Radiation Nulls Research Articles

A Compact Low-Profile Hybrid-Mode Patch Antenna With Intrinsically Combined Self-Decoupling and Filtering Properties

A new type of patch antenna with intrinsically combined self-decoupling and filtering properties is first proposed to address the mutual coupling between elements of the same bands and adjacent bands. By specially engineering the metallic patch of a conventional microstrip antenna into two tightly connected radiators, i.e., a primary patch radiator and a secondary stub-loaded inverted-F radiator, this novel hybrid-mode patch antenna under dual closely located resonances of a TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> patch resonator mode and an inverted-F resonator mode is favorably achieved. More importantly, the stub-loaded inverted-F radiator could not only introduce two radiation nulls allocated at both the lower and upper passband edges, leading to a good filtering response with a sharp band skirt and good selectivity in the boresight gain curve, but also function as an effective isolator that suppresses its near-field coupling, endowing its intrinsic self-decoupling property. Moreover, the developed patch antenna maintains the geometrical advantages of the typical microstrip antenna, including compact size, low profile, and single-layer configuration. In particular, the unique self-decoupling and filtering properties of the developed patch antenna make it a good candidate for multiantenna systems consisting of antenna elements operating at both the same bands and adjacent bands. Prototypes of the self-decoupled filtering patch antenna alone and two types of two-element arrays operating at the same band and adjacent bands, respectively, have been designed, fabricated, and measured. The measured results, in good agreement with their simulated values, validate its low mutual coupling performance for multi-antenna applications.

A novel single‐feed filtering dielectric resonator antenna using slotline‐loaded coupling structure

AbstractThis paper proposes a novel single‐feed filtering dielectric resonator antenna (FDRA) using fusion design method and the microstrip‐slot coupled feeding structure. Two pairs of slotlines are elaborately designed and perpendicularly loaded on the coupling slot to provide two radiation nulls at the edges of the passband. Therefore, a compact DRA with a quasi‐elliptic function bandpass response is constructed without extra filter circuits. Furthermore, two radiation nulls can be individually controlled through changing the length of the corresponding slotlines. For proving the effectiveness of the design, a prototype FDRA operation at 3.45 GHz is fabricated and measured. The measured results show that the peak realized gain is 5.84 dBi and the ‐10dB impedance bandwidth is 10.29% (3.29 ‐ 3.65 GHz). The proposed FDRA not only has good performance, but also has simple design.

High selective parallel‐scheme filtering antenna synthesized by transversal coupling matrix

A novel synthesis method based on transversal coupling matrix for the parallel-scheme filtering antenna with high out-of-band selectivity is proposed. The filtering antenna consists of three resonant radiation elements that are connected to a common feed point. By adopting the parallel scheme, the design of a third-order filtering antenna can be decomposed into three first-order sub filtering antennas. Each resonant antenna element can be separately designed and little adjustment is needed after combining these elements. Given a specification with up to two radiation nulls, the corresponding parameters of the three elements can be synthesized using the coupling matrix theory based on transversal topology. A practical filtering antenna centered at 5.74 GHz with the bandwidth of 410 MHz (7.2%) and two radiation nulls at 5.43 GHz and 6.13 GHz is fabricated. The measurements show the gain of 7.5 dBi and out-of-band suppression more than 30 dB at both passband sides can be achieved within the total size of 1.208λ0 × 1.725λ0 × 0.024λ0, where λ0 is the free space wavelength of the center frequency.

A High Selectivity and High Efficiency Filtering Antenna With Controllable Radiation Nulls Based on Stacked Patches

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.

Differential-Fed Dual-Polarized Filtering Fabry-Perot Antenna With High Isolation

In this paper, a dual-polarized filtering Fabry-Perot antenna (FPA) with high-isolation is proposed. It consists of a feed element of differential-fed dual-polarized square patch and a partially reflecting surface (PRS). The patch is capacitively coupled with T-shaped resonators and shorting-vias to obtain broadband characteristic and radiation nulls. The PRS structure is composed of two complementary metasurface layers are selected for achieving a positive reflection phase gradient within the broad frequency range. More interestingly, thanks to the frequency selectivity feature, the PRS significantly enhances the filtering characteristic of the FPA. For verification, a prototype of the proposed antenna operating at the 5.5-GHz center frequency has been fabricated and measured. The prototype with an overall size of ~2.0λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> × 2.0λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> × 0.49λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> (λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> is the free-space wavelength referring to the lowest operational frequency) result in an impedance bandwidth of 17.1% (5.02 – 5.96 GHz) for 10-dB return loss and a high isolation of ≥ 45 dB. Moreover, the far-field measurements result in a good dual-polarized radiation with the peak gain of 13.0 dBi, cross-polarization level of ≤ –25 dB within the passband, and out-of-band suppression level of ≥ 20 dB.

A Low-Cost Differentially Fed Dual-Mode Filtering MIMO Antenna With Enhanced Isolation Based on SISL Platform

A low-cost differentially-fed dual-mode multiple-input- multiple-output (MIMO) antenna is proposed for enhanced isolation and filtering response based on the substrate-integrated suspended line (SISL) platform. Stacked patches are placed above the driven patches to realize dual-mode performance and filtering response in the upper band. The stacked patches are widened and notched to enhance the isolation and the filtering response in the lower band. Eight metal stripes are set at both sides of the feed lines to enhance the frequency selectivity further. Compared with the conventional MIMO antenna based on patch elements, the isolation is enhanced by 7.6 dB, and the out-of-band suppression with 17.6 dB is achieved. To verify the design, a prototype is fabricated and measured. In a operating band of 4.8-4.96 GHz, maximum gain of 8.3 dBi, and isolation of 31.3 dB are realized. The filtering response is achieved by three broadside radiation nulls at 4.36 GHz, 4.62 GHz, and 5.08 GHz.

Design of Broadband Circularly Polarized All-Textile Antenna and Its Conformal Array for Wearable Devices

A broadband circularly polarized (BCP) all-textile antenna and its wearable conformal antenna array (WCAA) are investigated for body-centric communications. Initially, a circularly polarized (CP) microstrip patch antenna loaded with a piece of the modified metasurface is designed to achieve wide impedance and axial ratio (AR) bandwidths. The characteristic mode analysis is employed to understand the operating mechanism, which provides clear physical insight into each mode at various frequencies. Due to the adoption of textile (i.e., felt) as substrate and nylon conductive fabric as conductor, the proposed antenna is flexible, totally conforming to the curve-shaped human body. The antenna with broadside radiation is suitable for off-body communications. For verification, the prototype operating at 5 GHz (5.15–5.825 GHz) band was fabricated. The measured −10 dB impedance and 3 dB AR bandwidths of 35.1% and 17.5% with a peak gain of 8.5 dBi are achieved. Furthermore, the BCP antenna is used as an element to constitute the WCAA, and the omnidirectional radiation pattern in the azimuth plane is achieved for on- and off-body communications. The considerations about how to achieve omnidirectional radiation and avoid radiation nulls are studied in detail. Finally, the WCAA was fabricated and tested; the measured results guarantee its potential for wearable applications.

A filtering antenna with wide out‐of‐band suppression based on open‐stubs resonator

In this paper, a wide out-of-band suppression antenna with simple structure, low profile and filtering characteristics is presented. In order to improve the selectivity of the passband edge, two simple structures, namely U-shaped slot and two slits, are introduced into the antenna to generate radiation nulls. To obtain a wide out-of-band suppression, the feeder with π-shape stub is applied. The transmission nulls generated by the feeder are used to suppress stopband harmonics. In addition, a pair of parallel strips is introduced to enhance the gain suppression effect at the upper stopband. The measured results show that the average gain is 7 dBi, and the stopband suppression reaches 2.84 f0 (f0 is the center frequency of the proposed antenna). The overall height of the presented antenna is 0.03 λ0 (λ0 is the wavelength at the center frequency).

A Dual-Beam Wideband Filtering Patch Antenna With Absorptive Band-Edge Radiation Nulls

A dual-beam filtering patch antenna with two absorptive band-edge radiation nulls and four reflective stopband radiation nulls is proposed. By loading a pair of T-shaped metallic strip underneath the radiating patch, a modified TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sub> mode with TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> -like radiation pattern is obtained, which combines with the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> mode of the radiating patch, generating a wide operating band with symmetrical dual-beam radiation pattern. Two reflective radiation nulls are generated in both upper and lower stopbands for suppressing the out-of-band radiation. Through embedding two pairs of shorted small patch in the radiating patch, one absorptive radiation null combining with one absorptive resonant mode is produced at each band edge to absorb the band-edge incident energy, leading to a reduced reflection and sharp roll-off at both band edges, and therefore, the transceiver can be protected. With a total height of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.038~\lambda _{0}$ </tex-math></inline-formula> , a prototype is designed, fabricated, and measured, showing a −10 dB impedance bandwidth from 4.63 to 6.10 GHz with sharp band-edge roll-off, two radiation beams directed at ±40° with an in-band gain of 6.0 dBi, and high out-of-band suppression of over 15 dB.

Dual-Polarized Filtering Magnetoelectric Dipole Antenna Utilizing Intrinsic Highpass Filter Network and Integrated Lowpass Filter Network

This article presents an effective design method to integrate bandpass filtering response into an aperture-fed dual-polarized magnetoelectric dipole (ME-dipole) antenna. The antenna is composed of a traditional ME-dipole radiator and a modified aperture-coupled feeding structure. In one aspect, highpass filtering radiation response is realized by approximating the antenna radiator as a highpass filter network. In another aspect, by developing an improved aperture-coupled feeding structure with lowpass filter characteristics, the antenna obtains lowpass filtering radiation response. As a result, bandpass filtering radiation response is achieved. Since no intricate filter resonators are used, the in-band antenna gains are not degraded. The highpass/lowpass filter networks are studied and specific radiation nulls generated by the two networks are analyzed. For demonstration, a single-polarized model is presented first and its working mechanism is studied in detail. It realizes a 78.6% impedance bandwidth, flat in-band gains of 7.5–7.8 dBi, and more than 22 dB out-of-band radiation suppression level. Then, based on the same methodology, a dual-polarized antenna model i developed with 69.3% operating bandwidth, 7.1–9.3 dBi measured in-band gains, and integrated bandpass filtering radiation response.

Simple Patch Antenna with Filtering Function Using Two U-Slots

In this study, two U-slots of different sizes are used to combine the filtering function with a patch antenna. The U-shaped slots are etched into the patch, and currents in the opposite direction exist around these slots. Therefore, the currents cancel each other out, and a radiation null is formed. As a result, two radiation nulls are implemented on the left and right sides of the passband. To demonstrate the novelty of the proposed concept, a filtering patch antenna with a center frequency of 3.21 GHz and a 10 dB impedance bandwidth of 19.9% is designed and fabricated. High suppression levels of 25.33 and 19.32 dB in the lower and higher stopbands, respectively, are achieved. Therefore, a sharp band skirt and good selectivity are exhibited in the boresight gain response. The two radiation nulls are located at 2.4 and 3.7 GHz and can be independently adjusted.

A Novel Single-Feed Filtering Dielectric Resonator Antenna Using Slotline Stepped-Impedance Resonator

A novel single-feed filtering dielectric resonator antenna (FDRA) with quasi-elliptic bandpass response is proposed in this brief. The proposed FDRA consists of a shunted slotline stepped-impedance resonator (SSIR), a rectangular dielectric resonator antenna (DRA) and a microstrip feedline with a pair of transverse arms. The antenna is excited in the fundamental TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{11\delta }$ </tex-math></inline-formula> mode, the transverse arm mode and the two SSIR modes. Moreover, three radiation nulls are produced near the edges of the passband by the SSIR and the transverse arm of microstip feedline, respectively. A prototype FDRA is fabricated and measured, which offers a bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$| S_{11} | &lt; -10$ </tex-math></inline-formula> dB) of 21.14% (3.13 - 3.87 GHz), and a peak realized gain of 5.3 dBi within passband. The realized gain shows a decline of 20 dB at passband-edge, which exhibits high selectivity.

A wideband high-gain high-selectivity filtering antenna with two adjustable radiation nulls

In this paper, a high-gain filtering antenna is proposed without extra filtering circuits. The proposed filtering antenna is composed of a stacked patch, a driven patch with an Ω-shaped slot and a ground etched a θ-shaped slot. There are two radiation nulls located at the lower and upper edges of the passband, respectively, which can be independently tuned by the Ω-shaped slot and stacked patch. In this way, the proposed filtering antenna has a flat gain response within the passband and a high suppression level in the stopband. The Ω-shaped slot can also bring an extra resonant mode to broaden the operating bandwidth. The θ-shaped defected ground structure (DGS) is designed to improve the impedance matching without affecting the filtering performance and the radiation pattern. The proposed filtering antenna is simulated, fabricated, and measured. The simulated and measured results are in good agreement. The measured 10-dB impedance bandwidth is 22.2% from 2 to 2.5 GHz, the maximum realized gain is 9.74 dBi at 2.42 GHz, and the out-of-band suppression is more than 24 dB.

Wideband SIW Filtering Antenna With Controllable Radiation Nulls Using Dual-Mode Cavities

A wideband fourth-order filtering antenna consists of two substrate integrated waveguide (SIW) dual-mode cavities is presented in this letter. The first SIW cavity creates two resonant nodes and one radiation null (RN) located on the upper stopband. The second SIW cavity integrated with a slot cannot only achieve radiation function but also realize dual-mode resonance, which can produce another lower out-of-band RN. These two RNs can be controlled to improve frequency selectivity and design flexibility. The coupling matrix theory is adopted to guide the design of the filtering antenna, and the generation principle of these two RNs can be explained by cross coupling. Finally, such a filtering antenna operating at the center frequency of 5.4 GHz with a fractional bandwidth of 7.64% and a maximum gain of 5.3 dBi is fabricated and measured.

High selectivity and efficiency differential dual‐polarized filtering patch antenna

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.

Wideband Differentially Fed Dual-Polarized Antenna by Using Three-Strip Transmission Lines

A new method of designing a wideband differentially fed dual-polarized antenna by using three-strip transmission lines (TS-TLs) is presented. A wideband power divider composed of four TS-TLs is first proposed and illustrated by using its equivalent circuit. Based on the proposed power divider, a wideband differentially fed dual-polarized antenna with four in-band resonances is developed. To enhance the out-of-band selectivity, two radiation nulls with quasi-elliptic response are obtained by utilizing the specifically designed structures in the TS-TL-based power divider. The first radiation null at the lower out-of-band is produced by the resonance from the center strip of TS-TL and shorting coaxial cable. The second radiation null at the upper out-of-band is produced by the resonance from the slot formed by the dipole arm and the outer strip of TS-TL. Combining with the high second-order harmonic suppression owing to the differentially fed method, the presented differentially fed antenna is demonstrated that it not only has high in-band selectivity covering 1.67-2.91 GHz, but also has high out-of-band suppressions of 33.8 and 20.6 dB over the frequency bands of 0.6-1 GHz and 3.3-5 GHz. In addition, stable gain and beamwidth are achieved for base station applications.

Compact dual‐polarized filtering antenna with enhanced bandwidth for 5G sub‐6 GHz applications

A broadband dual-polarized filtering antenna with a compact size and high skirt selectivity for fifth-generation (5G) sub-6 GHz applications is proposed in this paper. The antenna is composed of two feeding networks and four shorted patches, which is based on a slot-aperture excitation scheme. By employing the novel defected ground LC resonator structures (DGLCRSs) and two different types of open-ended structures, the proposed dual-polarized antenna realizes satisfactory filtering performance as well as an improved operating bandwidth simultaneously. During which, four radiation nulls are generated at the both band edges and can be individually controlled. To further enhance the upper stopband performance, four pairs of meander-shaped slots are inserted on the patches symmetrically, which introduces another controllable radiation null. The working mechanism for achieving the filtering responses is provided. A fabricated prototype and experimental results demonstrate that an impedance bandwidth of 42.9% (3.3–5.1 GHz) is first obtained in a low-profile dual-polarization structure, covering the entire 5G N77/N78/N79 bands. The measured gain is about 8.1 dBi within the passband, while the stopband suppression is better than 16 dB up to 1.85 fc. These merits make the proposed antenna quite potential for the 5G new radio communication systems.

Filtering Antenna With Quasi-Elliptic Response Based on SIW H-Plane Horn

A filtering antenna with a quasi-elliptic response based on the substrate-integrated waveguide(SIW) H-plane horn is presented. It is mainly composed of two symmetrical horn elements embedded with the trapezoidal dual-mode cavity. By exploiting the cross couplings of the dual-mode cavity, two radiation nulls are introduced on the gain curve showing a quasi-elliptic filtering response without the increase of horn size. Then, a modified transition is printed in front of the horn aperture on both sides of the substrate, which acquires wider impedance bandwidth and maintains a low backlobe radiation throughout the bandwidth. Besides, the proposed antenna is designed, fabricated, and measured at Ku-band. Two measured radiation nulls can be observed at 14.02 and 17.98 GHz, where the gain drops significantly to below -28 and -38 dBi, leading to high frequency selectivity. A wide measured impedance bandwidth of 12.2% and a large front-to-back ratio of more than 20 dB are achieved. To the author's best knowledge, it is the first time that the filtering horn antenna with radiation nulls, wide bandwidth, and excellent radiation is designed.

A Dual-Layer Filtering SIW Slot Antenna Utilizing Double Slot Coupling Scheme

This letter presents a filtering substrate integrated waveguide slot antenna design with multiple radiation nulls based on a double slot coupling scheme. It consists of a dual-layer cavity resonator, a slot in the first layer, and two coupling slots inserted in the middle layer. The slot in the first layer functions as the antenna radiator. This radiator is etched in the first cavity instead of the last stage of the network, resulting in two radiation nulls. A double slot coupling scheme is employed in the middle layer to not only couple the two-layer cavity resonators but also generate two more radiation nulls. Owing to these radiation nulls, the antenna features high-frequency selectivity as well as out-of-band radiation suppression level. For demonstration, the proposed filtering antenna is implemented and tested. The antenna operates at the center frequency 4.5 GHz with 15.4% (4.2-4.9 GHz) measured bandwidth. The maximum gain within the operating band is 7.5 dBi and four radiation nulls are generated. Better than 21 dB out-of-band radiation rejection level is obtained.

A Single-Layer Dual-Circularly Polarized SIW-Cavity-Backed Patch Filtenna With Wide Axial-Ratio Bandwidth

A single-layer dual-circularly polarized cavity-backed patch filtenna with wide axial-ratio (AR) bandwidth is presented in this letter. The degenerated substrate-integrated waveguide (SIW) cavity modes TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">120</sub> /TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">210</sub> cooperating with the patch modes TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> /TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> are utilized to achieve a wide AR bandwidth. Simultaneously, two radiation nulls, which are inherently introduced by the SIW-cavity mode TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">110</sub> and mixed electromagnetic coupling between the cavity and patch, respectively, are realized at both band edges to achieve a bandpass filtering response. For demonstration, a sample was fabricated and tested. The measured results show that the proposed filtenna achieves an operating bandwidth of 12% with the center frequency of 10 GHz, a peak gain of 7.4 dBic, an in-band average gain of 6.7 dBic, and an out-of-band rejection level over -13 dB.