inverted-F Antenna Research Articles

Multiband antenna design based on Gosper fractal for implantable biomedical devices

AbstractIn this paper, a novel multiband implantable planar inverted-F antenna (PIFA) antenna based on Gosper curve fractal geometry is designed for biomedical telemetry applications. The antenna has covered four dedicated frequency bands; medical implant communication system band (MICS 402–405 MHz), industrial, scientific, and medical bands (ISM 902–928 MHz and 2.4–2.5 GHz), and wireless medical telemetry services (WMTS 1395–1400 and 1429–1432 MHz). The proposed antenna is designed on Rogers RO 3010 substrate of thickness 25 mil and volume equal to 153.67 mm3. The reflection coefficient and the radiation pattern are measured inside muscle-mimicking liquid tissue phantom. The antenna has achieved the impedance bandwidth of 126, 406, 168, and 175 MHz at MICS (403 MHz), ISM (915 MHz), WMTS (1400 MHz), and ISM (2.45 GHz) with maximum gain value −33.6, −21.04, −15.48, and −10.25 dBi, respectively. The data link range between the implantable antenna and off body antenna has been performed with −16 dBm input power. Additionally, the obtained specific absorption rate with the input of 25 μW power has also been obtained within the safety limit and hence ensures the reliability of the proposed antenna.

Design and analysis of high isolated super compact 2 × 2 MIMO antenna for WLAN application

In this article, a DGS structure is applied to enhance the inter-port isolation of super compact 2 × 2 MIMO antenna. Each element of MIMO antenna configuration is designed using a planar inverted-F antenna (PIFA) having dimensions 7 × 7 × 0.8 mm3 and elevated at 2.8 mm from the ground plane of dimensions 100 × 50 × 0.8 mm3 (comparable to the size of mobile handsets). The proposed antenna operates from 5.2 to 6 GHz resonating at 5.65 GHz which is suitable for WLAN applications. The proposed design with and without the isolation enhancement technique is resonating at 5.65 GHz. Therefore, the proposed DGS structure is acting as a perfect isolator without affecting the reflection coefficient of the MIMO antenna configuration. It provides high isolation enhancement from 12 to 25 dB at the resonance frequency. All the diversity parameters of the MIMO configuration are calculated and found within the desirable limits. Thus, it is found that the proposed antenna is well suited for modern wireless applications (WLAN). The radiation performances such as 2D and 3D patterns, total antenna efficiency, and peak realized gain are calculated and analyzed. Finally, a prototype is fabricated and validated experimentally.

Highly Integrated PA-PIFA With a Wide Frequency Tuning Range

This letter presents a highly integrated power amplifier (PA) antenna with the capability of frequency tuning. A planar inverted-F antenna (PIFA) is used to directly match the PA transistor. This mitigates the lossy output matching network in the PA-integrated antenna (PAIA). In order to achieve a wide frequency tuning range, a combination of capacitors is loaded at the PIFA to control the antenna input impedances so that matching can be maintained with frequency tuning. The antenna analysis and design procedure of the tunable PAIA are detailed. For verification, a prototype is designed, fabricated, and measured. The experimental results show that the frequency tuning range of the proposed PAIA covers from 2 to 4 GHz. Over this frequency tuning range, the effective isotropic radiation power and power-added efficiency are higher than 40.5 dBm and 60% at the input power of 26.5 dBm, respectively.

Erratum: Application of characteristic modes to design the platform-mounted inverted-F antenna [IEICE Communications Express Vol. 9 (2020) No. 6 pp. 159-163

Erratum: Application of characteristic modes to design the platform-mounted inverted-F antenna [IEICE Communications Express Vol. 9 (2020) No. 6 pp. 159-163

Compact PIFA Antenna with High Gain and Low SAR Using AMC for WLAN/C-band/5G Applications

In this paper, a novel low profile planar inverted-F antenna (PIFA) with high gain and low specific absorption rate (SAR) using a miniaturized artificial magnetic conductor (AMC) is investigated. The performance of the PIFA antenna is analyzed with AMC to understand the contribution of AMC. The gain enhancement of the PIFA antenna is achieved by applying AMC below the antenna. Furthermore, the placement of AMC also reduces the SAR of the antenna and improves the antenna front-to-back ratio (FBR). The proposed antenna when measured has an impedance bandwidth of 4.8–6.7 GHz (33% with center frequency at 5.75 GHz) which is suitable for Wireless Local Area Network (WLAN), satellite uplink C-band, and sub-6 5G applications with the maximum gain of 7.6 dBi. The performance of the proposed antenna is analyzed by full-wave commercial electromagnetic software and verified by measurements.

Wideband Slotted Planar Inverted-F Antenna using Eccosorb MCS Absorber for Millimeter-Wave Applications

This work investigates the performance enhancement of the slotted planar inverted-F antenna (PIFA) using Eccosorb MCS absorber. In order to check the enhancement of the antenna performance, structure of the PIFA antenna with and without absorber has been analyzed. This antenna structure consists of two slots etched on the patch, which are placed at a height of 0.18λ 0 from the substrate. We show that with the application of absorber, the radiation pattern can be transformed and produces the radiation beam in the desired direction. The proposed antenna is loaded with two layers of Eccosorb MCS absorber on the top of the substrate and with the other two layers below the substrate. Apart from providing radiation pattern in the desired direction, the antenna with absorber also provides wideband operation of 57.8 % bandwidth with high gain. The designs were first validated by simulations and then verified by measurements

Embroidered Textile Antennas: Influence of Moisture in Communication and Sensor Applications.

Moisture causes detuning and increased losses in textile antennas, and it affects resonant and wideband textile antennas differently. In this work, we studied the effect of moisture on a resonant textile planar inverted-F antenna (PIFA) and a wideband textile monopole antenna. Both antennas were manufactured by embroidering conductive yarn in denim textile. The input reflection coefficient, antenna gain, and gain patterns were measured on both antennas for different moisture contents. The results show that wideband antennas are less affected by moisture in comparison with resonant antennas. For communications applications, large moisture content in the textile antenna should be avoided; therefore a flexible, textile-based waterproofing antenna cover was proposed, manufactured, and tested. On the other hand, the effect of antenna detuning by moisture can be used for moisture-sensing application. This concept was demonstrated on the resonant textile PIFA in transmission and reflection setups, showing that the reflection setup gives better results.

High Isolation Eight-Element Mimo Antenna Array Tightly Arranged Based on Embedded Meta-Material Cells

Objectives: To design A high isolation eight-element multiple and input multiple output (MIMO) antenna array tightly arranged based on embedded meta-material cells for the applications of 5G mobile terminals. Methods: In this, antenna array with a four block structure in which every block is formed by a method of tightly arranging two Inverted-F Antennas (IFAs) is used. These IFAs antennas are designed by the novel MIMO meta-material Cells which composed of two layers that are mutually connected through shorted pins are embedded with the high isolation using the High frequency structured simulator (HFSS) in the FR-4 (glass-reinforced epoxy laminate material) substrate. Findings: Simulation results reveal that the proposed IFAs antennas can provide isolation with a mutual coupling reduction of 18 dB with respect to the transmission coefficients and can also obtain sufficient bandwidth by the proposed antenna array for the 5G mobile terminals applications. Novelty: Isolation of Ports in every block can be improved by using the inductor. Keywords: Multiple Input Multiple Outputs (MIMO); Meta-material cells; tightly-arranged pair and Inverted-F Antennas (IFAs)

Design of UHF RFID Sensor-Tags for the Biomechanical Analysis of Human Body Movements

This paper presents the design and the development of a Battery Assisted Passive Radio-Frequency IDentification (RFID) tag in the Ultra High-Frequency band integrated with inertial measurement unit (IMU) sensors tested for the biomechanical analysis of human body movements. Enhanced by a compact and efficient meandered Planar Inverted-F Antenna (PIFA), the device exploits a specific RFID chip having a dual-access -wired and wireless- to the memory. A properly decoupled cell battery is also foreseen to boost the chip sensitivity and to supply power to an ultra-low power microcontroller and to the sensors. The device has been realized using off-the-shelf low-cost discrete components on FR4 substrate, validated, and tested in capturing real human movements. Two sensor-tags have been applied on the pelvis and on the torso of an individual moving in front of the RFID Reader antenna. Afterward, sensor data have been collected, processed, and filtered with specific algorithms, and used to control a musculoskeletal virtual model in the OpenSense software tool. The results show that the whole system correctly reproduces the performed movements, demonstrating the appropriateness of the proposed RFID-sensor in wireless movement capture applications.

Bandwidth Improvement of an Inverted-F Antenna Using Dynamic Hybrid Binary Particle Swarm Optimization

This paper proposes a Dynamic Hybrid Binary Particle Swarm Optimization (DH-BPSO) algorithm to improve the bandwidth of an inverted-F antenna (IFA). The proposed algorithm improves upon the existing Artificial Immune System (AIS) algorithm by including a weighting factor that dynamically changes throughout the optimization. DH-BPSO activates or deactivates a 12 × 2 grid of parasitic patches incorporated between the IFA and ground plane. The DH-BPSO optimized and conventional IFAs are fabricated and compared while maintaining the same antenna volume. The measurement results show that the optimized IFAs have characteristics of 58.6% wider bandwidths and 5.8% higher antenna gain for various ground clearance lengths at Long Term Evolution (LTE) 700 MHz band compared to the conventional IFAs.

Novel design of a triple band PIFA antenna by using a binary genetic algorithm

In this study, we propose a miniature triple band PIFA antenna (planar inverted-F antenna) composed of uniform semi-patches for LTE2600/WLAN/WIMAX/HIPERLAN-2 applications. The binary genetic algorithm determines the shape of the antenna’s radiating plate to achieve multiband operation with good performance. The simulated results reveal that the proposed antenna has attained three bandwidths ( $$S_{11} <-\,10\mathrm{dB}$$ ). The first bandwidth is from 2.5 to 3.07 GHz with resonant frequency at 2.80 GHz. The second bandwidth takes the range from 3.79 to 3.99 GHz with an operating frequency at 3.89 GHz. The third bandwidth is from 5.64 to 5.94 GHz with resonance at 5.78 GHz. All three resonant frequencies demonstrate good impedance matching with high radiation efficiency and gain. The PIFA antenna design is constructed of two FR4 epoxy substrates and has dimensions of $$15 \times 30 \times 3.8\,\mathrm{mm}^3$$ . The proposed multiband PIFA antenna exhibits good performance with small size, making it suitable for several wireless systems applications.

Low-Profile Circularly Polarized Isoflux Beam Antenna Array Based on Annular Aperture Elements for CubeSat Earth Coverage Applications

This article presents an antenna array to produce a circularly polarized (CP) isoflux beam for CubeSat earth coverage applications. Distinguished from conventional arrays formed by identical elements, the proposed one is based on sequential rotation-fed concentric annular aperture elements. By adjusting the excitation phase, magnitude, and polarization of each annular aperture element, the radiation patterns of the array can be shaped to form isoflux beams. Radiation pattern modeling method is developed to obtain array radiation parameters. Besides, to effectively characterize the impedance matching of the radiators of the array with multiple excitations, an overall reflection coefficient is deduced from signal decomposition. A prototype operating at C-band (5 GHz) is designed, fabricated, and measured. It consists of a radiator and a feeding network. The radiator is formed by two annular aperture elements, of which the inner one is realized by a circular patch antenna while the outer one is formed by eight planar inverted-F antennas (PIFAs). The feeding network drives annular aperture elements in the manner of sequential rotation. In this way, a CP isoflux beam array with a low profile ( 0.078 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> ), lightweight, and ease-of-integration for CubeSat is realized. The proposed array can also be extended to realize other shaped beams.

Compact Co-polarized PIFAs for Full-Duplex Application Based on CM/DM Cancellation Theory

In this article, a compact co-polarized decoupled antenna for full-duplex application working at 1.71 GHz is proposed. The antenna is composed of two back-to-back air-dielectric planar inverted-F antennas (PIFAs) with zero edge-to-edge distance. The whole system is included in a compact volume of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.45\lambda _{\mathrm {\mathbf {0}}} \times 0.45\lambda _{\mathbf {0}} \times 0.02\lambda _{\mathbf {0}}$ </tex-math></inline-formula> . The proposed antenna is designed based on the common mode (CM)/differential mode (DM) cancellation theory and its design guideline is illustrated in detail. Isolation maximum of 42 dB, broadside gain of 6.7 dB, and efficiency of 90% have been achieved in the proposed structure. There is a 1.9 dB gain difference between the broadside gain and the maximum gain. The proposed antenna shows its potentials in the radio frequency front-end incorporate design.

Isolation Improvement between Closely-Spaced Antennas Using EBG

Isolation improvement between two closely spaced antennas using a single column EBG is proposed for compact wireless devices. The proposed design developed for the 2.4 GHz WLAN band achieves more than 17 dB isolation improvement between two planar inverted-F antennas (PIFAs) compared to the no-EBG case. As a result, improved MIMO capacity is also achieved. The proposed design can be scaled up or down in frequency and may be implemented for small devices such as, smart watches, Wi-Fi routers, internet of things (IoT) devices etc.

A Wideband PIFA-Pair-Based MIMO Antenna for 5G Smartphones

In this letter, a multiple-input–multiple-output (MIMO) antenna with wideband performance for 5G smartphones is presented. First, a planar inverted-F antenna (PIFA) with an inverted-T-shaped open-slot is introduced. The proposed PIFA operates with a wide bandwidth of 78% due to the multimode technology. Then, two such PIFAs are attempted to be merged as a PIFA-pair, constituting a 2 × 2 sub-MIMO antenna with a similar bandwidth as the PIFA-element. Additionally, the isolation between two PIFA-elements in a PIFA-pair is higher than 10 dB across the broadband. Finally, a 4 × 4 MIMO antenna, which is composed of two PIFA-pairs, is demonstrated to cover the 5G NR frequency bands: n77/n78/n79 and LTE band 46. The simulated and measured results are included for illustrating the performance of the proposed MIMO antenna.

Power Absorption and Skin Temperature Rise From Simultaneous Near-Field Exposure at 2 and 28 GHz

In international guidelines and standards for human protection from electromagnetic fields, mass-averaged specific absorption rate (SAR) is used as a metric to prevent excessive temperature rise at frequencies from 100 kHz up to 6 GHz. Above this transition frequency, including the frequency region assigned to fifth-generation (5G) wireless communication systems, area-averaged absorbed power density (APD) or epithelial power density is used as a physical quantity to specify restrictions on human exposure. In 5G wireless systems, frequencies above and below 6 GHz may be used simultaneously. The effect of the superposition of SAR and APD on temperature rise should be considered, especially regarding the prevention of excessive surface temperature. Herein, we considered simultaneous exposure from inverted-F antenna and patch antenna array operating at 2 and 28 GHz, respectively. Computational results showed that the effect of superposition was marginal. This result is attributable to the heat diffusion length in biological tissues ( $\sim 10$ mm). The effect of the superposition was higher than 15% only when the patch antenna array and inverted-F antenna were separated by less than 50 mm for the 5 mm antenna-body separation.

Penta-Band Inverted-F Antenna Tuned by High-Voltage Switchable RF Capacitors

A penta-band inverted-F antenna (IFA) tuned by two high-voltage aperture tuning networks is presented in the paper. The design is based on a singe, non-bended radiating arm IFA. Each of the two aperture tuners comprises a high-voltage switchable RF capacitor IC in parallel with an off-chip inductor. The antenna can be tuned to any of the 5 bands of sub-4 GHz cellular spectrum between 690 MHz and 3800 MHz with return loss exceeding 6 dB at the feed over more that 95% of the total frequency range. A systematic design and analysis of the penta-band IFA based on transmission line model is provided, tuning approach for carrier aggregation enablement over two bands at a time is discussed. A nonlinear performance of the designed antenna with RF capacitors fabricated in bulk-CMOS RF-switch technology is demonstrated.

A Decoupling Network for Resonant and Non-Resonant Sub-1 GHz MIMO Mobile Terminal Antennas With Improved Compactness and Efficiency

In this work, the design procedure of a new decoupling network for different antennas is presented for mobile terminals operating in the Sub-1 GHz band (from 0.698 to 0.96 GHz). To evaluate its applicability for different resonant and non-resonant antenna types, two antenna elements have been chosen to be decoupled using the proposed decoupling network: a printed inverted-F antenna and a capacitive coupling element antenna. Simulation and measurement results showed that the decoupling network offer promising improvements in terms of impedance matching, port isolation, envelope correlation coefficient (ECC), and total efficiency. In addition, the antennas are also investigated with the ergodic capacity, multiplexing efficiency, gain, and diversity gain (both calculated using maximal ratio combining technique). Due to the contribution of the decoupling network, the ECC of both types of multiple antennas are less than 0.3, with a 30 % improvement in total efficiency and an inter-element spacing miniaturization of 34 %.

Characteristic Mode Analysis of ESPAR for Single-RF MIMO Systems

A systematic method based on the Theory of Characteristic Modes (TCM) for finding orthogonal radiation patterns of any electronically steerable parasitic array radiator (ESPAR) is described. This method can be useful for designing single-RF front-end multiple-input multiple-output (MIMO) systems in which orthogonal patterns can be utilized as a basis set for space modulation (SM) or full multiplexed MIMO systems. The method is based on the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N$ </tex-math></inline-formula> -port formulation of TCM and is not restricted to antenna type or array configuration. It can also provide closed formed solutions for the antenna element currents required to generate the orthogonal patterns. In addition an approach to finding the required load reactances in ESPAR for generating the orthogonal patterns is provided and is based on the quasi-Newton method utilizing a closed form expression for the initial approximate solution. Approximate estimation of the effective aerial degrees of freedom of the ESPARs is also discussed. Two simulation examples of ESPARs, a 4-element linear dipole array and an 8-element rectangular planar inverted-F antenna array, using SM as well as full multiplexed MIMO are provided, demonstrating the effectiveness of the proposed method.

A Study on Decoupling Method for Two PIFAs Using Parasitic Elements and Bridge Line

In this study, a novel decoupling method using parasitic elements (PEs) connected by a bridge line (BL) for two planar inverted-F antennas (PIFAs) is proposed. The proposed method is developed from a well-known decoupling method that uses a BL to directly connect antenna elements. When antenna elements are connected directly by a BL, strong mutual coupling can be reduced, but the resonant frequency shifts to a different frequency. Hence, to shift the resonant frequency toward the desired frequency, the original size of the antenna elements must be adjusted. This is disadvantageous if the method is applied in cases where the design conditions render it difficult to connect the antennas directly or adjust the original antenna size. Therefore, to easily reduce mutual coupling in such a case, a decoupling method that does not require both connecting antennas directly and adjusting the original antenna size is necessitated. This study demonstrates that using PEs connected by a BL reduces the mutual coupling from -6.6 to -14.1dB, and that the resonant frequency is maintained at the desired frequency (2.0GHz) without having to adjust the original PIFAs size. In addition, impedance matching can be adjusted to the desired frequency, resulting in an improved total antenna efficiency from 77.4% to 94.6%. This method is expected to be a simple and effective approach for reducing the mutual coupling between larger numbers of PIFA elements in the future.