What is an active horn antenna and how does it differ from a passive horn?

An active horn antenna integrates a low-noise preamplifier (LNA) directly at the antenna feed point. This amplifies received signals before they travel through connecting cables, overcoming cable losses and dramatically improving measurement sensitivity — typically 30–40 dB better than a passive horn. A passive horn antenna has no built-in amplification and relies entirely on the receiver's sensitivity. Active horns are preferred when measuring low-level emissions above 1 GHz, where cable losses can exceed 10–20 dB and significantly degrade the signal-to-noise ratio.

What frequency ranges do the AHA-118 and AHA-840 cover?

The AHA-118 covers 1–18 GHz (usable from 700 MHz), making it suitable for 5G Sub-6 GHz (FR1), WiFi 2.4/5/6 GHz, Bluetooth, ISM bands, C/X/Ku-band satellite, and radar testing in the 1–18 GHz range. The AHA-840 covers 18–40 GHz for 5G mmWave (FR2), 24 GHz automotive radar, Ka-band satellite, and high-frequency R&D applications. Together, the two models provide continuous coverage from 700 MHz to 40 GHz.

Can active horn antennas be used for both emissions and immunity testing?

Yes. Both the AHA-118 and AHA-840 feature a bypassable preamplifier, allowing them to operate in transmit (immunity) mode as well as receive (emissions) mode. In receive mode, the preamp is active and provides 40 dB gain. In transmit mode, the preamp is bypassed and the antenna handles up to 300W (AHA-118 via coax) or 200W (AHA-840 via WR-28 waveguide). Always verify bypass is activated before applying transmit power to avoid damaging the preamplifier.

How do I power the preamplifier in an active horn antenna?

The preamplifier is powered via a bias-T (bias tee) inserted between the antenna and the receiver or cable run. The bias-T injects DC voltage (12–24 VDC) onto the coaxial cable while passing the RF signal simultaneously. Connect your DC power supply to the bias-T's DC port, the antenna to the RF+DC port, and your receiver to the RF-only port. Verify that the correct voltage is reaching the antenna — insufficient voltage is the most common cause of preamp failure in the field.

What EMC standards are active horn antennas used for?

Active horn antennas are used for radiated emissions measurements per FCC Part 15 (above 1 GHz), CISPR 32, CISPR 22, ETSI EN 301 893 (WiFi), ETSI EN 301 908 (5G/LTE), CISPR 25 (automotive, above 1 GHz), and MIL-STD-461 RE102/RE103. They are also used for chamber validation (site VSWR, quiet zone measurements) per CISPR 16-1-4 above 1 GHz, and for radiated immunity per IEC 61000-4-3 in transmit mode.

Can the preamplifier saturate, and how do I prevent it?

Yes. If the input signal exceeds approximately −20 dBm, the preamplifier can saturate, causing compressed or distorted readings. This is most likely to occur when testing near strong transmitters, outdoors on an OATS, or when measuring high-power devices at close range. Insert a 3–10 dB external attenuator between the antenna input and the preamp to prevent saturation. Always check for signs of compression (flat response across frequency sweep, unusually stable readings) and reduce input signal level if suspected.

How are active horn antennas calibrated?

Each active horn ships with NIST-traceable calibration data covering both the antenna factor and the preamplifier gain as a function of frequency. In measurement software, apply the net antenna factor (antenna factor minus preamp gain) to convert receiver readings (dBμV) to field strength (dBμV/m). Com-Power offers ISO 17025 accredited recalibration services. Annual verification of preamp gain with a signal generator is recommended, with full calibration every two years or following any physical incident.

How do I protect the preamplifier from static electricity and prevent it from blowing?

The integrated preamplifier is a sensitive low-noise amplifier (LNA) and is vulnerable to electrostatic discharge (ESD) and RF overload. Follow these precautions to protect it:

ESD Protection:

• Always wear an anti-static wrist strap grounded to the test bench when handling the antenna connector or making cable connections.
• Keep the antenna's RF connector capped with the supplied dust cap whenever the antenna is not in use — this also acts as a partial ESD shield.
• When connecting cables, ground yourself and the cable shield before mating the connector to the antenna port. Touch the cable connector's outer shell to the antenna body first, then seat and tighten.
• Store the antenna in its original anti-static foam case. Avoid storing it in standard foam or bubble wrap, which can generate static charge.
• In dry environments (humidity below 30%), ESD risk increases significantly — take extra care and consider using an ionizing air blower near the workbench.

RF Overload Prevention:

• Never apply transmit power to the antenna without first verifying and activating the preamp bypass. Even a brief burst of RF power with the preamp active can permanently damage or destroy the LNA.
• Always insert external attenuators (3–10 dB) when measuring strong signals or testing near high-power transmitters to keep input levels below −20 dBm.
• Do not connect the antenna to a powered amplifier output — even momentarily — without the bypass active and a directional coupler or power meter in line to monitor power levels.
• When switching between receive and transmit mode, always power down the amplifier fully before changing the bypass state, then bring the amplifier back up gradually.

General Handling:

• Verify DC bias voltage is within the specified range (12–24 VDC) before powering the preamp — overvoltage will damage the LNA circuit.
• Do not power the preamp without an antenna or matched load connected to the RF port — an open or short on the RF port under power can reflect energy into the LNA.
• Inspect connectors for bent pins, contamination, or corrosion before each connection. A damaged connector can cause impedance spikes that stress the preamp input stage.

Which active horn antenna should I choose — AHA-118 or AHA-840?

Choose the AHA-118 if your testing covers frequencies below 18 GHz — it handles 5G Sub-6, WiFi, Bluetooth, ISM, C/X/Ku-band satellite, and general microwave emissions from 700 MHz to 18 GHz. Choose the AHA-840 if you need to test 5G mmWave (FR2) bands, 24 GHz automotive radar, Ka-band satellite terminals, or other applications specifically above 18 GHz. For labs testing the full spectrum, both antennas together provide seamless coverage from 700 MHz to 40 GHz. If uncertain, use the Antenna Finder Wizard for a side-by-side comparison.

Key Advantage:

At microwave frequencies (>1 GHz), cable losses can exceed 10-20 dB. By amplifying signals at the antenna before cable transmission, active horns recover these losses and can detect emissions 30-40 dB lower than passive antenna setups with equivalent receivers.

📡 AHA-118: 1-18 GHz Active Horn (Usable from 700 MHz)

Applications & Use Cases:

• 5G Device Testing (Sub-6 GHz): Covers all 5G FR1 bands (600 MHz - 6 GHz) for testing smartphones, tablets, IoT devices, and wireless infrastructure. The 40 dB preamp enables detection of weak spurious emissions from power amplifiers and local oscillators.
• WiFi 2.4/5/6 GHz Testing: High sensitivity ideal for measuring low-level emissions from WiFi 6E devices (2.4/5/6 GHz) and WiFi 7 devices per FCC Part 15, ETSI EN 301 893
• ISM Band Testing: Covers 2.4 GHz (Bluetooth, ZigBee), 5.8 GHz (UNII bands), and other ISM frequencies for wireless sensor networks, smart home devices, industrial controls
• Automotive Radar Emissions: 24 GHz short-range radar (parking sensors, blind spot detection) emissions testing per CISPR, automotive OEM specifications
• Satellite Communications: C-band (4-8 GHz), X-band (8-12 GHz), Ku-band (12-18 GHz) emissions from satellite terminals, transponders, earth stations
• Radar Systems: Air traffic control, weather radar, marine radar, military radar emissions testing from 1-18 GHz
• Low-Level Spurious Measurements: The 40 dB preamp brings receiver noise floor down to -140 dBm or better, enabling detection of spurious emissions 60-80 dB below carrier in wireless transmitters
• Chamber Validation: High-sensitivity measurements for site attenuation, site VSWR, quiet zone verification in anechoic chambers >1 GHz

Test Environment Suitability:

• Semi-Anechoic Chamber: Excellent - high sensitivity maximizes dynamic range for low-level emissions in controlled environment
• Fully Anechoic Chamber: Excellent - preamp compensates for longer cable runs from chamber to control room
• Shielded Room: Very Good - improved sensitivity in isolated environment, but monitor for preamp saturation from nearby transmitters
• OATS: Good - weather-resistant construction suitable for outdoor use, but external RF may saturate preamp (use attenuators if needed)

Setup Tips: Power the preamp using a bias-T inserted between antenna and receiver. For high-amplitude signals (>-20 dBm), insert external attenuators between antenna and preamp to prevent saturation. When used for immunity testing, ensure preamp bypass is activated and verify 300W power handling is not exceeded.

📡 AHA-840: 18-40 GHz Active mmWave Horn

Applications & Use Cases:

• 5G mmWave Testing (FR2): Covers all 5G FR2 bands (24.25-29.5 GHz n257/258/260/261, 37-40 GHz n260) for testing 5G base stations, small cells, mobile hotspots, CPE equipment, smartphones with mmWave capability
• Automotive Radar (77-81 GHz): Although antenna operates to 40 GHz, it can detect harmonic emissions and intermodulation products from automotive long-range radar (76-81 GHz) that fall into the 18-40 GHz range. For fundamental 77 GHz testing, use spectrum analyzer with mmWave mixer.
• 24 GHz Automotive Radar: Direct fundamental measurement of short-range radar emissions (parking sensors, blind-spot detection) at 24-24.25 GHz per CISPR 25, automotive OEM standards
• Satellite Ku/Ka-Band: Ku-band (12-18 GHz, requires AHA-118) and Ka-band (26.5-40 GHz) emissions from satellite terminals, VSAT equipment, satellite phones, ground stations
• Point-to-Point Microwave Links: E-band (71-76/81-86 GHz) harmonics and spurious emissions that fall into 18-40 GHz range from wireless backhaul equipment
• Radar Cross-Section (RCS) Measurements: Used in bistatic RCS test setups at 18-40 GHz for defense, aerospace, automotive applications
• mmWave Research & Development: High sensitivity enables detection of low-level emissions from mmWave prototypes, beam-forming arrays, phased array antennas, and experimental wireless systems

Test Environment Suitability:

• Anechoic Chamber: Excellent - controlled environment essential for mmWave testing; preamp critical due to high cable losses (>20 dB at 40 GHz)
• Shielded Room: Very Good - provides isolation from ambient mmWave signals (5G base stations, radar), preamp maximizes sensitivity
• OATS: Fair - mmWave testing typically done indoors due to atmospheric attenuation, rain fade, and difficulty maintaining alignment outdoors

Setup Tips: Use high-quality 2.92mm precision cables rated for 40 GHz. Keep cable lengths <3 feet where possible. For power >10W, remove coaxial adapter and connect amplifier directly to WR-28 waveguide flange (200W capability). Verify preamp power supply provides clean 12-24 VDC via bias-T.

When to Choose Active Horns:

Choose active horns when measuring low-level emissions (<-60 dBm), testing in anechoic chambers with long cable runs (>10 feet), working above 10 GHz where cable losses are severe, or when maximum sensitivity is critical. Choose passive horns when measuring high-power signals, operating in high-RF environments (to avoid saturation), when simplicity is preferred, or when budget is constrained.

Receive Mode Setup (Emissions Testing)

1. Power Connection: Connect 12-24 VDC power supply to bias-T input. Verify preamp LED indicator (if present) illuminates.
2. Cable Connection: Connect bias-T RF output to spectrum analyzer or EMI receiver input using quality coaxial cable rated for operating frequency (Type-N for AHA-118, 2.92mm for AHA-840).
3. Antenna Connection: Connect bias-T RF/DC output to antenna input port. The bias-T supplies DC power while passing RF signal bidirectionally.
4. Preamp Verification: Inject a known low-level signal (e.g., -80 dBm from signal generator) and verify 40 dB gain. Measured level should be approximately -40 dBm.
5. Saturation Check: If measuring strong signals (>-30 dBm), insert external attenuators (3-10 dB) between antenna and preamp to prevent compression/saturation.
6. Calibration: Apply antenna factor correction (provided with antenna) PLUS preamp gain correction in measurement software or receiver.

Transmit Mode Setup (Immunity Testing)

1. Bypass Preamp: If antenna has physical bypass switch, activate it. If controlled electronically, apply bypass voltage per manufacturer instructions (typically 24V).
2. Remove Bias-T: Disconnect bias-T from signal path. Connect RF amplifier output directly to antenna input.
3. Power Verification: Verify transmit power does not exceed antenna rating: AHA-118 = 300W, AHA-840 = 10W coax / 200W waveguide.
4. Waveguide Option (AHA-840): For >10W, remove coaxial adapter and connect amplifier directly to WR-28 waveguide flange (200W capable).
5. Forward/Reflected Power: Insert directional coupler or power meter between amplifier and antenna to monitor forward/reflected power and ensure VSWR <2:1.
6. Field Strength Calibration: Measure field strength at test distance using calibrated field probe. Adjust amplifier output to achieve required immunity level (e.g., 200 V/m).

Common Setup Issues & Solutions

• Issue: No signal received / preamp not working
  Solution: Verify DC voltage at antenna port (should be 12-24V). Check bias-T connections and power supply.
• Issue: Signal levels too high / receiver overload
  Solution: Preamp may be saturating. Insert 6-10 dB attenuator between antenna and preamp input.
• Issue: Unstable measurements / intermittent signal
  Solution: Check cable connections, especially at 2.92mm connectors (AHA-840). Ensure torque wrench used for precision connectors.
• Issue: Low field strength in immunity mode
  Solution: Verify preamp bypass is activated. Check for high VSWR (>2:1) indicating impedance mismatch.