In the previous discussion (Indoor Mobile Signal Coverage: Why, What & How), we introduced the Distributed Antenna System (DAS), a system that deploys antennas throughout a building's spaces to provide bi-directional wireless signal services. As a primary solution for indoor mobile communication signal coverage, DAS is applicable in various settings, such as hotels, hospitals, shopping malls, residential areas, enterprises, and commercial buildings.

DAS can be categorized into passive, active, and hybrid systems based on its architecture. In this article, we will explore the components, structural differences, and the challenges and advantages of each type.

Key Components of Passive DAS

A. Coaxial Cable

Based on differences in materials, shielding, and manufacturing techniques, the market offers a variety of coaxial cables, such as 1/2" or 7/8" telecom-grade low-loss coaxial cables, LMR400, and CFD400. Generally, thicker cables result in less signal attenuation but also pose greater challenges in installation due to increased weight and reduced flexibility. This may require the use of a crane to move the cable rolls and install suspension hangers to fix the cables. Regardless of the cable type chosen, signal attenuation is directly proportional to both cable length and signal frequency—meaning the longer the cable and the higher the frequency, the greater the signal loss.

B. Connectors

Connectors must match the type of cables being used. Common connector types include N-Type, SMA-Type, and F-Type. Each connector introduces some energy loss, and as they age, they may lead to passive intermodulation (PIM), which negatively impacts signal quality and system functionality.

C. Splitters/Dividers

These components split a single signal path into multiple paths. Common types include 2-Way, 3-Way, and 4-Way splitters, with typical power loss values of -3dB, -5dB, and -6dB, respectively. However, actual values depend on the specific product specifications. When selecting a splitter, you should also consider the connector type, supported frequency range, and insertion loss to ensure compatibility with the system requirements.

D. Unequal Splitters/Couplers/Tappers

Couplers divide an input signal into two output paths with an unequal power ratio. Depending on the specifications, couplers can support distribution ratios ranging from 1 dB to 20 dB. As with splitters, it is essential to select couplers based on connector type, supported frequency range, and insertion loss.

E. Indoor Antennas

Depending on their radiation patterns, common types of indoor antennas include omnidirectional (ceiling-mounted) antennas, directional antennas, and panel (wall-mounted) antennas, each with varying gain or attenuation depending on the frequency range. The selection and installation of antennas must also consider connector types, supported frequency ranges, and match installation locations with engineering needs.

Active DAS – A State-of-the-Art Solution More Suitable for 5G

The signal source for active DAS comes from multi-band signals of different telecom operators by any method (For signal source methods, please refer to Indoor Mobile Signal Coverage: Why, What & How). These signals are processed through a central Master Unit (Base Unit or Head-End Unit) for combining, amplifying, and necessary adjustments. The output ports of the master unit are connected to relay hubs or extension devices via optical fiber or Ethernet cables. These devices then further transmit the signals to multiple Remote Unit or Radio Unit (RU) devices installed in indoor spaces where requiring signal coverage. The RU devices, equipped with built-in antennas, directly provide bi-directional signal services to mobile devices.

Differences among Active DAS Solutions

Different vendors provide various Active DAS solutions, with specification differences commonly seen in the followings:

• Supported Bands: Which bands and how many band can be supported per system.

•  Bandwidth: The supported bandwidth and frequency range for each band.

• Transmission Media: Use of fiber optic or Ethernet cables, including the number of cables and the length restriction.

• Supported Operators: How many telecom operators can be supported simultaneously per system.

• Mobile Technology: Support for 4G LTE or 5G-NR, or both simultaneously

• RU Specifications: Including maximum number of RU devices, maximum output power, power supply methods, and the number of built-in antennas.

• Signal Format: Analog or digital systems.

While base station signals are analog, many Active DAS solutions on the market are digital systems. These digital systems require analog-to-digital (ADC) and digital-to-analog (DAC) signal conversions back and forth in their structures. This incurs higher latency and significantly higher costs, making them primarily can only be afforded by large-scale telecom operator initiated projects such as airports or railway hubs, rather than general buildings.

Challenges of Active DAS

1.        Higher Equipment Costs:

Compare with passive DAS, Active DAS equipment is usually more expensive, especially digital Active DAS systems.

2.        Specification Restrictions:

Supported bands, bandwidth, the number of operators etc., the limitations may vary depending on the product models and vendors

Hybrid DAS – for Large-Scale Multi-Room Floor Layout

Hybrid DAS integrates the architectures of Active DAS and Passive DAS, combining active devices with passive components. A key feature of Hybrid DAS is that the RU device in the front-end Active system does NOT have built-in antennas. Instead, the Hybrid DAS RU is equipped with one or more signal output ports, which are connected to Passive DAS components such as coaxial cables, splitters/dividers, unequal splitters (couplers/tappers), and indoor antennas. Together, these components form a comprehensive indoor signal coverage system.

The signal output power of the Hybrid DAS RU can be configured up to its maximum limit. However, once the signal is transmitted through the passive components, it is no longer manageable by the front-end active system, and signal attenuation inevitably occurs during transmission. As a result, system design still requires precise calculations of attenuation values and verification of the signal strength (EiRP) at each indoor antenna to ensure sufficient power is allocated to every target area.

Advantages of Hybrid DAS

1.          Stable Signal Output Power:

No signal attenuation at the hybrid DAS RU, avoiding unstable output issues commonly seen in Repeater-based Passive DAS systems caused by incoming signal fluctuations

2.          Suitable for Larger-Scale Buildings:

Similar to Active DAS, Hybrid DAS is well-suited for medium to large-scale building scenarios.

3.          Ideal for floor layout with Multiple Partitioned Small Rooms:

Passive DAS antennas can effectively cover highly segmented areas within buildings, such as hotel rooms, hospital wards, and partitioned offices, overcoming signal barriers caused by walls and doors.

Zyxel Active/Hybrid DAS Solutions

Zyxel utilizes RF-over-Ethernet or RF-over-Fiber technology, eliminating the need for repeated signal conversions within the system. We proudly present the revolutionary ZoneDAS series—affordable, modular Active, and Hybrid DAS solutions. Whether you need a 1–4 band system for a single operator or an 8-band system supporting four or more operators, our future-proof solutions are designed to be cost-effective for projects of any scale. Additionally, our system can integrate with low-power Repeaters as a signal source for Active or Hybrid DAS implementations. By adopting our equipment, you can secure customer projects at more competitive prices. For more information, visit our ZoneDAS Series Product Page or Contact Us.