Design of Polygonal Patch Antennas with a. Broad-Band Behavior via a Proper Perturbation of Conventional Rectangular Radiators

Transcription

1 Università degli Studi ROMA TRE Dipartimento di Elettronica Applicata Via della Vasca Navale Roma Design of Polygonal Patch Antennas with a Broad-Band Behavior via a Proper Perturbation of Conventional Rectangular Radiators Filiberto Bilotti, Mauro Manzini, Andrea Alù, and Lucio Vegni 2003 IEEE AP-S INTERNATIONAL SYMPOSIUM Session 50: Broadband Microstrip Patch Antennas Tuesday, OUTLINE 1. Polygonal patch antennas for telecommunication purposes: multi-frequency operation and broadband behavior 2. Rigorous theoretical analysis based on the Spectral Domain Analysis and the Electric Field Integral Equation formulation 3. Method of Moment entire-domain basis functions for convex polygonal patches 4. Design procedure to synthesize algorithmically suitable patch antennas for UMTS and W-LAN applications 5. Conclusions 1

2 POLYGONAL PATCHES FOR TELECOMMUNICATION APPLICATIONS Need for multi- frequency operation (different services, different frequency bands in different countries, uplink and downlink, etc.) Need for compact antennas exhibiting a broadband behavior (multimedia services will require large impedance bandwidths) Why polygonal patches are good candidates for these applications? The irregular shape allows obtaining more than one resonance and such resonances can be arbitrarily spaced by properly choosing the patch dimensions and the number of polygon sides. THE BASIC IDEA (1) Rectangular patch Irregular patch The resonance locations on the frequency axis depend on the two side lengths of the rectangular shape The resonance locations on the frequency axis depend on the number of sides of the polygon, their lengths and their geometry 2

3 THE BASIC IDEA (2) Main advantages: new freedom degrees in the number and the location of the patch resonance frequencies reduction of weight and space occupancy (array configurations) reduction of the patch area at a fixed working frequency Some drawbacks: reduction of the impedance bandwidth for a single operation mode potential reduction of the polarization purity (not always required) potential variation of the radiation pattern shape (not always required) FULL WAVE ANALYSIS AND EFIE FORMULATION The radiating structure is analyzed in the spectral domain exploiting with the dyadic Green s function formulation for a linear, isotropic and homogeneous grounded slab. Imposing the boundary conditions of the electric field on the metallic patch, an integral equation (EFIE) in the unknown induced current density can be derived. Its solution is obtained with a Method of Moment formulation. ˆx ẑ ŷ 3

4 GEOMETRY OF A GENERIC CONVEX POLYGONAL PATCH X y 6 L 6 y 5 y N-1 y 4 L 5 The patch sides are numbered counter- clockwise. y N x N-1 x 1 x 6 x 2 x 5 x 3 = x 4 y 3 L N L 4 Y The origin of the reference system coincides with the most left polygon vertex. L 1 L 3 y 1 =y 2 L 2 DEFINITION OF THE MoM ENTIRE-DOMAIN BASIS FUNCTIONS Physically reasonable entire- domain basis functions should describe an induced current density whose: normal component (with respect to each edge) vanishes on the polygon perimeter; tangential component (with respect to each edge) is singular on the polygon perimeter. mπ J (x,y) = sin (x left) right left (edge) 1 J xk (x,y) = βk (k) y edgey xm mπ J ym (x, y) = sin (y bottom) top bottom (edge) 1 J yk (x,y) =+ αk (k) x edgex 4

5 DESIGN PROCEDURE FOR UMTS RADIATORS (1) Starting point: rectangular patch designed to resonate in the UMTS frequency range through a cavity model approach W L Original patch suspended on a 5 mm air substrate (W=7.2 cm, L=6.2 cm) DESIGN PROCEDURE FOR UMTS RADIATORS (2) Some considerations: In multi- path environments, we don t have any requirement on crosspolarization levels: the bandwidth can be widened by contemporarily exciting two orthogonal modes with sufficiently close resonance frequencies. In order to exploit this feature, the probe is located along the diagonal of the rectangular patch. The two dimensions are designed so that the resonance frequencies are approximately at the edges of the UMTS operational bandwidth. A significant mismatch is found at the center of the operational bandwidth and a perturbation of the original shape is needed to increase the mode coupling and consequently reduce this mismatch. 5

6 DESIGN PROCEDURE FOR UMTS RADIATORS (3) ϕ 0.25W 0.25L W L/2 L ŷ ˆx Tilting two sides: effects on the mode coupling. ϕ = 0 ϕ = 7 ϕ = 12 ϕ = 19 DESIGN PROCEDURE FOR UMTS RADIATORS (4) A first perturbation of the original size is performed by tilting the two sides. Its main effects are: a coupling of the two current modes on the patch, which in the original shape were spatially- orthogonal; a reduction of the effective patch length and width, inducing an increase in the two resonance frequencies; a better impedance matching between the two resonances, which brings the maximum in the UMTS range below the - 1 limit for standard matching requirements; an overall increase of the total bandwidth. 6

7 DESIGN PROCEDURE FOR UMTS RADIATORS (5) 0.25 W' 0.25 L' W' L' Input Reflection Coefficient Amplitude dB L'=L+0.3; W'=W+0.4 L'=L+0.3; W'=W+0.8 Further shape perturbations to bring the operation bandwidth back inside the UMTS range. DESIGN PROCEDURE FOR UMTS RADIATORS (6) y (0, 3.35) (1.6, 6.575) (2, 1.35) (6.6, 6.575) (0, 0) (7.2, 0) (8.375, 3.35) x Final perturbation: probe positioning for a better matching. Optimized shape

8 (0, 2.4) APPLICATION TO OTHER RADIATOR DESIGNS (1) (0.8, 3.2) (0.4, 0.4) (0, 0) (2.7, 0) (3.2, 3.2) (4.1, 2.6) (4.1, 0.9) Input Reflection Coefficient Amplitude Final shape and optimized feed position for a smaller antenna, obtained by increasing the substrate permittivity ε = ( ) r PRESENCE OF LOSSES (0.8, 3.2) (3.2, 3.2) (0, 2.4) (0.4, 0.4) (0, 0) (2.7, 0) (4.1, 2.6) (4.1, 0.9) Optimized antenna for the original case, considering losses (FR4, tan δ=0.019) 8

9 FINITENESS OF THE GROUND PLANE MOBILE HANDSET 5 cm (0.8, 3) (3.2, 3) (4, 2.4) (0, 2.2) 4 cm (0.4, 0.4) (4, 0.7) (0, 0) (2.6, 0) -1-2 ε r1 = mm Optimized antenna for the original case, for an handset (limited GP). 5 cm COVERING THE STRUCTURE (0, 2.2) (0.8, 3) (0.4, 0.4) (0, 0) (2.6, 0) ε r2 = 2.2 (3.2, 3) ε r1 = 4.4 (4, 2.4) 4 cm (4, 0.7) 1 mm 7 mm By adding a cover, the UMTS range is better 9

10 (0, 1.95) APPLICATION TO OTHER RADIATOR DESIGNS (2) (0.8, 2.75) (0.4, 0.4) (0, 0) (2.4, 0) (2.7, 2.75) (3.3, 2.25) (3.3, 1) Final shape and optimized feed position for a W-LAN antenna, with multi- ε = 4.4 frequency behavior ( ) r (-1.8, 1.4) (-1.8, -1.4) (-1.5, 0) APPLICATION TO OTHER RADIATOR DESIGNS (3) ŷ (1.8, 1.7) (0.7, 1.55) (0, 1.52) (-0.49, 0) (1.6, 0) (0, -1.52) (0.7, -1.55) (1.8, -1.7) ˆx [ref] this talk Improvement of an existing UMTS antenna: [ref]:y.j. Wang, et al., IEEE MTT, Vol. 9, No. 8, pp , Aug

11 We have shown: CONCLUSIONS how the application of polygonal shapes may improve patch performances for telecommunication purposes: multi-frequency operation and broadband behavior a rigorous theoretical analysis based on the Spectral Domain Analysis and the Electric Field Integral Equation formulation an efficient Method of Moment formulation based on entiredomain basis functions for arbitrarily convex polygonal patches an algorithmic design procedure to synthesize suitable patch antennas for UMTS and W-LAN applications 11