ab2S

      ab2S     Convert ab wave measurements from measure2Port() to S parameters
          S = ab2S(rec_tx1,rec_tx2,ports)
          input:
              rec_tx1,rec_tx2: [6,num_pts]
                  reciever recordings returned by measure2Port() with 'Tx1'
                  and 'Tx2' transmitting
              ports: map that associates a port number with each VNA Tx/Rx
                  possible keys: ['Tx1','Tx2','Rx1A','Rx1B','Rx2A','Rx2B']
                  possible values: [1, 2, 3, 4, 5, 6]
          output:
              S: [2,2,num_pts] stack of S parameter matricies in frequency