Millimeter Wave Beamforming and Antenna Design

In this article, I will introduce various aspects of millimeter-wave (mmW) beamforming and antenna technology and the technical design examples that I think are interesting and unique.

Beamforming

The beam forming network (BFN) is used to combine signals from small antennas into a more directional pattern than each individual antenna alone because of array factors . Beamformers are used for radar and communications. An example of a radar is a linear array that provides four azimuth beams for an automotive radar; a communication example is a two-dimensional beamformer for satellites covering a wide area of ​​the ground at multiple locations.

BFN can provide simultaneous beam coverage, such as satellite or single point coverage, just like a classic phased array radar system. Beam control computer controls can be used to fix the beam in the design or to adapt it.

There are two main types of phased-array beamforming networks: Passive Electronically Controllable Antennas ( PESA ) and Active Electronically Controllable Antennas ( AESA ). Dr. Sangkyo Shin of Keysight Technologies views this video in beamforming:

Brooklyn 5G Summit

5G in a User Equipment (UE), such as any device used by an end user to communicate with a network, is now a very hot topic. Nokia and Wireless Research Center at New York University School of Engineering at New York University Tandon has just completed a Brooklyn 5G 5th Summit (B5GS) at the end of April, two of the key issues is Intel's 5G mmWave phased array and Qualcomm's 5G UE phased Array design.

Ozge Koymen, Senior Technical Director of Qualcomm, demonstrated the 5G UE phased array design demonstration and discussed the challenges in this area, such as:

Fast switching and setup time

Minimize the loss of PA efficiency and thermal performance

Minimize pre-LNA loss to improve link budget

Space limitations in UE

cut costs

Two polarized spherical covers

In this section, we will deal with UE device face or edge design options to achieve two kinds of polarized spherical coverage. Qualcomm discussed the front and rear antenna modules for handheld devices ( Figure 1 ).

Figure 1 Front and rear antenna modules (Photo courtesy of Qualcomm)

Komen recommends using multiple modules that will help reduce hand clogging and reduce the effect of orientation ( Figure 2 ).

Figure 2 Hand Blocking in UE (Image courtesy of Qualcomm)

In handheld UE devices, there are two popular configurations, namely a face design or an edge design ( Figure 3 ).

Figure 3 Two Popular Configurations of Handheld UE Devices (Image courtesy of Qualcomm)

Koymen discusses the use of two (cross-polarization 7) having a planar array of 2 × 2 x-pol, 1 × 2 and 2 × 1 surface design recommendations dipole array uses three modules and a module edge design, the module There is a single 4 x 1 x-pol planar array.

Considering various types of beamforming architectures, Koymen commented that the maximum ratio combining (MRC) design of the device in all directions was adopted. He thinks this is an optimistic design, an upper bound scheme; 24 beams based on RF/analog beam codebooks are suitable for all modules/corresponding to P-1/2/3 initial scan and beam refinement - this is a suggested practical Scheme; and Optimal Antenna Selection (Traditional/LTE Design) - A pessimistic lower bound scenario. We will discuss MRC and multi-resolution codebooks in more detail on the next page.

Qualcomm has developed an RFIC that supports a variety of possible antenna designs and is used to demonstrate the appearance of smartphones for adaptive beamforming and beam tracking. Each of its eight RF front-end (RFFE) modules supports multiple alternative antenna arrays in the X, Y, and Z directions. Mobile OEMs now have the opportunity to begin optimizing their specific equipment as early as possible.

Maximum Proportional Combination (MRC)

Let's take a look at the MRC 1 architecture. This is a simple and effective adaptive antenna array combination scheme, which helps to reduce the influence of noise, fading and co-channel interference to some extent. The architecture does need to estimate the spatial characteristics of the signal of interest in the array, which is the channel gain and phase at each antenna element. Please refer to FIG. 4 for a conventional MRC receiver architecture.

Figure 4 Classic Pre-Censored MRC Receiver Architecture (Image courtesy of Reference 1)

The paper in Reference 1 proposes a general analysis framework for maximal ratio combining reception in which the spatial signature of the desired signal is estimated by correlation with a known training sequence.

Figure 5a depicts the architecture of performing the combination at baseband prior to detection. The author also suggests a better possibility of combining at intermediate frequency (IF) in Reference 1.

Figure 5a has an independent channel and carrier tracking MRC receiver. This is a baseband combined pre-detection MRC receiver using baseband compensated carrier phase jitter (picture provided by reference 1)

In Figure 5b , the weighting is applied by an adjustable delay element or a phase shifter. The single carrier recovery loop then brings the combined signal to baseband before the matched filtering is complete. This approach reduces RF hardware complexity by swapping N downconverters for only one downconverter and one upconverter .

Figure 5b MRC receiver with independent channel and carrier tracking. This is an IF combined pre-detection MRC receiver using a single carrier recovery loop. The box labeled x consists of an adjustable delay element or phase shifter followed by an adjustable attenuator. (Image courtesy of Reference 1)

The net result is the derivation of the normalized SNR (the inverse of which is the training loss), which is conditioned on the ideal SNR. This is the basis for obtaining various performance results in non-fading environments and irrelevant Rayleigh fading environments. It is found that the impact of training loss on the outage probability in the fading environment is greater than the average bit error rate (BER).

These types of results are useful for system designs that determine the length of a desired training sequence, and actually evaluate the performance of the system, including the effects of imperfect estimates without resorting to simulation.

Multi-resolution codebook

A codebook is a file that is used to collect and store code. The initial codebook was a book, but today's codebook is synonymous with a complete record of a series of codes, regardless of the physical format.

In order to overcome the higher path loss in the millimeter wave band, highly directional beamforming using large-scale or large-scale multiple input multiple output (MIMO) systems is crucial. The problem of channel estimation becomes challenging due to the large amount of training overhead required to issue all possible beam directions using a high resolution narrow beam. In order to solve and improve the beam search problem in millimeter wave systems, the paper in reference 2 describes a design of a multi-resolution beamforming sequence, which can quickly search the main channel direction in a binary manner. Given a multi-resolution codebook, the proposed multi-resolution beamforming sequence is designed to minimize training overhead 8 and maximize beamforming gain. This article discusses how to use a phase-shifted version of the Discrete Fourier Transform (DFT) matrix to design a multi-resolution codebook.

5G mmWave phased array

At the 5th Brooklyn 5G Summit, Intel’s Advanced Technology Director Batjit Singh discussed his company’s millimeter-wave array. One of the topics made me particularly interested in the movement of 5G 28 GHz cars.

Intel's design uses four panels that provide panel switching, beam selection, beam switching time optimization, and 360o coverage for mobile design. Their multiple field trials have demonstrated and demonstrated the mmW system (26.5 GHz to 29.5 GHz) ( Figure 6 ).

Figure 6 Intel 5G 28 GHz Automotive Mobile System (Image courtesy of Intel)

Experiments were conducted in Japan, Korea, and other countries. The test helps to evaluate critical mmW parameters such as modulation and coding scheme (MCS), received signal strength indicator (RSSI), offset received signal power (BRSP) performance, and intra/baseband unit (BBU) switching. See Figure 7 for the system deployed behind the top of the vehicle.

Figure 7 This is one of the test vehicles for the Intel 5G Automotive Mobile System. The car has a 5G millimeter-wave phased array system on the rear of the car for the car. (Image courtesy of Intel)

I hope V2X can improve the safety of driving in future self-driving cars, and 5G will provide support for this system.

Rotman Lens Beamforming

Let's take a look at this method of beamforming, which is crucial for drone collision avoidance, traffic monitoring and intruder detection.

In addition to detecting objects, radar can also measure the range and radial velocity of objects. It works well in most weather conditions, day or night. In collision avoidance, the radar needs to have the ability to detect the angle of the target object; this can be achieved using radar's mechanical or electronically steerable narrow antenna beams.

Size, weight, and power (SWaP) need to be trade-offs in sensor simplicity and viewing angle estimation capabilities, so it can be a good compromise to generate multiple fixed narrow antenna beams that radiate out front ends in different directions. Therefore, each beam will have its own perspective - this can be done with the flat Rotman Lens (RL) 4 .

Multi-Channel Frequency Modulated Continuous Wave (FMCW) radars operate in the 24 GHz ISM band. Receive (RX) antennas are based on RL and patch antenna arrays designed using microstrip technology. The transmit (TX) antenna uses a BFN and a patch antenna array.

The system used is based on the IMSTI 24 GHz multifunction radar product Sentire sR-1200e .

Radar system

Figure 8 Radar System Block Diagram presented in Reference 3 (Photo courtesy of Reference 3)

The main component of this radar front-end is a 9×14 RL, implemented using planar microstrip technology. This method was first mentioned in 1963 when Walter Rotman proposed a microwave lens 4 for the beamforming method . The lens may be configured as a parallel plate, waveguide or substrate integrated waveguide (SIW) structure for a linear beam array of antenna elements. The mathematical framework of ground calculations designed by the RL is referenced in Peter S. Simon 's paper 5 ( Figure 9 ).

Figure 9 Beamformer layout showing TX and RX beamforming networks including antenna ports and RL distribution networks (picture courtesy of Reference 3)

Integrated Phased Array IC Solutions: Provides Designers with Practical Solutions

The phased array radar system is moving toward the flat panel array and improves SWaP. Digital integration in silicon enables next-generation beamforming. GaN devices can provide high power and excellent power added efficiency (PAE), which is PAE (loaded RF power - RF power at the input of the device) DC power.

I really liked the Plank architecture proposed by Analog Devices and used their new ADAR1000 (a very unique Tile X/Ku-band Time Division Duplex (TDD) analog beamformer) to create an excellent evaluation system . The paper in Ref. 6 studies Frequency Division Duplex (FDD) and TDD and finds that TD-based beamforming based on reciprocity is the only viable option if robust operation under various propagation conditions is required. Figure 10 shows the block diagram of the device.

Figure 10 Block Diagram of ADAR1000 (Image courtesy of ADI)

The best part of this new product is not only highly integrated, it is amazing, and is used in the evaluation board available to the designer for building a phased array antenna board using the Plank architecture in which the IC is located perpendicular to the antenna of the board. board. In this way, the size of the ICs is less important because they do not need to fit the lattice spacing of the antenna design. These tools will shorten the developer's design time to market ( Figure 11 ).

Figure 11 Plank Architecture (Image courtesy of ADI)

The flat panel array can also be created on the antenna element on the side of the board and the IC on the backside - it is in this type of configuration that the antenna spacing 9 and the size of the IC become critical to prevent the grating split ( Figure 12 ).

Figure 12 Flat Panel Design Architecture (Image courtesy of ADI)

Analog/Digital Beamforming in Phased Array Signal Flows

Designers can set up analog/digital beamforming phased array signal streams based on their overall system goals. Each electronic design always has compromises and trade-offs. See Figure 13 for a general example of a signal design flow.

Figure 13 Generic Signal Flow Design for Analog/Digital Beamforming Phased Array Design Architecture (Image courtesy of Analog Devices)

Complete X/Ku Band Array with Analog/Digital (Hybrid) Beamforming

Figure 14 Analog/Digital (Hybrid) Beamforming X/Ku Band Array (Image courtesy of Analog Devices)

Here, Analog Devices really shines with Hittite Microwave and Linear Technology's high-power and high-speed acquisition technology.

Figure 15 Complete Evaluation Board Solution (Image courtesy of ADI)

As we implement 5G in life, I look forward to seeing more innovations mentioned in this article. I expect there will be more applications outside of 5G space .