A compact dual-band Dolly-shaped antenna with parasitic elements for automotive radar and 5G applications.

In this paper, a compact dual-band Dolly-shaped antenna (DBDSA), resonating at 23.52 GHz and 28.39 GHz, is proposed for automotive radar, 5G, and Industrial, Scientific, and Medical (ISM) applications. The antenna is designed on a 7 × 7 × 1.28 mm3 which is 0.541λ0×0.541λ0×0.099λ0 in electric size, where λ0 represents the free space wavelength at 23.16 GHz. Rogers RO3010 substrate with a dielectric constant of 10.2 and a loss tangent is about 0.0022 has been used. Two F-shaped parasitic elements and a rectangular slot have been used to achieve the desired electromagnetic antenna performances. After modeling and optimizing the proposed antenna configuration through High-Frequency Structure Simulator (HFSS) software, its prototype was manufactured and measured to validate the simulated results. The DBDSA achieves an overall radiation efficiency of 80% within the two operating frequency bands. The radar band exhibits a stable gain of 5.51 dBi, while the 5G band has a gain of 4.55 dBi. Furthermore, the experimental results show that the |S11|≤-10 dB bandwidths are 1.16 GHz (23.16 GHz-24.32 GHz) in the lower band and 634 MHz (28.078 GHz-28.712 GHz), respectively. A good agreement is found between the simulated and measured results.

Introduction

The millimeter wave technologies have attracted a lot of researchers from both industries and academia. Due to its attractive properties such as large bandwidth, miniaturization of RF front end including antennas, high resolution, and low interference, the mm-wave spectrum (30–300 GHz) is considered as the potential candidate for high-speed communication services in 5G networks [1]. For 5G antennas in one hand, high gain, low profile, low cost, broadband or multiband operation, multiploidization, and specific radiation direction are among several design parameters that have higher priorities than others [2]. Moreover, 5G networks are emerging as the foundation for advanced communication services and as the infrastructure supporting socio-economic development and driving industrial digital transformation [3]. The frequency bands centered at 28, 38, 60, and 73 GHz have been allocated for 5G mobile communications by International Telecommunications Union (ITU) [4]. Various types of planar antenna solutions for 5G communication systems have been developed over the past decade. Those antennas are either based on a single radiating element [5, 6, 7], MIMO or phased array antenna systems [8, 9]. The antennas based on MIMO technology despite their capabilities to improve the performance of the latter, have some drawback such as mutual coupling effect, surface wave and spurious waves as well as adequate techniques to solve those issues [10, 11, 12, 13, 14].

On the other hand, with increasing traffic density and road accidents, an increasing interest has emerged for additional electronic vision to improve comfort and safety. This includes closed-circuit television (CCTV), infrared sensors, laser, and radar [15]. As the core sensors of driver assistance systems, automotive radars can be broadly split into three categories: short range (SRR, up to a few 10 m) for parking aid, obstacle and pedestrian detection, medium-range (MRR, about 40–100 m) for cross-traffic alert and lane change assist, and long-range (LRR, up to 200 m or even 250 m) for Adaptive Cruise Control [16, 17, 18]. As for 5G antennas, automotive radar antennas require small size and depth for vehicle integration, high gain, and cost-effectiveness [19, 20]. The antenna proposed in [21] employs MIMO technology for the development of automotive radar for adaptive cruise control (ACC) and automatic emergency braking (AEB) in Moreover, a 12 × 8 antenna array designed at 24 GHz for automotive radar used for blind spot detection (BSD), Lane change assistance (LCA), and rear cross-traffic alert (RCTA) [22]. To meet the different needs of modern mobile communication, vehicles are loaded with various functional antennas, which can be used in emergency call, entertainment, navigation and positioning [23]. A significant amount of research has provided numerous MIMO and phased array antennas designs for automotive radar and 5G applications. However, multiple antennas in a confined space result into other issues such as mutual coupling or isolation between radiating elements [24]. Consequently, some recent works propose single element antennas for the same applications. For instance, in [25], a single element W-band plumb shaped patch antenna has been proposed for automotive radar and 5G applications. Similarly, in [26] an ultra-wideband mm-wave antenna for automotive radar and 5G applications is presented in the frequency range 16–40 GHz. In [27], another single element antenna is investigated for use in automotive radar and 5G applications. A rectangular shape is used, and the antenna exhibits 5.64 dB gain in its upper operating frequency band.

The antenna performance can be enhanced or degraded by the feeding technique, the parasitic patch elements, the defective ground structure, the slot, the air gap, the shorting pin, and the metamaterial [28, 29, 30]. From the literature, the parasitic element has two interesting features that can be exploited in antenna design engineering. Its helps in either generating a resonant frequency or enhancing the performances of the planar antennas [31, 32, 33]. Furthermore, the combination of automotive radar and 5G technologies has not yet attracted more researchers despite few works done.

This work proposes a novel antenna solution for automotive mobile communications and radar applications. This is to not only to maintain the devices miniaturized but also to prove the possibilities of using different applications by a single device. In the remaining part of this paper, the proposed antenna design methodology based on mathematical model is presented before discussing the simulated and measured results.

Antenna design

Antenna configuration

The proposed Dolly-shaped antenna (DSDBA) is designed on a single-layered substrate with an overall volumetric size of 7 × 7 × 1.28 mm3, corresponding to an electric size of 0.541λ0×0.541λ0×0.099λ0 where λ0 represents the free space wavelength at 23.16 GHz. The radiating patch is printed on a Rogers RO3010 substrate with a dielectric permittivity (εr) of 10.2 and a loss tangent of 0.0022. The analysis of the proposed Dolly-shaped antenna has been performed using HFSS software. Two F-shaped parasitic elements and a rectangle slot of 3 mm2 have been added to the antenna design structure to achieve the desired performance. The geometry of the proposed antenna design is presented in Figure 1. All the optimized antenna design parameters are listed in Table 1.

Figure 1

Geometry of the antenna: (a) top view, (b) side view.

Table 1

Design parameters of the proposed antenna.

Parameters	Description	Value
Wg	Width of the ground plane	7 mm
Lg	Length of the ground plane	7 mm
S	The surface of the radiating element	7.053 mm2
Xf	Length of the feedline	3.1255 mm
Wf	Width of the feedline	0.5 mm
L1	Length of the slot of the radiating element	3 mm
Ws1	Width of the slot of the radiating element	1 mm
L2	Length of the parasite element 1	5 mm
Ws2	Width of the parasite element 1	0.5 mm
Ws3	Length of the parasite element 2	0.25 mm
Ws2	Width of the parasite element 2	0.25 mm
Rc1	The radius of the big circle	2 mm
Rc2	The radius of the small circle	0.5 mm
R1	The major axis of the big ellipse	1 mm
R2	The Major axis of the small ellipse	0.5 mm
R3	The minor axis of the big ellipse (R3= r1×R1)	0.425 mm
R4	The minor axis of the small ellipse (R4=r2×R2)	0.25 mm
r1	The ellipticity ratio of the big ellipses (body of the Ant.)	0.425
r2	The ellipticity ratio of the small (hands and feet of the Ant.)	0.5

Mathematical modeling

By using the broadband planar monopole antennas principle described in [34, 35] and considering the above-given data in Table 1, the radiating total active area of the radiating element is equated to that of the equivalent cylindrical monopole antenna, yielding to.where L and r denote the length and the radius of the equivalent cylindrical monopole antenna and S the patch's surface.

Based on the geometry of the antenna, the surface of the proposed Dolly-shaped configuration is determined by:

The length of the equivalent cylindrical monopole antenna can be determined using the following formula:

From Eqs. (1) and (2), the radius r of the equivalent cylindrical monopole antenna is given as:

The width will be calculated using this formula:where W is the width of the patch.

The frequency of resonance of the lower band is therefore computed as per the following in [35]:P is the gap between the length of the feed line and the big ellipse's major axis.

The effective permittivity is determined using the following formula:

Antenna's shape effect

In order to validate the Dolly-shaped, a comparative study has been carried out. The empirical shapes with the same dimensions have been simulated in the same frequency range. The result is presented in Figure 2 below.

Figure 2

Comparative Study between the empirical shapes and the Dolly-Shaped.

From Figure 2, the Dolly-Shaped antenna provides encouraging performances compared to the empirical shapes.

Effects of the parasitic elements and rectangular slot

The parasitic elements (PE) and the slot help to create multi-band behavior and enhance the antenna performance [36, 37, 38]. Figure 3 illustrates the effect of the parasitic elements and the slot on the antenna's reflection coefficient.

Figure 3

Comparison of the simulated reflection coefficients.

From Figure 3, the simulated results show that the Dolly-shape antenna (DSA) alone resonates at 24.74 GHz. By inserting a rectangular slot in the DSA, the resonant frequency is shifted rightwards from 24.74 GHz to 24.94 GHz with a better reflection coefficient as compared to the first case. Furthermore, it can be observed that by adding the two F-shaped parasitic elements on the latter, the lower resonant frequency shifted slightly leftwards from 24.74 GHz to 23.86 GHz in the lower band while creating another resonant frequency at 27.93 GHz in the antenna's upper band. Finally, combining the rectangular slot and the two F-shaped parasitic elements with the DSA yields the optimal results. The resonant frequencies are shifted from 23.86 GHz and 27.93 GHz–24.08 GHz and 28.15 GHz, respectively. Moreover, the reflection coefficients have been improved, from -20.94 dB to -44.20 dB in the lower band and -32.08 dB in the upper band.

The methodology process can be summarized into three steps, as illustrated in Figure 4:

Figure 4

Summarized design process.

Design of a Dolly-shape antenna (Figure 4a)

Insertion of two F-shape parasitic elements (Figure 4b)

Insertion of a rectangular slot (Figure 4c)

Result and discussion

Reflection coefficient

To combine the useful with the pleasant, the proposed DBDSA has been manufactured to validate its results and its prototype is shown in Figure 5 below.

Figure 5

Fabricated antenna: (a) top view (b) Bottom view.

The simulated and the measured reflection coefficient versus frequency of the antenna are presented in Figure 6 for both bands. The measured |S11| ≤ -10 dB illustrates that the antenna achieves a bandwidth of 1.16 GHz (23.16 GHz–24.32 GHz) in the lower band and 634 MHz (28.078 GHz–28.712 GHz) in the upper band. The resonant frequencies were found at 23.52 GHz and 28.39 GHz with a return loss of -43.43 dB and -31.54 dB, respectively. Contrary to the mobile applications, this proposed antenna will exhibit at -6 dB, 3.25 GHz (22.85 GHz–26.10 GHz) in the lower band, and 1.09 GHz (27.87 GHz–28.96 GHz) in the upper band with the same return loss.

Figure 6

Reflection coefficient of the proposed Dolly-shape antenna.

The frequency band of 5G technology depends on the region. Table 2 below illustrates that the proposed antenna covers the ISM, radar and 5G frequency bands.

Table 2

Frequency band for 5G, Short-range radar and ISM band.

Regions	Frequency range				Application
	24–30 GHz	37–50GHz	64–71GHz	>95GHz
United States of America	24.25–24.45GHz24.75–25.25GHz27.5–28.35GHz	37–37.6GHz37.6–40GHz47.2–48.2GHz	37–37.6GHz37.6–40GHz47.2–48.2GHz	57–64 GHz64–71 GHz	5G
Canada	26.5–27.5GHz27.5–28.35GHz	-	37–37.6GHz37.6–40GHz	57–64 GHz64–71 GHz
France	26GHz		57–66GHz
China	24.75–27.5GHz	40.5–43.5GHz	-	-
Japan	26.6–27GHz27–29.5GHz	39–43.5GHz57–66GHz
India	24.25–27.5GHz27.5–29.5GHz	37–43.5GHz
Australia	24.25–29.5GHz	39GHz	57–66GHz
United Kingdom	24.5–27.5GHz		57–66GHz
South Korea	25.7–26.5GHz26.5–28.9GHz28.9–29.5GHz	37GHz	57–66GHz
United States of America	24–24.25 GHz			77–81 GHz	Automotive radars
United States of America	24–24.3 GHz		61.0–61.5 GHz		ISM Application

Gain and efficiency

Being the ability to radiate the received power in any direction compared to a theoretical isotropic antenna, the gain of the proposed antenna is depicted in Figure 7. A system configuration involving two identical antennas placed at 4 cm from each other has been simulated using Ansys HFSS. The transmission coefficient S21 was exported to evaluate the antenna gain using the two-antenna method [39] based on the Friis Eq. (8) as given below:where S21 is the transmission, fr the resonant frequency, and R the distance between the two antennas.

Figure 7

Gain of the proposed DSDBA antenna.

In Figure 7, the results show a stable gain of 5.51 dBi in the 24 GHz band and 4.55 dBi in the second band (28 GHz). This illustrates that the angle in which the radiation is constrained is reduced and antenna concentrates its energy towards a specific direction.

From simulation results, the efficiency is 87% and 81%, in the lower and upper band, respectively. Also, by considering the mismatch between the connector, the feedline, and the antenna, the total efficiency is 85% for the 24 GHz band and 68% for the 28 GHz band. This illustrates that the antenna radiates a minimum of 68% of the incident power.

Current distribution

The surface current distribution gives a better understanding of how the current flows in different antenna compartments at a given frequency. In Figure 8, the current distribution is shown at both resonant frequencies. As it can be noticed, the parasitic elements and rectangular slot played an essential role on both frequency bands in achieving the results.

Figure 8

Current distribution of the proposed antenna at 24 GHz (a) and 28 GHz (b).

In the 24 GHz band, the current is more vivid around the feedline's edges, the parasitic elements, the rectangular slot, and the edges of the whole antenna structure's edges with a maximum intensity of 357.7 A/m. The effect of parasitic elements is also observed at 28 GHz, where the surface current distribution seems to be equitable in the upper part of the structure and the feedline while being high toward the edges of the structure, specifically on the armpits of the Dolly-shape. The maximum intensity in the band of 28 GHz is 3639.8 A/m.

Voltage standing wave ratio and impedance matching

The voltage standing wave ratio (VSWR) indicates the mismatch amount between the antenna and the feedline connected to it. Generally, the value below two is considered as good matching in microwave engineering. Figure 9 presents the impedance matching of the proposed antenna in terms of VSWR. It is observed that the proposed antenna exhibits a maximum VSWR of about 1.05 for both simulation and measurement, as shown in below Figure 9.

Figure 9

VSWR of the proposed antenna.

The VSWR results plotted in Figure 9 demonstrates that the proposed antenna achieves a good matching across the two operating frequency bands. This implies that a maximum incident power is transferred to the antenna radiating element, which results in 87 % and 81 % radiation efficiency in the lower (24 GHz) and upper (28 GHz) bands, respectively.

The proposed antenna's performance is compared to the previous works on automotive radar and 5G in Table 3.

Table 3

Comparison of the results.

Ref.	Frequency band	Antenna size	Patch area	Gain	Radiation efficiency	Substrate	Substrate thickness	Applications covered
[40]	27.535–28.382 GHz	45.47 mm2	13.94 mm2	6.62 dB	70%	Rogers 5880	0.5 mm	5G applications
[41]	27.75–28.77 GHz	361 mm2	81 mm2	7.54 dB	62%	Rogers 5880	0.787 mm	5G applications
[5]	27.039–29.199 GHz	243 mm2	144 mm2	8.40 dB	83.51%	Duroid RO4003C	0.813 mm	5G applications
[42]	22.60–25.70 GHz	1800 mm2	400 mm2	9.7dB	Not provided	FR4	1.6 mm	Radar applications
[43]	23.95–24.53 GHz	792 mm2	112.68 mm2	11.9 dB	Not provided	Rogers 4350B	0.254 mm	Radar applications
[44]	27.697–29.33 GHz	36 mm2	27.17 mm2	10 dB	98%	RT/Duroid 5880	0.6 mm	5G applications
[45]	24–29.90 GHz	552 mm2	63.48 mm2	13.40 dB	98 %	Rogers 5880	0.79 mm	Radar application
[46]	23.89–25.11 GHz	621.62 mm2	311. 693 mm2	Not provided	Not provided	Rogers 5880	0.787 mm	Radar application
This work	23.16–24.32 GHz and 28.078–28.712 GHz	49 mm2	7.053 mm2	5.51 dBi and 4.55 dBi	87% and 81%	Rogers 3010	1.28 mm	Radar , 5G , and ISM applications

Most of the proposed antennas are focused on either MIMO or Wideband technologies [43, 46]. Moreover, from Table 3, the proposed antenna is the most miniaturized single element antenna that can operate covering simultaneously automotive radar and 5G applications. This is significant because, with an active patch area of 7.053 mm2 and an overall size of 7 × 7 × 1.28 mm3, the proposed antenna can easily fit in wireless systems' confined space.

Conclusion

This paper proposes the conception and experimental validation of a compact dual-band Dolly-shaped antenna (DBDSA) with a rectangular slot and two F-shaped parasitic elements using microstrip technology. Printed on a 7 × 7 × 1.28 mm3, which represents an overall electrical size of 0.541λ0×0.541λ0×0.099λ0, where RO3010 has been used, the DBDSA has a surface area of about 7.053 mm2. The λ0 represents the free space wavelength at 23.16 GHz. The radiating element compact size guarantees a -10 dB bandwidth of 1.16 GHz in the range (23.16–24.32) GHz and 634 MHz (28.078–28.712) GHz in the 24 GHz and 28 GHz bands, respectively. It has been pointed out 87% and 81% of the antenna radiation efficiency in automotive radar/ISM band and 5G band, while the in-band gains are 5.51 dBi and 4.55 dBi. The lowest return loss level is approximately -43.43 dB and -31.54 dB in the measurement, which eventually shows the perfect matching of the device in the telecommunication environment. Finally, the DBDSA device is a great and promising candidate for the mix of two leading technologies (radar for automotive and 5G), as experimental results have demonstrated through the prototype measurements. For future work, the design can be used for MIMO and array configurations to increase the data rate and meet other requirements of both 5G and automotive radar applications.

Declarations

Author contribution statement

Ce Lakpo Bamy: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data; Wrote the paper.

Franck Moukanda Mbango: Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data.

Dominic Bernard Onyango Konditi: Contributed reagents, materials, analysis tools or data.

Pierre Moukala Mpele: Performed the experiments; Analyzed and interpreted the data; Contributed reagents, materials, analysis tools or data.

Funding statement

This work was supported by the African Union Commission through the Pan African University Institute for Basic Sciences Technology and Innovation (PAUSTI).

Data availability statement

Data included in article/supplementary material/referenced in article.

Declaration of interests statement

The authors declare no conflict of interest.

Additional information

No additional information is available for this paper.