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This communication investigated a wideband filtering patch antenna with high gain and high selectivity. The antenna is mainly composed of an aperture-coupled driven patch, a stacked patch, and four center-shorted trapezoidal thin patches. The stacked patch can introduce a higher frequency resonant mode and a radiation null due to magnetic coupling. Four trapezoidal thin patches loaded with shorting vias are located around the driven patch, acting as a vertical split-ring resonator (SRR) and introducing a lower frequency resonant mode and a radiation null due to electric coupling. With two radiation nulls at the edges of the passband, the filtering gain response with high selectivity is achieved. As no filtering circuits are used, the antenna can obtain high gain and high efficiency. Due to the symmetrical structure, a dual-polarized filtering antenna is also presented for base-station application, demonstrating good radiation performances and an isolation of 20 dB. A fabricated dual-polarized antenna is measured, showing a wide bandwidth up to 18.8% (from 3.19 to 3.85 GHz), a peak gain of 9.5 dBi, and two near-band radiation nulls located at 3.13 and 4 GHz. [ABSTRACT FROM AUTHOR]

In this article, high selectivity filtering antennas are designed based on a mixed-mode cavity resonator, which is formed by adding a short-circuited metal cylinder at the center of a rectangular cavity. The resonant and coupling characteristics of the proposed resonator are analyzed in detail. The operating modes of the mixed-mode cavity are TE102 mode, TE012 mode, and quasi-TEM mode, which can be utilized to design filtering antennas with different transmission zero distributions. To demonstrate the concept, three slot antennas with 3rd-order filtering performance are designed and simulated, where two transmission zeros are introduced to improve the selectivity. Furthermore, a 5th-order filtering antenna array based on the mixed-mode resonator is designed and fabricated. The measured results are consistent with the simulated results, showing that a gain of greater than 13 dBi is achieved. [ABSTRACT FROM AUTHOR]

In this article, a radiant metal block structure is proposed for designing reduced-size cavity-backed filtering antenna. The method of characteristic mode analysis is used to investigate the characteristic current modes of the cubic metal block, one of which can maintain a high inherent radiation capacity over a wideband. In addition, the radiation quality factor of the utilized mode is described in detail. Based on this characteristic current mode, metal block antennas with different bandwidths can be designed to realize broadside radiation. The proposed metal block antenna element can maintain stable radiation characteristics in the passband and the realized gain is greater than 9 dBi. To design the filtering antennas, the proposed metal block is cascaded with traditional resonant cavities. A third-order metal block filtering antenna array is fabricated for verification. The measurement results are basically consistent with the simulated ones. The maximum measurement gain is 12.85 dBi and the gain in the passband is flat. [ABSTRACT FROM AUTHOR]

A wideband dual‐polarized planar antenna with triple radiators is proposed for the LTE600/LTE700/GSM850/GSM900 base station in this paper. A novel concept of multi‐radiator for multi‐resonance by close coupling feed is presented and analysed. The proposed antenna is mainly composed of two pairs of loop dipole, L‐shaped radiator, step dipole, two L‐shaped feed lines, balun and reflector. The reflector is designed with a centrosymmetric partible baffle for directional radiations, which contribute to stable radiations as well. Owing to the novel closely coupling scheme for multi‐radiators, three resonances are simultaneously excited within the desired band, producing a wide bandwidth of 47.7% (from 0.59 to 0.96 GHz) for |S11| < −15 dB with high isolation more than 30 dB. Moreover, an average gain of 8.8 dBi as well as stable radiation patterns are achieved simultaneously. [ABSTRACT FROM AUTHOR]

In this article, a wideband microstrip 4 × 4 Nolen matrix using novel phase shifters is proposed. Because of the unequal electrical paths connecting one input to every output, Nolen matrices in standard form usually introduce significant phase dispersion and amplitude instability, limiting the effective bandwidth. A novel phase shifter consisting of multiple open‐ and short‐circuited stubs is designed, whose rate of change of phase with frequency can be conveniently adjusted. This phase shifter can be used to balance the rate of change of phase with frequency of the unequal electrical paths to reduce the phase dispersion and amplitude instability, thus realizing wide bandwidth of the output phase differences and output amplitudes. To verify the proposed concept, a wideband 4 × 4 Nolen matrix operating at 6 GHz is designed and fabricated, showing a bandwidth up to 33% within ±15° phase imbalance and 21.5% within ±1 dB amplitude imbalance. [ABSTRACT FROM AUTHOR]

A broadband stacked patch antenna array with high port isolation is presented for in-band full-duplex (IBFD) applications in this article. A co-channel feeding scheme is proposed to simultaneously excite two ports of the patch antenna to achieve ± 45°dual polarization. An antenna system is then designed using a 2 × 2 stacked patch array, a parallel feeding network, and a hybrid coupler. The coupling between the Tx and Rx ports due to mismatch and coupling between the antenna elements is analysed in detail and shown to be eliminated completely. A demonstrator is fabricated and measured to endorse the accuracy of the proposed feeding scheme. The measured results show that the developed prototype can operate from 3.15 GHz to 4.0 GHz. The isolation level between Tx and Rx ports is higher than 45 dB within the operating band. The realized gains of two ports are higher than 10.5 dBi throughout the band of interest with the maximum gain of 13.9 dBi, which are congruent with the simulated ones. [ABSTRACT FROM AUTHOR]

In this article, a new class of tunable filters and diplexers operating in $X$ -band is presented. The proposed circuits are based on an in-line dual-post resonator, which consists of a pair of antipodal partial-height posts. The resonance and coupling characteristics of the proposed resonator can be regulated by the height and height difference of the posts. The most interesting feature of using the in-line dual-post resonator is that the input–output coupling and inter-resonator coupling are inversely proportional to the frequency within the tuning range, which is necessary for maintaining the fixed absolute bandwidth of the tunable filter. A prototype tunable filter is designed and fabricated, showing a low variation ($< \pm 3.9$ %) in the absolute bandwidth over a relatively wide tuning range of about 17%. The waveguide $H$ -plane static $Y$ -junction is designed and cascaded with two channel filters to implement the tunable diplexer. Noncontiguous and contiguous frequency plans can be realized by properly arranging the frequency band of the two channel filters. Measured results show that the tunable diplexer can obtain constant frequency spacing and approximately 10% tuning range with an insertion loss of less than 1.5 dB. [ABSTRACT FROM AUTHOR]

A high selectivity planar filtering quasi‐Yagi antenna employing the codesign of bandpass filter (BPF) and antenna is investigated in this article. A stub‐loaded resonator (SLR) and a half‐wavelength resonator are utilized as the feeding network to excite the driven dipole of the quasi‐Yagi antenna. The length of the driven dipole is about half‐wavelength, which can be equivalent to the last stage resonator of BPF, achieving a good filtering gain response. To improve the frequency selectivity, an elaborate balun structure is utilized, and a transmission zero (TZ) on the lower side of the passband is acquired. Together with the TZ introduced by the SLR at the upper edge, the antenna can achieve a sharp band‐skirt. An antenna prototype is fabricated and measured, showing a wide bandwidth up to 19.1% (from 3.1 to 3.76 GHz) with a flat gain response in band, an antenna peak gain of 4.85 dBi and a peak efficiency of −0.6 dB. [ABSTRACT FROM AUTHOR]

In this article, a method for designing a tunable coaxial filtering antenna is presented. The proposed filtering antenna has a simple structure, consisting of a standard waveguide and some metal cylinders. Instead of utilizing traditional coupling irises, an all-cylinder coupling structure is employed for flexible tuning. Thus, the center frequency and bandwidth of the coaxial filtering antenna can be conveniently tuned by adjusting the lengths of the cylinders. Theoretical analysis and design process of the filtering antenna are given in detail. A third-order tunable filtering antenna with Chebyshev response is designed to verify this method. The tunable range of the center frequency is from 9.25 to 10.75 GHz, and the tunable range of the fractional bandwidth (FBW) is from 2% to 8%. The measured gain of the antenna is flat and greater than 6.5 dBi along the tuning range. In addition, the antenna maintains good impedance and radiation characteristics throughout the tuning range. [ABSTRACT FROM AUTHOR]

This article presents a wideband 2‐D beam‐forming network (BFN) utilizing a three‐layer strip‐line structure, which has 16 input ports and 16 output ports. The BFN, composed of multiple 2‐D couplers, crossovers, and phase shifter groups, can provide an equal power signal distribution with ±45° or ±135° phase differences between the adjacent output ports, hence achieving 2‐D beam scanning in both azimuth and elevation planes. To validate the concept, a prototype operating in the frequency range of 2.25–3.75 GHz is fabricated, measured, and discussed. The measurement results coincide well with the simulation ones. [ABSTRACT FROM AUTHOR]

A high selectivity and high efficiency filtering antenna is presented in this communication. A double-layer filtering patch antenna is first proposed, which can generate a radiation null due to the mixed electric and magnetic coupling between the two patches. By changing the length of the slot line on the patch, the position of the radiation null can be flexibly set at the lower band edge or upper band edge. Based on this mechanism, a three-layer patch antenna with two radiation nulls is designed. Two radiation nulls are introduced on both sides of the passband, consequently, a quasi-elliptic bandpass response can be obtained. Moreover, the proposed antenna features high efficiency since no extra filtering circuit is utilized. A prototype antenna operating at 1 GHz is designed, fabricated, and measured for validity verification. The measured results agree well with the simulated one, showing that the prototype antenna has a fractional impedance bandwidth of 16% (0.91–1.07 GHz), a flat passband gain response with peak value of 8.83 dBi, a high efficiency about −0.41 dB in the passband. The band-edge selectivity is highly improved by the radiation nulls near the passband edge. [ABSTRACT FROM AUTHOR]

This article presented a high selectivity and efficiency differential dual‐polarized filtering patch antenna. A square driven patch together with a square parasitic patch are utilized to obtain a filtering performance. By loading an upper parasitic patch with a cross slot in the center, a radiation null is introduced on the high side of the passband. Two pairs of slots with the same size of folded U‐shape are symmetrically etched on the diagonal of the driven patch, generating another radiation null on the low side of the passband. Thus, the antenna can achieve a good filtering gain response with two radiation nulls, realizing high selectivity. Additionally, as no extra filtering circuit is utilized, high radiation efficiency is also acquired. An antenna prototype is processed and measured, showing a bandwidth of 7.4%, high isolation of 32 dB, an antenna peak gain of 9 dBi and an efficiency of −0.29 dB in the center frequency. [ABSTRACT FROM AUTHOR]

In this communication, a high-selectivity and high-gain filtering slot antenna operating in $X$ -band is designed based on a triple-mode cavity resonator. Three modes of the cavity resonator, namely, TE101, TE011, and TM110, are excited by properly selecting the position and size of the coupling aperture. By adjusting the frequency and external coupling of the three modes, transmission zero can be introduced on both sides of the passband, achieving high selectivity of antenna gain. Because the cavity has a high unload quality factor, the radiation efficiency in the passband is high and flat. In order to increase the gain of the filtering waveguide antenna, a grid-slotted patch is added on the top of the slot. To demonstrate the concept, an $X$ -band waveguide filtering antenna is designed and fabricated. Measured results show the filtering antenna can obtain a gain of greater than 8.5 dBi in the frequency range of 9.8–10.2 GHz. [ABSTRACT FROM AUTHOR]

In this article, a novel design approach for designing 4 × 4 and 8 × 8 filtering Butler matrices is proposed. The matrices, composed of combined 90° couplers and 180° filtering couplers as well as phase shifters, provide incremental phase shifts and a bandpass filter performance. The detailed design process and synthesis method for the Butler matrices are presented. A three-layer symmetrical stripline structure is used to realize the Butler matrix, allowing a fully planar structure without interlayer connections. For experimental verification, two prototype 4 × 4 and 8 × 8 filtering Butler matrices, operating at the center frequency of 2.4 GHz with a bandpass response, are devised, manufactured, and tested. The test results match well with the simulation ones. Based on the measurements, array factors have been calculated, which further indicate the acceptance of the measured results. [ABSTRACT FROM AUTHOR]

This article presents a novel quad-ridge cavity resonator to realize a trimode response based on the TE101, TE011, and TE111 modes. The basic structure of the quad-ridge resonator (QRR) contains four ridges located at the center around the cavities. With an appropriate combination of the main parameters (length and width of the resonator and heights of the ridges), the first three TE resonant modes can be flexibly controlled, and each mode can carry the signal of a channel. Compared with a traditional rectangular cavity, the QRR provides more design freedoms for controlling the first three TE resonant modes and features a wider spurious-free window. The electric field distributions of the QRR are thoroughly analyzed to guide the realization of a filtering response. Intracavity coupling is achieved by an all-iris structure, including horizontal and vertical coupling slots with offsets to the cavity center, capable of easy fabrication and assembly. A nine-pole triple-band filter and a 12-pole triplexer are designed and manufactured to validate the concept. A comparison with other reported multiplexers indicates that the proposed triplexer exhibits the advantages of size reduction and high isolation. [ABSTRACT FROM AUTHOR]

A method of designing a printed filtering dipole antenna using codesign of bandpass filter (BPF) and antenna is proposed in this article. The printed dipole antennas consist of two identical arms, which are placed on the opposite sides of the substrate. One arm of the dipole is used to construct the half-wavelength resonator of a typical BPF, and thus filtering and radiation performance can be obtained simultaneously. A third-order filtering dipole antenna is designed and analyzed in detail to demonstrate the codesign method. The measured S11 of the filtering dipole antenna is less than −11 dB in the range of 0.94–1.094 GHz and the peak gain is 7.8 dBi. To extend this design method, a third-order ±45° dual-polarized filtering dipole antenna is designed and measured. The measured S11 and S22 of the ±45° dual-polarized filtering dipole antenna are both less than −11 dB in the range of 0.94–1.08 GHz. Besides, the isolation between them is higher than 20 dB in the passband. The measured radiation patterns show that the dual-polarized filtering dipole antenna would be a potential candidate for base stations. [ABSTRACT FROM AUTHOR]

In this article, we present a design method of high-selectivity filtering antennas based on a dual-probe feeding structure. The first stage of the filtering circuit consists of two or three coupled resonators which are then coupled to the radiating patch acting as the last resonator of the filter. Cross-coupling is used to obtain transmission zero, and thus the selectivity of the filtering antennas is improved. A cascaded triplet (CT) filtering patch antenna, which produces a radiation zero at the high-frequency edge of the passband, and a cascaded quadruplet (CQ) filtering patch antenna, which produces radiation zeros at both edges of the passband, are designed for verification. The process of designing the filtering patch antenna is given in detail. The designed CT filtering patch antenna has a bandwidth of 1.029–1.17 GHz and a radiation zero at 1.19 GHz. The designed CQ filtering patch antenna has a bandwidth of 1.029–1.17 GHz and two radiation zeros at 1.012 and 1.19 GHz, respectively. The peak gain of the CT filtering patch antenna is 9.35 dBi and that of the CQ filtering patch antenna is 9.16 dBi. A dual-polarized CQ filtering patch antenna is fabricated, showing a good performance in measurement. [ABSTRACT FROM AUTHOR]

A method for expanding the bandwidth of slot and patch antennas is proposed in this article. The use of grid‐slotted patch helps to improve the impedance matching of the antenna, thus the bandwidth can be extended. The design process and an analysis of using a grid of slots to increase the bandwidth of a slot antenna is first given. The simulated S11 of the broadband slot antenna is less than −11 dB in the range of 2.6 to 3.42 GHz. To further demonstrate the method, an aperture‐coupled patch antenna with grid‐slotted patch is designed. The measured S11 of the broadband patch antenna is less than −10 dB in the range of 1.95 to 4.15 GHz and the peak gain is 9.6 dBi. [ABSTRACT FROM AUTHOR]

This paper proposes a compact and broadband dual-polarized base station antenna based on current path extension for 2G/3G/LTE base stations. The antenna is miniaturized by bending the end of the radiator to extend the current path. By bending the antenna, a new resonant mode is introduced to increase the bandwidth. In addition, a parasitic patch is placed above the antenna to improve impedance matching, and the introduction of artificial magnetic conductors reduces the profile of the antenna and significantly improves the radiation characteristics. The antenna radiator has a compact size of only 0.207 × 0. 207 λ L 2 at the lowest frequency with a total profile of 0.136 λ L. The measured results indicate that the proposed antenna has a substantial bandwidth of 45.5% and more than 34 dB of high port isolation with a gain of 7.9 ± 0.5 dBi. [ABSTRACT FROM AUTHOR]

A wideband and high-isolation mobile phone antenna pair with low envelope correlation coefficient (ECC) for fifth-generation (5G) smartphone applications based on four orthogonal modes is proposed in this communication. According to the characteristic mode analysis, except for the original two resonant modes, the other two resonant modes are introduced by arranging a metallic strip at the top of the vertical bezel. With the help of dual-mode excitation and orthogonal property, wideband and high-isolation merits are achieved for the shared radiator antenna pair. Finally, four antenna modules are deployed along the long edge of the system circuit board to form an 8 × 8 multiple-input multiple-output (MIMO) system. The measured results prove that the impedance matching bandwidth of the fabricated prototype ranges from 3.3 to 5 GHz while the isolation level is higher than 17.5 dB. The antenna efficiencies are higher than 45% and 48% for the two different antenna elements. Guaranteed by the orthogonal relationship between different characteristic modes, the extremely low ECC (< 0.04) is achieved. [ABSTRACT FROM AUTHOR]

This article presents a simple design of a coaxial dual-band cavity filter and diplexer using stub-loaded resonators (SLRs). Based on the resonance characteristics of a coaxial SLR, the first two resonant frequencies can be tuned over a wide range by adjusting their structural parameters. Controllable external quality factors can be acquired by using the modified tapping structure for the two designated passbands. A coupling window and a coupling pin are proposed to obtain the expected coupling coefficients in the two bands. To demonstrate this concept, a third-order dual-band bandpass filter and an eight-pole diplexer are designed and fabricated. The measured results agree well with the full-wave simulation results. [ABSTRACT FROM AUTHOR]

A novel broadband three-input four-output ($3 \times 4$) Butler matrix is proposed in this communication. The proposed Butler matrix achieves equal power division and −90°, 0°, and +90° phase differences between output signals in the 2–4 GHz frequency range. By using the $3 \times 4$ Butler matrix as a four-element antenna array feed network, a broadside beam and two symmetrical beams are realized over a wideband frequency range. The proposed Butler matrix has been verified by measurements of S-parameters and radiation patterns using the broadband four-element antenna array. The measurement results are in good agreement with the simulation results. In addition, the proposed $3 \times 4$ Butler matrix can be extended for use with antenna arrays with a higher number of beams. [ABSTRACT FROM AUTHOR]

In this communication, an approach for designing multi-band microstrip slot antennas is proposed. Multiple resonators are loaded on a conventional microstrip slot antenna to introduce multiple resonances. The number of the operational bands of the antenna can be easily controlled by varying the number of the loading resonators. The locations of each resonance can be adjusted by varying the positions and lengths of the loading resonators together with the geometry of the slot if necessary. For validation, prototypes with dual-, tri-, and quad-band operations are designed, fabricated, and measured. Since no modified slot is used in this design method, all the operating bands show good bidirectional radiation patterns. The measured and simulated results agree well. The proposed antenna features low profile, small radiating slot, and easy fabrication, showing promising application prospect for modern communication system. [ABSTRACT FROM AUTHOR]

In this paper, two novel $4 \times 6$ filtering Butler matrices with uniform and nonuniform power distribution are proposed. The matrices, consisting of a network of coupled resonators and two phase shifters, provide power division and phase shift together with a bandpass transfer function. The analytical synthesis procedures for the $4 \times 6$ filtering Butler matrices are presented. To verify the concept experimentally, two $4 \times 6$ filtering Butler matrices, operating at 2.4 GHz, with uniform and nonuniform power distribution are designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other. Multibeam antenna arrays are realized by using the Butler matrix, and the theoretical analysis has been confirmed by measurements of multibeam antenna arrays, which show reduced sidelobe level (SLL). [ABSTRACT FROM AUTHOR]

This article presents a ±45° dual‐band dual‐polarized filtering antenna. The filtering antenna element is a dual‐polarized patch antenna that loads a parasitic patch with two rectangle slots to achieve compact multi‐array. Multi‐array consists of three 1×2 subarrays arranged, which are designed for 1.8/2.1 GHz FDD band applications. Very close‐arranged antennas exhibit radiation pattern invariance as well as in‐band radiation property. Radiation patterns are conformal with a compact subarray distance of 45 mm (0.29λ0), which is 56% smaller than that of the array using traditional filtering elements. Moreover, the total width is only 180 mm for three subarray‐composed antenna arrays. The average gain is 8.7 dBi with a low profile of 0.069λ0. The proposed array exhibits the filtering property of the subarrays with a very simple structure. [ABSTRACT FROM AUTHOR]

This communication presents a wide stopband filtering antenna element and its application in multi-input multi-output (MIMO) system. Microstrip terminated coupled lines and a rectangle patch are utilized to generate the filtering function. By varying the length of the parallel coupled lines and open-circuited stubs, multiple transmission zeros can be introduced in the spurious band. Appropriate positioning the location of these transmission zeros enables a wide harmonic suppression. To demonstrate the proposed method, a wide stopband filtering antenna is designed and further applied in a four-element MIMO array. The measured and simulated results agree well. The proposed MIMO antenna obtains an attenuation of 12.6 dB up to $6.6\times $ the center frequency. [ABSTRACT FROM AUTHOR]

A novel broadband patch antenna with electric- and magnetic-coupled elements and its application in multiple-input-multiple-output (MIMO) system is proposed in this communication. Unlike the conventional gap-coupled patch antennas, the electric and magnetic coupling between adjacent patches is considered and studied. Also, for improved understanding of the broadband nature of the proposed configuration, the phase relationships between patch elements are studied. Two- and three-patch prototypes are designed for validation of the concept, and the three-patch antenna is fabricated and measured showing a good agreement between the measured and simulated results. Considerable selectivity is observed in the results of the three-patch antenna because of the radiation nulls introduced by the electric and magnetic coupling. Apart from the broadband operation, the proposed antenna elements show promise for application in high-isolation MIMO systems due to their inherent band-reject characteristic when they are closely placed. For validation in this application, a four-element MIMO antenna is designed, fabricated, and measured. The measured results agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

A tri-band patch antenna utilizing the TM10 mode together with modified TM20 and TM30 modes of a single patch is proposed in this communication. Through asymmetrically loading a stub on one radiating edge of the patch and cutting a rectangular slot offset from the other one, the current distributions of the TM20 and TM30 modes are perturbed, resulting in broadside radiation for all the first three modes of a single patch. Each operational frequency can be effectively controlled through varying the dimensions of the patch, slot, and loading stub. Good impedance matching is achieved simultaneously in three operational bands through aperture coupling. A prototype is designed, fabricated, and measured for validation. Based on this tri-band antenna, a new tri-band filtering antenna is further developed, showing good selectivity and broadside radiation characteristic. [ABSTRACT FROM AUTHOR]

In this paper, a novel filtering 180° hybrid coupler is proposed and used to design a $2 \times 4$ filtering Butler matrix. The filtering 180° hybrid coupler can provide power division and phase shift together with a second-order bandpass transfer function, and is based only on coupled resonators. The $2 \times 4$ filtering Butler matrix is easily realized by utilizing several hybrid couplers. The analytical synthesis procedures for the hybrid coupler and Butler matrix are presented in this paper. Finally, broadside and end-fire arrays are realized by using the Butler matrix. To illustrate the concept experimentally, a filtering 180° microstrip hybrid coupler and a $2 \times 4$ filtering microstrip Butler matrix are designed, fabricated, and measured. Simulation and measured results are found to be in good agreement with each other. [ABSTRACT FROM AUTHOR]

Moreover, they are particularly grateful to the authors of all the submitted papers for their efforts and contributions to this Special Issue, and to the reviewers for devoting their valuable time and expertise to review the submitted manuscripts. Authors of the accepted and presented papers during the iWEM 2021 were invited to submit expanded versions of their conference papers in this special issue. This special issue of Microwave and Optical Technology Letters (MOTL) includes nine expanded papers from the 2021 IEEE International Workshop on Electromagnetic: Applications and Student Innovation Competition (IEEE iWEM2021). [Extracted from the article]

This paper proposes a novel design approach for a filtering antenna, which contains an array of 4 by 2 waveguide aperture radiation elements. Coupling matrix theory is introduced in this paper to synthesize the multiple coupled-resonators circuit. Unequal amplitude excitation is applied to the 4 \times 2 elements so as to obtain a low sidelobe level. To demonstrate the concept, an X-band antenna array is designed and fabricated using a three-layer waveguide structure. Measured results show that the filtering antenna array can achieve a gain of more than 15.58 dBi and a radiation efficiency of higher than 90% over the passband (9.91–10.1 GHz). The sidelobe level is −18.3 dB in the {H} -plane and −21.1 dB in the {E}$ -plane. [ABSTRACT FROM AUTHOR]

A broadband dual‐polarised antenna with L‐shaped strips for long‐term evolution (LTE)/5th generation mobile networks (5G) is proposed in this article. Based on the principle of multi‐mode resonance, wide bandwidth is achieved with L‐shaped strips and H‐shaped strips. The metal strips and dipoles are printed on the same substrate, which also contributes to antenna miniaturisation. The short pins are designed for impedance matching and improving isolation. The metal reflector is designed to control beamwidth and increase gain. A prototype was fabricated using an easy Printed Circuit Board technique to verify the proposed design. Low‐profile of 0.2λ0 (λ0 is the free‐space wavelength at the centre frequency) is achieved. The measured results show that the relative bandwidth is 74% (2.3–5.0 GHz) at Voltage Standing Wave Ratio <1.8 while the isolation is more than 24 dB covering the LTE/5G modern band. In addition, the in‐band average gain is 9 dBi. [ABSTRACT FROM AUTHOR]

A novel wideband bandstop filter is proposed in this paper. Using one uniform impedance resonator and two stepped impedance resonators, five transmission zeros are introduced in the stopband. Appropriate positioning of these zeros ensures the high selectivity and flat rejection level of the stopband. The bandwidth of the filter can be conveniently controlled by the characteristic impedances of the connecting lines and resonators. A complete analytic analysis is proposed to fully control the positions of transmission zeros, and the design equations and design rules for the bandstop filter are given in detail by using the lossless transmission line model. To illustrate the concept, a wideband bandstop filter with center frequency at 2 GHz and rejection level below 20 dB is fabricated. Theoretical, simulated, and measured results are found in good agreement with each other, and the measured 20-dB rejection bandwidth is as wide as 150%. [ABSTRACT FROM PUBLISHER]

For the requirements of efficient integration and simple fabrication, a new codesign approach for a microstrip filter with an antenna array with reduced sidelobe level is introduced in this communication. The microstrip patch antennas and the stub-loaded resonators are used to illustrate the synthesis of a bandpass filtering antenna array. By controlling the coupling strength between the resonators, a uniform or nonuniform power divider network can be obtained. A nonuniform power division is used to reduce the sidelobe level. The equivalent lumped circuit model is developed and analyzed in detail. Two types of eight-element filtering antenna array with uniform and tapered power-distribution among the elements have been designed. Simulated and measured results provide a good verification for the theoretical concepts. [ABSTRACT FROM PUBLISHER]

ABSTRACT This letter reports a new kind of matching network to design diplexer. The matching network is comprised by two open-circuited and one short-circuited transmission lines. By properly adjusting the input admittance of the matching network, each channel of the diplexer can be designed independently. Therefore, the diplexer can be easily realized by the connection of different bandpass filters without further tuning. Moreover, the proposed matching network occupies little place, and thus the size of the diplexer is mostly determined by the filters. Systematic design procedure for the network is fully presented in this letter. To illustrate the concept, a diplexer is designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:315-318, 2017 [ABSTRACT FROM AUTHOR]

ABSTRACT A tunable bandpass-to-bandstop filter with controllable bandwidth is proposed in this article. The bandpass-to-bandstop transformation can be achieved by adjusting the PIN diode, and bandwidth of the bandpass filter can be controlled by adjusting the voltage of varactors, as the coupling coefficients and the external quality factors (Qe) can be tuned by changing the ratios of the loaded capacitances. In the bandpass mode, a tuning range of 805-1032 MHz (24.7%) with return loss better than 11.5 dB can be achieved. In the bandstop mode, a tuning range of 760-1228 MHz (47.1%) can be obtained. The rejection level of the bandstop mode is higher than 40 dB. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:110-113, 2017 [ABSTRACT FROM AUTHOR]

In this communication, a new design for the microstrip-fed slot antenna with a directive radiation pattern for WLAN/WiMAX application is presented. By utilizing a two-element array topology, a unidirectional radiation pattern is obtained. Without any directors and reflectors, the proposed slot antenna shows advantages in terms of compact size and high front-to-back gain ratio in the azimuthal plane. Four directional slot antennas are then placed in a square loop array to obtain nearly orthogonal patterns. Thus, a compact multiple input multiple output array with high isolation among those four elements is achieved. Simulated and measured results are presented to validate the practicality of the proposed antenna structures. [ABSTRACT FROM PUBLISHER]

This paper proposes a simple and effective method to designing wide-stopband bandpass filters and diplexers using uniform impedance resonators. Microstrip terminated parallel coupled lines are utilized to generate the filtering functions. By adjustment of the electrical lengths of the parallel coupled lines and open-circuited stubs, multiple transmission zeros can be obtained. Appropriate positioning of these zeros enables the suppression of spurious frequencies. A complete analytic analysis is proposed to fully control the positions of transmission zeros, and the design equations and design rules for both homogeneous and inhomogeneous mediums are given in detail. Different combinations of the frequency position of the transmission zeros can provide various characteristics. To extend the stopband bandwidth, one or more transmission zeros can be distributed on different harmonic frequencies. To demonstrate the proposed method, two bandpass filters and a diplexer are designed and fabricated. The measured results are in good agreement with the simulated ones. The first filter provides a high attenuation of 40 dB up to 6.8 times the fundamental frequency $(f_{{{0}}})$ and the second filter provides a lower attenuation of 28 dB, but this time extending up to $14.9f_{{{0}}}$ . [ABSTRACT FROM AUTHOR]

ABSTRACT This letter proposes a novel dualband filter consisting of one lowpass passband and one bandpass passband. The dualband filter is realized using stub-loaded transmission lines and stepped-impedance stubs. The key merit of the filter configuration is that the lowpass and bandpass passband frequencies can be flexibly controlled by tuning the impedances and lengths of the transmission lines. Without coupling gap between the transmission lines, the new filter shows low insertion loss and easy for fabrication. To illustrate the concepts, a dualband lowpass-bandpass filter is designed, fabricated, and measured. The cut-off frequency of the lowpass filter is selected to be 1 GHz. The central frequency of the bandpass filter is chosen to be 5.2 GHz. Experimental measurements are in good agreement with both simulations and theoretical expectations. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1858-1861, 2016 [ABSTRACT FROM AUTHOR]

This paper presents a novel lowpass-bandpass multiplexer consisting of one lowpass channel and four bandpass channels. Dumb-bell defected ground structures and stepped impedance resonators are employed to extend the stopband of the lowpass filter and bandpass filters, respectively. Stepped impedance stubs are used to bring a sharp selectivity in the lowpass channel design. Good isolation between channels is obtained by careful design of the input signal splitting structure, which is realized by utilizing four shunt open stubs with electric length of quarter-wavelength at the center frequency of the four bandpass channels, respectively. To verify the above concept, a lowpass-bandpass quintuplexer is designed, fabricated, and measured. The cut-off frequency of the lowpass filter is selected to be 1 GHz. The central passband frequencies are chosen to be 2.4, 3.5, 4.6, 5.8 GHz. Experimental measurements are in good agreement with simulations. [ABSTRACT FROM AUTHOR]

Compact microstrip low-pass filters (LPFs) with ultrawide stopband based on a defected ground structure (DGS) and their design procedures are presented in this paper. A key merit of the filter configuration is that the selectivity of the LPFs can be conveniently controlled, whereas the bandwidth is fixed. The LPFs are realized using open-circuited uniform impedance stubs and stepped-impedance stubs (SISs). The position of the transmission zeros can be freely controlled by tuning the impedance ratio of the SISs. To expand the stopband, the dumbbell DGS is used to suppress the spurious passbands of the LPFs. Two demonstration filters with a cutoff frequency at 1 GHz have been designed, fabricated, and measured. The measured results indicate good performance: broad stopband ( >15 fc or 20~fc ), low passband insertion loss (<0.3 dB), compact size, and sharp skirt characteristic. [ABSTRACT FROM PUBLISHER]

ABSTRACT This article proposes a novel type of microstrip cascaded triplet filter with controllable electric and magnetic coupling. The electric coupling can be tuned by adjusting the gap between the resonators, while the magnetic coupling is dominated by the diameter of the via-hole. A transmission zero on the upper stopband is produced by the inductive cross-coupling. To further improve the selectivity of the filter, the source-load coupling is also proposed to introduce two tunable transmission zeros. To expand the stopband, proper feeding position is selected to suppress the third and fifth harmonics. Based on the proposed structure, a third-order filter are designed and fabricated. Good agreement between the measured and simulated data is obtained. Measured results indicate that a rejection level of 20 dB up to more than six times the passband frequency can be obtained. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2937-2940, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT Compact microstrip triband bandpass filters are proposed and designed based on asymmetrically loaded resonators in this letter. By attaching single open-circuited stub or short-circuited stub at the proper position of the microstrip line and adjusting their lengths, the first three resonant modes of the proposed resonators can be usefully allocated within the three passbands of the triband filter. Two alternative triband filters with compact size are designed and measured. The measured results provide successful verification for the theoretical analysis. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1862-1865, 2014 [ABSTRACT FROM AUTHOR]

ABSTRACT Tri-band bandpass filter using centrally loaded resonators is presented in this article. The triple-passband characteristics are realized by properly controlling the lengths and impedances of the uniform impedance resonator and the stub. To illustrate the concept, two tri-band filters are designed, fabricated, and measured. Simulated and measured results are found to be in good agreement with each other. The prototype of the tri-band filters achieve insertion loss of 1.6, 1.9, and 1.9 dB at 2.4, 3.5, 5.8 GHz, 1.2, 1.3, and 1.3 dB at 1.57, 2.45, 5.2 GHz, respectively. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2695-2699, 2013 [ABSTRACT FROM AUTHOR]

A method of designing beam steering microstrip antennas using reconfigurable parasitic patches is proposed in this article. The first beam steering antenna is composed of a driven patch and two parasitic patches placed on the H‐plane of the antenna. The effect of the length and width of parasitic patches, and the spacing between the driven and parasitic elements on the radiation pattern of the antenna is analyzed in detail. The parasitic patch is loaded with a varactor in the center with its dc biasing network. By adjusting the capacitance value of the varactor, the electrical sized of the parasitic patch is changed to achieve beam steering. Maintained impedance matching can be obtained without compensation structure. An experimental antenna is designed and fabricated to verify the method. The measured return loss is better than 12 dB at the center frequency 2.4 GHz for all cases and the measured gain is from 6.5 to 7.6 dBi. The beam steering angles of the simulation and measured results are ±45° and ± 35°, respectively. [ABSTRACT FROM AUTHOR]

This letter presents a novel approach for designing quad-band bandpass filter with independently controlled center frequencies.Assembled resonator constructed by a stepped impedance resonator (SIR) and a stub-loaded SIR is employed to obtain quad-band responses. The SIR is designed to operate at the second and fourth passbands and the stub-loaded SIR is designed to operate at the first and third passbands. Good agreement is shown between the simulation and the measurement, the resonators are meandered to give an overall circuit size of about 21.8 × 30.2 mm. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:1305-1308, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25993 [ABSTRACT FROM AUTHOR]

This article presents a novel approach for designing dual- and tri-band bandpass filters with independently controlled center frequencies and bandwidths. λ/4 and λ/2 resonators are used to obtain dual- and tri-band responses. λ/4 resonators are designed to operate at the lower passband(s) and λ/2 resonators are designed to operate at the higher passband. The bandwidth of each passband can be tuned independently by adjusting the coupling gap. To verify the presented concept, two experimental examples of filters have been designed and fabricated and good agreements are shown between the simulation and the measurement. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 638–641, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24111 [ABSTRACT FROM AUTHOR]

Presents a study which concluded that diadenosine tetraphosphate has protective effects in the cortex and midbrain in defined rat models of stroke and Parkinson's disease. Materials and methods; Results; Discussion.

A modified wideband bandpass filter based on a bandstop filter is realised using half‐wavelength and one‐wavelength open‐circuited resonators. Six transmission zeros are utilised to obtain the sharp rejection characteristics over a broad stopband. The passband bandwidth can be varied by changing the impedance of the configuration. A compact prototype filter with 27% bandwidth is demonstrated. Without coupling gaps between resonators, the new filter shows low insertion loss and is easy for fabrication. To illustrate the concept, a bandpass filter is designed, fabricated and measured. Simulated and measured results are found in good agreement with each other. [ABSTRACT FROM AUTHOR]

Dual‐band bandstop filters using open‐circuited stub‐loaded resonators are presented. The first and second resonant frequencies of the open‐circuited stub‐loaded resonator can be flexibly controlled by tuning the length and position of the open‐circuited stub. To illustrate the concept, a dual‐band bandstop filter has been designed, fabricated and measured. The prototype of the dual‐band bandstop filter achieved attenuation of 42 and 44 dB at 2.4 and 5.2 GHz. [ABSTRACT FROM AUTHOR]