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Pattern Reconfigurable Wideband Circularly-

Polarized Quadrifilar Helix with Broadside and

Backfire Radiation Patterns

Wei Lin and Hang Wong

Department of Electronic Engineering and State Key Laboratory of Millimeter Waves (HK),

City University of Hong Kong

Tat Chee Avenue, Kowloon, Hong Kong,

Email: weilin6-c@my.cityu.edu.hk

Abstract—This paper introduces a pattern reconfigurable

wideband circularly-polarized (CP) quadrifilar helical antenna (QHA) with both broadside and backfire radiation modes. A

compact 1:4 power divider network is proposed to feed the QHA for obtaining the wide bandwidth. To realize pattern diversity, PIN diodes on the power divider are to reconfigure the sequences

of the output phases such that the direction of radiation pattern can be controlled alternatively for the broadside or the backfire radiation. The fabricated antenna prototype is compact and

light-weight. Measured results show that the broadside and backfire radiation modes can be switched by applying opposite voltages on the two DC bias. The proposed QHA has the wide

impedance bandwidth of 43% and the wide 3-dB AR bandwidth of 38%. The measured broadside and backfire radiations have the wide 3-dB gain beamwidth of 140°and 120° with the

maximum gain of 2.3 and 3.0 dBic respectively. The proposed antenna can be used in many applications as subway and railway communications, base station for narrow street coverage, RFID

or satellite systems.

Index Terms—pattern reconfigurable, quadrifilar helix

antenna, broadside and backfire radiation modes.

I. Introduction

With the rapid development of wireless communication

systems in recent years, antennas with reconfigurable functions

such as frequency, polarization and pattern reconfigurable

antennas have drawn much attention for many attractive

features [1]—[3]. For example, antenna with pattern diversity

can increase the channel capacity of wireless system, enhance

the signal-to-noise (SNR) ratio and provide larger radiation

coverage by reconfiguring the main beam.

Many efforts have been contributed to pattern

reconfigurable antennas as in [4]—[8]. For an instance, four

sequential rectangular patches with a reconfigurable feeding

network in [4] can generate either broadside or conical-beam

radiation patterns. In [5], a top-loaded monopole with a patch

embedded with diodes and varactors is able to radiate either

directional or omni-directional waves. In addition, a cross-

shaped patch with four reconfigurable parasitic patches in [6]

can realize a null scanning pattern by adjusting the varactors

between the patches. In [7], the antenna with a loop-and-dipole

Fig. 1. Configuration of the pattern reconfigurable quadrifilar helix antenna.

structure switches the main beam towards three directions by

controlling the switches for MIMO applications. Moreover, a

reconfigurable Yagi-Uda antenna proposed in [8] can change

the radiation into four directions by controlling RF switches.

All above examples exhibit different pattern diversity

characteristics. In this paper, we propose a new pattern

reconfigurable QHA with both broadside and backfire

radiation patterns. We applied a compact feeding network for

the QHA to obtain a wide bandwidth. Furthermore, we

introduced PIN diodes on the transmission lines of the feeding

network to reconfigure the phase differences of the four

sequential outputs. In this manner we alter the antenna

radiation between broadside and backfire modes through two

DC bias. The designed antenna has the wide overlapped

impedance and AR bandwidth of 38% and the wide 3-dB

beamwidth of 140 degree. In addition, the antenna has a

compact size and light weight. This unique pattern diversity

feature makes it useful in different applications such as subway

and railway communication, satellite communication, RFID or

communication inside a narrow street scenario.

Fig. 2. Configuration of the reconfigurable feeding network.

TABLE I

KEY ANTENNA PARAMETERS

Parameter Description Value

RSubstrate Radius of the substrate 28 mm

RHelix Radius of the helix 22.5 mm

LHelix Length of each helical arm 86 mm

Laz Height of the Helix 73 mm

Wt Width of the transmission line 2.72 mm

Ldiode Length of the PIN diode 1 mm

Lresistor Length of the isolation resistor 1.6 mm

II. Antenna Design

A. Antenna Configuration

The antenna consists of a QHA with a compact feeding

network as seen in Fig. 1. This compact feeding network

contains two identical Wilkinson power dividers stacked back

to back with a common ground. The transmission lines are

bended for size-reduction. Four output ports are aligned

sequentially to feed the helix with a short-circuited ring on the

top. For achieving reconfigurable patterns, we inserted PIN

diodes in the transmission lines to reconfigure the shape of the

feeding network so that broadside and backfire modes can be

switched. In addition, another substrate for DC bias lines is

placed below the feeding network. All the detailed parameters

are listed in the table I.

B. Reconfigurable Compact Feeding Network

One of the characteristics in this QHA is that the broadside

or backfire radiation pattern can be obtained by the different

phase outputs of the feeding network. For example, if the QHA

is right-handed winding, the broadside radiation pattern with

left-handed circular polarization (LHCP) is generated when the

Fig. 3. Characteristics of the PIN diode Bar50-02L.

TABLE II

RADIATION PATTERN BY DIFFERENT STATUS OF PIN DIODES

DC#1 DC#2 Red diodes Green diodes Pattern mode

3 V 0 V ON OFF Broadside

0 V 3 V OFF ON Backfire

Fig. 4. Antenna radiation pattern: (left) Broadside mode, (right) Backfire mode.

phases of the four sequential outputs are clockwisely delayed.

On the contrary, the backfire radiation mode is observed when

the four output phases are anti-clockwisely delayed. Therefore,

we modified our prior work as in [9] to realize a reconfigurable

feeding network which output phases are switchable.

Figure 2 shows the geometry of the reconfigurable feeding

network. Two sets of the PIN diodes (Type Bar50-02L from

Infineon Technologies [10] marked with red and green color)

are introduced in the feeding network. The characteristics of

the PIN diode as shown in Fig. 3 exhibit good isolation (more

than 18 dB) and low insertion loss (less than 0.45 dB) within

the antenna operating band. If all the red diodes are turned on

and all the green diodes are turned off, the four output phases

are clockwisely delayed, such that the broadside radiation

pattern is generated. On the opposite, if all the green diodes are

turned on and all the red diodes are turned off, the backfire

radiation pattern is generated. Therefore, by controlling the

status of the PIN diodes, the broadside mode and backfire

mode can be altered as shown in Table II and Fig. 4.

Fig. 5. Radiation beamwidth variation by different helical structure at the same

center frequency 1.5 GHz.

C. Design of the Quadrifilar Helical Radiator

Another important design consideration is the helical

structure which will determine the radiation pattern. To design

the QHA to operate at the center frequency 1.5 GHz, the length

of each helical arm is optimized to 83 mm according to the

analysis in reference [9]. The radiation beamwidth of the QHA

is strongly dependent on the winding shape of the helix. Figure

5 shows the radiation patterns of different helical structures at

the same resonant frequency. The QHA with less turns has

broader radiation beamwidth but lower gain. The radiation

beamwidth and broadside gain of QHA are varying in a

contradictory manner. This parametric study provides a

guideline to obtain the desired radiation patterns of the QHA

for different applications. For example, satellite navigation

systems like the GPS of the U. S. or CNSS of China require

antennas have broader radiation pattern as the 1/4 turn helix in

Fig. 5. On the contrary, other systems like RFID prefer

antennas with high broadside gain as the 1/2 turn helix.

III. Measured Results

The proposed antenna was fabricated as shown in Fig. 6. In

order to obtain the broader beamwidth, quarter turn helix was

chosen in the final implementation. The QHA radiator was

coiled by copper wires. All the substrates have the same

permittivity εr = 2.65, the thickness of 1 mm and the loss

tangent of 0.001 from Wangling Ltd. PIN diodes with surface

mount type 0403 (1 mm × 0.6 mm) were soldered between the

transmission lines for switching. Two DC bias lines were

adopted for controlling the diodes. One DC line was connected

to the two quarter-wave transformers as DC#1 and another was

connected to the four output ports as DC#2. The antenna is fed

by a coaxial cable in the center.

Fig. 6. Fabricated antenna model..

Fig. 7. Measured reflection coefficients and axial ratio bandwidths for the two

radiation modes.

Fig. 8. Measured broadside gain within the operating band for both modes.

Figure 7 shows the measured reflection coefficients and the

axial ratio bandwidths for both broadside and backfire modes

of the proposed antenna. A wide overlapped bandwidth for an

impedance bandwidth of 43% and an axial ratio bandwidth of

38% is obtained. Figure 8 exhibits the measured broadside gain

across the operating band for both modes. The maximum gain

is 2.3 dBic for the broadside mode and the peak gain for

backfire mode is 3.0 dBic. Measured radiation patterns at the

center frequency for both modes are found in Fig. 9. The

broadside radiation mode is realized when DC#1 is set to 3V

and DC#2 is 0V. The pattern has the broad beamwidth of 140

degree with the broadside peak gain of 2.3 dBic. The backfire

radiation mode can be achieved when DC#1 is 0V and DC#2 is

set to 3V. In this state, the pattern is pointing downward with

the beamwidth of 120 degree and the peak gain of 3.0 dBic.

IV. Conclusion

A pattern reconfigurable quadrifilar helical antenna is

studied in this paper. The QHA can obtain either broadside or

backfire radiation pattern by controlling the PIN diodes on the

feeding network. Good cardioid-shaped radiation patterns are

realized for both radiation modes. In addition, the antenna has

a compact size and light weight. The proposed antenna with

the unique pattern diversity is suitable to be used for many

applications such as subway and railway communication,

satellite communication, RFID or communication inside a

narrow street scenario.

ACKNOWLEDGMENT

This project was supported in part by the Research Grants

Council of the Hong Kong SAR, China (Project No. CityU

138413) and the Fundamental Research Program of Shenzhen

City under grant No. JCYJ20140509155229810.

Fig. 9. Measured radiation patterns at the center frequency 1.5 GHz: (left)

Broadside mode, (right) Backfire mode.

V. References

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[2] D. Piazza, J. Kountouriotis, M. D'Amico and K.R. Dandekar, “A technique for antenna configuration selection for reconfigurable circular patch arrays,” IEEE Trans. Wireless Commun., vol. 8, no. 3, 2009.

[3] W. Lin and H. Wong, “Polarization reconfigurable wheel-shaped antenna with conical-beam radiation pattern,” IEEE Trans. Antennas Propag., accepted, Dec. 2014.

[4] W. Q. Cao, B. N. Zhang, A. J. Liu, T. B. Yu, D. S. Guo, and K. G. Pan, “A reconfigurable microstrip antenna with radiation pattern selectivity and polarization diversity,” IEEE Antenna and Wireless Propag. Letters, vol. 11, pp. 453-456, 2012.

[5] Y. Y. Bai, S. Q. Xiao, C. R. Liu, X. Shuai, and B. Z. Wang, “Design of pattern reconfigurable antennas based on a two—element dipole array model,” IEEE Trans. Antennas Propag., vol. 61, no.9, pp.4867–4871, Sep. 2013.

[6] S. W. Yong and J. T. Bernhard, “A pattern reconfigurable null scanning antenna,” IEEE Trans. Antennas Propag., vol. 60, no.10, pp.4538–4544, Oct. 2012.

[7] C. Rhee, Y. Kim, T. Park, S. S. Kwoun, B. Mun, B. Lee, and C. Jung, “Pattern-reconfigurable MIMO antenna for high isolation and low correlation,” IEEE Antenna and Wireless Propag. Letters, vol. 13, pp. 1373-1376, 2014.

[8] C. Kittiyanpunya and M. Krairiksh, “A four-beam pattern reconfigurable Yagi-Uda antenna,” IEEE Trans. Antennas Propag., vol. 61, no.12, pp.6210–6214, Dec. 2014.

[9] Q. X. Chu, W. Lin, W. X. Lin and Z. K. Pan, “Assembled dual-band broadband quadrifilar helix antennas with compact power divider networks for CNSS application,” IEEE Trans. Antennas Propag., vol. 61, no.2, pp.516–523, Feb. 2013.

[10] Data Sheet of Bar50-02L PIN Diodes, Infineon Technologies, Application Note [Online]. Available: http:// www.infineon.com/.