What are biconical antennas used for in EMC testing?

Biconical antennas are the industry-standard receiving antenna for radiated EMI emissions measurements from 30–300 MHz, and can also be used as transmitting antennas for radiated immunity testing. They are required or recognized for testing per FCC Part 15, CISPR 11/22/32, EN 55011/55032, MIL-STD-461 RE102, RTCA DO-160, CISPR 25 (automotive), and IEC 60601-1-2 (medical devices). They are also used for normalized site attenuation (NSA) measurements to validate open area test sites (OATS) and semi-anechoic chambers (SAC).

What is the frequency range of Com-Power biconical antennas?

Com-Power offers biconical antennas covering 25 MHz to 6 GHz across the product line. The AB-300M and AB-900A both cover 25–300 MHz for standard FCC and CISPR commercial testing. The ABM-6000 microwave biconical covers 1–6 GHz and is specifically designed for CISPR 16-1-4 site VSWR (SVSWR) validation above 1 GHz.

What is the difference between the AB-300M and AB-900A?

Both cover 25–300 MHz and meet identical regulatory requirements — they are interchangeable for FCC, CISPR, and MIL-STD testing. The key difference is the feed design: the AB-300M uses a center-fed structure, while the AB-900A uses a gamma-match feed which can offer slightly improved VSWR at the band edges (25–30 MHz and 280–300 MHz). Both carry ANSI C63.5 and CISPR 16-1-4 compliance and come with individual NIST-traceable calibration. Choose based on lab preference, consistency with existing equipment, or specific test house requirements.

Should I choose fixed or collapsible elements?

Both provide equivalent RF performance and meet identical ANSI C63.5 and CISPR 16-1-4 requirements. Choose fixed elements for permanent lab installations where mechanical stability and simplicity are priorities. Choose collapsible elements for mobile test labs, field use, or multi-site testing — they fold down to roughly one-third the length for compact storage and transport in standard shipping cases.

Can biconical antennas be used for both emissions and immunity testing?

Yes. The AB-300M and AB-900A handle up to 50W continuous power, making them suitable as transmitting antennas for moderate radiated immunity levels (approximately 20–30 V/m at 1–3 meters with an appropriate amplifier). For higher immunity levels requiring more than 50W, a log periodic or CombiLog antenna is recommended instead. The ABM-6000 is primarily a receive or low-power transmit antenna used for site validation, not general immunity testing.

Are Com-Power biconical antennas individually calibrated?

Yes. The AB-300M and AB-900A are individually calibrated per ANSI C63.5 with NIST traceability, and each antenna ships with its own calibration data. Antennas conforming to ANSI C63.5 Figure G.1 physical dimensions can also use published Geometric Site Calibration Factor (GSCF) values for NSA measurements, eliminating the need for costly custom site calibration. ISO 17025 accredited calibration is available through Com-Power's calibration services.

Why is the ABM-6000 used for CISPR 16-1-4 site validation above 1 GHz?

CISPR 16-1-4 requires the transmit antenna for SVSWR measurements to have a dipole-like, omnidirectional radiation pattern. Horn antennas are too directional, and log periodic antennas lose their omnidirectional character at higher frequencies. The ABM-6000 maintains true biconical/dipole pattern characteristics throughout 1–6 GHz, making it the technically correct and standards-compliant choice for this specific site qualification procedure.

What EMC standards do Com-Power biconical antennas comply with?

Com-Power biconical antennas comply with FCC Part 15, CISPR 11, CISPR 22, CISPR 25, CISPR 32, CISPR 16-1-4, EN 55011, EN 55032, ANSI C63.4, ANSI C63.5, MIL-STD-461 RE102, RTCA DO-160, IEC 60601-1-2, and IEC 61000-4-3. The ABM-6000 additionally supports CISPR 16-1-4 Annex D (SVSWR) and IEC 61000-4-3 harmonic measurements above 1 GHz.

Why Biconical for 30-300 MHz?

This frequency range captures critical emissions from digital clocks (30-200 MHz), switching power supplies, microprocessors, and intentional radiators. Biconical antennas provide the flat frequency response and consistent measurement geometry required by regulatory test standards, and their physical dimensions conform to ANSI C63.5 allowing use of published gain and site calibration factors.

🔷 AB-300M: 25-300 MHz Standard Biconical

Applications & Use Cases:

• FCC Part 15 Verification: Primary antenna for Class A and Class B digital device testing at 30-300 MHz per ANSI C63.4. Covers emissions from desktop computers, peripherals, IT equipment, and unintentional radiators.
• CISPR 11/22/32 Compliance: ISM equipment, ITE (Information Technology Equipment), and multimedia equipment testing per EN 55011, EN 55032 for CE marking in European market.
• CISPR 25 Automotive: Radiated emissions from vehicle electronic components (ECUs, infotainment, sensors) and wiring harnesses per automotive OEM specifications and international standards.
• RTCA DO-160 Aviation: Avionics equipment radiated emissions testing for commercial and military aircraft certification (Section 21, Category M emissions).
• NSA Site Validation: ANSI C63.4 and CISPR 16-1-4 Normalized Site Attenuation measurements using AB-300M as both transmit and receive antenna. Physical dimensions match ANSI C63.5 Figure G.1 allowing use of published GSCF (Geometric Site Calibration Factor) values, eliminating expensive custom antenna calibration.
• MIL-STD-461 RE102: Radiated emissions measurements from military equipment and subsystems in 30-200 MHz region (typically transitions to horn antennas >200 MHz).
• Medical Devices (IEC 60601-1-2): Radiated emissions testing for medical electrical equipment and systems to ensure patient safety and device reliability in healthcare environments.
• Pre-Compliance Testing: In-house emissions screening before formal certification testing, identifying problem frequencies early in product development to reduce compliance costs.

Test Environment Suitability:

• Semi-Anechoic Chamber (SAC): Excellent - standard antenna for 3m/10m chamber testing per ANSI C63.4, CISPR 16-1-4
• Open Area Test Site (OATS): Excellent - weather-resistant construction, conforms to outdoor test site requirements, collapsible version portable for multi-site use
• Shielded Room: Very Good - omnidirectional pattern provides consistent coverage, minimal cable radiation when properly oriented
• Radiated Immunity: Good - 50W power handling suitable for moderate immunity levels (20-30 V/m at 1-3 meters with amplifier)

Setup Tips: Mount antenna with axis parallel to ground plane for vertical polarization measurements (standard configuration). For horizontal polarization, rotate antenna 90° on tripod. Maintain minimum height of 1 meter above ground plane per ANSI C63.4. Use collapsible element version for storage and transportation; fixed elements provide maximum mechanical stability for permanent installations.

🔷 AB-900A: 25-300 MHz Gamma-Match Biconical

AB-900A vs AB-300M - Which to Choose?

Applications:

All applications listed for AB-300M apply equally to AB-900A. Common reasons to choose AB-900A:

• Laboratory already uses AB-900A (consistency across test equipment)
• Preference for gamma-match impedance characteristics
• Backup antenna for AB-300M (diversified inventory)
• Specific test house or customer specification requiring gamma-match design

Setup Tips: Identical setup to AB-300M. Both antennas use same mounting hardware, cable connections, and polarization adjustment procedures. Calibration data specific to each antenna must be applied in measurement software.

🔷 ABM-6000: 1-6 GHz Microwave Biconical

Applications & Use Cases:

• CISPR 16-1-4 Site VSWR >1 GHz: THE primary application for ABM-6000. CISPR 16-1-4 Annex D specifies the Site Voltage Standing Wave Ratio (SVSWR) method for validating test sites above 1 GHz. The ABM-6000's dipole-like pattern and omnidirectional characteristics make it ideal as the transmit source antenna while a second antenna (typically horn or log periodic) serves as the receive antenna. This procedure validates the electromagnetic environment of semi-anechoic chambers and OATS facilities.
• Chamber Quiet Zone Verification: The omnidirectional pattern enables efficient mapping of field uniformity across the test volume in anechoic chambers at 1-6 GHz, identifying reflections or standing waves that could compromise measurement accuracy.
• WiFi 5/6 GHz Band Testing: Covers 2.4 GHz (WiFi 4/5/6), 5 GHz UNII bands (WiFi 5/6/6E), and 6 GHz (WiFi 6E) for radiated emissions measurements from wireless routers, access points, and client devices.
• 5G Sub-6 GHz Testing: Frequency range covers lower 5G FR1 bands (1-6 GHz) for testing base stations, small cells, and user equipment emissions.
• ISM Band Measurements: 2.4 GHz and 5.8 GHz ISM band emissions from Bluetooth, ZigBee, industrial wireless sensors, and license-free communication devices.
• Radar Emissions (Low Power): Detection of emissions from short-range radar systems, particularly 2.4 GHz and 5.8 GHz radar sensors in the covered frequency range.
• Research & Development: Pattern measurements, antenna characterization, and electromagnetic field mapping in 1-6 GHz range where omnidirectional pattern is beneficial.

Why ABM-6000 for Site VSWR?

Setup Tips: For SVSWR measurements, mount ABM-6000 as transmit antenna with axis perpendicular to measurement axis. Rotate receive antenna (horn or log periodic) through 360° while monitoring received signal to identify reflections and calculate SVSWR. Maintain antenna separation per CISPR 16-1-4 requirements (typically 3 or 10 meters).

How Biconical Antennas Work

The biconical antenna operates on the principle of a wideband dipole. The two conical sections form a balanced transmission line that gradually transitions from the feed point (50Ω coaxial cable) to free space (377Ω). This gradual impedance transformation provides broadband matching across a wide frequency range without the need for discrete matching networks.

Radiation Mechanism: Current flows along the conical elements, creating a radiation pattern similar to a dipole antenna. The cone angle and element length determine the operating bandwidth. Typical cone angles of 30-60° provide octave or decade bandwidth (e.g., 30-300 MHz = 1 decade).

Polarization: The antenna is linearly polarized along its axis. When mounted horizontally (parallel to ground), it produces vertically polarized radiation. Rotating 90° produces horizontal polarization. This makes biconicals ideal for regulatory testing requiring both polarization measurements.

Why Biconicals for NSA Measurements?

Normalized Site Attenuation (NSA) is the key validation procedure for Open Area Test Sites (OATS) and Semi-Anechoic Chambers (SAC) per ANSI C63.4 and CISPR 16-1-4. It verifies that the test site provides a free-space-equivalent electromagnetic environment by comparing measured site attenuation against theoretical values.

The ANSI C63.5 Advantage: Biconical antennas conforming to ANSI C63.5 Figure G.1 physical dimensions can use published Geometric Site Calibration Factor (GSCF) values. This eliminates the need for expensive custom NSA antenna calibration, reducing validation costs by $3,000-$5,000 per antenna pair.

Procedure Overview:

1. Place transmit biconical antenna at one end of test site (3m or 10m distance)
2. Place receive biconical antenna at opposite end, same height
3. Inject known signal into transmit antenna, measure received signal
4. Calculate actual site attenuation from signal levels and antenna factors
5. Compare to theoretical NSA values (includes GSCF correction)
6. Repeat at multiple heights (1-4m vertical scan) and both polarizations
7. Site passes if measured NSA is within ±4 dB of theoretical NSA at each frequency

AB-300M/AB-900A for NSA: Step-by-Step

Equipment Required:

• Two identical biconical antennas (AB-300M or AB-900A)
• Signal generator (tracking generator or separate CW source)
• EMI receiver or spectrum analyzer
• Low-loss coaxial cables (calibrated insertion loss)
• Height-adjustable antenna masts (motorized preferred)
• Antenna factors for both antennas (from individual calibration)

Critical Setup Parameters:

• Antenna separation: 3 meters or 10 meters (per test site design)
• Height scan range: 1 to 4 meters above ground plane
• Frequency range: 30-300 MHz (30-200 MHz for some standards)
• Both antennas oriented for same polarization (vertical or horizontal)
• Feed cables positioned to minimize radiation (perpendicular to measurement axis)

Radiated Emissions Testing Setup

1. Antenna Mounting: Mount biconical on tripod or mast. For vertical polarization, position antenna with axis horizontal (parallel to ground). Set initial height per standard (typically 1m for preliminary scans).
2. Cable Routing: Route coax cable perpendicular to measurement axis to minimize cable radiation. Use ferrite cores on cable near antenna if cable radiation suspected. Keep cable at least 0.5m from EUT.
3. Polarization Setup: For vertical polarization, antenna axis is horizontal. For horizontal polarization, rotate antenna 90° on mount (axis becomes vertical). Most testing requires both polarizations.
4. EUT Positioning: Place Equipment Under Test (EUT) on turntable at specified distance (3m or 10m from antenna). Height depends on product type: tabletop devices on 0.8m table, floor-standing on floor.
5. Height Scanning: During emissions testing, antenna height is varied from 1m to 4m to find maximum emission for each frequency. Automated positioners improve repeatability and reduce test time.
6. Measurement Procedure: Connect antenna to EMI receiver. Perform frequency sweep 30-300 MHz. Apply antenna factor correction (dB) to receiver reading (dBμV) to obtain field strength (dBμV/m). Compare to regulatory limit.

Radiated Immunity Testing Setup

1. System Configuration: Signal generator → RF amplifier (50W minimum) → biconical antenna → EUT. Use directional coupler between amplifier and antenna to monitor forward/reflected power.
2. Field Strength Calibration: Before testing, measure field strength at EUT location using calibrated field probe. Adjust amplifier output to achieve required immunity level (e.g., 3 V/m, 10 V/m per IEC 61000-4-3).
3. Antenna Positioning: Position antenna at specified distance (typically 3m) from EUT. Antenna height fixed at specific value (often 1.5m for tabletop EUT).
4. Power Monitoring: Continuously monitor forward power (should not exceed 50W) and reflected power (VSWR should be <2:1). High reflected power indicates impedance mismatch.
5. Frequency Sweep: Apply modulated RF field (80% AM at 1 kHz per IEC 61000-4-3) while sweeping 80-300 MHz (or other specified range). Dwell 15 seconds minimum at each frequency.
6. EUT Monitoring: Observe EUT for malfunctions, degradation, or loss of function during immunity sweep. Document any failures or anomalies.

Common Setup Issues & Solutions

• Issue: Measurement results differ significantly between vertical and horizontal polarization
  Solution: Verify antenna is properly rotated 90°. Check for cable radiation by re-routing cable perpendicular to axis. Ensure ground plane is adequate size.
• Issue: Measured emissions higher than expected
  Solution: Check for cable radiation (most common cause). Verify antenna factor calibration is correctly applied. Inspect for ambient RF interference.
• Issue: High VSWR in immunity testing
  Solution: Verify antenna is within 25-300 MHz operating range. Check cable connections. Consider optional 5dB impedance matching pad per CISPR 16-1-4 for immunity use.
• Issue: Inconsistent NSA results
  Solution: Verify both antennas are identical models with proper calibration data. Check for absorber degradation in chamber. Ensure no metallic objects in measurement zone.
• Issue: Collapsible elements not making good electrical contact
  Solution: Clean element joints with contact cleaner. Ensure elements are fully extended and locked. Check for corrosion (particularly after outdoor use).

Performance Equivalence:

When properly assembled and maintained, collapsible element biconicals provide equivalent RF performance to fixed element versions. Both meet identical ANSI C63.5 and CISPR 16-1-4 requirements. The choice is purely based on operational needs (portability vs permanent installation) rather than electrical performance.