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HenryD
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Joined: 14 Sep 2016
Posts: 2

 Posted: Wed Sep 14, 2016 10:41 pm    Post subject: Linear polarized microstrip patch antenna - design help hi there, im pretty new to antenna design, still have a lot of theory to go through, so please be kind. I have to design a linearly polarized microstrip patch antenna (rectangular) that is fed with 2 coaxial probe feeds. The patch should be a square (L=W), so i can place 2 feeds orthogonally to each other. That way i will hopefully be able to receive/separate the vertically and horizontally polarized signal "portion". (thats why the antenna needs to be a square, as both signal "portions" (vertical and horizontal) are on the same frequency). So far i have only modeled and simulated one coaxial feed, i would like to optimize the antenna first before adding the second orthogonal feed. I want to design the patch on FR-4 substrate for 867 MHz. I have done various calculations (found on the net and Balanis 3th edition) to get my patch width and length. Also tried to calculate the inset position so i can match the feed to 50 Ohm. I made a first design in CST and i just can not get rid of the "zero point" in the middle of the radiation pattern. Some hints on what else i could try to improve the radiation pattern of the antenna would be great! (radiation pattern: https://postimg.org/image/nb913a8id/) Is a good/the common radiation pattern even possible with a square shape (W=L)? Most patch antennas i saw so far with the common radiation (like e.g. this: http://forums.radioreference.com/attachments/scanner-receiver-antennas/32485d1305662856-radiation-pattern-dual-band-microstrip-patch-antenna-3.5-ghz.jpg) pattern are rectangular (W!=L). The return loss is quite good, about -31dB at resonance frequency of 867 MHz. I suspect the coaxial feed to be modeled so it does not result in a 50 Ohm impedance at the port, i used the following parameters in order to modulate my coaxial probe in CST: inner radius (pin): 0.5 mm outer radius (coating): 2.5 mm teflon: 2.1 What dimensions do you usually use for a coaxial feed to match to 50 Ohm? Some help/hints are highly appreciated! Thank you so much in advance! Kind regards, henry.

Joined: 03 Jan 2007
Posts: 197

 Posted: Thu Sep 15, 2016 6:25 pm    Post subject: Not sure exactly what is wrong in your simulation, but that radiation pattern you posted is not one of a square half-wavelength patch antenna
HenryD
Antenna-Theory.com Newbie

Joined: 14 Sep 2016
Posts: 2

 Posted: Mon Sep 19, 2016 4:03 pm    Post subject: hi, thank you for your answer! Your are right, i made a mistake. (it was a full wavelength patch )
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