Measurement of Ambient Millimeter Wave Exposure Levels around Small Base Stations

Abstract

Measurement of Ambient Millimeter Wave Exposure Levels around Small Base Stations My note: Averaging exposure over time, 30 minutes in this study, ensures very low power densities for 5G millimeter waves (MMW) especially when few (or no) 5G cell phones are downloading files using the MMW band. Assessing MMW exposure from a 5G base station is both a costly and tricky endeavor especially if one is concerned about peak exposures: "... when a UE was used to attract the beam toward the measurement location, the maximum instantaneous exposure measured was -60 dBm (0.8% public MPE)." This was 381 times the 30-min average maximum exposure at that location. Bushberg JT, Butcher MJ. Measurement of Ambient Millimeter Wave Exposure Levels around Small Base Stations. Health Phys. 2025 Jan 13. doi: 10.1097/HP.0000000000001935. Abstract This study investigated the implementation and impact of fifth-generation (5G) wireless millimeter wave (mmW) technology. 5G offers significant advancements over previous generations and supports additional frequency bands, including mmW, to enhance mobile broadband with ultra-reliable, low- latency communications, supporting a high volume of diverse communications. This technology is expected to enable billions of new connections in the Internet of Things (IoT), fostering innovations in various sectors including healthcare, manufacturing, and education. This research contributes to the understanding and safe implementation of this transformative technology. Global adoption of 5G is rapidly increasing, with over 1.5 billion subscriptions as of 2024, projected to reach 58% of all wireless subscriptions by 2029. Despite its benefits, 5G mmW installations have raised concerns regarding exposure to electromagnetic fields. This study was conducted using a dual-polarized horn antenna and relatively inexpensive spectrum analyzers to measure typical ambient mmW radiofrequency field power densities near operational radio base stations (RBS) in urban and suburban environments. The measurements were taken at various times of the day and in different weather conditions to ensure a comprehensive understanding of the ambient mmW exposure. The study's results provide reassuring evidence that the ambient mmW exposure from RBSs is significantly lower than the safety limits set by the Federal Communications Commission (FCC) and other international standards. The exposure levels ranged from 0.0003% to 0.0082% of the public maximum permissible exposure (MPE), with the highest levels being more than 25,000 times lower than the allowed continuous public exposure. This study concludes that typical mmW exposure from 5G RBSs is minimal and substantially below established safety limits. pubmed.ncbi.nlm.nih.gov Excerpts Table 1 - RF hardware. Device Description Manufacturer/Part Number Spectrum Analyzer #1 Spectrum Analyzer 24-43 GHz v.2 SAF/J0GSAP541B Spectrum Analyzer #2 Spectrum Compact 24-40 GHz v.2 SAF/J0GSAP741B Antenna 18.0-40.0GHz Dual Polarization Horn Antenna A-Info/LB-SJ-180400-KF RF Cable Assembly (x2) Sucoflex 102 500 mm Cable with 2.92 mm Connectors HUBER+SUHNER/SF102/11SK/11SK/500 mm Right Angle Adapter (x2) 2.92 mm Plug to 2.92 mm Jack Right Angle Adapter Dynawave/1101-9495-6200 Thirty-minute (30 min) measurements were made at three distance intervals (3-15, 15-30, and 35+ m) from the base of the RBS support structure as measured with a laser rangefinder (Fig. 3). These distance intervals were selected to highlight the fact that exposure levels can vary with distance and angle relative to the BTS. Locations were selected for alignment with the RBS antenna panels, line of sight to the antenna, and critically in a location that allowed for 30-min uninterrupted measurements. All the criteria could not be met for all locations. As seen in Fig. 4, the middle and far locations were selected off-boresight to avoid vehicle traffic and achieve line-of-sight. Following the 30-min measurement at each location, four additional 2-min measurements were made with the horn oriented at 0°, 90°, 180°, and 270° relative to the direction of the 30-min measurement to assess the presence of reflections and mmW signals from other RBSs in the area. An example is shown in Fig. 5. The first 2 min are oriented at the RBS, and the remaining time is at the other azimuths before returning to the RBS. At most of the measured RBSs, a 1-min sample acquisition was obtained with a mobile phone (UE) behind the horn antenna assembly. High-definition/large file-size video downloads were performed to attract the beam toward the measurement location. The increase in signal strength over the RBS signal bandwidth was used to confirm that the measurement equipment and RBS were operating as expected and to estimate the maximum exposure corresponding to the RBS operating close to full capacity. It was noted that some RBS operated at 800, 400, and 300 MHz, corresponding to eight, four, and three 100- MHz channels. The spectrum analyzers display and record received signal power in units of decibels relative to a milliwatt (dBm). The analyzers required a little over 10 s to scan the entire 1 GHz spectrum, using overlapping 100 kHz bins spaced every 30 kHz. SAF settings are listed in Table 2. Before measurements, the spectrum analyzers, the horn antenna, and the feedlines were checked with an RF source at mmW frequencies and found to agree with the expected levels. Each frequency bin was averaged throughout the measurement, and the bin with the highest received averaged power was selected to represent the highest time-average exposure at the base station. Extrapolating from the highest received averaged power bin provides a very conservative assessment of power over the entire spectrum based on the measurements. The highest received averaged power bin was converted to power received over the operating bandwidth, considering the ratio of the bin bandwidth to the observed bandwidth of the signal and the loss of the transmission lines. The power density for both polarizations was summed to determine the time-averaged total exposure and compared with the exposure limit. This result is presented for three distances for each RBS. RBSs in four geographic areas—Los Angeles, CA; Arlington, VA; Washington, DC; and Providence, RI—were selected. All have deployed different manufacturers’ equipment by different operators, including T- Mobile and AT&T. Locations included urban commercial and residential areas. Table 3 shows data of 30-min measurement results at different distance intervals, indicating the maximum average bin over that 30-min expressed as a percent of the General Public exposure limit. The ambient mmW measurements ranged from −77 dBm down to −94 dBm, which, when polarizations are combined, correspond to total exposure levels of 0.0082% to 0.0003% of the public maximum permissible exposure (MPE). The noise floor adjacent to the measured signal was −98 dBm (Fig. 6). By comparison, when a UE was used to attract the beam toward the measurement location, the maximum instantaneous exposure measured was -60 dBm (0.8% public MPE) (Fig. 7). At the same location, the 30-min average maximum 100 kHz bin is −83 dBm (0.0021% GP). The figures show only one polarization at RBS CYLA4-7 and include the 100 MHz channel average. Conclusions One of the distinguishing characteristics of 5G mmW base stations is dynamic beamforming using a multi-element antenna. When the scanning beams detect a UE in its service environment, the RBS creates a narrow beam directed toward UEs requesting service. Even when an obstacle in its direct path blocks the beam, the system will use multiple directed beams for spatial multiplexing. Spectral analysis of mmW signals typically requires expensive portable spectrum analyzer equipment, costing upwards of $70,000. Substantially less expensive equipment (approximately $20,000) can be used. This report demonstrates that a cross-polarized horn and two spectrum analyzers can make power density measurements of orthogonal polarization and capture the total mmW exposure from an RBS. RF surveys were conducted in the United States in various urban environments, using different frequency bands, operators, and equipment manufacturers. Measurements at several distances from operational radio base stations (RBS) indicate that the typical exposure from an mmW RBS at ground level was an exceedingly small fraction of the FCC public safety limit. The overall measurements of ambient mmW exposure ranged from 0.0003% to 0.0044% of the FCC public MPE. Even the highest exposure level was more than 25,000 times lower than allowed for continuous public exposure. This work is made possible through the funding provided by the Mobile & Wireless Forum under the project grant number TBD. The authors alone are responsible for the content of this paper.

AI evidence extraction

Main findings

Using a dual-polarized horn antenna and spectrum analyzers, 30-min ambient measurements near operational 5G mmW radio base stations in urban/suburban U.S. locations found exposure levels of 0.0003% to 0.0082% of the public MPE (reported as far below FCC and other standards). In a test intended to attract beamforming toward the measurement location using a user equipment (UE) download, the maximum instantaneous exposure reported was -60 dBm (0.8% public MPE), compared with a 30-min average maximum at that location of -83 dBm (0.0021% public MPE).

Outcomes measured

• Ambient mmW RF power density near operational 5G radio base stations expressed as % of public maximum permissible exposure (MPE)
• Maximum instantaneous exposure during UE-attracted beam test expressed as % of public MPE
• Received signal power levels (dBm) over measured bands

Limitations

• Specific mmW carrier frequencies were not stated in the provided abstract/excerpts (hardware described as covering ~18–43 GHz).
• Number of base stations/measurement sites and total number of measurements were not stated in the provided abstract/excerpts.
• Measurements were taken at selected ground-level locations with constraints (e.g., line-of-sight, avoiding traffic) and may not represent all possible positions/conditions.
• Primary results are time-averaged over 30 minutes; instantaneous/peak conditions were only assessed via limited UE-attraction sampling as described.

Suggested hubs

• 5g-policy (0.78)
  Study measures ambient 5G mmWave exposure near small base stations and compares to FCC/public MPE limits.

{
    "study_type": "exposure_assessment",
    "exposure": {
        "band": "mmWave",
        "source": "5G small base station / radio base station (RBS)",
        "frequency_mhz": null,
        "sar_wkg": null,
        "duration": "30-min measurements (plus additional 2-min azimuth checks; 1-min UE-attracted beam test at most sites)"
    },
    "population": null,
    "sample_size": null,
    "outcomes": [
        "Ambient mmW RF power density near operational 5G radio base stations expressed as % of public maximum permissible exposure (MPE)",
        "Maximum instantaneous exposure during UE-attracted beam test expressed as % of public MPE",
        "Received signal power levels (dBm) over measured bands"
    ],
    "main_findings": "Using a dual-polarized horn antenna and spectrum analyzers, 30-min ambient measurements near operational 5G mmW radio base stations in urban/suburban U.S. locations found exposure levels of 0.0003% to 0.0082% of the public MPE (reported as far below FCC and other standards). In a test intended to attract beamforming toward the measurement location using a user equipment (UE) download, the maximum instantaneous exposure reported was -60 dBm (0.8% public MPE), compared with a 30-min average maximum at that location of -83 dBm (0.0021% public MPE).",
    "effect_direction": "no_effect",
    "limitations": [
        "Specific mmW carrier frequencies were not stated in the provided abstract/excerpts (hardware described as covering ~18–43 GHz).",
        "Number of base stations/measurement sites and total number of measurements were not stated in the provided abstract/excerpts.",
        "Measurements were taken at selected ground-level locations with constraints (e.g., line-of-sight, avoiding traffic) and may not represent all possible positions/conditions.",
        "Primary results are time-averaged over 30 minutes; instantaneous/peak conditions were only assessed via limited UE-attraction sampling as described."
    ],
    "evidence_strength": "low",
    "confidence": 0.7399999999999999911182158029987476766109466552734375,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "5G",
        "millimeter wave",
        "mmW",
        "radio base station",
        "small cell",
        "ambient exposure",
        "power density",
        "beamforming",
        "spectrum analyzer",
        "maximum permissible exposure",
        "FCC",
        "urban",
        "suburban"
    ],
    "suggested_hubs": [
        {
            "slug": "5g-policy",
            "weight": 0.7800000000000000266453525910037569701671600341796875,
            "reason": "Study measures ambient 5G mmWave exposure near small base stations and compares to FCC/public MPE limits."
        }
    ]
}

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