Planar bandpass filters implemented with half-wavelength resonators exhibits inherently spurious responses at the multiples of center frequency f₀, which is undesirable for sensitive receiver for which wide upper stopband is essential to attenuate out-of-band signals interfering the system. Furthermore the filter size is comparatively large to be used in modern L-band communication systems. In this thesis, a novel cross-coupled filter with stepped-impedance resonator (SIR) and compact harmonic suppression cell (CHSC) is thus proposed to achieve simultaneous size miniaturization and spurious responses suppression. The introduction of the stepped-impedance resonator is beneficial for size reduction and spurious responses prolongation. Two filter examples simulation results show that more than 23 dB and 33 dB attenuation improvements are acquired at the uniform impedance resonator (UIR) 2ⁿᵈ and 3ʳᵈ spurious frequencies while passband characteristics are maintained. Furthermore the filter size is reduced by more than 8% in both examples. With the usage of compact harmonic suppression cell, wide upper stopband filter can be implemented. Experimental results of two filter design examples illustrate that improvement at UIR 2ⁿᵈ spurious frequency is almost 60 dB while more than 50 dB additional attenuation at UIR 3ʳᵈ spurious frequency is measured. On the other hand the size of the compact harmonic suppression cell is small, which is about 1.1% of a conventional eight-pole UIR filter size.