AXIOM® Series Circularly Polarized Master FM Antennas

The AXIOM® Series broadband circularly polarized FM (88 – 108 MHz) antenna combines the exceptional engineering features of an internally fed, fully pressurized system with superior fabrication characterized by totally welded feed connections, rugged brass material and TIG welding. The AXIOM antenna system provides high input power handling capability as an auxiliary master FM antenna for systems limited to a band width requirement of up to 18 MHz of the FM Band (8 MHz for the MPA Series).


  • Product Line:
  • Product Series:
    SHPA | MPA
  • Frequency Range:
    88 - 108 MHz
  • Multiplexed Versions Available:
  • Broadband Applications:
    Yes SHPA specified 18 MHz of FM Band (88 to 108 MHz)
  • Yes MPA specified 8 MHz of FM Band (88 to 108 MHz)
  • Polarization:
  • Azimuth
    ± 2 dB in free space
  • Axial Ratio
    Less than 3 dB in free space
  • VSWR at Input:
    1.25:1 maximum with field tuning
  • Maximum Power Rating:
    120 kW

ERI antennas are unchallenged in quality and dependability. ERI is the only manufacturer to use large diameter outer conductors and a completely enclosed, pressurized, internal series feed system. The result is a simple and reliable method of coupling power to the elements. Unlike competing designs, ERI series-fed antennas do not require a troublesome secondary current loop for element excitation with all the resulting disadvantages. All ERI antennas include brackets for mounting on leg, pole, or face mounting (up to 42-inch uniform cross-section tower), brackets for other mounting configurations are optionally available. The ROTOTILLER® series FM antenna’s unique design consists of two series fed, bent dipole elements which form a space phased, circularly polarized radiator. The antenna’s configuration and the large diameter of the radiating elements contribute to the excellent bandwidth of the antenna system, and also inhibits corona discharge.

ERI offers 4, 8, 12, and 16-bay versions of its AXIOM® master FM antenna in Medium and High Power versions. The AXIOM is a specially designed antenna system that provides high input power handling capability and can provide service as an auxiliary master FM antenna for systems that are limited to a bandwidth requirement of up to 18 MHz of the FM Band (8 MHz for the MPA Series) (88 MHz to 108 MHz). The antenna can be designed with a single RF input or can be configured as separate upper and lower antennas for higher power handling capability and redundancy.

The horizontally polarized azimuth pattern of the AXIOM series FM antenna is omnidirectional within ±2 dB when the antenna is pole or Lambda™ mounted atop a tower. Side mounting the antenna on a typical tower structure will affect the azimuth pattern. ERI offers a pattern measurement service to assist in determining the effect of the mounting structure on the antenna’s pattern. Using ERI’s pattern optimization service the pattern’s circularity may be improved through the addition of parasitically excited elements.

Utilize the ERI advantage, combine an ERI antenna with an ERI LAMBDA® Mounting Structure, Pattern Measurement, and Installation. Assure yourself of the best antenna/tower interaction. ERI’s Pattern Measurement service will provide the crucial answers concerning the relationship between the antenna mounting orientation and antenna pattern. Lambda Sections are designed to achieve optimum antenna performance while reducing weight and wind loads. Only ERI can offer you an antenna/tower/installation package that will achieve your highest expectations in a demanding FM radio market.


  • Low VSWR
  • Internal feed
  • Fully pressurized
  • Series fed radiating elements
  • Circular polarization
  • Welded feed connections
  • Superior VSWR band width
  • High input power capacity
  • Custom modifications are available
  • Corrosion resistant construction
  • Modular construction facilitates easy installation and repair
  • Minimal weather related VWSR problems
  • Beam tilt and/or null fill available
  • Half-wave spacing between elements available
  • Rugged brass construction
  • Stainless steel support brackets and hardware
  • Radomes or deicing heaters not normally required for radial ice less than ½-inch
  • Radomes or deicing heaters are available
  • Custom designed antenna supports; poles or Lambda™ tower sections are also available from ERI

Type Number Definition

a - b BC - HW - SP
  • a
    SHPA High Power AXIOM FM Antenna
  • MPA Medium Power AXIOM FM Antenna
  • b
    Number of bays (4, 8, 12, or 16)
  • Example
  • Description
    ERI AXIOM™ Series ROTOTILLER FM Antenna, twelve bay, 4 1/8 inch interbay line with 6 1/8 inch RF input, center fed, half wave length bay to bay spacing.
  • Special configurations available for up to 120 kW average power, when configured with a single RF input. Available with dual inputs for higher power handling capability.


  • Anti-rotation brackets
  • Beam tilt (center fed antennas only)
  • First null fill (center fed antennas only)
  • Second null fill (center fed antennas only)
  • Beam tilt and first null fill (center fed antennas only)
  • Radomes
  • Deicers (600w/220v)
  • Stem heaters (300w/220v)
  • Export packing

Mounting Information

Related Publications

AXIOM® SHPA Series High Power Circularly Polarized Master FM Antenna Product Brochure

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AXIOM® MPA Series Medium Power Circularly Polarized Master FM Antenna Product Brochure

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