A compact, wideband, and high-gain circularly polarized array antenna is proposed based on substrate integrated gap waveguide (SIGW) using sequential rotational phase (SRP). The array antenna consists of four $2\times2$ corner-cutting corner patches and an SIGW-SRP feeding network. The SIGW-SRP feeding network is achieved by utilizing the spatial vector addition property to compensate for phase, aiming to improve the bandwidth and gain. Unlike the traditional SRP feeding network, the proposed feeding scheme is simpler and easier to fabricate, and each port can achieve more stable phase and bandwidth. In addition, benefiting from the surface wave suppression and in-phase reflection property of SIGW, the proposed array antenna has a stable radiation pattern and low cross-polarization covering wideband frequencies. The measured results indicate that the −10-dB impedance bandwidth ranges from 12.2 to 17.3 GHz (34.6%), the 3-dB axial ratio bandwidth ranges from 13.5 to 16.7 GHz (21.2%), and the peak gain is 16 dBic.

This paper presents a compact broad dual-band rectifier based on a transmission line matching network. This method improves the overall impedance matching performance over two bands, and improves bandwidth of the rectifier’s efficiency. A π-type direct current filter with excellent harmonic suppression performance is proposed. The multi-section transmission line used as the dual-band input impedance matching network is analyzed to achieve an arbitrary frequency ratio. A rectifier is designed and implemented using a three-stage transmission-line matching network. Simulation and experimental results show that a dual-band rectifier is successfully performed with the measured power conversion efficiency (PCE) of 75.7% and 76.3% at 0.915 and 2.45 GHz, respectively. Additionally, the rectifier exhibits bandwidths of 0.48 and 0.25 GHz when the PCE exceeds 70%. Significant enhancement of bandwidth over conventional rectifiers is demonstrated.

This paper introduces a method to realize beam switching by using a substrate-integrated waveguide (SIW) Butler matrix combined with a slot array antenna. The Butler matrix consists of two hybrid couplers, two crossovers, two −45-degree phase shifters, and two 0-degree phase shifters. The slot array antenna is a 4 × 2 array. The operating frequency band of the slot array antenna, where the reflection coefficient is below −10 dB, is 26.5–31.5 GHz. The measured beamforming angles from input port 1 to input Port 4 of the Butler matrix are +46, −16, +15, and −50°, respectively. The corresponding antenna gains from input Port 1 to input Port 4 are 11.57 dB, 14.284 dB, 10.94 dB, and 12.864 dB, respectively. The dimensions of the Butler matrix and the slot array antenna are 56.8 mm × 21.2 mm × 0.254 mm. The dimensions of the SIW transmission channels between the Butler matrix and input Ports 1– 4 are 16.9 mm × 34 mm × 0.254 mm.

This paper presents a novel compact self-quintuplexing antenna using a half-mode substrate-integrated waveguide cavity to implement multi-operation wireless services. The proposed antenna design incorporates five triangular protrusions of different dimensions, assembled with SIW to function as the radiating elements. Each radiator supports the one-eighth mode of the SIW cavity. The resonance frequencies of radiators are 3.63, 4.44, 5.23, 6.21, and 7.05 GHz. Each radiator operates at a distinct frequency due to the differing dimensions and is independently driven by 50 Ω microstrip lines. The measured reflection coefficients and isolation among any two ports are less than −10 dB and better than 23.6 dB, respectively. The measured gains at their respective resonant frequencies are 5.66, 4.84, 5.03, 7.08, and 6.59 dBi. The front-to-back ratio is better than 8.7 dB in each band. The difference of co-to-cross-polarization is greater than 19.3 dB.

In this paper, pulse splitting approach is proposed to simultaneously reduce the sidelobe level (SLL) of fundamental signal and maximum sideband levels (SBLs) of harmonic signals for time-modulated linear array (TMLA). This is achieved by controlling only the periodic switching time sequence of each element of the TMLA. In pulse splitting, the on–off switching sequence of each radiating element is characterized by multiple rectangular sub-pulses within the modulation period which increase the degrees of freedom in order to better synthesize the desired fundamental pattern with simultaneous suppression of harmonic or sideband radiation. A genetic algorithm is employed to optimize the switch-on and switch-off instants of each sub-pulse for each element for 16-element uniform amplitude, phase, and space linear antenna array. The simulation results reveal that the proposed method can achieve the desired patterns with very low SLL and SBLs compared with previous published results.

This paper presents a flexible SiGe monolithic microwave integrated circuit (MMIC) chipset for 120 GHz ultra-wideband frequency-modulated continuous wave radar systems. The highly integrated chipset is implemented with multiple-input and multiple-output radar in mind which leads to transmit and receive MMICs with four integrated channels in each chip. The transmitter achieves an output power of 12.9 dBm with a total power consumption of only 403 mW. The receiver chip incorporates a sub-harmonic approach for suppression of leakage radiation at 120 GHz through a receive channel. Both chips integrate active multiplier chains that are driven by a third reference dual band voltage-controlled oscillator (VCO) MMIC that can deliver an output at center frequencies of 15 or 30 GHz. The reference VCO MMIC demonstrates relative tuning ranges of 32%.

In this article, a dual-sense triband circularly polarized modified slot antenna loaded with metamaterial structures such as split-ring resonator and cross strips is proposed. The first resonant frequency is generated using the modified square slot which produces the two degenerative modes required to achieve circular polarization (CP). The corners of slot antenna are extended to obtain the orthogonal modes. The second resonant band is obtained using the single split-ring resonator. Two micro-splits in Split Ring Resonator (SRR) orthogonal to each other produces CP due to electric field generated by the micro-splits. The third resonance band is obtained due to loading of cross strips. The orthogonal phase is adjusted by varying the length of cross strips, so that the CP is achieved. All resonance bands are tuned independently. The measured impedance bandwidth of 31.68%, 4.55%, and 8.6% is obtained in first, second, and third bands respectively. The axial ratio bandwidth of 13.04%, 2.7%, 8.6% and peak gain of 3.8 dBic, 3.9 dBic, 3.7 dBic are obtained respectively. The simulated radiation efficiencies of above 80% is achieved in all bands. The left-hand CP is obtained in first two band as co-polarization and right-hand CP is obtained at the third band as co-polarization with respect to cross-polarization radiation. The cross-polarization of minimum −10 dB is obtained in all three bands. The proposed design is well suitable for the Bluetooth, n78 and n79 5G applications.

This paper presents a systematic design approach for developing a semiflexible multiple-input–multiple-output antenna system operating in the millimeter wave frequency spectrum, specifically designed for body-worn applications in biotechnologies. The designed antenna features dual flower-shaped antenna radiators placed in a spatial diversity configuration. Strategic modifications have been implemented by integrating dual crescent-shaped slots in the ground layer to attain the targeted frequency band of 25.7–30.6 GHz. Later, the upper edge of the ground plane is truncated in order to achieve circularly polarized radiation characteristics at 29.4 GHz with 3 dB ARBW of 0.6 GHz (29.1–29.7 GHz). The realization of circular polarization in the antenna geometry is validated through the analysis of characteristic mode theory. A maximum gain of 5.6 dBi is attained along with a port isolation of >30 dB. The proposed antenna undergoes analysis to assess its performance in the bending conditions and specific absorption rate, besides validation of diversity metrics encompassing envelope correlation coefficient, diversity gain, channel capacity loss, total active reflection coefficient, and mean effective gain has also been conducted. Finally, the proposed antenna structure is fabricated, and its performance is validated and subsequently compared with that of its simulated counterpart.

A linearly polarized dual-resonant millimeter-wave absorber for Radio Detection And Ranging (RADAR)applications is presented in this paper. The frequency-selective absorber (FSA) is composed of solitarily using the distributed elements. The proposed FSA achieves a dual-band resonance characteristic utilizing the mutual coupling between concentric square loops, the second harmonic mode of the Jerusalem cross, and the corrugated cross grids. The proposed dual-band FSA operates from 25.5 to 26.5 GHz (1 GHz) (fL) and 31.8 GHz–32.5 GHz (0.7 GHz) (fH) with minimum absorptivity of 96% and 92%, respectively. The desired frequency response of the proposed unit cell is demonstrated by an equivalent circuit model. The FSA prototype is fabricated and the simulated results are validated using experimental measurements. The proposed FSA is a suitable candidate for stealth application in defense and military systems.

An ultra-wideband current-reused low-noise amplifier (LNA) monolithic microwave integrated circuit design is presented in this letter. Negative feedback networks are employed at both stages of the proposed LNA to expand bandwidth. Furthermore, source adaptive bias networks is designed in the first stage and combined with a current-reused construction to acquire a compact chip size and maintain low power consumption. Then, the validation of design theory is implemented by employing a 0.15-µm gallium arsenide pseudomorphic high-electron-mobility transistor process. The measured results show that the proposed LNA achieves a small signal gain of 15.5–17.8 dB, a noise figure of 3–3.65 dB, and an output 1 dB compression point (OP1 dB) of 14.5–15.5 dBm from the target bandwidth of 2–18 GHz. In addition, the fabricated LNA consumes 220 mW from a 5 V supply and occupies a chip area of 1.2 × 1.5 mm2.

A compact dual layer conformal wearable quad band antenna is proposed for wireless body area network applications. The proposed button like patch antenna resonates at 2.5 GHz (industrial, scientific, and medical bands)/3.6 GHz sub six 5G band/5.75 GHz (wireless local area network/ISM band)/ and 9.8 GHz (X band) frequencies. The circular textile antenna is constructed with jean and polydimethylsiloxane substrate having a slotted ground of radius 10 mm and thickness 1.5 mm. The simulated gains obtained at the operating bands are 1.85/2.03/1.49/3.27 dBi, respectively. The designed antenna’s directed radiation pattern assures reduced backward radiation to body tissue. The specific absorption rate (SAR) analysis for the antenna at multiple resonant frequencies has also been reported, which are well below the SAR threshold of 1.6 W/kg for 1 gm of tissue, indicating that the model works adequately for wearable applications. The experimental characterization on- and off-body of the fabricated antenna validates the simulated results.

Surface acoustic wave (SAW) resonator-based compact multi-band bandpass filters (BPFs) with quasi-elliptic transfer functions (TF) and reconfigurable reflective or quasi-reflectionless characteristics are reported. They utilize bandpass-type multi-resonant acoustic wave lumped resonator (AWLR) stages, shaped by multiple in-parallel cascaded distinct SAW resonators and one lumped-element (LE) inductor. By incorporating resistively-terminated bandstop-type AWLR stages at the Radio Frequency (RF) input/output, their power reflection response can be tailored to be quasi-reflectionless. The multi-band BPF can be expanded to TF with: i) a high number of passbands by increasing the number of the acoustic wave resonators (AWRs) in the AWLR stages, and ii) higher selectivity by cascading bandpass-type AWLRs stages using impedance inverters, and iii) symmetric quasi-reflectionless characteristics. For N in-series cascaded stages, each comprising K distinct AWRs, K passbands with enhanced fractional bandwidth (FBW) can be created, with overall TF having N•(K) poles and N•(K+1) transmission zeros (TZs). The operating principles of the multi-band BPF concept are provided through detailed design examples. The concept is demonstrated through detailed design examples, with three multi-band BPF prototypes manufactured and characterized, exhibiting dual-/triple-band centered between 1029.8 and 1039.9 MHz, FBWs> 0.4kt2, and effective Q-factors> 5,000. The quasi-reflectionless prototype showed a maximum reflection of -11.5 dB.

This study presents the design and realization of a dual-port multiple-input–multiple-output (MIMO) filtering antenna system. The device shows good response in the frequency rage 1 (4.1 to 7.125 GHZ) frequency band, which handles most of the cellular mobile communication traffic. First, the single element ultra-wideband (UWB) filtenna is designed by combining a UWB antenna and a band-reject filter (BRF) where the antenna works in the frequency range from 1 to 11 GHz and the BRF is rejecting the frequency range of 3–3.42 GHz with 3.2 GHz as its resonant frequency. Finally, the proposed two-port MIMO filtenna combines two single element UWB filtennas in antiparallel manner which shows impedance bandwidth from 2.59 to 7.1 GHz with a band notch from 3 to 3.42 GHz. The structure is built on cost-efficient FR4 substrate (εr = 4.4, tanδ = 0.02) of dimensions 0.68${{\boldsymbol{\lambda }}_{\boldsymbol{c}}}$×0.27${{\boldsymbol{\lambda }}_{\boldsymbol{c}}}$×0.01${{\boldsymbol{\lambda }}_{\boldsymbol{c}}}$ (mm3), which is compact in size and utilizes a defected ground structure for further miniaturization. The proposed design is simulated using Ansys HFSS software, and after fabrication, it is measured, and the output shows good results for the proposed application. The designed antenna system is suitable for fifth-generation (5G) wideband systems.

This paper presents a method to design the response threshold (RT) of energy selective surface (ESS) based on series LC circuits (SLC_based_ESS). A simple SLC_based_ESS structure composed of metal strips and PIN diodes is used for demonstration. According to our research, the RT is rarely related to the geometry parameters of unit cells. By contrast, the RT could be designed by introducing auxiliary structures (ASs) to SLC_based_ESS arrays. With the AS, the induced currents on diodes are enhanced and thus RT is greatly reduced. Prototypes are fabricated and measured under different power levels. The results agree well with simulations, proving an effective design of RT by the proposed method.

One-bit coding metasurfaces combine two basic unit cells with out-of-phase responses. Their potential in achieving diffuse scattering has already been demonstrated. These metasurfaces can subsequently be applied to radar-signature control. This paper presents a theoretical analysis linking the scattered field to the autocorrelation of the code that encodes the metasurface. This analysis leads to a focus on Minimum Peak Sidelobes codes with autocorrelation characteristics similar to the unit impulse. Advances in other research areas have greatly enhanced the search for these kind of codes, making them directly usable for coding diffuse scattering metasurfaces. This approach is compared with existing codes, specifically examining how it performs against the optimal code found through exhaustive search in small-scale scenarios. Then, it is shown that this coding strategy facilitates the design of metasurfaces with any and large electrical sizes, achieving results comparable to those obtained through optimization-based approaches, at a significantly reduced computational workload.

This paper presents a three-stage E-band low-noise amplifier (LNA) fabricated in a 28-nm Complementary Metal Oxide Semiconductor High-Performance Compact Plus process. The proposed E-band LNA achieves a peak gain of 16.8 dB, exhibiting a gain variation of less than ±0.5 dB across the frequency range of 67.8–90.4 GHz. The measured 3-dB gain bandwidth spans from 64 to 93.8 GHz, and the minimum measured noise figure (NF) is 3.8 dB. By employing a one-stage common-source with a two-stage cascode topology, the proposed E-band LNA demonstrates competitiveness in terms of gain flatness and NF when compared to recently published E-band CMOS LNAs.

The rapid expansion of digital media platforms and their growing user base in the wireless industry necessitate communication systems to provide information at high speeds with reliable connections. Therefore, wireless communication systems with a single antenna cannot accomplish these requirements. Consequently, the access and utilization of multi-input multi-output (MIMO) antennas are becoming more common in contemporary high-speed transmission systems. This article covers the fundamentals of MIMO antenna operation, the metrics for MIMO antenna performance parameters, and the design methodologies for specifying the three most commonly used antennas (two-port, quad-port, and eight-port). Additionally, it discusses their ability to improve channel capacity significantly. It focuses on designing MIMO antennas with ultra-wideband (UWB) for 5G systems operating between 1 and 27 GHz and millimeter-wave (mmWave) bands from 30 to 100 GHz. This article is valuable for researchers interested in developing MIMO antennas for diverse applications. It compiles advanced methods related to materials, advancements, challenges, and state-of-the-art technologies used in the design of high-performance MIMO antennas. We concluded that antennas that operate at mmWave frequencies have small dimensions and suffer from isolation problems in the MIMO formation. In contrast, antennas operating below 6 GHz are large and do not suffer from isolation problems.

Massive multiple input–multiple output (MIMO) antenna is required to meet the high data transmission rate in the current 5G and future 6G mobile communication. This paper presents a novel eight-port dual-band MIMO antenna operated within the 5G new radios N77 and N79 band. The designed MIMO incorporates a self-decoupling method to obtain high isolation of 22.96 and 25 dB at the two resonances 3.48 and 4.92 GHz, respectively. The basic antenna element consists of coupling between a staircase slot and a half-wavelength size loop branch. Additionally, an inverted U-shaped microstrip section is integrated with the radiating unit to serve the purpose of self-decoupling operation. The eight antennas are symmetrically located on the two narrow substrates (of size 5.8 × 150 mm2) as a pair of four arrays. The narrow substrates make the metal rim of the 5.5″ display mobile smartphone. The designed MIMO is practically realized and experimentally tested to validate the working mechanism. The envelope correlation coefficient and peak channel capacity are obtained as 0.174 and 35.5 bps/Hz in the lower frequency and 0.069 and 39.1 bps/Hz in the higher frequency.