Microstrip antennas are of significant interest and extensively utilized in communication systems because of their unique low profile. However, the general difficulty in microstrip antenna design lies in its wideband electromagnetic radiation within a low-profile structure. To enhance the bandwidth, superposing the fundamental mode and other high-order modes is the most common method, but this occupies a larger footprint than regular narrow-band modes. Here, as a counterintuitive way to broaden the bandwidth, a wideband miniaturized microstrip antenna is proposed by using two high-order modes. The avoidance of the fundamental mode allows for footprint miniaturization without decreasing the bandwidth, providing a different but feasible design strategy for wideband microstrip antennas. Compared with other microstrip antennas at the same profile, the proposed antenna achieves wider bandwidth and a smaller footprint. The experimental result shows a bandwidth of 4.81-6.01 GHz is achieved with a volume of 0.47 ×0.47 × 0.043 λ 0 ³ , where λ 0 represents the in-vacuum wavelength at the center frequency. Therefore, the proposed design provides an effective solution to the intrinsic contradiction between wideband electromagnetic radiation and compact antenna dimensions, not only in a low profile but in a small footprint, contributing to the fundamental development of microstrip antennas.

This paper proposes a dual-band circular-polarized (DBCP) microstrip antenna using flexible liquid crystal polymer (LCP) manufacturing process for on-smartphone ultra-wideband (UWB) positioning application. To achieve dual-band circular polarization in a low profile, the proposed antenna is designed with a cross-slot-loaded patch with four L-shaped feeding probes and a sequential phase feeding network. A circle of capacitive via fence are loaded surrounding the patch for area miniaturization, which is adaptive for the limited space of flexible printed circuit (FPC) in smartphones. Based on the UWB positioning protocol, a three-element antenna array is constructed in a low profile of 0.015 λ ₀ with required isolation of 17 dB. Experimental results show the overlap bandwidth of the efficiency and the axial ratio covering the demand bands of 6.30–6.80 GHz and 7.75–8.10 GHz. With the properties of dual wideband operation, circular polarization, and ultralow profile, the proposed antenna exhibits feasible solutions for the UWB positioning application in space-limited smartphones.

In this communication, a compact-size and high-efficiency air cavity antenna with a cage-like structure is proposed for 2.4-GHz Wireless Local Area Networks (WLAN). The air cavity antenna is constructed with four sides of hybrid metallized vias, including sparsely arranged blind vias and tightly arranged shorting vias. Firstly, the antenna size is significantly reduced by utilizing the shorting vias, which make the antenna operate at the high-order TM _1/2,1/2 mode. Then, by loading the capacitive blind vias at the radiating apertures, the antenna size is further miniaturized. Notably, high radiation efficiency is obtained attributed to the lower dielectric loss of the air-medium structure. Finally, a prototype of the proposed cage antenna has been fabricated and tested with good agreement between simulated and measured results. In such a compact size of 0.128 λ ₀ ×0.128 λ ₀ ×0.10 λ ₀ (λ ₀ is free-space wavelength at the center frequency), the measured total efficiency over 90% is achieved in the WLAN band by the cage structure. Compared with the existing 2.4-GHz antennas, the proposed one is with the ascendency of compact size and high radiating efficiency for WLAN applications.

This paper proposes a scalable dual-polarized antenna using the compact cavity and slot-dipole hybrid structure for omnidirectional radiation. For the horizontal polarization, an open-ended cavity is uniformly excited at its TE1/2,0,0 mode to achieve omnidirectional coverage. Based on this thin cavity, a hybrid structure with slots and parasitic dipole stub pairs is designed for vertical polarization, providing an omnidirectional pattern in the azimuthal plane. Measured results show that dual-polarized radiations with port isolation higher than 25 dB and gain variations lower than 2.7 dB are achieved in the band of 2.39~2.49 GHz, covering the frequency band of wireless local area network (WLAN) system. Moreover, to validate the scalability of the proposed antenna, a cascaded array is contrived to realize high-gain omnidirectional radiation. Compared with the existing works, the proposed omnidirectional dual-polarized antenna has the advantages of both compact volume and array scalability, exhibiting promising usage for high-gain router applications.

In this letter, a multiple beam antenna scheme with reduced port dimension is proposed for low-complex massive multi-input and multi-output (MIMO) systems. From practical scenario consideration, two 2-port and 8-element subarrays with dual 2-to-8 Butler matrix networks are designed for 3-dB beam coverage within 60° sector. Based on channel capacity analysis of an 8-subarray (8x8-element) antenna system, it is proved that only 25% number of radio frequency (RF) chains are utilized in the proposed scheme to achieve a competitive data transmission rate, compared with a regular 8x8-element and 64-chain massive MIMO system, with the advantages in low cost, low system weight, and low complexity of signal processing. The proposed 8-subarray system is built and measured to verify the antenna performance. The proposed multi-beam antenna scheme exhibits potential possibilities in low-complex and low-lost massive MIMO systems for the fifth-generation (5G) applications.

A hepta-mode wideband microstrip antenna is proposed for use on the back cover of mobile terminals, targeting Wi-Fi 6/6E and ultrawideband (UWB) channels 5–11 MIMO applications. This MIMO antenna design comprises four elements arranged in a sequential rotation pattern, each featuring four small patches with two asymmetric notches. Through proper adjustment of patch and notch dimensions, seven modes are effectively excited by a rotated L-shaped feeding probe, thereby amplifying bandwidth of the proposed antenna. Additionally, size miniaturization is achieved using a circle of blind vias. To validate the design strategy, a prototype of the MIMO antenna is constructed with dimensions measuring 60.6 mm × 60.6 mm × 2 mm. Meeting the requirements for mobile antenna specifications, the proposed MIMO antenna covers a wide range of frequencies, including Wi-Fi 6/6E and UWB channels 5–11, with a measured −6-dB impedance bandwidth of 5.14−9.05 GHz and an isolation of over 12 dB between each antenna element. Combining broad bandwidth, compact dimensions, and a low profile, this MIMO antenna demonstrates significant potential for supporting diverse wireless services on mobile terminals.