A 4-40 GHz wide bandwidth, magnetically tuned bandpass filter

In recent years, as microwave test equipment evolved, the need for a coaxial input-output bandpass filter that can tune from 4 to 40 GHz has become evident. This filter also needs a passband much wider than that of any of the previously available yttrium-iron-garnet (YIG) filters. To meet these needs, a special non-YIG ferrite filter was designed and built. A discussion is presented of the key problems and solutions in the development of this new microwave filter. It is shown that a 4-40-GHz bandpass filter can be realized if the tuning magnet uses conical poles and the filter´s coupling structure can be made small enough to prevent self-resonance from occurring below 40 GHz. Additionally, the passband bandwidth can be made greater than 100 MHz by using lithium-aluminum-ferrite (LAF) resonators instead of YIG.<>