Compare Passive DAS vs Active DAS vs Hybrid DAS & explore advantages and disadvantages

Distributed Antenna Systems (DAS) are crucial for enhancing wireless network coverage and capacity within buildings, stadiums, airports, and other complex environments. There are three main types of DAS solutions viz. Active DAS, Passive DAS, and Hybrid DAS; each with its own set of characteristics, advantages, disadvantages and use cases. Understanding the differences between these DAS types is essential for selecting the most suitable solution to ensure optimal network performance, coverage and cost efficiency based on specific deployment needs.

It is difficult to achieve appropriate signal strength inside indoor places to meet optimum Signal to Noise Ratio (SNR). DAS has been developed to overcome this situation. DAS uses single RF source and divides the same to various RF antennas installed as per requirements in indoor places for better signal distribution of cellular signal.

Active DAS | Active Distributed Antenna System

Active DAS systems use active electronic components like amplifiers, fiber optic cables, and remote radio units (RRUs) to distribute signals throughout a building or area. The primary advantage of active DAS is its ability to provide consistent signal strength over large distances without signal loss.

How Active DAS Works : The signal is typically brought into the system from a base station or the macro network and is converted to an optical signal. This optical signal is distributed via fiber optic cables to remote units that convert the signal back to RF and transmit it through antennas.

Applications: Active DAS is ideal for large buildings, high-rise structures, and venues like stadiums, airports, and hospitals where high signal quality and extensive coverage are needed.

Following are the features of active DAS system as shown in the figure-1.
• It distributes RF signal using RF coaxial cables but uses fiber/CATV along with ADC/DAC to cover longer distances. It uses power amplifier to compensate for path loss due to long distance. Hence longer range can be achieved compare to passive DAS type.
• RF source is very flexible PPC (Power Per Carrier) and can use power as low as 0 dBm.
• It uses transport mediums such as fiber for optical signal and CATV for baseband signal.
• It uses RF coax. cables with 1/2" dimension which are less expensive but offer more loss.
• Remote Power Amplifier having 5 to 15dBm PPC is used as per technology and number of channels.
• It offers lower EIRP per antenna compare to passive DAS.

Advantages of Active DAS system

Following are the benefits of active DAS system.
1. Can distribute signals over long distances without significant signal loss, making it suitable for large buildings, campuses, or tunnels.
2. Supports more users and higher data throughput, making it ideal for environments with high-density user populations (e.g., stadiums, airports, and hospitals).
3. Provides fine control over signal strength, frequency bands, and interference management.
4. Capable of supporting multiple carriers and frequencies, allowing integration of various wireless technologies (e.g., 2G, 3G, 4G, 5G, Wi-Fi).
5. Easier to expand coverage or add new frequency bands as needed, providing more flexibility in system design and future upgrades.

Disadvantages of Active DAS system

Following are the drawbacks of active DAS system.
1. Initial setup and equipment costs are higher due to the use of active components like amplifiers and signal processors.
2. More complex to install and configure due to the need for power at remote locations and careful planning of signal distribution.
3. Requires regular maintenance and an external power source for active components, leading to higher operational costs.
4. Active electronics may introduce latency, which can impact real-time communications.

Passive DAS | Passive Distributed Antenna System

Passive DAS uses passive components such as coaxial cables, splitters, combiners, and antennas to distribute the signal. Unlike Active DAS, Passive DAS does not use amplifiers, making it more cost-effective but less efficient over long distances due to signal loss.

How Passive DAS Works : The signal is brought into the system from a base station or repeater and distributed through coaxial cables. At different points, the signal is split and directed to multiple antennas to provide coverage.

Applications: Passive DAS is suitable for small to medium-sized buildings or areas where short cable lengths are required.

Following are the features of passive DAS system as shown in the figure-2.
• It distributes RF signal using coaxial cables to multiple antennas. Sometimes it uses RF amplifier to compensate for path loss if the distribution points are further away from the source.
• RF source of up to 43 dBm power per carrier is used.
• It uses RF coax. cable with 7/8" dimension which offers low loss at the high cost per ft.
• There is attenuation of about 30 dB between source and antennas. The indoor antennas having low gain of about 2 to 5 dBi are used.
• High EIRP per antenna can be achieved compare to either active DAS or hybrid DAS.

Advantages of Passive DAS system

Following are the benefits of Passive DAS system.
1. Lower initial cost compared to active DAS, as it uses passive components without the need for expensive active electronics.
2. Easier and quicker to install as it doesn't require power or active signal components.
3. As passive DAS does not use active electronic components, it does not introduce latency in the signal path.
4. Minimal maintenance is required since passive components are less prone to failure compared to active electronics.

Disadvantages of Passive DAS system

Following are the drawbacks of Passive DAS system.
1. Significant signal loss occurs over long cable runs, making it less suitable for large buildings or areas.
2. Can only cover small or medium-sized areas effectively due to the inherent attenuation of signals in passive components.
3. Cannot handle high user densities or multiple frequencies efficiently, limiting its applicability in high-traffic areas.
4. Expansion or modification of a passive DAS system is more difficult and may require significant changes to the existing setup.

Hybrid DAS | Hybrid Distributed Antenna System

Hybrid DAS combines the benefits of both Active and Passive DAS. It typically uses active components to transmit signals over long distances and passive components for shorter distances or areas that require simple distribution.

How Hybrid DAS Works: The system starts with active components like fiber optic cables and amplifiers to distribute the signal over long distances, followed by passive components like coaxial cables and splitters to distribute the signal in smaller zones.

Applications: Hybrid DAS is ideal for buildings or venues with both large and small areas, where active components are used to cover long distances and passive components are used for distributing signals in closer proximity.

Following are the features of hybrid DAS system as shown in the figure-3.
• It is combination of both passive DAS and active DAS.
• It supports more antennas per PA compare to active DAS.
• It offers lower EIRP per antenna compare to either passive DAS or active DAS.

Advantages of hybrid DAS system

Following are the benefits of hybrid DAS system.
1. Provides a cost-effective solution with a mix of active and passive components, offering a balance between performance and cost.
2. Easier to expand or reconfigure compared to a purely passive DAS, making it suitable for growing facilities.
3. Offers improved signal quality and control over passive DAS, especially in large or complex installations.
4. Can support multiple frequency bands and technologies, making it suitable for multi-carrier deployments.
5. Active components are used only where necessary (e.g., long-distance transmission), reducing the cost of a fully active solution.

Disadvantages of hybrid DAS system

Following are the drawbacks of hybrid DAS system.
1. While cheaper than a fully active DAS, hybrid DAS is still more expensive than a purely passive DAS.
2. Installation and configuration are more complex compared to passive DAS due to the combination of active and passive components.
3. Requires external power for the active components, adding to the overall power consumption and maintenance needs.

Difference between active, passive and hybrid DAS

Conclusion

Active DAS is best suited for large-scale deployments requiring high capacity, precise control, and multi-carrier support, while Passive DAS is more cost-effective for smaller areas with simpler coverage needs. Hybrid DAS combines the strengths of both, offering a balanced solution for medium to large installations that require cost efficiency and scalability with good signal quality. Choosing the right DAS depends on coverage area, user density, budget, and scalability requirements. Refer tutorial on DAS System basics and types >>.

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