This letter proposes a simple compact microstrip antenna with enhanced bandwidth. The antenna is composed of three narrow rectangular patches: one middle patch and two side patches. The side patches are staggered longitudinally with respect to the middle patch and connected using short strips. The antenna is printed on a thin single-layer dielectric substrate with a ground plane and fed by a coaxial probe at the center of the middle patch. By staggering the side patches with respect to the middle patch, two resonant modes are excited at two close frequencies and a wide bandwidth is obtained. The antenna has a compact size of 0.31 λ 0 × 0.29 λ 0 × 0.027 λ 0 (where λ 0 is the center operating wavelength in the free space) and a measured impedance bandwidth of 6.8% (return loss > 10 dB), which is approximately 2.3 times wider than that of a conventional square microstrip antenna on the same substrate. The antenna has a stable gain varying from 5.8 to 7.5 dBi and a low cross-polarization level less than −15 dB within the impedance bandwidth. The radiation characteristics are nearly constant over the entire impedance bandwidth.

A Simple Compact Wideband Microstrip Antenna Consisting of Three Staggered Patches

A low-profile broadband metasurface antenna (MSA) with dual-linear polarization is developed. The developed MSA mainly consists of a 4 × 4 grid-slotted patch array, two pairs of orthogonally printed feeding dipole strips, two vertically grounded and orthogonally placed microstrip Γ-shaped feeding structures, and an intact ground plane. It is demonstrated that the strip-excited MSA excites a leaky wave mode, a surface wave mode, and a dipole mode to provide a wide operational bandwidth. The prototype, with an overall size of 0.65 λ0 ×  0.65 λ0 × 0.07 λ0 (λ0 is the wavelength in free space at the center operating frequency) was fabricated and measured. Three modes with broadside radiation patterns for each port are simultaneously excited to create a wide impedance bandwidth 36% with the average gain value 9.3 dBi. Moreover, the port-to-port isolation and the cross-polarization discrimination (XPD) are, respectively, higher than 26 and 25 dB.

A Broadband Low-Profile Dual-Linearly Polarized Dipole-Driven Metasurface Antenna

A broadband metasurface antenna is proposed in this letter. The antenna is based on a nonperiodic metasurface. The modal behavior of the metasurface and the slot is analyzed using characteristic modes analysis (CMA). Three desired modes of the metasurface are found. Furthermore, the slot acts not only as a feeding structure but also as a metasurface-loaded antenna. By combining the three modes of the metasurface and the modes of the slot, the wide bandwidth is achieved under multimode resonance. To verify the design, the proposed metasurface antenna is simulated, fabricated, and tested. The results show that the proposed metasurface antenna achieves a wide impedance bandwidth above 79% and a wide 3 dB realized gain bandwidth of 77%.

Low-Profile Broadband Metasurface Antenna Under Multimode Resonance

A broadband printed monopole antenna is designed by using ELC (Electric Inductive–Capacitive) based metamaterial element for WLAN applications. The proposed antenna comprises single ring hexagon loaded with ELC metamaterial for broadband radiation. ELC is designed with a square loop nested inside the ring hexagon structure which is coupled by the small metal stub. By introducing ELC, it significantly improves the impedance bandwidth of the antenna due to unique EM wave property. The band characteristics of the ELC and its metamaterial property (negative permeability) are explained through waveguide setup method. The designed antenna involves with dimensions 30 × 30 × 0.8 mm3 and fabricated on a low-cost Flame Retardant-4 substrate having e r  = 4.4 and tan δ  = 0.02. It yields an impedance bandwidth of 2600 MHz (2.61–5.21 GHz) with a dual resonance of 3.21 GHz and 4.89 GHz, which is usable for WiMAX, C-band and WLAN applications. The measured far-filed pattern exhibits a stable pattern. The proposed antenna has many benefits, such as comprising compact size, simple structure, lower S 11 (dB) and capable of broadband characteristics.

Broadband µ-negative antenna using ELC unit cell

This article presents a planar, low-profile, and single-layer metasurface (MTS)-based wideband 4 $\times $ 4 array antenna operating in the 5G sub-6 GHz band. The proposed antenna consists of 4 $\times $ 4 unequal size MTS unit cells fed by a simple parallel microstrip feed network in the form of a thin strip cross dipole. The wide impedance bandwidth (IBW) and improved boresight gain characteristics are realized due, respectively, to the excitation of multiple TM resonance modes that are closely spaced and the relatively large lateral size that supports in-phase currents. With an overall size of $1.40\lambda _{0}\times 1.22\lambda _{0}\times 0.054\lambda _{0}$ (where $\lambda _{0}$ is the free-space wavelength at the center frequency of 5.64 GHz), the proposed antenna realizes an IBW of 41.13% (4.48–6.80 GHz), a peak boresight gain of 10.14 dBi, low cross-polarization in the E- and H-planes, and higher front-to-back ratio. Because of the advantages of low-profile, planar and single-layer structure, as well as equal E- and H-planes 3 dB beamwidth, the proposed antenna is a competitive candidate for several modern wireless communications systems, including 5G in the sub-6 GHz band.

A Single-Layer Low-Profile Broadband Metasurface Antenna Array for Sub-6 GHz 5G Communication Systems

A low-profile microstrip antenna that has a broad impedance bandwidth by exciting three resonant modes is proposed. The proposed antenna mainly consists of a grid-slotted radiation patch, a metal ground, four vertical metal strips, and a vertical grounded balun feeding structure. The TM10, TM12, and antiphase TM22 modes are excited simultaneously. The vertical grounded balun feeding structure is used to avoid etching slot on the metal ground to get a high front-to-back ratio. The four vertical metal strips are introduced to enhance the impedance matching and reduce the sidelobe of the radiation pattern of the antiphase TM22 mode. With a profile of 0.07 λ 0 ( λ 0 is the center operating wavelength in the free space), the measured −15 dB impedance operating band is 3.31–4.31 GHz, and the relative bandwidth is 26.2%. The measured front-to-back ratio is larger than 16 dB, and the sidelobe level is lower than −10 dB. The proposed antenna has a stable broadside radiation performance in the operating band.

A Broadband Low-Profile Multimode Microstrip Antenna

A differentially fed microstrip antenna is proposed. The antenna is mainly composed of four strips, two rows of shorting pins, and four pieces of parasitic patches. The TM10, antiphase TM20, and TM12 modes are excited and matched simultaneously over a broadband. The experimental results show that, though the proposed antenna has a low profile of 0.052λ0 (λ0 is the free-space wavelength at the center frequency), it has the −10 dB impedance operating band of 4.25–6.27 GHz and the relative bandwidth of 38.4%. The variation of the measured gain which is 7.21±0.36 dBi is less than 1 dB over the whole operating band. The proposed antenna achieves good performances of broadside radiation with the measured front-to-back ratio of larger than 17 dB, stable radiation patterns without null, and stable gain in the operating band.

Bo Cheng

Papers

A Broadband Low-Profile Multimode Microstrip Antenna

A Differentially Fed Broadband Multimode Microstrip Antenna