As 5G standards come closer to realization, mmWaves technologies are already being used in trials for Fixed Wireless Access. The short wavelengths at mmWave frequencies allow physically compact electronic steerable (active) antennas to be deployed that offer spatial diversity, spectrum reuse and high antenna directivity (gain) to overcome the higher path loss encountered at these higher frequencies.
The advancements in high frequency silicon integrated circuits, that combines the required beam steering functions with the traditional transmit/receive functions onto one chip, enables the fabrication of planar antennas for cost-effective assembly. Only by using silicon in these active antennas can the cost of these antennas be driven down by orders of magnitude, making them suitable for high volume, mass deployment systems like 5G infrastructure.
256 ELEMENT 28 GHz ACTIVE ANTENNA
Figure 1 AWA-0134 256 element active array for 28 GHz 5G wireless applications.
Developed in collaboration with Ball Aerospace, the AWA-0134 is an active array for 5G wireless applications developed using planar antenna technology resulting in a very low profile, lightweight unit (see Figure 1). The surface mount assembled antenna board is based on Anokiwave’s AWMF-0108 Silicon Quad Core IC and demonstrates the performance achievable using low power silicon integration and efficient antenna layout and design. Using the AWMF-0108, the antenna provides +60 dBmi (1000 W) of EIRP and a G/T of greater than ‐2 dB/K at boresight or an effective noise figure for the receive chain of approximately 5 dB. The electronic 2D beam steering is achieved using analog RF beam forming, with independent phase and gain control in both Tx and Rx operating modes.
As a planar antenna, it can be used either as a stand-alone component or combined and synchronized with other arrays to support hybrid beamforming and multiple-input-multiple-output (MIMO) functionality as part of a larger array. The 256 element array can also be used as four 64 element arrays for multi-user MIMO (MU-MIMO) applications. The array measures 26.4 cm × 14.2 cm × 6.9 cm and weighs 3 kg. It can be powered from either +12 V and consumes 47 W of DC power in receive mode and 65 W in transmit mode.
Figure 2 Beam gain for four pre-selectable states of the active array.
To support 5G beam acquisition and various channel needs, the array supports and provides multiple beamwidths. A wide beam is available to support channel state information measurements, search modes and broadcast channels. Multiple progressively narrower beams can be used for beam acquisition. The narrowest beams allow for interference mitigation, optimizing the signal to noise ratio, maximizing equivalent EIRP and range extension, as shown in Figure 2. A two-dimensional conical scan volume of ±60 degrees in both azimuth and elevation is supported. As this is a time-division duplex (TDD) system, the array operates in a half-duplex mode, enabling the same antenna to support both transmit and receive, with distinct transmit and receive beam settings if required.
The array also includes pre-stored beam states that, once loaded, can quickly be accessed in a beam acquisition protocol—an essential specification for any 5G radio physical interface. The embedded digital controller receives a desired “look vector” (beam position coordinates in theta and phi or radius and steering angle for a conical scan volume), calculates the required vector modulator settings at each element in the array and communicates with the silicon ICs to steer the beam within the allotted time slot. Completion of this entire operation within a sub-symbol interval is a critical requirement for the beam acquisition protocol of proposed 5G radio systems.
Other features of the array include temperature compensated gain with full array temperature mapping, temperature sense telemetry and transmit output power measurement at each antenna element reported back to the host system as telemetry. Remote monitoring and control of each antenna with real-time operational data allows for greater flexibility. The active array can be controlled through several interface options, allowing the array to be synchronized with the timing and data requirements of the baseband modem or with other antennas. The interface options are Ethernet, USB or high speed control low voltage differential signaling (LVDS).
Figure 3 Scan roll-off factor from 0 to 60 degrees.
Figure 4 256 element transmit cuts at 28 GHz over full scan showing greater than 26 dB isolation.
ARRAY PERFORMANCE
Figure 3 shows the far field antenna pattern of the array in receive mode for scan angles from 0 to 60 degrees. The patterns are well behaved with good sidelobe levels. Cross-polarization antenna patterns of the array in receive mode at both boresight and 60 degrees θ scan are shown in Figure 4. Excellent cross-polarization is observed under both scan conditions, with measured isolation between the polarizations greater than 26 dB. The measured transmit EIRP of the AWA-0134 achieves 1 kW at 1 dB compression.
The AWA-0134 antenna leads the way in showing how 5G coverage can be rolled out by network operators using the mmWave bands, with low power footprint and high energy efficiency, while meeting key operating specifications for data rate, latency, coverage and reliability. Based on highly integrated Si technology that includes embedded functions for remote telemetry and low latency fast beam steering of the entire array, the array enables real-time active beam steering.
Anokiwave Inc.
San Diego, Calif.
www.anokiwave.com