In this paper we investigate the properties of the generator matrices of a new class of convolutional codes, called product convolutional codes, which were previously defined and investigated by the authors. The new codes are constructed using the well-known method of the direct product for combining block codes. Convolutional codes are considered as block codes over the field of rational functions F(D). The description of convolutional codes as block codes allows the successful application of the direct product method to convolutional codes, and, in addition, leads to a general method to construct new convolutional codes based on already known combining methods for block codes. Expressions for the generator matrices of the product convolutional codes are given and several of their properties, which were not addressed before, are determined. The relationship between the properties of the direct product encoder generator matrix and the properties of the vertical and horizontal constituent encoders generator matrices is derived. Rational generator matrices, as well as polynomial generator matrices, are addressed.
