Near-field Resonant Parasitic Elements Research Articles

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.

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.

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%.

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.

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%).

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.

Effects of downscaling on radiation performance of impedance-matched ultrasmall antennas

This paper presents design and measurement verification of ultrasmall antennas with 1.16 GHz operating frequency. Two miniaturization techniques were applied including meander line-based near field resonant parasitic (NFRP) element and split ring resonator-based NFRP element. The designs were scaled down in four steps from ka = 0.825 to ka = 0.103 which is the ultimate design goal regarding the size of the antenna. Promising models were fabricated and corresponding results are measured. The gains of the antenna prototypes were compared among different designs and with the theoretical gain limit for different ka values. Promising models from this work can be applied for on-chip antenna design in the future.

Improved Signal-to-Noise Ratio, Bandwidth-Enhanced Electrically Small Antenna Augmented With Internal Non-Foster Elements

Non-Foster technology facilitates the ability to surpass the Chu bandwidth limit associated with electrically small antennas (ESAs). Nonetheless, in addition to challenging stability issues, the enhanced performance can come at the cost of increased noise and resistance losses generated by the active circuit. Consequently, low total efficiency and degraded signal-to-noise ratio (SNR) values can arise. Stability and SNR have dominated most reports to date; little has been discussed with regard to the underlying innovative physics of non-Foster augmented radiators. In this communication, we propose a broad bandwidth non-Foster ESA, emphasizing those aspects. By embedding a non-Foster element into the near-field resonant parasitic element of a metamaterial-inspired antenna, its electrically small size is maintained. On the other hand, a 5-times enhancement of its −10 dB fractional bandwidth (15 times its −3 dB bandwidth) is measured, significantly surpassing its passive Chu limit. Under a good matching, the measurements demonstrate that this non-Foster ESA achieves a 1.05 dBi peak gain and realizes average 5.0 dB SNR and 17 dB gain improvements over its passive counterpart.

Dual-Band, Linearly Polarized, Electrically Small Huygens Dipole Antennas

Two electrically small, dual-band Huygens dipole antennas are reported. In both designs, two pairs of magnetic and electric near-field resonant parasitic (NFRP) elements are combined organically within an electrically small, low profile package. The NFRP elements are excited effectively using only one coaxial-fed-driven element. One dual-band Huygens system produces parallel, linearly polarized (LP) fields at its two operating frequencies. The other dual-band system produces two orthogonal LP fields. Additional parasitic elements are introduced to mitigate the mutual coupling effects between the pairs of NFRP elements. The measured values for prototypes of both antennas in the L-band demonstrate their electrically small size ( $ka ) and low profile ( $\sim 0.03\lambda _{0}$ ). They also confirm their broadside radiation and polarization performance characteristics, as well as the isolation between each operating frequency. Their fractional bandwidths, peak realized gains, front-to-back ratios, and radiation efficiencies are, respectively, ~0.6%, > 2 dBi, > 10 dB, and > 60% at both frequencies. These dual-band systems would provide multifunctional performance in a variety of portable, compact wireless devices.

Electrically Small Huygens Antenna-Based Fully-Integrated Wireless Power Transfer and Communication System

This paper introduces the first reported electrically small Huygens dual-functional wireless power transfer (WPT) and communication system operating in the 915-MHz ISM band. It is realized by the seamless combination of a Huygens linearly polarized (HLP) antenna and a highly efficient HLP rectenna. The configuration consists of two orthogonally oriented HLP subsystems. Each one intrinsically combines two pairs of metamaterial-inspired near-field resonant parasitic elements, i.e., an Egyptian axe dipole (EAD) and a capacitively loaded loop (CLL). Through the development of a very tightly coupled feed subsystem that includes the WPT mode's rectifier circuit and the communications mode's feedline while preserving their isolation, the independent operation of both functions is facilitated in an electrically small volume (ka <; 0.77). The measured results of its fabricated prototype agree well with their simulated values. The communications mode antenna resonates at 910 MHz and radiates a cardioid-shaped Huygens pattern with the peak gain of 2.7 dBi. The Huygens-based WPT rectenna achieves an 87.2% peak ac-to-dc conversion efficiency at 907 MHz. The dual-functional system is an ideal candidate for many emerging Internetof-Things (IoT) wireless applications that require simultaneous wireless information and power transfer (SWIPT) and wirelessly powered communications (WPC).

Design of electrically small Hilbert fractal NFRP magnetic monopole antennas

ABSTRACTElectrically small, Hilbert fractal, near-field resonant parasitic (NFRP) antennas are reported and investigated in this paper. This type of electrically small antennas (ESAs) consists of Hilbert fractal curves as the NFRP resonators and small vertical monopoles as the driven elements. By offsetting the driven monopole off the centre position, good impedance matching can be easily realized. The current distributions on the fractal NFRP elements and the driven monopoles manifest that strong electric coupling could excite loop-mode currents along the Hilbert fractal NFRP structures, and thereby horizontal magnetic monopole patterns with broadside radiation property are realized. The results show that the 2nd-step evolution Hilbert fractal NFRP antenna witnesses an electrically size reduction of 25% compared to ka = 0.9622 of the square capacitively loaded loop (CLL) NFRP antenna, while maintaining its original broadside radiation. It is also demonstrated that there is a performance trade-off, i.e. higher fractal iteration orders leading to smaller resonant frequencies, narrower bandwidth and lower radiation efficiencies.

Electrically Small, Low-Profile, Planar, Huygens Dipole Antenna With Quad-Polarization Diversity

An electrically small, low profile, planar, Huygens dipole antenna with four reconfigurable polarization states is presented. The design incorporates both electric and magnetic near-field resonant parasitic elements and a reconfigurable driven element. The four polarization states include two orthogonal linear polarized (LP) and two circular polarization (LHCP and RHCP) states. A 1.5 GHz prototype was fabricated (partially with 3-D additive manufacturing), assembled, and tested. The measured results, in good agreement with their simulated values, demonstrate that even with its simple configuration, electrically small size ( $ka =0.944$ ), and low-profile height ( $0.0449\lambda _{0}$ ), this reconfigurable Huygens antenna possesses stable broadside radiation performance in all of its four 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, ~3303 dBi (2.97 dBi), ~10.7 dB (9.9 dB), and ~68.2% (67.5%). For the LHCP (RHCP) states, they are, respectively, ~2.82 dBi (2.74 dBi), ~11.4 dB (12.5 dB), and ~67.1% (65.9%).

Dual-Linearly Polarized, Electrically Small, Low-Profile, Broadside Radiating, Huygens Dipole Antenna

A dual-linearly polarized, electrically small, low-profile, broadside radiating Huygens dipole antenna is presented, that is, an advanced combination of electric and magnetic near-field resonant parasitic elements. Its prototype was fabricated and tested. The measured results are in good agreement with their simulated values. At 1.515 GHz, the prototype is electrically small ( $ka = 0.904$ ) and low profile ( $0.0483\lambda _{0}$ ). It exhibits high port isolation and a large front-to-back ratio (FTBR). The isolation between its two ports is demonstrated to be over 25.8 dB within its −10 dB fractional impedance bandwidth, 0.46%. When port 1 (port 2) is excited, the peak realized gain is 2.03 dBi (2.15 dBi) strictly along the broadside direction with a 12.4 dB (12.1 dB) FTBR.

Pattern-Reconfigurable, Flexible, Wideband, Directive, Electrically Small Near-Field Resonant Parasitic Antenna

A pattern-reconfigurable, flexible, wideband, directive, electrically small near-field resonant parasitic (NFRP) antenna is presented. The antenna consists of a pair of Egyptian axe dipole NFRP elements, together with a pair of shaped metallic strips that act as the driven element and are fed by a coaxial cable. These NFRP and driven elements are designed to achieve compactness. Two pairs of p-i-n diodes are integrated into the driven element to enable the pattern reconfigurability. The antenna has two switchable directive endfire states, each pointed in direct opposition to the other. Examples of the evolution of the antenna are used to illustrate its operating principles. A prototype of the optimized design operating in a frequency range centered at 1.8 GHz was fabricated and measured. The simulation and experimental results are in good agreement. The antenna exhibits a wide ~13.1% impedance bandwidth and a ~4.42 dBi peak realized gain in both pattern-reconfigurable states while maintaining its electrically small size: $\textit {ka} \sim 0.94$ . The flexibility of this antenna is demonstrated under different bending conditions by mounting it on cylinders with several different radii, and the results confirm that its performance characteristics are maintained under all of them.

Electrically Small, Low-Profile, Huygens Circularly Polarized Antenna

The design, simulation studies, and experimental verification of an electrically small, low-profile, broadside-radiating Huygens circularly polarized (HCP) antenna are reported. To realize its unique circular polarization cardioid-shaped radiation characteristics in a compact structure, two pairs of the metamaterial-inspired near-field resonant parasitic elements, the Egyptian axe dipole (EAD) and the capacitively loaded loop (CLL), are integrated into a crossed-dipole configuration. The EAD (CLL) elements act as the orthogonal electric dipole (magnetic dipole) radiators. Balanced broadside-radiated electric and magnetic field amplitudes with the requisite 90° phase difference between them are realized by exciting these two pairs of electric and magnetic dipoles with a specially designed, unbalanced crossed-dipole structure. The electrically small (ka = 0.73) design operates at 1575 MHz. It is low profile $0.04\lambda _{\mathbf {0}}$ , and its entire volume is only $0.0018\lambda _{\mathbf {0}}^{\mathbf {3}}$ . A prototype of this optimized HCP antenna system was fabricated, assembled, and tested. The measured results are in good agreement with their simulated values. They demonstrate that the prototype HCP antenna resonates at 1584 MHz with a 0.6 dB axial ratio, and produces the predicted Huygens cardioid-shaped radiation patterns. The measured peak realized LHCP gain was 2.7 dBic, and the associated front-to-back ratio was 17.7 dB.

A Wideband Single-Fed, Circularly-Polarized Patch Antenna With Enhanced Axial Ratio Bandwidth for UHF RFID Reader Applications

A wideband single-fed, circularly-polarized patch antenna with enhanced axial ratio bandwidth for RFID reader application is proposed. The antenna consists of a modified half E-shaped patch, a near-field resonant parasitic (NFRP) patch, and four rotated vertical metallic plates on the ground plane. The metallic plates surrounding the main radiator of the modified half E-shaped patch antenna are fabricated vertically on the ground plane. The operating frequency of the antenna decreases substantially with the vertical metallic plates, which is important for miniaturization of RFID applications. With an elliptical slot and a cut on the modified half E-shaped patch, antenna impedance bandwidth and CP performance both improve. A truncated corner patch as an NFRP element can generate an additional CP radiation mode and further enhances the axial ratio and impedance bandwidth. The measured results show that the antenna has an impedance bandwidth of 14.2% (833–960 MHz), a 3-dB AR bandwidth of 9.0% (846–926 MHz), and an average gain of 7.3 dBic over a 3-dB AR bandwidth. The proposed antenna has a compact size and a low profile ( $0.45\lambda _{0}\times 0.45\lambda _{0}\times 0.074\lambda _{0}$ ).