Flat Group Delay Response Research Articles

Generalized bessel polynomials with application to the design of bandpass filters with approximately flat group delay response

AbstractThe continued fraction expansion of the ordinary Bessel polynomials is modified by replacing the complex frequency variable p by p/(1+γp), where γ=⩾0. The resulting polynomials, when a reactance transformation is applied, are capable of providing bandpass filters with an approximately flat group delay response.

Generalized interdigital linear phase networks with optimum maximally flat amplitude characteristics

The closed-form solution is presented for microwave bandpass nonminimum phase transfer functions that exhibit an optimum passband maximally flat amplitude characteristic while maintaining a maximally flat group-delay response about band center. There are two basic transfer functions obtained depending upon whether the degree of the resulting network is even or odd. The transfer characteristics are shown to be capable of being realized by resistively terminated symmetrical generalized interdigital networks. Synthesis procedures are presented for the case of n odd corresponding to the input and output ports being situated at the same physical end of the generalized interdigital line and for the case n even where the ports are at opposite ends. These procedures are based upon the one-port synthesis of the even- and odd-mode forms. Finally, the synthesis procedure is illustrated for the case of n = 6 , and typical transfer characteristics are shown for this example.

Bandpass LC filters having prescribed amplitude and nearly constant group-delay characteristics

The paper describes the synthesis of arithmetically symmetrical, broadband LC filters having prescribed amplitude response and nearly constant group delay, with particular reference to i.f. filters for radio-relay systems. These filters must suppress unwanted signals, particularly the adjacent carrier frequencies, without significantly distorting the required signal. For low distortion, the filters must have both flat amplitude and constant group-delay responses over the passband centre. Filters synthetised for 1800- and 960-channel systems have satisfied these requirements, the transfer-function design and measured characteristics of the filter for the 960-channel system being given as an example. The filters have the advantages that they can be inserted in the i.f. chain without the need for further phase equalisation, and that they give improved amplitude responses compared with conventional filter and equaliser combinations.