Abstract
Existing and newly adapted techniques for suppressing harmonic responses in microstrip filters were combined. Stagger tuning using additional stubs to shift the resonances has been adapted to quarter-wave resonators and extended to the seventh-order spurious response. Suitable resonator overlap provided transmission zeroes to cancel spurious peaks. Coupling capacitor pads acting as shorting stubs have been developed. Spurious responses were suppressed to better than $-{\hbox{33 dB}}$ , up to 6.3 GHz, in a measured filter with 1-GHz center frequency and 42% bandwidth. Suitably placed resistors have depressed the spurious level further to $-{\hbox{50 dB}}$ up to 5.6 GHz, with only 0.07-dB extra passband loss.
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