In this paper, a low-profile fractal antenna with square ring slots is reported. The newly proposed fractal antenna includes circular ring radiating elements with orthogonally placed square shape slots to achieve ultra wideband operation. The compact antenna (32 × 28 × 1.6 mm³) is designed and fabricated on an FR4 dielectric substrate, and measurements are performed in the laboratory environment. The simulated and measured results demonstrate that the antenna has -10 dB impedance bandwidth of 9.4 GHz from 4.2 to 13.6 GHz in the ultra-wideband frequency. The measurement results reveal that the antenna has broadband radiation characteristics with peak gain of 5 dB in the desired band of operation. The proposed antenna has low cross polarization of -28 dB and radiation efficiency about 88% in the operating bandwidth. The large bandwidth, low cross polarization, and stable radiation characteristics of the proposed antenna confirm that the antenna may be suitable for ultra-wideband applications.

A Clown-shaped patch antenna for super wideband applications is presented. The radiator is placed on a 1.6 mm thick, RT/Duroid 5880 substrate and is fed using a 50 Ω symmetric coplanar waveguide. The size of the proposed antenna is 26 × 27 mm² (0.256λ_L × 0.266λ_L, where λ_L is the wavelength at the lower band edge frequency i.e. 2.96 GHz). The radiator is a combination of an ellipse, a rectangle, and a triangle. An impedance bandwidth of 2.96 GHz to more than 100 GHz (i.e. more than 33.78:1 ratio bandwidth) is achieved. Nearly-omnidirectional radiation patterns with an average gain of 6 dBi are achieved. A fractional bandwidth greater than 188.5%, a size reduction of ~97%, and a comparable bandwidth dimension ratio of 2768 are achieved. The investigated antenna has additional advantages like compactness, planar geometry, and super-wide bandwidth.

The aim of this study is to provide a topological optimization method for ship detection in synthetic aperture radar (SAR) imagery. The method consists of three steps: pre-processing, sparse representation and classification. For the first step, the variational model is used for SAR image filtering. For the second step, the curvature of the surface manifold is constructed for sparse representation of target. For the third step, the topological derivative method is adopted to locate the target. Experiments show that the proposed method is effective in reducing false alarms, and obtains a satisfactory detection performance.

This letter proposes a miniature bow-tie antenna element and its 2 × 2 arrays based on ball grid array (BGA) packaging technology for 5G millimeter-wave new radio (NR) applications. The antenna substrate uses ultra-economical single-layer FR4 printed circuit boards (PCB) to reduce manufacturing costs. By adopting solder balls, the antenna achieves the BGA packaging and realizes the surface mounting function. One bow-tie patch is excited by a plated through-hole (PTH) connected to the feeding point. The other bow-tie patch is directly short connected to the ground plane by another PTH. Besides, the bottom ground plane can be equivalent to a reflector, allowing the antenna element and array to obtain broadside radiation. For ease of integration, the input impedance of the antenna is set to 50 Ω. The measurement results show that the -10 dB bandwidth of the antenna element is 21% covering 25.2 to 31.1 GHz. The measured peak gains of the antenna element and the 2 × 2 arrays are 7.6 and 10.75 dBi, respectively. The proposed antenna element and array cover N257 (26.5-29.5 GHz) and N261 (27.5-28.35 GHz) bands. It is very suitable for the 5G millimeter-wave application.

A 37-43 GHz endfire antenna based on ball grid array (BGA) packaging is proposed for the fifth-generation (5G) wireless system. The antenna consists of a miniaturized radiator and reflector. Besides, the radiator is fed by a substrate integrated waveguide (SIW). Furthermore, the RF transition from the SIW to grounded coplanar waveguide (GCPW) and vertical quasi-coaxial is realized on the substrate. The antenna is implemented on a single-layer substrate using standard printed circuit board (PCB) technology to reduce costs. Then, the cost-effective antenna element is reflow soldered with solder balls to form a BGA packaging. The advantages of the BGA packaging and the three-dimensional (3D) integration are discussed in detail. The miniature packaging achieves a compact size of 7 mm × 3.4 mm × 0.6 mm. Finally, a prototype was manufactured to verify the performance. The measurement results show that the proposed antenna is a good candidate for 5G millimeter-wave (mmWave) New Radio (NR) applications.

The letter presents a compact, cost-effective, and surface-mount patch antenna element for 5G millimeter-wave (mmWave) system integration. The antenna element adopts ball grid array (BGA) packaging technology to achieve surface mount function, which can be applied to highly integrated systems. By adding a ring slot on the radiating patch, the proposed antenna obtains a wider impedance bandwidth. The antenna prototype has been simulated, manufactured, and verified. The proposed antenna element size is 5 mm × 5 mm × 1.3 mm. The measurement results show that the proposed antenna element can be used in the N257 (26.5 to 29.5 GHz) and N261 (27.5-28.35 GHz) frequency bands.

We demonstrate that the future sixth generation (6G) radio links can be utilized for sub-THz frequency imaging using narrow beamwidth, high gain, lens antennas. Two different lenses, a bullet or hemispherical shape, were used in radio link setup (220-380 GHz) for an imaging application. Lenses performed with the gain of 28 dBi, 25 dBi, and narrowed the beamwidths of 1° and 2.5°. Plants were used as imaging objects, and their impacts on radio beams were studied. For assessment, the radio link path loss parameter was -48.5 dB, -53.2 dB, and -57.1 dB with the frequency 220 GHz, 300 GHz, and 330 GHz, respectively. Also, the impact of the radio link distance on the imaging was studied by 50 cm and 2 m link distances. In addition, the 3D image was acquired using the phase component of the image, and it showed the leaf surface roughness and the thickness, which was similar to the measured value.

A novel wide beamwidth microstrip patch antenna fed by a 1:5 unequal Wilkinson power divider with a low profile of 0.027λ₀ is presented. A circular patch and an independent feeding concentric metal ring can realize the broad half-power beamwidth (HPBW) in the far field. A 1:5 unequal Wilkinson power divider is designed as the antenna feed. The HPBWs of the antenna reach 258° and 267° in XZ-plane and YZ-plane, respectively, covering the whole upper half space at central frequency (2.54 GHz). The results of simulation and measurement show great consistency.

A multi-stack anisotropic cylindrical dielectric resonator antenna with high gain and wide bandwidth is reported. This antenna is designed with three different stacks, and each stack consists of a multilayer dielectric structure to emulate uniaxial anisotropy. Multi-stack, multilayer structure is responsible for producing wide bandwidth and high gain. In addition, the antenna is surrounded by cylindrical metallic cavity to increase directivity in broadside direction. Similar simulated and measured results indicate a wide impedance bandwidth of 37% along with a maximum gain 9.25 dB.

In this paper, a compact and reconfigurable rectangular substrate integrated waveguide structure dual-mode configuration based dual-band band-pass filter has been presented for 5G communication and milli-meter-waves. The dual-band bandpass filter is realized by utilizing the two pairs of dumbbell-shaped defected ground structure. The dumbbell-shaped defected ground structures etched on both the ground and the top side of the cavity have been used to produce transmission zeros, minimize the circuit size, and enhance the passband characteristics at a particular frequency of operations. In an effort to demonstrate the proposed dual-band substrate integrated waveguide band-pass filter, the proposed configuration has been designed and fabricated at the 28.3 GHz and 38.5 GHz frequency using low-cost PCB technique. The centre frequency of the second pass-band has been easily tuned using the geometrical parameters of the filter to achieve the desired applications in the 5G frequency band. Furthermore, the measured in-band return loss (rejection attenuation) of the two bands is approximately better than 26 dB and 28 dB respectively. The insertion loss of not more than 01 dB for both bands of the filter has been achieved. This dual-band filter operating at the licensed frequencies for the 5G spectrum bands renders this filter appropriate for numerous 5G and millimeter-wave communication applications.

A dual band flexible antenna for applications at 900 and 2450 MHz is proposed in this paper. The antenna offers a compact size of 0.23λ_o × 0.120λ_o × 0.0007λ_o, where λ_o is the wavelength at the lower resonance. The antenna comprises a simple geometrical structure consisting of a W-shaped serpentine structure fed by a microstrip line, while a Defected Ground Structure (DGS) technique was utilized with a partial ground plane to achieve wide operational bandwidth. An additional capacitor was loaded in between the slots to achieve a higher resonance, thus resulting in a compact dual band antenna. Various performance parameters were analyzed, and results were compared with the measured ones. The antenna offers good performance in terms of size, bandwidth, gain, and radiation pattern and thus increases the potential of the proposed antenna for both rigid and flexible devices.

In this letter, a compact dual-band patch antenna based on ball grid array (BGA) packaging for 5G mmWave is proposed. The patch antenna adopts a U-slot and a shorting pin to achieve dual-band operation of 28 GHz and 37 GHz. A single-layer FR4 substrate provides cost-effective features for the massive application. The BGA packaging not only reduces the size but also enables the antenna to be surface-mounted with other components in the same package, which improves the integration. The antenna has been fabricated and measured, and an acceptable agreement was obtained between the simulation and measurement results.

A novel coplanar waveguide (CPW) fed wide slot antenna for broadband circular polarization (CP) operation is proposed in this letter. Utilizing an asymmetrical ground plane and an open slot, broadband axial ratio and good impedance characteristics can be obtained in the middle and low bands. The perturbation patch on the right side of the wide slot excites the upper-band CP mode. By adjusting the upper-part feedline and the wide slot structure, the axial ratio performance can be optimized to a wideband axial ratio bandwidth (ARBW). Compared with wide slot antennas of similar size, the proposed antenna has a simpler structure while achieving a wider ARBW. The proposed antenna has been fabricated and tested. The measured results show that the -10 dB impedance bandwidth (ZBW) is 2.40-7.55 GHz (103.5%); 3-dB ARBW is 2.47-6.2 GHz (86.0%); and the peak gain is about 4 dBic. Right-hand circular polarization (RHCP) radiation pattern is achieved in +z direction. The proposed antenna can be used in WLAN/WiMAX applications and various wireless communication systems which require broadband ZBW and ARBW.

This paper proposes two low divergence angle orbital angular momentum (OAM) Fabry-Perot (F-P) antennas with nonuniform superstrates. There are two steps to design the proposed two F-P antennas. First, two primary array antennas (a slot array antenna and a patch array antenna) are designed. Both antennas can generate OAM vortex beams with a mode of -1. Second, two F-P resonator cavity antennas are formed by loading a nonuniform partially reflective surfaces (PRS) superstrates above the two primary antennas in order to increase the antenna gain and reduce the divergence angle. The PRS is designed non-uniform for increasing the aperture efficiency. The measured results indicate that the F-P OAM antennas can obviously improve the performance of primary OAM antennas: (1) for the slot array antenna, the divergence angle reduces from 27° to 18°, and the maximum gain increases from 5.2 dBi to 7.5 dBi; (2) for the patch array antenna, the divergence angle decreases from 30° to 18°, and the peak gain increases from 3.4 dBi to 7.2 dBi.

Artificial material has the feature to realize a controllable effective permittivity, which leads to many potential applications in the RF and optical fields. In this study, an artificial material is proposed for a Resonant Cavity antenna (RCA) to enhance the gain of patch antenna. The artificial material is made of a lot of circular conducting patches in a uniform size hosted in an FR-4 substrate. The fabricated artificial material is in a square shape with a length and width of 52 mm × 52 mm and a thickness of 1.2 mm. The artificial material is set in front of a patch antenna to construct an RCA, and the gain property of the proposed RCA is evaluated with the simulation and measurement methods. The results by both the simulation and measurement methods prove that the gain is enhanced by the proposed artificial material. The maximum gains are 14.5 dBi in simulation and 12.8 dBi in measurement at 15 GHz for the RCA with on slab of the artificial material. The gain is improved compared to the gain of a patch antenna without the artificial material.

A low-profile half-mode substrate integrated waveguide (HMSIW) filtering antenna with high frequency selectivity is proposed in this letter. The proposed antenna with a height of 0.014λ₀ (λ₀ is the free-space wavelength) consists of a slot-loaded HMSIW cavity, two parasitic patches, and five shorting pins. An upper-edge radiation null is generated by the interaction between the HMSIW cavity and parasitic patches. A rectangular slot etched on the HMSIW cavity is adopted to generate another null to improve the filtering performances at the upper stopband. Besides, the radiation in the lower stopband is suppressed by two nulls which emerge due to placing shorting pins under two parasitic patches. Thus, four radiation nulls can be obtained to enhance the frequency selectivity. The measured results illustrate that the proposed antenna provides an impedance bandwidth of 4.3% ranging from 2.74 to 2.86 GHz and a peak gain of 6.76 dBi during the operating frequency band. Moreover, four radiation nulls appear at 2.34, 2.56, 3, and 3.24 GHz in the lower and upper stopbands.

In this work, a diversity antenna with a high level of isolation is presented in this paper. To make the antenna compact, the radiating parts are arranged on opposing sides of the substrate. The isolation between the ports is sufficient for the use of a MIMO system, which is achieved through the orthogonal positioning of radiating elements. Wideband and narrowband antennas are placed on opposite sides of the substrate. The suggested monopole antenna has an impedance bandwidth of 3.1 GHz to 14.9 GHz, whereas the rectangular narrowband antenna has an impedance bandwidth of 5.4 GHz to 5.62 GHz. More than 16 dB of isolation exists between the two ports. The proposed antenna has a maximum gain of 2.9 dB. The diversity nature of the proposed MIMO antenna is studied in terms of Envelope Correlation Coefficient (ECC), Diversity Gain (DG), and Total Active Reflection Coefficient (TARC).

In this paper, a design method of spaceborne multi-beam antenna array is proposed. Multi-beam is achieved by rotating subarrays. A high efficiency circularly polarized horn antenna array working in Ka band is designed and processed. The antenna array has 16 large axial ratio elliptical beams, which can achieve the beam coverage range of 53°×49.1°. The simulation results are basically consistent with the test results, verifying the effectiveness of the proposed method. The design method of multi-beam antenna proposed in this paper can meet the requirements of multi-beam seamless coverage.

This letter presents a low-cost dual-band circularly polarized microstrip antenna for GNSS applications. The dual-band operation is achieved by stacking two metallic patches on a conventional FR4 substrate. The designed antenna can cover GPS L1 band, BeiDou B1 band, Galileo E1, E5b bands, and GLONASS G1, G3 bands, through a bandwidth of 1.118 GHz-1.215 GHz in lower L band and a bandwidth of 1.55 GHz-1.61 GHz in the upper L band. In order to achieve a wide axial ratio bandwidth, a dual-feed mechanism utilizing a capacitively coupled probe feeding scheme is incorporated. The overall size of the proposed antenna is 100 mm by 100 mm. The measured results indicate an excellent correlation with simulations.

This paper introduces a novel planar super-wideband (SWB) antenna with reconfigurable band-notch characteristic. The antenna can work in band-notch mode or band-notch free mode. A good impedance matching is responsible for the SWB characteristic of the proposed antenna by adopting a gradient ground, a gradient feeder line, and a gradient radiating patch. Furthermore, to achieve a reconfigurable notched band function, a 0.3 mm deep slot which is 16 mm in length and 8 mm in width is dug near the antenna feeder for the placement of dielectric plates etched with different sizes of split ring resonator (SRR). The designed antenna has a size of 200 mm × 109 mm × 0.79 mm, and the measured frequency band of bandwidth covers 0.8-26 GHz with a reconfigurable band-rejection characteristic. The dielectric plates with different SRRs reject the part of WLAN band (5.44-5.55 GHz), X-band satellite downlink band (7.65 GHz-7.82 GHz), and 6.33 GHz-6.59 GHz. A good agreement is achieved within the super-wideband frequency range between simulated and measured results.

A low-profile coplanar waveguide fed four-band compact antenna for 5G and WLAN applications is presented in this letter. Multiple bands are generated using a cactusshaped patch, which consists of several inverted L-shaped slots and branches. The proposed antenna provides 150 MHz (2.10 GHz-2.25 GHz), 400 MHz (3.25 GHz-3.65 GHz), 1022 MHz (4.42 GHz-5.44 GHz), 1400 MHz (5.60 GHz-7.00 GHz) bandwidths of 10 dB return loss, corresponding to the target N1/N78/N79 5G bands and 5.8 GHz WLAN band, respectively. Moreover, the proposed antenna has a low profile of 21 mm × 29 mm × 1.6 mm, while maintaining tolerable gain in these operation bands. In addition, monopole-like radiation patterns are obtained, which is suitable for wireless communication. In order to verify this design, a prototype has been fabricated and measured. The measured results show satisfactory agreement with the simulated ones.

This letter presents a four-element MIMO phone antenna with a metallic rim and 2-mm ground clearance that operates in the low-frequency band. Characteristic mode analysis is used to design the metallic rim so that the structure supports four resonating modes that can be excited separately to obtain MIMO operation in the desired frequency range below 1 GHz. Four exciter elements with matching circuits are designed so that the coupling between the ports is moderate. The prototype is manufactured, and measurement results are shown to corroborate the increased capacity compared to traditional two-element MIMO solutions.

An innovative negative group delay (NGD) circuit topology based on asymmetric coplanar striplines (ACPSs) and double-sided parallel striplines (DSPSs) is proposed. The original NGD circuit topology consists of two sections of ACPS, one section of open-circuited DSPSs, a connecting hole, and a group of grounding holes. The NGD characteristic is achieved by the open-circuited DSPS combined with the connecting hole. To verify the proposed NGD circuit topology, a prototype is designed, fabricated, and measured. From the measured results, an NGD time of -2.42 ns at the center frequency of 1.577 GHz is obtained with an NGD bandwidth of 36 MHz (1.561-1.597 GHz). The insertion loss is less than 4.75 dB with the return loss larger than 11.7 dB in the NGD band.

In the paper, a miniaturized wideband rat-race coupler with improved phase performance is designed and analyzed. Flat output ports phase differences are obtained by utilizing a component-loaded T-type transmission line (CLT-TL) with a stub-loaded short-circuited coupled line (SLS-CL). Let the CLT-TL and SLS-CL sections be equivalent to uniform 90° and 270° transmission lines, respectively. Design equations are derived, and an optimization is proceeded to obtain the circuit parameters. For validation, a prototype is designed, fabricated, and measured. Including the feeding lines, the circuit size is 0.31λ_g × 0.31λ_g. Under the criterion of return loss (RL) > 10 dB, the measured bandwidths for ports 1 and 3 excitations are both reach 48%. For amplitude imbalance (AP) < 0.5 dB, the overlap relative bandwidth is 46.88%. The measured bandwidths with 2° phase imbalance are 49.58% and 54.01% for ports 1 and 3 excitations, respectively.

This paper presents a planar filtering magic-T with a simple structure. It consists of four half-wavelength microstrip resonators with one loaded with a shorted microstrip stub at its central location. The resonator loaded with a shorted microstrip stub has the even-symmetry resonant mode. Other three resonators have the odd-symmetry resonant mode. The planar filtering magic-T has four ports, which all adopt a tapped line structure. Its novelty lies in the simple structure. Compared with previous works in the literature, its inter-resonator coupling zones are apart away and have no influence on each other, which means a simple design. Furthermore, a different-properties coupling is not needed, and its filtering response can be easily extended to the high-order case. The operational mechanism and design method are introduced in details. A planar filtering magic-T with center frequency of 920 MHz was designed and fabricated. The measured results show that, at the center frequency, the return losses (S₁₁/S₄₄) is less than 20/12 dB; an isolation degree of 25 dB (S₄₁) can be observed; the insertion loss of the difference port (S₂₁/S₃₁) and sum port (S₂₄/S₃₄) are 4.5/4.7 dB and 4.3/4.6 dB; the phase unbalance is 8˚/7˚(Σ/Δ). Totally, these results can verify the effectiveness of the proposed novel planar fiiltering magic-T.

A compact 3-D, circular line matched dipole (CLMD) antenna is presented in this paper. The realization of the antenna is based on Laser Direct Structuring (LDS) plastronic technology, enabling metallization on plastic parts. Cylindrical holder is chosen to carry the dipole, which implies high bending constraints on the antenna. Miniaturization of the radiating element is obtained by an effective use of 3-D space, resulting in a very low profile length dimensions of 0.14λ × 0.14λ × 0.05λ operating at 868 MHz. Specific attention is paid to the input impedance change due to conformation. An equivalent circuit model is proposed to take into account the conformation and design the matching line. Both simulated and measured results demonstrate good performances, with a 30 MHz bandwidth (i.e., a relative bandwidth of 3.5% with S₁₁ < -10 dB) around the working frequency. The LDS prototype achieves a maximum gain of 1.2 dBi with a quasi-omnidirectional radiation pattern. This compact and conformed design presents a real interest for pervasive highly integrated ISM band IoT sensors.

In this letter, two cost-effective surface-mount patch antenna elements for millimeter-wave (mmWave) systems using ball grid array (BGA) packaging are presented. A single-layer substrate based on FR4 is used to meet the low-cost requirements. The BGA packaging makes the proposed antenna element compact and easy to integrate. A U-slot is added to the patch to improve the impedance bandwidth of the patch antenna, and a vertical transition is designed to transmit the excitation signal by using a plated through-hole (PTH). The design process of the antenna is illustrated in detail. The antenna prototype has been simulated, fabricated, and measured to validate the design. The size of the fabricated prototype is 5 mm × 5 mm × 1.3 mm, which is very suitable for integration into a mmWave system.

In this paper, a wide 3-dB gain bandwidth transmitarray (TA) antenna with low focal length to diameter ratio (F/D) is presented. The TA comprises four identical metasurface layers, and the metasurfaces are printed on thin dielectric substrates, which are separated by air gaps. The unit cells of the metasurfaces are constructed by etching slots on the metal layers, which include a serrated crevice and two disjunct slots. The F/D of the TA is designed as 0.48 to accommodate the applications required low profiles. A TA is constructed by arranging high transmission elements at the center and the other elements in the external of the aperture. A transmitarray antenna (TAA) operating at 9~13 GHz is designed by applying a horn antenna to the TA, which achieves a measured 1-dB gain bandwidth of 10.5% (3-dB gain bandwidth of 23.3% and measured maximum gain of 22.48 dBi at 10.5 GHz) and a maximum measured aperture efficiency of 38.4%. Compared to the reported works, the proposed TA has outstanding F/D and wide 3-dB gain bandwidth.

A coplanar tri-band wearable antenna combined with an electromagnetic bandgap (EBG) structure is described for sub-6 GHz 5G and wireless local area network (WLAN) applications. The proposed antenna is fully implemented in textile materials thus offering a robust, compact, and discreet solution to meet the requirements of wearable applications. The addition of the EBG structure increases the textile antenna performance in terms of radiation patterns in the presence of the human body. The experimental results show that the proposed design exhibits tolerance to various bending conditions as well as loading by body tissues. In addition, to ensure the safety of the design for human health, the values of the specific absorption rate (SAR) have been reduced by more than 95%, which complies with the international standard. This design could thus be considered as a good candidate for IoT applications compared to the current state of the art while having a tri-band behavior and smaller volume.

In this article, a compact dielectric resonator antenna (DRA) with partial ground plane for wireless applications is examined. The exhibited structure is fed by a microstrip line. To demonstrate the functionality of a tri-band, a circular dielectric resonator antenna with concentric circular rings is created. The developed antenna parametric analysis has been performed on HFSS platform. The configured design operates at three frequency bands, i.e. 1.98-2.59 GHz (ISM), 3.24-3.85 GHz (Wi-max), and 4.85-5.85 GHz (WLAN), with the fractional bandwidths of 26.6%, 20.4%, and 18.67%, respectively. The customized concentric rings are placed onto the substrate to reinforce the antenna appearance and also miniaturize the size. The measured outcomes are strongly in accordance with the simulated results. The designed model can be customized with certain attributes to wireless applications.

A compact dual-mode band-pass filter (BPF) with 7th-order harmonics suppression is proposed. The proposed dual-mode BPF is designed using a three-section stepped-impedance-variable feeding line (SIVFL) and a square resonator. The high-order harmonics suppression is achieved by the SIVFL structures, and the size reduction is achieved using meandered lines and a resonator with two degenerate modes. The proposed BPF has a wide stopband up to 7th-order harmonics and a compact size of only 7 x 7 x 0.3 mm. The proposed BPF is suitable for the fifth-generation (5G) N77 band applications due to its working frequency, compact size, and good performance. Comparison and discussion are implemented as well.

This paper presents two novel different feeding and coupling schemes to solve the problem of generating transmission zeros (TZ) in lower stopband and their applications to design single-band filters. The designed two filters are based on substrate integrated waveguide (SIW) square cavity with orthogonal ports. In the design of Filter A, two L-shaped stubs are introduced to form an addition coupling path between two ports, which cause the generation of one TZ. Other two TZs are formed due to the resonance characteristics of L-shaped stubs and ports offset. Two metal vias are used to adjust center frequency slightly. In the design of Filter B, other two stubs are designed to form two additional coupling paths, thus forming a total of three coupling paths with the original path. Two TZs are obtained by utilizing the phase difference between different paths, and one TZ is generated for the resonance characteristics of the proposed stub 3. Simultaneously, an L-shaped slot is used to adjust center frequency. Both designed filters use the coplanar waveguide (CPW) structure to control bandwidth. Two filters are set to operate at 14.4 GHz with bandwidth of 800 MHz. Both filters are fabricated and measured. The simulation results of two filters are in good agreement with the measured ones.

In this letter, a surface-mount planar inverted-F antenna (PIFA) is proposed for the 5G mmWave system using ball grid array packaging (BGA). To meet the requirement of cost-effectiveness, the proposed antenna element is designed on a single FR4 layer to achieve low cost. To achieve a compact size, the BGA packaging is used on the proposed antenna element. Finally, the size of the antenna prototype is only 4.5 mm × 4.5 mm × 1.3 mm. Besides, the surface-mount feature allows the proposed antenna to be integrated with other devices in the same system package. The simulation and measurement results are discussed in detail. The measurement results show that the impedance bandwidth of - 10 dB is 15.3 % (24.7-29.6 GHz), and the peak gain is 5.85 dBi at 28 GHz. The proposed PIFA can be used in the 5G NR bands N257 (26.5-29.5 GHz), N258 (24.25-27.5 GHz), and N261 (27.5-28.35 GHz).

A direct synthesis approach is presented to realize in-line topology filters with adjacent frequency-variant couplings implementing a transmission response with the same number of finite transmission zeros as poles. The proposed method starts with an N-order fully canonical filter response definition. A non-resonant node (NRN) is incorporated into the transversal network to make room for an extra coupling, and as a consequence of the extended similarity transformation applied, the NRN is transformed into a resonant node. The result is a network with N poles and N transmission zeros implemented with N+1 resonant nodes and N FVC, being able to describe a fully canonical response with an inline network without cross couplings.

In this paper, a modified circular loop FSS with a slot antenna is proposed for sub-6 GHz 5G applications. The proposed FSS reduces the resonant frequency to towards lower bands of conventional circular FSS without change in its size. The operating bandwidth (-10 dB) of proposed antenna loaded with polarization insensitive single-layer FSS varies from 3.6 GHz to 6.1 GHz with an average gain of 7-7.5 dB and a maximum realized gain of 7.87 dB. An FSS superstrate is loaded onto a slot antenna to increase the realized gain of 4 dB, where the FSS shows desirable electromagnetic wave reflection characteristics over operating bandwidth and can be used in 5G sub-6 GHz band applications.

A low-loss dual-band negative group delay circuit (NGDC) with a flexible design is proposed. The proposed NGDC consists of a transmission line coupled asymmetrically with two step-impedance open-loop resonators. The negative group delay (NGD) times and center frequencies of the lower and upper bands can be tuned independently. To verify the design concept, two dual-band NGDC prototypes I and II are fabricated and measured. The measured NGD times of prototype I are -4.9 ns and -4.8 ns at the center frequencies of 1.949 GHz and 2.054 GHz, respectively. The insertion loss is lower than 2.7 dB and the return loss larger than 11.2 dB in both NGD bands. For prototype II, the NGD times at 1.949 GHz and 2.086 GHz are -4.7 ns and -3.3 ns, respectively. The measured insertion loss is better than 2.4 dB with the return loss larger than 11.9 dB.

This paper proposes an improved mathematical formulation of Johnston's approach to measure the radiation efficiency of an antenna, based on the Wheeler Cap (WC) technique. The proposed modifications allow the measurement of the radiation efficiency of small antennas matched to complex loads implemented on Radio Frequency IDentification (RFID) tags. The studied structure is a low-cost, silver-printed, differentially-fed RFID dipole antenna. The antenna is printed on a flexible PET (polyethylene terephthalate) paper that is conformable on various objects. Link budget measurements validate the accuracy of the formulation, which can be applied to any dipole antenna matched to an RFID chip with a complex input impedance.

We report a reduction in crosstalk between a transmitting antenna and an adjacent receiving antenna due to the use of radiation patterns with different orbital angular momentum (OAM). This crosstalk reduction is based on the orthogonality between different OAM modes. To generate OAM beams, patch array antennas are designed using High frequency simulation software (HFSS). The designed antennas are fabricated and characterized. An experiment is carried out to determine the amount of crosstalk reduction achieved due to the OAM nature of the signals transmitted. The variation of this crosstalk reduction with the distance between the transmitting and receiving antennas is also studied. The results obtained are verified through theoretical analysis using simulations in HFSS. A maximum theoretical crosstalk reduction of 3.6 dB has been obtained, and a crosstalk reduction of 2.6 dB has been realized experimentally. The results may benefit full-duplex communication links.

The deformation behaviors of a droplet on surface of composite insulator can strengthen local electric field, which could finally lead to flashover. Both experiments and numerical simulations for dynamic behaviors of a droplet on the surface of a composite insulator under applied AC voltage are investigated in this paper. Experiments are performed to study the influences of water droplet's volume and conductivity on the dynamic behaviors. Two critical parameters are proposed to describe the morphological change process of water droplet, and it is shown that the process can be divided into three stages. Moreover, these motion laws are explained by establishing theoretical factors and physical influence models. In addition, we perform computer simulation to study the dynamic behaviors of a water droplet under AC field, and the findings are in good consistency with our experimental results, proving the rationality of the theoretical physical model. It is found that the vibration frequency of droplet changes regularly with at different stages under the AC electric field.

This paper presents a dual-band eight-element multiple-input multiple-output (MIMO) antenna for 5G applications. The 8-element antenna is formed into two 4×4 MIMO systems that operate at 2500-2600 MHz and 1800-2200 MHz bands. The antenna elements are mounted along the perimeter of a rectangular ground plane with a total size of 110 × 80 mm² and are printed on both sides of a low-profile PCB material. Elements radiate through open rectangular slots etched on the antenna's ground conductor. The open slots are excited by T-shaped microstrip lines fed by 50-Ω coaxial connectors. The size of the ground plane's slots, and the T-shaped radiators control the resonance of the antenna's elements. The proposed design employs orthogonal elements to mitigate mutual coupling. The isolation between ports is less than -10 dB. The radiation efficiency ranges from 40% to 65% across operating frequency bands.

Parasitic effects in a lumped-element multilayer LC resonator are analyzed with an equivalent circuit. An optimization technique is proposed. With this technique, undesired influences of parasitic effects may be reduced. Meanwhile, some of the parasitic effects may be used for the size-reduction and performance improvement. A lumped-element multilayer LC resonator is used for demonstration. The optimized resonator outperforms the resonator before optimization in both performance and size. A multilayer filter composed of four LC resonators is used for verification. The measurement results agree very well with circuit results. The measured parasitic resonances are higher than the third harmonic frequency. These facts show the effectiveness of the proposed technique.

This paper shows a dual-band frequency and pattern reconfigurable antenna. The proposed antenna is designed on an FR4 substrate of thickness 1.6 mm and size 25×15 mm². Depending on the ON/OFF states of the PIN diode, the proposed antenna resonates at two distinct frequencies, i.e., 3.5 GHz, and 5.2 GHz, and has a pattern tilt from -170˚ to +160˚ in yz plane. In HFSS simulation, lumped RLC elements are used to reconfigure the antenna frequency and pattern. For switching, the PIN diode is used for frequency and pattern reconfiguration in the fabricated antenna to verify the simulated performance. In the simulated and measured performance, the proposed antenna shows reasonable matching. The proposed antenna is suitable for WiMAX and WLAN applications.

An inline quarter-mode substrate integrated waveguide (QMSIW) filter with controllable finite transmission zeros (FTZs) is presented based on a novel frequency-dependent coupling structure, which is constructed by a microstrip line with a pair of symmetric metallized via/buried holes and a magnetic coupling iris between two resonant cavities. FTZ can be independently introduced and controlled on both sides of passband to achieve high selectivity while keeping the filter compact configuration unchanged. For demonstration, the proposed structure is analyzed in detail. An inline fourth-order QMSIW bandpass filter (BPF) with two upper FTZs is designed, fabricated, and measured. The synthesis results, EM results, and measured results are in accordance with each other, which confirms the effectiveness of the proposed method.

Wireless power transmission system (WPTS) based on near-field inductive coupling is an effective way to provide power for gastrointestinal micro-robot. WPTS is normally realized by a Helmholtz coil outside the body and a three-dimensional receiving coil in the micro-robot. Helmholtz coil has two types, circle and square. However, a quantitative comparison for them in the application of WPTS has not been available yet. In this paper, the calculating models of the electromagnetic field intensity (EMFI) for the circular Helmholtz coil (CHC) and square Helmholtz coil (SHC) are built. With the built model, the uniformities of the electromagnetic field (UEMF) of two Helmholtz coils are calculated. The actual coil system is built to verify the correctness of the built models. When the diameter of the CHC and the side length of the SHC are both 40 cm, the available areas (UEMF ≥ 90%) for powering the robot supplied by the CHC and SHC are 39% and 56%, respectively. Also, the consumed powers of the two coils, when identical EMFI is excited, are compared. When the EMFI at the center of the CHC and SHC are both 1 Gs, the consumed powers are 5.09 W and 4.62 W, respectively. The above results show that compared to the CHC, the SHCnot only has better uniformity, but also consumes less power. Thus, it is more suitable for the WPTS.

This paper proposes a dual-polarized and high gain, four-element based compact multiple-input-multiple-output (MIMO) antenna operating at 5.2 GHz. First, a hammer-shaped antenna has been designed with a gain of 5.3 dBi, impedance bandwidth of 400 MHz, and broadside radiation. A mathematical analysis for radiated electric field and an equivalent circuit model for the hammer-shaped antenna are developed. Using the hammer-shaped antenna as an element, four element MIMO design with shorting walls is proposed. The shorting walls near non-radiating edges improve isolation between the elements by changing the direction of the major lobe. The proposed design has an envelope correlation coefficient (ECC) < 0.15, measured gain of 5.5 dBi, and mean effective gain (MEG) ~ -3 dB. This design has a low profile and single layer planar structure of area 65 mm x 65 mm, which makes it a good contender for portable devices or low-profile hand-held applications in WLAN band.

A frequency reconfigurable antenna with dual-band operation is presented. The antenna has a circular radiating patch loaded with an annular slot, and the slotted patch is shorted to the ground plane with four conducting posts. The antenna has three feed ports. Two of the ports are used to excite the slot mode resonant at a lower frequency, and broadside radiation with dual orthogonal linear polarizations can be obtained. The other port is used to excite the monopolar-patch mode resonant at a higher frequency, and conical radiation with vertical polarization can be yielded. To reconfigure the operation frequencies, four varactors are symmetrically placed across the annular slot. The simulated results indicate that the resonant frequency of the slot mode can be tuned from 1.62 to 1.17 GHz when the capacitance of the varactors is varied from 0.6 to 1.8 pF; besides, for each capacitance value, the impedance bandwidth of the antenna operating in the monopolar-patch mode can cover the frequencies from 2.4 to 2.5 GHz. Experiments are also carried out to validate the simulated data.

In this paper, the thinning space is constrained to only outer sub-planar array elements instead of fully filled planar array. Since the amplitude weights of the outer elements have small amplitude excitations, they can be optimized to find the least useful elements and remove them without affecting the desired radiation characteristics. The binary genetic algorithm is used to perform such thinning optimization. Simulation results show that roughly the same performance can be achieved when the number of removed elements in the outer sub-array relative to the total number of the planar array elements does not exceed 19%. In addition, to keep the size of the thinned array equal to that of the original filled array, the perimeter elements were excluded from the thinning process. Also, some constraints on the thinned array pattern are imposed to control the null directions toward interfering signals.

A miniaturized four-port multiple-input multiple-output (MIMO) antenna for ultra-wideband (UWB) applications is presented. The proposed UWB MIMO antenna has a compact size of 34 × 34 mm². Four antenna elements are placed orthogonally, and the element is connected to the feed line through metal vias in the substrate. These metal vias increase the bandwidth of the high frequency part of the antenna. A T-shaped slit, a rectangular slit, and a triangular chamfer are etched on the ground between two adjacent antenna elements. The working bandwidth of the antenna is 2.5-11.6 GHz, covering the entire UWB application band. The isolation between antenna elements is more than 18 dB within the operating bandwidth. Details of the design methodology and results are presented and discussed. Envelope correlation coefficient is computed, and it is within the acceptable limit, which validates the design concept for building a compact MIMO antenna system with good performance.

A highly sensitive temperature sensor based on a polymer cavity of a Fabry-Perot interferometer (FPI) is experimentally demonstrated. The interferometer gives ease in fabrication, and it can be formed by the induction of a thermos-sensitive polymer layer in between two single mode fibers (SMFs). The polymer is used as an FPI cavity for temperature sensing. Due to high thermal expansion coefficient (TEC) and thermos-optic coefficient (TOC) of polymer make the interferometer highly sensitive to ambient temperature. The maximum temperature sensitivity of 2.2209 nm/°C for the polymer FPI cavity of 40.61 µm in the ambient temperature range of 28°C to 34°C is obtained. The proposed sensor shows the advantages of high sensitivity, compactness, simple fabrication, and low cost. Thus, it may become a part of various practical applications in the field of environmental science and engineering sciences.

This paper proposes a novel miniaturized bandpass filter by loading a stepped-impedance resonator (SIR). Owing to the intrinsic characteristic of SIR, a third-order bandpass filter with SIR is presented, which has a size reduction of 38% compared with the conventional hairpin-line filter. On account of the electrical tape gap effect of a defected ground structure (DGS), further miniaturization is realized by introducing a pair of complementary split-ring resonator (CSRR) DGSs. Besides, frequency selectivity and out-of-band rejection can be improved by adding CSRR DGS and source-load (S-L) coupling structures, which produce two transmission zeros at two side band of passband respectively. The results show that the passband range is 3.4-3.6 GHz, and the final size is reduced by 50.3%.