• Which Products are you interested in ?

    CST offers a wide range of EM simulation software to address design challenges across the electromagnetic spectrum, from static and low frequency to microwave and RF, for a range of applications, including EDA & electronics, EMC & EMI and charged particle dynamics.

  • Antenna Magus
  • IdEM
  • FEST3D
  • Optenni Lab
  • Looking for a Training, Workshop or eSeminar ?

    CST STUDIO SUITE® is being demonstrated at trade shows and workshops all over the world. Take a look at the list of conferences and exhibitions CST will be attending and get further information regarding CST workshops, eSeminars and training days.

  • TrainingsRegular training courses are held in CST's offices in Asia, Europe, and North America. Please check our trainings section for detail of trainings in all over the globe. Advance registration is normally required.

  • WorkshopsCST hosts workshops in multiple languages and in countries around the world. Workshops provide an opportunity to learn about specific applications and refresh your skills with experienced CST support staff. Make sure you visit our workshop section.

  • eSeminarsThroughout the year, CST simulation experts present eSeminars on the applications, features and usage of our software. You can also view past eSeminars by searching our archive and filtering for the markets or industries that interest you most.

  • Check our latest Events
  • Why create a MyCST Account ?

    A MyCST account may facilitate your access to many of the offerings on the CST website, for example the registration for eSeminars and the watching of eSeminars recordings, setting email preferences, and there is more functionality to come. It is required to participate in workshops and trainings.

  • Personal PreferencesAllows you to update your email preferences and areas of interest. It helps us to personalize your experience.

  • EventsSearch for events by location, industry and application. Once you are registered, you will be able to manage your registrations and check important details about your events. This section also provides you with a repository for Workshop & Training material.

  • LibraryYou can collect articles you find on the CST website to reference or read later by clicking on the “Add this article” button at the bottom of the article page.

  • Create Your Own Account
  • Need technical Support ?

    Customers can customize their accounts once they have completed the account creation process. This platform acts as vivid interface between CST and our customers.

    We therefore offer access to the latest Service Packs (including an automatic notification that a new Service Pack is available), a steadily growing database of Frequently Asked Questions (FAQs), Application Notes and Training Videos, as well as an individual FTP section for easy exchange of large files with our support team.

  • Do I need an Account?To access the Support Site a valid maintenance contract and a one-time registration is required.

    Please note that your Support login does not work for the MyCST account.

  • Get Support
  • How to request a Trial License ?

    Get your license in only three steps:

    1. Fill in the required fields in the contact form on the right and click "Send Us Your Request".

    2. Lean back and wait until one of our CST Experts contacts you.

    3. Enjoy a our trial license.

  • Student Edition

    Student Edition The CST STUDIO SUITE® Student Edition has been developed with the aim of introducing you to the world of electromagnetic simulation, making Maxwell’s equations easier to understand than ever. With this edition you have, bar some restrictions, access to our powerful visualization engine and some of the most advanced solvers of CST STUDIO SUITE.

    Student Edition

CST – Computer Simulation Technology

Thermal Analysis of a Two-Cavity Dual-Mode Bandpass Filter

The CST EM STUDIO® (CST EMS) Thermal Solver has been applied to the simulation of the temperature distribution in a dual-mode filter. The current density distribution inside lossy conductive metals is precomputed by CST MICROWAVE STUDIO® (CST MWS) and acts as the thermal source.

The dual-mode filter used in this application consists of two cavities separated by a thin wall containing a coupling slot. Tuning stubs enable the adjustment of the two orthogonal modes and the 45-deg slanted stubs allow for a proper tuning of the coupling bandwidth. The stubs have radiators mounted outside of the cavity. The metallic walls have a finite thickness with a finite electrical conductivity assigned which accounts for the surface currents.

Figure 1: The filter model

Prior to the thermal analysis the filter needs to be tuned for proper bandpass behavior. The tuning process was performed by varying the lengths of the tuning stubs: the group-delay response method was used to tune each stub individually. The final S-parameter response is shown in Fig.2 for a relative filter bandwidth of 1%. At the lower skirt of the reflection coefficient (at approximately 0.5% off the center frequency) a current density monitor was defined....

Figure 2: S-Parameters of the tuned bandpass filter

The selection of the frequency for a harmonic current denisty monitor is rather critical since the distribution of the currents varies greatly with frequency. At the lower side of the passband the current density monitor was assigned at a frequency of 99.5% off the center frequency. The current density distribution for this frequency is shown in Fig. 3. Note that the magnitude of the current density is scaled to 1 W peak and/or 0.5 W rms. Since the transmitted RF-power in reality is 5 kW, a scaling factor of 1e4 has to be applied for the proper magnitude of the thermal heat source.

Figure 3: Current density distribution

The next stage entails the definition of the thermal properties of the model. The HF simulation results are used for the thermal source. Thermal conductivities were assigned to the housing, cooling elements and tuning stubs (brass, copper, aluminum). For this study, the slot wall is assumed to be made of Invar with a rather low thermal conductivity of 13 W/(Km), which is about 30 times less than copper. Within CST EMS, thermal surface properties can be assigned to surfaces of thermal conductive materials. A thermal surface property definition describes the radiation and convection losses from a surface. At the outer walls of the housing a heat transfer coefficient of 5 W/(m^2.K) was assigned to take convection into account. In this filter example, the thin separating wall is of low thermal conductance, thus most of the heat needs to be transported via air convection. The air near the coupling slots heats up and begins to rise, forming a convection loop. To take this convection effect approximatively into account, another transfer coefficient of 15 W/(m^2K) has been assigned to the thin separation wall. The model is completely embedded into air with a low thermal conductivity. For the thermal boundaries, a fixed thermal temperature of 273 K was assigned to the bottom face, the top face was assigned to a constant floating temperature and the four vertical boundaries adiabatic (no heat transfer across).

In Figs. 4,5 and 6 the contour-plots of the temperature are depicted.

Figure 4: Temperature distribution: the hot spot is right at the coupling slot

Figure 5: Temperature-plot at the vertical cutplane with a clamped temperature range of max. 300 K

Figure 6: Close-Up look at the coupling slot

"Heat flow density" is a further post processing quantity of the thermal solver within CST EMS. Figs. 7 and 8 show contour and arrows plot at a user given cutplane respectively.

Figure 7: Arrow plot along a 2D plane cutting through the stubs

Figure 8: Contour plot of the thermal heat flow

Convection mechanisms are always connected to medium transportation. To take these effects properly into account, a computational Fluid Dynamics (CFD) program is required. As mentioned above, due to the heat generated at the separation wall, the air starts to circle around forming a convection loop. Fig. 9 shows the air-speed distribution in the dual mode filter [1]. (with courtesy and permission of the "Spinner GmbH, Feldkirchen-Westerham, Germany")

Figure 9: Air speed distribution (m/s) using the CFD software "Fluent" (with courtesy and permission of Spinner GmbH, Feldkirchen-Westerham, Germany)

It has been demonstrated that in a co-simulation of CST MWS and CST EMS the thermal analysis of a filter can be performed. The temperature of, for example, the hot spot in the vicinity of the separating wall computed by CST EMS (approx. 420 K) is in a good agreement with the CFD-code "Fluent" showing 405 K.


Dr. Spaeth, Dr. Lorenz : "CFD- Simulations at Spinner", Spinner Spotlight 4/2005, Page 4-6

Rate this Article

0 of 5 Stars
5 Stars
4 Stars
3 Stars
2 Stars
1 Stars
contact support

Your session has expired. Redirecting you to the login page...

We use cookie to operate this website, improve its usability, personalize your experience, and track visits. By continuing to use this site, you are consenting to use of cookies. You have the possibility to manage the parameters and choose whether to accept certain cookies while on the site. For more information, please read our updated privacy policy

Cookie Management

When you browse our website, cookies are enabled by default and data may be read or stored locally on your device. You can set your preferences below:

Functional cookies

These cookies enable additional functionality like saving preferences, allowing social interactions and analyzing usage for site optimization.

Advertising cookies

These cookies enable us and third parties to serve ads that are relevant to your interests.