 = 1 henry and capacitance C = 
 1 farad . This prototype can be impedance scaled and frequency scaled to the desired values . The low @-@ pass prototype can also be transformed into high @-@ pass , band @-@ pass or band @-@ stop types by application of suitable frequency transformations . 
 
 = = Cascading sections = = 
 
 Several L @-@ shape half @-@ sections may be cascaded to form a composite filter . Like impedance must always face like in these combinations . There are therefore two circuits that can be formed with two identical L @-@ shaped half @-@ sections . Where a port of image impedance ZiT faces another ZiT , the section is called a Π section . Where ZiΠ faces ZiΠ the section so formed is a T section . Further additions of half @-@ sections to either of these section forms a ladder network which may start and end with series or shunt elements . 
 It should be borne in mind that the characteristics of the filter predicted by the image method are only accurate if the section is terminated with its image impedance . This is usually not true of the sections at either end , which are usually terminated with a fixed resistance . The further the section is from the end of the filter , the more accurate the prediction will become , since the effects of the terminating impedances are masked by the intervening sections . 
 
 