Active vs. Passive

Introduction

Antennas are fundamental components of modern communication systems, serving as critical interfaces for transmitting and receiving electromagnetic waves. The proper selection of an antenna is vital to the overall performance of any communication system. An antenna must efficiently radiate or receive signals to minimize power loss and ensure optimal functionality.

This white paper explores the differences between active and passive antennas, providing insights into how to select the appropriate type to ensure reliable performance while meeting the specific needs of your application.

Active Antennas

Active antennas differ from passive ones by incorporating an integrated Low Noise Amplifier (LNA) that enhances the strength of weak incoming signals. The LNA is powered by an external source, such as a DC supply or batteries, and is critical for boosting signal gain while minimizing noise, particularly in low- signal environments. By amplifying weak signals before they reach the receiver, active antennas improve overall system performance, making them essential for long-range communication, satellite systems, and scenarios where signal attenuation is significant. The addition of the LNA allows the active antenna to deliver higher sensitivity and better signal-to-noise ratios, ensuring more reliable reception in challenging conditions. Maxtena active antennas are known for their high gain and low noise figures, making them ideal for UAV, UGV, IoT, smart cites, asset tracking, automotive applications.

For example, the M10HCT-A-TNC active GNSS antenna provides up to 35 dB of gain and a noise figure of 1.3 dB, ensuring reliable communication even in areas with weak signal coverage.

Passive Antennas

Passive antennas are widely employed in numerous applications, such as television and radio systems, due to their simplicity and effectiveness in environments with sufficient signal strength. They do not require an external power source and operate by receiving electromagnetic waves from the surrounding environment, which are then converted into electrical signals for use by connected electronic devices. The straightforward design of passive antennas makes them cost-effective and efficient for applications where signal amplification is unnecessary. Maxtena offers a wide range of passive antennas suitable for various applications. For example, the Maxtena M1575HCT-22P-SMA helical L1 passive GPS antenna is a reliable and durable option for GPS applications. This antenna provides a gain of up to 22 dBi and a VSWR of 1.5:1, ensuring accurate positioning and timing.

Comparison

The primary distinction between passive and active antennas lies in their approach to signal amplification. While passive antennas rely solely on the capture of ambient electromagnetic waves, active antennas incorporate an LNA to amplify weak signals. This amplification requires external power and enables active antennas to function effectively in situations where signal levels are insufficient, providing improved performance in long-distance or low-signal applications.

Antennas in GNSS Applications

For GNSS (Global Navigation Satellite System) applications, an active antenna is generally recommended over a passive antenna. Here are the key reasons:

Weak Signal Amplification

GNSS satellites are located at great distances (approximately 20,000 km from Earth), resulting in very weak signals by the time they reach a receiver on the ground. Active antennas, which incorporate a Low Noise Amplifier (LNA), amplify these weak signals before they reach the receiver, ensuring a stronger, more usable signal. In contrast, passive antennas rely solely on capturing the signal, which may be too weak to process effectively.

Enhanced Signal-to-Noise Ratio (SNR)

The inclusion of an LNA in an active antenna improves the signal-to- noise ratio (SNR) by amplifying the desired signal while minimizing noise. For GNSS receivers, this results in better performance, higher accuracy, and more reliable satellite tracking, which is crucial in applications that require precise positioning.

Cable Length Compensation

In many GNSS setups, the antenna is placed far from the receiver, such as on a vehicle’s roof or in outdoor environments. With a passive antenna, signal degradation over long cable runs can be a significant issue. However, an active antenna compensates for this loss by amplifying the signal before sending it through the cable, reducing the impact of attenuation.

Antenna is the more reliable and effective solution for ensuring strong signal reception and accuracy. When a Passive Antenna May Suffice A passive antenna may be a viable option for GNSS applications if:

• Signal strength is sufficiently strong, such as in low- interference environments.

• The antenna is positioned close to the receiver, minimizing signal loss due to cable length.

However, in most practical GNSS applications, particularly where signals are weak or cable runs are long, an active antenna is the more reliable and effective solution for ensuring strong signal reception and accuracy.