UWB communication systems transmit pulses instead of modulated sine waves

1
Introduction

• UWB communication systems transmit pulses instead
  of modulated sine waves
• Signal occupies a very broad BW (1Hz2GHz)
• Antenna can no longer be optimized at the carrier
  frequency (no carrier in UWB!)
• Frequency-independent antenna is needed

DSP
2
Challenges in UWB Antenna Design

• EM aspects of UWB communication systems have not
  been studied adequately
• Most of the conventional antenna analyses assume
  harmonic time dependent (not the case in UWB)
• Time-domain EM analysis/simulation are needed
• Issues in UWB antenna design
• Efficient pulse generation/reception
• Pulse dispersion problem
• Matching/Ringing problem

3
System Design Perspective

• UWB antenna is not likely to be a purely
  resistive load and may strongly influence the
  transmitter circuits
• Antenna/circuit co-design is necessary
• Efficient pulse-shape design
• Taking pulse-shape design into account adds one
  more dimension to improve the performance of the
  antenna

Pulse Generator
Transmission Line
Bonding Wire
Antenna
4
Antenna Specifications

• Requirements of UWB antenna
• 2-Dimensional
• Omni-directional field pattern
• Small size
• Low cost
• Possible candidates
• Dipole antenna
• Loop antenna
• Microstrip antenna

5
Dipole Antenna

• Consists of two straight wires
• Simple scheme, easy to analyze, mechanism
  is well-known
• Popular in narrow-band systems
• Humps in frequency domain
• Resistively loaded dipoles exhibit very broad BW
  since reflection on the antenna is suppressed,
  but
• Radiation efficiency is reduced
• Termination is a problem

Feed point
6
Loop Antenna

• Circular turns of wire
• To meet the 2D geometry spec only 1 turn is used
• Used for AM radio
• Radiate normally/axially if the loop is
  small/large relative to a wavelength
• A modified version, Large Current Radiator, is
  adopted by Aether Wire Location, Inc., an UWB
  localizer company. Large radiation power can be
  delivered, but its shape is 3D

Input
7
Microstrip Antenna

• Metallic patches sit on a dielectric substrate
• Usually made on PCB
• Low profile, conformable to various surfaces,
  inexpensive, durable, but narrow-band
• Modify the shape to broaden the bandwidth, e.g.
  bowtie antenna

Dielectric substrate
Antenna Patch
ground
8
EM Simulation Tool

• Remcom XFDTD
• Full-wave EM simulator based on Finite Difference
  Time Domain method
• Ex. Monopole antenna on a conducting box

9
Future Work

• Establish performance evaluation procedure in
  XFDTD and compare different antenna schemes
• According to reciprocity theorem, we can simply
  look at the transmitting antenna in early
  simulation
• Important parameters of the transmitting antenna
  s11, input impedance, radiation pattern, etc.
• After thorough investigation by simulation, build
  the antenna on PCB and experiment its
  practicability
• Transmitter design
• Pulse generator design
• Simulation of the antenna/circuit interface
• Combine SPICE/Spectre and XFDTD