NEAR-FIELD DIRECT ANTENNA MODULATION
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29-10-2010, 08:46 AM


NEAR-FIELD DIRECT ANTENNA MODULATION
PRESENTED
BY
NABEEL SALAM
NO.44
S7 EC
College Of Engineering, Trivandrum
2007-11 batch



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OUTLINE

Conventional Transmitter Architecture
Modulation at Baseband
Direct Antenna Modulation
Implementation of NFDAM
Applications of NFDAM
Improvements
60 Ghz Transmitter and NFDAM chip
Conclusions

CONVENTIONAL TRANSMITTER ARCHITECTURE
Signal is modulated at base-band
Antenna transmits the same information to all directions
Signals that are transmitted in different directions differ only in their power level and time delay


MODULATION AT BASEBAND

In conventional architectures, the radiation pattern of the antenna remains unchanged at each symbol transmission
For a fixed antenna pattern, any change in the phase or amplitude of the base-band signal is detectable in the desired direction as well as the undesired direction




DIRECT ANTENNA MODULATION

In the above transmitter architecture, the far-field of the antenna changes at each symbol transmission, but the change in the far-field is not the same for all angles
The antenna pattern needs to be varied at the speed of symbol-rate to be able to modulate the signal




DAM GENERAL CONCEPT
Diode switch ON (V > Vd)
Short circuit effectively exists between patch antenna and ground plane
Antenna radiation effectively ceases
Diode Switch OFF (V < Vd)
Diode at high impedance
Antenna fully radiates at resonance

ANTENNA MODULATION VIA REFLECTOR SWITCHING
Switching affects the scattering characteristics of the reflector
The phase and amplitude of the reflected signal vary by switching



ARBITRARY SIGNAL MODULATION
It is possible to increase the number of the constellation points by adding more reflectors and switches
Each additional switch doubles the number of the constellation points



NEAR FIELD DIRECT ANTENNA MODULATION
Reflectors are placed in the near-field of the antenna
CMOS switches can be used to implement the NFDAM transmitter

NEAR FIELD DIRECT ANTENNA MODULATION
An efficient switching PA can be used while transmitting a non-constant envelope modulated signal
As the PA amplifies the non-modulated carrier signal, it can be narrow-band


SECURE COMMUNICATION LINK

ERROR RATE DUE TO SIGNAL SCRAMBLING
By changing the angle, some of the constellation points move to adjacent cells and introduce error


NOISE INDEPENDENT ERROR RATE
A total number of 210 equally-spaced points are selected
Bore-sight is set to be the desired direction in this example
The desired direction can be steered by choosing a different set of switching combinations



ENHANCED SECURITY USING REDUNDANCY
For a total number of N switches on the reflectors, 2N configurations exist. For example: N=90→290~1027
Redundancy can be used to generate a single constellation point in the desired direction with many different switching combinations





MULTIPLE BEAM TRANSMISSION
Transmission of two independent streams in two directions at full rate without resorting to multiple access techniques
SPECTRAL CONTROL
To control the out-of-band EM emission radiated by the antenna
Directly moving from A to B causes out of band emissions
Redundancy concept is used to render any trajectory using multiple intermediate points


PHASED ARRAY CONFIGURATION
Each NFDAM system can behave as a single element in a phased array configuration
NFDAM system can control the information beamwidth
Phased-array functionality can be used to narrow the power beamwidth



60 Ghz NFDAM TRANSMITTER
Coverage of the signal constellation diagram is a function of size, shape, and location of the reflectors as well as their distance from the main antenna

TRANSMITTER WITH OPTIONAL COARSE CONROL UNIT
Coarse control unit acts as quadrant selector
Control signals A and B can take values 1 and -1

SWITCH AND REFLECTOR
Switches with a relatively high ratio of OFF to ON impedances must be implemented
A circular shielded transmission line is used to connect the drain and source of the NMOS switch
OFF impedance of 70 ohm at 60Ghz can be obtained

NFDAM CHIP MICROGRAPH
The chip includes on-chip antennas, switches, and reflectors as well as a digital control unit, receiver, and LO generation circuitry

CONCLUSIONS

Concept of Near-Field Direct Antenna Modulation has been introduced
NFDAM can be effectively used to establish a secure communication link
Multiple beam transmission is possible using NFDAM without any multiple access techniques
Spectral Control can be effectively done using NFDAM
NFDAM transmitter can be used in a phased array configuration to improves power efficiency
An example of a 60 Ghz NFDAM transmitter has been discussed

REFERENCES
A. Babakhani, D.B. Rutledge, and A. Hajimiri, ”Near-field Direct Antenna Modulation,” IEEE Microwave Magazine, vol. 17, no. 6, Feb. 2009, pp. 36 - 46
A. Babakhani, D.B. Rutledge, and A. Hajimiri, “Transmitter architectures based on near-field direct antenna modulation,” IEEE J. Solid-State Circuits, vol. 43, no. 12, Dec. 2008, pp. 2674 – 2682
A. Babakhani, D.B. Rutledge, and A. Hajimiri, “A near-field modulation technique using antenna reflector switching,” in IEEE ISSCC Dig. Tech. Papers,vol.10, no. 5, Feb. 2008, pp. 188–189


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