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Mohammed Antenna Theory Regular
Joined: 10 Nov 2009 Posts: 14 Location: malaysia

Posted: Thu Jan 07, 2010 4:29 pm Post subject: help regarding Microstrip patch antenna design ... 


alsallam alikom ....
Dear beloved Engineers ...
l'm doing a hand design for a microstrip single patch antenna and planar patch antenna separately ... but l have some problems ..such as ..
for the microstrip single patch antenna ... l got a problem of how to calculate the input impedance [ Z(edge) or Z(in) ] l got different formulas with different results and different result for the online calculator as well [http://www.emtalk.com/mpacalc.php?er=10&h=1.5&h_units_list=hmm&fr=0.9&Operation=Synthesize&La=79.2904389211&L_units_list=Lmm&Wa=101.430103242&W_units_list=Wmm&Rin=243]....
another question is that should l have the quarter wavelength (λ/4) transformer part or l can connect the 50 ohm transmission line to the rectangular patch directly ... and what is the function of the quarter wavelength (λ/4) transformer ?? (l guess l should have a quarter wavelength (λ/4) transformer for the single patch one, but not for the planar array ... am I right ...??) ...
l highly appreciate your help and support ...
thank you 

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admin Site Admin
Joined: 03 Jan 2007 Posts: 201

Posted: Fri Jan 08, 2010 4:37 am Post subject: 


The online calculators you use are approximations at best. They shouldn't be taken as exact truth.
A square patch antenna fed at the end should have an impedance between 200 and 300 Ohms, if resonant.
This high impedance leads to the reason for the quarterwave transformer, which can match a real impedance to 50 Ohms via selection of the characteristic impedance of the quarterwavelength transmission line.
For a planar array, the situation is more complicated because the feed to each element should be matched such that the total array matches the desired Receiver/Transmitter impedance. You don't need a quarterwave transformer, but you'll need some way of altering the impedance. 

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Mohammed Antenna Theory Regular
Joined: 10 Nov 2009 Posts: 14 Location: malaysia

Posted: Sat Jan 09, 2010 9:46 am Post subject: 


acually l got similar result for both the W and L .. but diff. results for impedance ... but since the only result above then 200 is the online one ..it's the best to take ...
But l'm still confused on how to match the planar array impedance ... so do u have any tutorail or any referance u advise me to refer to ...
thank you in advance.. ur information was really helpful .... 

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Mohammed Antenna Theory Regular
Joined: 10 Nov 2009 Posts: 14 Location: malaysia

Posted: Sun Jan 10, 2010 3:44 pm Post subject: 


hey boss .. l would like to ask u about the simulation program as well.... which the best program to use for my design application ( HFSS or CTS ) ??.... actually l would like to do design a single patch microstrip antenna and planar array 2*2, 4*4 and 8*8 .. then compare thier parameters such as directivity and efficiency ... etc ....
ur help and support are highly appreciated ... 

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admin Site Admin
Joined: 03 Jan 2007 Posts: 201

Posted: Sun Jan 10, 2010 7:41 pm Post subject: 


The matching problem is to get the receiver's impedance 50 Ohms to match what it is feeding (the antenna or antenna array) to be close to 50 Ohms over the desired band.
If you are feeding a single antenna, the antenna impedance should be close to 50 Ohms. If you are feeding a two element array, the antennas are in parallel, so the impedance of each (measured from the receiver or branch point) should be 100 Ohms (so the parallel combination is 50 Ohms). You can figure what you need for larger arrays. If you have an 8*8 array, you will probably have to feed them differently, but you'll have to come up with an intelligent feed geometry such that the overall array impedance is matched.
For which design software to use, that's a matter of personal preference and what you are comfortable with. If you are calculating efficiency, this will really just be a measure of how well your array is matched to the receiver, assuming no other losses in the system (the energy has to go somewhere). 

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