A Planar Huygens Antenna Utilizing Crossed Electric and Magnetic Dipoles

TL;DR

This work presents a planar Huygens antenna that realizes superdirective radiation by co-activating a magnetic dipole from a $0.5\lambda$ slot and a full-wavelength electric dipole from a printed dipole, arranged on a low-profile PCB-compatible disk. By engineering in-phase excitation and forward constructive interference while suppressing backward radiation, the design achieves a directivity of $8.37$ dBi with a simulated and measured radiation efficiency near $97\%$, yielding a realized gain close to the directivity ($8.27$ dBi). The device operates around $4.5\mathrm{GHz}$ and demonstrates a strong front-to-back ratio of about $12$ dB, with a configuration that requires no complex feeding and remains scalable to higher gains via low-permittivity dielectrics. This approach positions planar, low-profile Huygens sources as practical, high-gain alternatives to traditional end-fire arrays for low-power wireless applications. All numerical, simulated, and measured results are in good agreement, underscoring the method's viability for PCB-compatible, high-efficiency superdirective antennas.

Abstract

The natural source of a magnetic dipole in antennas is typically an electrically small loop, which can be utilized in conjunction with an electric dipole to realize an electrically small Huygens' antenna. However, these antennas suffer from low radiation efficiency and their theoretical directivity limit is 4.8 dBi. Magnetic dipoles with an electrical size larger than 0.5lambda are highly desirable for high-gain applications. This paper builds on the development of a magnetic dipole source that utilizes a 0.5lambda slot positioned near a printed dipole with a length twice that of the slot. Such a combination of electric and magnetic dipoles yields a highly directive radiation pattern, resulting in a higher gain than a uniformly illuminated antenna of similar size. The prototype is designed to operate at 4.5 GHz, with a directivity of up to 8.37 dBi. The analytical, numerical, and measured results agree fully. This high-gain superdirective antenna is highly desirable due to its excellent features, including being low-profile, PCB compatible, and having a low-complexity feeding topology, compared to the existing approach of the two-element end-fire array.

Figures (7)

• Figure 1: Topology of the proposed Huygens' superdirective antenna (a) $y$-aligned slot (magnetic dipole) on the top side (b) $x$-aligned printed electric dipole on the bottom side.
• Figure 2: The electric fields (a,c) and magnetic fields (b,d) over the designed Huygens' antenna, forming $x$-oriented electric dipole (a) and $y$-oriented magnetic dipole (d).
• Figure 3: Fabricated Huygens' antenna: (a) top side, (b) bottom side, and (c) its reflection response.
• Figure 4: Antenna's far-field measurement setup.
• Figure 5: 2D radiation pattern along $XZ$-plane and $YZ$-plane.