A rigorous analysis of the scattering of plane and cylindrical waves from a strip loaded single near zero and double near zero (DNZ) metamaterial cylindrical object is presented. The proposed problem has been solved using integral equations derived from Green’s theorem and usual tangential boundary conditions. During the analysis, it was found that by loading a strip onto the metamaterial cylindrical objects, one can enhance or diminish the scattering under some specified conditions. It is shown that an enhancement in the back scattering occurs for a strip loaded DNZ metamaterial cylinder as compared to the back scattering of an unloaded DNZ metamaterial cylinder for both types of incident polarization. In the case of a specifically located electric line source, it is argued that by loading a strip onto a DNZ metamaterial cylinder, one can reduce the magnitude of the total field significantly at specific observation azimuth angles. For a specific location of a magnetic line source, the magnitude of total field of a strip loaded mu near zero (MNZ) metamaterial can be significantly enhanced as compared to unloaded MNZ cylinder in the specific observation directions. This parametric investigation is helpful in the designing of cylindrical metamaterial-based devices.

Intelligent Reflecting Surface (IRS) technology operating at mm-wave frequencies is promising for 6G applications. However, this technique faces the challenge of beam splitting, as beams cannot be directed accurately at all frequencies. To enhance system performance and lessen the beam spillting effect, the IRS is developed using phase shifters and time delay modules, as the problem is analyzed in this paper. The results of the simulation revealed that the proposed system, which is based on sub-surface IRS and time delay modules, successfully overcomes the packet splitting challenge effectively. The proposed architecture was 94.5% better in gain compared with the traditional architecture. The results explained a 54% improvement in data rate when time delay is used in the Phase-shift-Time delay-Phase delay (PTDP) system compared to the conventional design. Moreover, the use of 2-bit phase shifting alone in the proposed design was appropriate to realize close to optimal performance due to the system capability to direct power in the desired direction through the use of precoding technology, which compensates for losses resulting from beam splitting.

A type of signal-interference fourth-order dual-band bandpass filter (BPF) with multiple out-of-band transmission zeros (TZs) is reported. A second-order dual-band BPF block is firstly discussed, which is composed of two microstrip-to-slotline vertical transitions that are back-to-back connected by means of an in-parallel asymmetrical microstrip-line-based closed loop. It exhibits spectrally symmetrical passbands regarding the design frequency fD and three TZs at the inter-band region. Subsequently, by using stepped-impedance-line segments at the longest path of the transversal signal-interference closed loop, its dual-band BPF counterpart with second-order spectrally asymmetrical dual passbands is presented. Next, in order to increase the filter order as well as the number of out-of-band TZs for augmented stopband attenuation, a fourth-order dual-band BPF circuit is conceived. To this aim, two Y-shaped stepped-impedance microstrip stubs are loaded at the input and output ports of the previously devised second-order frequency-symmetrical dual-band BPF block. The RF operational principles of all these dual-band BPFs are detailed through their associated transmission-line-based equivalent circuits. Moreover, for experimental-demonstration purposes, a 1.154-/2.818-GHz two-layer microstrip proof-of-concept prototype of a fourth-order sharp-rejection dual-band BPF is designed, simulated, and characterized. It features inter-band power-rejection levels higher than 28.68 dB and lower-/upper-stopband attenuation levels above 40.92 dB from DC to 4.64 GHz.

This paper presents a novel design of quad-band rat-race couplers (RRCs) based on a modified T-shaped structure (MTSS). Two coupled lines are incorporated into the conventional dual-band T-shaped structure to create the MTSS, making it equivalent to a quarter-wavelength transmission line at four operating bands. The ABCD matrix method is applied to analyze the quad-band MTSS, deriving closed-form equations for calculating parameters of the structure. Then, a conventional RRC is separated into quarter-wavelength transmission lines, which are replaced by the proposed MTSS. To validate the design method, a quad-band RRC operating at 0.6, 1.196, 1.853, and 2.45 GHz is designed, fabricated, and tested. Simulation and experimental results demonstrate excellent agreement with theoretical prediction. The measured results show that input return loss exceeds 21.75 dB, isolation is greater than 21.6 dB, and insertion loss is less than 4.4 dB at all four operating frequencies. Phase deviations observed from the measured in-phase and out-phase responses are within 0o ± 4.6o and 180o ± 6.7o, respectively. Compared to most previously reported quad-band RRCs, the proposed circuit features a simple design and offers superior performance in isolation, return loss, and insertion loss.

The study introduces a novel dual-reflector antenna featuring a modified sub-reflector design aimed at improving aperture efficiency. A cylindrical-shaped keeper is introduced to enhance the performance of the sub-reflector. The dual-reflector configuration comprises a main parabolic reflector and a modified sub-reflector, with diameters of 16.5 λ and 2.2 λ, respectively, operating at 5.5 GHz. The antenna demonstrates a bandwidth (BW) of approximately 25.4% (4800–6200 MHz). Experimental measurements indicate favorable characteristics, including low cross-polarization levels (<−25 dB), minimal back lobe levels (F/B > 30 dB), high isolation between ports (>38 dB), and VSWRs less than 1.5:1 for both port1 and port2. The antenna exhibits an efficiency of around 58% and achieves a measured peak gain of approximately 32 dBi within the operating BW.

An highly miniaturized multiband polarizer for C to Ka-band applications is proposed. The polarizer design consists of resonating patch printed on top of the FR-4 grounded substrate. During reflection, the x/y polarized incident EM wave becomes circularly polarized with Axial Ratio (AR ≤ 3 dB) from 7.88 to 8.01 GHz, 9.01 to 11.65 GHz, 15.36 to 36.57 GHz, and 31.88 to 35.38 GHz, respectively. In addition, this design also demonstrates linear–cross conversion with a minimum 90% Polarization Conversion Ratio (PCR) from 8.28 to 8.60 GHz, 12.56 to 14.19 GHz, and 28.26 to 30.59 GHz. Transfer Matrix Method (TMM) explains the polarization conversion phenomena, and surface current distribution at resonant frequencies supports the multi-polarization conversion phenomena. The proposed design is compact with a periodicity of 0.063λL × 0.076 λL, where λL is the free-space wavelength corresponding to the lowest operating frequency. The fabricated prototype is verified experimentally. The authors believe that the features of the proposed design, like multiband, miniaturized unit cell architecture, and better angular stability, make it a promising contender for satellite applications.

This paper proposes a new surface fitting method based on double model comparison to solve the aspherical surface parameters, allowing for the simultaneous extraction of the surface deviation and the optimal surface fitting parameters for the radio antenna’s main reflector. This method employs the laser tracker to obtain the 3D coordinates of the points on the antenna surface, which can be expressed in terms of Zernike polynomials. Then compare the Zernike polynomial description with the ideal aspherical equation description to establish a discrepancy model in the optical design software. Finally, by optimizing this model, the optimal surface parameters can be obtained. The simulation results show that the method is suitable for high-precision fitting of aspherical surfaces with cone coefficient K in the range of [−4, 0.3], with the maximum deviation percentage of the radius of curvature at 0.036% and the cone coefficient at 0.14%. Experimental research is conducted on the 3.2 m sector sub-aperture spliced radio antenna; the fitted radius of curvature is 2012.3204 mm, the conic coefficient is −1.0476, and the Root Mean Square (RMS) is 0.6232 mm, confirming the adaptability of this method.

In this paper, a millimeter-wave (mmWave) wideband high-gain low-temperature co-fired ceramic (LTCC) phased array using ridged substrate integrated waveguide (RSIW) element is proposed, which can cover n257/n258 bands (24.25–29.5 GHz). First, a novel widebeam and high-gain RSIW slot antenna subarray is designed, which is constructed by staggered longitudinal slot that incorporated with additional radiating elements on the non-scanning plane. Further, the proposed widebeam antenna subarray is applied to construct a 1 × 4 array integrated in an LTCC package with small element spacing of about 0.41λ0. Moreover, by adding isolation slots and metal vias between adjacent array elements, the isolation of ports thereby is reduced below −15 dB, and the scanning range is increased up to ±7°. A wideband and low-loss feeding network is realized by series-parallel combined feeding, further improving isolation and scanning performance after assembly. The simulation and measurement demonstrate that the antenna array possesses satisfied beam-scanning capabilities over wide bandwidth of ∼20%, achieving maximum scanning angle up to ±62° while maintaining desirable gain above 14.5 dBi. Furthermore, within the entire operating bandwidth, the scanning angles extend to ±55° with minimal variation. These features show that the proposed antenna array is promising for 5G mmWave communications.

This paper presents an Substrate Integrated Waveguide (SIW) cavity-backed symmetric dual-beam self-diplexing slot antenna for short-distance multiuser point-to-point communications using mm-wave frequency bands. The antenna is fed by two capacitive-gap-coupled microstrip lines, which help the antenna to operate at two different frequency bands with a self-diplexing property. Independent frequency tunability at both the operating bands can be achieved by varying the capacitive gap position along the microstrip feed lines. To enhance port isolation and achieve dual-beam characteristics the design incorporates an L-shape folded slots, centrally located shorting via, W-slot, corrugated microstrip structures and mender line slot. The beams are directed at ± $\theta = \pm 43^\circ$ with a half-power beam width of 56∘ each. The antenna offers peak realized gains of 5.95 and 6.21 dBi at the lower and upper band, respectively. The antenna is fabricated and measured, which shows a good agreement between simulation and measurement, confirming its suitability for short-distance multiuser point-to-point communications

This study introduces a low-profile, broadband antenna with filtering features and tunable radiation nulls. The antenna consists of an arc-shaped slot, a sawtooth square slot, a Y-shaped filtering branch, two rectangular metal cavities, and curved current loops. High-frequency current balancing technology is used in this research, two rectangular metal cavities are added above the slot to balance the current strength and reduce cross-polarization. By introducing a Y-shaped filtering branch based on the reverse diversion technique, the filtering capability of the antenna can be significantly enhanced. The electric and magnetic field intensity in the specific area is enhanced through arc-shaped slot tuning technology, and the bandwidth is effectively broadened. The radius adjustment of the sector-shaped feeding network controls the position of the high-frequency radiation null, and the curved current loops control the low-frequency radiation null, the two modulate to regulate the roll-off rate of the radiation characteristic. Experimental tests demonstrate an impedance matching bandwidth greater than 55%, a peak gain of 4.5 dBi, and out-of-band suppression of 25 and 21 dB in the low and high-frequency bands, respectively. Moreover, the cross-polarization level obtained in the xoz plane is lower than –35 dB. The designed antenna demonstrates considerable potential for broadband filtering applications.

A Chebyshev-distributed 1 × 8 beamforming network with improved phase flatness is presented, where four beams with constant beam pointing and low sidelobe levels (SLL) can be generated. It consists of two arbitrary-amplitude 4 × 4 Blass-like matrices and one 1 × 8 switch control circuit. The newly introduced 4 × 4 Blass-like matrices can obtain arbitrary amplitude and phase differences by adjusting the transmission coefficient and phase of each unit. Besides, four output phase differences can be generated by controlling the 1 × 8 switch control circuit. An example is implemented for validation and phase compensation method is adopted for minimizing the phase difference error within the operated bandwidth to maintain constant beam pointing. Measurements show that the prototype exhibits output amplitude ratios of 0.143:0.341: 0.71:1:1:0.71:0.341:0.143, which fits the Chebyshev distribution. Under the criterion of |S11| < −10 dB, an overlapped fractional bandwidth of 24.1% is obtained. In addition, from 5.5 to 6.1 GHz (10.3%), the maximum amplitude and phase difference errors are 1.5 dB and 15°, respectively. Finally, the proposed network is connected to a 1 × 8 array. Within 10.3% bandwidth, the SLLs of less than −20 dB are realized without beam-pointing deviation.

This research explores a circularly polarized (CP) multiple-input-multiple-output (MIMO) dielectric resonator antenna (DRA) designed specifically for 5G Sub-6 GHz and WiMAX applications. The antenna system utilizes a unique H-shaped feeding strip to excite each DRA element. This specialized feeding mechanism facilitates the activation of higher-order degenerate modes, including TE$_{\delta13}^x$ and TE$_{1 \delta 3}^{y}$, which are essential for achieving circular polarization. The antenna exhibits a reflection coefficient of −37.52 dB at 3.49 GHz, covering the entire CP passband and operating over a broad bandwidth of 1.35 GHz (3.40–4.75 GHz) yielding a return loss of 35.52%, making it suitable for Sub-6 GHz applications. An axial ratio bandwidth of 24.6% (3.4–4.2 GHz) is observed, with inter-port isolation of greater than −25.3 dB throughout the usable frequency band with a maximum efficiency of approximately 98%, indicating near-lossless power radiation. Additionally, the estimated gain is 5.95 dBic. The proposed MIMO design presented effectively reduces the intersecting spatial field components between antenna elements, leading to a lower envelope correlation coefficient and enhanced inter-port isolation. This diversity gain of the proposed antenna is a strong candidate for use in rich multi-path environments, helping to mitigate the effects of channel fading.. Initially, the proposed antenna design was examined using the time-domain solver of CST, followed by the fabrication of a prototype for experimental validation. The antenna exhibits a stable response, making it well-suited for 5G Sub-6 GHz and WiMAX applications.There is a satisfactory alignment between the results obtained from simulations and those observed experimentally.

In this work, a wideband filtering antenna based on substrate integrated waveguide (SIW) cavities is proposed. The SIW cavities with zigzag topology excite multiple modes to increase the potential filtering bandwidth. The radiation slot etched on the cavity merges the resonant modes into a single frequency band, thereby enabling directional broadband radiation. Moreover, two supplementary slots are introduced to facilitate wideband impedance matching without increasing the overall size. Furthermore, both the cavities and the slots work together to create three radiation nulls, improving the filtering performance. The proposed SIW slot filtering antenna achieves good frequency selectivity and meets the increasing demand for wideband and integration of multifunctional devices. To validate the design, a prototype antenna was fabricated and tested. The measured results show that the prototype has an operating bandwidth of 10.1% at the center frequency of 11.16 GHz. The peak gain within the passband is 6.19 dBi, and the out-of-band radiation rejection level is better than 20 dB.

This paper presents a low-profile miniaturized dual-band antenna utilizing the quarter-mode substrate integrated waveguide (QMSIW) structure. The two modes of TE110 and TE220 of a single QMSIW structure are employed, enabling a dual-band operation. The frequency ratio between the two bands can be tuned by loading a capacitive structure, which is comprised of a capacitive-loaded patch and a short circuit post, inside the QMSIW structure. By introducing parasitic QMSIW structures through magnetic coupling, a dual-band antenna with enhanced bandwidths is achieved. The antenna has dimensions of smaller than 400 mm2 (0.048λL2) with a uniform height of 1.4 mm (0.016λL). Measurement results indicate that the −6 dB impedance bandwidths of the antennas can cover the 5G N78 (3.3–3.6 GHz) and N79 (4.8–5 GHz) bands, and the average efficiencies is better than −2.5 dB. To the authors’ knowledge, the proposed designs offer dual-wideband operation while having the smallest planar dimension compared to the previously reported antennas. Furthermore, an extended electric coupling dual-band antenna configuration is also described and measured, which achieves similar bandwidth extension as the proposed antenna.

This paper presents the design and analysis of a conformal dual-band quasi-Yagi antenna tailored for Internet of Medical Things (IoMT) and 5G-enabled Wireless Body Area Network (WBAN) applications. The antenna is fabricated on a flexible polyimide substrate, ensuring mechanical conformability and stable performance on curved surfaces. The proposed design is based on a wedge-shaped quasi-Yagi radiator, incorporating a microstrip-to-slot transition for efficient excitation. The antenna features three pairs of wedge-shaped radiating arms and an arc-shaped director to enhance gain and directionality. Simulated results demonstrate dual-band operation at 2.45 and 3.4 GHz, with fractional bandwidths of 8.16% and 8.59%, respectively, and a reflection coefficient |S11| ≤ −10 dB. The design is further extended to an eight-element Multiple-Input Multiple-Output configuration, ensuring enhanced spatial diversity, low mutual coupling (<−15 dB), and improved gain (>5 dBi). The antenna’s performance is validated through simulations, demonstrating its suitability for real-time medical data transmission. With its compact size, high efficiency, and conformal nature, the proposed antenna effectively addresses the challenges of wearable IoMT and WBAN communication systems.

A fused deposition modeling (FDM)-based polarization-dependent frequency-agile Frequency Selective Surface using distilled water is proposed in this paper. The FSS consists of a periodic array of vertically meandered square loops with two rectangular fluidic cavities embedded within the substrate. The resonant frequency is dynamically tuned across three distinct operating states by selectively filling one or both embedded cavities with distilled water, achieving a 47.42% tuning range in TE mode (2.15–3.45 GHz) and a 10.28% range in TM mode (3.32–3.68 GHz). An equivalent circuit model is developed to explain this tuning behavior by emphasizing the impact of fluid-induced permittivity changes in the substrate. Experimental results from a fabricated prototype validate the simulated performance, demonstrating angular stability up to 45∘. The proposed geometry is low-cost, lightweight, and energy-efficient, making it ideal for integration into adaptive communication systems, reconfigurable antennas, and electromagnetic shielding applications.

This manuscript presents a novel three-series-only topology P-insulator-N (PIN) diode single-pole-double-through (SPDT) switch designed to address the challenges of high power handling and low insertion loss in Q-band and V-band communication systems. The manuscript provides a detailed theoretical analysis of series-connected PIN diodes, offering insights into their behavior under both small- and large-signal conditions. Based on GaAs PIN diode technology, the switch operates across a frequency range of 37.7 to 61 GHz, achieving a low insertion loss of 0.707 dB and providing an isolation of 24.6 dB. The proposed SPDT switch demonstrates a high $\text{IP}_{\text{0.1~dB}}$ of 37.6 dBm at 38 GHz. With a compact chip size of $0.905\times 0.885 \text{mm}^2$, including all pads, this work offers excellent power handling capability, making it highly suitable for advanced communication systems in Q-band and V-band applications.

In the advanced era of compact and convenient devices, electromagnetic microwave brain imaging systems have emerged as substitutes for large and bulky imaging devices such as X-rays, CT scans, MRIs, and ultrasounds for diagnosing brain disorders. This article introduces a compact monopole antenna specifically tailored for microwave imaging in brain stroke detection. The bidirectional antenna incorporates a triple hollow rectangular patch and a hexagonal slotted ground for enhanced performance. The antenna is constructed on an FR-4 substrate with a thickness of 1.6 mm. The design is finalized using CST, with parameters adjusted to achieve the desired bandwidth and gain performance. The antenna provides a bandwidth of 2.16 GHz, spanning from 1.35 to 3.51 GHz, with a return loss |S11| < 10 dB (VSWR < 2) and a peak gain of 5.1 dBi at 3.5 GHz, while maintaining stable radiation characteristics across the entire frequency range. Simulation results indicate that the proposed antenna is well-suited for microwave-based brain stroke detection and imaging applications. The fabricated antenna has been tested for brain stroke detection with an innovative setup in the lab. It is observed that the stroke models have been detected clearly.