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The RF (Radio Frequency) signals carry both energy and information. Harvesting energy from these RF signals leads to new technology such as WEH (Wireless Energy Harvesting). In this paper, the design of a microstrip-fed spurious free slant antenna array for wireless energy harvesting applications. A prototype antenna operating at 2.45 GHz is designed and fabricated. Defected ground structure (DGS) and stubs have been used to suppress the spurious responses. The measured results show 19% 10 dB return loss bandwidth, 7.11 dBi average gain, and more than 80% radiation efficiency. Spurious radiations up to third harmonics resulting from higher-order modes are effectively suppressed. [ABSTRACT FROM AUTHOR]

A wideband filtering antenna design has been proposed in this paper. The proposed filtering antenna design is cavity-backed substrate integrated waveguide (SIW) based on a single layer slot antenna. Two E-shaped slots are engraved onto the ground face of the design to improve filtering selectivity and operational bandwidth. For achieving wideband response, a modified half-TE110 mode and a decreased radiation null are all produced by the E-shaped slots in the right-half cavity. The design is simple and compact, with only one substrate layer and a larger working bandwidth than its counterparts. The filtering antenna has a 13.1 % fractional bandwidth and works at a frequency of 28 GHz. The proposed prototype has been structured, tested, and the simulation and measurement results were analyzed. [ABSTRACT FROM AUTHOR]

The application of ceramic for a circularly polarized (CP) filtering antenna is studied in this paper. The dielectric resonator (DR) of sintered aluminum oxide (Al2O3) ceramic has a dielectric constant of 9.5 and low dielectric loss of 0.003, and excellent mechanical properties. The dielectric resonator antenna (DRA) consists of two parts, the upper part is a DR, and the lower part uses a feeding network containing two hairpin bandpass filters. The measured |S11| of the DRA is 48.0 % and the axial ratio (AR) bandwidth is 33.5 %. Meanwhile, the peak gain of the DRA is 6.13 dBi, and the suppression level across the stopband exceeds 15.2 dB. The DRA uses the hairpin bandpass filters to improve the filtering characteristics of the antenna and uses the corner-cutting processing of the DR to improve the AR, which can be implemented to reduce the cost of fifth-generation (5 G) communication.

A highly selective planar microstrip filtering antenna for point-to-point communication is proposed in this paper. The bandpass filter is composed of a rectangular split-ring coupling resonator, and a portion of the filter is equivalent to a microstrip monopole antenna. Two rectangular split-ring structures with their openings aligned generate resonant characteristics, and U-shaped microstrip coupling structures are wrapped outside to optimize the passband characteristics. One of the U-shaped microstrip structures is transformed into a one-side bent structure as a radiation unit and serves as the resonant structure of the final stage of the filter, reducing the connection loss between the filter and the antenna. The operating frequency band of the filtering antenna is from 6.38 to 6.63 GHz with a reflection coefficient of less than -10 dB, a fractional bandwidth of 3.8%, and a peak gain of 4.46 dBi. The filtering antenna has excellent frequency selectivity, good out-of-band suppression, high gain, and small device size, in addition to its low cost after system integration. The simulation results are consistent with the experimental test results. The filtering antenna as a novel radio frequency sensor can be applied to the point-to-point communication of automated guided vehicles in the logistics field. [ABSTRACT FROM AUTHOR]

This paper presents a compact wideband circularly polarized cross-dipole antenna with a low-pass filter response. It consists of two pairs of folded cross-dipole arms printed separately on both sides of the top substrate, and the two dipole arms on the same surface are connected by an annular phase-shifting delay line to generate circular polarization. A bent metal square ring and four small metal square rings around the cross-dipoles are employed to introduce new resonant frequencies, effectively extending the impedance and axial-ratio bandwidth. Four square patches printed on the middle substrate are connected to the ground plane by the vertical metal plates in order to reduce the antenna height. Thus, a compact wideband circularly polarized antenna is realized. In addition, a transmission zero can be introduced at the upper frequency stopband by the bent metal square rings, without using extra filter circuits. For verification, the proposed model is implemented and tested. The overall size of the model is 90 mm × 90 mm × 33 mm ( 0.37 λ 0 × 0.37 λ 0 × 0.14 λ 0 ; λ 0 denotes the center operating frequency). The measured impedance bandwidth and 3 dB axial-ratio (AR) bandwidth are 53.3% and 41%, respectively. An upper-band radiation suppression level greater than 15 dB is realized, indicating a good low-pass filter response. [ABSTRACT FROM AUTHOR]

This communication discusses and examines a dual port filtering hybrid (Silicon-graphene) based antenna. The main appearances of the designed THz radiator are: (i) a modified circular patch created HEM 11 δ x and HEM 11 δ y inside silicon ceramic, which in turn created a circularly polarized wave from 2.59 to 2.89 THz (axial ratio ≤3 dB); (b) a defected ground structure (DGS) along with patch creates band pass filtering features (5.0 dBi within the operating band and −15 dBi outside the operating band) within the operating band; and (c) coating of graphene material over the ceramic adds the re-configurability feature in proposed radiator. The designed radiator works effectively in between 2.49 and 3.29 THz (|S11|≤ −10 dB) with more than 25 dB isolation (due to orthogonal orientation). Due to the aforementioned features, the designed radiator is employable for different wireless THz applications. [ABSTRACT FROM AUTHOR]

The application of ceramic for a circularly polarized (CP) filtering antenna is studied in this paper. The dielectric resonator (DR) of sintered aluminum oxide (Al 2 O 3) ceramic has a dielectric constant of 9.5 and low dielectric loss of 0.003, and excellent mechanical properties. The dielectric resonator antenna (DRA) consists of two parts, the upper part is a DR, and the lower part uses a feeding network containing two hairpin bandpass filters. The measured | S 11 | of the DRA is 48.0 % and the axial ratio (AR) bandwidth is 33.5 %. Meanwhile, the peak gain of the DRA is 6.13 dBi, and the suppression level across the stopband exceeds 15.2 dB. The DRA uses the hairpin bandpass filters to improve the filtering characteristics of the antenna and uses the corner-cutting processing of the DR to improve the AR, which can be implemented to reduce the cost of fifth-generation (5 G) communication. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Test & Measurement Technology is the property of Publishing Center of North University of China and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, a single‐layer filtering antenna based on half‐mode patches is proposed. It consists of a main driven patch and a parasitic patch. A U‐shaped slot is first etched on the main driven patch to generate a new resonant mode and a radiation null simultaneously. Four pairs of shorting pins are introduced on the main driven patch to raise its operating frequency to near that of the U‐shaped slot, thus broadening the impedance bandwidth (IBW). Additionally, a parasitic patch is introduced near the driven patch to introduce an extra half‐TM10 mode and an extra radiation null, significantly enhancing the IBW and the upper‐edge selectivity of the antenna. A prototype was fabricated and tested for validation. It achieves a peak realized gain of 6.55 dBi and −10‐dB IBW of 8.8%, and exhibits good out‐of‐band rejection performance while maintaining a low profile of 0.017 λ0 and a compact transverse size of 0.29 λ02. [ABSTRACT FROM AUTHOR]

Copyright of Electronic Components & Materials is the property of Electronic Components & Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This work developed two cavity-backed slot antennas based on substrate integrated waveguide (SIW) technology. The designs offer the advantages of single-layer structure, dual-band operations, circular polarization, and filtering performance. Antenna I features a perturbed aperture on an SIW cavity and four cross slots distributed near its corners to excite seven resonant modes. Among them, two sets of orthogonal modes, namely TE120/TE210 and TE230/TE320, are used to create the first (3.7 GHz) and the second (5.6 GHz) operating bands, respectively, and to establish dual-band circularly-polarized properties for 5G NR n46 and n78 applications. The remaining three modes, TE110, TE220, and TE330, serve to generate radiation nulls to increase stopband rejection. Measured results indicated a peak gain value up to 7.1 dBic. The rejection levels at the lower, middle, and upper stopbands were 23, 10, and 17 dB, respectively. Antenna II further improves the rejection level at the middle stopband by introducing three complementary split-ring resonators (CSRRs) to the SIW feed line. It allows a broader stopband between the two passbands and enhances the corresponding rejection level. The middle CSRR is etched on the top of the SIW, whereas the other two CSRRs are on the bottom to avoid undesired resonance and to improve the rejection level effectively. The measured realized gain was as high as 7.78 dBic with excellent filtering characteristics. The rejection levels of 24, 24, and 20 dB were observed at the lower, middle, and upper stopbands, respectively.

To achieve a low-profile, wide-bandwidth, and highly selective design, this paper presents a substrate integrated suspended line (SISL) based broadband filtering dielectric resonator antenna (DRA) with the improvement of suppression level. The dielectric resonator is cylindrical and fed from the bottom by a microstrip-coupled slot. The dual head structure with the designed open stub can provide two radiation nulls on both sides of the passband for the filtering function and can excite three resonant modes (HEM $_{11\delta} $ , HEM $_{11\delta} $ , and TE131 mode) at different resonant frequencies to enlarge the impedance bandwidth of the proposed antenna. Then, adding a metal branch perpendicular to the feeder can offer a radiation null to eliminate the undesired resonances in the right stopband. Finally, the suppression level at high frequency is improved further by filling Sub2’s cavity with FR4. A prototype has been manufactured and measured for demonstration. Measurement shows that the proposed antenna has a - 10-dB impedance bandwidth of 32.9% (2.98-4.15 GHz), a flat gain within the passband, and the gain suppression level within the stopband exceeds 15.5 dB.

A class of dielectric filtering inverted-L antenna with reflective- and quasi-reflectionless-type radiation nulls is proposed to achieve wideband or dual-band operation. To this aim, a dual-function dissipative branch is exploited, which is in-parallel loaded at the feedline of the microstrip-fed dielectric inverted-L antenna. This absorptive branch, which is terminated in a grounded resistor, exhibits a quasi-complementary frequency response with regard to the one of the antenna. In this manner, it can mostly absorb the out-of-band RF-signal power not radiated by the antenna, hence creating quasi-reflectionless-type radiation nulls. Furthermore, the loaded branch can also generate a notch band giving rise to a reflective-type radiation null, which comes determined by the length of the branch and it is independent of the quasi-reflectionless radiation nulls. Thus, by controlling the spectral location of the notch band out of or within the operational frequency band of the dielectric inverted-L antenna, wideband or dual-band operational capabilities can be functionalized into it. For experimental-validation purposes, proof-of-concept prototypes for the two devised wideband and dual-band antenna approaches are designed, manufactured, and characterized. The measured results are in reasonably-close agreement with the simulated ones. The measured fractional impedance bandwidths of the two antenna prototypes are 28.3% (wideband one), 3.1% and 4.2% (dual-band one), respectively.

The fifth generation (5G) mobile communication systems employ technologies such as massive MIMO, millimeter-wave (mmWave), and ultra-dense networks to support higher transmission data rate and lower latency, thereby enabling commercial deployment. Furthermore, the forthcoming sixth generation (6G) networks will integrate terrestrial and non-terrestrial networks, aiming to achieve full spectrum, full applications, and global coverage. Whether in the context of 5G or 6G networks, base transceiver stations (BTS) require a substantial number of radio frequency (RF) transceiver chains and antenna array, particularly in mmWave frequency bands. It is known that bandpass RF filters between antenna elements and transceivers are key components for suppressing out-of-band spurs and interference. The single board seamless integration of transceivers and antennas has become a growing trend. It means there is no extra room for a large number of filters at mmWave bands, leading to the emergence of integrated designs that combine filtering circuitry with antennas, known as filtenna or filtering antenna. With illustrated examples, the design methodologies, operational principles, and implementation strategies of filtennas are reviewed in this paper.

This paper presents a dual-band shared-aperture antenna array using a filtering magnetoelectric (ME) dipole antenna for the application of mobile-communication base station. It is realized by interleaving a lower-band (LB) filtering ME dipole antenna operating from 1.7 to 2.8 GHz and four higher-band (HB) patch antennas in the band of 3.3-3.9 GHz. The filtering performance of the proposed ME dipole antenna is realized by U-shaped slots etched on the radiating arms and a cross-shaped microstrip line inside the aperture of the magnetic dipole, and used to realize a high cross-band isolation. The loss caused by the filtering structure is quite low. The gain suppression of the LB filtering ME dipole antenna reaches about 18 dB in the HB. Results demonstrate that both the HB and LB antennas can maintain stable broadside radiation patterns within their operating bandwidths. The magnitude of the cross-band isolation reaches more than 25 dB.

This paper introduces a novel filtering approach that employs integrated periodic structures with a conventional Vivaldi antenna to achieve a fully integrated bandpass filtering antenna. The approach results in a wide out-of-band suppression, high passband selectivity, adjustable operational bandwidth, and low insertion loss. The proposed filtering approach maintains the original size of the conventional Vivaldi antenna (base antenna) without requiring additional modifications. To validate the approach, we present two filtering Vivaldi antennas: filtering antenna I (center frequency: 18GHz, fractional bandwidth: 21%, insertion loss: 0.32dB) and filtering antenna II (center frequency: 6.5GHz, fractional bandwidth: 12%, insertion loss: 0.6dB). Their wide out-of-band gain suppression (typically $\geq 15$ dB) covers the conventional Vivaldi antenna’s frequency range (4-24GHz). A prototype of the filtering antenna I is manufactured. Its measurement results validate the proposed approach and show good agreement with the simulated reflection coefficient, realized gain, and radiation patterns. The features of the proposed filtering antenna approach, make it suitable for various applications requiring efficient frequency filtering.

A millimeter-wave wideband filtering on-chip antenna is proposed in this paper. Its operation frequency covers 32 GHz to 63 GHz, and the impedance fractional bandwidth reaches 63%. Based on the corner-fed patch antenna, the antenna in this work has a quasi-omnidirectional radiation pattern, and peak efficiency reaches 91.7%. By square slotting on the four sides of the patch and cross slotting on the center of the patch, the high-order mode is suppressed, which supports the wide operating frequency range with filtering characteristics. Split ring resonators are etched on the ground to strengthen filtering characteristics. Based on thin-film integrated passive device (IPD) technology, the proposed structure is applicable to the on-chip wideband and high-efficiency antenna array. [ABSTRACT FROM AUTHOR]

A compact filtering antenna with multi-adjustable radiation nulls is designed. Initially, a conventional aperture-coupled antenna is crafted by fine-tuning positions of the gap and radiation patch, achieving a radiation null. Additionally, an aperture-coupled filtering antenna is created by cascading a resonator with a microstrip feedline. Subsequently, the integration of the aperture-coupled antenna and the filtering antenna results in a dual-slot aperture cross-coupling filtering antenna, with two radiation nulls at both ends of the passband. Finally, a pair of slot lines is etched on the radiation patch, introducing an extra radiation null to enhance selectivity further. The measured results show that the proposed filtering antenna has a bandwidth from 2.44 to 2.64 GHz for |S11|<−10 dB, a peak gain of 5.5 dBi, and three radiation nulls at 2.3, 2.75, and 3.15 GHz enhancing the selectivity. [ABSTRACT FROM AUTHOR]

This paper proposed a novel filter antenna with the conical beam, which consists of four magnetoelectric (ME) dipole antennas. By printing parasitic patches and etching open slots on the bottom of the substrate, two radiation nulls near the high frequency of the passband are introduced. Combined with the intrinsic radiation null of the ME-dipole antenna, the filtering response is obtained. In order to verify the design method, a prototype is manufactured and measured. The measurement results show that the impedance bandwidth (VSWR <2) of the antenna is 1.48 ~ 2.61 GHz (55.3%). In addition, the out-of-band suppression is more than 17.4 dB and the maximum radiation direction of the conical beam is stable around to Theta = 30°. The proposed antenna array can be promising candidates for multi-rotor unmanned aerial vehicle (UAV) measurement systems. [ABSTRACT FROM AUTHOR]

A novel wideband high-selectivity substrate-integratedwaveguide (SIW) filtering antenna with controllable radiation nulls is proposed. This antenna is composed of a two-layered SIW resonator, two radiating slots on the top layer, and two coupling slots on the middle layer. A vertical SMA connector is located at the bottom and feeds two SIW cavities simultaneously. By adjusting the parameters of these slots, three radiation nulls will be achieved, and two radiation nulls can be easily controlled. For demonstration, one prototype of the filtering antenna is fabricated and measured. Measurement results show that the fractional bandwidth for |S11| < -10 dB is 8.9% (3.86-4.23 GHz), the gain is 6.08 dBi at center frequency 4.05 GHz, three radiation nulls are achieved at 3.7 GHz, 4.3 GHz, and 5.19 GHz, respectively. The out-of-band skirt selectivities of two sidebands are 150 and 332 dB/GHz, respectively. [ABSTRACT FROM AUTHOR]

A compact high‐gain filtering patch antenna with harmonic suppression characteristic is proposed. The antenna mainly contains a coupled transmission line and a central rectangular patch. The capacitive coupling between the coupled transmission line and the rectangular patch generates a radiating null at high frequencies. Then, acrossing the hybrid coupling principle, the structure of the microstrip‐to‐slotline transition builds two coupling paths, which generate a radiating null at low frequencies. In addition, two vertical slots are carved into the rectangular center patch to truncate the lateral current. That removes the higher order resonant modes and suppresses the parasitic passbands at high frequencies outside the passband. A fabricated 2 × 2 filtering antenna array is measured, showing a bandwidth up to 3.9% (8.68–9.03 GHz), a peak gain of 14.43 dBi, and two near‐band radiation nulls located at 8 and 9.55 GHz, demonstrating good radiation performances and an isolation of 25 dB. [ABSTRACT FROM AUTHOR]

In this paper, a single‐fed broadband circularly polarized (CP) filtering patch antenna based on metasurface is proposed. It consists of a corner‐truncated square patch, a nonuniform metasurface, and a U‐shaped strip. By placing the metasurface above the driven patch antenna, a radiation null is realized at the upper band, and an additional axial ratio (AR) minimum is simultaneously generated to enhance the CP bandwidth. Besides, two more radiation nulls are achieved at each side of the band edges by introducing a U‐shaped strip underneath the patch and embedding a shorting pin into the patch, which further improves the frequency selectivity and suppresses the radiation level. Measured results show that the designed antenna has a wide impedance bandwidth of 19.7% (4.8–5.85 GHz), a CP bandwidth of 19.9% (4.75–5.8 GHz), and an in‐band average gain of 7 dBic with suppression level of more than 18 dB at out of band. [ABSTRACT FROM AUTHOR]

In this letter, a wideband cavity‐backed filtering antenna based on 3‐D printing technology is proposed for millimeter wave applications. This antenna is made up of an air‐filled metal cavity, attached with two transverse slots on its upper surface. By exciting one TE110 cavity mode and two slot modes simultaneously, wideband performance can be obtained. Besides, by properly bending one slot into U‐shape, two radiation nulls appear at two sides of the passband, yet causing the increase of the cross‐polarization in H‐plane. To remedy this, the U‐shaped slot is further bent at its ends, successfully suppressing the cross‐polarization by 7 dB. The final proposed filtering antenna is implemented and measured, showing a wide bandwidth of 37.3%, covering from 21.4 to 31.2 GHz. And the measured maximum gain is 6.6 dBi in band, with two radiation nulls at 14.6 and 40 GHz. [ABSTRACT FROM AUTHOR]

A filtering antenna consists of a reflective filtering antenna (RFA) and a bandstop filter (BSF) is presented. Due to the L‐shaped feeding structure, slots etching on the radiator and the ground plane, the RFA obtains good impendence matching, stable in‐band gain, as well as four reflective radiation nulls, and that contribute an operating band of 19% and good frequency selectivity to the proposed filtering antenna. The RFA and BSF are cascaded directly, and the compact BSF is terminated by a resistor to absorb the stopband energy of the RFA, bringing good reflectionless characteristics in a wide frequency range to the proposed filtering antenna. The proposed filtering antenna has a 2‐dB gain bandwidth of 22% (1.78–2.22 GHz), in‐band gain of about 6.81 dBi, radiation suppression levels of higher than 23.4 and 21.4 dB for the lower and upper stopbands, respectively. Within 1.0–3.0 GHz, |S11| ≤ −12 dB, implying slight effect of reflected wave on the devices connected to the proposed filtering antenna. [ABSTRACT FROM AUTHOR]

A compact low‐profile planar filtering antenna with an enhanced suppression level is presented in this paper. The presented antenna has a simple structure, consisting of an E‐shaped driving patch, a shorted parasitic patch, and a defected ground structure (DGS). The E‐shaped driving patch serves as an effective radiator and facilitates the filtering response. The shorted parasitic patch is horizontally arranged and coupled with the driving patch through the radiating edge. And a radiation null and an extra in‐band resonance can be generated, which would simultaneously broaden the impedance bandwidth and improve the suppression level. In addition, a DGS on the metalized ground plane is etched to introduce another radiation null, and the out‐of‐band suppression level would be significantly enhanced. The filtering antenna with a center frequency of 3 GHz was constructed and tested to verify its performance. The measured values, which indicate a bandwidth of 10% (2.85–3.15 GHz) and a peak realized gain of 5.2 dBi, are in agreement with the simulated values. The presented filtering antenna features a low profile of 0.016λ0, a compact antenna size of 0.16λ20, as well as an improved suppression level of more than 22 dB. [ABSTRACT FROM AUTHOR]

This article presents a W‐band three‐layer reflectarray antenna that can be easily fabricated using printed circuit board (PCB) process. The proposed reflectarray element is composed of substrate integrated waveguide (SIW) structure and slot‐coupled patch. By controlling the length of SIW in each element, the compensation phases required for the reflectarray to generate focused beam at in‐band frequencies are realized. However, at the out‐of‐band frequencies, the elements fail to provide the required compensation phases as the incident electromagnetic wave cannot couple to the SIW. Thus, filtering performance is realized. A circular aperture prototype reflectarray comprising of 5024 elements are employed to yield a high‐gain narrow beam. The measured results show that the proposed reflectarray antenna attains a peak gain of 40.5 dB at 94 GHz with aperture efficiency of 41.3%, and out‐of‐band suppression higher than 22 dB. [ABSTRACT FROM AUTHOR]

In this paper, a two-port alumina-based filtering antenna is designed and investigated. The feeding structure of the proposed antenna creates dual radiation nulls inside the cylindrical ceramic, which in turn produces the filtering characteristics. A metasurface is suspended over the two-port radiator to convert linear waves into circular waves. The designed metasurface also reduces the mutual coupling between two ports by an amount of −15 dB because it acts as a single negative material. Experimental results are in good agreement with simulated outcomes. It works efficiently between 2.31 GHz and 2.62 GHz with an isolation level of more than 35 dB. 3 dB axial ratio is obtained between 2.4 GHz and 2.61 GHz. Out of the frequency band, the gain value is less than −15 dB, while it is 4.28 dBi in the functioning frequency range. Stable radiation properties make it suitable for B41/n41 (2.5/2.6 GHz) applications.a standard retrieval procedure. [ABSTRACT FROM AUTHOR]

Copyright of Electronic Components & Materials is the property of Electronic Components & Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, a compact integrated circular polarization filtering antenna is proposed based on substrate integrated waveguide (SIW) cavity. Firstly, a dual-mode (TE102 and TE201 modes) rectangular cavity is utilized as a common feeding cavity to achieve a dual-mode filtering response. And then, an additional rectangular patch with a slot is coupled from the feeding cavity for circular polarization radiation. To verify the proposed concept, a prototype circular polarization filtering antenna is simulated. The circular polarized filtering antenna resonates at 4.225 GHz with a low cross-polarization and a high gain of 7.23 dBi. [ABSTRACT FROM AUTHOR]

This paper presents a compact wideband circularly polarized cross-dipole antenna with a low-pass filter response. It consists of two pairs of folded cross-dipole arms printed separately on both sides of the top substrate, and the two dipole arms on the same surface are connected by an annular phase-shifting delay line to generate circular polarization. A bent metal square ring and four small metal square rings around the cross-dipoles are employed to introduce new resonant frequencies, effectively extending the impedance and axial-ratio bandwidth. Four square patches printed on the middle substrate are connected to the ground plane by the vertical metal plates in order to reduce the antenna height. Thus, a compact wideband circularly polarized antenna is realized. In addition, a transmission zero can be introduced at the upper frequency stopband by the bent metal square rings, without using extra filter circuits. For verification, the proposed model is implemented and tested. The overall size of the model is 90mm×90mm×33mm (0.37λ0×0.37λ0×0.14λ0; λ0 denotes the center operating frequency). The measured impedance bandwidth and 3 dB axial-ratio (AR) bandwidth are 53.3% and 41%, respectively. An upper-band radiation suppression level greater than 15 dB is realized, indicating a good low-pass filter response.

A compact substrate‐integrated waveguide (SIW) filtering multiple‐input multiple‐output magnetic dipole antenna with high selectivity and high isolation is proposed. Each filtering antenna element contains a SIW cavity, a half‐mode SIW cavity, and a magnetic dipole antenna with backed ground. Meanwhile, the SIW cavity and the half‐mode SIW cavity are vertically connected through magnetic coupling, and second‐order filtering frequency responses can be obtained. Owing to the cross‐coupling between the feeding line and antenna, two radiation nulls can be created to realize high selectivity. Based on the radiation mechanism of the magnetic dipole antenna and polarization diversity, high isolation can be obtained. The measured isolation and the envelope correlation coefficient are greater than 24 dB and less than 0.004, respectively. [ABSTRACT FROM AUTHOR]

This paper presents the review on the design of various reconfigurable antennas and their applications in the current scenario. There are more challenges involved in the design of these antennas. This paper also describes the various methods used for reconfiguring the frequency bands. The single parameter reconfiguration and hybrid reconfiguration examples are analyzed with their performances. The parameters such as gain, efficiency, and size of the existing antenna is compared. The various switches deployed in the antenna for achieving the reconfiguration are presented in this paper. The switches such as pin diodes, varactor diodes, MEMS, and mechanical switching are also elaborated with their corresponding merits and demerits. The diodes are switched on and off to activate and deactivate the structure of the antenna. Similarly, mechanical actuators are used for mechanical switching mechanism. The polarization reconfiguration mechanism between linear and circular; pattern reconfiguration mechanism between directional and omnidirectional are reviewed with various examples. In addition to that, several designs of reconfigurable filtering antennas, MIMO antennas are also reviewed in detail. Key Points: The different techniques used for various reconfigurations such as frequency, pattern, and polarization are discussed in this manuscriptThe applications of reconfigurable with filter structures, antenna arrays are analyzed in terms of its performance such as gain, efficiency, and bandwidth [ABSTRACT FROM AUTHOR]

In this letter, a single‐layer differential‐fed dual‐band filtering antenna for wireless local area network application is proposed. The proposed antenna consists of a square patch, and two pairs of stepped impedance resonators (SIRs). The lower operating passband is realized by exciting the square patch with a pair of differential ports. Then, a pair of SIRs is connected with the radiating edge of the square patch to introduce another resonance, thus forming the upper passband. And a radiation null is simultaneously produced to enhance the frequency selectivity between the two passbands. Moreover, another pair of SIRs is utilized to connect with the nonradiating edge of the square patch, which generates an additional high‐frequency in‐band resonance and a radiation null to further improve the bandwidth and frequency selectivity of upper passband. The developed prototype was fabricated and measured to verify the design concept. The measured results are in good agreement with the simulated ones, demonstrating that it exhibits −10 dB fractional impedance bandwidths of 3.68% and 7.35%, maximum realized gains at boresight direction of 5.5 and 8.7 dBi, and cross‐polarization levels smaller than −30 dB, in lower and upper passbands, respectively. [ABSTRACT FROM AUTHOR]

A dual-band filtering antenna, comprising a quasi-Yagi antenna and similar etched interdigital structures featuring high selectivity and wide impedance bandwidth, is proposed and analysed in this paper. Differing from the existing filtering antennas, the performance of the novel one can be improved with the help of the proposed interdigital structure etched on metallic ground instead of adding parasitic strips connected to the feedline of the top layer. Moreover, the proposed low-profile antenna performs as expected; the peak gain is 5.1 dBi and relative impedance bandwidth surpasses 36.4% in the former band within 3.6–5.2 GHz compared to conventional antennas. Meanwhile, it will work with the similar performance in multi-band due to the arrangement of symmetric etched interdigitals. For verification, a 35 × 55 × 1-mm3 prototype operating in dual-band is fabricated and experimented to compare with simulated results. In the end, the measured results are found in a good agreement with those of the simulated ones in designed band. [ABSTRACT FROM AUTHOR]

In this paper, a compact quasi-Yagi antenna with embedded resistor-loaded arms is proposed to obtain a filtering response with four radiation nulls. The embedded resistor-loaded arms achieve two additional radiation nulls caused by reverse currents and absorb the unwanted out-of-band resonant points brought by themselves. The director close to the driver provides a resonant point and a radiation null caused by opposite currents between the driver and the director. Compared with other filtering quasi-Yagi antennas, the proposed one can achieve a filtering response with a compact size along the endfire direction. For demonstration, a balun-integrated prototype covering the 5G band N78 (3.3–3.8 GHz) is designed with the size along the endfire direction (without ground) of 0.13 λ0 (λ0 is the wavelength in the free space at center frequency), and the measured results show a 10 dB impedance-matching bandwidth of 22.9% (3.21–4.04 GHz), four radiation nulls, and a peak gain of 4.73 dBi. [ABSTRACT FROM AUTHOR]

A high-gain filtering Fabry-Perot antenna (FPA) with radar cross Section (RCS) reduction is proposed. The design utilizes a partially reflecting surface (PRS) which is integrated with a chessboard arranged metasurface (CAMS) in a single-layered substrate. The CAMS is composed of periodic strip arrays to reduce monostatic RCS based on the phase cancellation principle. The PRS structure is a cross-slot array which is designed to work with both orthogonal orientations of the CAMS elements while yielding a high reflection magnitude. Accordingly, the proposed FPA achieves a high-gain broadside radiation and wideband RCS reduction. The filtering functionality is achieved from a T-shaped feed patch, which is, interestingly, enhanced by the integration of CAMS in the PRS. For validation, a prototype operating at 6.0 GHz has been fabricated and measured. The antenna with an overall size of $3.2\lambda _{{0}} \times 3.2\lambda _{{0}} \times 0.57\lambda _{{0}}$ at 6.0 GHz exhibits an impedance matching bandwidth (BW) of 5.73 – 6.23 GHz, a 3-dB gain BW of 5.76 – 6.17 GHz with the peak gain of 14.63 dBi, and an out-of-band suppression of ≥20 dB. Meanwhile, it achieves an RCS-reduction bandwidth of about 4.0 to 9.0 GHz (76.9%).

This work presents a combination of a cup-shaped monopole antenna and an E-shaped Multi-Mode Resonator (MMR) with the presence of a pair of PIN diodes and a varactor diode to form a compact reconfigurable communication filtering antenna for interweave Cognitive Radio (CR) systems. The proposed filtering antenna operates in the WiMAX band, and it is fabricated on an FR4 substrate with overall dimensions normalized to the wavelength ( $\lambda _{o}$ ) of the first resonant frequency $(0.413\lambda _{o}\times 0.516\lambda _{o}\times 0.0165\lambda _{o})$ . The step and continuous tuning serve the secondary user of the WiMAX CR system to communicate in the absence of the primary users at modifiable resonant frequencies and data rates.When the PIN diodes are OFF, the filtering antenna operates with a fixed odd mode resonant frequency and tunable even mode resonant frequency. This state results in a tunable antenna bandwidth covering a maximum measured frequency range of $3.25-4.02~ GHz$ and a minimum measured range equal to $3.25-3.58~ GHz$ . The ON state of the PIN diodes eliminates the antenna matching at the even mode resonant frequency while keeping a strong matching at the odd mode resonant frequency. The resulted operational measured frequency range of the antenna in this state is fixed at $2.9-3.28~ GHz$ . The filtering antenna has acceptable gain values at the pass band of the E-shaped MMR with a maximum simulated gain value equal to $2.5~ dB$ and a measured maximum gain equal to $2.48~ dB$ . The simulated and measured power patterns of the antenna for all diodes states are omnidirectional, which are convenient for portable CR gadgets.

This paper introduces novel dual-polarized/duplex filtering antennas with a novel filtering feeding network. The feeding network consists of an all-resonator structure, which shares a common dual-mode resonator. This structure facilitates the isolation of two well-isolated channels through the exploitation of the even and odd modes of the dual-mode resonator. By applying balanced excitation to the odd mode and unbalanced excitation to the even mode, the two modes can be separated, creating a hybrid-like feeding structure. Despite the common resonator, the channels exhibit high isolation, and the overall size of the filtering circuit is much smaller than conventional cascaded-resonator designs. To demonstrate the effectiveness of the proposed feeding network, we have designed, fabricated, and measured a dual-polarized and a duplex filtering antenna. The simulated and measured results agree well, showing isolations greater than 34 dB and 38 dB for dual-polarized and duplex cases, respectively. Our proposed antennas are compared with state-of-the-art developments, demonstrating the advantages of compact size, flexible decoupling frequency ratio, and high isolation.

The present study proposes a dual-polarized bandwidth-enhanced filtering specialized dipole antenna design for 5G by employing a wide printed dipole, filtering resonators, a reflector surface, and specially designed balun structures. Such a configuration is commonly deployed in conventional base stations. To increase the antenna impedance and radiation bandwidth, a specifically designed, wide-printed flared dipole antenna structure is used as the main radiator element. Transmission zeros are introduced at both pass band edges to create a filtering response by engaging parasitic elements. The parasitic element for the higher frequency edge of the filtering is placed close to the maximum amount of the induced current on the radiator at the operating frequency, whereas the parasitic element for the lower frequency edge of the filtering is located close to the perpendicularly polarized structure. The antenna aims to create radiation nulls at the impedance bandwidth limits; therefore, the parasitic arcs are used to create surface currents that cancel the broadside radiation at the limits of the impedance bandwidth. The study illustrates a complete analysis of the broadband printed patch antenna having a filtering effect by parametric investigations on the dimensions and resulting physical phenomenon in detail. To demonstrate the approach, a prototype of the antenna is fabricated and measured. According to the measurement results, the antenna performs 76% impedance bandwidth between 2.49 GHz and 5.59 GHz with $|S_{11}|$ and $|S_{22}| < -10$ dB by providing exceptional isolation values of $|S_{21}| < -20$ dB in entire operating band. The fabricated antenna has a stable radiation beamwidth with less than $\pm 5^{0}$ variation and the measured gain in the operating frequency is almost constant and equal to 8.2 dBi.

Leaky-wave antenna (LWA), as a special kind of waveguiding structure simultaneously characterized by both the guidance and radiation of electromagnetic waves along it, has received much attention and has been in the spotlight of both academia and industry since its inception in the 1940s. This is mainly because LWAs possess many appealing properties such as the highly directive beam, easy feeding mechanism, simple configuration, and particular frequency-driven beam-scanning, which enable them to hold promise in the development of a unique front-end antenna solution than others (e.g., reflector antenna and phased array). In addition to these inherent features, the exploitation of LWAs featuring multifarious sophisticated electrical functionalities (i.e., functional LWAs), with resort to engineering relevant radiating discontinuities and waveguiding structures, constitutes one mainstream research in the communities and increasingly prevails in the research & development of modern multifunctional wireless RF/microwave systems recently. This article is structured under this background, which is mainly dedicated to reviewing and investigating several enabling concepts, structures, and techniques that are specifically applied to the design of functional LWAs characterized by, for example, simultaneously low side-lobe and cross-polarization behaviors, rapid beam-scanning, stable radiation, frequency-selectivity, and open-stopband suppression. To make the technical discussions much more self-contained and systematic, this article begins with leaky-wave basics as well as general geometrical and electrical characteristics of LWAs. In addition, some representative system-level applications enabled by LWAs are briefly described, together with several promising research directions that can be further explored and galvanized, from the authors’ perspective.

This paper presents a single-layer dual-polarized filtering antenna with good out-of-band suppression. By using inherent characteristic of the patch’s eigenmode and meanwhile merging four filtering strategies, i.e., parasitic patches, slot on the driving patch, and defected ground structure (DGS), a low-profile filtering antenna design with five radiation nulls has been realized. With the designed filtering antenna, a conventional 1×2 array with a spacing of 0.91λ is first developed. In order to reduce the sidelobe level of the array, a sharing patching scheme is introduced to decrease the interspace between the elements as 0.44λ, with the same physical size as the conventional array. In addition, a concept to measure total isolation between two kinds of the polarized ports in the array, i.e., SddVH, has been derived for the first time. The prototype of the proposed array is fabricated with a profile of 0.038λ. Measured results indicate that the designed novel array has an operational band of 3.53–4.06 GHz, SddVH better than 41 dB, a sidelobe level below −18 dB, and a suppression level above 20 dB with the stopband up to 0.5 GHz and 5 GHz.

In recent years, there has been a development of multifunctional components, including filtering antennas. Co-designing the filter and antenna can effectively reduce the overall size and thus realize high integration. A new coplanar waveguide (CPW) omnidirectional filtering antenna with a pair of gain zeros is presented using separation electric/magnetic coupling (SEMC) paths that greatly enhance frequency selectivity and effectively suppress the spurious responses of the circular patch radiator. The impedance bandwidth of the filtering antenna can also be controlled/adjusted through electric/magnetic coupling. The design results demonstrate that the filtering antenna achieves an omnidirectional pattern with a center frequency of 3.7 GHz, an impedance bandwidth of about 3%, a gain of 2.7 dBi, and a pair of gain zeros. [ABSTRACT FROM AUTHOR]

The filtering antenna provides both radiation and filtering features and is an important component for the RF front-end of wireless devices. The main function of a filtering antenna is to reject out-of-band signals, thus reducing the interference from adjacent channels. The aim of the present work is to design a 2.6 GHz microstrip filtering antenna for 4G and 5G global mobile services. The filtering antenna is designed using a hairpin bandpass filter integrated with an elliptical microstrip aerial. Good impedance matching is obtained by using appropriate dimensions of the hairpin bandpass filter. The 10 dB return loss bandwidth of the filtering antenna is approx. 5.7%, with the maximum gain for the elliptical filtering antenna of approx. 2.2 dB. Good agreements between the measured and simulated results are obtained for the proposed filtering antenna and the bandwidth covers almost the entire 2.6 GHz band. [ABSTRACT FROM AUTHOR]

In this work, a computationally efficient method based on data-driven surrogate models is proposed for the design optimization procedure of a Frequency Selective Surface (FSS)-based filtering antenna (Filtenna). A Filtenna acts as a module that simultaneously pre-filters unwanted signals, and enhances the desired signals at the operating frequency. However, due to a typically large number of design variables of FSS unit elements, and their complex interrelations affecting the scattering response, FSS optimization is a challenging task. Herein, a deep-learning-based algorithm, Modified-Multi-Layer-Perceptron (M2LP), is developed to render an accurate behavioral model of the unit cell. Subsequently, the M2LP model is applied to optimize FSS elements being parts of the Filtenna under design. The exemplary device operates at 5 GHz to 7 GHz band. The numerical results demonstrate that the presented approach allows for an almost 90% reduction of the computational cost of the optimization process as compared to direct EM-driven design. At the same time, physical measurements of the fabricated Filtenna prototype corroborate the relevance of the proposed methodology. One of the important advantages of our technique is that the unit cell model can be re-used to design FSS and Filtenna operating various operating bands without incurring any extra computational expenses. [ABSTRACT FROM AUTHOR]

A filtering antenna based on the Substrate Integrated Suspended Line (SISL) platform applied for the n78 band of 5G is presented in this paper. The antenna has a segmented feed line, a rectangular driven patch etched with a double I-slot, and a squared stacked patch with grooves at the edges of both sides. The etched slots and the stacked patch introduce two new resonance frequencies increasing the bandwidth. Furthermore, the etched slots excite a deep radiation null in the low-frequency band, and the stacked patch coupled with the driven patch produces two deep radiation nulls in the high-frequency band. Three radiation nulls enable high selectivity of the antenna. The filtering antenna works at 3.2–3.89 GHz, which can be applied to the 5G (n78, 3.3–3.8 GHz) frequency band. The peak gain in the band can reach 9.21 dBi, and the out-of-band suppression levels are higher than 18.47 dB. [ABSTRACT FROM AUTHOR]

A new simple design of an inverted microstrip Gap Waveguide filtering antenna integrated with two stopband filters is proposed in this work. In order to simultaneously provide filtering and radiating functions, we use the direct integration approach to cascade two periodic sets of coplanar coupled EBG resonators with a slot antenna. The analysis shows that the filters can be easily adjusted in the same feeding layer of the antenna, without extra circuitry and without modifying the lines. EBG-filters are compact and offer great flexibility in determining the frequency, width and selectivity of the rejected bands. Experimental results for an X-band filtering antenna prototype are provided showing a 7.3% transmission band centered at 10.2 GHz and a realized gain peak of 2.1 dBi. The measurements demonstrate the filtering capability of the proposed antenna, achieving rejection levels greater than 12 dB and 20 dB for the bands below and above the operation band. The proposed low-complexity design offers good performance as a filter and as an antenna, showing the essential advantages of the Gap Waveguide Technology, including low losses, self-packaging and limited cost. This work demonstrates the possibility of integrating the new coplanar EBG-filters into future Gap Waveguide antenna designs to avoid unwanted radiation, to reduce interfering signals or to provide high isolation in multiband systems. [ABSTRACT FROM AUTHOR]