SPICE radio frequency amplifier design and optimization

[Ivan_Ryger]

Dear all.
Recently I have started designing a radio frequency amplifier based on dual-gate MOSFET BF998. I have simulated it in HSPICE simulation software, designed input and output matching networks. Unfortunately, This is a four-parameter problem which is suitable to be solved by optimization technique. I need to optimize three inductors and one capacitor. The goal is to achieve at least 20dB (better 30dB) gain at 200 MHz, input match to 50 Ohm at same frequency and the unconditional stability. I am quite new in SPICE simulation. Can anyone help me? I attach a piece of my SPICE source code.

$amplifier with BF998 transistor

.inc "BF998.LIB"
.param Vagc=8 $voltage on G2 BF998

V1 Vcc 0 DC 10 pwl(0,0 1n,10)
	
.subckt C0805 1 2 cap=10p
R1 1 11 R=1
L1 11 12 L=3n
C1 12 2 C=cap
.ends

.subckt R0805 1 2 res=100
L1 1 11 L=3n
C1 11 2 C=0.4p
R1 11 2 R=res
.ends

$transistor BF998
$   1.: SOURCE;  2.: DRAIN;  3.: GATE 2;  4.: GATE 1;
X1 0 2 3 4 BF998

$ XR1 0 4 R0805 res=100k
L1 in 0 115n $NEEDS TO BE OPTIMIZED
R1 in 0 4333 $ Q=30
L2 in 5 255n $NEEDS TO BE OPTIMIZED
R2 in 5 9600 $ Q=30
XR3 4 5 R0805 res=15

V2 3 0 DC Vagc pwl(0,0 1n,Vagc)

L3 2 Vcc 85n $NEEDS TO BE OPTIMIZED
R3 2 Vcc 3202
XC2 2 out C0805 cap=4.7p $NEEDS TO BE OPTIMIZED

P1 in 0 port=1 z0=50 AC=1				$ input port
P2 out 0 port=2 z0=50				$ output port

.op

.AC dec 1000 1meg 1000meg sweep L1 105n 120n 5n $AC analysis, 
.PRINT S11(DB) S11(PHASE)  S21(DB) S21(PHASE) S12(DB) S12(PHASE) S22(DB) S22(PHASE) K_STABILITY_FACTOR
.LIN sparcalc=1 filename =amplifier_BF998 format=touchstone dataformat=db	$ S parameters output

.option post list nomod unwrap $co=132 post=2 runlvl=6
.end