This study aimed to investigate the structural design of a cantenna with Woodpile shaped electromagnetic band gap (EBG) for gain enhancement and to increase the efficiency of signal transmission for measuring the moisture content and the bulk density of goat manure, which can help farmers reduce the cost of buying chemical fertilizers. From the test of operating frequency ranges from 2 to 3 GHz, it was found that the frequency band that responds to humidity the best is 2.60 GHz, increasing the efficiency of the gain with the 6x6 cm² Woodpile shaped EBG. It was arranged in transverse electric (TE) and placed parallel to the end of the cantenna. This allows the gain to be increased to 9.31 dBi, in which the cantenna structure without EBG has the gain of 7.32 dBi. When the cantenna is used to determine the moisture content (MC) and bulk density, the transmission distance between the cantenna Tx/Rx is 3 cm with an average power rating of 0.0001-0.5 mW. This cantenna can measure humidity in the unit of wet basis (wb.) as low as 0.14% wb., at an average power of 0.5 mW.

A novel miniature antenna is proposed for wireless communications in the K-band and Ka-band of the electromagnetic spectrum. The frequency band of this antenna extends from 18 to 40 GHz. The proposed antenna is a planar monopole printed on a thin dielectric substrate of 0.25 mm thickness. To enhance the frequency bandwidth of this antenna it is constructed as five circular sectors placed with sequential rotations and merged to form a multi-leaf shaped monopole patch antenna. To enhance the antenna performance, the monopole patch is fed through a coplanar waveguide (CPW) structure. This enables the overall antenna structure and the feeding CPW to be printed on only one side of the dielectric substrate leaving the other side blank, which reduces the dielectric loss and enhances the radiation efficiency. The assessment of the antenna performance is achieved through simulation as well as experimental work. A prototype of the antenna is fabricated for this purpose. The experimental results show excellent agreement with the simulation ones. The antenna is printed on a Rogers' RO3003 substrate of 0.25 mm thickness. It is shown, through both results, that the antenna has 2.2:1 ratio bandwidth, 76% percentage bandwidth, and 278 bandwidth-dimension ratio. The radiation efficiency is maintained above 99% over the entire bandwidth (18-40 GHz).

Exceptional point (EP) and exceptional ring (ER) are unique features for non-Hermitian systems, which have recently attracted great attentions in acoustics due to their rich physical significances and various potential applications. Despite the rapid development about the study of the EP and ER in one-dimensional acoustic systems, the realization of them in two-dimensional (2D) non-Hermitian structures is still facing a great challenge. To overcome this, we numerically and theoretically realize an ER in 2D reciprocal space based on a square-lattice non-Hermitian sonic crystal (SC). By introducing radiation loss caused by circular holes of each resonator in a Hermitian SC, we realize the conversion between a Dirac cone and the ER. Based on the theoretical analysis with the effective Hamiltonian, we obtain that the formation of the ER is closely related to different radiation losses of dipole and quadrupole modes in the resonators. Additionally, in the non-Hermitian SC, two eigenfunctions can be merged into a single self-orthogonal one on the ER, which does not exist in the Hermitian SC. Finally, by verifying the existence of the EP in every direction of 2D reciprocal space, we further demonstrate the ER in the proposed non-Hermitian SC. Our work may provide theoretical schemes and concrete methods for designing various types of non-Hermitian acoustic devices.

In this letter, a broadband proximity coupled millimeter-wave microstrip array antenna is presented for automotive radar applications. The antenna array consists of a microstrip line and a series of trapezoidal radiating elements that are periodically arranged on both sides of the microstrip line, at intervals of about half the guided-wavelength. The introduction of the trapezoidal radiating patch enhances the excitation coupling while suppressing out-of-band frequencies, and it has a wider impedance bandwidth than the rectangular patch. In the design of proposed antenna, the normalized resistance of the trapezoidal radiating element is controlled by adjusting the gap with the microstrip line, so that a low-sidelobe level (SLL) can be achieved. Taking the 77-81 GHz frequency band allocated to automotive radar applications as an example, a 1×16 linear array is designed and fabricated. The measured SLL is better than -20 dB. The measured gain of 1×16 array is higher than 15 dBi over the operating frequency range of 77-81 GHz. The 1×16 linear array can achieve an impedance bandwidth of 7.6% (75.6-81.6 GHz).

In this paper, a novel ultra-wide band (UWB) antenna with a planar single-layer structure is proposed. The antenna consists of a main circular patch that is capacitively coupled to six circular patches of very small size relative to the main patch. The coupling is achieved through narrow gaps of semicircular shape which are uniformly distributed on the circumference of the main patch. A coplanar waveguide (CPW) is used for feeding the antenna to get the complete antenna structure with the feeding line printed on one face of a flexible dielectric substrate. The antenna is fabricated and subjected to experimental assessment of its performance regarding the bandwidth, gain, and radiation efficiency. The measurements show good agreement with the simulation results. It is shown that the proposed antenna operates efficiently over the frequency band of 3.1-10.6 GHz. The antenna has a radiation efficiency that ranges from 99% to 100% over the entire band. This high efficiency is attributed to the planar single-layer structure of the antenna and the use of a thin low-loss substrate. The antenna maximum gain ranges from 2 dBi to 5 dBi over the entire frequency band. The substrate material is Rogers RO3003^TM which is flexible and can be conformal to planar and curved surfaces. The total substrate dimensions are 35 × 39.4 × 0.5 mm.

A novel signal processing scheme for identification of jet fighter targets by the onboard radar of active and hybrid homing missiles is proposed in the present work. For a specific target, the frequencies of the internal resonances of the cavity-backed apertures existing as the air-inlet pipes of the jet engine are used to construct an interior signature function for the proposed target identification scheme. For the purpose of quantitative description and assessment of the proposed scheme, electromagnetic simulation is used where the air-inlet pipe is modeled as an open-ended conducting cylinder with a number of radial conducting blades placed inside the cylindrical cavity near the open end. The transmitted radar pulse is formed by frequency chirping using linear frequency modulation (LFM) to include the frequencies in the band 1.0--2.0\,GHz with high sweep resolution. The selected frequency band is wide enough to distinguish among various jet fighter targets. The CST® simulator is used to evaluate the radar cross section (RCS) of the open-ended pipe model with the internal blades due to an incident chirped pulsed plane wave as mentioned above over the frequency band 1.0-2.0 GHz. The proposed target identification algorithm is mathematically described and computationally applied to identify different targets with different dimensions of the jet engine pipe. The effect of the additive white Gaussian noise (AWGN) on the correctness of the target identification decision using the proposed scheme is investigated by calculating the false alarm rate (FAR) with varying the signal-to-noise ratio (SNR). The numerical examinations show that the proposed algorithm succeeds in taking the correct decision regarding the target identification with FAR<10% for SNR} ≥ 12 dB.

The design and analysis of a compact printed Archimedean spiral electromagnetic bandgap (EBG) structure are presented for frequency shielding in microwave circuits, including antenna and bandpass filters. The EBG characterization resonating at 7.7 GHz is done through a performance matrix such as transmission and reflection coefficients and equivalent circuit modeling, which demonstrates excellent resonance stability. The EBG unit cell is investigated for achieving frequency rejection in the printed monopole-based ultra-wideband (UWB) antenna and bandpass filter circuits. By introducing the Archimedean EBG unit cell on the UWB antenna ground plane, dual-frequency rejection, at 7.4, and 7.7 GHz, was realized. Further, such structure is utilized in a multi-mode resonator (MMR) based UWB bandpass filter to attain band-notched functionality at 7.6 and 7.8 GHz with a maximum attenuation of -16.5, and -15.6 dB, respectively. The prototypes of the EBG-loaded UWB antenna and EBG-Loaded UWB filter are fabricated and characterized. Excellent agreement is achieved between simulated and measured results of both prototypes.

A novel ultra-broadband Polarization Rotation (PR) Reflective Surface (PRRS) is presented, which can reflect the linearly polarized incident wave in orthogonal polarization state. The proposed PRRS consists of a periodic array of double split ring patches printed on a substrate, which is backed by a metallic ground. A PRRS composed of circular split ring units can realize polarization rotation in two wide frequency bands. When two circular split rings with gradual radii are arranged concentrically, an ultra-broadband polarized rotation will be obtained. This paper explains the mechanism of polarization rotation and the mechanism of Radar Cross Section (RCS) reduction and studies the influence of structural parameters on the polarization rotation frequency band. Simulation results show that a 101.6% PR bandwidth is achieved. Meanwhile, by arranging the unit cells of the PRRS in four orthogonal directions, the monostatic RCS reduction band ranges from 8 GHz to 21.8 GHz (or 92.6%) for arbitrary polarization of the incident wave.

A hot-via chip-to-substrate interconnect with its operation frequency up to W-band for ultracompact radio frequency (RF) system in package (SIP) is reported in this paper. In order to improve the accuracy of the simulation model in millimeter wave bands, a trapezoidal platform model is established for modeling the RF performance of the hot-via which is formed by inductively coupled plasma (ICP) etching process. A three hot-vias structure in a gallium arsenide (GaAs) chip is employed to form a Ground-Signal-Ground (GSG) transition structure. Bumps on the Silicon substrate are designed as a half quasi-coaxial structure to make it compatible with the assembly process of SIP. A full-wave simulation model is established for a hot-via chip-to-substrate interconnect structure with HFSS, based on which structural parameters, such as the gap between the hot-vias and the radius of the quasi-coaxial structure, are optimized for the best performance over 92-96 GHz. A prototype of the hot-via chip-to-substrate interconnects in their back-to-back connected form has been fabricated. Measured results demonstrate that the overall insertion loss is less than 1.85 dB, and the return loss is better than 12 dB from 92 GHz to 96 GHz.

This paper presents a CPW-fed, UWB-extended bandwidth, dual band-notched on-chip antenna with its equivalent circuit model. The UWB-extended bandwidth is realized by truncating the bottom corners of a rectangular patch radiator while a 90º-rotated `C'-shaped slot in the patch and a `U'-shaped slot in the feedline are used to achieve two notch bands for mitigating the signal interference in the frequency bands of 5.15 to 5.925 GHz and 7.9 to 8.8 GHz. Based on the fundamental theory, different parasitic as well as distributed circuit parameters associated with the designed on-chip antenna are extracted, and then the corresponding equivalent circuit model is configured from them. The resultant circuit is validated with the well approved full-wave electromagnetic simulation result and is found in close approximation with each other.

A concentric circular array consisting of two rings is proposed to focus the radiated field at a point in the near-field zone. In the proposed two-ring array, the radius of the outer ring was chosen so that the radiated fields from all elements on the two rings add constructively at the focal point, thus no phase shifter is needed in this design. The N elements of the inner ring are uniformly excited in amplitude and phase, while the M elements on the outer ring are excited uniformly in phase, and given uniform magnitude excitations of N/M of that given to the inner. Therefore, two deep nulls are achieved on both sides of the focusto enhance the focal width. The focusing properties are investigated by exploring the array parameters, such as variation of the focused field along the normal to the array, field distribution on the focalplane, and depth of field (size of the focal spot). Computer simulations using the MATLAB environment are performed by point source radiators. For verification, the array was simulated using the CST microwave studio, and the obtained results showed good agreement. The array is useful for hyperthermia and imaging applications.

A thin dual band circularly polarized (CP) patch antenna with a wide 3-dB axial ratio beamwidth (ARBW) is presented for BeiDou Navigation System (BDS) application. The CP radiation is achieved using simple stacked square patches for dual band radiation in the BDS B1 band (1561±2 MHz) and B3 band (1268±10 MHz). A `string moon' type branch extension technique is proposed to enhance the ARBW and axial ratio bandwidth in both operating bands. Loading 30° gap-type annular parasitic metal strips (APMS) further improves the ARBW in both operating bands. The experimental results show that the impedance bandwidth of the antenna is 6.3% (1.25-1.33 GHz) and 4.5% (1.52-1.59 GHz), and the axial ratio bandwidth is 1.6% (1.26-1.28 GHz) and 1.2% (1.55-1.57 GHz), respectively. In addition, the 3-dB ARBWs in the φ=0° and φ=90° planes are 185° and 184° at 1.268 GHz, respectively; and 222° and 211° at 1.561 GHz, respectively. The simulated results are in good agreement with the measured ones.

This paper presents the design, analysis, and developments of a reconfigurable hybrid metal-graphene filter for terahertz applications. In fact, through the graphene material, we can reconfigure both the resonance frequency and the bandwidth. Further, the variation in chemical potential, relaxation times, and temperature of graphene provides excellent proprieties performances, with a variation of the resonant frequency from 8.60 THz to 8.85 THz, good return loss reaching -22.94 dB and a bandwidth reconfiguration from 1.717 THz to 1.930 THz. The simulation of the proposed filter is performed using CST software.

In this paper, a bandwidth improvement technique in SIW slotted antennas is presented. Distinct from conventional SIW antennas with multiple cavity modes, a single cavity mode (TE₂₁₀) is utilized to improve the bandwidth. When a rectangle slot is loaded at bottom surface of the cavity, the TE₂₁₀ cavity mode is perturbed. As a result, two independent modes (odd TE₂₁₀, even TE₂₁₀) are introduced and merged in close proximity. Finally, the antenna is fabricated and tested. The measured results render an impedance bandwidth of 12.8% and a maximum gain of 7.1 dBi. The cross-polar level of maximum -29 dB and -34 dB is at 9.73 GHz and 10.63 GHz, respectively. The proposed design holds many features such as easy fabrication and light weight. Besides, the proposed design is a single-layered that makes it extremely convenient to integrate with other planar configurations.

This paper presents the analysis and design of in-phase/out-of-phase power dividers with compact-size and ultra-wideband characteristics. The proposed designs are composed of a T-junction microstrip (MS)-to-slotline power divider with a shorting via and two slotline-to-MS transitions. The phase response at the outputs can be controlled by arranging the MS-line direction of the transition, i.e., the same direction results in the in-phase, whereas the opposite MS-line directions reverse the electrical field, thus resulting in the out-of-phase. Thanks to utilizing the MS-to-slotline power divider and circular slots and circular stubs at the transitions, the proposed structures achieve ultra-wide bandwidth and compact size simultaneously. The dividers are theoretically analyzed using transmission-line equivalent circuit, and then verified computationally and experimentally. Simulation and measurement indicate that the proposed power dividers yield ultra-wideband performance across 1.2-11.0 GHz (~160%) with magnitude difference ±0.5 dB and phase difference ±5° at the outputs. As an example of application, a differential-fed Vivaldi antenna fed by the proposed out-of-phase power divider is implemented. The antenna yields a 160% bandwidth (1.2-11.0 GHz) for 10-dB return loss and a stable end-fire radiation within the whole impedance bandwidth.

This paper presents a low profile and low-cost patch antenna with dual circularly polarized (CP) capability in X-band at a canter frequency of 8.3 GHz. The dual-CP antenna is divided into three layers, composed of a parasitic square patch, radiation square patch with four equal arms, and 90˚ patch coupler. Two arms of the radiation patch are connected to the 90˚ hybrid coupler using two metalized vias. right-handed circular polarization (RHCP) and Left-handed circular polarization (LHCP) is achieved by exciting two different ports. To validate the proposed design, the prototype of dual-CP antenna is fabricated and measured. Based on the measurement, the structure of proposed antenna has an excellent circular-polarization purity of less than 3-dB over the whole operational frequency bandwidth of the antenna (8 GHz-8.47 GHz) with a wide 3-dB axial ratio (AR) beamwidth of 133˚ across the angular range from -55° to +78° at 8.3 GHz.

This article presents a novel electrically small asymmetric coplanar strip (ACS) fed metamaterial inspired antenna for quad band operation. A metamaterial inspired open split ring resonator (OSRR) is the radiator which is fed using ACS to obtain four operating bands. The proposed antenna with a compact size of 18 mm × 15.5 mm × 1.6 mm is fabricated and tested. The experimental results are in good compliance with simulated ones. The proposed electrically small antenna has a radian sphere (ka) of 0.65 and achieves an average gain of 2.24 dBi with requisite radiation properties suitable for WiMAX and WLAN applications.

In this paper, novel mode switchable microwave coupled line couplers on ferrite substrates are presented. The couplers are realized in Composite Right/Left Handedcoplanar waveguide configurations. Two different types of mode switchable couplers are proposed. The first one can switch the power from the backward coupling port to the through port. The second one can switch the power from the backward coupling port to both the through and forward coupling ports. In both cases, the mode switching is achieved by varying the applied DC magnetic bias. The theoretical analysis of the switching mechanism has been carried out based on the general coupled mode approach. The analysis is then verified numerically and experimentally. The measurement results confirm the switching functionalities of the fabricated couplers with better than 10 dB isolation between the switched signals. Moreover, these novel mode switchable couplers are compact and require very low external DC magnetic bias due to their CPW configurations. These new proposed switrches can be applied in the smart microwave compoennts in different radar/communication application.

A novel compact two-side anti-metal tag antenna for radio frequency identification (RFID) applications is proposed in this paper. The proposed tag antenna is composed by three aluminum patches separated by two layers of foam substrates. Particularly, the middle patch of the antenna is designed as three nested deformable rings for the miniaturization of antenna and realizes better power transmission coefficient (PTC) between the antenna and tag microchip. The antenna operates at the center frequency of 915 MHz and maintains a compact size of 35 mm × 22 mm × 2.15 mm (0.1068λ₀ × 0.0671λ₀ × 0.0066λ₀). When the front or back side of the tag antenna is mounted on a large background metallic plate and tested with an effective-isotropic-radiated-power (EIRP) of 4 W, the antenna can achieve the maximum read distances of 6.23 m or 6.08 m. The tag antenna shows various advantages, including small size, low profile, and good antenna performance. Most importantly, the proposed tag antenna has two-side anti-metal property compared to a traditional single-side anti-metal antenna, which fulfills the emerging demands in the industrial internet of things field.

Limited endurance has become a bottleneck restricting the wide application of unmanned aerial vehicles (UAVs), and wireless power transfer (WPT) technology is expected to become an effective means to help UAVs break this bottleneck. UAV has strict restrictions on the weight of onboard system, so the lightweight design of the receiving side has become the core goal of UAV WPT systems design. In order to achieve this goal, this paper first proposes a novel magnetic coupler based on hollow copper-coated aluminum tubes, in which the receivers act as both landing gears and energy pick-up. The coupling mechanism of the magnetic coupler is analyzed. Secondly, based on the LCC-S resonant compensation network with a simple structure on the receiving-side, the system circuit is designed, and the system transmission model is established. Finally, a UAV WPT prototype is built and tested. The experimental results show that the transmission power of the designed system can reach 157 W, the overall efficiency 80%, and each receiver (also acting as landing gear) weight only 22 g. The weight power density ratio is 3.568 W/g.