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HFSS_Antenna_04_Lecture4_HFSS Lumped_Wave Port Basics Flipbook PDF
HFSS_Antenna_04_Lecture4_HFSS Lumped_Wave Port Basics
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Lecture 04: HFSS Lumped/Wave Port Basics
HFSS Ports and Excitations in the Simulation Workflow Geometric Structure Materials Boundaries Simulation Space
Lumped port
Ports & Excitations Simulation Setup Adaptive Process
wave port
Simulation Setup - Fr equency Sweep Simulation Results
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HFSS Excitations Include Lumped and Wave Ports
This text graphic comes from the "An Introduction to HFSS", Chapter 3 "HFSS Excitations".
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Ports Are Excitations That Provide Fields and S-Parameters Two main port types are wave ports and lumped ports. Both wave and lumped ports provide S,Y,Z parameters and field information. Ports are the only excitations that can be used to compute Network Parameters (S, Y and Z Parameters). Both types of ports are planar, defined in 2D. Both wave and lumped ports can be defined on a 2D surface in an HFSS model.
Wave Port on microstrip
Driven Modal Solution Type
Lumped Port on microstrip Driven Terminal Solution Type
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Lumped versus Wave Ports for Planar Filters – Lumped ports can be used to feed printed transmission lines. • S-parameters normalized to user-specified characteristic impedance • Single mode propagation • No de-embedding operations available • Port must be located inside the model
– Wave ports can be used to feed printed transmission lines. • S-parameters normalized to computed characteristic impedance (Generalized S-Parameters) • Multiple propagating modes possible • De-embedding available as post-processing operation • Port must touch background object (or be backed by conducting object)
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Lumped vs. Wave Ports for Planar Filters - Simulation Comparison The lumped port and wave port simulation results compare very closely.
Lumped Ports
Wave Ports 51
When Lumped Ports Are Used HFSS Lumped ports are used for: • Signal integrity applications • TEM (transverse electric magnetic) single-mode propagation • Circuits that are not well-defined wave guides
microstrip patch antenna lumped port internal to substrate structure
• Structures with non-uniform shapes, like connectors and BGAs (ball grid arrays) • Open structures like antennas
signal ground
lumped port from HFSS example package.aedt
signal ground 52
Lumped Ports Span Gaps Between Conductors Lumped ports are used to drive input signals spanning a gap between two conductors, often from a transmission line signal conductor to ground. Microstrip is an example where a lumped port spans from the signal conductor to a ground plane. Structurally, the lumped port is placed on a single geometric surface (which connects from signal to ground). A lumped port cannot be placed across the end of a coaxial cable where there is no surface, but a sheet can be created. A lumped port needs a surface you can click on and select.
Trace
Gnd
See also "HFSS.pdf", Chapter 19 "Assigning Excitations for HFSS…" 53
Lumped Ports Are Like Current Sheets A lumped port is analogous to a current sheet source and can be used to excite commonly used transmission lines. While the lumped port spans a physical distance in an HFSS model and includes an area, the lumped port functions as a lumped circuit element in an HFSS simulation. The parasitic inductance of a rectangular lumped port can be calibrated out of the S-parameter response with the de-embedding option for lumped ports. Uniform electric field
User-defined Zo
Zo
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Internal Refers to Structure and Boundaries Lumped ports are generally applied internally to the solution space. This includes:
patch
1. Internal to the structure Several of the pictures of packaging and connectors show lumped ports embedded inside of a structure. This patch antenna shows a lumped port embedded in the substrate.
port substrate
2. On the surface of a structure, but still within a region (within the meshed simulation space)
open region
This microstrip bend shows a lumped port on the outer surface of the structure, but inside the simulation space because of the region surrounding the structure.
By comparison, a wave port cannot be placed internally unless there is a PEC backing or electrical conductor behind the wave port.
port
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Lumped Port Impedance - User Specified The complex impedance Zs, defined when the port gets created, serves as the reference impedance of the S-matrix of the lumped port. The impedance Zs has the characteristics of a wave impedance; Zs is used to determine the strength of a source, such as the modal voltage V and modal current I, through complex power normalization. It should also be noted that when the reference impedance is a complex value, the magnitude of the S-matrix is not always less than or equal to 1, even for a passive device. See also "HFSS.pdf", Chapter 19 "Assigning Excitations for HFSS…"
A lumped port, in a driven terminal solution type simulation, can be placed without specifying impedance. But the impedance does appear in Properties.
See also An Introduction to HFSS, Chapter 27 Technical Notes > HFSS Technical Notes > Excitations > Lumped Port Theory and Chapter 27 Technical Notes > HFSS Technical Notes > HFSS Solution Process > Port Solutions > Calculating Characteristic Impedance for details. 56
When Wave Ports Are Used HFSS Wave ports are used for: • Closed structures like waveguides and coaxial cables
waveguide combiner port 2 mode 2
• multiple propagation modes like waveguides and odd/even modes on differential pairs • Surfaces exposed to background object • Structures with uniform waveguide or transmission line where the port attaches.
Viawizard.aedt example WavePortOUT5
The waveguide combiner is a closed waveguide structure that can support multiple propagation modes. The document "An Introduction to HFSS", Chapter 3 "HFSS Excitations" is available in the installation directories /Help/HFSS/GSG. See also HFSS.pdf, Chapter 19 Assigning Excitations for HFSS… available in the HFSS installation directories Help/HFSS. 57
Placing Wave Ports on a Flat Plane or Surface To place a wave port on a waveguide, simply select the face, right-click, choose Assign Excitation > Wave Port to bring up the dialog box.
In the case of the end of a coaxial structure, the wave port is planar, but there is not a complete geometric surface to which it attaches. In Face select mode, point to the outer edge to select this area for the port. For an open structure, like a microstrip, create a rectangle for the port. Pay careful attention to the size of the rectangle…more information to follow.
coax tee
microstrip
See also HFSS.pdf, Chapter 19 Assigning Excitations for HFSS … > Wave Ports > Wave Port Size. 58
Wave Port Sizing • Closed Transmission Line Structures - The boundary enforced on the port’s edge implies the transmission line modeled by the Wave Port always sits inside a waveguide structure. The enclosing material forms the port’s edge boundary.
Coax
• Open transmission line structures require additional consideration
Waveguide
- Microstrip, Co-Planar Waveguide, Slotline - Wave Ports must be large enough to capture the entire transmission line’s field structure • For open transmission line structures the Wave Port must surround the entire structure. • Make sure the transmission line fields are not interacting with the port’s boundary condition. • Wave Ports too small can lead to incorrect characteristic impedances, and add additional reflection to the results.
10w 8h
microstrip wave port
w
h 59
Microstrip Wave Port Size and Impedance
The choice of Wave Port Size for open structures is important and requires engineering judgement.
See HFSS.pdf, Chapter 19 Assigning Excitations for HFSS… > Wave Ports > Wave Port Size.
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Wave Ports - Port Solver 2D Solution for Modes - Z0 g HFSS first calculates a 2D solution for the wave port and subsequently uses that solution as the source for the 3D model. Initially, 2D fields in this semi-infinite waveguide are solved. Those same fields are impressed onto the port region of the 3D model to obtain a solution to the 3D model. The port solver assumes that the wave port you define is connected to a semi-infinitely long waveguide that has the same cross-section and material properties as the port. Each Wave Port is excited individually and each mode incident on a port contains one watt of time-averaged power. Wave ports calculate characteristic impedance, complex propagation constant, and generalized S-Parameters.
Right-click on
Analysis and select Profile.
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Wave Port Modes and Port Solution in 2D Initially, HFSS computes the modes on the cross-section of the waveguide. These modes serve as port excitations for the waveguide. HFSS uses a two dimensional FEM solver to calculate these modes. This initial calculation is referred to as the “port solution.”
Mode 1
Mode 2
Integration lines can be used to define and specify the modes and their polarity. In some cases the default settings can be used without defining an integration line. See An Introduction to HFSS.pdf, Chapter 1 Fundamentals of HFSS at the end of the section Mathematical Method Used in HFSS. 62
Setting Wave Port Mode Polarity with Integration Lines
Integration lines can be used to define and specify the modes and their polarity. Clicking in the Integration Line box can bring up a menu for drawing a new line.
See HFSS.pdf, Chapter 19 Assigning Excitations for HFSS… > Wave Port Dialog for Modal Solutions > Set Mode Polarity Using Integration Line. 63
Integration Line Examples for Microstrip, CPW, and Slotline
Microstrip line
Slotline
Waveguide
Microstrip
Grounded CPW Zpv
Zpv Zpv with Integration Line between trace and ground
Zpv with Integration Line between trace and ground
Slotline Zpv Zpv with Integration Line between ground planes
Integration line examples for microstrip, grounded coplanar waveguide (CPW), and slotline. See HFSS.pdf, Chapter 19 Assigning Excitations for HFSS… 64
HFSS Excitations - Ports and Solution Type • Port Selection: When to select a Wave Port or Lumped Port? - Wave Ports: Use for closed port definitions. Examples of closed structures are Coax and Waveguides. - Lumped Ports: Use for all other port definitions. • An exception to this guideline would be to use Wave Ports for Stripline.
• Solution Type: When to select Driven Modal or Driven Terminal? - Driven Terminal is typically faster to use because HFSS automates much of the setup • In general Driven Terminal should be used for any TEM/Quasi-TEM structures such as coax, microstrip, stripline, or co-planar waveguide. • In the case of a design that only uses Lumped Ports, the resulting S-parameters will be identical in Driven Terminal and Driven Modal Solution Types, therefore the ease of setup is usually the determining factor in the choice of Solution Type.
- Driven Modal is required for Waveguides • In some cases, the fields post-processing might be easier when the excitations are defined in terms of Power (Driven Modal) instead of Voltage (Driven Terminal).
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Ports and Solution Types Lumped Ports with Driven Terminal Solution Type
Wave Ports with Driven Modal Solution Type
These are common combinations. Notice that the type of port is listed in Properties when the port is highlighted. 66
Selecting HFSS Solution Type As a general rule, one could choose the solution type based on the type of transmission line that is being analyzed.
• Driven Modal • Hollow waveguides (metallic rectangular, circular…etc.) Driven Modal is required for waveguides. • Any problem where a symmetry boundary condition is applied In some cases, the fields post-processing might be easier when the excitations are defined in terms of Power (Driven Modal) instead of Voltage (Driven Terminal).
• Driven Terminal
• Microstrip, stripline, coax, coplanar waveguide • Driven Terminal is typically faster to use because HFSS automates much of the setup • In the case of a design that only uses Lumped Ports, the resulting S-parameters will be identical in Driven Terminal and Driven Modal, therefore the ease of setup is usually the determining factor.
Select HFSS > Solution Type to access this dialog box. 67
HFSS Excitation Methods, Propagation, and Solution Type Driven Modal • Fields based transmission line interpretation • Port’s signal decomposed into incident and reflected waves • Excitation’s magnitude described as an incident power Modal Propagation •Energy propagates in a set of orthogonal modes •Modes can be TE, TM and TEM w.r.t. the port’s normal •Mode’s field pattern determined from entire port geometry •Each Mode has its own column and row in the S, Y, and Z parameters.
Driven Terminal • Circuit Based transmission line interpretation • Port’s signal interpreted as a total voltage (Vtotal = Vinc + Vref) • Excitation’s magnitude described as either a total voltage or an incident voltage • Supports Differential S-Parameters Terminal Propagation •Each conductor touching the port is considered a terminal or a ground •Energy propagates along each terminal in a single TEM mode •Each Terminal has its own column and row in the S, Y and Z parameters •Does not support symmetry boundaries or Floquet Ports
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Excitations: Modal vs. Terminal in Stripline Mode 1 (Even Mode)
Integration Line
Mode 2 (Odd Mode)
Integration Line
Port1
Terminal Transformation
T1
2 Modes
Modal
Port2 2 Modes
T2
SPICE Differential Pairs
T1
T1 Port1
T2
Terminal
Port2 T2
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