This paper presents a compact dual-band four-element multiple-input multiple-output (MIMO) antenna system for the fifth-generation (5G) laptops with a large display-to-body ratio. The four antenna elements, each being a three-dimensional inverted-F antenna (IFA) of the same structure and size, are constructed on the same T-cross-sectioned substrate, the vertical part of which is embedded in the 1 × 64 mm2 clearance area created from the upper edge of the display ground plane. They are configured into two dual-antenna units. Within each unit, the two IFAs are arranged to be skew-symmetric with respect to the display ground plane, and their short-circuit points are brought close to each other to achieve the so-called short-circuit decoupling. In addition, the two units are mirror imaged of each other with a small gap in between and are connected by two decoupling chip inductors to form a high-isolation four-element MIMO antenna system. In the operating bands of 3300–3600 and 4800–5000 MHz required by 5G, the measured isolation is larger than 10 dB, and the measured antenna efficiency is beyond 35 %, both being large enough for practical applications. In particular, the proposed MIMO antenna system has a profile height of only 1.4 mm, which is possibly the smallest one achieved so far in the literature, making it suitable for laptops with a large display-to-body ratio.

This paper proposes a two-element multi-input multi-output (MIMO) open-slot antenna implemented on the display ground plane of a laptop computer for eight-band LTE/WWAN operations. The metal surroundings of the antennas have been well integrated as part of the radiation structure. In the single-element open-slot antenna, the nearby hinge slot (which is bounded by two ground planes and two hinges) is relatively large as compared with the open slot itself and acts as a good radiator. In the MIMO antenna consisting of two open-slot elements, a T slot is embedded in the display ground plane and is connected to the hinge slot. The T and hinge slots when connected behave as a radiator, whereas the T slot itself functions as an isolation element. With the isolation element, simulated isolation between the two elements of the MIMO antenna is raised from 8.3–11.2 to 15–17.1 dB in 698–960 MHz and from 12.1–21 to 15.9–26.7 dB in 1710–2690 MHz. Measured isolation with the isolation element in the desired low and high frequency ranges is 17.6–18.8 and 15.2–23.5 dB, respectively. Measured and simulated efficiencies for the two-element MIMO antenna with either element excited are both larger than 50% in the desired operating frequency bands.

A sub-6-GHz four-element multi-input multi-output (MIMO) slot antenna system was proposed in this study for fifth-generation (5G) tablet computers, where each antenna element was constructed using a slot structure. To effectively use the available space in a tablet and maximize the screen, we have deployed the MIMO antenna system on the left side-edge frame of the tablet. The MIMO antenna system measuring 37.2 × 7 mm2 consists of two identical 13.6 × 7 mm2 dual-slot-antenna units that are separated by 10 mm. The two closely spaced slot antennas in the same dual-slot-antenna unit are arranged asymmetrically mirrored of each other with respect to the system ground plane. Although the dual-slot-antenna unit is very compact, the isolation between the two slot antennas in the same unit can be enhanced by using an ungrounded full-wavelength strip resonator. With the two ungrounded resonators in the MIMO slot antenna system, the simulated intra-unit isolations at the mid-band frequency can be enhanced by about 3.5 dB to meet the design requirement. As a byproduct, the two ungrounded resonators in the MIMO antenna system can also enhance the simulated mid-band antenna efficiency by about 4.5% and lower the worst simulated ECC by 0.195, from 0.518 to 0.323. This MIMO antenna system can support the frequency band of 3400–3600 MHz for 5G. In the operating band, the measured isolation is larger than 11 dB, and the measured antenna efficiency is larger than 40%. The envelope correlation coefficients (ECCs) calculated from the measured complex E-field radiation patterns are all smaller than 0.23, making the proposed design suitable for 5G mobile communications that require fast transmission.

This paper presents a novel design of a differentially-fed wideband circularly-polarized (CP) slot antenna. The CP antenna consists of two opposite-fed C-shaped radiating patches and a stub-loaded corner-truncated rectangular slot. With the slot designed to be anti-symmetric with respect to the bisection plane and oppositely fed by two microstrip lines, good differential-mode (DM) performance was obtained. On the other hand, the radiations contributed by the corresponding parts of the anti-symmetric CP antenna will be destructive when in common-mode (CM) operation. This results in high CM suppression without a preceding CM-rejection bandpass filter. Also, low DM axial ratios were achieved by tuning the truncated corner length, the protruded stub length, and the coupling length and gap of the C-shaped radiating patches. Measurement shows that the designed CP antenna has a wide 10-dB DM impedance band of 5-6.49 GHz and a 3-dB DM axial-ratio band of 4.94-6.03 GHz, corresponding to a CP fractional bandwidth of 18.7%. Also, in 4.5-6.5 GHz the proposed antenna can effectively reject CM input signals because the measured CM return loss is smaller than 2.91 dB, and can convert only very little DM input power into CM reflected power since the DM-to-CM conversion is less than -50 dB.

This paper presents the design of a compact double-loop sub-6-GHz dual-band MIMO quad-antenna system for 5G laptops. To meet the market demand for laptops with a high screen-to-body ratio, the sub-6-GHz dual-band MIMO quad-antenna system is realized to have a low-profile height of only 3 mm. To make the MIMO quad-antenna system suitable for laptops with a narrow bezel, the four antenna elements are printed on the same FR4 substrate, which is mounted on the upper edge of and coplanar with the display ground plane of a laptop. The four antenna elements have the same double shorted loop structure and the same size of $15\times $ 3 mm ² . In the loop structure, a meandered path is embedded in one of the two shorted-end sections, and a series chip capacitor is embedded in the other. The low-frequency resonance mode can be adjusted by varying the meandered path, and the high-frequency resonance mode can be tuned using the meandered path and the series chip capacitor. The four antenna elements are aligned in the same direction with an end-to-end gap of 5 mm so that satisfactory isolation can be achieved without any additional isolation elements. The MIMO quad-antenna system, although measuring only $75\times $ 3 mm ² with the three gaps included, can cover 3400–3800 and 4800–5000 MHz for 5G dual-band operations. The measured isolations between the four antenna elements are larger than 10 dB, the envelope correlation coefficient (ECC) values calculated from the measured radiation patterns are all below 0.27, and the measured radiation efficiencies of all four antenna elements are over 42%.

The contribution of this work is to propose a half-mode substrate integrated coaxial resonator (HMSICR) and its application in bandpass filter (BPF) design. The proposed HMSICR is formed by evenly bisecting a square substrate integrated coaxial resonator (SICR), which is a cavity composed of two dielectric substrates and three metal layers. The SICR’s sidewalls are mimicked by periodically spaced thru-via arrays, and a circular patch is embedded in the middle metal layer of the SICR with the patch shorted to the cavity’s bottom wall by a circular array of blind vias. This HMSICR can drastically lower the cavity’s resonance frequency. The achieved frequency reduction rate of the proposed HMSICR, as compared with that of its conventional substrate integrated waveguide (SIW) cavity counterpart, reaches 70%. A sample four-HMSICR BPF is built for the circuit verification measurement. To further reduce the sample filter’s area, the composing HMSICRs are vertically stacked in a back-to-back configuration. We believe that its obtained size-reduction rate reaches the highest record.