The invention discloses a photo detector with first and second groups of electrodes. The electrodes of each group are connected to a first common conductor for the group, and are located on a layer of photosensitive material. The electrodes are parallel to and interlaced with each other. The first common conductors are essentially plane, arranged at the same end of their group of electrodes, and arranged as upper and lower conductors parallel to and overlapping each other separated by a dielectric material, and form a signal electrode and a ground plane of a first microstrip line. The first microstrip line acts as a first combiner for currents induced in the electrodes of the two groups and as a matching network for the electrodes and for a load which can be connected to the photo detector.