Search

This paper presents a wideband circular antenna array with a frequency domain and space domain reconfigurable radiation pattern. A wideband circular array antenna is designed with omni-directional radiation pattern, in azimuth direction, throughout the whole frequency band. The antenna array consists of eight TEM horn antennas. The antenna array exhibits an omni-directional azimuthal radiation pattern when all eight ports are excited with signals of the same magnitude and phase. The antenna array is fed through eight reconfigurable bandstop filters and a power splitter. This enables it to provide an omni-directional azimuthal pattern along with a single directional pattern null in a given spatial direction and at a certain frequency. Both the spatial direction and the frequency can be altered. The antenna works from 0.8 GHz to 3.0 GHz. The antenna array will be useful in combating interference in wideband communication systems. It will also be of value in surveillance military applications.

The interuser interference between wireless body area networks worn by two moving persons in an indoor environment at 60 and 2.45 GHz is experimentally investigated. Both omnidirectional antennas (monopoles) and directional antennas (horns) were used in the measurements. The interference power-level variation and carrier-to-interference ratio (CIR) were measured and characterized. Median interference power-level reduction of nearly 20 dB was achieved in all measured channels by adopting 60-GHz radio transmissions compared to 2.45 GHz, both with omnidirectional on-body antennas. A further 20 dB of interference-level reduction was achieved at 60 GHz by adopting directional antennas confining the radiated wave along the body surface. Level crossing rates for interference power variation using omnidirectional antennas range from 2.7 to 7.2 $\text{s}^{-1}$ at 2.45 GHz and 32–64 $\text{s}^{-1}$ at 60 GHz for static to progressively more dynamic links, whereas the corresponding range using 60-GHz directional antennas is reduced to 39–54 $\text{s}^{-1}$ . The median improvement in the instantaneous CIR for the chest-head channel between 60 and 2.45 GHz was approximately 30 dB. The measured interference power level and CIR, in dB, were found to satisfactorily fit the normal distribution according to the normalized root-mean-square error-based fit metric.

Novel miniaturized two-layer electromagnetic band gap (EBG) structures are presented for reducing the electromagnetic coupling between closely spaced ultra wideband (UWB) planar monopoles on a common ground. The proposed EBG structures employ two closely coupled arrays, one comprising linear conducting patches and the other comprising apertures (slits) in the ground plane. The two arrays are printed on either side of a very thin dielectric layer ( $\bf{55}\;\upmu\mathrm{m}$ ) with a rotation between the elements to produce maximum coupling for miniaturizing. A microstrip line excitation is initially used for the efficient analysis and design of the slit–patch EBG structures, which are subsequently employed between two UWB printed monopoles. The proposed EBG structure has a small footprint and produces a significant reduction of the mutual coupling across the wide operating band of the UWB antennas. Simulated results and measurements of fabricated prototypes are presented.

A method for designing sub-wavelength-profile and broadband high-gain planar antennas is presented. A novel multi-layer periodic array design is proposed for sub-wavelength Fabry-Perot cavity type antennas with enhanced bandwidth performance. Three double-sided periodic arrays are designed and optimized, each double-sided array consisting of a capacitive artificial impedance surface (AIS) and an inductive partially reflective surface (PRS) printed on either side of a dielectric substrate. They are placed at about sixth of a wavelength from a ground plane and from each other. Thus, three air cavities are created with a total profile of $\lambda/2$ . The proposed antenna has been simulated using CST Microwave Studio and measured achieving 16.9 dBi directivity with 10.7% 3 dB bandwidth. The gain-bandwidth product of the proposed designs outperforms any previous Fabry-Perot antenna design with this profile.

A novel microstrip log-periodic array based on the broadly-matched complementary strip-slot radiating element is proposed. The array consists of microstrip-fed log-periodically-scaled slots on the ground plane and their complementary stubs on the microstrip layer. Since the radiating element is not resonant, the analysis differs from the previously reported log-periodic arrays. Low scale factor (τ) with high radiation efficiency is possible, since the element radiation efficiency is not resonant and the relative spacing (σ) does not have to be selected for good matching, because the element is intrinsically matched. A design example with τ = 0.909, σ = 0.17 and 15 elements has been analyzed. The achieved bandwidth goes from 2.7 to 8.7 GHz, with a radiation efficiency and a gain of better than 85% and 5 dB, respectively. Moreover, the antenna can be terminated in an open circuit without affecting its performance. Simulated and experimental results show that the radiation pattern is stable over frequency. A method for computing the radiation pattern using equivalent circuits as well as results with a reflector plane for cancelling the beam in one half-space are also included. Due to the good performance, simplicity and low cost, this antenna can be suitable for broadband applications.

This paper describes an investigation into the polarization behavior of on-body wireless communication channels at 2.45 GHz. The effect of the polarization of an antenna on the channel path gain has been studied and the channel cross-polarization discrimination (XPD) has been quantified, using both simulation and measurement. In simulation, short dipole antennas, which significantly reduce the simulation time, were used to investigate path gain behavior in different channels for vertically and horizontally polarized antennas. Measurements were taken in an indoor environment using a novel dual-polarized antenna, producing normal and parallel polarizations to the body surface. The measured signals were also analyzed to extract the Rician K-factor which was defined as the ratio of the power in the line of sight (LOS) signal to the scattered power for various polarization combinations.

A compact wideband circularly polarized (CP) printed antenna design is presented in this communication. The proposed antenna consists of two Archimedean spiral slots, loaded with two chip resistors and fed by a coplanar waveguide (CPW) transmission line. The antenna is situated in one plane and fed without using an external balun or a matching network. The antenna has wideband input impedance bandwidth with circular polarization (CP), and broad beamwidth radiation pattern over 1.6:1 bandwidth. The study has shown that the proposed antenna is capable of improving the CP bandwidth and reducing the overall antenna size.

The improvement in terms of channel capacity provided by using a MIMO antenna system in personal area networks is investigated. Two on-body channel models derived in the 2.45 GHz frequency band are also presented and applied to two on-body links. The first proposed model uses, for each spatial subchannel, the same average values for the Rician factor, received power, and shadowing deviation. The second model encompasses the polarization loss in the on-body channels by utilizing different values of these parameters per each spatial subchannel. Furthermore, the joint correlation matrix is used instead of the classical Kronecker product. It is shown that the second model results in a better agreement of the achievable capacity with the measured channel. Also, the equal power and waterfilling power allocation schemes are compared in such on-body channels and it is shown that, adopting waterfilling instead of the equal power provides a higher capacity in the low SNR range while yielding the same achievable capacity in high SNR.

A novel reconfigurable wideband to narrowband Vivaldi antenna is presented. A single pair of ring slot resonators is located in the Vivaldi to realize frequency reconfiguration, maintaining the original size unchanged. The proposed antenna is capable of switching six different narrow pass bands within a wide operating band of 1-3 GHz, offering added prefiltering functionality. A fully functional prototype has been developed. PIN diode switches were employed at specific locations in the resonator to change its effective electrical length, hence forming different filter configurations. Antenna performance obtained from simulation and measurement results shows good agreement, which verifies the proposed design concepts. The antenna is potentially suitable for applications requiring dynamic band switching such as cognitive radio.

Ultrawideband (UWB) systems require band notch filters in order to prevent sensitive components, within the front-end of the receiver, from being overloaded by strong signals. Recently, it has been shown that these filters can be integrated into the UWB antenna, to great advantage. This communication presents a new method for forming a notch band within the frequency response of a UWB antenna. An open loop notch band resonator is located on the back of the substrate, used to support the UWB monopole. The act of separating the resonator from the antenna means that they can now be designed in isolation, using the standard approach described in the literature, and then combined. A prototype was constructed and good agreement has been obtained between simulation and measurement. The radiation patterns are consistent over the frequency range of interest.

An integration concept for multi-standard antennas is described. This technique is based on utilizing a relatively large antenna that is printed on the top side of a substrate, acting as a ground for a smaller antenna. The smaller antenna is printed onto the bottom side of the substrate. To validate this concept, an integrated wide-narrowband demonstrator antenna is presented. This antenna is composed of a shorted microstrip patch integrated with a coplanar waveguide (CPW) fed ultrawideband (UWB) antenna. A prototype of the integrated antenna was fabricated and its performance was verified. This arrangement is a promising candidate for applications where some level of reconfigurability is required. For this reason, a set of external tuning circuits were designed to demonstrate the potential of the proposed configuration for such applications. In order to improve the isolation between the wideband and narrowband ports several modified arrangements were presented and investigated.

A novel Vivaldi antenna with added switched band functionality to operate in a wideband or narrowband mode is presented. The antenna reconfiguration is realized by inserting four pairs of switchable ring slots into the ground plane of the structure. A wide bandwidth mode from 1.0-3.2 GHz and three narrowband modes can be selected. A fully functional prototype with PIN diodes switches has been developed. Measured results shows good performance of the proposed designs. The antenna could be a suitable solution for a multimode application requiring wideband and frequency reconfigurable antennas, such as in military applications and cognitive radio.

Tunable left-handed (LH) wire antennas over a ground plane are presented in this paper. These antennas are small and have a wide tuning bandwidth and are matched to 50 Ω within the operation range. Two kinds of antennas have been developed: the monopole antenna and the half-loop antenna over ground plane. In both cases, the antennas are designed, manufactured and measured at fixed frequencies as a first step. After that, a study to replace some LH components with variable capacitors has been carried out for each antenna. Tunability over a wide bandwidth has been achieved. Finally, some prototypes of both antennas have been manufactured and measured. The tunable LH monopole antenna has been measured showing a monopolar radiation pattern with a 28% tuning bandwidth (695-924 MHz). Its radiation efficiency takes values between 50% and 70% within all the tuning bandwidth and the maximum dimension varies only between 0.11λ0 at 695 MHz and 0.15λ0 at 924 MHz. The tunable LH half-loop antenna over a ground plane has a radiation pattern with maximum radiation orthogonal to the ground plane. It has a 1.64:1 measured tuning bandwidth properly matched to 50 Ω (considering |s11

A study is presented of wireless on-body communication links, with the body in motion. This paper compares simulations and measurements of the path gain (PG) on moving male and female bodies. Simulations using avatars derived from an animation software have been performed at 2.45 GHz. Male and female avatars walking and a male rising from a chair have been simulated and the results are compared with measurements carried out in an anechoic chamber. The results show that good agreement between simulation and measurement of slow fading features can be achieved for a reasonable computational effort.

Rejection of interference from a nearby body area network (BAN) becomes significant in BAN applications, where a number of BANs are operating in the near vicinity of each other. Two interference rejection combining (IRC) techniques, optimum combining (OC) and Weiner-Hopf (WH) solution, are applied to the on-body wireless communication channels, and a more robust interference rejection technique, applicable to on-body channels, is proposed and compared to the conventional IRC algorithms. Three on-body channels are investigated by real time measurements of the desired and interference signals in an indoor environment with the antennas mounted on two human subjects walking around each other. The output signal to interference plus noise ratio improvement achieved with each algorithm is presented for the three channels and the dependence of the interference rejection gain on the average desired signal to interference ratio has been shown along with the covariance matrices for each channel. OC gives around 3-5 dB interference rejection gain for belt-wrist and belt-head channels. The WH solution gives the worst performance for all the channels. The proposed algorithm gives a flexible handle on the interference rejection gain and gives better rejection than the two conventional algorithms with proper interval selection.

Statistical analysis of the on-body diversity combined and branch signals are presented. The distribution of short-term fading envelopes of the branch and combined signals show that the fading environment for the on-body channels is Rician. The long-term fading best fits the log-normal distribution. The average best fit parameters are presented for short-term and long-term fading envelopes of the branch and combined signals. The Doppler spectra are also presented. Three different types of antennas were used and two on-body channels were characterized at 2.45, 5.8, and 10 GHz.

An experimental investigation to characterize the transient and spectral behavior of the ultrawideband (UWB) on-body radio propagation channel for body-centric wireless communications is presented. The measurements were performed considering over thirty on-body links in the front of human body in the anechoic chamber, and in indoor environment. Two different pairs of planar antennas have been used, namely, CPW-fed planar inverted cone antennas (PICA), and miniaturized CPW-fed tapered slot antennas (TSA). A path loss model is extracted from measured data, and a statistical study is performed on the time delay parameters. The goodness of different statistical models in fitting the root mean square (RMS) delay has been evaluated. Results demonstrate that the TSA, due to its more directive radiation behavior is less affected from the reflections from body parts and surrounding environment. The antenna shows significant size reduction and improved time delay behavior, and hence is an ideal candidate for UWB body area networks (BAN).

Using multiple antennas at the transmitter and receiver has shown a remarkable scope for capacity increase for indoor wireless mobile and PAN communications and is here extended to on-body channels. The capacity and multiple-input multiple-output (MIMO) channel correlation analysis has been performed at 2.45 GHz frequency using planar inverted-F antennas (PIFA) for three on-body channels. The improvement offered by 2 × 2 MIMO over the conventional single-input single-output link for the on-body channels has been discussed. The variation of capacity with Rician K-factor is shown and the MIMO channel spatial correlation matrices are presented. The effect of correlation on the channel capacity is discussed.

A study of the efficiency of small dipole antennas loaded with a left-handed transmission line is described. The antenna is composed of a ladder network periodic structure of a number of unit cells. Left-handed performance can be obtained in straight or meandered capacitive-inductive (CL) lumped loading. Its performance is compared to a right-handed dipole with inductive (L) lumped loading. Differently loaded dipoles with four unit cells with the same size reduction have been compared. Right-handed loading gives the best efficiency as expected, but left-handed loading shows the greater degree of freedom to achieve a desired impedance at the terminals. The efficiency is also increased when the CL-loaded dipole is meandered, because of the higher radiation resistance. Moreover, different numbers of unit cell have been compared in order to clarify the number for the best efficiency with size reduction. In a low-order mode, an inductively loaded dipole has highest efficiency for two unit cells, with reduced efficiency with the number of loading elements. However, the reverse is true for the CL-loading. The efficiency of a meandered CL-loaded dipole becomes comparable to the conventional L-loading for higher than four cells. CL-loading with higher mode number gives higher efficiency than a conventional dipole with multiple inductive loads.

Diversity is one of the methods to overcome the multipath effect in the mobile environment. A pattern diversity antenna with four beams was used to investigate the diversity performance in the onbody environment. A switched diversity combining method-switch-and-stay strategy-was used to analyze the data. Finding an angle of arrival (AoA) of different multipath components is very useful since it allows optimization of the base-station antenna radiation patterns and can be used to locate and track the handsets that operate in a particular cell. Similarly, in onbody communications, knowing the AoA enables determining the position of the antennas relative to each other and supports the design of antennas with optimized radiation patterns. Diversity and AoA measurements have been performed for five randomly movements body channels. In diversity measurements, the antenna beams are switched quickly considerably faster than the body movements. The results show that significanct gains are achieved for non-line-of-sight channels and no gain is obtained for the LOS channel since the signal is received by the same beam during the measurement. During AoA measurements, the 2-D process is chosen in which the angles are in a 2-D plane around the ground plane of the antenna. The main propagation paths of the transmitted signal are limited to a limited interval of the AoA range. These AoA estimates for onbody propagation channels can be used for designing better fixed beam and pattern diversity antennas.

On-body communication has numerous applications in the context of personal communications systems. Multiple antenna reception is an effective way to combat fading and improve the performance. This paper describes the improvement achieved by using two antennas at the receive side for on-body communication channels. Three different types of antennas are used at 5.8 and 10 GHz to analyze the diversity performance. Diversity gains and correlations are calculated and diversity performance of the antennas at the two frequencies is compared. The repeatability and reliability of the measurements and the uplink and downlink diversity is also discussed. High diversity gains are achieved for most of the channels and almost similar at both the frequencies.

A varactor-loaded H-shaped antenna with radiation pattern control is described. The antenna has a varactor in each of the four arms. A cylindrical wire model with four varactors is analyzed by the method of moments. The analysis, using the "FEKO" simulator, shows the figure-of-eight radiation pattern is rotated by 360deg in the plane of the antenna with variation of capacitances of the four varactors. An optimum set of capacitances is derived, considering the beamwidth, null level of the radiation pattern, and voltage standing wave ratio (VSWR). A prototype antenna implemented on FR4 substrate has dimensions of 60 mm by 200 mm with a line width of 2 mm. The DC voltages were supplied to the four varactors via the antenna arms where slits were inserted. A 110 Omega feed line and 110 Omega-to-50 Omega balun were designed for the minimum VSWR, whilst maintaining good radiation properties. The antenna exhibits rotation of a figure-of-eight radiation pattern with a VSWR less than 2.7, and the maximum gain from -2.9 dBi to 1.4 dBi at 750 MHz.

The performance of broadband dipole antennas above electromagnetic bandgap (EBG) structures is investigated. Two different structures are examined. One is a diamond dipole over an EBG with square patch elements optimized by hand and the other an open sleeve dipole over an EBG optimized by a genetic algorithm (GA). Both configurations demonstrate that a low profile dipole antenna over an EBG can have a broad bandwidth. Careful design of both is required and in particular for best results, the antenna-EBG system should be optimized together, rather than as separate components. The performance is compared to an absorber backed wideband dipole antenna and it is found that the gain is significantly increased, whilst the bandwidth is reduced. In general, for the diamond dipole antenna return loss bandwidths of over 2:1 (67%) have been achieved, although radiation pattern control is difficult and reduces the bandwidth to the order of 1.4:1 (33%). The sleeve dipole over an EBG achieved a bandwidth of 1.28:1 (26%). The realized gain, which is power gain reduced by input match loss, of both structures are approximately the same. GA optimization and parametric studies seem to suggest that bandwidths significantly greater than these are difficult to achieve.

A new type of dipole antenna using a left-handed transmission line is proposed. The antenna is composed of a transmission line loaded periodically with shunt inductors and series capacitors. The placement of capacitors into one side only of the line leads to currents of different amplitude on the two sides. Because out-of-phase currents have different amplitudes, they do not completely cancel in the far field, and as a result radiate. Numerical investigation of a wire model shows a unique feature of left-handed transmission lines, which is a reduced wavelength with decreasing frequency. Measured results of two antennas are presented. One is a short dipole antenna working at n=-1, based on conventional resonance numbering. The antenna of 0.18 wavelengths in free space has a gain of -3.9 dBi and bandwidth of 1.7% for |S11

On-body propagation channel measurements using two microstrip patch antennas for various links are presented and statistically analyzed. The attenuation attributed to factors such as the body, head and clothing are: 19.2, 13.0, and 1.7 dB, respectively, when measurement performed in the anechoic chamber. Measured cumulative distribution function (CDF) of data in the chamber and lab fits to lognormal distribution with deviation factors comparable in both cases. The results demonstrate that the human body is a major shadowing contributor in body area network (BAN) radio systems. The performance of potential radio systems under the measured channel variations is also investigated. Excellent system performance is achievable with power levels as low as 0.01mW. These results support the significance of channel characterization and modelling in producing suitable wireless systems for ultra low power BANs

This paper describes the multiband behavior of a series of perturbed fractal Sierpinski gasket antennas. Sierpinski gaskets, with periodic ratios of 0.5, 0.65, and 0.75 were fabricated and tested. Two methods are presented that improve the inherently poor input impedance match of the antenna with a 50 /spl Omega/ port. Theoretical simulation is used to give an insight into the field distribution of the antenna as the perturbing ratio varies. Different properties and merits of the antenna due to perturbation were noted. These improved feeding methods will allow further flexibility to the application of these multiband antennas.

This paper proposes two novel designs of a multiband antenna using multiple rings. The first design consists of a set of self-similar circular rings. This is an alternative to the recently reported triangular fractal Sierpinski gasket monopole antenna, and comparison is made to this and the circular disk monopole antenna. The second design is realized by varying the shape of the circular structure to an elliptical one. Larger bandwidth and improved patterns are achieved. In comparison to the circular disk, improved radiation pattern control at higher operating bands, due to the discrete structure of the multiple rings, is shown by numerical and experimental results. The bandwidth is significantly larger than the Fractal Sierpinski gasket and Parany monopole.

A small short-circuited H-shaped GaAs monolithic microwave integrated circuits (MMICs) patch antenna is presented. Resonant at 5.98 GHz, it is the lowest frequency MMIC patch antenna reported that we are aware of and is intended for short-range communications (e.g., vehicular). Initial experimental and theoretical characterization of the proposed structure has been carried out on soft microstrip substrates. It has been shown that the size of an H-shaped patch antenna can be reduced to as low as one tenth of that of a half wavelength patch antenna resonant at the same frequency, saving valuable substrate space. The resonance frequency, radiation patterns and gain have been investigated. Ground plane truncation effects, which are important for MMIC applications, have been examined using the finite-difference time-domain (FDTD) method.

The topic of body centric communications can be divided into three domains: (1) Communications from the body surface to a nearby base station; (2) both antennas are on the body surface; and (3) at least one antenna may be in a medical implant within the body. These three domains have been called off-body, on-body and in-body, respectively. The classification serves to highlight some of the technical challenges. They may also be encountered by the reader in some of the papers in this Special Issue. However the papers in the Issue have not been arranged in this way but rather in terms of the main topic, namely antennas and propagation.

An active antenna consisting of an integrated oscillator with a passive radiator has been arrayed and beam-scanned using a new principle for phase shifting. The radiating elements consist of a transistor oscillator whose frequency is controlled by a rectangular microstrip patch antenna. Each oscillator is injection locked to an external source. The phase control of the radiated wave is achieved by varying the bias on the transistor. Individual element performance has been characterized for potential use as an array element and is comprehensively reported. Methods used to achieve configurations with full 360/spl deg/ phase control have been investigated utilizing novel configurations and cascaded oscillator pairs. Close to 360/spl deg/ of radiated phase control from each element has been achieved. Measured results on an experimental four-element S-band array indicate that beam scanning in excess of /spl plusmn/60/spl deg/ can be achieved. Mutual coupling effects on this new form of array are studied both experimentally and theoretically. A van der Pol (1934) model for the weak coupling that is occurring on the array is developed and used to qualitatively predict the phase offsetting on array elements. Reasonable agreement between theory and experiment is obtained and it is observed that good control of the coupling mechanism is essential to array performance within this new form of active integrated phase shifterless array.

Cellular telephone handsets are now being designed to have dual-mode capabilities. In particular, there is a requirement for internal antennas for GSM and DCS1800 systems. This paper describes a novel planar dual-band inverted-F antenna for cellular handsets, which operates at the 0.9-GHz and 1.8-GHz bands. The dual-band antenna has almost the same size as a conventional inverted-F antenna operating at 0.9 GHz and has an isolation between bands of better than 17 dB. The bandwidths of the antenna are close to those required for the above systems. Good dual-band action is also obtained for other frequency ratios in the range of 1.3-2.4. Studies also show that the dual-band antenna can operate with one or two feeds. A finite-difference time-domain analysis has been shown to give calculated results close to those measured.

In the production of the above titled paper (ibid., vol. 57, no. 1, pp. 248-255, Jan 09), typographical errors occurred in (4) to (6). Corrections are presented here.

The fundamental radiation mechanism occurring at an open-circuit discontinuity is discussed to reveal limitations on bandwidth, efficiency, and sidelobe level control inherent in microstrip antennas, based on resonator action. Extraneous radiation from feed transitions is also assessed and shown to be a problem in some cases. Novel two-dimensional arrays using resonant elements are described which illustrate these performance limitations. In contrast, a nonresonant circularly polarized spiral element has a very wide bandwidth at the expense of lower efficiency. Other designs are then noted to show how a particular parameter or aspect can be optimized for antenna applications demanding choice of polarization, frequency scanning, log periodic behavior, low angle radiation, and integration with circuitry on a common substrate.