本文讨论了其通带具有等波动性的4阶低通原型滤波器的一些特性。明确给出了相应的晶体带通滤波器的元件值。可以看出,可达到的带宽仅取决于低通原型滤波器的一个参数。对于低通原型滤波器可能产生的失匹,有两种解决方法,其中一种方法是取设计的允许带宽大于通常匹配情况的带宽。 This article discusses some of the features of 4th-order low-pass prototype filters with constant passband passband. The corresponding crystal bandpass filter element values ​​are clearly given. It can be seen that the achievable bandwidth depends only on one parameter of the low pass prototype filter. There are two solutions to the possible loss of low-pass prototype filter, one of which is to design the allowable bandwidth greater than the bandwidth normally matched.