physical and effective aperture of antenna

What is the relation between physical and effective aperture of antenna ?

The physical aperture is what you can measure with a ruler. The effective aperture is how it behaves when radiating an electromagnetic wave.

In addition, thik in a receiving antenna.
Its effective area (or aperture) is the area over which the antenna would "collect" all the power or energy of a plane wave:

delivered_power [Watts] = power_density [Watts/m^2] * effective_area [m^2]

Regards
Z

You probably encountered that Prx = Aeff*PFD

Prx = received power (W), Aeff = effective aperture (m2), PFD = power flux density (W/m2).

Theoretically, antennas can have Aeff > Aphysical. From a more practical standpoint of view, only electrically small antennas (size < 0.25 lambda) can have significant larger Aeff. This is due to resonance.

A half wave dipole has small physical area (just two thin wires), but Aeff = 0.125*(lambda)^2 (approximately). Making the wires more thick, doesn't increase Aeff, but does increase the useful relative bandwidth.

Electrically large broad side antennas have Aeff < Aphys. If there are strict side lobe requirements, Aeff reduces further (due to field taper, so the transmitted field reduces when approaching an edge).


One can view the effective aperture also from a transmitting standpoint of view. By observing the radiation pattern caused by the antenna current, one can calculate the directivity. When losses are known, one can calculate the Gain. Based on the gain, one can calculate Aeff:

Aeff = gain*lambda^2/(4*pi), gain based on isotropic radiator, and not in dB.

but is there any genral relation between them, like any mathematical formula ?

Pulkit Varshney said:

but is there any genral relation between them, like any mathematical formula ?

Click to expand...

No, as far as I know, there is no relation between Aeff and Aphys. Sometimes you see "aperture efficiency" Aperture efficiency = 100%*Aeff/Aphys.

There are many antenna types. Within each type there is lots of variation (depending on the most important design goal). Two antenna with same physical appearance can have different effective aperture (for example because of different side lobe level requirements).

If one knows the 3D radiation pattern, antenna efficiency and frequency of operation, one can calculate (numerical integration) Aeff. Also when the gain and frequency is known, one can calculate Aeff.

i have a microstrip patch antenna ,,how can i increase its' effective area with and without making arrays ?

No formula can express the difference between the "geometrical" theory and reality.

Take two standard aperture antennas: a pyramidal horn has the geometric aperture AxB; usually, the "real" aperture is close to it if you measure the real directivity or gain.
A parabolic dish with a primary feed has the geometric aperture equal to the circular area, pi x d squared/ 4. But the real aperture is degraded by "efficiency", typically < 50%; this is based upon measuring a real effective directivity or gain.
Many other antennas like dipoles, patches, etc., have their efficiency defined empirically, by measuring their real directivity and gain.

Designing and making a good antenna is still an art. There are many theories and today also computer models. Try to make a good antenna; you will be surprised by the result. This is why really good antennas are quite expensive.

---------- Post added at 22:45 ---------- Previous post was at 22:41 ----------

The easiest way is to follow how Yagi antenna works. You can add several directors to your antenna and take your patch as the "fed dipole"; you can add a reflector or tuned reflector to it; you can use the patch in a "backfire" design, or as a primary feed in a parabolic reflector.

If you have a patch antenna, and you can't change size/material, you can't increase gain (or Aeff). If you have bad dielectric you may increase the height to increase the efficiency.

If you may change size and material: maximize the efficiency (so all RF input is converted to radiation and not into heat), use material with lowest dielectric constant (for example air or foam, this reduces sideways radiation), increase the groundplane to reduce backwards radiation. This is the best you can do in case of a half wave patch antenna and you may get around 9 dBi.

You can use this half wave patch to excite other structures, but than it becomes a complete other antenna.

Probably you did some research and found "superdirectivity".Theoretically one can make an antenna with increased gain (or aperture) with respect to exisiting good antennas, however practically spoken, both loss and Q-factor increase dramatically.