coupler 3-Section branch line Coupler
Even and Odd Mode Analysis
.
Decomposition of the branch-line coupler into even- and odd-mode excitations.(a) Even mode (e). (b) Odd mode (o).
Proposed Design
Port 1 – Input port Port 3 - Direct port
Port 2 – isolation port Port 4 - Coupled port
Z1 = 35.35 Ω , Z2 = 120.7 Ω
Effects of High Frequencies
Effects of Discontinuities
Simulation Results and Discussions• Performance was evaluated using Ansoft Designer microwave Tool.
• Substrate characteristics: Dielectric constant εr = 2.2 Height H = 10mil (0.254mm) Loss tangent δ = 0.001
• Electrical characteristics: Characteristic impedance Z0 = 50Ω Physical Dimensions of the structure Electrical length = 90 degrees Design frequency f0 = 33GHz
Return loss for 1-Section, 3-Section and 5-section branch line couplers
Coupled line theory• When two unshielded lines are placed close together, power can be
coupled between the lines due to the interaction of the EM fields.
• Coupled lines has perfect matching and directivity.
• Exits two types of propagation modes :
Even mode : Currents with same amplitude and in same direction.
odd mode : Currents with same amplitude and in opposite direction.
• Even mode :
• Odd mode :
Design of -3dB coupler at 18-40 GHz
Configurations :
Edge Coupled lines .
Broad side coupled lines.
Vertically installed planar coupled lines.
Off set parallel coupled lines.
Problems :
• Tight coupling requires narrow spacing between coupled lines which is
practically unrealizable.
• In Microstrip , even and odd mode phase velocities are not equal which
effects the directivity ,return loss and isolation
• High frequency effects
-3dB Coupler configurations:
• Lange Couplers
• Tandem couplers
• Re-entrant couplers
Phase velocity compensation techniques for Microstrip lines :
• By adding lumped capacitances at the ends of the coupled lines.
• By adding a dielectric overlay on top of the coupled lines.
• By using Wiggly lines.
Coupler with tight coupling of -3dB has been designed using re-entrant configuration with multiple dielectric layers to compensate narrow spacing between the coupled lines and also to equal the even and odd mode phase velocities of Microstrip coupled lines.
Re-entrant coupler ( Hopfer Coupler ) design
• A , B --- inner coaxial conductors
• C --- Outer conductor
• The conductor C is at floating potential with respect to the conductors A, B and the outer conductor D.
• The transmission line between C and D is in series with the two coaxial lines contained in C, acting as a mutual coupling medium.
• Zo1 ---- Impedance between outer conductor C and ground plane D.
• Z02 ---- Impedance between inner conductors A , B and ground plane D.
Re- entrant cross section using coaxial lines
Design relations
• Even mode impedance
• Odd mode impedance
• Overall impedance
where k -- coupling factorc -- coupling (dB)
Design using Microstrip lines
• The Microstrip version of a re-entrant coupler consists of a coupled line on the
middle layer sandwiched between the floating conductor on the top layer and a
floating conductor in the rectangular ground plane slot underneath the coupled