Mobile Communication / CBRS
- Band Pass Filters
- Manually Tunable Band Pass Filters
- Digitally Tunable Band Pass Filters
- Band Reject / Notch Filters
- Manually Tunable Band Reject / Notch Filters
- Absorptive Filters (BP/BR)
CBRS: Technology and Filter Requirements
CBRS (Citizens Broadband Radio Service) represents a significant evolution in spectrum management, utilizing the 3.5 GHz band (3550 MHz to 3700 MHz) in the USA, defined as 3GPP Band 48. Its technological uniqueness is based on a three-tier spectrum access hierarchy managed by a centralized Spectrum Access System (SAS). This system coordinates access in real-time between privileged military users (Incumbents), Priority Access License (PAL) holders, and the broad General Authorized Access (GAA) tier. This dynamic allocation imposes massive requirements on hardware selectivity, as utilized channels can shift within milliseconds, and coexistence with critical naval radar systems must be guaranteed. Wainwright Instruments develops specialized RF components for this demanding environment, tailored precisely to the requirements of Citizens Broadband Radio Service Devices (CBSDs). To meet the strict FCC Part 96 regulations, filters in CBRS networks must feature extremely steep rejection skirts that isolate the desired signal from the adjacent n77 band (C-Band) and military signals. Our solutions minimize Adjacent Channel Interference (ACI) and ensure signal purity, which is indispensable for private LTE and 5G networks in industrial applications to guarantee constant Quality of Service without packet loss.
Typical Deployment Scenarios:
In modern CBRS infrastructures, filters function as critical barriers against interference to ensure the reliability of private broadband connections in complex RF environments.
- Private Campus Networks: In large-scale industrial sites, our filters secure the exclusive use of Band 48 against ingress from public networks, enabling seamless communication for autonomous transport systems within corporate premises.
- Smart Manufacturing & Industry 4.0: Inside factory halls, CBSD Category A devices must be precisely filtered to enable ultra-reliable low-latency communication (URLLC) for robotic controls in environments with high metallic reflection.
- Wi-Fi Offloading in Educational Institutions: Universities use CBRS to offload saturated Wi-Fi structures; here, our filters ensure highly efficient channel selection so that hundreds of parallel connections in lecture halls remain stable.
- Ports and Logistics Terminals: In maritime environments, coexistence with military radar systems in the 3550 MHz to 3650 MHz range is critical. Our filters support necessary Environmental Sensing Capability (ESC) through high stopband attenuation.
- Fixed Wireless Access (FWA): Regional internet providers use CBRS for "last mile" connectivity; our high-performance filters ensure signal integrity over long distances and protect receiver sensitivity from overloading.
- Healthcare & Hospitals: Private CBRS networks offer a secure alternative to Wi-Fi for vital monitoring systems. Wainwright filter solutions prevent clinical equipment from being disturbed by high transmit power from CBSD Category B antennas.
- Smart City & Video Surveillance: Urban networks often transmit high-resolution 4K data streams over CBRS. Our filters eliminate narrowband interference that can arise from diverse radio applications in densely populated areas.
- Research & Development: In laboratory environments for SAS validation, our high-precision filters serve as reference components to characterize end device behavior under extreme coexistence conditions and rapid frequency shifts.
Suitable Filter Categories for Mobile Communications / CBRS
The CBRS spectrum demands RF solutions that cover both the high power of base stations and the precision required for private networks. Wainwright Instruments offers a technological portfolio optimized for maximum selectivity and minimal thermal drift.
Band Pass Filters
Our CBRS Band Pass filters enable excellent selection across the entire Band 48 spectrum (3.55 GHz to 3.7 GHz). These filters are specifically designed to comply with strict FCC emission limits, particularly to avoid interference with adjacent services in the n77 band. Thanks to their high quality factor, they offer very low insertion loss, maximizing the range of private networks. Thermal stability ensures that the center frequency remains absolutely precise even at high transmit power from CBSDs. Infrastructure manufacturers benefit from high power handling, which is indispensable for Category B CBSDs.
Manually Tunable Band Pass Filters
For the development of CBRS hardware in laboratory environments, we offer manually tunable Band Pass filters covering the range from 3.3 GHz to 3.8 GHz. Via high-precision tuning elements, the center frequency can be adjusted exactly to the specific test channel assigned by the SAS. This flexibility is invaluable for engineers validating prototype sensitivity at the band edges. Field technicians also use these filters for on-site interference analysis to isolate interfering signals with frequency precision. The robust construction guarantees permanent reproducibility of the filter characteristics without loss of quality.
Digitally Tunable Band Pass Filters
Electronically reconfigurable filters support the requirements of modern Software Defined Radio (SDR) systems operating within the CBRS band. Via digital interfaces such as SPI, filter curves can be adjusted in real-time to instructions from the Spectrum Access System. This is particularly valuable for agile gateways that must switch between different GAA channels to avoid DFS-like shutdowns. Our digitally tunable filters combine necessary skirt steepness with fast switching times, massively increasing the spectral efficiency of the overall system. They are optimized for use in test environments and development systems.
Band Reject Filters / Notch Filters
Our CBRS notch filters serve to eliminate narrowband interfering signals that could impair the sensitivity of Band 48 receivers. Especially in coastal areas where military radar signals may appear in the lower spectrum, these filters provide critical protection for receiver frontends. They feature extremely deep stopband attenuation with negligible impact on adjacent CBRS channels. This prevents the saturation of low-noise amplifiers (LNAs) by strong external signals and ensures maximum data rates even in difficult coexistence scenarios. By using our notch filters, the robustness of the infrastructure against external RF influences is massively increased.
Manually Tunable Band Reject Filters / Notch Filters
Frequency-tunable notch filters provide a flexible solution for interference suppression directly in the field. System integrators use manual tuning to respond immediately to new interference sources in the 3.5 GHz range, such as those caused by poorly performing neighboring networks. These filters allow for immediate on-site signal quality optimization without time-consuming hardware swaps. The mechanical construction is optimized for frequent use in mobile test setups and provides stable stopband performance across wide temperature ranges. This makes them the first choice for commissioning teams.
Digitally Tunable Band Reject Filters / Notch Filters
In intelligent CBRS infrastructures, digitally tunable notch filters enable an automated response to dynamic interference scenarios. Controlled by monitoring algorithms, these filters can dynamically mask interfering signals in real-time to maintain Quality of Service (QoS) for critical applications. Their integration into automation concepts for radio optimization allows for autonomous radio optimization across entire campus areas. Thanks to remote controllability, operators can adjust filter characteristics centrally, significantly reducing operating costs. This technology is particularly valuable in dynamic Smart City environments.
Monoplexer / Diplexer / Duplexer / Triplexer
For CBRS-Advanced systems, high-performance multiplexers are required to combine different frequency blocks or services onto a shared antenna. Our duplexers enable reliable separation of transmit and receive paths in FDD-like configurations with highest isolation and minimal insertion loss. Triplexer solutions are used when CBRS signals must be combined with other cellular bands. Wainwright Instruments manufactures these components with a focus on minimum PIM (Passive Intermodulation) to maximize system capacity in dense indoor deployments. Precise tuning prevents signal crosstalk and protects sensitive receiver paths. Our multiplexers are optimized for use in industrial equipment and base stations.
Absorptive Filters
Absorptive filters play a crucial role in high-power CBRS transmit stages, particularly for Category B CBSDs, to increase system linearity. They convert unwanted harmonics and out-of-band signals directly into heat rather than reflecting them back to the power amplifier. This protection against reflection damage is essential for complying with strict FCC certification guidelines and significantly extends the life of active hardware. Our absorptive filters are designed for high continuous power in the 3.5 GHz range and are used in both macro cells and test equipment. By improving signal purity, they contribute directly to increasing data rates.