Two metasurface-inspired antennas embedded in a metallic cavity are introduced here. They are expected to be integrated on fast moving platforms enduring harsh accelerations and shocks. The metasurface allows enlarging the antenna bandwidth that is intrinsically reduced for small antennas embedded in sub-wavelength metallic cavities. The first one is only 60 × 60 × 20 mm3 (0.23λ1 × 0.23λ1 × 0.08λ1 at the frequency of 1164 MHz) and presents a dual-band behavior, covering both the lower and upper global navigation satellite systems (GNSS) bands (all GNSS bands are covered). It is fed by four probes and a dedicated circuit, ensuring the phase quadrature between adjacent feeds to achieve circular polarization over these two bands. For the second proposed antenna, circular polarization is achieved using two feed points connected to the radiating aperture of size 50 × 50 × 20 mm3 (0.26λ0 × 0.26λ0 × 0.10λ0 at the frequency of 1559 MHz). It covers the E1, L1, B1, and G1 GNSS bands. The numerical results are successfully validated by measurements.

This paper presents the design, manufacturing, and measurement of a novel substrate integrated waveguide (SIW) pedestal filtering antenna solution for use in 5G New Radio sub-6 GHz communications. Miniaturization is achieved through the use of SIW pedestal resonators and integration of the radiating element into the filter design, resulting in higher order suppression. The design generates a third order filtering response utilizing SIW pedestal resonators and a patch antenna element. The manufactured SIW pedestal filtenna achieves a 10 dB return loss bandwidth of 4.29% about a center frequency of 3.63 GHz, and a boresight gain of 3.66 dBi. Using the SIW pedestal filtenna elements, two array configurations are measured, a 1 × 1 linear array and 2 × 2 planar array. Beam-steering capability for the linear array is demonstrated in simulation, while the 2 × 2 array is shown to be suited to both dual- and single-mode operation.

Attaching a wireless transmission system comprising a radio frequency (RF)-chip and a dipole antenna to dielectric material of largely different permittivity leads to strong variation of the antenna feed impedance. Due to the severe impedance mismatch between the RF-chip and the antenna, the performance of the system may deteriorate drastically. The proposed antenna provides three feed points, which show respective feed-point match to 100 Ohm balanced feeds for three different dielectric environments (free-space and half-spaces of permittivity 4 and 42, respectively). Thereby, the RF-chip incorporates three 100 Ohm balanced output ports that are connected to the antenna from whom only one can be selected to provide the output signal. The respective other two output ports are shorted by an internal switching circuit that is controlled by external DC voltages. The measurement of the reflection coefficient of the stand-alone antenna and the chip agree well with the simulations, allowing to interconnect these two components. Further, the radiation pattern of the whole system is measured for two different scenarios showing good functionalities.

Due to increasingly complex and automated manufacturing processes, the demands on the control parameters of these processes are also increasing. One parameter is the fill quantity of, e.g., liquids in production plants, whose precise determination is of ever-growing importance. Up to now, the exact level of determination under difficult conditions, such as high ambient temperatures, has been a particular challenge. This paper demonstrates a novel method by which an M-sequence UWB radar can determine levels of low-permittivity materials in small metal containers. For this purpose, hot melt is used as an example. Thus, the influence of large temperature differences on the long-term stability of level measurement can also be investigated. The measurements show that the level of hot melt can be measured to be long-term stable with an accuracy of better than 3 mm. Furthermore, the precise determination of the empty state is highly important for many applications. For this reason, this paper shows a method for determining the empty state without complex calibration procedures. For the empty level indication, an accuracy of up to 0.5 mm could be achieved for molten hot glue and 3% of the tank volume, independent of the shape or aggregate state of the medium.

A strictly physically based design theory of a new class of Spatial Harmonic Magnetrons (SHM) is thoroughly derived which leads to analytically evaluable expressions. Thus two advantages are obtained: (1) The design parameters appear grouped into two separate categories – one just containing geometrical and material parameters, the other one exclusively containing beam current-related ones, which are in product-form determining performance. The influence of each parameter can thus easily be discovered and investigated. (2) Numerical efforts for any new design will be reduced by at least one order of magnitude. Subsequently and based on feature (1) it is derived that loading the anode structure by a suitably selected meta-material will increase output power and efficiency, will pave the way to CW operation, and can extend oscillation frequency well into the sub-THz range. Finally, it is shown that the Rising Sun Magnetron is a first step toward a meta-material loaded SHM offering the same but quantitatively reduced features and less stringent requirements to fabrication technology.

This paper presents a novel, simple, and efficient pulse generation technique using BJTs in avalanche mode with mixer effect. The presented design is an improved version of the basic single transistor avalanche pulse generator, and it composes of two identical pulse generators that drive a common 50-Ω load resistor at the output. The output signal exhibits wider bandwidth and narrower pulsewidth, compared to the basic single transistor circuit. The presented pulse generator also provides increased power output without using any power amplifier, and can be used in ground-penetrating radar and ultra-wideband communication systems.

A high image rejection 38 GHz demodulator in TSMC 65-nm CMOS process is presented. To achieve better than −40 dBc image rejection ratio (IRR), a low I/Q mismatch 45° LO power splitter of sub-harmonic mixer is proposed. In this design, the 45° LO power splitter is composed of a Wilkinson divider, a series delay line with electrical length of 45° on one side of the divider, and a shunt 90° transmission line on the other side. This configuration is attractive because of its design simplicity and easy fabrication. Compared with the conventional techniques that utilize capacitors and inductors instead of the shunt 90° transmission line, the proposed LO power splitter can alleviate the issue of process variation. The demodulator demonstrates an IRR lower than −40 dBc from 37.5 to 41.5 GHz. In addition, conversion gain is 1.3 ± 0.9 dB from 33 to 41 GHz with 6 dBm LO power. The total direct current power consumption is 78 mW from 1.0 V supply voltage. At the modulation scheme of 4096-QAM, the proposed demodulator demonstrates 1.7% (−35.1 dB) error vector magnitude (EVM), which is very close to the EVM measurement floor 1.6% (−36 dB) of our millimeter-wave signal analyzer.

This paper introduces a symmetric bar chart-shape (SBCS) microwave sensor for measuring permittivity of fluidic samples. For designing purposes, the introduced sensor was used based on the field changes between the SBCS and rectangular loop microstrip (RLM) structure. When a sample is placed on the sensing location, interaction between SBCS and RLM varies the field intensity. The vinegar samples were combined with water and then they are placed on the sensor. The change in field intensity changes the resonance frequency. However, there is a relationship between the permittivity of samples and the resonance frequencies. The proposed sensor is implemented on the substrate of RO4003C. The relative permittivity of samples changed from 59 to 77 and the resonance frequencies changed from 2.3 to 1.4 GHz. The quality factor is 3544 and the sensitivity is 2.2%.

This paper presents a planar microwave sensor for the noninvasive detection of glucose concentration in diabetic patients. The designed sensor operates from the 3.8 to 6.2 GHz frequency band, which covers the 5.8 GHz Industrial Scientific and Medical (ISM) band. The designed sensor shows a percentage bandwidth of 23.8% with a reflection coefficient (S11) of −50 dB at the resonance frequency of 5.7 GHz. The detection was carried out by varying the relative permittivity of the blood in accordance with the glucose concentration based on the Cole–Cole model. The measured result is calculated in terms of varying resonance frequency with variation in the reflection coefficient |S11| of the designed sensor. The observed frequency shift and corresponding sensitivity of the sensor are found at 1.7 GHz and 0.089 MHz/mg dL−1, respectively. An experimental validation has also been performed, and the frequency shift is analyzed by interacting the human thumb with the sensor. The simulated and experimental results of the designed sensor suggest that it can be useful for detecting glucose concentration noninvasively for diabetic patients.

Wireless-connected wearable electronics are finding extensive usage for diagnostic and therapeutic purposes after the globally spread pandemic disease of COVID-19. Although they are undoubtedly helpful for keeping physical distance, their health effects are still under investigation from different aspects and are still a concern for the end-users. In this study, a custom M-shaped wearable antenna covering the wireless body area network and wireless local area network frequencies is designed, built, and measured. A beret cap made from a 2 mm thick textile is used as a substrate. The specific absorption rate (SAR) in a realistic human-head model due to electromagnetic energy produced by the antenna is evaluated using the finite-difference time-domain method. The SAR distributions for 1-g and 10-g tissues are calculated at 2.4 and 5.8 GHz. It is shown that the obtained maximum SAR values for 1-g and 10-g tissues at each frequency of interest were less than the limits determined by IEEE RF exposure guidelines and standards.

A closely confined coplanar waveguide (CPW) fed MIMO antenna sheltering the entire ultra-wideband (UWB) spectrum with high isolation as well as dual-band rejection attributes is presented and evaluated. The intended wideband multiple-input multiple-output (MIMO) radiator embodies a pair of similar planar monopole elements (PME) together with the integration of the ingredients like a defected ground structure with Koch fractal boundaries, parasitic strips, cross-linked C-shaped parasitic resonators, and a Hilbert fractal neutralization line. The suggested UWB MIMO antenna houses an extensive bandwidth spanning between 2.64 and 12 GHz, sharply rejecting a pair of bands centered at 3.3 and 4.5 GHz. The wideband diversity antenna is realized in a closely packed measure of 26.50 mm (L) × 29.84 mm (W). A minute inter-element spacing of 0.51 mm is attained with the suggested layout. The numerical and experimental investigations of vital diversity parameters such as the envelope correlation coefficient, mean effective gain, total active reflection coefficient, as well as multiplexing efficiency depict high diversity performance. The consistency amidst the simulation as well as the empirical results recommends the worthiness of the intended antenna for handy UWB and UWB MIMO systems.

In this paper, a frequency selective surface (FSS) based shared-aperture antenna is designed for 5G/Wi-Fi applications. The 5G and Wi-Fi channel are separated to achieve different polarizations and simultaneous work. The proposed antenna is of ±45°-polarization in the 5G N79 band and vertical polarization in the Wi-Fi5.8 GHz band. The antenna is vertically stacked with the N79 band antenna located above the Wi-Fi band antenna. The N79 antenna is composed of FSS units with transmissive characteristics in the Wi-Fi band, and serves as an electromagnetically transparent surface to avoid blocking the Wi-Fi antenna. A prototype of our design is fabricated, assembled and tested, and measured results show that the prototype is able to cover the entire N79 band (4.1–5.2 GHz, 23.7%) and Wi-Fi5.8 GHz band (5.73–5.89 GHz, 2.8%). Measured average gain is 8.2 and 7.8 dBi in the N79 and Wi-Fi band, respectively, and radiation efficiency is over 86 and 80%. The proposed design exhibits separated channels, tri-polarizations, high gain and compact size, which is sufficient for regular 5G/Wi-Fi applications. The antenna also achieves a relatively wide and highly consistent signal coverage in the two bands, making it suitable for 5G/Wi-Fi multi-function communication and indoor 5G blind compensation.

This paper presents a multi-band rectangular slot antenna, which can be used in Beidou navigation system, 4G, WLAN and 5G system. The proposed antenna adopts a single feeding line, generating circular polarization for satellite navigation, and linear polarization for mobile communication systems. The proposed antenna consists of three c-type resonators and three rectangular loop slots. A c-type resonator and a rectangular loop slot work together to produce a usable frequency band. Multiple frequency bands can be generated by increasing the number of c-type resonator and rectangular loop slots. It is found that the c-type resonator changes the current distribution on the antenna surface, making the axial ratio less than 3 dB in the low frequency bands. Eventually, five operation frequency bands are realized. Experimentally, it is verified that the impedance bandwidths of each frequency band are 11.8% (1.12–1.26 GHz), 15.4% (1.5–1.75 GHz), 11.9% (2.36–2.66 GHz), 19.7% (3.15–3.84 GHz) and 2.6% (4.47–4.59 GHz), respectively. The measured 3 dB axial ratio bandwidths are 20 MHz at 1.2 and 1.56 GHz, fully covering BDS B1 and B2 bands. The measured gains are 3, 3.59, 4.07, 4.2 and 4.35 dBi, respectively.

This research investigates the MIMO antenna by using the Theory of Characteristics Mode (TCM) where 10 modes are subjected in designing. Also, 5 modes are the significant mode and 2 modes correspond to non-significant which defines the operating bandwidth and notched bands. The proposed 2 × 2 MIMO antenna configuration is designed for wideband applications with a size of 0.44 × 0.68 mm2. The two isolated 12-sided polygons radiating patches placed adjacent to each other share a common ground which is printed on an FR4 substrate. The measured impedance bandwidth covers bandwidth 3.11–11.98 GHz with two bands rejecting capability: Wireless Local Area Network (WLAN) and Downlink-Uplink Satellite (DUS) system. These two interfering bands are mitigated by etching a C-type slot on the radiating patch and an inverted U-type slot in the microstrip feed. The simulated and measured results are also compared in the far-field region (Normalized Radiation Efficiency (NRE), Peak Gain (PG), and 2-D/3-D radiation pattern). Proposed MIMO antenna also offers good diversity performance with ECC2×2 < 0.00001, DG2×2 > 9.999 dB, TARC2×2 < −15.0 dB, CCL2×2 < 0.001 b/s/Hz and MEG2×2 ≅ −3.0 dB.

Magneto-dielectric antennas (MDAs) provide small sizes, enhanced bandwidths, and frequency/polarization agility. We describe the fabrication and efficiency characterization at 0.4–0.8 GHz of five microstrip MDAs, whose gradually thicker substrates were 3D-printed using an off-the-shelf polylactic acid (PLA) filament doped with ferromagnetic particles. It was experimentally discovered that efficiency increases monotonically from 12% (−9.2 dB) to 37% (−4.3 dB) as substrate thickness goes from 1.6 to 4.3 mm; the rate is faster than expected for microstrip antennas. Numerical analysis indicated that the apparent magnetic loss tangent of the MD substrate experiences a threefold decrease as the 3D printer deposits more layers of iron-doped PLA. The MDAs exhibit radiation quality factors that are 3.7–7.2 times better than the dielectric counterparts. Moreover, a simple optimization of ground plane size could increase efficiency to 55% (−2.6 dB). The reduction in magnetic loss is attributed to a reduction in eddy current loss due to the separation of agglomerate iron particles. Therefore, despite the inherently lossy material used, the potential of 3D-printed MD substrates in providing acceptable antenna efficiencies is demonstrated together with unprecedented design freedom and fabrication flexibility.

A linearly polarized dual band reflectarray (RA) antenna designed, fabricated, and tested to operate in the Ku and K band frequencies is reported in this paper. The 24 × 24 cm2 size RA is developed using 1058 integrated elements etched over a 0.275 mm thick Rogers RT5870 substrate. The integrated elements include concentric circular rings distributed co-centric with the source and the Malta cross elements distributed offset from the source. The distribution of these elements is done based on the 590 and 360° phase change observed at 14.25 (Ku) and 22.5 (K) GHz by varying the size of the circular rings and the Malta cross respectively. The designed RA offers a simulated gain of 28.62 dBi at 14.25 GHz and 26.92 dBi at 22.5 GHz. These results are validated experimentally using the fabricated prototype. A measured peak gain of 28 and 26.4 dBi are observed with sidelobe levels (SLL) of −21 and −11 dB at 14.25 and 22.5 GHz respectively. The cross-polarization levels measured at the resonant frequencies are <−31 and <−28 dB. The proposed dual-band RA covers the entire Ku band uplink frequencies utilized for fixed satellite services and the K band downlink frequencies useful for earth exploration satellite services.

This article explores the possibilities of incorporating a defected ground structure (DGS) for widening the 3 dB axial ratio beamwidth (ARBW) of a simple low-profile planar circularly polarized (CP) antenna. Two pairs of DGSs are etched symmetrically along the diagonals of the ground plane to overcome the limited 3 dB ARBW performance of a crossed-slotted circular-shaped planar CP antenna. Here, one pair of DGSs is orthogonal to another pair of DGSs. The distance between the pairs of DGSs plays a key role in enhancing the 3 dB ARBW by 40.62%. A gap of 0.18λ0 is considered between the DGSs to maintain the symmetrical electric field distribution in the substrate. It also helps to reduce orthogonal current components and provides uniformly distributed patch surface currents. These phenomena collectively help the proposed CP antenna to exhibit right-handed circular polarization radiation with the 3 dB ARBW of 186° and 188° in the E-plane and H-plane, respectively. The measured results yield impedance bandwidth (S11 ≤ −10 dB) of 2.6% (2.283–2.342 GHz), CP bandwidth of 0.9% (2.294–2.315 GHz), gain higher than 4.8 dBic, and total antenna efficiency more than 64% across the entire CP band.

A compact, two-element textile MIMO antenna is designed with enhanced isolation by using modification in the ground, open-ended slots along with shorting pins. Maximum 27.8 dB isolation is achieved in two-element antennae, where the edge-to-edge distance is kept at 0.19 λ0 which is less than the conventional half wavelength. The Y-shaped decoupling and shorting pins improve the isolation up to 14 dB and can mitigate the current moment between the two ports effectively. The open slots in the ground are enhancing the mutual impedance and shift the operating band of the antenna toward the lower frequency band and thus size miniaturization is also achieved. The textile antenna achieves a 10 dB impedance bandwidth from 4.24 to 5.38 GHz with more than 21.1 dB isolation in the entire band. The phantom wrist model and bending analysis are carried out with the textile antenna to validate the on-body effects of the antenna in wearable and 5G applications.