Single Monopole Antenna Research Articles

Simple Dual-Feed Dual-Circular Polarization Antenna with High Isolation

A dual-feed antenna system with circular polarization (CP) diversity and high isolation is proposed in this paper. The proposed antenna consists of two bent monopole antennas and an isosceles triangular partial GND on a single layer. To simply design an antenna with dual-feed dual-CP characteristics, CP bandwidth (BW) is optimized based on a single antenna. The proposed antenna is structurally different from conventional antennas in three ways. Structural asymmetry is realized by bending the shape of the antenna and moving the position, and thus good CP characteristics are obtained. The feeding structure is changed from a linear type to a meander type. As a result, a single monopole antenna has a CP BW of 36%. Next, an antenna system with dual-CP characteristics is introduced by implementing two monopole antennas on a single layer. In this structure, the resonant frequency is controlled by the antenna geometrical parameters, and the null frequency at S21 is controlled by the distance between the two antennas. The measured results show that the CP BW of the proposed antenna is 40.6% (1.51–2.28 GHz). The measured isolation is below -20 dB within the operating BW.

Conjoined, Two-Monopole Antenna Pair with Decoupling Inductor for Wi-Fi 6E Notebook Applications

A low-profile, conjoined and yet decoupled two-monopole design for Wi-Fi 6E notebook applications is presented. The single monopole antenna has a small size of 4 mm × 18.7 mm. The antenna is composed of a two-branched monopole with two shorting inductors for producing the 5 GHz (5150–5825 MHz) and 6 GHz (5925–7125 MHz) bands, and an inductor loaded at one branch end and connecting to a tuning portion for 2.4 GHz (2400–2484 MHz) operation. Two symmetrical monopoles are further conjoined by a chip inductor that connects the open ends of the tuning portions, forming a compact footprint of 4 mm × 38.4 mm for the two-notebook antenna design. With the use of the decoupling inductor and a proper two-monopole arrangement, acceptable isolation and a low envelop correlation coefficient (ECC) can be attained.

Compact planar ultra‐wideband pattern diversity antenna

AbstractA two‐port planar ultra‐wideband (UWB) pattern diversity antenna is proposed in this letter. The design consists of an array of two rotated identical monopole antennas and two feeding ports with 0° in‐phase and 180° out‐of‐phase excitations. The single monopole antenna includes a circular patch, a rectangular truncated ground plane and a fork‐shaped feeding structure. In this antenna, a modified partial common ground plane is used to enhance the input matching, increase the isolation between antenna elements and improve the desired radiations. The measured results show an |S11| < −10 dB bandwidth ranging from 2 to over 20GHz, with conical and broadside beams, high efficiency, and good isolation across the entire UWB band. Also, the proposed antenna exhibits a smaller footprint, larger bandwidth, and more straightforward design compared with the existing designs. To the best of authors’ knowledge, all these characteristics have never been presented in previously reported UWB pattern diversity antennas.

A novel shaped antenna for designing UWB-MIMO system in microwave communications

This paper designed and fabricated a UWB-MIMO antenna based on novel inverted comma-shaped antenna and a CPW-feeder structure. The proposed single monopole antenna is designed by combing an elliptical geometry with merging several circular shapes. The novel structure provides a wide impedance bandwidth from 2.469 to 14.203 GHz. The dimensions of the designed unit cell are 21 mm × 16 mm (0.172λL×0.131λL) and the overall size of dual symmetric antennas is 21 × 34 × 1 mm3. This compact antenna is then used to design 2 × 2 Multiple Input Multiple Output (MIMO) antennas. The proposed low-profile MIMO antenna contains two similar geometries placed with a T-shaped decoupling structure. Measurement results show multiple diversity metrics of the MIMO antenna such as low-value mutual coupling characteristics, better channel capacity losses of less than 0.29 bits/s/Hz, envelope correlation coefficient smaller than 0.004 by far-field radiation, total active reflection coefficient below − 10 dB, diversity gain of less than 9.98 dB and acceptable mean effective gain (MEG ≤ 0.5, MEG ratio = 1). The proposed antenna offers a maximum peak gain value of 6.18 dBi at operating frequency of 13.4 GHz.

Bandstop Filter Decoupling Technique for Miniaturized Reconfigurable MIMO Antenna

In this work, a switchable bandstop filter is used as a decoupling structure for developing a miniaturized reconfigurable multiple input multiple output (MIMO) antenna. Initially, a dual band ((2.43-2.60 GHz and 3.51-3.79 GHz)) single monopole antenna structure is developed on FR4 substrate. Then the single monopole antenna and its replica are accommodated in a small space with an edge to edge separation distance of 11 mm to form a 2 port MIMO antenna. Now, a switchable bandstop filter is used as a decoupling network between two closely spaced monopole antenna elements to prevent mutual coupling and reconfigure the antenna characteristics. The dual pole switchable bandstop filter is configured in such a way that one of its poles lies at 2.5 GHz in one state (Mode 1) and at 3.68 GHz in another state (Mode 2) under the switching action of two PIN diodes. Controlling the ON/OFF states of the PIN diodes in the bandstop filter, high isolation is achieved alternately in lower (2.43-2.60 GHz) and upper (3.51-3.79 GHz) frequency bands of the MIMO antenna. Also, stub network is used to improve impedance matching in the upper frequency band. The proposed isolation technique helps the antenna to yield high isolation (>30 dB), fair gain (>2.97 dBi), reasonable radiation efficiency (>86.8 %), low envelope correlation coefficient (< 0.16), high diversity gain (DG >9.88 dB), low Mean effective gain ratio (MEG 1/MEG 2 < 0.05 dB) and low channel capacity loss (CCL < 0.06 bits/s/Hz) for both the operating frequency bands. The overall dimension of the antenna is restricted to 44mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 22mm ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.36\lambda _{o}\,\,\times \,\,0.18\lambda _{o}$ </tex-math></inline-formula> ) for its easy integration in compact wireless devices. This type of reconfigurable MIMO antenna is best suited for cognitive radio communication, which promotes efficient spectrum utilization.

A Novel Ultrawideband Gear-Shaped Dielectric Ring Resonator Antenna

In this study, a novel ultrawideband (UWB) dielectric ring resonator (DRR) antenna has been proposed. DRR antennas include a single monopole antenna in the center of a ground plane and a dielectric with a symmetric structure around the monopole. This structure will lead to ultrawide band antenna. However, it is still possible to enhance the antenna bandwidth. In this study, we combine the DRR structure with an array antenna. The proposed antenna includes a circular array of four triangle resonators, which is rotated around the center of the triangle base to form a gear-shaped ring resonator antenna. In this design, characteristics of all these antennas are combined to enhance the antenna bandwidth including triangular dielectric resonator, circular array antenna, dielectric ring resonator structure, and a quarter-wave electric monopole. Triangular dielectric resonator antennas are wideband and in small size. Ring resonator antennas are inherently ultrawideband. Quarter-wave electric monopole and circular array structure can also enhance antenna bandwidth. This novel shape of the DRR antenna possesses the wider impedance bandwidth compared to similar works. Impedance bandwidth is 150% (5.2–36.1 GHz), and the bandwidth ratio is 1 : 6.9, which is much greater than earlier reports.

Isolation Enhancement in Dual-Band Monopole Antenna for 5G Applications

This brief presents a novel design of high-isolation dual-band antenna with a close distance for 5G applications. The proposed antenna consists of two symmetrical monopole antenna elements. Two resonance frequencies of the monopole antenna are independently tunable. The defected ground structure (DGS) and grounded branches are loaded to reduce mutual coupling of the lower band by changing the current distribution on the ground plane. And a T-shaped parasitic element is placed between the two antenna elements. The parasitic element introduces an inverse path for mutual coupling cancellation, which greatly increases the isolation of the higher band. As a result, the proposed antenna achieves 5G dual-band of 3.409-3.601 and 4.76-5.04 GHz ( S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> & S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sub> <; -10 dB, S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> & S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> <; -26 dB). Compared with the single monopole antenna, the bands of the proposed antenna don't shift and the impedance matching is improved. With the decoupling structure, the isolations are -29 and -41.4 dB at 3.5 and 4.85 GHz, respectively. In addition, the proposed antenna also has the advantages of small size, more flexibility, and simple structure.

Thermally Beam-Direction- and Beamwidth-Switchable Monopole Antenna Using Origami Reflectors With Smart Shape Memory Polymer Hinges

This letter presents a thermally reconfigurable antenna with beam-direction- and beamwidth-switching capability using origami reflectors with smart shape memory polymer (SMP) hinges. The proposed antenna consists of a single monopole antenna with four origami reflectors. We employ SMP hinges to actuate the origami reflectors. When all origami reflectors are unfolded on the ground plane (Mode I), the monopole antenna exhibits omnidirectional radiation because the reflectors operate as dummies. When two origami reflectors are folded perpendicular to the ground plane, forming a corner reflector (Mode II), the proposed antenna operates as a directional antenna. Beam direction can be switched to 45°, 135°, 225°, and 315° by actuating various origami reflector pairs, with increased peak gain from 4.5 dBi (Mode I) to 11 dBi (Mode II). When one origami reflector is folded perpendicular to the ground plane (Mode III), the 3 dB beamwidth increases from 52° (Mode II) to 140° (Mode III). Beam direction of Mode III can also be switched through 0°, 90°, 180°, and 270° by actuating each origami reflector. The proposed antenna performance was successfully demonstrated from electromagnetic simulation and measurement.

A Tunable, High-Gain, Very Low-Profile Composite Monopole Antenna for Low-Frequency Applications

This paper presents an extremely low-profile frequency-tunable composite antenna with enhanced gain and an omnidirectional radiation pattern. The antenna is based on a recently developed very short two-legged monopole antenna and consists of one driven element and eight identical parasitic coupled elements. By utilizing the mutual coupling between elements, the radiation resistance of the antenna is significantly increased, leading to considerable gain enhancement and better matching performance. The composite antenna has the same height as the single monopole ( $\lambda _{0}/150$ ) but a larger lateral dimension ( $\lambda _{0}/16$ ). The performance of the proposed antenna is compared with that of a single monopole antenna. It is shown that the peak gain of the composite antenna is about 10 dB higher than that of the monopole antenna. The design is then modified for frequency tunability to achieve frequency agility and higher bandwidth for certain modulations like frequency hopping spread spectrum. The fractional bandwidth of the tunable antenna is 3.32%, and the gain is further improved at higher frequencies. A new method of effectively measuring a monopole antenna with an electrically small ground plane using cascaded transformers is also presented and discussed.

Dual-Antenna Concept With Complementary Radiation Patterns for Eyewear Applications

A dual-antenna concept to be integrated in a smart eyewear device is presented. The two antennas are printed on FR4 substrate and placed inside an Acrylonitrile butadiene styrene dielectric eyewear frame manufactured using 3-D printing technology. One of the two antennas is a monopole situated at the back of the eyewear with a specifically shaped ground plane underneath. The second antenna is a balanced-fed loop antenna placed in front of the eyewear with an integrated balun circuit. Both antennas are designed to operate in the 2.4 GHz band of the 802.11b/g/n standard. When compared to a reference single monopole antenna usually used in commercial eyewear, higher gain and complementary radiation patterns are obtained in several useful directions using our dual-antenna solution: 1) in front of the eyewear to communicate with a laptop; 2) in the side direction of the eyewear to communicate with a fixed hotspot access point; and 3) in downward direction of the eyewear to communicate with a peripheral smartphone in the pocket of the user. S-parameters and radiation pattern measurements are given with the eyewear placed over a specific anthropomorphic mannequin head phantom to validate the advantages of this novel dual-antenna concept. Specific absorption rate simulation results are presented showing the proposed antennas stay within the authorized limits.

New design concept of monopole antenna array for UHF 7T MRI

We have developed and evaluated a monopole antenna array that can increase sensitivity at the center of the brain for 7T MRI applications. We have developed a monopole antenna array that has half the length of a conventional dipole antenna with eight channels for brain imaging with a 7T MRI. The eight-channel monopole antenna array and conventional eight-channel transceiver surface coil array were evaluated and compared in terms of transmit properties, specific absorption ratio (SAR), and sensitivity. The sensitivity maps were generated by dividing the SNR map by the flip angle distribution. A single surface coil provides asymmetric sensitivity resulting in reduced sensitivity at the center of the brain. In contrast, a single monopole antenna provides higher sensitivity at the center of the brain. Moreover, the monopole antenna array provides uniform sensitivity over the entire brain, and the sensitivity gain was 1.5 times higher at the center of the brain compared with the surface coil array. The monopole antenna array is a promising candidate for MRI applications, especially for brain imaging in a 7T MRI because it provides increased sensitivity at the center of the brain.

In-Phase Versus Out-of-Phase Distributed Antenna Systems for Wireless Handheld Devices

Hand loading usually degrades the performance of handset antennas. With the aim of providing a solution robust to the human presence, this paper discloses a distributed antenna system fed in-phase capable of mitigating undesirable hand loading effects while providing enhanced performance. The solution consists of a passive array of two resonant coplanar monopole antennas inspired in the Hilbert geometry. Input impedances of both monopoles are combined into a single input-output port through two transmission lines featuring equal phases. This combination allows not only improving the performance of the radiating system with respect to that attained by a single monopole antenna, but also providing a symmetric solution immune to the finger location. The solution is compared with a single monopole and a distributed antenna system fed out-of-phase. Simulated and measured results demonstrate that the proposed design is capable of providing operation in the communication standards GSM850/GSM900 as well as in the UHF part of the LTE-Advanced while maintaining the same electromagnetic performance with certain independence of the finger location.

Distributed Antenna Systems for Wireless Handheld Devices Robust to Hand Loading

The performance of handset antennas is strongly affected by the user interaction. In particular, the close proximity of the user's hand when holding the phone usually degrades the behavior of the antenna by introducing detuning effects and efficiency decrements. With the aim of mitigating such negative effects, the present paper proposes a distributed antenna system comprising three monopoles strategically arranged along the ground plane of a wireless handheld device. This configuration not only improves the performance of the radiating system with respect to that attained with a single monopole antenna or a distributed antenna system of two monopoles, but also increases its robustness to the hand loading effect. In order to assess the benefits of the proposed technique, simulated and measured results in free-space as well as regarding the presence of a hand phantom are compared with previous techniques based on a single monopole and a distributed antenna system of two monopoles. The experimental results demonstrate that the proposed distributed antenna system of three monopoles improves the bandwidth (34% for SWR ≤ 3 (693-978 MHz)), the efficiency in free-space, and becomes more robust to the hand loading effects than a single monopole solution and a distributed system of two monopoles.

Expanded modeling of temperature-dependent dielectric properties for microwave thermal ablation

Microwaves are a promising source for thermal tumor ablation due to their ability to rapidly heat dispersive biological tissues, often to temperatures in excess of 100 °C. At these high temperatures, tissue dielectric properties change rapidly and, thus, so do the characteristics of energy delivery. Precise knowledge of how tissue dielectric properties change during microwave heating promises to facilitate more accurate simulation of device performance and helps optimize device geometry and energy delivery parameters. In this study, we measured the dielectric properties of liver tissue during high-temperature microwave heating. The resulting data were compiled into either a sigmoidal function of temperature or an integration of the time–temperature curve for both relative permittivity and effective conductivity. Coupled electromagnetic–thermal simulations of heating produced by a single monopole antenna using the new models were then compared to simulations with existing linear and static models, and experimental temperatures in liver tissue. The new sigmoidal temperature-dependent model more accurately predicted experimental temperatures when compared to temperature–time integrated or existing models. The mean percent differences between simulated and experimental temperatures over all times were 4.2% for sigmoidal, 10.1% for temperature–time integration, 27.0% for linear and 32.8% for static models at the antenna input power of 50 W. Correcting for tissue contraction improved agreement for powers up to 75 W. The sigmoidal model also predicted substantial changes in heating pattern due to dehydration. We can conclude from these studies that a sigmoidal model of tissue dielectric properties improves prediction of experimental results. More work is needed to refine and generalize this model.

Application of Transmission-Line Model to Dual-Band Stepped Monopole Antenna Designing

This letter presents a novel approach for designing a dual-band planar antenna with only a stepped monopole. Transmission line theory and the resonator model are adopted to analyze the operating frequencies of the proposed antenna. A suspended stripline resonator is applied to emulate the radiation patches of the antenna. A design curve is established and used to develop a single-monopole antenna with dual operating frequencies. A closed form to design the antenna is derived under a specific condition. The proposed approach facilitates the design of the antenna without the time-consuming tuning of parameters and repeated electromagnetic (EM) simulation. Satisfactory agreement between the simulation results and the measurements validates the proposed design approach.

Genetic approach to the minimization of the coupling between aircraft antennas

In this study, the optimization of the electromagnetic interference (EMI) induced by two aircraft onboard VHF–UHF transreceiver antennas is aimed. The EMI reduction is implemented by varying the antenna positions and orientations. The transreceiver antennas are modelled as single monopole antennas therefore the problem is reduced to antenna-to-antenna coupling optimization. The Method of Moments (MoM) is selected for the EMI analysis and the continuous parameter Genetic Algorithm (CPGA) is chosen for the optimization method. The results of the numerical analysis are verified by the measurement on a 1:10 scaled model in an anechoic chamber.