ISSN: 2224-6274, RNPS: 0514, Vol. 21, No. 1, january - july, 2025.

Implementation of a Smart Beam-

Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar

Eng. Yunior Ibarra GuerraTornes

& PhD in Technology Noslen Rojas

Ramírez

Received: 06/2023 | Accepted: 04/2024 | Published: 9/2024

RESEARCH

1* Centro de Investigación y Desarrollo de Electrónica y Mecánica

“CID MECATRONICS”, Cuba, cid3@reduim.cu

2 Centro de Investigación y Desarrollo de Electrónica y Mecánica

“CID MECATRONICS”, Cuba, cid3@reduim.cu

3 Centro de Investigación y Desarrollo de Electrónica y Mecánica

“CID MECATRONICS”, Cuba, cid3@reduim.cu

Abstract

Last decades have been marked by an increase in the number of

users employing the various developed communication services.

This has made it necessary to evolve the technologies used to better

satisfy current demands. This paper shows the proposal for the

development of a smart antenna array with beam switching for use

in a communication system. It uses ARRadio-HSMC radio frequency

cards as an implementation platform coupled to the TR4 development

board. The proposed design allows dynamic control of the main

direction of seven digitally synthesized radiation patterns, ensuring

spatial coverage of an angular sector of 100º. Doing this project

opens a line of work applicable in dierent systems, capable of easily

adapting to complex antenna geometries and with the possibility of

incorporating adaptive algorithms to increase the performance of the

digital beamformer for each beam.

Keywords: digital beamformer, smart antennas, switched beam

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Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

Introduction

Controlling an antenna’s radiation pattern increases the

performance of radio communication systems in which user locations

or spectral operating conditions change over time. Smart antennas

are key elements to solving this problem. These antennas combine an

array of radiation units with digital signal processing blocks to ensure

dynamic beam formation based on real-working needs (Ong, 2015).

Initially, smart antennas were only used for radar, sonar, and

military communications applications. However, advancements

achieved in digital signal processing technology have made it

possible to integrate smart antennas into the world of modern

telecommunications systems (Zhai, 2017). Smart antennas form the

basis of satellite links using Space Division Multiple Access (SDMA)

techniques and are incorporated into IEEE 802.11ac and Long Term

Evolution (LTE) telecommunications standards (Chen & Haas, 2015).

Switched beam systems are one type of smart antenna

implementation. These systems form multiple xed directional

beams. The reception system activates in each direction to

identify signals. Once a useful information source is detected, the

user’s identication and location are stored in order to establish

communication through the predened radiation pattern that

points in their direction. As the source moves, the patterns switch to

maintain the link with the maximum possible antenna gain (Sharma,

Sarkar, Maity, & Bhattacharya, 2014).

Several authors have addressed the development and use of

this technology. Rosa presents the implementation of a Local Area

Network with electronic switching of eight antennas arranged

in a cylindrical geometry (Rosa, Supriyanto, Rahman, Rahim, &

Moradikordalivand, 2014). Almorabeti proposes a design based on

the Butler matrix to form four orthogonal patterns, implements it on

microstrip, and incorporates a switch with PIN diodes (Almorabeti, Ri,

Terchoune, & Tizyi, 2018). Ahmed and Tiang analyze the use of beam

switching in Vehicle-to-Vehicle (V2V) communication systems (Ahmed,

Tiang, Mahmud, Gwo-Chin, & Do, 2023; Settawit Poochaya, 2016).

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This paper presents the implementation of an antenna array with

digital formation of multiple radiation patterns for a switched beam

system. The design is based on ARRadio-HSMC transceiver cards

coupled with the TR4 development board. The main objective is to

present a design architecture applicable to this smart system variant,

which can adapt to complex antenna geometries and incorporate

adaptive algorithms to improve the performance of the digital

beamformer for each beam. While the development does not include

the signal search and identication algorithm, it provides a platform

that ensures the formation and switching of multiple beams during

reception. The work’s main contribution is presenting a design variant

for developing smart antennas in telecommunications systems.

Materials and Methods

To implement the switched beam smart antenna system, we used

a hardware architecture consisting of a TR4 development board with

a Stratix IV EP4SGX230C2 FPGA as the main processing core and

four ARRadio-HSMC daughter cards equipped with Analog Devices

AD9361 transceivers, which provided a total of eight independent

reception channels. The antenna array consisted of eight half-

wave dipoles arranged in a uniform linear conguration, spaced

between elements by 0.6 at the operating frequency of 2.412 GHz.

The experimental methodology consisted of three sequential phases:

hardware conguration, signal processing programming, and

metrological validation.

The experimental methodology was structured in three sequential

phases: hardware conguration, signal processing programming, and

metrological validation. Initially, the operational parameters of the

AD9361 RFICs were congured using an NIOS II softcore embedded

in the eld-programmable gate array (FPGA). This softcore was

managed via a serial peripheral interface (SPI) to control the center

frequency, bandwidth, gain, and sampling rate. The FPGA-based

digital signal processing included in-phase and quadrature (I/Q) data

acquisition and demultiplexing, followed by a frequency-domain

calibration algorithm based on the discrete Fourier transform (DFT)

Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

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ISSN: 2224-6274, RNPS: 0514, Vol. 21, No. 1, january - july, 2025.

to compensate for amplitude and phase deviations. Finally, seven

directional beams were synthesized by applying precalculated

complex weights. Experimental validation was performed in an

anechoic chamber using a 2.4121 GHz reference sinusoidal signal to

characterize system performance. Radiation patterns were measured

via angular sweep with a rotary positioner, and the obtained data

was exported to MATLAB for comparative analysis with theoretical

simulations. Specically, the analysis evaluated the sidelobe level

and radiation angle accuracy.

Digital Beamforming

In a conventional antenna, the electromagnetic eld contribution

in dierent directions in the far-eld region is determined by the

current distribution law on the radiator’s surface. Thus, the antenna’s

directional characteristics depend on its geometry and the feed point

(Stincer, 2001).

An antenna array consists of independently fed radiation units. By

modifying the amplitude and phase of the input signals, an equivalent

current distribution is established, which allows for the desired

directional characteristic to be obtained. This process is known as

radiation pattern formation (Rodríguez, García, & Miller, 2017).

The use of digital beamformers is a crucial leap for the development

of smart systems. In these systems, signals acquired by the elements

are digitized and sent to a signal processor. A complex weight factor is

then applied to each channel to ensure pattern synthesis. Operating

in the digital domain enables the shaping of multiple beams with

dierent, dynamic characteristics without altering the antenna array’s

physical structure, a feature exploited by switched beam systems

(Bailleul, 2016).

Reception and Processing Platform

The rst step in digital beamforming is acquiring and digitizing the

signals at the input of each element. Peter Delos (2017) proposes using a

Radio Frequency Integrated Circuit (RFIC) for this purpose. In the work

(Delos, Frick, & Jones, 2020), a prototype based on the AD9061 four-

channel transceiver is shown. Direct operation with the available RFIC

Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

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requires advanced mounting technology capable of supporting complex

designs. For example, the integrated AD9361 requires a connection of

144 pins in a 102 mm² area (HSMC ARRadio Daughter Card).

One solution is to use evaluation boards that include the RFIC and the

necessary hardware elements for their operation.

This paper uses the ARRadio-HSMC card. This card can be coupled to

an external handling device via the High-Speed Mezzanine Card (HSMC)

interface and contains the AD9361 two-channel transceiver RFIC as its

base element.

The processing stages in digital beamformers are characterized by

their hybrid architecture (Yu, 2017). Digital Signal Processor and Field

Programmable Gate Array (DSP and FPGA, respectively) predominate

in digital beamforming performance. The selection of one or the other

depends on the specic application being developed, although most

literature on the subject favors the use of FPGA (Dikmese, Küçük, Şahin,

& Tangel, 2010).

The AD9361 RFIC has two 12-bit data buses, through which interleaved

transmission and reception (in baseband) signals from two transceivers

circulate. It also has a control bus for communication management

and a Serial Peripherical Interface (SPI) for conguring the system’s

operational parameters, such as frequency, bandwidth, sampling rate,

etc. The ARRadio guarantees access to all these signals through the HSMC

connector. The device used for digital data processing must be able to

connect to this interface.

The need to use multiple acquisition cards and the associated

control issues led to the selection of the TR4 Development Board. This

board has six HSMC connectors for transceiver cards and features the

EP4SGX230C2 FPGA from the Stratix IV family as its processing core.

System Architecture

Based on the selected reception and processing platform, the

connection scheme shown in Figure 1 is proposed for the switched

beam antenna system. This scheme includes four ARRadio-HSMC cards

that are connected to the TR4 development board. These cards allow for

the processing of signals from eight antennas to form multiple radiation

patterns digitally.

Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

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The image on the left shows the communication path between the

integrated transceivers and the TR4 development board. The AD9361s

are linked with the FPGA through the HSMC lines, where the bulk of

processing takes place. The image on the right shows the points for

connecting a local oscillator to ensure the radio frequency coherence

of signals from each channel, as well as the clock distribution mode to

guarantee baseband synchronization.

The FPGA fullls three essential functions for the system. First,

it congures the transceiver cards. Second, it ensures the correct

reception and calibration of signals from the AD9361. Third, it performs

digital synthesis of the seven digitally formed radiation patterns. Figure

2 shows the functional diagram displaying its key elements.

Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

Figure 1. Diagram of the smart antenna array. a) Connection between

the transceivers and the processing system. b) Connection of signals for

multichannel coherence.

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The Softcore, developed by Altera NIOS II and embedded in the

FPGA, is used to initialize the operational parameters of the AD9361.

Through the SPI communication interface, the Softcore sends a

conguration sequence that includes:

• Enablement of two receiver channels.

• Radio frequency receiver bandwidth conguration.

• Operating center frequency conguration.

• Signal sampling rate conguration.

• Internal digital lter programming.

• Manual gain conguration.

• Internal calibration of reception oset and I/Q channel balance.

The communication control logic is developed based on the

communication protocol established by the AD9361 manufacturer.

Based on the data sampling clock dened during initialization, the

logic recovers the data from each channel, which are interleaved with

the sequence I1, Q1, I2, Q2, where I and Q represent the in-phase and

quadrature components of the signals, and the numbering indicates

the transceiver channel.

Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

Figure 2. Functional diagram of the FPGA design.

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The rst processing block that the acquired signals pass through

is the calibration block. This begins operating during system

initialization, where it uses a reference signal generated by one of the

transmitters and distributed to all receiving channels to determine

the amplitude and phase dierences between channels. To do this, it

uses an algorithm based on the Fourier transform. Once the dierences

have been determined, the correction coecients are calculated and

applied continuously throughout system operation.

The calibrated signals are sent to the block where directional

patterns are digitally formed. The block consists of seven similar

subsystems, each of which is responsible for synthesizing a beam.

The desired radiation directions are applied to each subsystem as

appropriate. Weights for forming each beam are calculated using a

conventional algorithm based solely on the input radiation direction

(S. Venkata Rama Rao, 2019).

As a switching circuit, the simple scheme shown in gure 3

is proposed. In this conguration, a xed directional pattern is

established in the synthesized channels for sequential reading of

each output. This conguration is useful when the data processing

units following the antenna array cannot handle large amounts of

information. The developed platform enables the implementation

of complex processing architectures, such as adaptive systems or

others, in which each beam operates independently and switches

sequentially.

Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

Figure 3. Beam switching system.

Discussion and Outcomes

The technology proposed in this paper for developing smart

antennas with beam switching was validated to conrm its real

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capabilities for implementation. To do so, a verication system

consisting of eight reception lines, each with an antenna separated by

0.6 times the operating wavelength, was used. Tests were performed

at the frequency of 2.412 GHz, which corresponds to the rst Wi-Fi

access channel.

Calibration is a key to forming the correct directional pattern, so

it was the rst element checked. Figure 4 shows the in-phase and

quadrature components of the signals received by the receivers before

and after this process was performed.

Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

Uncalibrated I-channel

Calibrated I-channel

Uncalibrated Q-channel

Sample numbers

AmplitudeAmplitudeAmplitude

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The alignment of the signal phase and the compensation of

the amplitude dierences between the channels can be seen. As a

reference, a sinusoidal signal shifted 0.1 MHz from the center of the

operating frequency was used.

To assess the calibration behavior between channels over time,

40 captures of the output signals were made, distributed in groups of

10 captures, separated from each other by one hour. This provided

information during the rst three hours of system operation after

calibration (the rst group of data corresponds to the moment when

the weights were applied). The data were processed using the MALTAB

computer tool, and the results are presented in Table 1.

Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

Calibrated I-channel

Sample numbers

Amplitude

Figure 4. Signals received before and after calibration.

Table 1. Behavior of amplitude and phase errors between channels after

calibration.

The values in the table indicate an increased tendency for

deviations after calibration. This is due to temperature variations in

the transceiver system elements. Nevertheless, amplitude and phase

errors remain small, even in the worst case. Therefore, radiation

pattern formation can be guaranteed without introducing signicant

errors in the synthesized patterns (Mailloux, 2018).

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Subsequently, the formation of the directional characteristic

was veried using the measurement scheme shown in Figure 5. This

check was performed in an anechoic chamber to emulate free-space

conditions. The resulting signals from each beam were sent to a PC

via a serial communication interface. A program developed for system

verication is responsible for graphing the shape of the digitally

synthesized directional pattern.

Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

Figure 5. Diagram for measuring the directional characteristic.

As a result, the radiation patterns shown in figure 6 were obtained.

Figure 6. Radiation diagrams generated digitally Top: 0º, Bottom 19º

Radiation pattern with scan angle: 0º Radiation pattern with scan angle: 19º

Amplitude

Figure 6 shows the measured and simulated diagrams for two

channels of the switched beam antenna system. The two are

correspondingly similar, with an absolute error of less than 1.5 dB in

the level of the side lobes and 0.39° in the radiation angle. The key

dierences between the two are evident in the depth of the radiation

nulls and are a direct consequence of the amplitude and phase errors

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present in the system. With the geometry used, employing seven

directional patterns, it is possible to cover a scanning system of 100º

for the switched beam antenna system, as shown in Figure 7.

Implementation of a Smart Beam-Switching Antenna System

Eng. Alexander Rogelio Ramírez Zaldívar, Eng. Yunior Ibarra Guerra and PhD in T. Noslen Rojas Ramírez

Received power (dBW)

Scan angles ( °)

Figure 7. Directional characteristic of the system with multiple beams

Conclusions

The implemented system guarantees the formation of multiple,

simultaneous, directional reception beams, making it suitable for use

in a switched beam system. This paper presents the main technological

elements that made its development possible. In addition to being

applicable to smart antennas with beam switching, the proposed

design architecture can adapt to complex antenna geometries.

This is because forming the diagram with digital techniques only

requires modifying the equation for determining the weights in the

beamforming block. This same feature also enables the development

of adaptive algorithms. These ndings conrm the fulllment of the

objective proposed for the completion of the work.

The correct formation of the radiation pattern was veried in the

performed measurements. The amplitude and phase errors measured

in each reception channel were less than 0.3971% and 0.7538°,

respectively. Consequently, the dierences between the beams

measured in the anechoic chamber and the simulated beams did not

exceed 1.5 dB for the lower sidelobe level or 0.39° for the radiation angle.

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