The users of portable platform such as laptop expect reliable wireless connectivity, independent on a unit location and orientation. The laptop antenna performance plays an important role in living up to the user's expectations, and in the very competitive global market can provide product differentiation [1]. The laptop antenna characteristics are strongly affected by the adjacent, densely packed PC's components. Moreover, due to the extensive use of conducting layers minimizing the radiation from today's very high speed processors [1], laptop's keyboard base and display work as shielding screens for internal antenna. Therefore the design of the integrated antenna which possesses omnidirectional properties, desirable for mobile units, is a challenging task. The complexity of problem grows when aiming at multi-band operation.

In this paper the E-shaped Omnidirectional Wrapped Microstrip Antenna (OWMA) is introduced. This novel element uses the laptop's display panel (represented here as a simple metal plate) as it's ground plane. Two identical E-shaped microstrip patches [2] are located on the front and back side of the screen edge symmetrically. Front and back patches are connected by a horizontal joining section forming the entire wrapped microstrip radiator [3]. Proposed antenna is fed by microstrip inverted line with the tuning stub integrated into the backside of laptop's display.

The E-shaped OWMA antenna exhibits dual band operation. Due to it's unique geometry two resonant frequencies can be tuned almost independently by modifying slot length and joining section width. Therefore tuning process can be performed without changing the patch external dimensions, usually forced by other design constraints. In this article antenna operating in ISM2.4GHz (2.400GHz-2.484GHz) and U NII 5.2GHz (5.150GHz-5.350GHz) is presented. Thanks to the patch symmetry the antenna horizontal plane (total gain) far field radiation pattern is almost omnidirectional in both frequency bands. In spite of the presence of the large ground plane constituted by laptops screen, the front-to-back ratio is as low as 2dB and 0.5dB in lower and higher resonant frequencies, respectively.

The described low profile compact radiator and feeding network can be integrated into the plastic laptop screen case. The proposed feeding method allows also integration of RF front-end components into the laptop screen backside.

[1] D. Liu, B. P. Gaucher, E. B. Flint, T. W. Studwell, H. Usui and T. J. Beukema, "Developing integrated antenna subsystems for laptop computers", IBM Journal of Research and Development, Vol. 47, No. 2/3, pp. 355-367, Mar./May 2003.
[2] N. Jin, Yahya Rahmat-Samii, "Parallel Particle Swarm Optimization and Finite-Difference Time-Domain (PSO/FDTD) Algorithm for Multiband and Wide-Band Patch Antenna Designs", IEEE Transactions on Antennas and Propagation, Vol. 53, No. 11, pp. 3459-3468, Nov. 2005.
[3] J. Guterman, A. A. Moreira, and C. Peixeiro, "Integration of Omnidirectional Wrapped Microstrip Antennas into Laptops", accepted for publication in IEEE Antennas and Wireless Propagation Letters, Vol. 5, 2006.

A new multi--band microstrip patch antenna element with three folded shaped slots and two coaxial feeds is presented. The designed antenna covers frequency bands ranging from GPS (1.575 GHz) to WLAN, 5.8 GHz and new DSRC, 5.9 GHz.

With phenomenal growth of wireless communication and proliferation of radio system standards compact multi-band radio and antenna modules with escalating complexity and higher performance has been subject of extensive research over last few years. Users are now surrounded by increasing number of communication and navigation services such as cellular phones (GPRS), global positioning system (GPS), and wireless local area networks. Examples include GPS at 1.57-1.58 GHz, GPRS at 1.8/1.9 GHz, 3G-PCS at 2 -2.1 GHz, WLAN IEEE 802.11b at 2.4 GHz, WiMAX at 2.5/3.6 GHz, Hi-LAN at 5.15-5.35 GHz, WLAN IEEE 802a at 5.725-5.825 GHz and finally new DSRC for car-to-car communication at 5.850-5.925 GHz. Covering all these services by one radio system such as a car-mounted unit, handset, or notebook computer module, requires a multi-band antenna with adequate performance.

Dual-frequency microstrip patch antennas have been studied for many years. A number of techniques for bandwidth improvement or multi band applications have been proposed, but these approaches cannot offer good bandwidth and high gain simultaneously. Furthermore most of the existing designs have no provision for pattern or polarization control. A rectangular patch microstrip antenna with a V-slot is a good candidate for wide band or multi band operations [1].

In the present paper a novel patch antenna with three folded optimally shaped slots is proposed and studied. The objective was to provide good performance at 5 frequency bands: 1) GPS with circular polarization, 2) linear polarized (LP) GPRS, 3) LP 2.4 GHz WLAN, 4) LP 5.8 GHz WLAN, and 5) LP DSRC at 5.9 GHz. The antenna has two probe-feeds to provide additional polarization flexibility for each band.

A prototype antenna has been fabricated and tested. The measured response matches with the numerically simulated results over all bands (Fig. 1). This validates the design concept. The antenna radiation pattern behavior satisfies GPS, GPRS, WLAN and DSRC applications requirements.

[1] Gh. Rafi and L. Shafai, " A Broadband Microstrip Patch Antenna with V-Slot," IEE Proceedings, Microwaves, Antennas and Propagation, Volume: 151 , Issue: 5 , Oct. 2004, pp. 435 –440.

Abstract a reduced size wearable button antenna is introduced in this paper. The antenna uses the shape features of a wearable button to create an antenna that can be easily hidden in standard clothing. The antenna presented in this paper is the result of implementing different antenna miniaturization techniques on a dual band button antenna [1] recently developed by the authors of the present manuscript. The dual band antenna is made up of a metal cylinder which is filled with dielectric material and a top disc made up of FR4 metal clad on both sides. A centre via connects the upper metal cladding to the ground plane and there is a second via connection between the top and bottom metal cladding of the FR4 disc. A cross section is shown in Fig.1. The antenna covers the 2400 MHz Bluetooth and 5200MHz WLAN bands.

The small size button antenna has a total height of 8.9mm and top disc diameter of 17mm. The dimensions of the novel wearable antenna are those of a standard jeans button and 37% smaller than previous button antenna development [1]. The antenna was mounted on a Velcro substrate and fed by a 50Ù microstrip line, though other textile materials and 50 Ù feeding techniques could be employed. The novel centre via connection reduces the antenna dimensions but also improves the attachment to the clothing substrate. The shorting metal via between the top metal cladding of the FR4 and button shaped cylinder reduces the height of the FR4 substrate while keeping a good matching at the lower frequency band.

The measured -10dB S11 bandwidths of the antenna on air were 5.1% at 2.4GHZ and 13.5% at 5.2GHz which is suitable for WLAN bands. Omni-directional radiation patterns were obtained which is the desirable characteristic for on body transmission.

In conclusion, a novel small size wearable button antenna has been presented. The antenna uses dielectric and shorting vias to miniaturize a wearable button antenna. The antenna achieves the size of standard button antenna and works at the 2.4GHz and 5.2-5.5GHz WLAN bands. Good omnidirectional patterns were measured. CST Microwave studio was used to simulate the structure.

References:

[1] Benito Sanz-Izquierdo, F. Huang and J.C. Batchelor, "Dual Band Button Antennas for Wearable Applications", IWAT2006, White Plains, New York, March 6-8

A dual-band metal-insulator-metal (MIM) composite right/left-handed (CRLH) [1] resonant ring antenna with multi-polarization radiation (linear/circular) capability is presented.

A dual-band CRLH ring antenna was introduced in [2]. The antenna proposed here includes two additional aspects compared to the one of [2]. Functionally, it is capable of multi-polarization, including linear and circular, in addition to dual-band operation. Technologically, it is implemented in the simpler, more compact and spurious-free MIM CRLH technology [3]. The combination of these two aspects leads to a highly versatile and cost-effective antenna solution for modern wireless communication systems (e.g. IEEE 802.11a,b,g).

The layout of the proposed antenna is shown in Fig. 1. The ring is composed of eigth unit cells - top and bottom view is depicted in Fig. 2/3. The ring circumference L is lambda_g in the operating mode. This is practically the dominant mode of the structure due to its 360° rotational symmetry (lambda_g / 2 not available) although a zeroth order-mode would also be possible. Due to the CRLH nature of the ring, the length of L = lambda_g is automatically achieved at two different frequencies, one in the left-handed band (β = - 2 pi/L) and one in the right-handed band (β = + 2 pi/L), which can be tuned by varying the LC loading of the CRLH transmission line loop. These two modes, since they have nearly identical field distribution along the structure, exhibit nearly identical radiation pattern and input impedances, and can therefore be simultaneously feed by a unique and simple feeding mechanism. The structure is thus inherently dual-band.

Additionally, multi-polarization capability is achieved by a spatially-orthogonal two-port feeding structure including a 90° CRLH dual-band phase-shifter. Its design procedure is presented as well. The MIM implementation allows simple design, unit-cell compactness and avoidance of spurious transverse resonances sometimes restricting the bandwidth of interdigital CRLH implementations.

[1] C. Caloz and T. Itoh, Electromagnetic Metamaterials, Transmission Line Theory and Microwave Applications, Wiley and IEEE Press, 2005.
[2] S. Otto, A. Rennings, P. Waldow, C. Caloz, and T. Itoh, "Composite right/left-handed lambda-resonator ring antenna for dual-frequency operation," in Proc. IEEE AP-S, June 2005, CD-ROM.
[3] H. V. Nguyen and C. Caloz, "Broadband highly selective bandpass filter based on a tapered coupled-resonator (TCR) CRLH structure," Proc. of the European Microwave Association, vol. 2, March 2006.

Our research aims to produce Electromagnetic Bandgap structures for mobile and wireless applications to allow the development of compact antennas over high impedance ground planes. This paper discusses some results from an ongoing study of creating compact antenna structures for automotive and aerospace applications. The paper will focus on dual band designs. New element geometries will be presented that are small compared to the wavelength yet have sufficient bandwidth for mobile communication applications. CST Microwave Studio has been used for the simulation of the complete antenna with the EBG structure. The aim is to produce antennas just 5-6 mm thick at low frequencies around 1 GHz. Fig.1 shows an EBG element geometry based on a Sierpinski shape that is dual band. There are no vias connecting the elements to the ground plane and the structure is 5mm thick. Fig.2 shows the simulated band gaps predicted by the software. The periodicity of the sirface was 22.8 mm. Zero phase response is found at around 930 MHz and 1740 MHz where the surface can be operated as a high impedance ground plane. The lower frequency band gap width at 11% is greater than that at the upper frequency but this can be changed by study of the element geometry. Other element geometries are also candidates and will be reported in the paper together with a dual layer design to give greater band gap flexibility. The application demands that a complete low profile antenna structure must be designed. Two designs to date incorporate either high band width monopole antennas or a dual band dipole antenna. It is necessary to design the complete antenna as a unit as when the EBG material and antenna structure are integrated the operating frequencies differ from those of the individual parts. To complete the design the radiation patterns of the complete band gap structure integrated with the antenna have been nmeasured. The structure was placed on a large ground plane for measurements to make sure that the antenna/band gap material was not affected. Return loss measurements were unaltered and a radiation pattern measured in one plane is compared with a simulated one from the software. There was reasonable agreement. The full paper will present the overall performance of integrated band gap antenna structures.

The internal planar inverted-F antenna (PIFA) is presently the most popular antenna for mobile terminals due to its compact size and good performance. The PIFA uses its ground plane as part of the radiator [1]. Recently, it has been shown that a folded loop antenna which has a self-balanced structure can reduce the currents on the ground plane radically whilst maintaining a good performance [2], [3].Therefore, the ground plane of the antenna is behaving as a reflector rather than as a radiator. The folded loop antenna was further investigated in our previous study by loading a dielectric slab into the antenna – Dielectric Loaded Folded Loop Antenna and four such antennas have been successfully used in designing a compact diversity system on a Personal Digital Assistant (PDA) for the MIMO system [4].

In this paper, we have proposed an antenna which has only half the length of the dielectric loaded folded loop antenna. The proposed antenna (i.e. dielectric-loaded folded half-loop antenna) is designed to operate at 5.2GHz for the IEEE802.11a wireless system. The proposed design of the antenna is simulated using the CST Microwave Studio^TM package, which utilises the Finite Integral Technique for electromagnetic computation. The antenna's return loss and radiation patterns are also experimentally verified in the Antenna Measurement Laboratory at Queen Mary, University of London. Since the ground plane is acting as a reflector to the antenna, the front-to-back ratio of the radiation patterns is found to be approximately 10dB. The sensitivity of the antenna’s return loss due to its locations and orientations on the ground plane is also accessed in this study. It is found that the proposed antenna is not much detuned when the antenna is in different locations and orientations. With this advantage, the antenna can be placed on a handset in different locations and orientations without redesigning the antenna.

References:

[1] H.Morishita, Y.Kim and K.Fujimoto, "Design concept of antennas for small mobile terminals and the future perspective," IEEE Antennas & Propagation Magazine, vol. 44, no.5, pp. 30-43, Oct 2002.
[2] H.Morishita, Y.Kim, Y.Koyanagi, and K.Fujimoto, "A folded loop antenna system for handsets," IEEE AP-S Proc., vol. 3, pp. 440-443, Jul 2001.
[3] Y.Kim, H.Morishita, Y.Koyanagi and K.Fujimoto, "A folded loop antenna system for handsets developed and based on the advanced design concept," IEICE Trans. Communication, vol. E84-B, no. 9, pp. 2468-2475, Sept 2001.
[4] C.C. Chiau, X. Chen and C.G. Parini, "A compact four-element diversity antenna array for PDA terminal in a MIMO system," Microwave and Optical Technology Letters, vol. 44, no. 5, pp. 408-412, March 2005.

I. Introduction

MIMO systems are promising to achieve high data-rate wireless access. High antenna gains are required to ensure the desired multi-antenna performance. However, in the case of inverted-L antennas, which are popularly used for mobile equipments, radiation efficiency is deteriorated due to the mutual coupling between antennas, and the pattern averaging gain (PAG), which is one of the main criteria for the effective antenna gains in general use, is degraded due to the mismatch between the antenna radiation patterns and the power angular distributions in the mobile propagation environment. This paper proposes a novel multi-antenna configuration for internal antennas equipped in a notebook PC which improves the antenna performance by applying the folded dipole elements.

II. Antenna Configurations

The antenna configurations and notebook PC model are shown in Fig.1. Quad half-wavelength folded dipole antennas are arranged vertically at both the sides of the upper ground plane of the notebook PC model. The directions of antenna elements at each side are oppositely arranged.

III. Calculation and Measurement Results

The calculated current distributions on the antenna element and the edge of the ground plane are shown in Fig.2. It can be seen that three half-wavelength currents flow on the antenna element including the ground plane and two are reversed-phase components, indicating that the unnecessary current on the ground plane can be eliminated. Fig.3 shows the mutual coupling characteristics. It can be observed that folded dipole antennas enable us to improve by 10 dB of s21 characteristics compared to inverted-L antennas. Typical calculated radiation patterns are shown in Fig.4. The inverted-L antenna has the dual polarized properties with many ripples. On the other hand, the folded dipole antenna has the vertically polarized and the half-wavelength dipole equivalent directional properties which have a high peak gain, above 0 dBi. In the case of the folded dipole antenna, it seems obvious that most of the power is concentrated in the horizontal direction compared to the inverted-L antenna. Consequently, the PAG of the folded dipole antenna is higher than the inverted-L antenna. Since arriving waves in the mobile propagation environment are mainly vertically polarized and distributed mainly in the horizontal direction, these properties of the folded dipole antenna are suitable for the internal antennas equipped in a notebook PC. Moreover, by arranging the folded dipole elements on each side oppositely, the beam direction can be approximately perpendicular to that of the other in the azimuth plane. Thus, correlation coefficient between the antenna elements can be suppressed. The beamforming gain and MIMO channel capacity are also investigated. Using the quad folded dipole antennas resulted in +6 dB more beamforming gain and double channel capacity compared to quad inverted-L antennas. Concerning the significant improvement in beamforming gain and channel capacity, the high effective antenna gains in general use and the low mutual coupling properties of quad folded dipole antennas can be understood as a substantive benefit.

A coplanar-square-patch antenna for Iridium satellite reception via handset is proposed. With the introduction of some asymmetry in the structure to a single-feed ring microstrip antenna, it is possible to excite two orthogonal degenerate resonant modes for circular polarization (CP) radiation. Since printed-slot antennas usually have a wider-impedance bandwidth than microstrip antennas, the obtained CP bandwidth for a printed-coplanar-patch antenna can be expected to be greater than that of a microstrip antenna operated in the fundamental mode. Some prototypes of the proposed CP design CSPA antennas have been implemented and experimental results are presented and discussed.

Antenna Designs, Simulations and Experimental Results

In Fig. 1(a) the proposed coplanar-square-patch antenna is shown. The antenna is printed on a microwave substrate, Rogers TMM4, of thickness h=1.6 mm and relative permittivity ε_r=4.5. For the coplanar-square-patch antenna, the outer-and inner-linear dimensions are L₁ and L₂ , respectively, and the slot width is W .

Fig. 1. Model of the coplanar-square-patch antenna. (a) the surface current simulation at 1.5 GHz (b), simulated/measured return loss (c) , and E-plane radiation patterns (d).

The rectangular slot section of length l₂ is placed at the center of on side of the square patch with centered a metallic strip of width 1 mm and length l₁ = l₂ + 0.5 W + 0.5 mm. A square slot around the patch has width W. A 50-Ω microstrip feed line with a widened tuning stub of length lt and width w_t, printed on the opposite side of a laminate is used to feed the ring slot along the diagonal direction. w_t is chosen to be about two times w_f in this study, and good impedance matching for achieving CP radiation can be achieved. The fundamental resonant mode for the coplanar-square-patch antennas, occurs at the frequency whose wavelength in the ring slot approximately corresponds to the mean circumference of the ring slot. That is, we have
where c is the speed of light in free space. In this study, the differences between the measured data and calculated results are within 5%. Also note that the design arrangements shown in Fig. 1(a) and (b) radiate a RHCP wave and when the microstrip feed line excites antenna along the other diagonal direction LHCP radiation can be obtained. The CSPA antenna parameters were analyzed using IE3D and Fidelity computer codes of Zeland Software Ltd.. Simulated and measured return loss and radiation patterns of a prototype of coplanar-square-patch antenna are presented in Fig. 1c and d. The measured antenna gain is about 3.2 to 4.8 dBi, and the 3-dB axial-ratio bandwidth is about 3% referenced to the center frequency at 1520 MHz.

A self-complementary equiangular spiral antenna is a frequency-independent antenna that radiates a circularly polarized wave. This frequency independency holds true when the conducting spiral arms (or complementary spiral slot arms) are of infinite length. In reality, however, the spiral arms are finite, and hence the radiation characteristics are affected by this finite length.

This paper investigates a finite-sized equiangular spiral antenna. First, the investigation is performed for the situation where the spiral slot arms are cut into a conducting sheet of finite size (see Fig. 1). The sheet is round and located in free space. Three diameters are chosen for the sheet: D = 12 cm, 14 cm, and 16 cm. Note that the spiral slot arms cut into these conducting sheets have the same shape. The analysis shows that the input impedance is not sensitive to the diameter of the conducting sheet. In addition, it is found that the axial ratio does not vary remarkably with frequency. In a frequency range of 2 GHz to 20 GHz, the axial ratio is less than 3 dB. However, the variation in the gain is relatively large (approximately 4 dB in the same frequency range). It is also revealed that, as the frequency increases, attenuation of the magnetic current within the spiral slot arms increases. The radiation for this configuration is bi-directional.

Next, based on the above investigation, unidirectional radiation is realized by backing the spiral with a cavity (see Fig. 2). The diameter and height of the cavity are selected to be D_cav = 12 cm and H = 0.7 cm, respectively.

Note that the small cavity height H realizes a low-profile antenna structure. Also, note that an absorbing strip (ABS) is attached to the inside vertical wall of the cavity. The analysis for a absorbing strip thickness of T = 1.8 cm reveals that the input impedance shows a constant value of approximately 160 ohms for the frequency range from 3 GHz to 20 GHz. The axial ratio is less than 3 dB over most of this frequency range, as desired, and the gain relative to a right-hand circularly polarized isotropic antenna is approximately 7 dBi.

Some new antennas that radiate linearly polarized toroidal beams are presented. Two prototypes have been constructed, see Figs. 1 and 2, c, d. Their design procedure is based on the use of a Method of Moments commercial software tool. Very accurate toroidal beams are obtained, as shown in Figs. 1 and 2, a, red dotted line; large operating relative bandwidths are reached, up to 24% in one of the models, as can be seen in Figs. 1 and 2, b, red dotted line. Experimental results are also referred, see Figs. 1 and 2, a, blue solid lines. Fairly good agreement between calculations and measurements are obtained, as far as the radiation pattern is concerned. As far as the scattering matrix entry S₁₁ is concerned, there is essentially a relative frequency shift of the order of 6%, particularly evident in Fig. 2,b. The reason of such a shifting is under investigation

Figures 1 and 2 c and d also show the depiction of the designs and the photograph of the prototypes, respectively.