def _extract_sicd_tx_rcv_pol(str_in):
    """
    Extract the tx and rcv components from the sicd style tx/rcv polarization string.

    Parameters
    ----------
    str_in : str

    Returns
    -------
    str, str
    """

    if str_in is None:
        return 'UNKNOWN', 'UNKNOWN'

    if not isinstance(str_in, str):
        raise TypeError('requires a string type input.')

    if str_in in ['OTHER', 'UNKNOWN']:
        return 'UNKNOWN', 'UNKNOWN'

    return str_in.split(':')