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.

A 6-element MIMO antenna system is introduced in this paper for N77, N78, and N79 (5G) communication bands. The proposed antenna element is composed of a four-section coupled line folded antenna. The performance of this antenna element is improved by using a partial ground plane combined with the DGS between the different elements of the MIMO antenna. The separated single antenna in this case has a reflection coefficient less than -10 dB over the frequency band from 3 GHz to 5 GHz. For the complete MIMO configuration, the reflection coefficientis less than -7 dB over the same frequency band for all the antenna elements. On the other hand, the isolation between antenna elements in the MIMO configuration is greater than 15 dB. The values of the MIMO parameters are calculated. These parameters include the Envelope Correlation Coefficient between the different elements (ECC), Diversity gain (DG), Total Active Reflection Coefficient (TARC), Channel Capacity Loss (CCL), and Mean Effective Gain (MEG). Good results are obtained for the MIMO parameters where ECC < 0.006, DG = 10, TARC < -7, CLL < 0.6, and -3 < MEG < -8. These performance parameters of the proposed MIMO system indicate that this antenna is suitable for 5G applications. The effect of the human hand on the S-parameter is also investigated. The proposed antenna is fabricated and measured to verify the simulation results.

A bidirectional, circularly polarized antenna with a miniaturized design and broadband capabilities is proposed for consideration in WLAN 2.4/3.65-GHz, WiMAX 2.3/2.5-GHz, 4G, and 5G frequency bands. The frontside of the antenna consists of a hexagonal slot, a hexagonal patch, ten meander tips, and rectangular corner notches to achieve broad impedance and axial ratio bandwidth. The feedline on the backside of the antenna with accompanying shorting pin is offset to further increase the common bandwidth. Also, the four corners of the antenna substrate are removed to decrease the electrical size. The designed antenna is fabricated and measured to validate simulation results. From measured results the antenna has a -10-dB impedance bandwidth of 89.7% (1.60-4.20 GHz) and a 3-dB axial ratio bandwidth of 70.5% (1.80-3.76 GHz). The peak realized gain in the boresight direction is 3.65 dBi, which occurs at 1.88 GHz.

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 robust constant false alarm rate (CFAR) method to detect continuous noise jamming in coherent radar systems with a single antenna having no pattern control. The proposed detector is robust to interfering signals such as strong spikes from neighboring radars and returns from targets of interest and is resistant to land, sea, and weather clutter. The detector operates on data vectors extracted from a real-valued Range-Doppler data matrix generated at the output of Doppler processing for each azimuth cell within the entire scanning sector. Each data vector consists of statistically independent range samples associated with one of the specified Doppler bins. These samples are selected from non-overlapping range intervals allocated within the noise-dominant region in the full range coverage to mitigate the effect of clutter on the detector's performance. To perform jamming detection for each cell under test (CUT) in the current antenna scan, the proposed detector uses the CUT-associated data vectors generated in the current antenna scan and CFAR reference data vectors generated in the previous antenna scan. These reference data vectors are extracted from Range-Doppler data matrices associated with reference azimuth cells uniformly distributed within the entire scanning sector. The proposed detector achieves robustness to interfering signals by using a two-step detection algorithm. The first step performs censored video integration (CVI) for the CUT and reference data vectors and individual adaptive CFAR detection in each specified Doppler bin. The detector applies the "m-of-m" detection strategy to a complete set of decisions declared by the individual CFAR detectors in the second step. This strategy provides immunity to the simultaneous presence of interfering signals in the specified Doppler bins. The robustness of the proposed noise jamming detector is verified using Monte-Carlo simulations.

In this paper, the design of a Metasurface incorporated Frequency Reconfigurable Planar Antenna (MS-FRPA) for Wireless Applications is presented. The structure of projected MS-FRPA consists of a patch with a metasurface placed one above the other with no gap between them. The MS is composed of an array of alternately placed dual split ring resonators arranged periodically in both horizontal and vertical directions. Frequency reconfiguration is achieved by rotating the MS relative to the designed patch antenna. The projected reconfigurable antenna is constructed on Rogers RO4350B material with thickness 1.524 mm. High Frequency Structure Simulator software is employed for analysis of the structure. The results clearly reveal that frequency tuning is achieved in 4.35 to 5.33 GHz with a fractional tuning range of 20.2%. The proposed structure provides appreciable realized gain with stable radiation patterns at all rotation angles. Further, the measured outcomes of the developed prototype show good correlation with the simulated outcomes.

The method of retarded potentials is used to derive the Biot-Savart law, taking into account the correction that describes the chaotic motion of charged particles in rectilinear currents. Then this method is used for circular currents, and the following theorem is proved: The magnetic field on the rotation axis of an axisymmetric charged body or charge distribution has only one component directed along the rotation axis, and the magnetic field is expressed through the surface integral, which does not require integration over the azimuthal angle φ. In the general case, for arbitrary charge distribution and for any location of the rotation axis, the magnetic field is expressed through the volume integral, in which the integrand does not depend on the angle φ. The obtained simple formulas in cylindrical and spherical coordinates allow us to quickly find the external and central magnetic field of rotating bodies on the rotation axis.

This paper presents an electrically small antenna (ka = 0.87) with ultra-low-profile 0.005λ₀ and six reconfigurable endfire radiation patterns, which cover the entire 360° azimuth plane. An equivalent magnetic dipole and six switchable equivalent electric dipoles form the six reconfigurable endfire radiation patterns by switching the ON/OFF states of six PIN diodes. The designing bright point is the dual side printed loop, that is, an Alford loop and six loaded circular arc stubs, which form the equivalent magnetic dipole. This technique can reduce the size by 77% compared with single side printed loop, expand the bandwidth, and produce a strong and uniform near magnetic field, which leads to a high F/B ratio. Compared with published pattern-reconfigurable ESAs with endfire radiation characteristics, the proposed antenna has highet F/B ratio about 35.6 dB, more switchable states and expanded bandwidth. In addition, the measured peak realized gain and radiation efficiency at 1.5 GHz are 3.52 dBi and 77.6%, respectively.

In this paper, a rectangular monopole antenna engraved with a complementary split-ring resonator is proposed for dual-band operation. The proposed antenna is fabricated on an FR4 substrate with a dimension of 20 x 34 x 1.6 mm³. The entire simulation is done using CST EM studio software. The proposed antenna exhibits dual-band operation from 1.78 GHz to 1.90 GHz and from 3.45 GHz to 6.58 GHz. The band from 1.78 GHz to 1.90 GHz is due to the inclusion of CSRR, and its corresponding bandwidth is 120 MHz. It is validated with the quasi-static analysis. The permittivity characteristics of the proposed CSRR are retrieved using the NRW method and presented. The resonant frequency of the band created by the CSRR is 1.83 GHz with -37.68 dB as its return loss values. The second wider band is due to the combination of the mode created by the CSRR along with the radiating patch from 3.45 GHz to 6.58 GHz with 3132 MHz which has a dual resonance at 3.65 GHz and 5.59 GHz with a return loss of -30.23 dB and -29.80 dB. The optimal values are chosen with the help of parametric analysis. The designed antenna is fabricated and measured. The measured results of return loss, gain, E-plane, and H-plane are compared with simulated results, and they are complying with each other. The dual-band operation, compact size, stable radiation pattern along with gain above 2.3 dBi in the whole resonating band make it suitable for the GSM and WLAN/WiMAX/5G Sub-6 GHz band (new radio band).

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.

Through-the-earth (TTE) communication systems are useful for post-disaster emergency communications due to their likelihood of surviving a mine disaster. The wireless channel and electromagnetic environment (EME) are two primary factors that affect the performance of a TTE system and have not been well understood in a mining environment. This paper reports our recent measurements conducted in an active coal mine to characterize the wireless channel and EME of a TTE system. TTE transmissions were successfully demonstrated in a mine location with a depth of 567 m (1,860 ft) by using ground rods installed on the surface and existing roof bolts in the underground. The results show that the EME in the mine is dominated by the 60-Hz signal and its harmonics for both surface and underground environments. The signal attenuation caused by the channel increases for frequencies greater than 90 Hz, which appears to be an optimum frequency point showing the smallest attenuation. An analytical path loss model for TTE channels is developed and validated using measurement results. This paper provides a measured data set as well as a model that an electric-field TTE system operator or system designer can reference when implementing TTE technologies in a mining environment.

Unconditionally stable approximate Crank-Nicolson (CN) perfectly matched layer (PML) implementation is proposed to treat open region problems for a bandpass rotational symmetric structure. To be more specific, this implementation is based upon the CN Douglas-Gunn (DG) procedure and the complex envelope (CE) method in body of revolution (BOR) finite-difference time-domain (FDTD) lattice. The proposed scheme inherits the advantages of the CNDG procedure, CE method, and BOR-FDTD algorithm which can improve the efficiency, enhance the absorption, and maintain the calculation accuracy. The effectiveness which includes accuracy, efficiency, occupied resources, and absorption is illustrated through a numerical example. The numerical results reveal that the proposed scheme provides considerable accuracy, creditable absorption and outstanding efficiency. Meanwhile, it can also verify that the proposed scheme is stable without the limitation of Courant-Friedrich- Levy (CFL) condition.

This paper introduces a dual-band circularly polarized antenna modeled on an FR4 substrate with an optimized dimension of 48 mm × 29.5 mm × 1.6 mm. A maximum usable circularly polarized bandwidth of 90% is obtained in the lower band (3.08 GHz to 3.75 GHz). A square slot etched in the ground plane loaded with asymmetric plus-shaped slits and tabs aids the impedance bandwidth enhancement. The dual-band operation is accomplished by facilitating parasitic square patches in the slot. The simulated impedance bandwidth of the proposed antenna is 740 MHz (3.07 GHz to 3.81 GHz) for the lower band and 1.57 GHz (4.64 GHz to 6.21 GHz) in the upper band. The impedance and axial ratio bandwidth percentages for lower and upper-frequency bands are 21.5%, 19.6%, and 29.4%, 10.54%, centered at 3.5 GHz and 5.5 GHz, respectively. The simulated and measured results are in reasonably good agreement.

Steel-tower structure buildings are different from traditional buildings and lack of effective channel models. A ray-based channel model suitable for severe multipath effects is proposed in this paper. The calculation method of channel parameters is introduced in detail, and the statistical characteristics at different frequencies are also analyzed based on the ray tracing (RT) method. We compare the RT-based channel data at 800 MHz, 2.4 GHz, 6 GHz, and 28 GHz with different positions of transceivers, and obtain the corresponding characteristics of channel parameters. According to the probability density distribution of each parameter, it is shown that the angle offset, delay, and power attenuation can be well fitted by Laplace distribution, Gaussian distribution, and exponential distribution, respectively. On this basis, the power delay profile at different positions is analyzed. These results can be used to optimize the deployment of sensor networks and evaluate the performance of communication systems inside the tower structure buildings.

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.

Although spiral antennas have undergone continuous development and refinement since Edwin Turner conceived them in 1954, only a few compact planar arrays exist. The shortcoming is even more significant when it comes to spiral antenna arrays in mode M2 operation. The present work addresses this issue, among other things. It presents two planar arrays of spiral antennas operating in the same frequency band and radiating for the first one an axial mode M1 and a conical mode M2 for the second. Both arrays are modeled, simulated, and fed with a corporate feeding network embedded in a dielectric substrate. It is shown that keeping the same topology, the array for conical M1 mode can be obtained from the array for mode M2 by a simple introduction of a phase shift on one branch of the feed and vice versa, providing thus the possibility to obtain in the same structure a spiral antenna array operating in both modes in the same frequency band simultaneously. Comparison between simulated and measured data shows good agreement.

A novel compact branch-line coupler operating in two arbitrary frequencies is proposed, analyzed and designed. Stepped-impedance stubs are used in the branch-line coupler to achieve dual-band applications. Parameters of the structure are chosen and provided for design guidelines. Broader operating frequency ratios and compactness are achievable. For the purpose of validation, a microstrip coupler operating at 2.4/5.2 GHz is fabricated and measured.

This paper presents a compact CPW fed circularly polarized AMC integrated monopole antenna with low SAR and high gain for 2.4 GHz WBAN applications. The proposed design is achieved through a four-stage progression. Stage-1 consists of a straight monopole with an extended vertical stub at one of the ground planes to generate circular polarization. In stage-2, a novel ring-type isotropic AMC is implemented beneath the monopole antenna to mitigate the antenna's back radiations towards the human body. On the body at `0' mm distance, it reduces the SAR by 99.47% and increases the impedance bandwidth, radiation efficiency, and gain to 480 MHz, 77% and 7.1 dBi, respectively. However, there is a decrease in AR bandwidth that indicates AR > 3-dB, which is compensated in stage-3 by optimizing the monopole. The optimization results an AR BW of 190 MHz and a size reduction of monopole antenna by 30.862%. Due to the size reduction of monopole with same AMC, the SAR reduction and peak gain are improved to 99.63% and 7.4 dBi, respectively. In Stage-4, the 3×3AMC is replaced by 2×2 AMC, results in total size and SAR reduction of 55.56% and 97.72% respectively. Stage-4 provides a simulated impedance bandwidth of 350 MHz, peak gain of 6.4 dBi and AR bandwidth of 170MHz, whereas the fabricated structure on felt substrate provides 650 MHz, 6.5 dBi and 150 MHz respectively.

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 set of statistical channel models based on 60 GHz radio measurements in a server room. The channel models are developed for possible use-cases, corresponding to potential deployment scenarios in wireless data centers (WDCs). A simple parametric channel model is used to model both the deterministic and stochastic channel parameters in the delay domain, within the 57-64 GHz unlicensed band. A simulation framework is accordingly provided to generate channel realizations for WDC use cases. The accuracy of the simulation framework is verified using the delay spread as a validation metric. The reported models are useful for practical system design and evaluation of WDCs millimeter-wave systems.