ICT083 Antenna Design

Patch Antennas

I. Theory

1. History

First published: G. Deschamps and W. Sichak, "Microstrip microwave antennas", Proc. 3rd Symp. USAF Antenna Research and Development Program, Oct. 18-22, 1953.

First patented: H. Gutton and G. Baissinot, "Flat aerial for ultra high frequencies", French Patent No. 703 113, 1955.

Widely used since 1970's.

2. Rectangular Patch Antenna

2.1 Structure

- Ground plane

- Dielectric substrate

- Patch

- Feeding probe

Figure: Patch antenna structure [Kopper(2016, thesis)]

2.2 Principles of Operation

- Half-wave dipole: Center-fed, R_in = 72 Ω (thin-wire dipole), 10% bandwidth

- Stip dipole: Center-fed, Rin = 50 Ω (printed on PCB), 5% bandwidth

- Rectangular patch antenna: Probe-fed, Rin = 50 Ω (printed on PCB), 2% bandwidth

Figure: Similarities between a wire dipole [CST Studio], a strip dipole [Ferreira(2012)], and a rectangular patch antenna [www.mweda.com]

Figure: Current distributions on a wire dipole, a strip dipole, and a rectangular patch antenna

Figure: Current distribution on a rectangular patch antenna

Figure: Electric field and surface current distributions on a rectangular patch antenna [Kopper(2016, thesis)]

2.3 Feeding Methods

- Patch edge feeding by microstrip line

Figure: Feeding methods of a patch antenna. Edge feeding [Mishra(2016)], coaxial probe feeding [Mishra(2016)], inset feeding [Islam(2018)], and quarter-wave transformer feeding [EM Talk]

2.4 Design

- Patch mode: TM_01-to-z mode

- Patch length

- Patch width

W > L for higher bandwidth

W < 2L to avoid TM₀₂ mode excitation

- Feed position

y₀ : Distance from the patch edge

3. Microstrip Line

3.1 Structure and Fields

Figure: Structure and parameters of a microstrip line

Figure: Electric and magnetic fields in a microstrip line [3DS]

3.2 Design

1) Effective dielectric constant:

2) Characteristic impedance:

3) Guided wavelength:

: Guided wavelength

: Wavelength in vacuum

: Phase constant

: Wave after traveling a distance L on a transmission line

: Eelectrical length (radian)

4) Design programs:

- CST Studio wizard

- Source Forge 'mcalc', http://mcalc.sourceforge.net/

Figure: 'mcalc' microstrip line analysis program [Source Forge]

4) Wave port for a microstrip line simulation:

Figure: Wave port set up for a microstrip line [Research Gate]