See this

http://onlinelibrary.wiley.com/doi/10.1002/mop.10184/pdf

I am designing simple rectangular patch antenna...can you suggest me the formula of input impedance of it?

Go for your simple way of patch antenna engineering and refer this link;

http://www.antenna-theory.com/antennas/patches/patch3.php

For rectangular Patch Antenna:

Zin= 90*( Sqr(er)-1)/er* sqr(L/W)

er= Dielectric constant

Sqr= denotes the square.

see this:

http://www.emtalk.com/mpacalc.php?er=3.55&h=.5&h_units_list=hmm&fr=10.5092454168&Operation=Synthesize&La=7.4&L_units_list=Lmm&Wa=10.1&W_units_list=Wmm&Rin=6666

how do we calculate input impedance for different modes of microstrip antenna like TM11,TM01,TM10,TM20....etc?

A starting point to find the input impedance of a patch antenna is:

At resonance; Rin < (1/(2G1)), where:

G1 = (W/(120*lambda0))*(1-((1/24)*(k0*h)^2))

Rin is the input resistance of the antenna at resonance.

This is given in the text book of Antenna Theory by Balanis!