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An antenna is designed for VHF and UHF DVB operation using Antenna Magus, a matching network is designed in Optenni Lab and the full combination simulated in FEKO.
Television broadcasts are moving to digital formats all over the globe, with DVB being supported in various flavors, e.g. DVB-H (handheld), DVB-T (terrestrial), DVB-S (satellite), etc. RF spectra in countries where DVB is rolled out is being reorganized in the change-over from analogue to the new digital standard. Depending on the location of any particular receiver, a new antenna may be required to receive DVB signals. The following is a case study that assumes terrestrial DVB signal reception in both VHF and UHF bands for a receiver in a fixed location. An antenna is designed for this purpose using Antenna Magus and matched to a 50Ω receiver over the entire band of operation.
The operating bands for DVB that will be considered are:
- VHF-III (170 – 230 MHz)
- UHF-IV/V (470 – 862 MHz)
Antenna Magus Dual-Band LPDA Design
The frequency bands that were considered for this design require a dual-band (or wide-band) solution that can operate in both VHF and UHF frequency bands. Three keywords were used to find appropriate antenna configurations in Antenna Magus:
“Simpler is better” was applied as design philosophy and a dual-band LPDA was selected as the best solution for the current DVB requirement. The operating bands were specified as follows as requirements for the Antenna Magus design process:
- Centre frequency 1 = 200 MHz, bandwidth = 30%.
- Centre frequency 2 = 660 MHz, bandwidth = 30%.
FEKO Simulation of Non-Matched Antenna
The resulting design was exported to FEKO where it was simulated to confirm that radiation gain was sufficient over all bands of interest.
Radiation gain of the LPDA
The key point to note about this antenna is that it has a characteristic impedance of roughly 200Ω. Even though the antenna works as required in a 200Ω impedance system, the current requirement is for an antenna that operates in a 50Ω impedance system. FEKO was thus used to generate an S-parameter block of data, characterizing the input impedance of the unmatched antenna over the entire frequency range of interest.
Optenni Lab Matching of Antenna to 50Ω
The S-parameter block characterizing the unmatched antenna was imported in Optenni Lab, where a matching network was easily designed to match the antenna to a 50Ω system. Experimenting with various matching topologies was a simple process, which resulted in the selection of a 6-element matching network as the least complex network that matched the antenna well over the required frequency range of interest.
This matching network was characterized by Optenni Lab as an S-parameter block of data that was exported to be used in FEKO as a matching network that is coupled to the antenna.
Simulation Antenna and Matching Network Combination in FEKO
The S-parameter block of data that characterizes the matching network that was designed by Optenni Lab was imported into FEKO as a non-radiating network and was easily connected to the 200Ω antenna’s feed port using the schematic lay-out tool in CADFEKO.
The new system, with the matching circuit connected to the antenna, was simulated in a 50Ω characteristic impedance environment and the resulting input impedance was compared to the input impedance of the antenna before it was matched to this system. A Cartesian representation of input reflection coefficient referenced to 50Ω characteristic impedance with and without the matching network demonstrates how the complete system, with matching network, is well matched over both frequency bands that are of interest to the current DVB application. The Smith chart representation also clearly demonstrates that the matching network draws the antenna’s performance closer to the centre of the chart, improving overall match performance.
Comparison of matched to unmatched antenna
This white-paper demonstrates how Antenna Magus, FEKO and Optenni Lab may be used in combination to solve design problems:
- Antenna Magus leverages expertise in antenna design and selection of appropriate antenna solutions for a particular situation. This knowledge is presented to the user in easy to understand terms and a “ready-to-run” FEKO simulation model is exported upon completion of the design.
- FEKO provides powerful EM simulation abilities for the antenna and simple interfaces for the addition and testing of matching networks to the antenna.
- Optenni Lab delivers a simple interface for the design of optimal matching networks.
The demonstrated tool chain delivered a powerful and valuable antenna design, optimisation and matching schema for both novice and expert engineers.