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Meander‐line and multi‐layer antennas have been used extensively to design compact UHF radio‐frequency identification (RFID) tags; however the overall size reduction of meander‐line antennas is limited by the amount of parasitic inductance that can be introduced by each meander‐line segment and multi‐layer antennas can be too costly. In this paper, a new compact antenna topology for passive UHF RFID tags based on zeroth order resonant (ZOR) design techniques is presented. The antenna consists of lossy coplanar conductors and inter‐connected inter‐digital capacitor (IDC) unit‐cells with a ZOR frequency near the operating frequency, which is a key component in the design process because the unit‐cells chosen for the design are inductive at the operating frequency. This makes the unit‐cells very useful for antenna miniaturization. The new design in this work has several benefits; namely the coplanar layout can be printed on a single layer, matching inductive loops that reduce antenna efficiency are not required and ZOR analysis can be used for the design. Finally, for validation, a prototype antenna was designed with a unit‐cell ZOR resonant frequency of 900 MHz, fabricated and characterized. A maximum read‐range of 7.6 m was determined.

A high sensitivity Class-3 ultra high-frequency (UHF) radio-frequency identification (RFID) system based on harmonic backscattering to achieve a long read-range is presented. Harmonic backscattering is a promising solution to solve the carrier leakage issue of UHF RFID reader to improve the sensitivity. In the proposed RFID system based on harmonic backscattering, the RFID reader transmits data with the fundamental frequency carrier and receives data with its second harmonic carrier, and the RFID tag employs a rectifier to generate both DC power and the second harmonic carrier for backscattering without impedance mismatch. The first harmonic Class-3 UHF RFID system based on National Instruments software defined radio platform is proposed and implemented. The proposed semi-passive harmonic RFID tag has − 20 dBm sensitivity. Test results show that the harmonic RFID system has a − 101 dBm sensitivity with the harmonic RFID tag whose signal-to-blocker ratio is − 7 dB at 20 m communication distance.

A simple internal antenna that combines a planar inverted F antenna (PIFA) and a loop antenna to achieve wideband (BW ∼ 48%) operation in ultra-high frequency (UHF: 470–771 MHz) band for digital television (DTV) applications is presented. The design allows the installation of an antenna within a TV model, thereby addressing the limitations of space. The 49-inch DTV is used for the practical implementation experiment. The TV bezel (made of polycarbonate-acrylonitrile butadiene styrene (PC-ABS): er = 3.5; tan δ = 0.005) is used as the substrate for the antenna design. The antenna is placed on the top edge of the TV model. With the combination of the PIFA mode and loop mode operations, the operating bandwidth of the proposed PIFA-loop antenna is significantly broadened. The measured results show that the proposed antenna has wide bandwidth of about 410 MHz (460–870 MHz) and suitable radiation performance with higher than 2.2 dBi of peak gain and 47% of efficiency within the operating bandwidth.

A multiple-port reader antenna for ultra-high frequency (UHF) radio-frequency identification (RFID) near-field and far-field applications which has three modes is proposed and studied. Three fed-ports are designed into the structure, which provide different radiation properties. Specially, far-field radiation for two orthogonal polarisations and near-field operation based on magnetic field coupling can be modified by feeding different corresponding port. The RFID reader antenna can work at three different operations within 820–880 MHz, including European UHF (865–868 MHz) and Chinese UHF (840–845 MHz) bands. Design details, simulation, and measured results are also presented.

The fabrication and analysis of a flexible and stretchable 3D printed passive ultra-high frequency (UHF) radio-frequency identification (RFID) tag are presented. The tag is fabricated on a flexible 3D printed Ninjaflex substrate and the conductive part of the tag consists of stretchable silver conductive paste dispensed with direct write method. The details of the 3D printing of the substrate, the characterisation of the substrate material at the UHF band, the direct write dispensing of the tag antenna, and the simulation and wireless measurement results of the fabricated tag are outlined. Moreover, to verify the flexibility and stretchability of the tag, strain reliability results of the tag are presented. Measurement results show that initially the manufactured tag achieves a 10.6 m read range. After 100 times of harsh stretching, the read range is still 7.4 m. Overall, the performance of the tag is robust and concludes that the fabrication methodology can be used in the manufacturing of RFID tags for future identification and sensing applications.

A planar broadband circular tag antenna operated at ultra-high frequency (UHF) band for radio-frequency identification (RFID) system is proposed. By adding a pair of T-arc-shaped strips and parasitic step strips, excitation of multi-resonant modes can approximate reach with the operating half-power band from 848 to 963 MHz, which covers the required bandwidth for worldwide UHF RFID (860–960 MHz) system. Moreover, the measured read distance of this design can reach 3.8 m, and exhibits good unidirectional radiation patterns in the X–Z and X–Yplanes.

The ultra-high field (UHF) small-animal MRI (sa-MRI) device provides a powerful platform for translational imaging. To achieve a high signal-to-noise ratio, as well as sufficient signal homogeneity in abdominal imaging, the RF coil has to be precisely tuned. A novel geometry for a high-permittivity material (HPM) was designed and integrated into an enlarged (90 mm) birdcage (BC) RF coil. The geometrical design of the HPM attachment was based on a computational calculation, and was compared with the commonly used 72 mm bandpass filter BC coil without any HPM attachments. The resulting RF transmission (|B 1 +|) map clearly shows that the increased coil diameter led to a decreased |B 1 +| intensity. However, this loss in field intensity was mitigated by optimally integrating the HPM attachment with the coil. As a result of this attachment, the proposed design exhibits superior |B 1 +| intensity and uniformity along the main magnetic field z-direction.

A simulation model of RFID backscatter signals developed under Ansoft designer environment is proposed. Despite the complexity of RFID tag and the hybrid properties of the backscatter signal, the model fits very well with measurement. An example of application that reveals the collision problem in multi-tag environment is performed and confirmed by measurements.

Diode-switching that can be used to introduce frequency agility into antennas produced by thermal transfer printing is demonstrated. The particular example is a triangular Sierpinski fractal pattern with two PIN diodes to switch between operation optimised for the 800 MHz ultra-high frequency (UHF) band (diodes on) and 2400 MHz ISM band (diodes off). Our measured results show an improvement in S 11 in the UHF band from −2 to −28 dB and from −7 to −30 dB at 2400 MHz, when switching the diodes appropriately. The measured bandwidth is 200 (1000) MHz, and the measured directivity is 3.1 dB (5.2 dB) while the measured gain is −5.2 dB (6.7 dB) for the diodes on (off).

An ultra-compact water loaded, 3D reconfigurable antenna is presented for digital video broadcasting-handheld (DVB-H) and ultra-high frequency (UHF) applications. By integrating a varactor diode, the operating frequency of this antenna can be continuously tuned from 463 to 900 MHz. A mixture of the water and water holder is effectively utilised as a dielectric loading to reduce the size of the antenna by 50%. The radiating element occupies a very compact volume (0.013λ × 0.016λ × 0.005λ at 470 MHz). Measurements are conducted to qualify and validate the antenna performance. It is demonstrated that this new antenna is an excellent candidate for UHF and DVB-H applications.

As an alternative to classical ultra-high frequency (UHF) radio-frequency identification (RFID) tag localisation methods (e.g. angle of arrival or received signal strength), a new angle-of-activation approach is presented that uses digital multichannel transmit beamforming. By pivoting the main lobe of the interrogator's transmit antenna array utilising the very sensitive response threshold of passive UHF RFID tags, the tag direction is estimated. The presented three-channel digital beamforming hardware pivots the main lobe of a circularly polarised antenna array in a range of ±52° with an angular resolution of 0.02°. It estimates the direction of a circularly polarised tag with a mean measured accuracy of 0.9° in a basic multipath environment.

A new method for the wireless monitoring of a battery-free threshold temperature sensor based on a passive ultra-high-frequency radio-frequency identification (RFID) tag integrated with a bimetal thermostat switch is presented. The strategic placement of the switch brings about a strong modification in the tag antenna impedance as the temperature crosses over a threshold value. Optimisation of the narrow-band tag antenna to operate at the edges of the 902–928 MHz frequency-hopping spread spectrum RFID in the different switch states provides separate sub-bands for the readout above and below a threshold temperature. The results show that this enables an unambiguous sensor readout by monitoring the backscattered signal strength.

A balun designed on laminated epoxy PCB to measure inductive ultrahigh- frequency-balanced antennas is presented. Its objective is to minimise the reflection coefficient at its unbalanced input when the antenna is connected to its balanced output. This improves the accuracy in the posterior extraction of the antenna parameters from the measurement of its reflection coefficient. Theoretical considerations, design parameters and experimental results with an evaluation antenna are shown. Fil: Peruzzi, Marcelo. Universidad Nacional del Sur. Departamento de Ingeniería Eléctrica y de Computadoras; Argentina Fil: Masson, Favio Roman. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones en Ingeniería Eléctrica "Alfredo Desages". Universidad Nacional del Sur. Departamento de Ingeniería Eléctrica y de Computadoras. Instituto de Investigaciones en Ingeniería Eléctrica "Alfredo Desages"; Argentina Fil: Mandolesi, Pablo Sergio. Universidad Nacional del Sur. Departamento de Ingeniería Eléctrica y de Computadoras; Argentina Fil: Perotoni, M.. Universidade Federal do ABC; Brasil

For demonstrating autonomous operation of the Internet of things (IoT) smart sensors, the compact folded dipole rectenna with radio frequency (RF) energy harvesting is proposed. The rectifying circuits in the proposed rectenna consist of the impedance matching network and the voltage multiplier for the optimised received power. It has achieved the RF-dc conversion efficiency of approximately 23% when illuminated by a radio signal of 1 mW available power from the commercial UHF RFID reader.

The fragment-type appearance of two-dimensional barcodes provides the hint of embedding a fragment-type ultra-high frequency radio frequency identification (UHF RFID) tag into the barcode. In this reported work, genetic algorithm searching is used to select which modules in a quick response (QR) barcode should be metalised and connected to form the RFID tag antenna. The design is demonstrated by embedding a 915 MHz UHF RFID tag in a QR barcode label of dimensions 14.5 × 14.5 mm on a single-sided PCB.

A new chipless radio-frequency identification (RFID) tag using the micro-electro-mechanical system (MEMS) technology is presented. The tag can operate at the conventional UHF band for RFID applications and can be implemented using a basic fabrication process. In the presented scheme, MEMS switches are used as programmable elements to support the communication between the tag and RFID interrogators.

Two shorted inverted-L radiating elements are located on the orthogonal corner of the square substrate and connected to each output port of a Wilkinson power divider. A shorted inverted-T strip is placed on the other corner of the square for a perturbing resonator to generate circularly-polarised (CP) radiation in the UHF band. Proper adjusting of the horizontal and vertical lengths of the inverted-T strip will differentiate two orthogonal linearly modes with 90° phase difference for a good CP radiation. Simulated and measured results indicate that the proposed structure can achieve circular-degree polarisation operation. A measured impedance bandwidth (VSWR ≤ 2) of about 16.4% (810–960 MHz) and a 3 dB axial-ratio (AR) bandwidth of about 4.4% (890–930 MHz) at 915 MHz were obtained.

The design and implementation of an electrostatic discharge protection suitable for UHF RFID devices in CMOS technology is presented. The circuit implements three fundamental functions for the RF interface: power limiting, backscatter modulation and electrostatic discharge protection. Since all functions are achieved by the same MOS device the additional shunt capacitance at the RF inputs is limited. Therefore the maximum reading distance of the RFID device is improved without sacrificing the electrostatic protection level.

Presented is a methodology for measuring the power backscattered by ultra-high frequency radio frequency identification (UHF RFID) tags by using a modes stirrer reverberation chamber. The actual measurement methodology is described and its advantage and disadvantage against the conventional setup using anechoic chambers are outlined. Then, some results of power measurements performed with the three Gen2 class 1 tags are presented. The experimented tags' sensitivity and radiation efficiency as a function of incident power are finally derived. The results are very encouraging and demonstrate the feasibility of such a characterisation in modes stirred reverberation chambers. All the measurements were carried out at a single frequency of about 866 MHz.

A wideband coupled transmission line (CTL) cell to measure the operating range of an UHF RFID (ORUR) is presented. Also, an ORUR test system is proposed to increase the isolation to more than 55 dB. It is shown that the ORUR measured by this proposed cell agrees well with the measured data using a fully anechoic chamber.

Inkjet printing and photonic sintering parameters for silver and copper nanoparticle inks on flexible polyimide and environmentally friendly cardboard substrates have been studied. The results were utilised to manufacture prototype passive ultra-high frequency (UHF) radio-frequency identification (RFID) tag antennas. The manufactured tags showed peak read ranges of 2.9–5.5 m.

Results are presented of high-resolution time delay and angle-of-arrival measurements behind a large building in an urban microcell. It is demonstrated that in this particular case the electromagnetic field is dominated by contributions resulting from transmission through the building. The associated loss over free-space loss is < 30 dB. This makes clear the importance of modelling propagation through buildings surrounding the base station in the planning stage of urban microcells.

A four-way travelling-wave power divider/combiner was designed and implemented by using lumped LC π-networks. For application around the upper VHF and the lower UHF bands, microstrip line is not suitable as the physical quarter-wave length is too long. Therefore, the authors introduce another implementation method of using lumped elements.

A wideband adaptive isolator for a UHF RFID reader with a minimum component count is introduced. The operation of the device is based on a reflection from a variable load, which is connected to a port of a hybrid coupler. The other ports are connected to the receiver (RX), transmitter (TX) and antenna ports of the reader. The isolator provides an isolation of 50 dB from TX to RX at the 800 MHz-1 GHz band, covering the worldwide UHF RFID bands. The adaptive system ensures high isolation up to an antenna return loss of 6 dB, or reflection coefficient of 0.5. The measured loss in the TX-to-antenna and antenna-to-RX paths is 4 dB.

Field tests have been performed in a high density urban environment to evaluate two important aspects of shadowing variability in land mobile radio links. These factors are the magnitude of variability and the rate at which variations decorrelate with time and spatial movement. The former was found to be significantly influenced by the size of the field test area. 1/e decorrelation times of the order of 15 s and decorrelation distances on the order of 100 m appear common.

A low-cost, wideband, flexible antenna for radio frequency identification tags mountable on curved metal surfaces is presented. The antenna consists of a label-type patch adhering to a flexible polyvinyl chloride substrate. A novel balanced feed method using two orthogonal slits on the patch is proposed to perform simple and wideband impedance matching between the antenna and a tag chip. A prototype antenna was fabricated and tested with a commercial tag chip. It has a 3 dB return loss bandwidth of 70 MHz and a uniform read range of over 9.7 m in the 902 - 928 MHz range when it is mounted on a cylindrical metal plate with a radius of curvature of 150 mm.

A wideband circularly-polarised (CP) antenna with a simple structure is proposed for universal ultra-high frequency (UHF) radio-frequency identification (RFID) reader applications. The antenna is composed of two patches, an L-shaped ground and an SMA connector. The main patch which is truncated to generate CP radiation is fed directly by the SMA connector oriented in the same plane via the vertical part of the L-shaped ground. The parasitic patch used to enhance the bandwidth is placed at the same layer of the main patch. These two schemes realised a directly-fed single-layer structure. The 3 dB axial ratio bandwidth and impedance matching bandwidth for 14 dB return loss overlap within the universal UHF RFID band (840 960 MHz), while high gain with an average level of 7.3 dBi is achieved. Simulation and measurements are in good agreement.

An electrically tunable small microstrip antenna for telemetry sensor applications in the UHF band (425 MHz) is presented. The proposed antenna is miniaturised by loading horizontal interdigital plates at both radiating edges. Varactor diodes are installed between the radiating edges and the ground plane to control the resonant frequency by adjusting the DC bias asymmetrically. The designed antenna is 65 × 50 × 20 mm 3 in size (0.092λ × 0.071λ × 0.028λ). It is as much as 80% shorter than conventional microstrip antennas. The reconfigurable frequency range with a return loss of less than - 10 dB is 388.7- 462.8 MHz (74.1 MHz, 17.4%).

A segmented loop antenna with capacitive couplers is proposed for ultra-high frequency (UHF) near-field radio frequency identification (RFID) applications, which is capable of generating a strong and uniform magnetic field in a near-field zone even though the perimeter of the loop is comparable to the operating wavelength. As an example, an antenna printed onto an FR4 printed circuit board with an interrogation zone of 154 × 154 mm exhibits good impedance matching and uniform magnetic field distribution over an operating bandwidth of 790-1000 MHz, which is desirable for UHF near-field RFID reader applications.

A new dual-polarised microstrip antenna with high isolation is presented. The high isolation is achieved by using dual capacitive feeds with open-circuited microstrip stubs placed above the radiating patch. The antenna is designed to operate at around 915 MHz for UHF radio frequency identification applications, and experimental results show that it has more than 33.3 dB isolation over the impedance bandwidth of 5.3 .

An on-chip antenna suitable for radio frequency identification at UHF band is presented. It is integrated with an EPC Class 1 Generation 2 compatible tag in SMIC 0.18 m standard CMOS process. The tag achieves a 1 cm communication distance with 1 W reader output power.

International audience; A dual-band HF and UHF RFID tag antenna with two feeding points is presented, fabricated and measured. A convenient HF resonance is obtained with an HF ASIC chip as well as good impedance matching with UHF ASIC chip in the European RFID UHF band. Tuning techniques of the design parameters are proposed, and tag performance in both frequency bands is evaluated.

A simple and successful design for a UHF cavity is presented with a rejection factor inferior to -47 dB for a difference of 1.6 MHz between the transmit frequency and the receive frequency, the insertion loss being less than 1 dB. A coil connected to the resonator ensures a 50Omega adaptation. Modelling of the device, based on Pspice software, is described.

A segmented loop antenna is presented for ultra-high frequency (UHF) near-field radio frequency identification (RFID) applications. The proposed segmented configuration makes the current along the loop remain in-phase even though the perimeter of the loop is comparable to the operating wavelength, so that a strong and uniform magnetic field is generated in the region surrounding the antenna. The antenna printed on a FR4 printed circuit board (PCB) with an overall size of 160 times 180 times 0.5 mm achieves good impedance matching and uniform magnetic field distribution over an operating bandwidth of 800-1040 MHz, which is desirable for UHF near-field RFID reader applications.

A novel UHF RFID tag antenna with broadband characteristic is presented. The structures of T-matching network and double symmetrical radiating patches shorted to the ground plane are employed. The measured half-power bandwidth of the proposed antenna is 12.9% and it covers two major frequency bands. The maximum readable distance of the tag achieved 6.5 m in the RFID bands for North America and Europe. All the results show that the proposed antenna can work not only in air but also on metallic objects in the North America and Europe UHF RFID band.

A broadband ultra-high frequency radio frequency identification (UHF RFID) tag patch antenna with a pair of U slots is presented. By embedding a pair of U slots on the patch, a new resonant mode adjacent to the origin mode is excited and a broadband characteristic is achieved. The measured half-power bandwidth of the proposed antenna is 133 MHz and it covers all UHF RFID frequency bands. Measurement results show that the proposed antenna can work on metallic objects of different sizes in both North America and Europe bands.

Linearity requirements characterised by second-order intercept point (IP2) and third-order intercept point (IP3) are recapitulated for the proposed zero-IF receiver in accordance with ETSI and EPC global UHF radio frequency identification (RFID) protocols. To improve linearity of the downconversion mixer without noise penalty, the common mode intermodulation signal feedback through the bleeding current path and the inductively degenerated common source transconductance are adopted. The circuitry is demonstrated in 0.18 m standard CMOS process. The average IP3 for 23 samples is of 15 dBm and the IP2 is boosted from 37 to 52 dBm while drawing 8.7 mA from a 3.3 V power supply. These results show that the mixer is also very promising for other high linearity RF receiver applications.

An embedded patch-type RFID tag antenna (UHF band) using ceramic material for tagging metallic objects is presented. The proposed RFID tag is embedded in the metallic object; the diameter of the proposed tag is 34 mm and the height is 5 mm. It is shown that a suitable embedded tag antenna can be made from two PIFAs with horizontal slits in the metallic object. The embedded tag antenna satisfactorily operates in the metallic object and the proposed design is verified by simulation and measurements, which show good agreement.

A novel single-layer, dual-fed technique for a bidirectional radiated circularly polarised square-ring antenna operated in the UHF band is presented. The two feed ports of the square-ring radiating element are placed in orthogonal directions and connected to a feeding network with a Wilkinson power divider in the same plane. Properly adjusting the size of the capacitive coupling groundplane results in good impedance matching and circularly polarised radiation, and a broad impedance bandwidth ( S 11 les -10 dB) of about 45.2% and a 3 dB axial-ratio bandwidth of about 8.7% were obtained.

A 0.6 V 720 nW relaxation oscillator fabricated in a standard 0.13 mum CMOS process is proposed as the clock generation circuit for EPC standard UHF RFID transponders. A less than 2% frequency variation is achieved at the frequency of 5.65 MHz when supply voltage varies from 0.6 to 1.0 V.

A miniaturised dual-band S-shaped RFID tag antenna, which is mountable on a metallic surface, and which can handle UHF bands (Korea band: 908.5-914-MHz, Europe band: 865-868-MHz), is presented. The antenna was designed with a meander and spiral structure, through modifying the microstrip feeding line and ground line, and was miniaturised to a size of 20-mm (width)-33.5-mm (length)-2-mm (height). The maximum read ranges were 1.6-m (Korea band, EIRP of reader: 4-W) and 0.75-m (Europe band, EIRP of reader: 1-W), respectively.

To offer RFID services on mobile phones, the RFID reader must be embedded on the handset as a chip. However, the directional coupler, a ceramic passive component used in conventional RFID readers with identical Tx/Rx carrier frequency, has been too large for cellular handset applications. A miniaturised directional coupler design for UHF RFID mobile readers using an IPD (integrated passive device) process is presented. Parallel-coupled line theory has been used for formulation of a T-type and a -type coupler. Couplers with dimensions of 1.74 1.6 mm and 1.32 1.4 mm were assembled using the IPD process.

A varactor diode for a ultra-high-frequency (UHF) TV tuner that can be operated within 5 V of tuning voltage (V T ) is presented. The fabricated diode has a shallow junction with a heavily doped p ++ region on a steep hyperabrupt n + region. Depletion capacitance was from 18.2 pF at V T =0.5 V to 2.8 pF at V T =5 V. This enables the diode to tune the UHF full band without a DC-DC converter. The quality factor of the diode was 20 at V T =0.5 V and 470 MHz of tuning frequency (f T )

The differential radar cross-section (RCS) of an RFID tag is an important parameter which determines the power of the modulated backscattered tag signal. The vector differential RCS of an RFID tag as seen by the reader is analysed and, for the first time, compared with experimental results in UHF band.

A compact half-Sierpinski fractal antenna is presented for UHF RFID applications. Taking the thickness of the substrate (177 µm) and compactness (length: width

A power retrieving circuit for a UHF RFID passive tag is proposed. The circuit is implemented with a 0.18 µm standard digital technology, and allows the empowering of the tag at more than 5 m from a 500 mW ERP interrogator.

A CMOS programmable gain amplifier suitable for low-voltage operation over the very high frequency range is presented. The scheme is based on a very simple common-mode feedforward pseudo-differential pair with resistive loads. Post-layout results for a 1.8 V-0.18 mum CMOS design show a linear-in-dB programmable gain from 0 to 12 dB with a -3 dB bandwidth above 1.4 GHz and power consumption below 17 mW over all the gain range.

A small rectangular loop antenna (RLA) for RFID tags has been designed and fabricated for the UHF band. As the structure of a meander line and a folded meander line is applied in a general RLA, the RLA is miniaturised. The size reduction rate of meander line RLA and folded meander line RLA are 85.4 and 92.2% compared with a general RLA, respectively. The radiation patterns are omnidirectional in the z–y plane (horizontal pol.). Also the gain of the meander line RLA and folded meander line RLA are −2.47 and −4.01 dBd, respectively.

A very low profile antenna with a simple structure and operation, for use inside a handheld mobile phone, is presented. The antenna achieves a triple-band response, covering the E-GSM (880–960 MHz), DCS (1710–1880 MHz) and PCS (1850–1990 MHz) bands for a voltage standing wave ratio less than 3 and a total radiation efficiency of more than 50%, in all bands. Because of its novel design and structure it occupies only 1.15 cm3 of volume. Computed and measured results are presented and compared.

A circular slot antenna fed by a coplanar waveguide (CPW) is proposed for dual-band operations. Dual frequency bands that cover the 2.4 GHz (2400-2484 MHz) and 5 GHz (5150-5825 MHz) bands were obtained by embedding a pair of slits in the circular back-patch that is printed on the backside of the substrate and concentric with the circular slot. This design resulted in broadside far-field patterns with low cross-polarisation levels in both frequency bands and a small antenna size of 40/spl times/40 mm with the ground plane regarded as part of the antenna structure.