In this article, I will cover various aspects of millimeter wave (mmW) beamforming and antenna technology with what I consider interesting and unique technical design examples.

Beamforming

Beamforming networks (BFN) are used to combine signals from small antennae into a pattern that is more directional than each individual antenna alone because of the array factor. Beamformers are used in radar and communications. A radar example is a linear array capable of four beams in azimuth for an automotive radar; a communications example is a two-dimensional beamformer used in a satellite to cover a broad ground area in multiple spots.

BFN can provide simultaneous beam coverage, such as in a satellite, or single-point coverage, like that of a classic phased array radar system. Beams can be fixed in a design or adaptive using beam-steering computer control.

There are two main kinds of phased array beamforming networks: passive electronically steerable antenna (PESA) and active electronically steerable antenna (AESA). See this video by Keysight’s Dr. Sangkyo Shin on beamforming:

Brooklyn 5G Summit
5G in user equipment (UE), such as any devices used by the end-user in communications with a network, is a really hot topic right now. Nokia and the NYU Wireless research center at NYU Tandon School of Engineering has just finished the 5th Brooklyn 5G Summit (B5GS) in late April and two of their key topics were 5G mmWave Phased Arrays by Intel and 5G UE Phased Array Design by Qualcomm.

Ozge Koymen, senior director of technology at Qualcomm, gave the 5G UE phased array design presentation and discussed challenges with that effort such as:

  • fast switching and settling times
  • minimizing post-PA loss with regard to efficiency and thermal performance
  • minimizing pre-LNA loss for an improved link budget
  • space constraints in UE
  • minimizing cost
  • spherical coverage for both polarizations

In this section, we will deal with UE device face or edge design options for spherical coverage for both polarizations. Qualcomm discussed a front and a back antenna module for a hand-held device (Figure 1).


Figure 1 Front and back antenna modules (Image courtesy of Qualcomm)

Koymen suggested that using multiple modules would help reduce hand-blocking as well as lowering the impact of orientation (Figure 2).


Figure 2 Hand-blocking in a UE (Image courtesy of Qualcomm)

In a hand-held UE device, there are two popular configurations, face design or edge design (Figure 3).


Figure 3 The two popular configurations for a hand-held UE device (Image courtesy of Qualcomm)

Koymen discussed proposed face designs which use two modules that have a 2×2 x-pol (cross-polarized7) planar array, 1×2 and 2×1 dipole arrays and edge designs that use three modules which have a single 4×1 x-pol planar array.

Looking at multiple types of beamforming architectures, Koymen commented that a maximal ratio combining (MRC) design along all of the directions of the device was employed. He felt that this was the optimistic design, upper bound scheme; an RF/analog beam codebook-based 24 beams for all modules/corresponds to P-1/2/3 initial sweep and beam refinement—this was a suggested practical scheme; and best antenna selection (legacy/LTE design)—a pessimistic, lower bound scheme. We will discuss MRC and multi-resolution codebook in more detail on the following page.

Qualcomm developed an RFIC that supported several possible antennae designs and used this in a demo smartphone form-factor showcasing adaptive beamforming and beam tracking. Each of their 8 RF front end (RFFE) modules supports multiple selectable antenna arrays in the X, Y, and Z directions. Mobile OEMs now have the opportunity to get an early start to optimize their particular devices.

[Continue reading on EDN US: Maximal ratio combining]

Steve Taranovich is a senior technical editor at EDN with 45 years of experience in the electronics industry.


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