This communication demonstrates a method to design filtering antennas by using the filtering-radiating patch (FRP). The socalled FRP is a structure of a rectangular patch etched with slots. It inherits the radiation performance of conventional patch antennas, and more importantly, introduces filtering feature with a radiation null at either the upper or lower band edge of radiation efficiency curve. The frequencies of radiation nulls are easy to control. Based on the FRP, a novel filtering antenna is proposed. Two radiation nulls are realized at both band edges of the antenna efficiency curve, leading to a sharp band skirt and good selectivity in the boresight gain response. The locations of the two radiation nulls can be flexibly controlled by the lengths of slots. A prototype is fabricated and tested. The measured results show an impedance matching bandwidth of 7% with a center frequency of 5.24 GHz, two radiation nulls at 4.7 and 5.85 GHz, respectively, a realized gain of 6.6 dBi, the cross-polarization rejection larger than 23.4 dB, and the front-to-back ratio better than 15 dB. The presented method demonstrates the capability of not only achieving good filtering-radiating performances but also possessing very simple structures by only etching slots on the patch of a conventional microstrip antenna.

This paper presents a novel circularly polarized (CP) planar aperture antenna for cost-sensitive millimeter-wave, particularly fifth generation (5G), applications. The proposed antenna, which is a differential one, has high gain and wide bandwidth and can be built on a single-layer laminate using standard printed-circuit board (PCB) technology. This makes the antenna both low cost and easy to integrate with common differential circuits. The antenna consists of an opening cavity formed by metalized vias, which encloses a set of loop-like strips that are fed differentially. The strips carry traveling wave current which together with the aperture's E-fields distribution give rise to CP radiation. The aperture size of the antenna can be extended for higher gain by adopting a dual- or quadruple-loop-like strips configuration enclosed by a larger opening cavity. The fabricated quadruple-loop-like strips-based antenna prototype designed to operate at 60-GHz band could achieve 3-dB axial ratio (AR) bandwidth of 16.7% (56-66.2 GHz) within its -10-dB impedance bandwidth and stable right-handed CP (RHCP) gain throughout the operating bandwidth with a peak of 14.6 dBi.

This communication presents new designs of dual-circularly polarized (CP) planar aperture antenna and array for 60 GHz applications. First, a four-port planar aperture antenna with its feeding network is developed that exhibits wide impedance bandwidth, dual-CP radiation as well as high gain. Then, based on the proposed antenna, a new scheme of building a dual-CP array is proposed. With this new scheme that combines the power splitting network and series feeding method, four sequentially fed antenna elements are successfully combined to form a CP radiation array. The experimental results show that the -10 dB impedance bandwidths of the antenna and the array are more than 18.2% (55-66 GHz). While the 3 dB axial ratio bandwidths are from 54.2 to 64.3 GHz (17.2%) for the antenna and from 54.8 to 65 GHz (17%) for the array. The maximum gains achieved are 13.7 and 17.85 dBic for the antenna and array, respectively.

A wideband highly isolated MIMO patch antenna with an artificial magnetic conductor (AMC) ground plane is proposed in this letter. The antenna, which is rotationally symmetrical, is constructed by V-shaped patches coupled-fed by a bowtie dipole. The bowtie dipole and the V-shaped parasitic patches produce two resonant modes that are coupled together. Therefore, a wide impedance bandwidth is obtained. Thanks to the orthogonal feeding and the rotational symmetrical geometry, the antenna exhibits high port isolation as well as symmetrical radiation patterns with a compact size of 40${\times}$40${\times}$1.524 mm3. By placing an artificial magnetic conductor (AMC) ground plane with a distance of 10.5 mm below the radiating element, the antenna can achieve a unidirectional high gain with a lower height of the profile compared to that with PEC ground. Measured results show the antenna has an impedance bandwidth of 31.0% (3.0-4.1 GHz) with port isolation as low as -25 dB. The peak gain can reach 7.1 dBi with stable and symmetrical radiation patterns.

A new differential frequency-reconfigurable antenna based on dipoles is presented in this letter. The basic structure of the proposed antenna consists of two pairs of vertical arms forming two dipoles, the feeding structure, mode switching structure, and p-i-n diodes. By switching “on” and “off” p-i-n diodes, the antenna can resonate at two states, and thus work centered at 3.5 and 5.5 GHz, respectively. Though the two states correspond to different resonant modes, the effective radiation parts are the same and the mode switching structure will not contribute to the far field for both states. This results in similar radiation patterns for both states. Besides, the proposed antenna is also simple in structure and wide in bandwidth. The measured -10 dB impedance bandwidths are 2.89-4.07 GHz (33%) and 5.1-6.19 GHz (19.8%) for the two states, respectively.

This paper presents a novel dual polarized planar aperture antenna using the low-temperature cofired ceramics technology to realize a novel antenna-in-package for a 60-GHz CMOS differential transceiver chip. Planar aperture antenna technology ensures high gain and wide bandwidth. Differential feeding is adopted to be compatible with the chip. Dual polarization makes the antenna function as a pair of single polarized antennas but occupies much less area. The antenna is ±45° dual polarized, and each polarization acts as either a transmitting (TX) or receiving (RX) antenna. This improves the signal-to-noise ratio of the wireless channel in a point-to-point communication, because the TX/RX polarization of one antenna is naturally copolarized with the RX/TX polarization of the other antenna. A prototype of the proposed antenna is designed, fabricated, and measured, whose size is 12 mm × 12 mm × 1.128 mm (2.4λ ₀ × 2.4λ ₀ × 0.226λ ₀ ). The measurement shows that the -10 dB impedance bandwidth covers the entire 60 GHz unlicensed band (57-64 GHz) for both polarizations. Within the bandwidth, the isolation between the ports of the two polarizations is better than 26 dB, and the gain is higher than 10 dBi with a peak of around 12 dBi for both polarizations.