Design of a low noise, wide band, active dipole antenna for a cosmic ray radiodetection experiment (CODALEMA) Didier CHARRIER Subatech, Nantes, France Didier.charrier@subatech.in2p3.fr the CODALEMA collaboration http://codalema.in2p3.fr SUBATECH, Nantes Observatoire de Paris-Meudon Observatoire de Nançay LAL, Orsay ESEO, Angers LPSC, Grenoble LPCE, Orleans LAOB, Besançon (FRANCE) IEEE International Symposium on Antennas and Propagation, June 10-15 2007, Honolulu, Hawai'i, USA
Outline Motivation Gain & Antenna impedance simulations Active antenna concept Antenna frequency response Preamplifier Active antenna sensitivity Antenna results Conclusion Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 2
Earth Atmosperic layer Motivation: cosmic ray detection by a new method 12 km 5 km Primary particle (>10 17 ev, 90% Proton) Atmospheric interaction Secondary particle & Induced electric field Pulse Shape x(t)=t.e (-t/τ) CODALEMA: Need Triggered Antenna to detect PULSES Time domain processing ANTENNA REQUIREMENT Wide bandwidth 100kHz to 100MHz active antenna High sensitivity: 1 μv/m/mhz Ideally sky noise dominated High dynamic 80dB within 1MHz Radio transmitter! Linearity Avoid intermodulation Easy to built and to install For a few km 2 array Cheap antenna Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 3
Radiator design Antenna radiator: 2 aluminium blades Dipole antenna held horizontaly above the ground e=10mm L=1.21m gap=10mm a=0.1m Towards 12 bit DAC Antenna used under f 0 With L=1.21m f 0 =111MHz Ground effect (image antenna) hmax<3/8.λ (zenith gain) hmax=1.12m h=1m Ground Fully differential preamplifier Rloss & Q-factor : Fat dipole a=0.1m R loss Antenna capacitance 2 frequencies mode Short dipole : 100k / 25MHz Linear dipole : 25M / 100MHz Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 4
Antenna gain simulation Simulation software: EZNEC Equivalent cylinder antenna: L=1.21m, d=55mm 17 segments, No loss Zenith gain Free space: nearly constant gain 3-100MHz Perfect GND: LF : Power x 4 (+6dB) 100MHz : destructive interference effect (-3dB) Real GND gain? Between perfect GND & free space curves! Half Power Beam Width Nearly constant 3-50MHz HPBW H-plane>HPBW E-plane Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 5
Antenna impedance simulation : Z a =R rad +jx a R rad X a R rad variation, for f < 25MHz ( short dipole) Free space : R rad f 2 R rad =20π 2 (Lf/c) 2 Perfect GND plane : R rad f 4! (coupling with virtual image antenna) X a variation, for f < 25MHz X a = -j3826ω @ 5MHz Ca=8.5pF f 0 (free space) = 111,5 MHz ; f 0 (GND plane) = 117,5 MHz Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 6
Va Active antenna concept : no power matching! Capacitive loaded antenna Ca Cs Cin A Vout Cs : parasitic shunt capacitance Ca : antenna capacitance 50Ω for f < 25 MHz (f o, resonance frequency) V out /V a =A.C a / (C in +C s +C a ) Transfered Power = 0 W for f=f 0 Induced current is small (capacitive input impedance) Short circuit loaded antenna Ca Cf for f < 25 MHz V out /V a =-C a /C f C s independent (virtual GND) Transfered Power =0 W Va Cs Zin for f=f 0 Vout 50Ω Induced current is higher (short circuit ) Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 7
Antenna frequency response : calculation Rrad(f) La Ca E Leff Va Za = Rrad+jXa Cs V in Cin (R loss is neglected) Vout=A(f).Vin Zin L eff : effective length: V a =E.L eff With or H(f): transfer function : V in =H(f).V a V in /E=L eff.h(f) Knowledge of Z a & G(θ,ϕ,f) for f< 25 MHz : L eff =L/2(free space), and if C a =C in V in /E=L/4 Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 8
Antenna frequency response (V in / E) (V in Calculated from the simulated values of Z a and G(zenith) Free space: Constant value (0.25m) from DC to 40MHz 7.6dB difference from DC to 100MHz Antenna 1m above a perfect GND plane cancellation for long wavelength 30dB difference from 3MHz to 100MHz! Antenna 1m above real GND plane? between the two curves! Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 9
Rrad Preamplifier : noise consideration Za La Ca V n 2 Cs Cin I n 2 V in 2 Noiseless preamplifier Total LNA input noise: Zin LNA noise 2 For f< f o /5 : I n 2 must be kept small when f CMOS transistor (I n 2 =0) For a MOS transistor: Input thermal noise choice of a WIDE input PMOS transistor K: technological constant ID: drain current W: transistor Width L: transistor length Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 10
Preamplifier: measured features Bandwidth: 80kHz(limited by the output transformer) to > 200MHz Preamplifier input noise: Less than 1nV/ Hz from 30M to 200MHz 1.47nV/ Hz @ 1MHz, 2.8nV/ Hz @ 100kHz C in = 9pF Max input dynamic : 24mVp-p Consumption : ¼ W Preamplifier transfer function : Vout / Vin Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 11
Preamplifier: : ASIC Layout Designed at subatech Techno:AMS BiCMOS 0.8μ Size:3mm2 400 circuits are available Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 12
Active antenna sensitivity and sky noise Preamplifier input noise contributions i galactic noise > preamplifier from 40 to 200MHz But only towards galactic center 40MHz/140MHz: the measured galactic noise fairly matches simulation for a perfect ground 6MHz/20MHz: sensitivity is electronic noise dominated 100kHz/6MHz: atmospheric noise dominated Preamplifier total input noises, simulation vs measurement Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 13
Antenna results for the CODALEMA experiment Pulse spectrum An array of 2 lines composed of 7 active antennas Each antenna output is sampled by a 12 bits DAC, 1Gs/s After a trigger signal generated by the coincidences of a few particles detectors Pulses are extracted from noise after a 30-70MHz Frequency, digital filtering MHz and a Treshold level filtering Time, μs Pulses generated by a cosmic ray on the antenna line Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 14
Power, dimensionless A candidate for LF radio astronomy? CasA signal received by an array of 72 log-periodic antenna (25.4dB gain) at the Nançay radio observatory. 20 21 22 23 24 23 24 Time UTC 20 21 22 Frequency, MHz 40 38 36 34 32 interference fringes obtained by correlation between the antenna array and one active antenna Fringes spread over the whole duration of the transit of CasA 30 Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 15
Conclusion This antenna gives good result for its application An array of 14 antenna is used for CODALEMA since May 2005 in France at Nançay A small array of 6 antennas is working since january 2007 in Argentina at Malargue The ground need to be modelised more accurately The antenna radiator should be improved Decreasing of the Shunt capacitance Design of a fater dipole to increase LF sensitivity Design of a crossed dipole antenna (X,Y, (Z) polarisations) Design of a better preamplifier with a low cost technology Under study in AMS 0.35μ CMOS technology simulated sensitivity is improved: +4.5dB Better linearity Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 16
Thank you for your Attention Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 17
A few spectrum measured with the active antenna Output noise density, substract 35 db for input noise LW band SW band FM band Spectrum measured in a desert area in Argentina (400km below Mendoza) Galactic noise Atmospheric noise Output noise density, substract 35 db for input noise Night spectrum Spectrum measured at the Nançay radio observatory (france) Day spectrum 0.1 1 10 100 Frequency, MHz Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 18
The CODALEMA Technique for Transient Detection Nançay 1-1201 120 MHz Expected shape of a shower transient Datation: t Threshold: n.σ Full band Noise: σ Filtered band Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 19
Active antenna frequency response (Vout/E) Calculated with the previous antenna simulated response (V in /E) and the measured LNA transfer function H(f) Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 20
Antenna impedance: measurement setup Vector network analyzer: R&S ZVRE Antenna radiator BALUN transformer h=1m 15m cable Grass Vector Network Analyser connected to the Antenna radiator through a BALUN transformer (ADT4-6T) Calibration, Open/Short/Match behind the RF BALUN Accuracy test with RLC dummy impedance Xa accuracy : better than 1% from 10MHz to 200MHz Rrad accuracy : +/- 10% from 50 to 130MHz S11 measurement Z a =Z c.(1+s11)/(1-s11) Include parasitic C s Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 21
Antenna impedance: measurement Rrad measurement From 50 to 130MHz, Measurement free space simulation, after Shunt Capacitance correction Xa measurement X a = -1590Ω @ 10MHz C a +C s =10pF C s =1.5pF F 0 = 112.5 MHz ( 111.5MHz, free space simulation) Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 22
Active dipole antenna Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 23
Prototype of a cross polarised dipole antenna Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 24
Nançay log-periodic antenna array Didier Charrier, IEEE International Symposium on Antennas and Propagation, Hawai i June 10-15 2007 25