Overlapped Feeds to Increase the Edge of Coverage Gain in Multi Beam Reflector Antennas G. Gerini(1) , A. Neto(1), N. Llombart(1), M. Bonnedal(2), P. De Maagt(3) 1 TNO Defense, Security and Safety - The Netherlands 2 Saab Space - Sweden 3 ESA-ESTEC - The Netherlands Overlapped Feeds ... for reflector antennas
Multi Spot Beam Satellite Scenario Four colours reuse scheme Maximize Edge of Coverage Gain X X out Y, Y out �� �� �� �� Reuse scheme (x4) Focal plane array 2 Overlapped Feeds ... for reflector antennas 9 April 2008
The Imaging Problem (F/D)=1 Spill over efficiency 58% � 3dB = � � 0 / D � � � � � + ���� 3dB ���� ���� ���� Similar efficiency for different F/D: ��� ��� ��� ��� d /F � � � � 0 q F/D d = � � � � 0 (F/D) Cos q ( � � ) � � 3 Overlapped Feeds ... for reflector antennas 9 April 2008
Free Space Configuration EoC Gain Case 2 EoC Gain for different reflector diameters 41.0 2.1 m F/D=0.95 2.2 m F/D=0.90 2.3 m F/D=0.87 40.5 2.4 m F/D=0.85 EoC Gain [dBi] 40.0 39.5 39.0 38.5 9.4 9.6 9.8 10 10.2 10.4 10.6 Frequency [GHz] Only solution to date: Gain is moderate…. 4 reflector antennas (combined Tx and Rx) 4 Overlapped Feeds ... for reflector antennas 9 April 2008
Leaky Wave Approach More layers equivalent to higher dielectric constant Oliner, Jackson, Di Nallo, Jecko, Mittra, Albani etc… Enhanced radiation by leaky-wave excitation Equivalent dielectric layers can be realized with metallic FSS 5 Overlapped Feeds ... for reflector antennas 9 April 2008
Leaky Wave Pole Localization � � 1 � � ebg Y s GF Re k lw � � � � � � k lw f k j ( ) sin 0 6 Overlapped Feeds ... for reflector antennas 9 April 2008
BW and Coupling Limits � � 1 ebg � � Y s GF Re k lw � � � � � � k lw f k j ( ) sin 0 ebg Y f k f ( ) BW ( ) � 1 lw 2 ebg k f Y f ( ) ( ) lw 1 2 BW � � , coupling � 1/ � � � 1 ebg � � � � jk Y s GF e Re lw ij k lw Antenna BW very narrow � � � � � � k lw f k j and mutual coupling very ( ) sin 0 high except for low � � r ! � � 7 Overlapped Feeds ... for reflector antennas 9 April 2008
Higher order leaky modes Optimizing the parameters of the dielectric stratification: • distance of the first dielectric layer from the radiating plane • distance between layers in a multilayer structure You can end up with configurations where also higher order leaky- wave modes are excited: 0.5 � � 0 � � e.g. third leaky mode, TM, …………..neglected by everyone Three Leaky Poles + Space Wave 8 Overlapped Feeds ... for reflector antennas 9 April 2008
Mode Suppression Double Iris design 0.6 � � � 0 � M. Qiu, G. Eleftheriades, A reduced surface-wave…, IEEE Microwave Wireless Components Lett. , pp. 459-461, Nov. 2001. 1 � � � � 0 Cancellation by matching with zero of the M s current 9 Overlapped Feeds ... for reflector antennas 9 April 2008
Prototype Implementation • Resistive Frequency loading Polarization discrimination discrimination • Reactive loading 4x reuse scheme 10 Overlapped Feeds ... for reflector antennas 9 April 2008
Enhanced Feed System Performance 50 50 EoC EoC EoC EoC Nominal Nominal 45 Adjacent 45 Adjacent 40 40 35 35 [dB] [dB] 30 30 eoc eoc G G 25 25 20 20 15 15 10 10 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 -1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 � (degrees) � (degrees) Enhanced Feed Free Space (Resistive loading) Case 3 EoC Gain for different reflector diameters 41.0 Enhancement of 0.6 dB over 12% BW: 40.5 EoC Gain [dBi] moderate due to: 40.0 • Stein Losses 39.5 39.0 2.1 m F/D=0.95 • Pattern widening due to mutual coupling 2.3 m F/D=0.87 2.4 m F/D=0.85 38.5 9.4 9.6 9.8 10 10.2 10.4 10.6 11 Overlapped Feeds ... for reflector antennas 9 April 2008 Frequency [GHz]
Reactive Loading Same configuration � r =4.5 � � � Isolated Array Period d = 2.4 � � � � 0 Equivalent short circuits loads for neighboring waveguides 12 Overlapped Feeds ... for reflector antennas 9 April 2008
Demonstrator 2: Measured Patterns H-plane E-plane 13 Overlapped Feeds ... for reflector antennas 9 April 2008
Comparison 41.5 Reactive Loads Best�Case�(F/D=0.87) 41 40.5 Matched Loads [dB] Worst�Case (F/D=0.85) 40 eoc G 39.5 Reference (F/D=0.85) 39 38.5 9.4 9.6 9.8 10 10.2 10.4 10.6 f�[GHz] • With single dielectric slab, EoC Gain increase 0.85 dB over 3% BW • Adding reactive loadings (filters), EoC Gain increase 1.6 dB over 3% BW 14 Overlapped Feeds ... for reflector antennas 9 April 2008
Larger F/D and more directive feeds F/D=1.71; Period ( d ) = 4.8 � 0 � 0 =17 o Feeds with higher directivity are required. Analyzed three different solutions, which do not require feeds of larger dimensions: • Single dielectric layer of high permittivity: � r =20.25 • Two dielectric layers of low permittivty: � r =4.5 • Metallic FSS (to avoid the use of dielectric layers) 15 Overlapped Feeds ... for reflector antennas 9 April 2008
Patterns Double Dielectric Case FSS Primary Secondary 16 Overlapped Feeds ... for reflector antennas 9 April 2008
Impedance Matching Double Dielectric Case h 1 =15 mm h 2 =3.535 mm d=144 mm FSS Case h 1 =14 mm t=0.25 mm d=144 mm 17 Overlapped Feeds ... for reflector antennas 9 April 2008
Comparison - Frequency range of applicabiltiy - Best case: � 2.0 dB, in � 4.0 % BW 18 Overlapped Feeds ... for reflector antennas 9 April 2008
New Demonstrator - Filters 19 elements (F/D=1.7; d= 4.8 � � ) 4x reuse scheme (2 pol. – 2 freq.) Filter High (10.01 – 10.10 GHz) Filter Low (9.875 – 9.965 GHz) • VSWR < -20 dB • Rejection > 28 dB 19 Overlapped Feeds ... for reflector antennas 9 April 2008
Recommend
More recommend
