This paper introduces a new way to reduce the length of a
microstrip end-coupled resonator by loading its ends by a
lumped capacitors. A new way of controlling the frequency
of the 2nd harmonic even mode by loading the center of the
resonator by a lumped capacitor directly or through less than
0.125 λgo part of a microstrip transmission line. Compact dual
and triple modes bandpass filters with good selectivity are
obtained. The length of transmission line section controls the
phase and transforms the impedance of the capacitor which
controls the bandwidth and generates transmission zeros. The
transmission zeros can be located at upper or lower side of
the passband by adjusting the loading capacitor values or the
length of the transmission line. A second order bandpass
filter with center frequency of 4 GHz is designed, fabricated
and measured. The filter has a passband from 3.6 GHz to 4.4
GHz with a transmission zero at 4.8 GHz. The filter has good
stopband performance with a rejection higher than 20 dB up
to more than 10 GHz. Insertion loss of less than 0.75 is
achieved within the passband. The measured results exhibit
good agreement with the simulation one. An efficient global
hybrid optimization method is proposed combining the
Central Force Optimization (CFO) as a global optimizer and
Hillclimbing (HC) algorithm as a local optimizer. After the
final global iteration, a local optimization can be followed to
further improve the solution obtained from the CFO. The
hybrid Central Force Optimization and Hillclimbing (CFOHC)
algorithm is used to optimize the dimensions and values
of the capacitance which contact them the filter, the (CFOHC)
algorithm was implemented using MATLAB-software
and linked to the CST simulator to simulate the filter, In
addition the optimized filter is simulated by the Finite
Difference Time Domain (FDTD) program written with
matlab to validate the results.