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Cellular Repeater

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Idea to amplify signals in US Cellular frequency bands to prevent dropped ... Slow to respond or get back to us. Necessary to accomplish functionality ourselves... – PowerPoint PPT presentation

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Title: Cellular Repeater


1
Cellular Repeater
  • ECE 345 Project 9
  • Mark Nowak
  • Kevin Swanson
  • TA Lee Rumsey
  • December 2, 1999

2
Project Overview
  • Idea to amplify signals in US Cellular
    frequency bands to prevent dropped calls in areas
    of poor coverage
  • Applications
  • Tunnel entrances
  • Parking garages
  • Dead spots in cell coverage areas
  • Underground areas (e.g. subways malls)

3
Initial Specifications
  • Frequency Ranges
  • From Base Station 824-849 MHz
  • From Handsets 869-894 MHz
  • Amplifier must cover both ranges
  • Gain
  • Site specific
  • Make measurements to determine gain needed
  • We supposed site requiring 40 dB gain

4
Our Site of Application
  • Traffic tunnel
  • Concrete walls (e 3, ? 218 O)
  • For ?i 45o and 150 ft. tunnel
  • About 10 bounces at - 4.2 dB/bounce 42 dB
    loss
  • Repeater therefore needs about 40 dB of gain
  • to compensate losses from tunnel
  • Likely to have better line of sight and less
    bounces than this
  • Less gain necessary then

5
Original Block Diagram
6
Amplifier Selection
  • Hewlett-Packard HPMX-3002
  • RFIC 900 MHz Driver Amplifier
  • 150-960 MHz Operating Range
  • Input well matched to 50 W from 100 MHz to 1.1
    GHz
  • Easy to externally match output to 50 W for
    maximum power output
  • 50 dB power control range

7
Amplifier Functional Block Diagram
(2) VCC1 (1st and 2nd stages)
(4) RFIN
(6) RFOUT and Vcc2 (3rd stage bias, open
collector)
(1,3,7,8) Ground
(5) Power Control
8
Antenna Selection
  • Antenna radiation patterns can not overlap
  • Solution Micropatch antennas
  • Radiate perpendicular to plane of board
  • Problems
  • Not available commercially _at_ 800-900 MHz
  • Impractical to design and construct ourselves
  • Solution Quarter-wave dipole with shielding
  • Larsen NMOQ800B 806-896 MHz

9
Circulators/Duplexors
  • Antennas both receive and transmit
  • Must isolate Rx and Tx paths to avoid feedback
    loops
  • Solution Circulators and duplexors prevent
    output of one amplifier from feeding into input
    of other amplifier
  • Circulators
  • 3-port device permitting flow of microwave energy
    in one direction only
  • Duplexors
  • Rx and Tx path filters
  • Only useful if Rx and Tx frequencies different

10
  • Problems with circulators and duplexors
  • Vendors reluctant to deal in small quantities
  • These products are custom designed and built
  • For small orders, development costs may exceed
    price of units
  • Slow to respond or get back to us
  • Necessary to accomplish functionality ourselves

11
Proposed Solutions
  • Design and construct bandpass filters
  • Problem small normalized bandwidth
  • lt 3 for BW 25 MHz and fc 837 882 MHz
  • Lumped component design
  • Leads to unrealizable capacitor and inductor
    values
  • Microstrip transmission line design
  • Difficult to realize precision line widths
  • Work-around implement repeater in one direction
    only
  • Trivial going from one-way to two-way repeater if
    matched circulators or duplexors available

12
Modified Schematic
13
Amplifier Construction
  • Chose to fabricate boards ourselves
  • Etched boards using pcb kit from RadioShack
  • Created screw holes and vias with xacto knife
  • Plated thru holes to ground plane necessary to
    avoid stability problems
  • Soldered all components by hand
  • Surface mount IC, chip caps and inductors
  • Cut and applied Cu tape for transmission lines
  • Calculator available on Rogers web site
  • Mounted N-type connectors on board and antennas

14
Test Procedure
  • All characterization and verification done with
    network analyzer
  • First measure s-parameters of amplifier alone
  • Compare with data sheet
  • Next measure performance of antennas alone
  • Finally connect board to antenna and measure
    improvement in gain

15
Test Results S21
  • S21 represents the gain of the amplifier

16
Test Results S11
  • S11 represents the input reflection coefficient

17
Test Results S12
  • S12 represents
  • the reverse gain
  • of the amplifier

18
Test Results S22
  • S22 represents
  • the output
  • reflection
  • coefficient

19
Antenna SWR
SWR close to 1 shows good power transfer well
matched to 50O
20
Antenna and Amp S21
21
Comparisons
  • Gain of amplifier alone consistent with
    improvement amplifier adds to antenna gain

22
Total Cost
Total Cost 14,547
23
Conclusions/Recommendations
  • Better environment for testing antennas
  • Professional fabrication techniques to improve
    amplifier performance
  • Improved linearity over frequency
  • Optimal layout of components
  • Continue search for micropatch antennas and
    suitable duplexors for application

24
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