Circular Microstrip Antennas_2.pdf

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  • Circular Microstrip Antenna and Properties Improvement

    EL5056 & ET4056 - Elektronika Frekuensi Radio Lanjut

    Program Studi Teknik TelekomunikasiSekolah Teknik Elektro dan Informatika

    Institut Teknologi Bandung

    1

  • Circular Patch

    x

    y

    h

    a

    2

  • Circular Patch: Resonance Frequency

    a PMCFrom separation of variables:

    ( ) ( )cosz mE m J k =

    Jm = Bessel function of first kind, order m.

    0za

    E

    = = ( ) 0mJ ka =

    3

  • Circular Patch: Resonance Frequency (cont.)

    mnka x= a PMC(nth root of Jm Bessel function)

    2mn mnr

    cf x =

    Dominant mode: TM11

    11 112 r

    cf xa = 11 1.842x

    4

  • Fringing extension: ae = a + a

    11 112 e r

    cf xa =

    Long/Shen Formula :

    a PMC

    a + a

    ln 1.77262r

    h aah

    = + 21 ln 1.7726

    2e r

    h aa aa h

    = + + or

    Circular Patch: Resonance Frequency (cont.)

    5

  • Circular Patch: Patterns(based on magnetic current model)

    ( ) ( )( )1

    1

    1coszJ k

    E , J ka h

    = (The edge voltage has a maximum of one volt.)

    a

    yx

    E-plane

    H-plane

    In patch cavity:

    The probe is on the x axis.

    2a

    rh

    infinite GP and substrate

    0 rk k =

    x

    The origin is at the center of the patch.

    6

  • Circular Patch: Patterns (cont.)( ) ( ) ( ) ( )0 1 1 0

    0

    2 tanc cos sinR zEE r, , a k h J ' k a Q

    =

    ( ) ( ) ( ) ( )1 00 10 0

    sin2 tanc sin

    sinR z

    J k a EE r, , a k h P k a

    =

    ( ) ( )( ) ( )( )( ) ( )02

    cos 1 costan sec

    TE jN P k hN jN

    = =

    ( ) ( ) ( )( )( ) ( )0

    2 cos1

    tan cos

    r

    TM

    r

    j N

    Q k h N j

    N

    = =

    ( ) ( )tanc tanx x / x=where

    ( ) ( )2sinrN = 7

  • Circular Patch: Input Resistance

    ( )( )

    21 0

    21

    in edge

    J kR R

    J ka

    a

    0

    8

  • Circular Patch: Input Resistance (cont.)

    12edge rsp

    R eP

    =

    ( ) ( )( )( ) ( ) ( ) ( )

    / 22 2

    0 00 0

    2 22 21 0 0

    tanc8

    sin sin sin

    sp

    inc

    P k a k hN

    Q J k a P J k a d

    = +

    ( ) ( )1 /incJ x J x x=

    where

    Psp = power radiated into space by circular patch with maximum edge voltage of one volt.

    er = radiation efficiency

    9

  • Circular Patch: Input Resistance (cont.)

    20

    0

    ( )8sp c

    P k a I=CAD Formula:

    43c c

    I p= ( )6 20 20

    kc k

    kp k a e

    == 0

    2

    43

    64

    85

    107

    12

    10.400000

    0.0785710

    7.27509 10

    3.81786 10

    1.09839 10

    1.47731 10

    eeeee

    ee

    == == = = =

    10

  • Feeding Methods

    Some of the more common methods for feeding microstrip antennas are shown.

    11

  • Feeding Methods: Coaxial Feed

    Advantages: simple easy to obtain input match

    Disadvantages: difficult to obtain input match for thicker substrates,

    due to probe inductance. significant probe radiation for thicker substrates

    2 0cosedgexR R

    L =

    12

  • Feeding Methods: Inset-Feed

    Advantages: simple allows for planar feeding easy to obtain input match

    Disadvantages: significant line radiation for thicker substrates for deep notches, pattern may shown distortion.

    13

  • Feeding Methods: Proximity (EMC) Coupling

    Advantages: allows for planar feeding less line radiation compared

    to microstrip feed

    Disadvantages: requires multilayer fabrication alignment is important for input match

    patch

    microstrip line

    14

  • Feeding Methods: Aperture Coupled Patch (ACP) Advantages: allows for planar feeding feed radiation is isolated from patch radiation higher bandwidth, since probe inductance

    problem restriction is eliminated and a double-resonance can be created.

    allows for use of different substrates to optimize antenna and feed-circuit performance

    Disadvantages: requires multilayer fabrication alignment is important for input match

    patch

    microstrip line

    slot

    15

  • Improving Bandwidth

    Some of the techniques that has been successfully developed are illustrated here.

    (The literature may be consulted for additional designs and modifications.)

    16

  • Improving Bandwidth: Probe Compensation

    L-shaped probe:

    capacitive top hat on probe:

    17

  • Improving Bandwidth: SSFIPSSFIP: Strip Slot Foam Inverted Patch (a version of the ACP).

    microstrip substrate

    patch

    microstrip line slot

    foam

    patch substrate

    Bandwidths greater than 25% have been achieved.

    Increased bandwidth is due to the thick foam substrate and also a dual-tuned resonance (patch+slot).

    18

  • Improving Bandwidth: Stacked Patches

    Bandwidth increase is due to thick low-permittivity antenna substrates and a dual or triple-tuned resonance.

    Bandwidths of 25% have been achieved using a probe feed.

    Bandwidths of 100% have been achieved using an ACP feed.

    microstrip substrate

    driven patch

    microstrip lineslot

    patch substratesparasitic patch

    19

  • Improving Bandwidth: Stacked Patches (cont.)

    -10 dB S11 bandwidth is about 100%

    stacked patch with ACP feed3 4 5 6 7 8 9 10 11 12

    Frequency (GHz)

    -40

    -35

    -30

    -25

    -20

    -15

    -10

    -5

    0

    Ret

    urn

    Loss

    (dB

    )

    MeasuredComputed

    20

  • Improving Bandwidth: Parasitic Patches

    Radiating Edges Gap Coupled Microstrip Antennas (REGCOMA).

    Non-Radiating Edges Gap Coupled Microstrip Antennas (NEGCOMA)

    Four-Edges Gap Coupled Microstrip Antennas (FEGCOMA)

    Bandwidth improvement factor:REGCOMA: 3.0, NEGCOMA: 3.0, FEGCOMA: 5.0?

    21

  • Improving Bandwidth: Direct-Coupled Patches

    Radiating Edges Direct Coupled Microstrip Antennas (REDCOMA).

    Non-Radiating Edges Direct Coupled Microstrip Antennas (NEDCOMA)

    Four-Edges Direct Coupled Microstrip Antennas (FEDCOMA)

    Bandwidth improvement factor:REDCOMA: 5.0, NEDCOMA: 5.0, FEDCOMA: 7.0

    22

  • Improving Bandwidth: U-shaped slot

    The introduction of a U-shaped slot can give a significant bandwidth (10%-40%).

    (This is partly due to a double resonance effect.)

    Single Layer Single Patch Wideband Microstrip Antenna, T. Huynh and K. F. Lee, Electronics Letters, Vol. 31, No. 16, pp. 1310-1312, 1986.

    23

  • Improving Bandwidth: Double U-Slot

    A 44% bandwidth was achieved.

    Double U-Slot Rectangular Patch Antenna, Y. X. Guo, K. M. Luk, and Y. L. Chow, Electronics Letters, Vol. 34, No. 19, pp. 1805-1806, 1998.

    24

  • Improving Bandwidth: E-Patch

    A modification of the U-slot patch.

    A bandwidth of 34% was achieved (40% using a capacitive washer to compensate for the probe inductance).

    A Novel E-shaped Broadband Microstrip Patch Antenna, B. L. Ooi and Q. Shen, Microwave and Optical Technology Letters, Vol. 27, No. 5, pp. 348-352, 2000.

    25

  • Multi-Band Antennas

    General Principle:

    Introduce multiple resonance paths into the antenna. (The same technique can be used to increase bandwidth via multiple resonances, if the resonances are closely spaced.)

    A multi-band antenna is often more desirable than a broad-band antenna, if multiple narrow-band channels are to be covered.

    26

  • Multi-Band Antennas: Examples

    Dual-Band E patch

    high-band

    low-band

    low-band

    feed

    Dual-Band Patch with Parasitic Strip

    low-band

    high-band

    feed

    27

  • Miniaturization

    High Permittivity Quarter-Wave Patch PIFA Capacitive Loading Slots Meandering

    Note: miniaturization usually comes at a price of reduced bandwidth.

    General rule: maximum obtainable bandwidth is proportional to the volume of the patch (based on the Chu limit.)

    28

  • Miniaturization: High Permittivity

    It has about one-fourth the bandwidth of the regular patch.

    L

    W E-plane

    H-plane

    1r = 4r =

    L=L/2

    W=W/2

    (Bandwidth is inversely proportional to the permittivity.)

    29

  • Miniaturization: Quarter-Wave Patch

    L

    W E-plane

    H-plane

    Ez = 0

    It has about one-half the bandwidth of the regular patch.

    W E-plane

    H-plane

    short-circuit vias

    L=L/2

    30

  • Miniaturization: Planar Inverted F Antenna (PIFA)

    A single shorting plate or via is used.

    This antenna can be viewed as a limiting case of the quarter-wave patch, or as an LC resonator.

    side view

    feedshorting plateor via top view

    / 4dL