Radiation pattern of planar optoelectronic antennas for broadband continuous-wave terahertz emission

Abstract

In future wireless communication networks at terahertz frequencies, the directivity and the beam profile of the emitters are highly relevant since no additional beam forming optics can be placed in free-space between the emitter and receiver. We investigated the radiation pattern and the polarization of broadband continuous-wave (cw) terahertz emitters experimentally and by numerical simulations between 100 GHz and 500 GHz. The emitters are indium phosphide (InP) photodiodes with attached planar antenna, mounted on a hyper-hemispherical silicon lens and integrated into a fiber-pigtailed module. As both packaging and material of the emitter was identical for all devices, similarities and differences can be directly linked to the antenna structure. We found that the feeding point structure that connects photodiode and antenna has a large influence on the radiation pattern. By optimizing the feeding point, we could reduce side lobes from −2 dB to −13 dB and narrow the 6dB beam angle from ±14° to ±9° at 300 GHz.

Coherent Wireless Link at 300 GHz With 160 Gbit/s Enabled by a Photonic Transmitter

“…1 shows the antenna design and the power spectrum of the two different PD emitters investigated in this work. We restrict our analysis to these two types as they are the most promising designs from previous studies [14]. The upper part of each subplot depicts the indium phosphide (InP) chip with the optical waveguide and the metallic bowtie (BT) antenna.…”

“…The augmented view shows the feeding point of the device, i.e., the structure that connects the PD with the antenna. The extended bowtie (b) corresponds to BT#1 in reference [14] and represents the state-of-the-art PD emitter, which is commonly used for terahertz spectroscopy. The merged bowtie (a) corresponds to BT#3 in reference [14], which is the new design with an improved beam profile.…”

“…A detailed description and comparison of UTC-and PIN-PD-based terahertz emitters can be found in [13]. However, the fabrication of PIN-PDs is based on mature processes originally developed for fiber optical communication systems and PIN-PDs have been used as broadband terahertz emitters for spectroscopy for more than 10 years [14]. Thus, we used a PIN-PD-based emitter in this work.…”

“…In wireless communication, the beam profile is highly relevant because no additional beam forming or guiding elements can be used at any point of the free-space link. Therefore, we investigated the radiation pattern of state-of-the-art PIN-PD emitters [16] and compared it to alternative antenna designs [14]. In [14], we reported on reduced unwanted side lobes in the radiation pattern of this new antenna design, which should help to avoid multi-path interference in a communication link.…”

“…Therefore, we investigated the radiation pattern of state-of-the-art PIN-PD emitters [16] and compared it to alternative antenna designs [14]. In [14], we reported on reduced unwanted side lobes in the radiation pattern of this new antenna design, which should help to avoid multi-path interference in a communication link. In addition, we expect an improved signal integrity of this new emitter design due to an improved feeding point structure.…”