Beamforming Networks using a Broadband 4x4 Butler Matrix with

Wideband Crossovers and Couplers

Salah Ihlou

, Hafid Tizyi

and Ahmed El Abbassi

Team Electronics, Instrumentation and Systems Intelligent, Faculty of Science and Technology Moulay Ismail University,

Errachidia, Morocco

STRS Laboratory, INPT, Rabat, Morocco

Keywords: Beamforming Network, Miniaturized butler matrix, Schiffman phase shifter, 0 dB crossover.

Abstract: In this work, a novel and miniaturized 4*4 Butler matrix will be presented. This proposed butler matrix

comes with four 3 dB quadrature forward wave coupled line coupler, two 45 Schiffman phase shifter and

one crossover. This BM has been created a centre frequency of 5.8 GHz using FR4 substrate. The crossover

of this BM has substituted with a 0 dB. The proposed BM occupies a total area of (84.74 mm)*(76.56 mm).

It exhibits high isolation and wideband 4x4 Butler matrix designed and simulated by employing a single-

layer FR4 substrate. The return losses are better than 28 dB with its good performance.

https://orcid.org/0000-0002-2253-5298

https://orcid.org/0000-0003-1582-7732

1 INTRODUCTION

The number of wireless communication system

users, combined with the restricted number of radio-

frequency channels, represents a source of

interference in certain areas. This lowers the

efficiency of wireless transmissions and restricts

their capabilities, such as cellular bandwidth and

frequency efficiency. Several methods, including

innovative antenna arrays, have recently been used

to improve communication efficiency even in

unfavourable environments. There are two

categories of intelligent antenna systems: adaptive

arrays and switched beam systems (Lehne, 1999).

The first is a system that effectively rejects

interference by adjusting to the environment in real-

time and using adaptive algorithms. It is, though,

more complex and requires more signal processing

than the above group. Since the second form does

not employ controllers, it is less powerful and less

expensive than the first. To ensure mobile tracking

in a dynamic environment, a switched beam system

generates several beams and selects the appropriate

beam that produces the strongest signal powerful

from among them. As the mobile travels, this

mechanism shifts from one shaft to another. In

switched-beam antenna systems, the Butler matrix is

a well-known beamforming network. N input ports

and N output ports feed N antennas in an NxN

Butler matrix.

Planar or waveguide technology that could be

used to build the Butler matrix. The Butler matrix

comprises three main components: 3-dB/90

quadrature couplers, crossovers, and phase shifters.

Wideband 3-dB couplers and crossovers are

necessary to achieve wideband features. Microstrip

multi-section branch-line structures were used to

perform these characteristics (Deb et al. 2020).

Several wideband Butler matrix configurations using

Conductor Backed Coplanar Waveguide (CB-CPW)

technology (Abdelghani et al. 2012), Substrate

Integrated Waveguide (SIW) technology (Djerafi

and Wu, 2012), and single layer r planar technology

(Denidni and Libar, 2003) have recently been

published in the literature. The authors of (Denidni,

and Libar, 2003) proposed a Butler matrix for

obtaining a wideband of 250 MHz and return losses

less than 22.05 dB, using regular 3-dB quadrature

couplers and four-section branch-line crossovers.

According to the findings in (Denidni and Libar,

2003), the bandwidth can reach 1.92 and 2.17 GHz

and return losses and isolation are greater than 23

and 26 dB, respectively. Identically, the simulation

Ihlou, S., Tizyi, H. and El Abbassi, A.

Beamforming Networks using a Broadband 4x4 Butler Matrix with Wideband Crossovers and Couplers.

DOI: 10.5220/0010732100003101

In Proceedings of the 2nd International Conference on Big Data, Modelling and Machine Learning (BML 2021), pages 255-259

ISBN: 978-989-758-559-3

255

results of the 4x4 Butler matrix are to be presented

in this paper. The matrix operates over a frequency

range of 5.4GHz to 5.95 GHz and provides good

return losses and separation of better than -28.26 dB

at the operating frequency.

2 DESIGN CONFIGURATION

As shown in the layout below, the 4x4 Butler matrix

comes up with four couplers (Hock and

Chakrabarty, 2005), one wideband crossover (Deb et

al. 2020), and two-phase shifters (Zhai, 2014).

The first order microstrip line calculations were

performed manually (Pozar, 2011), and then using

the ADS calculator to optimize them. The

components are based on a 1.6 mm thick FR-4

substrate with a dielectric constant of 4.4.

The output of BM is highly dependent on the

coupler and crossover features; they are each

simulated and configured separately before

combining them to form the Butler matrix's entire

architect using Advanced Design System Simulator.

2.1 Coupler

In the BM, the coupler is the most critical

component. It's a -3 dB directional coupler operating

a frequency of 5.8 GHz that splits the input signal

into two equal-amplitude output signals. Input port

1, output port 2 (direct route), port 3 (coupled

channel), and isolated port 4 (Hock and Chakrabarty,

2005) are the four ports.

Figure 1 depicts the proposed coupler's

configuration, while Figure 2 depicts the simulated

S-parameters.

Figure 1: Layout of S-parameters of the coupler

Figure 2: Simulation S11, S12, S13 and S14 of the

coupler.

Figure 3: Simulated S12 and S13 phase difference

between the output ports.

The S14 return loss and S11 isolation, respectively,

are roughly -22,23 dB and -32,08 dB. It's also

apparent that we've got a good match and excellent

operating frequency isolation. At 5.8 GHz, the

coupling is about -3, which means that power on

both output ports is halved. The phase difference

between the output ports is around 72.25°, as

anticipated.

2.2 Phase Shifter

Phase shifters are one of the essential commonly

used methods in RF.

Beamforming nets, Phase discriminators, optical

beam-scanning phased arrays, and other applications

use it. It shifts the signal into a Predetermined step

(Zhai, 2014)

. Figure 4 depicts this.

BML 2021 - INTERNATIONAL CONFERENCE ON BIG DATA, MODELLING AND MACHINE LEARNING (BML’21)

256

Figure 4: The structure of the Schiffman differential phase

shifter

The phase shifter used is a Schiffman phase shifter,

consisting of two coupled transmission lines with

one folded side. Two 45 phase shifters make up the

BM. The following formulation (Srivastava and

Gupta, 2006) defines the line length corresponding

to the step shift of 45:

ΔL =









)

In a microstrip line, the wavelength is defined as:

where the phase θ change is located.

𝜆 =











)

The wavelength is λ0, and εeff is the microstrip

line's effective dielectric constant. Figure 5 depicts

the phase shifter configuration as well as the

simulation performance. The phase difference

between ports 1 and 2 is about 45 at the operating

frequency.

Figure 5: Simulated phase difference between the ports 1

and 2 of -45° phase shifter

2.3 Crossover

Crossover is the most complicated aspect of

realizing the Butler matrix. In order to avoid

overlapping signals at crossings, the crossover

should be used in a fair degree of separation between

the input ports. As they have four symmetrical

ports, with two inputs and two outputs (Deb et al.,

2020). If every neighbouring port is isolated, then

we get the best crossover configuration.

The geometry and momentum S-parameters of a

potential crossover are shown in Figures 6 and 7,

respectively. It shows that the suggested crossover

has ideal characteristics in terms of isolation and

parameter lack of return. The S11 return loss is -

43.38 dB, indicating that the 5.8 GHz resonant

frequency is a perfect match. -1.18 is the entry

failure from coupling port S13. The coupling ratio is

approximately 0 dB, implying that the power at Port

1's input fully transfers to Port 3. At 5.8 GHz, S12

and S14 are separated by -40.15 dB and -37.20 dB,

respectively.

Figure 6: The structure of the proposed crossover

Figure 7: Simulated return loss S11, insertion loss S13,

isolations S12 and S14 of the crossover.

The suggested BM is shown in Figure 9. It comes

with a miniaturized shifter, coupler, and 0 dB

crossover built-in.

Beamforming Networks using a Broadband 4x4 Butler Matrix with Wideband Crossovers and Couplers

257

Figure 9: Proposed 4*4 BM

A N*N BM has N input lines and N output lines

(where N is an even number and must be greater

than or equal to 4). Between the output lines of N

unit BM, there is a phase difference.

Figure 10: Simulated S11 and S22 of the four input ports

Figure 11: Simulated insertion losses of the port 1

The virtual coefficients S17, S15, and S18, S16 are

approximately -8 dB and -7 dB, respectively, which

is substantially different from the ideal value of -6

dB. Because of this, the control of port one is also

split between the output ports. We believe the results

obtained are promising.

Table 1: Performance comparison of proposed work with

exciting work.

Ref freq

(GHz

)

Substrate

material

Total size

Return

Loss

S11(dB)

(Rifi et

al.

2018)

5.8 FR4 90.61×96.54 -24.69

(Nacho

uane et

al.

2014)

2.4 FR4 173.7×173 -35

(

Abdel

ghani

et al.

2012)

5.8 RO4003 90*70 <-11

(Bhow

mikand

Moyra,

2017)

2.5 FR4 115.18*64.4 -20

This

work

5.8 FR4 44.25 *

39.92

-28.26

The comparison shows that the BM has good

characteristics in terms of return loss and total size,

as shown in Table 1.

3 CONCLUSIONS

As a conclusion, a new wideband 4x4 Butler matrix

has been analysed, developed, and simulated. The

high bandwidth is reached by using broadband

systems such as crossovers and couplers. Its good

performance makes it ideal for wireless

communication systems as beamforming for multi-

beam antenna arrays for angle diversity to minimize

interference.

Experimentation is needed to validate the design.

As compared to other structures in the literature,

the proposed matrix has robust characteristics in

terms of substrate material, return loss and total size,

as shown in Table 1.

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