There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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Computational Methods For Electromagnetics

In this communication, a novel dual-band dual-polarized filtering antenna with high selectivity is proposed. By etching four slots at each side of a square radiating patch, dual operation bands as well as a natural radiation null between the two bands are observed. Another two radiation nulls are generated by introducing a novel feeding structure, which is composed of a microstrip line with open-circuit stepped-impedance resonators (OCSIRs). Thus, a dual-band bandpass filtering response of the realized gain is obtained. Each polarization of the antenna is differentially fed, and the differential port isolation is better than 37 dB. A prototype of the antenna element and a $1\times 4$ array is fabricated and tested to validate our design. Measured results show that the antenna element has dual operation bands of 3.28–3.71 and 4.8–5.18 GHz for VSWR < 1.5. Besides, a high out-of-band gain-suppression level which reaches 17.7 dB is also obtained. Good performance of the proposed antenna makes it a promising candidate for 5G sub-6 GHz base station systems.

Differentially Fed, Dual-Band Dual-Polarized Filtering Antenna With High Selectivity for 5G Sub-6 GHz Base Station Applications

A novel compact differential-fed dual-polarized filtering patch antenna is proposed. Specific filtering response with radiation nulls is firstly realized for the dual-polarized antenna element by symmetrically loading defected ground structures (DGSs), a cross slot, and eight shorting pins without extra circuits. The DGS with pins can generate a lower edge radiation null for a sharp roll-off rate and simultaneously introduce extra in-band resonance for wide passband. Meanwhile, the cross slot with pins can offer an upper edge null and an in-band resonance. Combining with inherent higher order-mode null of the patch itself, the skirt selectivity and stopband suppression at upper band can be significantly improved. Meanwhile, the $\vert $ Sdd $11\vert $ at the upper and lower stopbands is close to 0 dB to achieve high stopband suppressions. As a result, a compact high-gain dual-polarized filtering patch antenna is readily constructed. Thanks for complete symmetry of above structures, the proposed method is very suitable for dual-polarized antennas, where all the performance for both polarizations are identical. For demonstration, a prototype of the proposed antenna is fabricated and measured. Good agreements between the measured and simulated results are observed, indicating good performance with a large bandwidth of about 23% and a peak gain of up to 8.9 dBi within the passband, as well as out-of-band suppression levels of more than 20 dB. Compared with other reported filtering antennas, the proposed filtering patch antenna not only exhibits good wideband dual-polarization radiation but also features high gain in a compact structure for very high aperture efficiency and ultralow cross-polarization level due to the differential feeding and complete symmetry.

Novel Compact High-Gain Differential-Fed Dual-Polarized Filtering Patch Antenna

A simple, compact filtering patch antenna with wide out-of-band suppression is presented, where the filtering mechanism is first analyzed and implemented based on mode analysis of a conventional patch antenna. According to the mode analysis, undesired higher-order modes can be effectively suppressed by selecting a proper length ratio of two sides of the patch and the feeding position, thus realizing a wide upper stopband. To further enhance the filtering response, another two simple filtering structures loaded on the patch antenna are also proposed. First, a split-ring-shaped slot is etched on the patch to generate a radiation null at the lower-band edge for improving skirt selectivity. Second, a U-shaped strip is etched underneath the patch and connected with the feeding probe, which can introduce another null at the upper band edge. As a result, a high suppression level of 23 dB in lower and upper stopbands can be realized, respectively, for the proposed filtering antenna, while the upper stopband can extend up to $2.3 f_{0}(f_{0}$ is the center frequency of the antenna). Furthermore, wide passband response can also be achieved by the extra in-band resonances existing in the slot and the strip. A filtering antenna prototype is fabricated and measured for demonstration. Good agreements between the simulated and the measured results are observed, indicating a large impedance bandwidth of 22.6%, high antenna efficiency of 95.6%, and an average gain of about 7.4 dBi. Compared with the reported filtering antennas, the proposed filtering antenna can achieve better wideband filtering response but with a simpler configuration.

A Simple, Compact Filtering Patch Antenna Based on Mode Analysis With Wide Out-of-Band Suppression

A dual-beam filtering patch antenna consisting of a slotted patch, a metal strip underneath the patch, two pins, and a ground plane is proposed for wireless communication application. A wide operation band with stable symmetrical dual-beam far-field radiation pattern is obtained, and two radiation nulls at the lower and the upper band edges, respectively, are controlled to ensure a sharp rolloff rate at the band edges for both reflection coefficient and realize gain. Undesired higher modes can be suppressed over the stopband by changing the spacing between the patch and ground pane With entire height of $0.058~\lambda _{0}$ , the proposed antenna is implemented to show a −10 dB bandwidth of 3.0–3.8 GHz, a consistent realized gain of about 6.8 dBi within the passband for both two radiation beams directed at ±30°, out-of-band radiation suppression level of higher than 17 dBi, and good band-edge selectivity.

Dual-Beam Filtering Patch Antennas for Wireless Communication Application

A shared-radiator dual-band dual-sense circularly-polarized (CP) microstrip antenna with duplexing and filtering functions is presented. For each band, there is a coupling network, which consists of a hairpin resonator, a straight slot, and a U-slot, and thus two paths with an inherent 90° or −90° phase difference are available for the input signal to couple to the patch, left-handed CP (LHCP) characteristic and right-handed CP (RHCP) characteristic are respectively realized at different bands for the proposed antenna with a single patch. Such a dual-band dual-sense CP patch antenna is highly integrated and outperforms other traditional CP antennas state-of-the-art. Moreover, the duplexing and filtering functions are seamlessly integrated into the dual-band patch antenna with a low-profile ( $0.044\lambda _{o}$ ), and application of such an integrated device in wireless systems can potentially reduce the volume, complexity, and cost of RF front-ends. Based on resonator-based topologies, the principles of achieving the dual-sense CP, duplexing, and filtering functions are illustrated. As a proof-of-concept, an antenna working at C-band is prototyped and tested. Good agreements between the measured and simulated results are achieved, showing an LHCP radiation characteristic for the low-band operation and a RHCP radiation characteristic for the high-band operation, respectively. The antenna also exhibits very good frequency selectivity and out-of-band rejection performance. At the low-band, the impedance and 3-dB axial-ratio (AR) bandwidths are 4.7% and 1.1%. At the high-band, the impedance and AR bandwidths are about 7.3% and 3.2%. The isolation between the two channels/bands is over 24 dB.

/pdf/a-left-right-handed-dual-circularly-polarized-antenna-with-b9td5f1hut.pdf

A Left/Right-Handed Dual Circularly-Polarized Antenna With Duplexing and Filtering Performance

A compact high isolation ultrawideband (UWB) multiple-input-multiple-output (MIMO) antenna is designed. The proposed MIMO antenna consists of a rectangular monopole antenna and a slot antenna fed by two microstrip lines, respectively. To improve the impedance matching, a circular coupling structure is designed to feed the tapered slot antenna. The parasitic resonance introduced by the ground stub helps to extend the impedance bandwidth of monopole antenna at the upper UWB band. Commonly used complex decoupling or coupling structures are eliminated that endow the proposed antenna minimized foot print, which is preferred in mobile handset. Although without decoupling structure, high isolation is obtained between two antenna elements. Simulation and measurement verify the antenna’s desirable performance, showing a broad impedance bandwidth of 3.1–10.6 GHz with |S11| < −10 dB and |S21| < −20 dB over 3.4–10.6 GHz, and |S21| < −18 dB from 3.1–3.4 GHz.

/pdf/design-of-a-compact-uwb-mimo-antenna-without-decoupling-2vmk906r2z.pdf

Design of a Compact UWB MIMO Antenna without Decoupling Structure

A substrate-integrated waveguide (SIW) tapered slot antenna for broadband multiple-input-multiple-output (MIMO) applications is presented in this study. The proposed MIMO antenna consists of two broadband tapered slot antenna elements, two SIW structures for feeding and two microstrip-to-SIW transitions. Four circular openings are designed on both sides of the SIW to improve the antenna's performance. The slots are etched on the connection of SIW and tapered slot antenna to adjust the input impedance of the antenna. The SIW structure and the shorting pin are used to isolate the feed lines and elements. Simulated and measured results verify the performance of the antenna. It shows that the proposed antenna has a broad bandwidth of |
 S
 11
| <; -10 dB and |
 S
 12
| <; -17 dB from 8.0 to 15.0 GHz covering the X-band and the lower K
 u
-band.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-map.2017.0327

SIW-tapered slot antenna for broadband MIMO applications

In this paper, a stacked circular polarization (CP) patch antenna with broad impedance bandwidth, axial-ratio (AR) bandwidth, and flat gains is investigated. The antenna is composed of a square ring, double layers’ stacked patches, and four vertical patches. The corner truncated loop served as a sequential phase feeding structure for four driven patches. To improve the impedance matching, four square patches are stacked on the bottom layer. Furthermore, four vertical patches are introduced on the ground plane to broaden the AR bandwidth. Simulated and measured studies are conducted on an antenna prototype to validate the proposed design. The proposed design shows that the measured impedance bandwidth is 4.65–7.21 GHz (43.2%), measured 3-dB AR bandwidth at broadside is 4.9–6.4 GHz (26.5%) and the 1-dB gain bandwidth is 4.75–6.6 GHz (32.6%). Compared with other similar CP stacked patch antennas, the antenna owns advantages of wide bandwidth, compact size, and flat gain.

/pdf/a-stacked-patch-antenna-with-broadband-circular-polarization-h6fbzw6jni.pdf

Duo-Long Wu

Papers

Dual-Beam Filtering Patch Antennas for Wireless Communication Application

A Left/Right-Handed Dual Circularly-Polarized Antenna With Duplexing and Filtering Performance

Design of a Compact UWB MIMO Antenna without Decoupling Structure

SIW-tapered slot antenna for broadband MIMO applications

A Stacked Patch Antenna With Broadband Circular Polarization and Flat Gains