Electronic BeamWidth Control Principle

Samuel Cherukutty C208114018

M.Tech

Quick Recap

Problems With LW antennas

Frequency Scanned No broadside radiation and continous scanning capability Require fixed frequency operation for effective

channelization Not that good solutions

Horn's antenna using diodes as switch

Maheri's antenna using dc magnetic field tuning Good Solution

Varacter Diode BE LW antenna

Varacter Diode BE LW antennas

Uses Varactor diode

Control beamwidth by varying reverse bias

Continous beam steering

Beam-width control by non uniform bias distribution Advantages

Only 1 radiating element

Simple and compact feed mechanism

Not necessiating any phase shifters

Electronic Scanning Principle

θ MB = θ MB(β)

For antenna

β = β(ω;LR ,CR ,LL,CL)

For CRLH MTM

θMB = θMB(ω)

θMB = θMB(V)

Electronic Beamwidth Control Principle

Electronic Scaning

Bias Distribution is uniform

Results in periodic structure(uniform)

Incremental length radiate to same direction-max directivity

Electronic Beamwidth Control

Different cell radiate at different angle

Beamwidth increased( via superposition)

Control beamwidth

Bias progressively unifrom from backfire to endfire

The Structure

2 Series and 1 Shunt varactor diodes for

Wide scanning range

More degrees of freedom

Anodes of varactors are grounded for simpler bias

Different… but with similar performance

The Analysis

(CLvar

andCRvar

) decrease exponentially with increasing reverse bias

Z(V)and Y (V) decrease (at typically low voltages) as V increases

cos(βp)=1+Z(V)Y(V)1 as V increases,β→0

Main beam angle steere d broadside with increasing voltage

Observed as dθMB

(V)/dV=(∂β/∂V

)/ (1−(β/k0)2)0.5

The Measurement

Voltage above 3.5v results in backward radiation(uniform bias)

Increased backward radiation with nonuniform 5 → 15 v

Large insertion loss

Radiation leakage

Resistance loss

In varactors

Gain 18 db brodside

S11

= -12 → -8 db

THANK YOU!!!!