A partial notch loading technique for E-plane sidelobe reduction and gain enhancement of higher order TM₃₀ and TM₇₀ mode rectangular patch antennas is proposed. In this technique, out of phase surface current distribution regions of higher order mode patch antennas are partially removed to create new radiating edges. It is shown that superposition of radiated fields of these additional radiating edges and that of unperturbed mode can be used to achieve sidelobe reduction and gain enhancement in single-layer configuration. Two novel single layer, easy to fabricate higher order mode patch antennas, namely, notch loaded TM₃₀ mode patch antenna (Antenna 1) and notch loaded TM₇₀ mode patch antenna (Antenna 2), are presented. Antenna 1 shows a measured gain of 12.9 dBi and E-plane sidelobe levels (SLL) of −10.5 dB, whereas Antenna 2 shows a measured gain of 16 dBi and SLL of −12.8 dB. To the best of authors’ knowledge, this is the highest reported antenna gain for single-layer TM₇₀ mode rectangular patch antenna. Due to their high gain, proposed antennas are suitable for short range point to point communication applications.

A proof of concept of application of nano-ionic conductive-bridging metal–insulator–metal (MIM) switches in electronically reconfigurable band-stop filters, through design, and experimental results are presented in this article. Two similar designs of band-stop filters with a different mechanism of operation are proposed herewith. One is a microstrip, resonant open stub-based band-stop filter and the other is a microstrip tuned shorted stub-based band-stop filter. The electrical length of the stubs in both these devices are tuned by an integrated MIM switch forcing them to resonate at different frequencies and thus achieving electronically switchable band stop filtering characteristics. Working mechanism of the devices is validated with the help of developed electrical equivalent circuit models. Analysis of time stability of switch states for 1000 min with affirmative results is also presented herewith. These devices are fabricated without any soldered electrical components and without the use of any cleanroom technologies, using proven low-cost method, and are promising to work at very low power and have the potential to be directly printed on low-cost flexible substrates like paper, for potential disposable applications.

A novel compact cylindrical dielectric resonator antenna (DRA) with improved bandwidth is proposed in this study. By loading the shorting pins around the nodal line of electric fields of TM₀₁₁ mode of the DRA, an additional shorting-pin mode could be excited for the antenna, while keeping an almost constant frequency of TM₀₁₁ mode. After that, the DRA loaded with two, three, and four shorting pins is further studied. The results indicate that the resonant frequency of the shorting-pin mode is progressively pushed up by increasing its number. With these arrangements, an improved-bandwidth is obtained for the DRA loaded with four pins. Finally, the proposed DRA is fabricated and measured to validate the predicted performances. The results show that the DRA has gained an enhanced-bandwidth (|S ₁₁| < –10 dB) of about 17% (3.65–4.33 GHz) under the radiation of dual modes, while keeping the stable conical radiation patterns. Most importantly, the height and diameter of the dielectric radiator are maintained as small as 0.09 and 0.32 free-space wavelength, respectively.

This article presents a novel approach to improve the efficiency of a radiative near-field wireless power transfer (WPT) system by using metasurface. The WPT system is designed particularly for implantable applications, which operate at the industrial, scientific, and medical (ISM) 2.40–2.48 GHz band. To construct the WPT link, a patch antenna is used as the transmitting element whereas a small planar loop antenna is considered as the receiving element. The receiving antenna is implanted under the skin tissue model operating at 2.45 GHz. The metasurface with a high refractive index is placed above the surface of the skin layer to improve the power transfer efficiency. Regarding the motion of the human body, different misalignment tolerances between the transmitter and the implant receiver are discussed. Also, the effect in the change of the skin property and placement depth of the Rx antenna inside the skin tissue model is studied. Furthermore, the study of specific absorption rate for the proposed configuration is performed. Finally, the proposed WPT system is designed and experimentally verified with and without metasurface. The experimental result confirms a significant amount of improvement in power transfer efficiency due to the integration of metasurface.

This study describes the concept and design of a low-cost super broadband dipole antenna with a passive matching network. The proposed dipole antenna is designed in three steps. First, a simple planar dipole antenna with six different loads and a balanced to unbalanced (Balun) transformer is designed by the genetic algorithm optimisation. The position and value of the loads are optimised to achieve an acceptable radiation pattern and voltage standing wave ratio (VSWR) over the desired frequency bandwidth. In the next step, the shape of the printed strip dipole antenna is optimised to improve the frequency response of the designed antenna. Finally, an LC network is added to the antenna feed point to reduce the antenna VSWR at low frequencies. The final dipole antenna has a length of 1.7 m and can operate over 30–1200 MHz with VSWR ˂3 and broadside gain >−10 dBi. The proposed antenna can easily be fabricated at a low cost via the printed circuit board technology. An industrial prototype of the proposed antenna is fabricated and measured. A good agreement between measurement and simulation results is observed.

A novel ultra-high frequency radio frequency identification tag antenna designed for multi-usage is proposed in this study, which can work on the human body, blood bags, and water-filled container as well as free space. The tag antenna is fabricated on the F4B-2 substrate, whose relative permittivity is 2.65 and dielectric loss tangent is 0.002. The radiation unit is formed by four main circular loops, two semicircle loops, and four round arcs, all these loops and arcs are surrounded by an elliptical loop located on the outer edge of the substrate. The antenna has an elliptical structure, whose long axis and short axis are 76, 32 mm, respectively. In different applications, the presented antenna maintains a stable operating frequency and has good conjugate impedance matching with the tag chip.

Wireless power transfer (WPT) system with multiple transmitters (TXs) and one receiver (RX) can effectively enlarge the range of power transmission region. The power delivered to load (PDL) and power transfer efficiency (PTE) of two-TX WPT system has been intensively studied in the past few years. To achieve a wider range of power transmission, the multiple-TX system should be investigated urgently. Using Kirchhoff's voltage law (KVL) and RX-side reflected load theory (RLT), this study analyses a general multiple-TX and single-RX systems in detail. The explicit closed-form equations for the highest PDL, PTE and corresponding optimal loads are derived from the two methods. The constraint of feeding amplitude ratios need be equal to the mutual inductance ratios for the highest PTE deduced from KVL; on the other hand, inspired by TX-side RLT using in the multiple-RXs system, RX-side RLT is first proposed and can readily derive the highest PDL, PTE and optimal loads compared with KVL. Numerical simulations for three- and four-TX systems are implemented to intuitively illuminate the theoretical analysis. Experiments for two-, three- and four-TX systems have verified the accuracy of the proposed analysis.

In this study, a generalised approach for the design of high-performance differentially fed coupled-line directional couplers in inhomogeneous medium is presented for the first time. Conditions for the realisation of ideal coupled-line section under differential excitation are provided and it is shown that generally in such medium couplers feature different capacitive and inductive coupling coefficients, which significantly deteriorate circuits' performance. Therefore, the compensation technique is proposed allowing for equalisation of the differential coupling coefficients by adding appropriate compensating elements to the per-unit-length capacitance and inductance matrices of the coupled-line section. The proposed approach allows for realisation of quasi-ideal differential coupled-line couplers designed in arbitrarily chosen dielectric stack-up, and almost for arbitrarily chosen coupling. The provided theoretical analysis and resulting design methodology are verified experimentally with a 3-dB differential coupler operating at f ₀ = 1.5 GHz and realised in suspended microstrip technique. Moreover, a combination of laminate and additive manufacturing technologies was used for higher design flexibility and low-cost manufacturing.

This study proposes a compact sept-band bandpass filter (BPF) with controllable centre frequencies and bandwidths. To achieve compact size and low insertion loss, the filter deploys a single multi-mode resonator and abandons conventional source–resonator coupling structure to reduce the order of coupling sections. The fabricated BPF demonstrates seven passbands located at 1.0, 1.6, 2.3, 2.8, 3.5, 4.2, and 5 GHz, which are targeted for global system for mobile communications (GSM), wireless local area network, WIFI, and 4G/5G communication. Within the seven passbands, the minimum insertion losses are 0.9, 1.5, 0.5, 1.2, 0.9, 1.9, and 1.6 dB, respectively. The overall size of the fabricated filter is 0.1λ _g × 0.21λ _g. This work provides a new approach to obtain the most passbands of BPF while achieving less insertion-loss and enhanced selectivity simultaneously.

A simple and compact triple-band dual-sense circularly polarised (CP) microstrip line fed planar monopole antenna is presented here with ultra-wide impedance bandwidth. The proposed antenna comprised a slit-loaded semi-circular radiating patch and a stub-loaded modified ground plane. By properly embedding a slit into the patch and a stub into the modified ground plane, the proposed monopole structure radiates triple band CP in broadside direction. The overall size of the proposed antenna is 40 × 40 × 1.6 mm³. The proposed antenna is capable of generating right hand CP wave in the lower and upper CP band, while left hand CP wave is generated by the middle CP band. The measured − 10 dB impedance bandwidth is 122% (2.74–11.32 GHz) and 3-dB axial ratio bandwidths for the triple bands are 41.55% (4.08–6.22 GHz), 17.03% (7.52–8.92 GHz) and 14.68% (9.34–10.82 GHz), respectively. The measured peak gains within three CP bands are 4.24, 4.02 and 3.78 dBic, respectively.

A compact, low-cost Wilkinson power divider (WPD) of 1.3 GHz (f ₀) operating frequency, with a low-pass filtering response, is presented in this study. Power division and low-pass filtering responses are both achieved by using two symmetrical units of interdigital line resonators (ILRs). Each square unit of ILR exhibits a low-pass filtering response, with a minimum insertion loss of 0.3 dB. The dumbbell-shaped, defected ground structures are introduced for widening the attenuation band by suppressing the harmonics up to 14 GHz (up to 10.76 f ₀) and also for miniaturising the circuit. An isolation resistor of 100 Ω is placed between two output ports of the WPD for obtaining good isolation. The operating frequency of the low-pass filter is 2 GHz with an attenuation of −17 dB up to 20 GHz. The proposed structure is fabricated using low-cost substrate material FR4. Both the low-pass filter and the power divider are fabricated and measured. The electromagnetic-simulated and measurement results are experimentally verified.

A complementary metal–oxide–semiconductor (CMOS) trombone true-time delay (TTD) operating from 2 to 18 GHz is presented. The second-order all-pass network (APN) is used to construct the delay lines. The higher-order delay response of the APN allows for a better trade-off between the delay and bandwidth compared to the artificial transmission line structures. The all-pass characteristic of the APN further improves the matching performance of the TTD. In order to improve the insertion loss (IL) variations between different delay states, the source degeneration by resistor–capacitor structure is used for the switching amplifiers. Two 3-bit TTDs are fabricated in a standard 0.13 µm CMOS process, namely TTD 1 and TTD 2. TTD 1 is based on conventional switching amplifiers and TTD 2 adopts the proposed source degeneration technique. The measurement results show that the root-mean-square IL variation of TTD 1 and TTD 2 is better than 2 and 1.4 dB. The input and output return loss of the two TTDs is >12 dB. Delays of 270 and 265 ps are achieved by TTD 1 and TTD 2. The power consumption for TTD 1 is 2–6.2 mW and is 2–3.6 mW for TTD 2.

Two single-layered broadband dual-band dual orthogonal polarisation reflectarrays are designed and developed in the X- and Ku-bands. The well-known holographic technique is employed such that one antenna generates a single radiation beam in two bands and another generates a five-beam pattern in two bands simultaneously. For both antennas, a subwavelength Jerusalem-Shaped unit cell is employed to independently realise two impedance distributions for each band and, consequently, not only broaden the operational bandwidths for both bands, but also limit the mutual coupling between two sets of impedances. As a typical case, an X/Ku band 20 cm × 20 cm five-beam dual-band reflectarray with dual linear polarisation is designed and fabricated for the experimental verification. The measurement results show that the fabricated antenna has 21% 1-dB gain bandwidth (from 8.5 to 10.5 GHz) with vertical polarisation and has 8.8% 1-dB gain bandwidth (from 14.65 to 16 GHz) with horizontal polarisation. Furthermore, the maximum measured aperture efficiencies in the X- and Ku-bands are 57 and 69%, respectively.

In this study, an ultra-wideband (UWB) monopole antenna with a dynamically reconfigurable notch band, along with the associated RF-triggered power management unit (PMU) that enables the dynamic reconfigurability, are presented. The UWB monopole antenna has a rectangular slot which hosts a J-shaped stub, electrically connected with the radiator using one PIN diode switch. When the diode is OFF, the monopole antenna has a UWB characteristic, while when it is turned ON a frequency notch is created at 5.6 GHz. The diode is fed from a PMU that consists of a rectenna and a DC-to-DC active booster. When the rectenna that consists of a patch antenna and a rectifier receives a −11 dBm or higher 5.6 GHz signal, it rectifies the RF signal into a sufficiently high DC voltage. The rectified DC voltage is applied to the cascaded DC-to-DC booster as enabling signal, and the booster provides at its output terminal sufficient DC power to actuate the PIN diode and thus dynamically reconfigure the UWB antenna. The dynamically reconfigurable notch band is created immediately in response to the reception of an external, −11 dBm RF signal at 5.6 GHz, and it disappears in real time immediately after the external RF signal is removed.

A flexible dual-band dual-polarised CPW-fed monopole antenna with discrete-frequency reconfigurability is presented here. In the proposed antenna, to achieve dual-band performance, a U-slot is incorporated within the CPW-fed monopole. The antenna is fabricated on a flexible and transparent substrate so that it can be used for conformal applications. The effect of antenna bending on its performance is discussed here. Further, the proposed antenna structure is extended to achieve discrete-frequency reconfigurability. Two p-i-n diodes are incorporated within the monopole to achieve reconfigurability of higher band. A simplified equivalent circuit of the reconfigurable antenna is also presented and validated using full wave EM simulation. To validate the proposed structure, dual-band antenna and discrete frequency reconfigurable antenna have been fabricated and tested.

This study proposes a highly sensitive sensor based on localised spoof surface plasmons (LSSPs) for omni-directional cracks inspection in metal surfaces. A defected ground structure based on the complementary metallic spiral structure (CMSS) is embedded on the ground of a microstrip line to excite LSSPs, and the mode characteristics of these LSSPs are studied. Then an equivalent lumped circuit method is presented to reveal the operation mechanisms behind the trapped LSSPs. Due to the strong field confinement, LSSPs are used as a sensor to inspect cracks in a metal surface, where a 0.2-mm-wide and 2-mm-deep crack yields a 400 MHz resonance frequency shift. Meanwhile, a big resonance frequency shift is also obtained for omni-directional detection of surface cracks because of the rotational symmetry of the CMSS. It indicates that the proposed sensor is orientation independent, so that any cracks would not be missed in the testing and cracks would be located more easily. Therefore, the proposed sensor has more potentials than other sensors in actual practice.

A 100 W electronically controlled impedance tuner is introduced and experimentally investigated here. The proposed tuner is composed of two individually controlled coupled evanescent-mode (EVA) cavity resonators implemented on a printed circuit board (PCB) using substrate-integrated waveguide (SIW) technology. The contactless tuning mechanism relies on two high-resolution external linear actuators controlling the gap size of each resonator with submicron accuracy. A 3.3 GHz prototype tuner successfully handled up to 100 W of input power with ∼90% Smith chart coverage at the centre frequency and about 52% bandwidth demonstrating at least 50% coverage. Exhibiting low loss of 0.56 dB and very high stability as well, the proposed impedance tuner is a viable solution for high-power applications where electronic precise tuning is desired.

This study presents a push–push oscillator architecture based on differential gate equalisation to enhance the oscillation frequency while providing relatively high output power with ultra-compact layout form factor. The frequency enhancement is derived as a function of the equivalent RLC model of the oscillator's main constituents. The proposed principle is applied to a terahertz oscillator in the 200–300 GHz range to mitigate the excessive substrate and skin effect losses in standard digital 65-nm complementary metal–oxide–semiconductor technology at such high frequencies. The design concept is validated using two single-stage push–push oscillators. The first oscillator shows −8.1 dBm output power at 250 GHz oscillation frequency and −106.8 dBc/Hz phase noise at 10 MHz offset while consuming 76 mW power from 1.5 V DC supply voltage. The chip area is 200 × 250 μm². The second oscillator provides −14.8 dBm output power at 285 GHz and −106 dBc/Hz phase noise at 10 MHz offset with 80 mW power consumption from 1.5 V DC supply. The chip area is 200 × 200 μm².

Here, a small-size band-pass filter is designed using a new split-ring resonator (SRR). First, the geometric optimisation method is used to obtain the high miniaturisation of the proposed SRR compared to the conventional structures. Accordingly, the reduction rate has reached 51%. The second part of this study is devoted to the development of a band-pass filter using the proposed SRR topology. A Chebyshev-type band-pass filter has been designed. The purpose is to have a miniaturised structure, low insertion loss, and high out off-band rejection. This filter is composed of two integrated arms SRR placed in series with a defected ground structure (DGS) to increase the coupling between the resonators, and a low-pass filter integrated into the resonators to improve the level of rejection. The resonance frequency has been approximately measured at 1 GHz and the size has been valued at 0.114λg × 0.083λg, thus achieving miniaturisation up to 78% compared fabricated and experimentally validated. The measured insertion loss has been found to 0.8 dB and two transmission zeros helped to ensure the steep sides of the transmission band.

In this study, a suitable sub-mW frequency down converter for internet of things is presented. It is based on a single balanced switched transconductance mixer driven by a current-reuse LC voltage controlled oscillator (LC-VCO). For cognitive radio demonstration, the frequency converter is implemented with a tunable low-noise amplifier (LNA) in 0.13 µm standard complementary metal oxide semiconductor (CMOS) technology. Post-layout simulations return a gain conversion of 27 dB with a single-sideband noise figure of 8 dB (LNA included) for a consumption of 0.97 mW under a voltage supply of 1.2 V and an active area of 0.4 mm². The stand-alone LC-VCO prototype exhibits a measured phase noise of −102 dBc/Hz at 1 MHz offset while showing −114 dBc/Hz in the post-layout simulation. The LC-VCO measured power consumption is only 260 µW from 1 V voltage supply with an active area of 0.173 mm².

In this study, an internal antenna integrated into a 49-inch TV model is presented, operating in the ultra-high frequency (UHF: 470‒771 MHz) band for signal reception in ultra-high definition television (UHD-TV) applications. The design of the proposed antenna has encountered major challenges such as relatively narrow impedance bandwidth, limited space, the effect of material properties, and the electromagnetic interference from the other components inside the TV that deteriorate the performance of the antenna considerably. The antenna is positioned directly on the bezel frame (made of polycarbonate-acrylonitrile butadiene styrene: ԑ _r = 3.5, tan δ = 0.005) of the TV model as the substrate for the antenna. A monopole-type antenna is chosen to easily implement along the long side of the bezel frame in a very narrow spacing between the display and the casing of a TV (∼2.5 mm). Combined with a sleeve feed, tapered line, and parasitic strips, the proposed internal antenna exhibits a wideband impedance characteristics. The measured results show that a radiation efficiency of higher than 70% and a peak gain of 4.8 dBi are obtained over the operating frequency range of 430‒940 MHz (relative bandwidth of 75%), which cover the entire UHF band. These results indicate that the proposed antenna is very suitable for UHD-TV applications.

It is well known that the beamwidths of horn antennas are inversely proportional to frequency. Previous studies point to minimum ±12% beamwidth stability within a maximum of 2.5:1 bandwidth (BW) ratio. To extend this BW, a design methodology for broadband double-ridged horn antenna (DRHA) is proposed and applied to 4.5–18 GHz frequency band. Firstly, a conventional DRHA is designed and studied to compare the beamwidth variation of wideband horn antennas. By explicitly addressing the shortcomings of conventional DRHA, DRHA is redesigned and near-constant beamwidth DRHA is proposed using the modifications implemented on the sidewalls. The antenna utilises ridges to extend the frequency band, unlike other wideband constant beamwidth horns. The authors show that ridged horns, whose dimensions are appropriately designed and modified, can have stable beamwidths. Then, properly positioned curved pinwalls are designed to provide considerable improvement in H-plane beamwidth constancy. Broadband double-ridged waveguide-to-coaxial adapter is also designed for 50 Ω reference. The prototype is manufactured, and the measured antenna exhibits wideband characteristics with 30.9° ± 2.7° half power beamwidth in H-plane over 4:1 BW ratio. This variation corresponds to ±8.7% beamwidth stability along with the target frequency band.

In the past few years, the limitation of homogeneous electromagnetic metamaterial (EMMM) in magnetic field modulation had been proved by many researches. The introduction of inhomogeneous EMMM (IEMMM) provided a significant progress in improving the range and efficiency of the wireless power transfer system (WPTS). An IEMMM with three kinds of effective permeability came up here. By analysing the effective permeability characteristics of the circular, square, and ‘8’-shaped coil unit cell and the modulated regulation of magnetic field by negative permeability medium, a two-dimensional IEMMM with combinations of square and ‘8’-shaped coil unit cell were studied. The finite element simulation results of WPTS with IEMMM proved an improvement in magnetic field modulation and flux leakage control. In the WPTS, the designed IEMMM is able to improve the power transmission efficiency by up to 28%.

In this study, a dual band band-stop filter based on split ring resonators (SRR) over a ground plane with unequal rings is proposed and characterised. The proposed SRR design method, which is demonstrated here, ensures the control of the resonance frequencies and their respective bandwidths. The lengths and coupling regions of each ring are arbitrary, making possible the control of, not only the separation between the two generated resonances, but also the bandwidth ratio between the pass-bands, or quality factors. The full characterisation of the resonators involves the computation of the resonant frequencies and the current distributions at the resonances. These current distributions are used to obtain the electromagnetic energy stored in the resonator that, in turn, is required to estimate the quality factor of each resonance. The dual band band-stop filter is composed by four proposed SRRs coupled to a transmission line showing that, indeed, both the centre frequencies and its bandwidth ratio can be controlled. The presented results confirm the reliability of the proposed method in the design of passive devices.

Here, a compact balanced bandpass filter (BPF) with high selectivity and good common-mode (CM) suppression is proposed by adopting the TM dual-mode substrate integrated waveguide (SIW) cavity. The SIW cavity is connected to the input and output by the way of microstrip-slotline transition. Under differential-mode (DM) operation, two TM modes (TM₁₂₀, TM₂₁₀) of the SIW cavity can be effectively excited, and simultaneously two transmission zeros (TZs) can be generated near the passband edges. Meanwhile, by designing the rotation angle and size of coupling slots reasonably, the deep stopband performance can be realised over a wide frequency range. Furthermore, the CM signal is effectively rejected because the magnetic current cannot be transferred to the coupling slot from the virtual open-ended microstrip feedline. Finally, a compact balanced BPF prototype for WLAN application has been designed and fabricated. Good agreement between simulated and measured results is obtained.

A coplanar waveguide fed metamaterial antenna based on two-unit cell composite right/left handed transmission line (CRLH-TL) loaded with resonating rings is presented. The bandwidth is enhanced by merging the zeroth-order resonance and first positive-order resonance of CRLH-TL with two additional resonances due to resonating rings. The measured results show a – 10 dB fractional bandwidth of 71.11% (2.9–6.1 GHz) with realised gains of 2.35, 3.2, 3.75 and 3.6 dBi at the resonant frequencies 3.4, 4.3, 5.3 and 5.7 GHz, respectively. The peak realised gain is found to be 4.5 dBi at 4.9 GHz. The simulated radiation efficiency is >61% for the entire band of operation with a peak value of 88.75%. A good agreement is found between measured and simulated results. The proposed antenna is suitable for WiMAX (3.3–3.8 GHz) and WLAN (5.15–5.85 GHz) applications.

Here, a silicon-substrate-based four element antenna system is investigated by using a coplanar frequency selective surface (FSS) as a novel parallel reflector to improve radiation and transmission characteristics of the antennas. The four antennas are arranged around the square FSS, and one of the antennas is used as the transmitting element, while the other three as the receiving ones. It is found that, owing to the stopband filtering and the linearly changing reflection phase of the designed coplanar FSS, the gain and directivity of the transmitting antenna have been greatly improved, and that the antenna system transmission coefficients, including S ₂₁, S ₃₁ and S ₄₁, have been significantly increased. Two types of the antenna systems have been designed and fabricated on a P-type silicon wafer substrate for the cases with and without a coplanar FSS reflector. The measured S-parameters are essentially consistent with those simulated. In comparison with the case without the FSS, the transmission coefficients of S ₂₁, S ₃₁ and S ₄₁ for the system with the FSS have been increased about 6.42, 5.97 and 5.89 dB at the center frequency of 5.42 GHz, respectively. Furthermore, the proposed coplanar FSS exhibits distinct advantage of low-profile compared to the conventional vertical FSS reflector.

This study presents a new design of a reduced volumetric ultra-wideband (UWB) antenna using innovative dielectric based on the use of geopolymer material which is safe and eco-friendly. The created antenna is intended to radiate in the air. The impedance mismatch due to interface dielectric/air at the aperture of the antenna imposes to choose dielectric material with an appropriate permittivity value. In this study, the authors focus on the experimental protocol that they use to elaborate a dielectric material with suitable dielectric properties over an UWB domain. An experimental phase of dielectric properties assessment is also described. The conceived antenna is inspired by K-antenna which constitutes the starting point of the proposed new antenna design, particularly because of their small dimensions. The antenna is intended to operate in a frequency band ranging from 300 MHz to 3 GHz. The authors demonstrate that the use of an appropriate innovative dielectric material like a geopolymer is an efficient way to reduce the antenna size. Furthermore, the behaviour of the antenna filled with geopolymer is validated using experimental results.

Software-defined radio (SDR) is an advanced wireless transmission paradigm that supports all the consumer wireless protocols such as 2G, 3G, Long-Term Evolution, Wi-Fi (2.4 and 5 GHz), Bluetooth, and Zigbee, by software rather than hardware. A typical frequency band of operation is in the range of 0.5–6 GHz. The challenge to bring an SDR system on portable devices is the availability of ultra-wide-band compact amplifiers with a high gain over a wide frequency band. A novel hybrid silicon bipolar junction transistor (BJT) and an enhancement-mode pseudomorphic-high-electron-mobility-transistor (E-pHEMT) matrix amplifier with two rows and four columns (2 × 4) of transistors are designed, realised, and tested demonstrating a 0.65–5.8 GHz frequency band to satisfy the SDR specifications. The novel optimum filter-matching technique is applied to optimise the performance and overcome the limit of the hybrid approach. The proposed matrix amplifier exhibits an average gain of 37.5 dB and an average output power of 18 dBm across the 0.65–5.8 GHz band with only 3 V supply voltage. The gain is the highest in the state of the art for the frequency range. A bandwidth of 5.15 GHz, 20.3 dBm above the 1-dB compression point at 1.35 GHz, 10–16% power added efficiency, and 1.2 W DC power consumptions are obtained.

Most of target identification methods compare information of the backscattered field with an existing lookup table. Therefore, the identification of targets outside the table is impossible. However, by applying proper signal processing algorithms, some information about the target can be deduced. In this study, a new approach to estimate the circumferential size of radar targets, without their identification, is proposed on the base of a transient scattered field. Scattered transient response from the target consists of two parts: early time and late time. The early-time response corresponds to direct reflection and the late time is related to oscillation phenomena corresponding to surface-creeping waves and cavity waves. The time difference between the the start of early time and late time responses corresponds to a time interval in which creeping wave travels the geodesics surface path of the target. Therefore, by calculating the time difference between these two successive parts of response, the circumferential size of the target can be estimated. The start time of these two parts is determined by the matrix pencil method. In this study, the circumferential sizes of various simple targets such as cylinder, disc, cube, and a complex object, with an estimation error of <10% are calculated.

Due to the time-dependent load-elongation characteristic of cables, the cable-net reflector antenna shows a creep and recovery behaviour which has limited the development of the cable-net reflector antenna with high frequency and high stability. Therefore, this study is dedicated to investigating a time-dependent radiation pattern analysis method for cable-net reflector antennas. Based on the physical optics (PO) method, formulas are firstly established for the time-dependent far-field radiated pattern analysis. To avoid the repetitive computation of PO radiation integrals and improve the calculation efficiency, the exponential error terms are expanded by the Taylor series at the mean values of phase errors in each small region and the time factor is separated from the integral for some special case. Eventually, an axis-symmetric reflector antenna is taken as a numerical example to verify the practicability, validity and robustness of the proposed method.

A four-way power combiner with small cross-sectional size and high power capacity is investigated in this study. The design is based on the cascaded structure of three rectangular hybrid rings and one coaxial-to-waveguide transition. The combiner consists of coaxial and waveguide structures to ensure high power capacity. The compact cross-sectional size (0.71 λ × 0.74 λ at the centre frequency) is achieved by employing transverse electric magnetic (TEM)-mode coaxial line structures. A prototype power combiner is fabricated and tested to verify the design results. It has been demonstrated that the proposed power combiner has a power capacity of 16 kW. The return loss is better than 25 dB, isolation degree higher than 27 dB, and amplitude imbalance within 0.16 dB limits in the operating band 8–9 GHz, validated with both simulations and experiments. The proposed structure is suitable for kW-level power combining and it can also be implemented in planar forms for a wider range of applications.

In this study, a compact low-pass filter (LPF) and two compact dual-wideband band-pass filters (BPFs) are proposed based on a connected network of complementary split-ring resonators (CSRRs) and open CSRRs (OCSRRs). The LPF is designed based on microstrip structure, and then the structure is changed to quarter-mode substrate integrated waveguide for designing the dual-band BPFs. The 3 dB cutoff frequency of the LPF is 1.84 GHz and its size is 0.094λ _g × 0.094λ _g, where λ is the guide wavelength at 3 dB cutoff frequency. The LPF has a wide stop-band, up to 16 GHz. The first proposed dual-wideband BPF has the centre frequencies of 3.85 and 8.03 GHz, with 3 dB fractional bandwidths of 31.69 and 13.7%, respectively. Finally, a sharper dual-band BPF is obtained by cascading two proposed dual-wideband BPFs and optimising them for the desirable response. The measured centre frequencies of the second dual-band BPF are 3.65 and 7.15 GHz with 3 dB fractional bandwidths of 28.21 and 12.52%, respectively. The measurement results of the fabricated filters are in good agreement with the simulation ones. The filters are compared with similar reported filters in the literature, which confirm the compactness of the proposed filters..

In this study, an investigation is conducted to realise the possibility of organic materials use in radio frequency (RF) electronics for RF-energy harvesting. Iraqi palm tree remnants mixed with nickel oxide nanoparticles hosted in polyethylene, INP substrates, is proposed for this study. Moreover, a metamaterial (MTM) antenna is printed on the created INP substrate of 0.8 mm thickness using silver nanoparticles conductive ink. The fabricated antenna performances are instigated numerically than validated experimentally in terms of S ₁₁ spectra and radiation patterns. It is found that the proposed antenna shows an ultra-wide band matching bandwidth to cover the frequencies from 2.4 to 10 GHz with bore-sight gain variation from 2.2 to 3.43 dBi at maximum. The antenna size is compacted to a 32 mm × 24 mm using a fractal-shaped MTM when mounted on the INP substrate with a relative permittivity ɛ _r = 3.106−j0.0314 and a relative permeability µ _r = 1.548−j0.0907. Finally, the maximum obtained voltage from the proposed antenna is found about 2 V at 2.45 GHz and 2.5 V at 5.8 GHz, where, the corresponding measured equivalent isotropic radiated power is about 2.35 W at 2.45 GHz and 6.12 W at 5.8 GHz.

A new compact four-port multi-input-multi-output (MIMO) dielectric resonator (DR) antenna is proposed with pattern diversity. The antenna contains four DR elements, the epsilon-shaped and cylindrical. These four DR elements are placed together such that they resonate at the same frequency. The specific geometry of the DR elements allows to place them at separation which is much smaller than operating wavelength. Hence, the combination of the four DR elements acts as a single DR. This helps in maintaining the compactness of the antenna structure. The antenna operates with the hybrid of modes and excited in epsilon-shaped and cylindrical DR elements, respectively. The excitation of these orthogonal modes helps in obtaining the pattern diversity allowing the antenna for multi-directional coverage. The antenna provides 15.73% overlapping 10 dB impedance bandwidth with the variation of gain within ranges 4–6 and 6–6.5 dBi at port 1/2 and port 3/4, respectively. In addition, the antenna provides the high radiation efficiency >93% at port 1/2 and 97% at port 3/4. Other parameters required for MIMO applications such as envelope correlation coefficient and diversity gain are within the acceptable limits.