Search

PIN diodes, as inertial nonlinear elements, are widely used in transceiver equipment of various frequency ranges as limiters, attenuators and phase shifters. Also, with their help, it is possible to implement double-sided switching elements used, among other things, in switches and automatic antenna-matching devices of the HF range. Literary sources note that PIN diode switches in the HF range are capable of switching power up to 2 kW. In this case, only the task of switching the sub-octave bandpass filters of the transmitter is meant when operating at a perfectly matched load in a 50 Ohm path. The article discusses the features of the operation of PIN diodes in the HF range and determines the limiting values of the switched power depending on the parameters of the device and the load resistance. Examples of the circuit design of high-speed control circuits are given. The analysis of the maximum power of an automatic antenna-matching device of the HF range, carried out using the example of the most famous samples, with a load mismatch with PIN diodes, showed that in the case of a matched load, they can be used up to power levels practically equal to 2 kW. With a strong load mismatch, which is observed in most practical cases, especially when using communication facilities on mobile objects with electrically short antennas, the maximum power levels are reduced to 170 W when operating at frequencies above 3 MHz and to 100 W when operating at frequencies above 1 MHz.

ESD discharges to antennas can damage the RF front end. In particular, antennas with highly inductive ground connections allow large ESD-induced voltages at their RF terminals. This work investigates the ESD properties of an RF switch used as an antenna tuner by measuring the voltages and currents at its terminals and building a SPICE model. The goal is to predict the damage threshold when the switch is used in an RF front end.

Synchronously tuning an electrically small antenna at the symbol rate of a frequency shift keyed (FSK) modulation has been shown to efficiently increase the throughput of the transmitter. A major challenge for realizing synchronous antenna tuners is identifying a tuning element that can both block high voltages and retune quickly. This paper explores using a switched, inductive, parasitic tuning element to quickly tune a medium-power HF transmitter.

Digital forms of communication with error-correcting coding and automatic change of operating frequencies have made it possible to simplify HF radio communication. At the same time, the problem of automatic antenna matching in a wide frequency range has become more actual. PIN diodes are widely used in radio transmitting and receiving devices from high frequencies to microwaves. With their help, attenuators, phase shifters and two-way switches may be implemented. The use of PIN diodes, which are switching elements of the microwave range, in the high-frequency range imposes certain restrictions both on the magnitude of the maximum switched current and on the amplitude of the control signals. An analysis of the achievable power values of HF automatic antenna tuning unit (ATU) switched using by PIN diodes showed that in the case of a matched load, they can be used up to power levels almost equal to 2 kW in the HF range. With a strong antenna mismatch, the maximum power levels are reduced to 170 W when operating at frequencies above 3 MHz and to 100 W when operating at frequencies above 1 MHz.

International audience; We identify five types of antenna tuner control scheme, which are suitable for a wireless transmitter using a single antenna. Four of them use a sensing unit measuring electrical variables either at the radio port or at the antenna port of the antenna tuner. We also define and discuss four types of antenna tuner control scheme which are relevant to a transmitter utilizing several antennas for MIMO radio transmission. The accuracy and other characteristics of the different schemes are discussed and compared.

In this paper, a highly integrated frequency-modulated continuous-wave (FMCW) radar system with a single-antenna interface for range sensing is proposed. In this paper, a circulator structure was developed and used in the radar system with the single-antenna interface. This structure capitalizes on frequency orthogonality to separate transmitted and received signals; thus, the isolation can be improved by using integrated filters to further suppress transmitter leakage. Without an additional back-end leakage cancellation mechanism and antenna tuner, the single-antenna FMCW radar system can be devised. The proposed system is composed of a radar transceiver, a frequency synthesizer, an analog signal processor, and an AD converter; the system is fabricated using a 65-nm CMOS technology, occupies a chip area of 1.9 mm2, and consumes 147-mW dc power under a 1.2-V power supply. The implemented front-end circuit can provide an output power of 10.5 dBm with power efficiency of 30%, over 1-GHz impedance matching, an insertion loss of 2 dB, a maximum noise figure of 16.8 dB (including the following IF amplifier), $P_{1\,\text {dB}}$ of 2 dBm, and IIP3 of 7 dBm. A wireless measurement process proved that the system can provide a 37-cm range resolution over a 50-m range for a $20 \times 20$ cm2 copper plate. Finally, an FMCW radar front-end board and a digital signal processing board were implemented for data analysis, thus completing the FMCW radar sensor unit. The proposed system can be utilized for multiple applications including 1-D object tracking, 2-D localization, and 3-D object tracking.

A novel frequency reconfigurable Quasi-Yagi antenna is proposed. The antenna has two dipoles on different layers of the substrate and they are fed by two coplanar striplines. Four PIN diodes, loading inside the coplanar striplines, are used as the switches. By switching the states of the four diodes, the antenna can work in three modes with different working bands around 3.5 GHz (cover the band of WiMAX), 5.2 GHz (cover the band of WLAN) and 7 GHz respectively. In addition, the working bands can be independently tuned by adjusting several parameters of the antenna. A prototype antenna was fabricated and tested. Good agreement between the simulation and the measurement is achieved. The results prove that the antenna can realize frequency reconfiguration effectively while maintaining the pattern characteristic of Yagi antenna at all frequency.

This paper presents the analysis and design of a passive front-end (PFE) for low-power receivers. The freedom of the antenna impedance is observed and exploited to propose an inductive-antenna-based PFE. Analytical methods for the desired signal transfer and noise behavior of the proposed PFE are presented to offer insight into the proposed technique and facilitate the design. The analysis suggests that the inductive-antenna-based PFE offers higher voltage gain and lower noise figure than a standard $50~\Omega $ -based PFE does, which is confirmed by simulations. The proposed PFE and a baseband bandpass amplifier are designed in 0.18- $\mu \text{m}$ CMOS technology for the 402–405 MHz band of the IEEE 802.15.6 WBAN standard. Their combination exhibits a passive voltage gain of 11.6 dB, a NF of 14.7 dB, and an in-band IIP3 of 3.6 dBm, while dissipating 1.1 mW from a 1.2 V supply.

In this letter, an integrated multiple-input–multiple-output (MIMO) antenna system is presented. The proposed design consists of a two-element printed inverted F-shape (IFA) MIMO antenna integrated with a two-element frequency-agile annular slot-based MIMO antenna system. The IFA operates at the WLAN band, while the annular slots act as an isolation enhancement structure between the two IFA elements. Furthermore, the annular slots are tuned over the bands from 1.73 to 2.28 GHz with a minimum bandwidth of 60 MHz. The slots are made reconfigurable using varactor diodes. The integrated MIMO antenna system is designed on commercially available FR-4 substrate with dimensions $\text{50} \times \text{110} \times \text{1.56}\,\text{mm}^{3}$ . All the antenna elements are of small size, low profile, and planar in structure and hence can easily be accommodated in wireless devices for second-generation cognitive radio applications.

A dual-band electrically small antenna based on impedance matching circuit is proposed. Which is fed by coplanar waveguide (CPW). The antenna includes two twin-spiral type slot-line short stubs and three open-circuited series-stubs with slot-line loaded at the central feed line of the CPW as impedance matching network. The total size of the antenna is 12.45 mm × 13.05 mm × 0.8 mm , with K α = 0.45 and 0.95 at 2.4 GHz and 5 GHz respectively. By the introduction of the proposed impedance matching network, the syntonic frequency of the antenna is achieved at 2.4 GHz and 5 GHz. And the measured bandwidth of S 11 - 10 dB is about 7.5% and 12% of the two resonant frequencies. The proposed antenna has a very small ground plane ( 0.9 mm × 1.8 mm ). And it is appropriately applied to wireless communication for considerable radiation efficiency.

A millimeter-wave (mm-Wave) dual-feed square loop antenna is presented in this paper for 5G communications. It synthesizes identical far-field radiation patterns as a conventional single-feed square loop antenna. The dual-feed antenna (DFA) also simplifies or even eliminates the lossy power-combining network between the transmitter and antenna, achieving direct on-antenna power combining. The proposed antenna concept significantly improves the total radiated power and power efficiency of a wireless transmitter, particularly useful for 5G transmitters that normally require large output power to compensate the high mm-Wave path loss. Compared with antenna-array-based spatial power combining, the DFA only requires a single-antenna footprint and maintains the single-element beamwidth, ideal for mobile 5G communications. The dual-feed square loop antenna is designed and characterized at two potential 5G bands, i.e., 38.5 and 73.5 GHz. Conventional single-feed square loop antennas are implemented as reference designs. Closely matched antenna characteristics are achieved in measurement between the proposed DFA and conventional single-feed antenna. The dual-feed square loop antenna has measured broadside gain of 2.9 and 3 dBi, and fractional bandwidth of 13% and 14%, at 38.5 and 73.5 GHz, respectively. High-speed modulation test is also performed. A 4.3% error vector magnitude (EVM) with a −33.2-dBc adjacent channel leakage ratio (ACLR) for 6-Gb/s 64QAM is achieved at 38.5 GHz, and a 5.6% EVM with a −33.4-dBc ACLR for 6-Gb/s 64QAM is measured at 73.5 GHz, which demonstrates the viability of the proposed DFA for high-speed and complex modulations required by 5G communications.

We assess the potential error in measurements of the power transfer function corresponding to a reverberation chamber set-up when different antenna types are used for the reference and device-under-test measurements. We derive a mathematical description of the transfer function that accounts for differences in the amount of unstirred energy, represented by the spatially averaged K factor, arising from various antenna types. Our results show that loaded chamber configurations, combined with reference/device antenna pairs having significantly different radiation patterns, can result in statistically significant errors in the prediction of the transfer function. If it is possible to obtain an estimate of the K factor associated with the device antenna, this correction can improve the estimate of the transfer function that would be experienced by the device under test. Finally, we develop a method that could be used in standardized test methods to bound the uncertainty associated with the unknown K factor for common antenna types.

In this paper, a novel tunable tri-band antenna\ud is presented for concurrent, multi-band, single chain radio\ud receivers. The antenna is manufactured on a 50×100 mm FR4\ud printed circuit board (PCB), and is able to provide three concurrent,\ud independently tunable operating bands covering a frequency\ud range from 600 MHz to 2.7 GHz. The antenna performance\ud is investigated for both numerical and experimental methods\ud when using, first, varactor diodes and, second, digitally tunable\ud capacitors (DTCs) to tune frequencies, which shows the antenna\ud gain can be improved by up to 2.6 dBi by using DTCs. A\ud hardware-in-the-loop test-bed provides a system level evaluation\ud of the proposed antenna in a direct RF digitized, concurrent,\ud tri-band radio receiver. By measuring the receiver’s error vector\ud magnitude, we demonstrate sufficient isolation between concurrent\ud bands achieving 30 MHz of aggregated bandwidth as well\ud as strong resilience to adjacent blockers next to each band. The\ud data reported in this article are available from the ORDA digital\ud repository (https://doi.org/10.15131/shef.data.5346295).

Three ultra-high frequency (UHF) radio-frequency identification (RFID) tag antenna-based sensor designs for steel corrosion sensing with miniaturization are proposed in this paper. To characterize corrosion, a new antenna adopts the structure of patch antenna with a meanderline feed based on microstrip line theory. The impedance change of the meanderline feed results in detuning in the tag antenna so that this change can be captured with threshold power of the tag. Folded antenna with 3-D structure has been redesigned for miniaturization from the non-folded antenna to reduce the antenna size for spatial resolution enhancement, but the gain is reduced as well as sensitivity. A T-shape antenna is proposed to increase the gain of the miniaturized antenna and the sensitivity. Experimental studies with ThingMagic development kit on dedicated corrosion samples have been undertaken to validate the antenna designs. Resonant frequency features of the developed antenna are studied for corrosion characterization, but the bandwidth of UHF RFID limits the measurement range. Principal component analysis method is applied to evaluate different corrosion stages and reduce environmental interference.

This paper presents a multifeed antenna structure that synthesizes the desired far-field radiation characteristics with on-antenna power combining and increases the total radiated power of a wireless transmitter. The driving signals at the multiple antenna feeds are scaled properly in amplitude and phase, so that they collectively synthesize the desired on-antenna current/voltage distribution and achieve the resulting desired far-field radiation pattern. The proposed multifeed antenna offers flexibility to optimize the antenna driving impedances based on the locations of the feeds. It also simplifies the passive impedance matching and power-combining networks between the antenna feeds and the transmitter outputs, substantially increasing the total transmitter power efficiency. Most importantly, the proposed multifeed antenna achieves on-antenna low-loss power combining, which, compared with antenna array-based spatial power combining, does not suffer from narrowed beamwidth or enlarged antenna panel size. As proof of concept, multifeed slot antennas and a multifeed square loop antenna are designed and characterized at 10.3 GHz. Conventional single-feed slot antennas and a single-feed square loop antenna are also implemented as reference designs. Well matched antenna gains and radiation patterns between the proposed multifeed antennas and the conventional single-feed antennas are achieved in the measurements, demonstrating the on-antenna power combining of the proposed multifeed antennas without distorting the far-field radiation patterns.

Electrical balance duplexers (EBDs) present a potential alternative to the fixed-frequency duplexing filters used for frequency division duplexing in cellular handset radio frequency front ends. However, the transmit-to-receive (Tx–Rx) isolation can be affected by interaction between the antenna and the environment, and therefore, the EBDs balancing impedance must adaptively track time-domain antenna impedance variation. A rail scenario presents a potentially demanding use case for an EBD, as fast moving trains in the vicinity of the antenna may cause dynamically changing reflections, which can be received as self-interference. In this paper, measured dynamic antenna reflection coefficients at 745 and 1900 MHz from train mounted antennas are included in the EBD circuit simulations in order to investigate the resulting variation in Tx–Rx isolation, and determine requirements for balancing impedance adaptation. This paper also presents the results from rail-based field trials of a hardware prototype EBD, which implements real-time antenna impedance tracking. Results show that the rail scenario does result in variation in Tx–Rx isolation, but that rebalancing the EBD at the intervals of 5 ms was sufficient to maintain >50 dB isolation for ~95% of the time.

Passive implantable sensors have received considerable attention for wireless in vivo measurement of physiological parameters in challenging locations of the human body. They are considered promising alternatives to the existing catheter-based biomedical transducers and battery powered implants. In this paper, we report a novel planar reader antenna for wireless interrogation of $LC$ -based passive implantable sensors. The antenna utilizes two planar, electromagnetically isolated loops for wireless detection of the resonance frequency of the $LC$ sensors. 2-D and 3-D versions of the antenna with the identical geometry were developed for a comparative study. A comprehensive analysis of the antenna together with in vitro evaluation of the antenna performance is presented. With the proposed antenna topology, the isolation level of 58 dB within the frequency range of 1–50 MHz, and at least 37 dB up to 100 MHz was achieved. The 3-D version of the antenna demonstrated improved performance by the T/R isolation of at least 64 and 44 dB within the frequency bands of 1–50 and 50–100 MHz, respectively.

In this paper, we propose a technique for comprehensive analysis of nonlinear and dynamic characteristics of multi-antenna transmitters (TXs). The analysis technique is enabled by the development of a Volterra series-based dual-input model for power amplifiers (PAs), which is capable of considering the joint effects of PA nonlinearity, antenna crosstalk, and mismatch for wideband modulated signals. By combining multiple instances of the PA model with linear dynamic antenna simulations, we develop the analysis technique. The proposed method allows the prediction of the output signal of every antenna in an arbitrarily sized TX array, as well as the total far-field radiated wave of the TX for any input signal with low computational effort. A 2.12-GHz four-element TX demonstrator based on GaAs PAs is implemented to verify simulation results with measurements. The proposed technique is a powerful tool to study hardware characteristics as, for example, the effects of antenna design and element spacing. It can be used in cases where experiments are not feasible, and thus aid the development of next generation wireless systems.

A new set of measurement system on the Experimental Advanced Superconducting Tokamak (EAST), based on voltage and current probes, is installed on transmission line between matching system and ion cyclotron range of frequencies antenna to measure the antenna input impedance. The data can be used for impedance-matching points optimizing, as well as coupling coefficient assessment by deducing the antenna coupling resistance from antenna input impedance. The measurement error of amplitude and phase difference show distinct impact on the coupling resistance. Generally, the amplitude measurement error has a small impact on coupling resistance, while the phase measurement error significantly affects the coupling resistance. Instead of using phase detectors, phases can be extract from the power measurements. Thus, the antenna input impedance and coupling resistance can be deduced from the amplitude of voltage probe, amplitude of current probe, as well as the antenna feeding power. on previous experiments, the impedance measurement technique based on voltage probes array is utilized to evaluate coupling resistances. In EAST 2016 campaign, the load coupling resistance calculated by using such two techniques were detected and the results showed agreement.

A mechanism for driving current off-axis in high beta tokamaks using fast electromagnetic waves, called Helicons, will be experimentally tested in the DIII-D tokamak. This method is calculated to be more efficient than current drive using electron cyclotron waves or neutral beam injection, and it may be well suited to reactor-like configurations [1] , [2] . A low power (100 W) 476 MHz “combline” antenna, consisting of 12 inductively coupled, electrostatically shielded, modular resonators [3] , was recently installed in DIII-D. Initial operation showed that the plasma operating conditions were achieved under which helicon waves can be launched. Plasma operations also showed that the location of the antenna has not reduced the performance of, or introduced excessive impurities into, the discharges produced in DIII-D. The development of a high power (1 MW) Helicon system is underway. This antenna consists of 30 modules mounted on the inside of the outer wall of the vacuum vessel slightly above the midplane. Carbon tiles around the antenna protect the antenna from thermal plasma streaming along field lines. A 1.2 MW, 476 MHz klystron system will be transferred from the Stanford Linear Accelerator to DIII-D to provide the RF input power to the antenna. A description of the design and fabrication of high power antenna and the RF feeds, the klystron and RF distribution systems, and their installation will be presented.

A novel multi frequency printed antenna is presented in this article. This type of antennas is very useful for the wireless world of today. The proposed antenna covers the low frequency biomedical band as well as various mobile wireless bands such as GSM bands, Bluetooth, ZigBee, Wi-Fi, WLAN and LTE bands etc. The antenna has multi resonating point between 0.5 and 5.6 GHz. The antenna is compact and its size is 32 × 40 × 1.6 mm3. Coplanar waveguide (CPW) feed is used to excite this antenna. CPW feed improves the bandwidth of every resonating point between the above said frequency range. A detailed parametric study of the proposed prototype is presented in this paper. The results show that gain is improved from low frequency to high frequency range. The radiation pattern is directional, which is the most important need of biomedical and specific mobile wireless applications, and radiation efficiency is also good. The prototype is designed and simulated using HFSS. Further measured and simulated results are compared and a good impedance match is found between them. Overall this antenna can be used as a module with bunch of wireless applications.

© 2017 IEEE. An ultrawideband conformal capsule slot antenna, which has a simple configuration and a stable impedance matching characteristic, is described in this paper. In the past, wideband outer-wall antennas have been proposed for capsule-type applications. However, this paper shows that the outer wall is not a good choice for placing capsule antennas, since such a choice exhibits a high specific absorption ratio, low gain, and low efficiency. Instead, the antenna proposed in this paper is conformal to the inner wall of a capsule shell, and it provides a wide impedance bandwidth ranging from 1.64 to 5.95 GHz (113.6%). Furthermore, the impedance matching remains stable even with a change in the operating environment. Since in a typical application scenario a capsule will move through the digestive system, and thus experience varying environments, a wide bandwidth and stable performance are both very desirable attributes of the antenna, whose design is discussed in this paper. Moreover, the proposed antenna continues to maintain a stable impedance match even when a battery is added inside the capsule, or when there is a change in the battery size and/or its position. Given these advantages, we argue that slot antennas are well suited for incorporation into capsule antennas for the present application.

A novel shared antenna structure is presented in this communication for near-field communication and ultrahigh-frequency (UHF)-radio frequency identification (RFID) reader applications. This design is developed based on a circularly polarized gap-loaded loop antenna and then evolved to contain a two-turn coil for inductive coupling. The design procedure and the operating principles in the two scenarios are interpreted. Experimental results confirm the good performances of the proposed design with low profile and simple structure. The measured 15 dB impedance matching and 3 dB axial ratio bandwidths can fully cover the entire UHF-RFID band of 840–960 MHz. In the high-frequency band, the optimal matching circuit of the proposed structure is determined and an average transmission coefficient of 0.61 is achieved within the operating range of 50 mm.

A broadband dipole antenna with a very simple low-cost mechanical structure is proposed. This dipole of the height of 173 cm with inductor/resistor ( LR ) loading circuits is designed to operate in the frequency range of 30–512 MHz—hence a 17:1 bandwidth (178%). By choosing the optimized location of LR loads, the radiation pattern is controlled. Meanwhile, the VSWR 1:3.5 is adjusted by an input matching circuit, tuning a number of LR loads, and using a transmission line transformer. The impedance matching is better than −6.5 dB in whole frequency bandwidth. The antenna gain is gradually increased from −20 dBi at 30 MHz to −2 dBi at 512 MHz. The manufactured prototype is presented along with its measured characteristics which map well onto software simulated counterparts. The antenna is considered to be used in portable applications. Therefore, the simulations and the measurements are conducted near the human body. A simple model of the adult human body at the frequency band of the proposed antenna is used, which helps to study the effects of the human on the antenna performance. Moreover, the electromagnetic exposure on the human body is investigated. Experimental evidence is presented to verify the conclusion.

Wearable antennas are prone to bending and crumpling. This work presents the analysis of input impedance of a wearable patch antenna with milli bends using Finite Difference Time Domain (FDTD) method. FDTD method using stair case scheme is used to model milli bends at different places along the length of a wearable patch antenna and the effect of milli bends on input impedance of the wearable patch antenna is presented developing a FDTD code for it. It is shown that presence of milli bends in a wearable patch antenna significantly changed the input impedance of the antenna under consideration. It is observed that milli bends closer to the feeding strip line provided better input impedance matching. Results concluded that change in input impedance leads to change in resonant frequency and reflection coefficient of the antenna. General Terms: RF and microwave communication, Antenna design and analysis.

A novel integrated antenna that consists of spectrum sensing and frequency reconfigurable antenna, printed on a single substrate is presented here. The integration of both antennas is based on the fact that reasonably large metallization area of UWB antenna can be use as a space for printing another narrowband antenna. Prominently, the second antenna should be place on region of large UWB antenna where there is less distribution of E field. The proposed antenna senses the spectrum over a wide frequency range from 2 GHz – 12 GHz via a U shape monopole having partial ground structure. After sensing the spectrum condition, the slot antenna with reconfigurable feeding structure can switch its operating bands among six narrowband: 5.65 GHz, 3.6 GHz, 5 GHz, 2.94 GHz, 4.5 GHz, 2.15 GHz and two dual bands at 2 GHz, 5.48 GHz and 1.7 GHz, 5 GHz. In addition to this, proposed antenna can also reconfigure its frequency in wide-bandwidth using two ground stubs. Since wide band response for spectrum sensing and each of eight frequency state works independently, therefore, there is no interference among various signals.

A compact ultra-wideband (UWB) planar printed bow-tie quasi-Yagi antenna is proposed and experimentally studied in this paper. It is composed of three wideband configurations: micro-strip-line to slot-line transition structure with a shorting vias (balun), a pair of bow-tie driver, and rhombus director, which aims at breaking the bandwidth limitation of the conventional micro-strip (MS) quasi-Yagi antenna. To further improve the impedance matching, the tapered co-planar strip-line is adopted between the bow-tie driver and the balun as bridge. The overall size of the proposed antenna is only 30 mm × 27 mm. A prototype UWB quasi-Yagi antenna is fabricated and measured to verify the validity of this design. The measured impedance bandwidth, defined by −10 dB reflection coefficient, can reach an operating bandwidth of 101% from 3.62 to 11 GHz, over which the antenna exhibits excellent end-fire radiation with a front-to-back ratio of greater than 19 dB and a moderate gain of better than 3.81 dBi. In co...

A non-Foster matching network has been designed for a small cylindrical slot antenna, and its broadband matching capability has been examined at varying signal power levels. It has been observed that the non-Foster circuit (NFC) impedance changes considerably as the signal power increases, thus reducing its matching capability as well as introducing stability problems. To analyze its true advantage in transmit applications, the third-order intermodulation output intercept point (OIP3) and the gain-bandwidth product of the non-Foster matched antenna have been compared with the unmatched antenna, when both are attached to the same power amplifier. Simulations show that the unmatched antenna has a higher OIP3 and gain-bandwidth product, despite being more poorly matched. Although the OIP3 can be slightly improved by increasing the bias current of the NFC, improved linearization techniques should be studied to offset distortion effects in NFCs.

A broadband magnetic coupling antenna with low far-field gain for ultrahigh frequency radio frequency identification near-field applications is presented in this communication. The proposed antenna is consisted of a number of loop units and each unit has in-phase current along the loop. It generates a strong uniformly distributed magnetic field over a large interrogation. To meet different scenarios, the interrogated area can be adjusted by changing the number of units. The proposed antenna has low far-field gain and broadband characteristics. Mechanism analysis is carried out to provide the guidelines for the antenna design. As an example, a 10-unit antenna has been fabricated and measured. The experimental results show that the antenna achieves the impedance matching over the frequency range from 740 to 4600 MHz. And the proposed antenna achieves 100% reading rate with 140 button tags in the region of 100 mm $\times750$ mm $\times12$ mm.

The upcoming standards of wireless communications result in additional and more stringent requirements for antennas in mobile phones. In this paper, we present a frequency-reconfigurable antenna that could potentially be suited for future mobile devices. Frequency reconfigurability is achieved through a cluster of mutually coupled antenna elements that is excited with frequency-dependent weights using a multichannel transceiver. We report a mobile handset antenna cluster measuring 15 $\times $ 15 $\times $ 1.6 mm3 that covers the frequency bands of 1.7–2.7, 3.3–4.5, and 5.475–6.425 GHz with an antenna efficiency better than 90%. The operation of the antenna cluster is experimentally verified by feeding all the antenna elements with proper weights using tailor-made power splitters that represent a multichannel transceiver with adjustable amplitude and phase in each branch. The results obtained with the feed networks suggest the feasibility of the reconfigurability concept and pave way for codesign of the antenna and the transceiver.

This paper presents a narrow band frequency reconfigurable antenna for global navigation systems. Proposed frequency tunable antenna operates for GLONASS (1.601 GHz), GPS (1.575 GHz) and COMPASS (1.561 GHz) navigational systems. Antenna design consists of rectangular patches, two pin-diode switches, feed network, biasing circuitry and supply lines to make antenna operational for three frequency bands. Antenna is simulated and optimized using CST—Computer simulation technology and is fabricated on Roger RO4350b substrate. The demonstrated antenna along with being frequency agile possess essential performance characteristics like high gain, stable radiation patterns and good radiation efficiency for all three frequency bands, making it prospective choice for wireless navigational systems.

As technology is moving towards miniature structures, demand for designing efficient compact antennas is increasing simultaneously. So it would be valuable to improve the features of small antennas, such as bandwidth and gain. A compact chip-resistor loaded microstrip antenna at 2.48 GHz frequency for industrial scientific and medical (ISM) band, with dimensions of 10 × 10 mm2 is presented in this paper. With a novel geometry design, antenna is promoted to an active integrated antenna (AIA) on a two-layer printed circuit board (PCB), which contains passive antenna and active circuitry with a common ground plane. A monolithic amplifier is used to have an improvement around 10 dB in antenna gain. The impedance bandwidth has been increased during chip-resistor loading and adding active circuitry processes. For chip-resistor loaded antenna, that is 5.7 and 9.48% in simulation and measurement respectively. Moreover, the active integrated antenna has the measured impedance bandwidth of 58.7%. Since the low gain and narrow bandwidth of compact microstrip antennas might be a challenge for their operation, by compensating these drawbacks, proposed antenna would become more practical for special medical diagnostic applications, where doctors need stronger signals for monitoring.

A concept of scalable antenna arrays with an even number of radiating elements and nonuniform element spacing has been proposed. It has been shown that the proposed arrays can be fed with a frequency-selective network based on a well-known directional filter and with such a network the beamwidth can be kept constant across one frequency octave. The appropriate adjustment of coupled-line sections in such a directional filter allows for flexible selection of transmission coefficients between two outputs, and therefore, can be used for gradual switching of the signals between radiating elements. The proposed frequency-selective feeding network has been applied in a six-element antenna array operating in 1.75–3.5 GHz frequency range in which constant beamwidth around 16° has been achieved.

A low-sidelobe air-filled slot array is proposed and fabricated using silicon micromachining technology for millimeter-wave application. As is well known, the high-permittivity silicon prohibits the silicon-based antenna from having good performance. Here, this problem is addressed through manufacturing air-filled antenna on silicon substrate. An eight-way unequal power divider is adopted to excite eight air-filled slots and the excitation coefficients present a taper. At the end of the power divider, an air-filled substrate integrated waveguide cavity is used to improve antenna performance and suppress wave leakage, and eight silicon cuboids are stretched into the cavity beneath each slot to acquire good impedance matching. The input interface is selected as the ground-signal-ground structure to facilitate antenna-in-package solution that requires the integration of the antenna and chips or integrated circuits. The three-layered antenna is fabricated using through-wafer etching, gold-plating, optical alignment, and wafer bonding processes. The measured −10 dB impedance bandwidth is 1.27 GHz, and a measured fan-shaped beam at 58.5 GHz with a broadside gain of 11.95 dBi and a sidelobe level of 18.6 dB is obtained. The 3-dB beamwidth is about 14° in H-plane and 8-dB beamwidth is more than 175° in E-plane.

A single open-slot antenna for long term evolution (LTE)/ wireless wide area network (WWAN) operation is proposed for smartphone applications. To achieve dual-band operation, the narrow open-slot is fed by a simple 50- $\Omega$ vertical feedline with two horizontally protruded feeding structures. To further attain good impedance matching for these two operating bands, an L-shaped metallic plate is used. From the measured results, good antenna efficiencies of more than 40% are demonstrated across the LTE/WWAN operation in the 698–960 MHz and 1710–2690 MHz bands.

In this paper, small printed flower-shape triple notch ultra-wideband (UWB) monopole antenna with high band rejection is presented. Notch bands include WiMAX (IEEE802.16 3.30–3.80 GHz), WLAN IEEE802.11a/h/j/n (5.15–5.35, 5.25–5.35, 5.47–5.725, 5.725–5.825 GHz), and X-band downlink satellite system (7.1–7.9 GHz). By including inverted T-shape stub and etching two C-shaped slots on the radiating patch, triple band-notch function is obtained with measured high band rejection (VSWR = 14.52 at 3.58 GHz, VSWR = 15.88 at 5.69 GHz and VSWR = 6.95 at 7.61 GHz) and covers a UWB useable fractional bandwidth of 114.30% (2.74–10.57 GHz = 7.83 GHz). In short the antenna offers triple band-notch UWB systems as a compact multifunctional antenna to reduce the number of antennas installed in wireless devices for accessing multiple wireless networks with wide radiation pattern. The proposed antenna has a small size of about 0.25λ × 0.30λ at 4.2 GHz (first resonance frequency), which has a size reduction of 30% with respect to the earlier published antenna. Both the experimental and simulated results of the proposed antenna are presented, indicating that the antenna is a good candidate for various UWB applications.

In this paper, a novel topology of the coplanar waveguide fed truncated octahedron-shaped antenna is proposed. The linearly polarized antenna operates over the triple radio frequency identification technique (RFID) bands of 858–930MHz, 2.4–2.454 GHz, and 5.725–5.875 GHz at ultrahigh frequency (UHF), microwave-, and super high-frequency bands, respectively. In addition, it also supports long-term evolution 4G, TV broadcasting, and 5G bands of the electromagnetic spectrum. The $S_{11} = -10$ dB impedance bandwidth is 294 MHz (697–991 MHz), 120 MHz (2.38–2.5 GHz), 310 MHz (3.07–3.35 GHz), and 310 MHz (5.61–5.92 GHz) in the various bands. The antenna is fabricated on a polyguide substrate of $0.3023\lambda _{L}\times 0.209\lambda _{L }\times 0.014\lambda _{L}$ dimension, where $\lambda _{L}$ is the free-space wavelength at the lowest operating frequency. The antenna’s $S_{11}$ and the radiation patterns have been measured, and a good agreement between simulated and the measured results has been found. In addition, the proposed antenna is also experimentally verified for the UHF band RFID detection and the global standard for mobile communications 900 band cellular applications. We also propose a system-level schematic to integrate this antenna to other communication standards for the automated RFID applications needed for the Internet of Things.

A concept of a low-profile monopolar antenna operating in two independently reconfigurable frequency bands is introduced in this paper. For the lower band, the design utilizes a center-fed patch with shorting rods at its edges, forcing the patch to radiate as an equivalent magnetic-current loop. For the upper band, another magnetic current loop is created by adding four symmetrical resonant slots on the patch, which radiates almost independently of the shorted patch. To allow coverage of a larger bandwidth, two sets of varactor diodes are used to independently control the resonance frequencies of the two bands. As a validation of the proposed concept, two antenna prototypes, with and without reconfigurabilities, have been optimized and fabricated. Measurement results show that the low-profile reconfigurable monopolar antenna achieves two independent tunable bands, with −10-dB-tuning ranges of 31% and 22% centered at about 0.9 and 1.7 GHz, respectively. The antenna height is only $0.020\lambda _{\text {min}}$ , where $\lambda _{\text {min}}$ is the free-space wavelength at the minimum operating frequency. Importantly, stable omnidirectional patterns and vertical polarization are consistently achieved across both tuning ranges.

A design frame for developing miniature implant- able antennas at medical device radiocommunications band (401–406 MHz) is being sketched by addressing issues of resonance, efficiency, bandwidth (BW), and robustness. To that end, we visit fundamental design concepts of geometry, impedance matching, and quality factor Q and we show that a very small antenna insensitive to environmental variations and of optimum efficiency can be obtained. It is the first time, to our knowledge, that a Q calculation for miniature implanted antennas is conducted. In this paper, we consider a skin-tissue implantation scenario and planar dipoles with extremely thin profile and small aperture size. Notably, antennas’ physical volume does not exceed 25 mm3. Results indicate a strong dependence of resonance frequency on the antenna geometry for fixed physical size. In addition, external impedance matching proves to be inferior to integral matching via metallization in relation with antenna radiation performance (gain, efficiency, and quality of communication link). Finally, the quality factor Q of small fixed-size antennas highlights the influence of the design on the exhibited resonance and sensitivity response (impedance BW, tolerance to detuning, and gain stability). Simulations are accompanied by measurements with very good agreement underlying the importance of our approach.

This paper presents and characterizes a novel high gain circularly polarized (CP) antenna array for 5G applications. The array element is an antipodal curvedly tapered slot antenna (ACTSA) generating circularly polarized field. The CP ACTSA fed by substrate integrated waveguide (SIW) is convenient to integrate with substrates. By introducing two sheet metals on the two sides of the rectangular Rogers 6002 substrate, an impedance bandwidth of 18.2%, a wide 3-dB axial ratio (AR) bandwidth of 16.9%, and stable gain of 8 ± 0.6 dBic over the operating band are achieved. By employing the proposed CP ACTSA as radiating elements, a 4 × 4 high-gain wideband antenna array is proposed for 5G $E$ -band and $W$ -band millimeter-wave applications. Fabrications are carried out using wire cutting electrical discharge machine and print circuit board process, which have advantages of low cost. The whole feeding network is realized by SIW with low insertion loss at millimeter-wave band. Benefiting from the wide impedance and AR bandwidth of the new antenna element, good impedance matching and AR characteristics can be achieved over the whole working frequency band from 81 to 95 GHz by this antenna array. Gain up to 18.5 ± 1.3 dBic is also obtained.

In this paper, a novel reconfigurable open slot antenna has been proposed for LTE smartphone applications to cover a wide bandwidth of 698–960 and 1710–2690 MHz. The antenna is located at the bottom portion of the mobile phone and is integrated with metal rim, thereby occupying a small space and providing mechanical stability to the mobile phone. Varactor diode is used to cover the lower band frequencies, so as to achieve a good frequency coverage and antenna miniaturization. The operational principles of the antenna are studied and the final design is optimized, fabricated, and tested. It has achieved the desired impedance bandwidth and the total efficiency of minimum 50% in free space throughout the required bands. The antenna performance with mobile phone components and human hand is also been studied. Furthermore, the SAR in a human head is investigated and is found to be within allowable SAR limits. Finally a multiple-input multiple-output antenna configuration with high isolation is proposed; it has an identical reconfigurable open slot antenna integrated at the top edge of the mobile phone acting as the secondary antenna for 698–960 and 1710–2690 MHz. Thus the proposed antenna is an excellent candidate for LTE smartphones and mobile devices.

An antenna system for high resolution airborne synthetic aperture radar (SAR) is developed at X-band. Basic specifications of the antenna are obtained from the swath and azimuth footprint requirements of the SAR system. Series-fed printed antenna is developed to achieve these specifications. To meet stringent requirement of isolation between the transmitting and receiving antenna, an optimized ground plane with horn flares is designed. Complete antenna system is simulated and measured for return loss, mutual coupling and radiation patterns. Measured results are in agreement with the simulated results as well as the requirements of the system. Achieved isolation between the transmitting and receiving antennas is better than 64 dB at the operating frequency.