Near-field Resonant Parasitic Research Articles

Superdirective Unidirectional Mixed-Multipole Antennas: Designs, Analysis, and Simulations

Highly directive antenna systems that will address the needs of space-limited Internet-of-Things devices and their NextG applications are in demand. Compact high-frequency high-directivity alternatives to complex, power hungry phased arrays are desired. Several compact, unidirectional mixed-multipole antennas (UMMAs) based upon mixtures of primarily dipoles and quadrupoles are reported. The simulated performance characteristics of these 28 GHz near-field resonant parasitic (NFRP) antennas, notably their large peak directivities and front-to-back ratios, are presented; they are all demonstrated to be superdirective while having attractive radiation efficiencies. Uniform endfire arrays of active closely-spaced equal-length idealized wire dipoles are exemplified as reference cases. The Rayleigh quotient (RQ) method typically used to determine their amplitude coefficients is extended for the first time to achieve unidirectional versions. Comparisons between these unconstrained and constrained RQ-designed arrays are made. While the performance characteristics of the single-source broadside-radiating UMMAs approach those of the reference arrays, a direct comparison of a realizable UMMA with the analogous unequal-length, non-uniformly-spaced idealized dipole array demonstrates its superiority. A two-element UMMA array that is scalable to a larger number of elements is also presented and shown to be superdirective, illustrating that the attractive properties of its individual elements are maintained even when mutual coupling occurs.

Omnidirectional-Radiating, Vertically Polarized, Wideband, Electrically Small Filtenna

An omnidirectional, vertically polarized (VP), wideband, electrically small near-field resonant parasitic (NFRP) filtenna is presented. First, a specially-engineered tridimensional inverted-F structure is developed as the driven element to replace the feed copper pin of the shorted top-hat loaded monopole, forming a new NFRP VP antenna with a smaller size, a wider fractional bandwidth (FBW), and a radiation null in the low frequency band edge. Next, a pair of C-shaped slots are etched on the NFRP element to further expand the FBW through introducing an additional resonance, and meanwhile bring a radiation null in upper frequency band edge. The collaboration of the upper and lower radiation nulls empowers the developed antenna an excellent band-pass filtering property. Particularly, the equivalent circuit and surface current distribution are demonstrated to provide a clear insight into the mechanism of the two radiation nulls. Then, the developed inverted-F driven structure is evolved into a coupling-fed version to further improve the FBW, size and filtering performance. Finally, the developed filtenna is fabricated, installed, and measured. The measured results, which are in good agreement with the simulated values, demonstrate that, with a low profile ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.069\mathbf {\mathrm {\lambda }} _{\mathrm{ L}}$ </tex-math></inline-formula> ) and an electrically small size (ka = 0.74), the developed VP NFRP filtenna achieves a wide FBW of 32% and an enhanced peak realized gain of 6.1 dBi, exhibiting comprehensive advantages in the electric size, profile, FBW and realized gain.

A Compact Near-Field Resonant Parasitic Slot Helix Antenna With Wide Axial Ratio Bandwidth

A compact near-field resonant parasitic (NFRP) slot helix antenna with wide axial ratio bandwidth is developed in this Letter. The developed antenna consists of one hemispherical metallic surface (HMC) etched with dual curved helical slots and one driven helical monopole nested beneath. The working mechanism of wideband circular polarization radiation of a single-slot NFRP helix antenna is first investigated. Then, a dual-slot NFRP helix antenna with wider working bandwidth in a lower frequency range is evolved by organically collaborating two helical slots etched on the HMC. An optimized prototype of this dual-slot NFRP helix antenna was fabricated, assembled, and tested. The measured results, in good agreement with the simulated values, demonstrate that it possesses a compact size, and an effective fractional bandwidth of 19.15% along with the realized gain values of 3.52 ± 2.25 dBic. The above advantageous performance characteristics enable it to be a good candidate in applications into many wideband space-limited platforms, such as aerospace and mobile communication systems.

Low-Profile, Electrically Small, Ultrawideband Antenna Enabled With an Inductive Grid Array Metasurface

A low-profile, electrically small, ultrawideband (UWB) antenna enabled with a grid array metasurface is presented. The design incorporates a driven dipole, an electric near-field resonant parasitic (NFRP) element, and a grid array structure which operates as an inductive metasurface. The NFRP element is an Egyptian axe dipole (EAD) that is excited by the driven dipole. This combination itself is an electrically small NFRP dipole antenna. In contrast to previous versions, its operation in both its first and third resonant modes is established. The presence of the grid, which consists of identical interconnected rectangular loops, then provides a new dipole mode and facilitates the reduction of the frequency ratio of the NFRP dipole’s modes. The resulting overlap of these three resonant modes yields the UWB operation. The electrically small ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ka</i> = 0.92), low-profile ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.003\lambda _{0}$ </tex-math></inline-formula> ) antenna exhibits uniform radiation patterns and stable and high radiation efficiency (RE) performance characteristics. The antenna was optimized, fabricated, and tested. The measured results, in good agreement with their simulated values, demonstrate that the antenna yields an ultrawide, 67.7%, −10 dB impedance bandwidth with stable realized gain (RG) values, ~1.6 dBi, and high RE values, RE >77%, over its entire operational bandwidth.

Flexible, Bandwidth-Enhanced, Electrically Small, Electric Near-Field Resonant Parasitic Antenna With Filtering Performance Characteristics

In this communication, a flexible, bandwidth-enhanced, electrically small, electric near-field resonant parasitic (NFRP) filtering antenna is presented. The inherent radiation null of the dipole-driven NFRP antenna is first presented. In addition, by properly adjusting the relative position of the NFRP element and the driven dipole, this radiation null can be placed at either the lower or upper operational band edge. Then, by implementing multiple NFRP elements and properly allocating their relative positions, excellent bandpass-filtering response together with the enhanced bandwidth of the electrically small NFRP filtenna is accomplished. A prototype of the optimized design operating centered at 1.9 GHz was fabricated and measured. The simulation and experimental results are in good agreement, indicating that the antenna exhibits a wide ~11.3% impedance bandwidth with good out-of-band rejection, while maintaining its electrically small size: <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ka</i> ~ 0.924. The flexibility of this antenna is experimentally analyzed under different bending conditions and the results confirm that its performance characteristics are substantially maintained.

Electrically small, low‐profile, full‐duplex Huygens dipole filtenna

AbstractAn electrically small, full‐duplex Huygens dipole filtenna (HDF) is realized as a dense array of two HDF elements consisting of Egyptian axe dipole and capacitively‐loaded loop near‐field resonant parasitic (NFRP) elements. The dual‐band HDF elements operate at two very nearby frequency bands and are physically separated by only 0.12 λLB. Benefitting from the HDF element's good out‐of‐band rejection performance characteristics, high isolation levels between the lower‐band (LB) and higher‐band (HB) ports are obtained without any decoupling structure. The measured results, in good agreement with their simulated values, demonstrate that the entire system is electrically small (ka = 0.975) and low‐profile (0.041 λLB). The measured isolation levels at its LB (HB) port is, respectively, over 33.9 (29.2) dB. When the LB (HB) port is excited, its fractional bandwidth, broadside realized gain, front‐to‐back ratio, and overall efficiency values are, respectively, 0.86% (0.77%), 2.1 (2.31) dBi, 8.1 (9.6 ) dB, and 62.1% (62.8%).

Broadside Radiating, Low-Profile, Electrically Small, Huygens Dipole Filtenna

An electrically small, low-profile, Huygens dipole filtenna is presented that operates near 1.28 GHz. The design incorporates a pair of magnetic and electric near-field resonant parasitic (NFRP) elements and a driven element. Two pairs of interdigitated capacitor structures are integrated into the magnetic NFRP element to produce two deep radiation nulls at both the lower and upper frequency edges of the passband, respectively. The two nulls can be independently controlled to achieve good out-of-band suppression levels. A prototype was fabricated and tested. The measured results, in good agreement with their simulated values, demonstrate that the Huygens dipole filtenna is electrically small ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ka</i> = 0.943) and low-profile (0.0385 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ), together with enhanced out-of-band rejection performance characteristics. Its fractional bandwidth, broadside realized gain, front-to-back ratio, and overall efficiency values are, respectively, 1.16%, 2.33 dBi, 8.45 dB, and 63.1%.

AWE-Inspiring Electrically Small Antennas

Anytime-wireless-everywhere (AWE) aspirations for Internet-of-Things (IoT) applications to be enabled through current 5G and evolving 6G and beyond ecosystems necessitate the development of innovative electrically small antennas (ESAs). While a variety of ESA systems are reviewed, those realized from the near-field resonant parasitic (NFRP) antenna paradigm are emphasized. Efficiency, bandwidth and directivity issues are highlighted. Multifunctional, reconfigurable, passive and active systems that have been achieved are discussed and illustrated; their performance characteristics and advantages described. This overview finalizes by going back to the future and considers enterprising research areas of current and forward-looking interest.

Electrically Small, Planar, Frequency-Agile, Beam-Switchable Huygens Dipole Antenna

An electrically small, planar, frequency-agile, beam-switchable Huygens dipole antenna is investigated in this article. The near-field resonant parasitic (NFRP) design incorporates an Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL) that function as the electric and magnetic NFRP elements, respectively. A varactor diode is integrated into each of these NFRP elements to facilitate simultaneous tuning of its operating frequency and switching its main beam direction. By changing the capacitance values of these two varactor diodes, the antenna realizes two independent, antipodal, unidirectional endfire radiating states with similar realized gain (RG) and front-to-back ratio (FTBR) values within virtually the same frequency-agile ranges. The experimental results demonstrate that the developed antenna exhibits a 5% frequency-agile fractional impedance bandwidth in both of its two oppositely directed endfire states. The antenna is electrically small at the highest frequency of this bandwidth ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${ka}_{high} &lt; 0.86$ </tex-math></inline-formula> ) and has measured relatively high radiation efficiency (RE >67.7%), peak RG (2.1–3.19 dBi), and FTBR (5.61–13.4 dB) values, together with stable and uniform radiation patterns, over this frequency-agile range.

Wideband, Compact Antennas With Interdigitated Magnetic-Based Near-Field Resonant Parasitic Elements

Wideband, compact antennas based on interdigitated magnetic-based near-field resonant parasitic (NFRP) elements are presented. The interdigitated NFRP elements, driven with coax-fed monopole antennas, facilitate the realization of two adjacent resonant modes whose combination yields the enhanced bandwidth. The resulting wideband compact antennas exhibit broadside radiation performance. Linearly polarized (LP) and circularly polarized (CP) prototypes based on this interdigitated NFRP element concept were designed, simulated, fabricated, and measured. The measured and simulated results are in good agreement. The NFRP radiating element of the LP antenna is electrically small with <inline-formula> <tex-math notation="LaTeX">$ka = 0.921$ </tex-math></inline-formula> and yields a wide, 17.4&#x0025;, &#x2212;10 dB impedance bandwidth with a stable realized gain, &#x007E;5.5 dBi, over its entire operational bandwidth. The NFRP radiating element of the CP antenna is also electrically small with <inline-formula> <tex-math notation="LaTeX">$ka = 0.923$ </tex-math></inline-formula> and exhibits a wide, 8.6&#x0025;, 3 dB axial ratio bandwidth. Stable realized gain, &#x007E;5.2 dBi, and uniform radiation patterns along with relatively high radiation efficiency, RE &#x003E; 88&#x0025;, are achieved over its entire operational bandwidth.

A Novel Printed Monopole Antenna With A Tapered-line Resonator Loading

In this paper, a novel compact printed monopole antenna is presented. The antenna consists of a planar monopole antenna and a tapered-line resonator with inner coupled section, which works as a near-field resonant parasitic (NFRP) element. The resonant frequency can be decreased dramatically by the strong coupling between the resonator and the monopole antenna. Thus, the miniaturization of the antenna is realized. The simulated results show that the resonant frequency decreases from 2.98 GHz to 2.4 GHz and the electric length of the antenna is reduced from 0.32 λ to 0.25 λ by loading a tapered-line resonator as NFRP element. After theoretical analysis is presented, sample antenna is manufactured and measured to verify the predictive performance of the proposed antenna. The overall size of the antenna is only 44.6×31.8×0.5mm3, and the operation frequency of the antenna ranges from 2.59 GHz to 2.85 GHz (9.5%) based on |S11| ≤ -10 dB, the gain is about 1.98dBi, which are in well agreement with the simulated results.

Single-Layer, Unidirectional, Broadside-Radiating Planar Quadrupole Antenna for 5G IoT Applications

In this article, an innovative quadrupole-based broadside-radiating unidirectional antenna is designed at 28.475 GHz for fifth-generation (5G) Internet of Things (IoT) applications. The planar antenna is based on a single-layer technology and realized on a flexible substrate to facilitate conformal applications. It consists of a coax-fed-driven dipole and two quadrupolar near-field resonant parasitic (NFRP) elements. The broadside-radiating design achieves a unidirectional pattern with a realized gain of 4.85 dBi and a front-to-back ratio of 9.4 dB. The total efficiency of the antenna is 85%. A differential-fed prototype was designed, fabricated, and tested at 1.579 GHz to make the measurements more manageable. The measured and simulated results are in good agreement.

A Metamaterial Inspired Compact Miniaturized Triple-band Near Field Resonant Parasitic Antenna for WLAN/WiMAX Applications

This paper presents a metamaterial-inspired triple-band antenna specified for WLAN and WiMAX applications with a compact size of 24mm × 18mm × 1mm (at 2.4 GHz). It consists of a dual-band left-handed metamaterial (LHM) unit surrounded by a G-style monopole antenna. The LHM is first designed and analyzed with equivalent circuits and simulations. A loop antenna based on the LHM unit is designed and simulated to investigate the radiating performance of the LHM unit structure. We also ran simulations for the G-style monopole. Later, the LHM unit is employed as a near-field resonant parasitic (NFRP) element that surrounded by the G-style monopole. A prototype of this antenna is fabricated. Simulations and measurements were carried out and the results match well, identifying good omni-directional radiating performance. Radiation comparisons with the loop antenna and the G-style monopole indicate that due to NFRP, the G-style monopole’s pass bands are shifted to lower frequencies to satisfy 2.45 GHz and 5.5 GHz bands requirements, meanwhile the LHM unit structure operates a third pass band of 3.5 GHz. The compact size and good radiation properties of the antenna render it suitable for WLAN/WiMAX applications.

A Compact, Low-Profile, Broadside Radiating Two-Element Huygens Dipole Array Facilitated by a Custom-Designed Decoupling Element

A compact, low-profile, broadside radiating, two-element Huygens dipole array is developed for in-band full-duplex (IBFD) applications. Each radiating element is a multilayer near-field resonant parasitic (NFRP) design that is electrically small with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ka=0.76$ </tex-math></inline-formula> at its resonance frequency, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{0} = 1.511$ </tex-math></inline-formula> GHz. The center-to-center distance between the elements is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.3\lambda _{0}$ </tex-math></inline-formula> . The array’s outstanding performance is facilitated by a custom-designed decoupling element. This specially engineered scatterer is printed on an additional layer and consists of a pair of meander-line resonators connected by a metallic strip. The overall height of the entire system is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}/20.3$ </tex-math></inline-formula> . The passive decoupling element operates as several electrically small electric dipoles whose scattered fields mitigate the interactions between the two radiators. It provides very high isolation levels between them and improves the overall directivity of the array. The optimized array was fabricated, assembled, and tested. The measured results, in good agreement with their simulated values, confirm that the developed decoupling structure not only increases the peak isolation level from 14.4 to 50.4 dB but it also improves the peak realized gain in the broadside direction by 0.5 dB and the corresponding front-to-back ratio (FTBR) value by 14.4 dB.

A novel printed monopole antenna with folded-line SIR loading

A novel printed monopole antenna with simple, low-profile and convenient design is presented in this paper. The antenna composes of a printed monopole antenna and a folded-line stepped impedance resonator (SIR) loaded on the bottom of the substrate. The resonant frequency is decreased by the coupling between the folded-line SIR as the near-field resonant parasitic (NFRP) element and radiation patch of the monopole antenna. The stronger the coupling, the lower the frequency. At the same time, the introduction of the NFRP element does not require an additional circuit for impedance matching, a novel the printed monopole antenna can be achieved. After analyzing the principle of the proposed antenna, a sample antenna has been manufactured and measured to prove the estimated performance of the proposed antenna. The measured results of the proposed antenna are consistent with the simulation, which shows that the design method in this paper is accurate and effective.

Polarization-Reconfigurable Yagi-Configured Electrically Small Antenna

An electrically small, high-directivity, Yagi-configured, near-field resonant parasitic (NFRP) antenna with four reconfigurable polarization states is presented. The antenna is composed of two NFRP elements and a customized, electrically controlled, reconfigurable driven element. The elements are stacked vertically in a Yagi configuration. The upper NFRP element acts as the director, and the lower one acts as the reflector. Both elements have a cross-shaped Egyptian axe dipole form. By integrating four p-i-n (PIN) diodes into its coax-fed asymmetric driven element, four polarization states, i.e., two orthogonal linear polarization (LP) and two circular polarization (LHCP and RHCP), are enabled which are controlled with the ON/OFF-states of the PIN diodes. The measured and simulated results of this electrically small (ka = 0.7) sized polarization-reconfigurable system are in good agreement. This simple, Yagi-configured antenna exhibits stable radiation performance in all four of its polarization states. The measured results demonstrate that, in its x (y)-LP state, the peak realized gain, front-to-back ratio, and radiation efficiency values are, respectively, ~3.08 (3.2) dBi, ~11.0 (11.05) dB, and ~77% (73%), and that, in its LHCP (RHCP) state, they are, respectively, ~3.0 (3.1) dBi, ~12.1 (11.18) dB, and ~72% (70%).

Compact, Low-Profile, Linearly and Circularly Polarized Filtennas Enabled With Custom-Designed Feed-Probe Structures

Compact, low-profile, linearly polarized (LP), and circularly polarized (CP) patch-based filtennas are realized with a custom-designed coupling probe. It introduces a deep null at both the lower and upper band edges of the filter response. These two nulls facilitate a quasi-elliptic bandpass behavior and can be independently controlled to achieve sharp band-edge skirts and high out-of-band suppression levels. The CP version evolves from the LP design by introducing a T-shaped nearfield resonant parasitic (NFRP) element near the probe to create two transmission paths with an inherent 90° phase difference. Its presence facilitates the simultaneous excitation of the TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">10</sub> and TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</sub> modes of the patch without the need for any power divider or phase delay line, reducing the design complexity and lowering the insertion loss. Prototypes were fabricated, assembled, and tested. The measured results agree well with their simulated values. They are low profile (0.03 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> height) and compact in size (0.04 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> footprint). The LP and CP prototypes exhibit, respectively, a -10-dB fractional impedance bandwidth of 7% and an overlapping axial ratio fractional bandwidth of 4.5%. Excellent measured performance characteristics are demonstrated, including flat passband realized gain values and filter responses with sharp roll-off rates and high out-of-band suppression levels.

Electrically Small, Single-Substrate Huygens Dipole Rectenna for Ultracompact Wireless Power Transfer Applications

An electrically small, single-substrate Huygens dipole rectenna with exceptional physical and radiation performance characteristics is reported. A highly efficient rectifier circuit is seamlessly integrated with an ultrathin, electrically small, Huygens dipole antenna (HDA) on a single piece of Rogers 5880 substrate. It consists of two metamaterial-inspired near-field resonant parasitic (NFRP) elements, an Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL) that are etched on the top and bottom metallization layers of the substrate, respectively. A printed receiving dipole is amalgamated tightly with the rectifier on the CLL layer. This ultracompact rectenna system has a large electromagnetic wave capture capability and achieves nearly complete conversion of the incident energy into dc power. The HDA prototype has a realized gain of 4.6 dBi and a half power beamwidth (HPBW) greater than 130°. The entire rectenna is electrically small with ka =0.98, is low cost and easy to fabricate, and has a measured 88% ac-to-dc conversion efficiency. The developed rectenna system is the ideal candidate for ultracompact far-field wireless power transfer (WPT) applications.

Two-Port, Dual-Circularly Polarized, Low-Profile Broadside-Radiating Electrically Small Huygens Dipole Antenna

A two-port dual-circularly polarized (CP), low-profile broadside-radiating electrically small Huygens dipole antenna is presented that has an advanced feed network and multilayer stacked layout of its electric and magnetic near-field resonant parasitic (NFRP) elements. It radiates left-hand CP (LHCP) or right-hand CP (RHCP) fields at its 1.5 GHz resonance frequency depending on the selected feed port. The measured results, in good agreement with the simulated values, demonstrate that the antenna is electrically small ( ka = 0.94) and low profile ( $0.053\lambda _{0}$ ), relative to the longest wavelength in its −10 dB impedance bandwidth. The port isolation is over 15.6 dB within its 0.99% fractional impedance bandwidth. When port 1 (port 2) is excited, its measured peak realized gain and front-to-back ratio (FTBR) values are, respectively, 1.82 dBi (1.81 dBi) and 4.1 dB (4.5 dB).

Wideband, Electrically Small, Near-Field Resonant Parasitic Dipole Antenna With Stable Radiation Performance

A wideband, electrically small, and near-field resonant parasitic (NFRP) dipole antenna with stable radiation performance is presented. Inspired by recent metasurface antennas (MSAs), a coax-fed dipole antenna is loaded with a specially-engineered interdigitated NFRP element. It exhibits identical operating mechanisms to a developed electrically large slot-fed MSA, i.e., it has the similar adjacent fundamental mode and antiphase mode, and thus has a wide bandwidth property and uniform radiation patterns. The electrically small prototype was fabricated and measured. The measured results, in good agreement with their simulated values, demonstrate a wide 14.4% −10 dB impedance bandwidth along with a stable realized gain of 1.4 dBi over the entire band. Moreover, stable and uniform radiation patterns together with high radiation efficiency values were also measured. These performance characteristics make the reported electrically small antennas attractive for wideband and space-limited applications.