PRINTED ACTIVE RADIATORS (from the active antenna concept till the usual technology)

1. PRINTED ACTIVE RADIATORS (from the active antenna concept till the usual technology) Daniel Segovia Vargas Vicente González Posadas Carlos Martín Pascual

2. Active Antenna Concept

3. R d Rx Gr(σ) Gt CIRCUITRY CIRCUITRY Tx Pr PR PT Pt Noise Lr S/N? Lt Frequency Transmission line losses+… EIRP Mispointing Distance Radio channels (I) Friis Equation Gt, Gr are GAIN (include mismatch, Xpol, antenna losses)

4. S/N> threshold allowing information extraction Power sum: P C Rx Na NA NR Nb Radio channels (II) • In Friis Equation: • If d is link range PR is the minimum detectable signal • In a link budget: • What about noise? • Incoherent • Incorrelalated • Random Polarization

5. ΩR ΩT B Noise Source Brigthness Friis Radio channels (III)

6. Spectral density of brigthness Directivity Spectral density of power Spectral density of flux b) For a “point” source: Ωs=(ΩT)<< θ3dB(rec. ant.): Sf Bfs Ωs Radio channels (IV) a) For a widespread source

7. (f ↓) Rayleigh-Jeans Law For f 300 GHz Bf(Rayleigh-Jeans)<1.03 Bf(Planck) Blackbody radiation (Planck)

8. For Δf Bf almost constant AntennaTemperature Random polarization Antenna temperature For a “non black” (i.e: grey) body: Bf =Bf(bb) •ε(θ,φ,f,surface) Brigthness temperature T = ε•T emissivity

9. G/T • Characteristic of the whole receiving chain • (constant value along chain)

10. Sky temperature, Ts(θ,Φ) Attenuation: A, Tm NA • Common absorbing media: • Atmosphere: T0, A0 • Radomes: Tr, Ar • Dielectric masts: Td, Ad • ….…. Nm+N’s If the absorbing medium occupies the whole main lobe and Ts is constant: RX Hertz channels: absorption

11. Atmospheric absorption

12. Antenna structure trade-off in 70´s

13. IDEAL L REAL (all ohmic losses including cables, lines,etc) RX (Fn) RX (Fn) CIRCUITRY G’, T’A G, TA G, TA 1) What about L if it corresponds to the “connecting” devices(cables,lines,...)? 2) What about arrays, where “connecting lines” BFN are intrinsic constraintments of the antenna? Active antennas (I) X D

14. RX (Fn) Gi, Fni …. a …. b c L RX (Fn) G1, Fn1 G1, Fn1 G’, T’A G, TA Active antennas (II) SOLUTION TO 1 • Put an LNA as near as possible to the antenna • The L contribution to noise is divided by GA SOLUTION TO 2 ACTIVE (Rx) ANTENNA • a, b, c, …are the places(by priority order) where to put LNA´S

15. Classical array concepts Scanning Array Multibeam Array

16. Active array concept (I) Other way of thinking: DISTRIBUTED CONTROL OF POWER (several receivers). CAN BE EXTENDED TO TX (several transmitters)

17. T/R module Active array concept (I)

18. A monolitic T/R module is adequate only for very big active systems For more reduced sytems, the preferred choice is a hybrid assembly of chips T/R modules MMICs in active antennas • High reliability • Compactness • High cost • More losses than conventional devices, especially in switches and phase-shifters

19. Block diagram of a conventional antenna Power radiated Active Device Transmission Line RF ANTENNA Block diagram of an active antenna Power radiated Active Antenna RF Device Active radiator NO (50Ω) interface!!!

20. New design concepts (Antenna-amplifier interface not necessary) Active radiators • Amplifying radiators • Rx • Tx • Self oscillating radiators • Simplicity of the BFN (good) • All the radiators must work with phase-looking (difficult). • The IF I/O active radiators • Mixer active device • External LO • The fully active radiator • Self diplexing antenna (!) HARD + ..................

21. One active module per subarray Easy characterization (separate measurements of the radiators and active circuits) Economy of diplexers One active circuit per radiator High beam agility Allows a large physical separation between the antenna and the transceiver Many diplexers are required, increasing the interest of self-diplexing elements Active system vs. Array of active elements Array of active elements Active system

22. Alternatives for active antenna systems (I) Partially active antenna (TX) Fully active antenna (RX)

23. BFN1 Matrix BFN2 Matrix N radiators Alternatives for active antenna systems (II) Semiactive antennas ….. ….. …..

24. Beam forming matrices

25. Classification of active antennas ACTIVE ANTENNAS ACTIVE RADIATORS ACTIVE ARRAYS Partially active Totally active Semiactive Arrays (mainly TX) Quasi-conventional arrays (T/R modules) Transmitters Receivers ExternalDiplexer Self diplexed Circuit Interface * RF * IF (up and /or down converters) OL AMP * optical

26. General effects of active antennas • At Rx • Increase of the system figure of merit G/T • At Tx • Less effect of the control circuit losses (if BFN is done at low power RF or IF level) • Increase of EIRP • Better efficiency if solid-state devices are used • Lower cost (higher conversion efficiency) • Easier thermal control

27. Adaptive antenna concept (I)

28. Demod. Reference signal Adaptive antenna concept (II) ADAPTIVE ARRAYS ARE ACTIVE ARRAYS

29. BFN for active antenna Usual frequency for phase shifting

30. Today trade-off

31. Printed active antennas

32. Active radiators design Which parameter does control the impedance magnitude? Which parameter does control the imaginary part slope? • No antenna circuit interface (virtual, not Z0) • Zant fixed by the amplifier (mixer, oscillator, etc…) design needs • (minimum noise, stability, etc…) • The antenna must offer a great impedance margin: resonant antennas

33. The core concept of the array design • Good aperture efficiency interelement spacing is about elementary radiator electrical size • Interelement spacing is usually fixed by the desired beams. • In general: 0.5λ (≈ 0.25λ) ≤ d ≤λ • Is there a radiator with this degree of freedom? CIRCULAR PATCHES

34. Patch antennas PATCH GEOMETRY RECTANGULAR PATCH ELIPTICAL TRIANGLE RING and others ....(pentagone,..) SQUARE RECTANGULAR LINEAR CIRCULAR

35. Advantages and drawbacks of printed antennas vs non printed Disadv. Adv.

36. The basic and useful geometries are: ONLY !!!! Rectangular Circular Ring Shortcircuited Ring

37. Patches behaviour Patches are the dual elements (Babinet sense) of open waveguides: Modes TMmnp=0 Radial pseudo period Azimuth period repetition The fundamental mode: TM11 (TM10 in rectangular patch) Dipolar mode

38. M=3 M=0 M=1 M=2 N=1 N=2 Field distribution of TMmn modes

39. 11Mode (Circular patch) Field Ez Current Lines

40. 11Mode (Circular patch) Field HΦ Field Hr

41. 11Mode: Impedance (Circular patch)

42. 11Mode: Impedance (real part)

43. 11Mode: Impedance of the ring patch (real part)

44. Summary of circular geometries Electrical size λ f() f() f() f() λ/2 The most versatile radiator? Yes, at least for arrays

45. Patch impedance Imaginary part slope depends on Q or bandwidth, which is (mainly) function of thickness Z magnitude depends on radial position of the feeding

46. Active and/or integrated technologies Patches are very well suited: • Easy integration of circuits with antenna in the hidden feeding layer or on the patch surface. Several Technologies (FET,BIPOLAR,MESFET,HEMT...) • High power is difficult because the heat dissipation (short circuited ring or center short circuited patches) • Multilayer structures(BFN*, Phasing, Amplifiers, frequency conversion) • *2 BFN’s for layer in arrays (2 polarizations, or 2 beams, or 2 frequencies..)

47. Some examples