AD9361的数字滤波器HB1,HB2,HB3/DEC3均为固定系数的数字滤波器，其对应的幅频特性如下所示：

仿真代码：

H_len=2048;
hb1=[-8,0,42,0,-147,0,619,1013,619,0,-147,0,42,0,-8];
hb2= [-9,0,73,128,73,0,-9];
hb3=[1,4,6,4,1];
dec3=[55,83,0,-393,-580,0,1914,4041,5120,4041,1914,0,-580,-393,0,83,55];
%hb1频率响应
[H1_fir,w]=freqz(hb1,1,H_len,'whole');
figure(1)
subplot(4,1,1)
plot(w/pi,20*log10(abs(H1_fir)));
grid on;
xlabel('\omega/\pi');
ylabel('Gain,in dB')
title('HB1频率响应');
%hb2频率响应
[H2_fir,w]=freqz(hb2,1,H_len,'whole');
subplot(4,1,2)
plot(w/pi,20*log10(abs(H2_fir)));
grid on;
xlabel('\omega/\pi');
ylabel('Gain,in dB')
title('HB2频率响应');
%hb3频率响应
[H3_fir,w]=freqz(hb3,1,H_len,'whole');
subplot(4,1,3)
plot(w/pi,20*log10(abs(H3_fir)));
grid on;
xlabel('\omega/\pi');
ylabel('Gain,in dB')
title('HB3频率响应');
%dec3频率响应
[DEC3_fir,w]=freqz(dec3,1,H_len,'whole');
subplot(4,1,4)
plot(w/pi,20*log10(abs(DEC3_fir)));
grid on;
xlabel('\omega/\pi');
ylabel('Gain,in dB')
title('DEC3频率响应');