Halim Boutayeb
email: halim.boutayeb@huawei.com

Paul Watson

Toby Kemp

New Reconfigurable Power Divider Based on Radial Waveguide and Cylindrical Electromagnetic Band Gap Structure for Low Power and Low Cost Smart Antenna Systems

A new low power and low cost technique is proposed for designing agile antennas by using a reconfigurable radial waveguide excited by a central probe and feeding multiple radiating elements. The power distribution of the radiating elements is controlled by a cylindrical Electromagnetic Band Gap structure with PIN diodes allowing azimuth beam steering and multiple-beams. The proposed technique permits any polarization and it can be used for beam steering in both azimuth and elevation by adding control circuits in the radiating elements. Numerical and experimental results are presented for validation. I.

INTRODUCTION

Cylindrical Electromagnetic Band Gap (CEBG) structures were first proposed and analysed in [START_REF] Boutayeb | Analysis of radiusperiodic cylindrical structures[END_REF][START_REF] Boutayeb | Étude des Structures Périodiques Planaires et Conformes Associées aux Antennes. Application aux Communications Mobiles[END_REF]. In [START_REF] Boutayeb | Étude des Structures Périodiques Planaires et Conformes Associées aux Antennes. Application aux Communications Mobiles[END_REF][START_REF] Boutayeb | New beam steering base station antenna using EBG material[END_REF], CEBG structures made of metallic wires periodically loaded with PIN diodes were proposed to be used for designing base stations agile antennas. In these designs, the EBG structures were acting as reconfigurable parasitic reflectors and a single radiator was located in their center. This technique can have several drawbacks: it can require more than 10V DC voltage because of the number of PIN diodes in each wire, it can present prohibitive cost and loss because of the total number of diodes, it can be used only for vertical polarization and it is limited to azimuth beam forming.

In this work, we propose a new concept for designing an agile antenna with lower cost and better performance. The proposed technique consists of using a radial waveguide, a CEBG structure made of loaded wires and transitions from the radial waveguide to radiating elements. With this concept, it is possible to control the beam forming with a DC voltage lower than 1V. Also, any polarization can be obtained and the number of diodes is minimized. Furthermore, the proposed concept can be extended to azimuth and elevation beam steering by adding control circuits in the radiating elements. Using such reconfigurable antennas, it is possible to increase the communication capacity thanks to interferences mitigation or media-based modulation [START_REF] Khandani | Media-based modulation: A new approach to wireless transmission[END_REF].

The remainder of the paper is organized as follows. In Section II, the concept is described. Section III presents results for the reconfigurable power divider and the full antenna. Finally, concluding remarks are given in Section IV.

II. PROPOSED CONCEPT

The proposed concept is illustrated in Fig. 1. A periodic structure made of metallic wires is integrated in a radial waveguide. The metallic wires are loaded with PIN diodes (or MEMS) controlled by a DC circuit. The radial waveguide is excited by a coaxial probe which couples to radiating elements arranged around the periphery of the periodic structure.. The pass-bands and stop-bands characteristics of the periodic structure, which is called Cylindrical Electromagnetic Band Gap (CEBG) structure, can be analyzed by using the techniques described in [START_REF] Boutayeb | Analysis of radiusperiodic cylindrical structures[END_REF][START_REF] Boutayeb | Étude des Structures Périodiques Planaires et Conformes Associées aux Antennes. Application aux Communications Mobiles[END_REF]. Using these techniques the parameters (periods and wire diameter) of the CEBG structure are optimized for operating at 5.8 GHz. Port 11

Transition from radial waveguide to radiating element designed (using HFSS software) and fabricated. Figs. 23show the design and photo of fabricated prototype. Since there are 20 groups of diodes, there are 2 20 different possible states. Fig. 4 shows photo of the S parameters measurement setup and Fig. 5 presents simulated and measured S21 and S101 parameters for State 1 shown in Fig. 8. One can note that a good agreement is observed between theoretical and experimental results. Also, one can note that there is more than 30dB difference between S21 and S101 at 5.8GHz. At this frequency, S11 is below -12dB (not shown here). IV. CONCLUSION A new technique has been proposed for designing agile antennas by using a cylindrical EBG structure integrated in a radial power divider. More details on the performance of these types of antennas will be presented during the conference.

Fig. 1 1 Port

 11 Fig. 1 Principle of proposed smart antenna III. RADIAL POWER DIVIDER AND AGILE ANTENNA

Fig. 4 SFig. 8

 48 Fig. 4 S parameters measurement setup for the power divider


Fayez Hyjazie
email: fayez.hyjazie@huawei.com

Paul Watson

Halim Boutayeb

Dual Band Interleaved Base Station Phased Array Antenna With Optimized Cross-Dipole and EBG/AMC Structure

In this work, a new base station antenna is proposed. Two separate frequency bands with separate radiating elements are used in each band. The frequency band separation ratio is about 1.3:1. These elements are arranged with different spacing (wider spacing for the lower frequency band, and narrower spacing for the higher frequency band). Isolation between bands inherently exists in this approach. This avoids the grating lobe effect, and mitigates the beam narrowing (dispersion) seen with fixed element spacing covering the whole wide bandwidth. A new low-profile cross dipole is designed, which is integrated in the array with an EBG/AMC structure for reducing the size of low band elements and decreasing coupling at high band.

I.

INTRODUCTION

In an array of elements with fixed locations, the characteristics of the radiated pattern vary with frequency (Fig. 1): the main beam narrows and grating lobes appear as the frequency increases. If a wide bandwidth element is used, the beam narrowing is excessive at the high band end. In addition, isolation between array input ports must be achieved with a diplexer, which introduces loss as well as expense and complexity. To resolve this issue, using separate elements in base station array antenna for each of two bands, with independent spacing (Fig. 2) has been often used. However, this technique has been usually used for bands which are multiples of one another [START_REF] Lee | Dual-band, dual-polarization, interleaved cross-dipole and cavity-backed disc elements phased array antenna[END_REF], (i.e. 900MHz, 2100MHz bands co-existing on the same conductive reflector).

In the proposed approach, the frequency bands are not near multiple factors of one another. In fact, the 1800MHz, 2100MHz low bands and the 2690MHz high band are relatively close to one another. Different element spacings were chosen for low band (e.g. 85mm) and high band (e.g. 63mm), resulting in no co-located elements, and asymmetry in the array. This gave independent and electrically optimal element spacing in each band. Choosing separate elements takes advantage of the isolation inherent between the elements to increase the isolation between bands at the antenna input ports, reducing filtering requirements. The main challenge with this approach is to limit the effects of the closely-spaced elements on adjacent elements. This includes mutual coupling as well as perturbation of the individual element patterns. This approach is useful for relatively closely spaced frequency bands in the same antenna, somewhere about 1.3:1.

Based on [START_REF] Hyjazie | Cup dipole antenna design and analysis[END_REF][START_REF] Li | A broadband printed dipole and a printed array for base station applications[END_REF], a new printed cross-dipole antenna element has been designed with low profile. We have also introduced an Artificial Magnetic Conductor (AMC) to reduce the size of the low band element. The AMC structure is made of conductive patch in a printed circuit board. This structure presents an Electromagnetic Band Gap (EBG) behavior in the high band.

In the paper, 1710-2170MHz and 2490MHz-2690MHz will be, respectively, called the low band and high band. The proposed array has 8 ports: each band has ±45 polarization ports and two beams ports (for dual sector base stations). Top and side views of the array are shown in Figs. 3 and4, respectively. Azimuth beam forming is obtained with a wideband butler matrix and elevation beam tilting is controlled with phase shifters.

As shown in Fig. 4, two cross-dipoles with low profile are used for low band and high band. These antennas were optimized with return losses and cross-polarization coupling less than -15dB. To reduce further the size of the low band cross-dipole, an EBG/AMC structure is placed around it. The EBG/AMC structure is designed such that the AMC behaviour is observed in the low band (Fig. 5) and the EBG behaviour is observed in the hig h band (Fig. 6).

The full-wave simulated co-pol radiation patterns of the full array, for two sectors and one elevation downtilt, are presented in Fig. 7, showing fairly low dispersion.

Fig. 1

 1 Fig. 1 Undesired dispersion effect in radiation patterns of wideband array

Fig. 3

 3 Fig. 3 Top view of the 8-port interleaved array

Fig. 5

 5 Fig. 5 Phase of reflection coefficient of the AMC structure analyzed using Floquet boundary conditions