Multi-Mode Antennas for Hemispherical Field-of-View Coverage

Multi-Mode Antennas for Hemispherical Field-of-View Coverage D.S. Prinsloo P. Meyer R. Maaskant M.V. Ivashina Dept. of Electrical and Electronic Engineering Dept. of Signals and Systems Stellenbosch, South Africa Gothenburg, Sweden 20 April 2015 Multi-Mode Antennas for Hemispherical Field-of-View Coverage 1 of 25

Outline 1 Introduction 2 Cylindrical Quad-Mode Antenna 3 Conical Quad-Mode Antenna 4 LOFAR Comparison 5 Conclusion Multi-Mode Antennas for Hemispherical Field-of-View Coverage 2 of 25

Introduction Motivation Motivation To develop antenna elements that achieve near-hemispherical field-of-view coverage by utilizing multiple orthogonal excitation modes present within multi-conductor antenna feeds Multi-Mode Antennas for Hemispherical Field-of-View Coverage 3 of 25

Cylindrical Quad-Mode Antenna 1 Introduction 2 Cylindrical Quad-Mode Antenna Design Excitation Modes 3 Conical Quad-Mode Antenna 4 LOFAR Comparison 5 Conclusion Multi-Mode Antennas for Hemispherical Field-of-View Coverage 4 of 25

Cylindrical Quad-Mode Antenna Design Cylindrical Quad-Mode Antenna Cylindrical quad-mode antenna integrates and co-locates two perpendicularly oriented cylindrical dipole elements with a cylindrical monopole element [1] Antenna excited through a quadraxial transmission line supporting four orthogonal excitation modes y Dipoles x x Monopole Sleeve Quadraxial Feed Each inner conductor connected to one of the dipole arms Cylindrical monopole element realized by extending the ground shield of the feed and folding it back over itself [1] D. Prinsloo, et al., "A quad-mode antenna for accurate polarimetric measurements over an ultra-wide field-of-view," in 8th European Conf. on Antennas and Propag. (EuCAP), April 2014, pp. 3794-3797. Multi-Mode Antennas for Hemispherical Field-of-View Coverage 5 of 25

Cylindrical Quad-Mode Antenna Excitation Modes Quad-Mode Antenna Excitation Modes Port electric field distributions TEM 1 TEM 2 TEM 3 TEM 4 Radiated far-field distributions TEM 1 TEM 2 TEM 3 TEM 4 y y y y z x z x z x z x Multi-Mode Antennas for Hemispherical Field-of-View Coverage 6 of 25

Conical Quad-Mode Antenna 1 Introduction 2 Cylindrical Quad-Mode Antenna 3 Conical Quad-Mode Antenna Conical Quad-Mode Antenna Design Simulated and Measured Response Quad-Mode Receiver Model Gain and Sensitivity (SNR) over FoV Polarimetric Performance over FoV 4 LOFAR Comparison 5 Conclusion Multi-Mode Antennas for Hemispherical Field-of-View Coverage 7 of 25

Conical Quad-Mode Antenna Conical Quad-Mode Antenna Design Conical Quad-Mode Antenna Conical quad-mode antenna integrates [1] two perpendicularly oriented bow-tie dipole antennas with a conical monopole element excited through a quadraxial transmission line supporting four orthogonal excitation modes Bow-tie dipoles printed on FR-4 substrate with each arm connected to one of the four inner conductors of the quadraxial transmission line Conical monopole element connected to the ground shield of the quadraxial feed [1] D.S. Prinsloo, P. Meyer, R. Maaskant, and M.V. Ivashina, "Quad-mode antenna for wide-scan sparse arrays," 2015 Int. Symp. Antennas Propag., Jul. 2015, accepted for publication. Multi-Mode Antennas for Hemispherical Field-of-View Coverage 8 of 25

Conical Quad-Mode Antenna Simulated and Measured Response TEM Input Reflection Coefficients Using multi-pin port excitations, the input reflection coefficients of the four TEM modes are simulated in CST. 0 y 5 z x 10 y 15 z x db 20 y 25 Γ MM1 30 Γ MM2 z x Γ MM3 y 35 Γ MM4 40 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 Frequency [GHz] z x Modes MM 1 MM 3-10 db bandwidth approximately 30 percent Multi-Mode Antennas for Hemispherical Field-of-View Coverage 9 of 25

Conical Quad-Mode Antenna Simulated and Measured Response Measured Response 0 5 ΓMM1 Measured ΓMM2 Measured 10 db ΓMM3 Measured ΓMM4 Measured 15 Γ MM1 CST ΓMM2 CST ΓMM3 CST 20 ΓMM4 CST 25 30 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 Frequency [GHz] Multi-mode response calculated from single-ended S-parameters and radiated far-field pattern measurements [1] [Phi = 90, f = 0.8 GHz] 10 10 5 MM1 CST 0 MM2 CST 5 MM4 CST 0 MM3 CST MM1 Measured MM2 Measured 10 db db 5 [Phi = 90, f = 1.1 GHz] 5 10 MM3 Measured MM4 Measured 15 20 100 50 0 50 θ, deg 100 15 20 100 50 0 θ, deg 50 100 [1] P. Meyer, D.S. Prinsloo, "Generalized mixed-mode scattering parameters and antenna far-field conversions," IEEE Trans. Antennas Propag., submitted for publication. Multi-Mode Antennas for Hemispherical Field-of-View Coverage 10 of 25

Conical Quad-Mode Antenna Quad-Mode Receiver Model Quad-Mode Receiver Model Frontend e Ideal Beamformer + Quad-mode antenna modelled as a four element array Each excitation mode represented by an array element Receiver model assumes identical and isolated SE Low-Noise Amplifiers (LNAs) connected to each of the four inner conductors of the quadraxial feed SE LNA noise model: T min = 37 K, R n = 3Ω, Γ opt = Γ MM1 TEM Receiver Noise Model Receiver noise matched to passive input impedance of mode MM 1 Multi-Mode Antennas for Hemispherical Field-of-View Coverage 11 of 25

Conical Quad-Mode Antenna Gain and Sensitivity (SNR) over FoV Max-SNR Beamformer: Gain and SNR f = 0.8 GHz Gain SNR f = 1.1 GHz db Gain db SNR Variation in gain and sensitivity 3dB 4dB over the hemispherical FoV coverage Multi-Mode Antennas for Hemispherical Field-of-View Coverage 12 of 25

Conical Quad-Mode Antenna Polarimetric Performance over FoV Max-SNR Beamformer: IXR [1] Quad-Mode Antenna f = 0.9 GHz 90 60 30 db Dual-Polarised Dipoles f = 0.9 GHz 90 60 30 db Quad-mode antenna nearly quadruples polarimetric performance with respect to FoV coverage IXR values above 15dB achieved up to 60 from zenith [1] T. Carozzi and G. Woan, "A fundamental figure of merit for radio polarimeters," IEEE Trans. Antennas Propag., vol. 59, no. 6, pp. 2058 2065, June 2011. Multi-Mode Antennas for Hemispherical Field-of-View Coverage 13 of 25

LOFAR Comparison 1 Introduction 2 Cylindrical Quad-Mode Antenna 3 Conical Quad-Mode Antenna 4 LOFAR Comparison Single Quad-Mode Antenna Maximum Gain Onsala LOFAR Station Maximized Gain 5 Conclusion Multi-Mode Antennas for Hemispherical Field-of-View Coverage 14 of 25

LOFAR Comparison Single Quad-Mode Antenna Single Quad-Mode Antenna Quad-mode antenna designed for a center frequency of 55 MHz 15 Realized Gain of Quad Mode Antenna [φ=0] y 10 Dipoles x 5 0 Monopole Sleeve db 5 Quadraxial Feed 10 TEM 1 15 TEM 2 TEM 3 TEM 20 4 100 80 60 40 20 0 20 40 60 80 100 θ [deg] Multi-Mode Antennas for Hemispherical Field-of-View Coverage 15 of 25

LOFAR Comparison Maximum Gain Maximizing the Gain (QMA vs LBA) Gain maximized at each scan angle by applying conjugate field matching [1] Maximum Gain: QMA vs LBA [φ=0] 10 5 dbi 0 http://www.lofar.org QMA LBA 5 100 80 60 40 20 0 20 40 60 80 100 θ [deg] Quad-mode antenna achieves a gain variation below 3dB over the scan range from -90 to 90 [1] M. Ivashina et al., "An optimal beamforming strategy for wide-field surveys with phased-array-fed reflector antennas," IEEE Trans. Antennas Propag., vol. 59, no. 6, pp. 1864-1875, June 2011. Multi-Mode Antennas for Hemispherical Field-of-View Coverage 16 of 25

LOFAR Comparison Onsala LOFAR Station Onsala LOFAR Station Layout LBA station comprises 96 elements placed within a circular area with 60m diameter 40 Onsala LOFAR Array Configuration 30 Embedded element patterns of LBA and QMA solved over infinite ground plane using CAESAR [1] 192 excitations for LBA array 384 excitations for QMA array Distance [m] 20 10 0 10 20 30 40 40 30 20 10 0 10 20 30 40 Distance [m] [1] R. Maaskant et al., "Fast analysis of large antenna arrays using the characteristic basis function method and the adaptive cross approximation algorithm," IEEE Trans. Antennas Propag., vol. 56, no. 11, pp. 3440-3451, Nov. 2008. Multi-Mode Antennas for Hemispherical Field-of-View Coverage 17 of 25

LOFAR Comparison Maximized Gain Maximized Gain over Hemispherical FoV Using conjugate field matching the gain of both the LBA and QMA arrays can be maximized at each scan angle [1] G(θ,φ) = 2π η N 2 w m f m (θ,φ) m=1 w [ H I S H S ] w LBA Array: N = 192 QMA Array: N = 384 [1] D.S. Prinsloo, P. Meyer, R. Maaskant, and M.V. Ivashina, "Irregular quad-mode antenna array: Field-of-View comparison with the Swedish LOFAR station," in 9th European Conf. on Antennas and Propag. (EuCAP), Lisbon, April 2015. Multi-Mode Antennas for Hemispherical Field-of-View Coverage 18 of 25

LOFAR Comparison Maximized Gain Maximized Gain over Hemispherical FoV QMA Array LBA Array Quad-mode antenna array shows 5dB increase in gain toward the horizon A 2dB increase in gain variation is observed in the array environment Multi-Mode Antennas for Hemispherical Field-of-View Coverage 19 of 25

Conclusion Conclusion Conclusions Single element multi-mode antenna designs illustrate improved FoV coverage with respect to gain, sensitivity and polarimeteric performance Preliminary investigation of an irregular sparse array of quad-mode antennas show promising results On-going work Wide-band quad-mode antenna with integrated slot antennas improve match of fourth excitation mode Investigate feasibility of an irregular sparse MFAA of quad-mode antennas Multi-Mode Antennas for Hemispherical Field-of-View Coverage 20 of 25

Continued Work Quad-Mode Antenna with Integrated Tapered-Slot Antenna elements Multi-Mode Antennas for Hemispherical Field-of-View Coverage 21 of 25

Continued Work Quad-Mode Antenna with Integrated Tapered-Slot Antenna elements 0 Input Reflection Coefficient 5 10 db 15 20 TEM 1 25 TEM 2 TEM 3 TEM 4 30 0 0.5 1 1.5 2 2.5 Frequency [GHz] Multi-Mode Antennas for Hemispherical Field-of-View Coverage 22 of 25

Continued Work Acknowledgements Square Kilometre Array Project South Africa National Research Foundation South Africa Vinnova (Sweden) Swedish Research Council Marie Curie International Research Staff Exchange Scheme Fellowship within the 7th European Community Framework Programme, contract no. 612599 Multi-Mode Antennas for Hemispherical Field-of-View Coverage 23 of 25

Continued Work QMA Array Mutual Coupling QMA array mutual coupling of excitation mode TEM 1 compared to mutual coupling of LBA array QMA Array LBA Array Multi-Mode Antennas for Hemispherical Field-of-View Coverage 24 of 25

Continued Work QMA Array Mutual Coupling QMA array mutual coupling of excitation modes TEM 3 and TEM 4 QMA Array QMA Array Mutual coupling of each excitation mode below -15dB for all 96 elements Multi-Mode Antennas for Hemispherical Field-of-View Coverage 25 of 25