Problem with the output in a gilbert cell mixer design

[sapnak8]

Hi
I am designing a gilbert cell mixer.But its not working properly.In output I am not getting the exact output means I am not getting the down converted frequency and output is no longer amliplified version of input.Gain is decreases.even in the output I am getting the freq of local oscillator not of the converted frequency.I am attaching my code here. Please help me out. LO freq 2.1Ghz RF freq 2.4Ghz so IF=300meg.

mtail 1 16 0 0 CMOSN l=0.5u w=80u
Vbias 16 0 0.8v

m1 3 2 1 0 CMOSN l=0.5u w=65u
m2 5 4 1 0 CMOSN l=0.5u w=65u
m7 7 6 3 0 CMOSN l=0.5u w=65u
m8 8 6 5 0 CMOSN l=0.5u w=65u
Vbias1 6 0 1.8v

m3 10 9 7 0 CMOSN l=0.5u w=217.5u
m4 12 11 7 0 CMOSN l=0.5u w=217.5u
m5 10 11 8 0 CMOSN l=0.5u w=217.5u
m6 12 9 8 0 CMOSN l=0.5u w=217.5u

mc1 15 13 7 0 CMOSN l=0.5u w=48.5u
mc2 15 13 8 0 CMOSN l=0.5u w=48.5u
Vbias3 13 0 1.2v

m9 15 14 10 0 CMOSN l=0.5u w=72u
m10 15 14 12 0 CMOSN l=0.5u w=72u
Vbias2 14 0 0.8v

vdd 15 0 1.8v

Vlo 9 11 ac sin(1.8v 100mV 2.1Ghz)
*Vlo 9 11 pulse(0 1.8v 10ps 10ps 10ps 0.238095238ns 0.476190476ns)
Vrf 2 4 ac sin(1.4v 50mV 2.4Ghz)

.lib "18um_model12" cmos_models

.tran 10ns 100ns
.plot tran V(12) v(10) v(12,10) v(9,11) v(2,4)
.FOUR 2.1Ghz V(12) v(10) v(12,10)
.FFT v(12,10) np=1024 start=10us stop=10ms freq=1meg window=kaiser alfa=3
.measure tran x pp v(12,10) from=5ns to=15ns
.measure tran y pp v(2,4) from=5ns to=15ns
.measure tran gain PARAM = '20*log(x/y)'

.MEAS TRAN Th1 WHEN V(12,10)=0.525 CROSS=1
.MEAS TRAN Th2 WHEN V(12,10)=0.525 CROSS=2
.MEAS TRAN Th3 WHEN V(12,10)=0.525 CROSS=3
.measure freq param = "1/(th3-th1)"

.op
.option post
.option gdcpath
.probe
.print
.end