What is a log periodic dipole array (LPDA) antenna and how does it work?

A Log Periodic Dipole Array (LPDA) consists of multiple dipole elements of graduated sizes arranged along a common feed line, with element lengths and spacing following a logarithmic progression. This geometric relationship creates a “frequency-independent” antenna that maintains relatively constant gain, impedance, and radiation pattern across multi-octave bandwidths. At any given frequency, only a small group of elements near resonance (the “active region”) contribute significantly to radiation — and as frequency changes, the active region shifts automatically along the array. This eliminates the need for element tuning, switching, or operator intervention during swept-frequency measurements, making LPDAs far faster to use than tuned dipoles across the same frequency range.

What frequency ranges do Com-Power log periodic antennas cover?

Com-Power offers three log periodic antenna models covering different frequency bands. The ALC-100 covers 300 MHz to 1 GHz (usable from 200 MHz) and is the compact, lightweight option for emissions and light immunity testing. The ALP-100 covers 200 MHz to 1 GHz with 500W power handling, designed for high-power radiated immunity and dual-purpose emissions use. The ALFM-80120 covers 88 MHz to 108 MHz (usable from 80 MHz to 120 MHz) with 2500W power handling, purpose-built for FM band radiated immunity testing. Together they cover the upper half of the standard FCC/CISPR radiated emissions test range and all common cellular, FM, VHF/UHF, and ISM frequency bands.

What is the difference between the ALC-100 and ALP-100 log periodic antennas?

Both cover 200–1000 MHz and deliver identical RF performance characteristics. The key difference is power handling: the ALC-100 handles up to 50W continuous and is compact (approximately 13 inches shorter, 2 lbs / 0.9 kg), making it the preferred choice for radiated emissions measurements, pre-compliance scanning, and portable use. The ALP-100 handles up to 500W continuous and is heavier (5 lb / 2.2 kg) with extended elements designed for the power load, making it the correct choice for radiated immunity testing requiring 30–150 V/m field strengths at 3 meters. Labs doing both emissions and immunity work in the 200 MHz–1 GHz range often prefer the ALP-100 as a single antenna for both applications.

Which EMC standards can be tested with Com-Power log periodic antennas?

Com-Power log periodic antennas support testing under a wide range of standards including FCC Part 15, FCC Part 18, CISPR 11, CISPR 22, CISPR 25, CISPR 32 (radiated emissions), IEC 61000-4-3 (radiated immunity), ISO 11452-2 (automotive radiated immunity), MIL-STD-461 RE102 and RS103 (military radiated emissions and susceptibility), RTCA DO-160 Section 20 (avionics radiated susceptibility), SAE automotive EMC standards, and applicable EN/CE standards for the European market. The ALP-100 and ALFM-80120 high-power models are particularly suited for standards requiring field strengths above 10 V/m.

How do log periodic antennas compare to tuned dipoles and biconical antennas for EMC testing?

Tuned dipoles require physical element adjustment at every test frequency — for a 200 MHz–1 GHz sweep this means 15–20 tuning stops, adding 2–3 hours of test time. Log periodic antennas sweep the entire range continuously without any reconfiguration, reducing test time dramatically. Compared to biconical antennas, log periodics offer better directivity (5–7 dBi vs. near-omnidirectional for biconicals) which reduces multipath reflections in chambers, and they start at 200 MHz rather than 30 MHz. The typical practical combination for FCC/CISPR testing is a biconical antenna for 30–200 MHz and a log periodic for 200 MHz–1 GHz — requiring only one antenna swap at 200 MHz rather than 15+ tuning stops. For NSA site calibration, tuned dipoles remain the mandated reference; log periodics cannot substitute for that specific application.

How are Com-Power log periodic antennas calibrated?

The ALC-100 and ALP-100 are individually calibrated per ANSI C63.5 with NIST traceability. The ALFM-80120 is individually calibrated per SAE ARP 958 with NIST traceability. All calibration certificates and calibration data files (antenna factor vs. frequency tables) are provided with every antenna. ISO 17025 accredited calibration is also available upon request for labs whose quality systems require an externally accredited certificate. The individual antenna factor data — rather than published nominal values — should always be loaded into your EMI receiver or measurement software before testing to ensure accurate field strength calculations.

What field strengths can the ALP-100 generate for radiated immunity testing?

At 3 meters test distance, the ALP-100 at 500W continuous input can generate approximately 100–150 V/m depending on frequency and antenna gain. At lower power levels: 100W produces approximately 30–40 V/m (suitable for commercial IEC 61000-4-3 immunity), 200W produces approximately 50–60 V/m (industrial immunity), and 350W produces approximately 70–90 V/m (automotive and aerospace). These are approximate values — field strength varies with frequency and antenna gain across the band. Always perform field uniformity mapping per ISO 11452-2 Annex A using a calibrated field probe before beginning immunity tests. Monitor forward and reflected power continuously to protect your amplifier.

What is the ALFM-80120 used for and why does it handle 2500 watts?

The ALFM-80120 is a purpose-built high-power LPDA for the FM broadcast band (88–108 MHz, usable from 80 to 120 MHz). The extremely high 2500W CW power rating is required because generating strong RF immunity test fields at these lower frequencies demands significantly more transmit power than at higher frequencies — at 100 MHz, producing 100 V/m at 3 meters requires approximately 5–10× more amplifier power than at 500 MHz for the same antenna aperture. The 7-16 DIN female connector is used instead of Type-N to handle this power level safely. Typical applications include automotive FM immunity testing (SAE J551, ISO 11452-2), broadcast equipment immunity verification, and avionics FM band susceptibility per RTCA DO-160. Its calibration per SAE ARP 958 with NIST traceability makes it directly applicable to automotive and aerospace test programs.

📊 ALC-100: Compact Log Periodic Antenna (300 MHz – 1 GHz, 50W)

Key Applications:

• Radiated Emissions (FCC Part 15, CISPR 22/32): Primary antenna for 200–1000 MHz sweep. Eliminates 15–20 tuning stops required by tuned dipoles. Single setup for VHF communications, UHF TV, cellular bands, and ISM 900 MHz.
• Pre-Compliance Testing: Rapid emissions screening during product development. Sweep 200 MHz–1 GHz in minutes. Compact size enables easy relocation between chambers, benchtops, and troubleshooting setups.
• Automotive Component Testing (CISPR 25): Radiated emissions from vehicle ECUs, sensors, and entertainment systems. Directional pattern isolates component emissions during troubleshooting.
• Light Immunity Testing (IEC 61000-4-3): 50W power handling suitable for 10–20 V/m at 3 meters. Covers commercial immunity requirements in 200 MHz–1 GHz range.
• NSA Site Validation (Alternative Method): Many labs use calibrated log periodics as a practical alternative for 200 MHz–1 GHz NSA region. Must use individual calibration data and document deviation from standard procedure.
• Medical Device Testing (IEC 60601-1-2): Radiated emissions from medical electrical equipment covering microprocessor, display, and telemetry emissions.

📊 ALP-100: High-Power Log Periodic Antenna (200 MHz – 1 GHz, 500W)

Key Applications:

• Radiated Immunity Testing (IEC 61000-4-3, ISO 11452-2): 500W generates 100–150 V/m at 3 meters, meeting automotive (80–200 V/m), industrial (10–30 V/m), and military immunity requirements across 200 MHz–1 GHz in a single sweep.
• Automotive Immunity (ISO 11452-2): Meets automotive OEM requirements for safety-critical ECU immunity testing (ABS, airbag, steering). Covers cellular, FM, and VHF/UHF communication bands.
• MIL-STD-461 RS103: Radiated susceptibility for military and aerospace equipment. Covers 200 MHz–1 GHz portion of RS103 for ground, shipboard, and airborne platforms.
• RTCA DO-160 Section 20: Avionics radiated susceptibility across VHF/UHF communication and navigation bands. Covers all Categories A through M field strength levels.
• Dual Emissions / Immunity Labs: Full-service EMC labs use the ALP-100 as one antenna for both 200 MHz–1 GHz emissions measurement and immunity field generation, maximizing ROI.

📊 ALFM-80120: FM Band High-Power Log Periodic Antenna (88–108 MHz, 2500W)

Key Applications:

• Automotive FM Immunity (SAE J551, ISO 11452-2): Generating high-power RF fields in the FM band for automotive component immunity testing. The 2500W rating is required to achieve mandated field strengths at FM frequencies where physical antenna aperture is much larger.
• Broadcast Equipment Immunity: Testing FM receivers, tuners, and broadcast equipment for immunity to co-channel and adjacent-channel RF environments.
• RTCA DO-160 FM Band: Avionics FM navigation and communication band radiated susceptibility testing.
• High-Power EMC Labs: Purpose-built for labs with high-power amplifiers (1–3 kW) needing to test at the FM band frequencies that form part of a broader immunity sweep.