An Ultra-Wideband Low-Profile Dipole Patch Antenna for VHF-Band Probing Radars

TIAN Yuxiao; ZHANG Feng; MA Zhangjun; WANG Jiacheng; JI Yicai

doi:10.11999/JEIT260105

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TIAN Yuxiao, ZHANG Feng, MA Zhangjun, WANG Jiacheng, JI Yicai. An Ultra-Wideband Low-Profile Dipole Patch Antenna for VHF-Band Probing Radars[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT260105

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TIAN Yuxiao, ZHANG Feng, MA Zhangjun, WANG Jiacheng, JI Yicai. An Ultra-Wideband Low-Profile Dipole Patch Antenna for VHF-Band Probing Radars[J]. Journal of Electronics & Information Technology. doi: 10.11999/JEIT260105

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An Ultra-Wideband Low-Profile Dipole Patch Antenna for VHF-Band Probing Radars

doi: 10.11999/JEIT260105 cstr: 32379.14.JEIT260105

TIAN Yuxiao^{1, 2},
ZHANG Feng^{1
,
,},
MA Zhangjun^{1, 2},
WANG Jiacheng^{1, 2},
JI Yicai¹

1.
Key Laboratory of Electromagnetic Radiation and Sensing Technology, Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100190, China
2.
School of Electronic, Electrical, and Communication Engineering, University of Chinese Academy of Sciences, Beijing 101408, China

Funds: National Key Research and Development Program of China under Grant 2024YFB3908003

Received Date: 2026-01-28
Accepted Date: 2026-03-16
Rev Recd Date: 2026-03-16

Available Online: 2026-03-31

Abstract

Abstract

Objective In radar systems, the limitations of traditional narrowband antennas in terms of data transmission rate and resolution have become increasingly apparent. Consequently, a wide variety of ultra-wideband (UWB) antennas have been proposed, exhibiting excellent range resolution and strong anti-interference capability. However, at low-frequency bands, existing UWB antennas often suffer from excessively large physical dimensions, which makes antennas bulky while ensuring mechanical strength and posing significant challenges for airborne or vehicle-mounted radar assembly. However, compact antennas that are easy to install suffer from low gain, which fails to meet the penetration depth requirements for deep subsurface detection. Balancing antenna size and radiation gain over an ultra-wideband range to fulfill the needs of VHF wideband probing radars remains a critical challenge. To jointly optimize bandwidth, size, and gain, this paper presents a planar dipole antenna loaded with an artificial magnetic conductor (AMC) structure and metallic shorting walls. The proposed antenna achieves stable radiation performance over a wide frequency range while maintaining a low-profile configuration and a structurally simple design. As a result, it provides an effective solution for VHF-band detection radar antennas. Methods By comparing the reflection phase characteristics of AMC unit cells with different geometrical shapes, square-shaped unit cells were selected to form a 9×7 AMC reflective layer. Owing to its in-phase reflection property, the AMC structure overcomes the conventional limitation that requires a quarter-wavelength separation between the antenna and a metallic ground plane, thereby significantly reducing the antenna profile height. The dipole patch employs an optimized meandered current-bending technique, which effectively reduces the horizontal size of the antenna. Meanwhile, metallic shorting walls are vertically loaded at both ends of the antenna. According to the image theory, equivalent currents will be generated on the outer surface of the metal walls when the antenna operates, thereby effectively extending the equivalent electrical length, leading to improved low-frequency performance without increasing the physical size. In addition, two vertical metallic walls are connected to the ground plane on both sides of the antenna, jointly forming a reflective back cavity. This structure enhances the unidirectional radiation characteristic and improves the antenna gain. As a systematic co-design to break the physical constraints, four 125-Ω resistors are bridged between the antenna feed point and the metallic sidewalls. This resistive loading effectively suppresses low-frequency strong resonances and broadens the impedance bandwidth at the cost of acceptable Ohmic losses. Results and Discussions A prototype antenna with favorable simulated performance was fabricated and measured in a microwave anechoic chamber. The measured impedance bandwidth (VSWR < 2) ranges from 50 MHz to 400 MHz, which agrees well with the simulated bandwidth of 84 MHz to 366MHz. The measured impedance matching performance is slightly better than the simulated result, mainly due to the reduced reflections caused by cable losses and power divider losses in the feeding network. The measured antenna gain follows the same trend as the simulated gain, with deviations within an acceptable range of 1dBi. Radiation pattern measurements demonstrate that at 100 MHz, 200 MHz, and 300 MHz, the measured co-polarization patterns agree well with the simulated results, and the maximum radiation direction is consistently normal to the antenna plane, validating the effectiveness of the proposed antenna design. As shown in figure 5, on the radiating patch layer, the current mainly flows along the +x direction, thereby generating a radiating electric field along the +z direction. The current distribution on the AMC unit can be equivalent to a current loop oriented along the +z direction. At this frequency, the x-direction current and the parasitic current loop of the AMC jointly enhance the radiation gain of the antenna. This proves the mechanism by which the AMC structure improves antenna gain. However, when the operating frequency increases to 400 MHz, the electrical size of the antenna reaches approximately $ 1.6\lambda $, resulting in main lobe splitting and a shift of the maximum radiation direction toward 90°. Although high-frequency beam splitting introduces spatial clutter, it is a reasonable physical trade-off for achieving the 0.07 λ_L ultra-low profile, and the overall UWB characteristics still provide high time-domain resolution for detection radar systems. At 400 MHz, the measured H-plane co-polarization level is slightly higher than the simulated result, which may be attributed to the coupling effect between the feeding cable and the vertically mounted antenna. Conclusions This paper proposes a low-profile ultra-wideband planar dipole antenna. By introducing an AMC layer and resistive loading, the impedance matching performance is significantly improved while maintaining a compact antenna size. In addition, a reflective back cavity is incorporated to enhance backward reflection, thereby increasing the realized antenna gain. A prototype of the proposed antenna was fabricated and experimentally characterized, and the measured results show good agreement with the simulations. The antenna achieves a measured impedance bandwidth of 100 MHz–366 MHz under the condition of VSWR < 2, while maintaining a compact size of 0.38λ_L × 0.18λ_L × 0.07λ_L. The maximum measured gain within the operating band reaches 6 dBi. This co-design demonstrates a comprehensive advantage in balancing key performance indicators such as wide bandwidth, low profile and relatively high gain, providing a practical and valuable implementation approach for the engineering design of low-frequency band detection radar antennas.
- Artificial magnetic conductor,
- Low-profile,
- Ultrawideband,
- Gain enhancement

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References(27)

References

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