transmission line this allows the voltage to build up in the gas discharge tube until ionization occurs the coupled transmission lines 46 and 47 provide a series resonant circuit another quarter wave strip transmission line 48 is in shunt with the transmission line 33 the actionof the shunt transmission line 48 is to provide another resonant circuit the action of the two shunt resonant circuits and the series resonant circuit is to form a bandpass filter structure that transfers a narrow band of frequencies along the line while blocking the transmission of signals outside the narrow band of operation the network also provides animpedance match at the microwave frequencies while suppressing extraneous vhf uhf signals the quarter wavelength sections are accomplished with strip transmission lines whose characteristic impedances are determined bymodern filter synthesis techniques it is understood from practical experience that the length of the strip transmission lines can vary considerably from the nominal quarterwave depending upon the various parasitics that are to be absorbed in the filter network for example thefirst transmission line shunted with the gas tube is shorter than the nominal quarter wavelength in order to absorb parasitic capacitance of thegas tube fig5 shows the equivalent circuit with like reference numerals referring.