# voltage and current profiles on patch antenna

#### yef smith

Joined Aug 2, 2020
602
Hello on the antenna bellow we have L=half wave length.
I understand that we have open circuit on the edges so currect is zero on edges
but why its maximal in the middle ,and why voltage acts by going from +vmax on one edge to -Vmax on other edge.
is there some physical explanation for it?
Thanks.

#### Papabravo

Joined Feb 24, 2006
20,598
I don't know for certain if this is relevant to patches, but in transmission lines whenever there is an impedance discontinuity there will be transmission or absorption, and reflection. You can calculate a reflection coefficient at each discontinuity and obtain some sense of what is happening. Normally each time there you have a reflection there is attenuation so the repeated reflections tend to die out over time. We know that an antenna is a good radiator when the reflected power (measured by return loss) is a small fraction of the incident power.

#### yef smith

Joined Aug 2, 2020
602
Hello Nsaspook, for half wavelength,current will be zero on the edges.
but why voltage is +-Vmax on edges and0 in the middle?

Look at the rate of change in potential across the antenna for the standing RF. Where are the current maximal and minimal?
The Maxwell–Faraday equation states that a time-varying magnetic field always accompanies a spatially varying (also possibly time-varying), non-conservative electric field, and vice versa.

#### nsaspook

Joined Aug 27, 2009
12,266

#### yef smith

Joined Aug 2, 2020
602
Hello Nsaspook, What in the mode in which it resonates?
I am trying to find the link between TM01 and the currect profile of the patch antenna.
I am not sure if the current profile is TM01
is there something you could help me with?

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#### nsaspook

Joined Aug 27, 2009
12,266
A half wave long patch operates in what we call the fundamental mode: the electric field is zero at the center of the patch, maximum (positive) on one side, and minimum (negative) on the opposite side. These minima and maxima continuously change side like the phase of the RF signal. The electric field does not stop abruptly near the patch's edges like it would in a cavity: the field extends beyond the outer periphery. These field extensions are known as fringing fields and cause the patch to radiate. Some popular analytic modeling techniques for patch antennas are based on this leaky-cavity concept and the fundamental mode of a rectangular patch is often denoted using cavity theory like the TM10 mode. This TM notation often leads to confusion and here is an attempt to explain that: Figure 1 uses a Cartesian coordinate system, where the x and y axes are parallel with the ground-plane and the z-axis is perpendicular to it.

#### yef smith

Joined Aug 2, 2020
602
Hello Nsaspook,I have tried to go further and develop the modes shown bellow.
Bellow i shown the electroomagnetic equations.
how can i test whether TM010 could form in the microstrip based on the equations?
I know that for TM ,Hz=0
for TE Ez=0
how prove that TE010 could not form in the structure?
What conditions i should in put for TE and what conditions i shown input for TM?
Thanks.

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