In this study, a single-sideband time-modulated phased array (STMPA)-based hyper beamforming (HBF) system for automobile radar is suggested. The left beam and the right beam are generated once the improved STMPA is split into two subarrays. The HBF method is then used to produce the hyper beam. The switching sequence may be adjusted to generate the hyper beam in the desired direction. This study's benefits may be summed up as follows: (1) The hyper beam's sidelobe level is lower and its beamwidth is narrower than the conventional beam, which can help with estimating the direction of arrival. (2) The HBF can be achieved over a very wide scanning range. (3) With time as an additional controllable variable, the system's control mode is flexible and only two channels are needed, which lowers the system's cost and complexity. The effectiveness of the algorithm is tested through simulation, and the results highlight the system's potential when used with automobile radar.

Interrupted sampling repeater jammer generates multiple false targets to confuse chirp radar systems. In practical situations, maintaining separation between true target echo and jamming signal is not possible because the jamming pulses and the true target echo are overlapping in both time and frequency domains. A new anti-jamming technique against interrupted sampling jamming of self-protection repeater jammer is proposed without the knowledge of the jamming parameters. The proposed technique is based on fractional Fourier transform that can separate the overlapping true target echo and jamming pulses in the fractional domain, and then the resulting pulses are returned to the time domain, the true target can be easily distinguished from the false ones because the jamming pulses lag behind the true target echo by the jammer's delay. The theoretical analysis and simulation results demonstrate the efficiency and validity of the proposed technique.

A distributed basic matching network (MN) designed method that can achieve multioctave bandwidth and highly efficient power amplifier (PA) for multiband applications is presented in this letter. The distributed network unit with a left-rotating T-type structure is employed to construct the wideband MN, whose topology and circuit parameters are acquired through optimization. Finally, the impedance realized by the designed MN falls into the target impedance region obtained by using multi-harmonic bilateral pull technique in the desired frequency band. For the proof of the method, a broadband highly efficient PA has been designed, fabricated, and measured using commercialized GaN high electron mobility transistors (HEMT). The measured results show that the implemented PA achieves a bandwidth of 137.8% from 0.7 to 3.8 GHz. The drain efficiency is between 59% and 70% with an output power of greater than 39 dBm and a gain ranging from 9 to 12.1 dB.

In this paper, flexible substrate integrated waveguide (SIW) resonators have been designed and fabricated on polyimide substrates for humidity sensing applications. The proposed SIW resonant cavity allows the resonator to obtain the maximum humidity sensitivity and meet the demand for flexible microwave sensing detection. Meanwhile, the humidity response performance can be further significantly enhanced by introducing nanodiamond (ND) sensing material. Three prototypes of ND-coated SIW sensors with different bending radii are measured to analyze their humidity sensing performance. The experimental results demonstrate that the proposed ND-coated SIW sensor with the minimum bending radius can achieve a maximum humidity sensitivity of 1.09 MHz/% relative humidity (RH) in the high RH region (>75.3% RH) and a low humidity hysteresis of 1.8% in the range of 11.3–97.3% RH. This study provides a promising candidate to realize flexible microwave sensors with excellent sensing performance.

Passive millimeter-wave imaging systems (PMWIS) are employed for detecting concealed objects by mapping millimeter waves emitted from materials or living tissues. The emitted waves are measured by a receiver or radiometers without employing external wave sources. In this paper, a new super-heterodyne receiver front-end of a PMWIS at 35 GHz with an even order band pass filter is simulated and implemented. The receiver has a suitable temperature resolution for the use of hidden object imaging, is integrated and lightweight assembled on one-layer board. It has a bandwidth of 1.5 GHz, a noise figure (NF) of 2.2, and a temperature resolution of 0.126 K. The even order filter is implemented based on the substrate-integrated waveguide (SIW) technology, with Chebyshev response. The filters are designed at the central frequency of 35 GHz with the bandwidth of 1.5 GHz and one of them has controllable transmission zeroes. The filters are made by printed circuit board technology, employing SIW as resonators, having a high-quality factor of 23.33. Additionally, a triple-stage radio frequency (RF) low noise amplifier has been implemented having the specification of: RF 34.25–35.75 GHz; bandwidth 1.5 GHz; gain >60 dB; NF <2.3 dB, which are better indexes compared to some other works.

In this paper, a new dual-band Wilkinson power divider (WPD) is designed and fabricated using novel low and high impedance stubs instead of quarter-wavelength transmission lines. The proposed circuit was analyzed using odd and even mode analysis, and the optimal values of design parameters were obtained using the particle swarm optimization algorithm. The designed power divider has input reflection coefficients (S11) of −22.1 and −17 dB at the first operating frequency of 2.2 GHz and the second operating frequency of 14.2 GHz, respectively. It also improves stop-band and fractional bandwidth (FBW) while maintaining a simple topology. The proposed WPD suppresses undesired harmonics from the second to the fifth with an attenuation level of less than −20 dB in the first band and generates a broad stop-band (4.4–11.5 GHz). In the first band, the FBW is 54.5%, and in the second band, it is 20.1%.

This paper presents a broadband Butler-based slant ±45° dual-polarized omni-directional antenna working at the frequency band of 1.69–2.69 GHz for extending wireless communication network capacity in the limited service size. The proposed antenna realizes a 360° full coverage with wider bandwidth in a compact cylinder and increases the network capacity to 6 × 6 MIMO instead of using three traditional 2 × 2 MIMO omni-directional antennas. Theoretical analysis, simulation, and fabrication are conducted to validate the idea of the proposed omni-directional antenna. The measured results show 46% bandwidth with 15 dB return loss, 2.2 dB azimuth null and 8.9–10.5 dBi gain for port-C with 0° phase increment, and 14.1 dB azimuth null and 9.6–10.6 dBi gain for port-L/R (left/right) with ±120° phase increment, respectively.

A rectangular monopole antenna with an extended ground, excited by Coplanar Waveguide (CPW) and backed by a 6 × 6 array of fractal artificial magnetic conductor (AMC) unit cells, resonating at 5.8 GHz in Industrial, Scientific, and Medical (ISM) band, is presented in this manuscript. To attain the objective of proposing a compact and economical antenna solution for employment in wearable biomedical domain, a novel approach of utilizing both surfaces of the same dielectric for engraving antenna element as well as AMC array is adopted. It results in the elimination of layers of expensive substrate (RO3003) and of thick separator (foam) between antenna and AMC array. During measurement in open space, the proposed antenna system exhibited an impedance bandwidth of 570 MHz with a gain of 7.9 dBi. While a total realized gain of 7.5 dBi, amounting to a gain enhancement of about 3 dB as compared to that of monopole alone, is observed when the integrated antenna system is placed just over a three-layer rectangular human body equivalent model. Specific absorption rate values, as calculated at 5.8 GHz and averaged over 1 and 10 g of human tissue, are 0.0117 and 0.00244 W/kg, respectively. Obtained results strongly advocate the use of the proposed antenna system in smart wearable healthcare devices.

This article presents a flexible wearable KIT monopole antenna for biomedical application. A metamaterial unit cell is proposed to improve the antenna performance. The proposed antenna and the metamaterial are fabricated on 1 mm-thick polydimethylsiloxane substrate to operate in the ISM frequency band of 2.45 GHz. Integration of the metamaterial improves the gain and reduces the specific absorption rate (SAR) of the antenna. The overall dimension of the antenna with the metamaterial is 49 × 49 × 19 mm3. The designed antenna is investigated for the loading effect of the body by placing on the hand phantom model. Bending tolerances are also analyzed for x and y direction with various bend radii. Gain and SAR of the proposed antenna are 4.61 dBi and 0.868 W/kg. The results of the fabricated prototype show that the proposed wearable antenna is safe for biomedical applications.

A two-element low-profile closely coupled dual-band MIMO antenna is demonstrated for WiMAX applications. Based on the principle of metasurface (MTS) decoupling, a double-layer MTS consisting of pairs of elliptic patches with two different sizes is proposed. The MTS is loaded above a coupled dual-band MIMO antenna, and the mutual coupling in the lower and upper band is reduced by the larger and smaller elliptic patches, respectively. The edge-to-edge distance of antenna elements is only 0.01λ0 (λ0 is the free-space wavelength at 2.6 GHz). The measured results show that the working bandwidths of the MIMO antenna are 2.5–2.69 and 3.4–3.69 GHz. The −10 dB impedance bandwidths in two bands are 8.83% (2.49–2.72 GHz) and 8.50% (3.38–3.68 GHz), and the isolation between antenna elements is enhanced by 13.5 and 18.4 dB in two bands, respectively. Moreover, broadside radiation performances in two bands are obtained.

In this paper, a novel circularly polarized (CP) high-gain low-profile single-layer metasurface (MTS) antenna fed by a coplanar waveguide is presented for wideband low radar cross-section (RCS) applications. Characteristics mode analysis (CMA) technique is employed to simultaneously excite the useful modes rather than using conventional technique to achieve circular polarization in the wideband. By analyzing the characteristics modes of the antenna, gain of the antenna is also improved. Experimental results verify good performance of the proposed antenna with a compact size of 0.67λ0 × 0.67λ0 × 0.040λ0. The measured results of the antenna exhibit UWB impedance bandwidth of 96.93% in the frequency range of 3.7–10.65 GHz and 3 dB axial ratio bandwidth of about 41.8% in the frequency range of 5.3–8.1 GHz. The antenna shows a good radiation pattern with a measured peak gain of 7.9 dBic at 7.97 GHz. The proposed antenna achieves out-of-band scattering suppression in the wide range of 10–24 GHz because of MTS structure with peak RCS reduction of 19 dB at 12 GHz. The proposed antenna can be used for c- and x-band applications.

This work proposes a novel, extremely miniaturized wideband linear–circular and linear–cross metasurface-enabled reflective polarizer. This design comprises a Meander-line structure with horizontal dipoles as the top frequency selective surface, printed on a 1 mm thin-grounded FR-4 substrate. The x/y-polarized incident electromagnetic wave is converted as circularly polarized from 10.60 to 10.92 GHz (LHCP/RHCP), 12.12 to 17.32 GHz (RHCP/LHCP), and 22.72 to 37.76 GHz (LHCP/RHCP) during reflection with 2.97, 35.33, and 49.74% Fractional Bandwidth (FBW). In addition, this design shows linear–cross conversion with a minimum 90% polarization conversion ratio from 11.41 to 12, 19.01 to 22.34, and 40.74 to 46.82 GHz with an FBW of 5.04, 16.11, and 13.89%. The device performance is considerably stable under different oblique incidences, and the polarizer's unitcell is compact with a structural periodicity of 0.089 × 0.064 $\lambda _L^2$, and ultra-thin low-profile substrate thickness of 0.035λL. The proposed prototype is fabricated, and the measured results are in good agreement with the simulated one. This article also mentions how this polarizer could be tuned for dual-band K- and Ka-band satellite applications. The authors believe that the design's novelty lies in the multiband conversion with circular-polarization orthogonality, a highly miniaturized unitcell's volume of 0.199 $\lambda _L^3$/1000, and better angular stability made this design a potential candidate for real-time satellite applications.

A 2 × 2 dual band MIMO flexible antenna with a low profile and CPW feeding is designed for Internet of Things (IoT) domains, operating in 5G (3.3–3.6/4.8–5.0 GHz), WiMAX (5.25–5.85 GHz) and WLAN (5.15–5.35/5.725–5.825 GHz) bands. Two resonant frequencies are generated by L-shaped branches and a rectangular monopole. The mentioned MIMO antenna comprises four elements arranged vertically. With the addition of an orthogonal branch, significant isolation is attained, which exceeds 21 dB in the entire bands. The four-element MIMO antenna is fabricated and experimented to analyze the performance. According to the measurement, the antenna can operate bandwidth covering 3.156–3.84 GHz (19.55%) and 4.638–6.348 GHz (31.13%). Furthermore, the provided four-element MIMO antenna possesses a number of advantageous properties, such as ECC, DG, and TARC, indicating its suitability for 5G/WiMAX/WLAN applications. In accordance with the results of bending measurement and human body influence, it is evident that the presented liquid crystal polymer antenna could be an ideal candidate for integrating into wearable 5G/WiMAX/WLAN devices.

A compact quasi-Yagi antenna with a modified ground plane is designed for a through-wall radar on-chip. A slot-based ground plane modification in the proposed antenna results in significant miniaturization with an increase in the impedance bandwidth by 44.62%. The antenna has a high directivity of 9.02 dBi and a front-to-back ratio of 25.76 dB at 2.4 GHz. Based on experiments in real-world deployment scenarios, the performance of the proposed quasi-Yagi antenna is found to be comparable to that of a Vivaldi antenna and a commercial-off-the-shelf horn antenna. Spectrogram-based signatures of a moving person behind a wooden partition and a 40 cm thick masonry wall are successfully obtained using the designed antenna, demonstrating the suitability of the quasi-Yagi antenna for portable applications using a radar-on-chip.

This paper furnishes a compact modified hourglass-shaped aperture-coupled antenna for radar applications. The effect of slots of various shapes and various slot lengths on the input impedance, radiation pattern, and gain of the antenna are analyzed. The proposed antenna, designed using a modified hourglass-shaped aperture, offers a gain of 8.214 dBi for an compact antenna with a dimension of 20.4 × 20.4 × 1.041 mm3 and an aperture area of 2.495 mm2. Implementation of this proposed modified hourglass-shaped aperture offers a high gain per unit radiating patch area of 40.26 dB/$\lambda _g ^2$ and a high gain per unit aperture area of 1324.84 dB/$\lambda _g ^2$. The proposed aperture feeds a circular patch which radiates at its resonant frequency of 10.5 GHz. The proposed design is fabricated and the simulated results are verified experimentally. Equivalent circuit analysis is also done. A measured gain of 7.2 dBi is observed at 10.5 GHz. The physical area of the antenna is reduced without compromising the gain by judiciously choosing the shape of slot with more degree of freedom for impedance matching. The proposed antenna is well suited for the unit cell of phased array antennas for X-band missile radar applications.

In this work, a compact size 4 ports multiple input multiple output (MIMO) slot antenna with the connected ground for Ultra-Wide Band (UWB) and X band applications is introduced and discussed. The single antenna is a cross-shaped slot antenna in the ground plane and a 50 Ω microstrip line with a small L-stub is used to feed the antenna on the other side. The suggested MIMO antenna has four identical elements arranged to be orthogonal to each other to enhance the MIMO system performance. The antenna elements are connected with a small strip to compose the proposed connected ground antennas. The suggested MIMO antenna has an overall size of 47 mm × 47 mm. The antenna has tested and simulated bandwidth with S11 < −10 dB extended from 4– 14 GHz and has isolation greater than 20 dB between ports without utilizing the decoupling elements and with good consistency between results. The MIMO antenna has peak gain and efficiency, envelope correlation coefficient, diversity gain, and channel capacity loss of 5.6 dBi and 80%, <5 × 10–3, 10 dB, and <0.4 bit/s/Hz, respectively which prove that our antenna can be suggested for the UWB MIMO applications.

This paper presents a new design of a reconfigurable miscrostrip patch antenna based on a substrate-integrated waveguide (SIW). The antenna is resonant at the millimeter-wave (mmWave) 5G spectrum. The tuning technique consists of using a nematic liquid crystal (K15). An adjustable frequency band from 30.191 to 32 GHz is obtained, giving a tunable range of Δfr = 1.809 GHz. The maximum gain and efficiency reach the values of 7.61 and 9.07 dBi and 93 and 94%, respectively. The proposed SIW antenna loaded with liquid crystal was fabricated and tested. The experimental results correlated well with the simulation; however, the measured reflection coefficient plot shows a shift of the tuning range of 284 MHz, which is an acceptable outcome compared to simulation. A new approach of adopting the magnetic field as a technique to tune the resonance frequency has been used. The structure is characterized by its design simplicity, compactness, and fabrication process. The proposed antenna proves that the liquid crystal improves the performance of the antenna in the Ka band for 5G applications and satellite communication systems.

This communication presents the significance of a four-port 2×2 multiple input multiple output antenna operating in mid-band frequency for 5G handheld device application. A microstrip-fed reference truncated decagonal monopole antenna operating at 3.9 GHz and a modified split-ring resonator (SRR)-based low-pass filter that excites at a cut-off frequency of 6.5 GHz are designed. On introducing a stub line in the SRR structure, the proposed filter shows a good out-of-band rejection beyond 6.5 GHz. By integrating the filter into the reference monopole, a wideband filtering monopole with improved stopband performance is obtained. A four-port MIMO array is constructed by orthogonally positioning the antenna with a center-to-center separation of 0.25λ0. To improve isolation, a pair of inverted L-stubs of varying lengths is introduced. The closed loop formed by the interconnection of stubs enhances isolation within the frequency range of 3–3.5 GHz. The fabricated prototype fosters an impedance bandwidth of 66.67%, isolation >18.5 dB, an average suppression of 15 dB, an average peak gain >3.7 dB, envelope correlation coefficient < 0.015, Actual Diversity Gain (ADG) > 9.9 dB, Effective Diversity Gain (EDG) > 8.8 dB, and efficiency >88%. The proposed design is suitable for 5G sub-6 GHz applications such as n48, n77, n78, n79 bands, WiMAX, and LTE bands 42, 43, 46, 47, 48.