Last year on Broadcast Dialogue – The Podcast, the RF experts at Dielectric discussed how FM broadcasters were on the verge of seeing a tried-and-true TV antenna design optimized for radio. The vast majority of UHF North American broadcast antennas today are slotted cylinder pylon antennas, which offer benefits including smaller tower footprints, fewer parts, lower windload and superior pattern flexibility. Unfortunately for radio broadcasters, their narrow bandwidth characteristics were impractical for passing full-band FM signals.
Just in time for the 2022 NAB Show and the company’s 80th year in business, Dielectric has unveiled its innovation to resolve these bandwidth limitations with the FMP family of FM pylon antennas. The FMP family represents the broadcast industry’s first slot cavity microstrip FM antenna product line, and Dielectric will demonstrate its benefits in Booth W7107 at the Las Vegas Convention Center from April 24-27.
“Television broadcasters have long valued pylon antennas for their straightforward designs, versatility and structural benefits,” said Keith Pelletier, Vice President and General Manager, Dielectric. “Our engineering breakthroughs introduce techniques to increase bandwidth for radio broadcasters, making full-band FM operation in pylon antennas a reality.”
The engineering breakthroughs include reducing the antenna Q factor, which improves the bandwidth from one to 20 percent; and stabilizing the H:V ratio across the band. The 20 per cent bandwidth translates to full-band FM operation, which is the key goal of the FMP antenna’s design. Dielectric has also included its patented parasitic dipole, which adds a vertical component to the existing horizontal signal. This creates more pattern options for FM broadcasters, including elliptical and circular polarization, and contributes to the substantial bandwidth increase.
While Dielectric’s special pylon designs for FM radio differ from TV systems, the FMP family carries over many traditional pylon antenna benefits including optimal downward radiation, smaller size and lower weight. For example, FMP antennas reduce the number of parts used in commonly used ring-style antennas by more than 60 percent. The streamlined componentry also improves reliability over the long term as there are far fewer parts to repair or replace.
Pylon antenna designs also provide broadcasters and tower crews with top-mounting options, in addition to the traditional side-mounted configurations of ring antennas. This is ideal for high-power FM stations that want a true top-mounted omnidirectional antenna. The FMP can handle input powers of 100kW and higher, which also makes the antenna excellent for combined operation of multiple stations.
Dielectric’s FMP designs use full-wavelength spacing between antenna elements. This reduces the number of antenna elements required compared to ring-style designs, which require half-wavelength spacing, hence more elements, to cover the full FM band. The efficient design is also easy to scale. Antennas are built in four-layer building blocks and can be increased to eight or 12 bays to suit higher power requirements and elevation pattern gains.
Dielectric’s abilities and drive to push innovation is showcased further with the actual FMP antenna design process, which was completed in a virtual environment and then quickly built to validate the designs. This process would traditionally take years and numerous iterations of parts to develop the antenna. Dielectric recently established a team of specialized engineers to create new designs quickly and efficiently using HFSS (High Frequency Simulation Software), which greatly accelerated the development process.
“We are always looking at ways that we can bring antenna design concepts from one market to another and advance the technology for modern and future broadcast systems,” said Pelletier. “We have now adapted what was long a solution for mostly single-channel TV operations for both broadband TV and FM broadcasting, which very much differentiates our product portfolio from competitors.”