It is difficult to package and interconnect components and devices at millimeter-waves (mm-waves) due to excessive losses experiences at these frequencies using traditional techniques. The problem is multiplied manifold at terahertz (THz) frequencies. In this article, we review the current state of THz packaging and describe several novel techniques. As we will show, micromachined packaging is emerging as one of the best choices for developing advanced THz systems.

We have demonstrated corrugated horn antennas at 560 GHz fabricated with a deep reactive ion etching (DRIE) process on silicon. The measurement of two of the ( 2 times 2)560 GHz array antenna has shown that the return loss and directivity are 13 dB and 22 dB, respectively. All of the measured antennas had below-25 dB of the cross-polarization and symmetrical beam patterns. The silicon microfabrication technique enables us to build hundreds of horn antennas at once, allowing construction of multi-pixel heterodyne imagers and spectrometers at submillimeter wavelengths.

In this review paper we explore different antenna technologies at terahertz frequencies for space science and other applications. We show that the antenna technologies generally used at lower frequencies are difficult to implement at terahertz frequencies. Additionally, one has to take a few extra steps and special care for designing antennas for space-based applications. In this paper, we review different design and implementation options for millimeter-wave and terahertz antennas for space applications. We detail how antenna design has to be a part of the overall system design for the success of the instruments for space missions. We also look into low-mass and low-profile conformal antenna technologies that will have a profound impact on future space instruments at terahertz frequencies.

We have demonstrated corrugated horn antennas at 340 GHz and 560 GHz fabricated with deep reactive ion etching (DRIE) process on silicon. The measurement of a single 340 GHz antenna showed that the return loss and gain are approximately 25 dB and 21 dBi, respectively. The measurement of two of the 2x2 560 GHz array antenna showed that the return loss and directivity are 13 dB and 22 dB, respectively. All of the measured antennas had below -25 dB of the cross-polarization and symmetrical beam patterns. The silicon microfabrication technique allows fabrication of hundreds of horn antennas at once, allowing construction of multi-pixel heterodyne imagers and spectrometers at submillimeter wavelengths.

Terahertz antennas present a different set of challenges to the antenna designer typically striving for very high performance while at the very limit of the chosen fabrication process. Many of the same design techniques used at lower frequencies are still applied, but fabrication constraints impose significant limitations on the type of structure that can be used, forcing the designer to consider unique fabrication processes or completely new antenna structures. Through advances in fabrication and computational techniques, the variety of terahertz antennas is growing. This chapter presents a range of antennas applied at these frequencies from 1.9 THz horn antennas to superconducting planar arrays. The chapter will cover different antenna technologies and feeds such as corrugated horn antennas, smooth-walled profiled horn antennas, multi-flare angle horn antennas, lens antennas, microlens leaky wave antennas, metasurface antennas, antenna arrays, off-chip antennas, and others. It will detail theory, simulation, fabrication techniques, and state-of-the-art antenna results in all these different technologies at millimeter and terahertz frequencies. The chapter will also provide details for terahertz antennas in the context of terahertz systems.

Using newly developed silicon micromachining technology that enables low-loss and highly integrated packaging solutions, we are developing vertically stacked transmitters and receivers at terahertz frequencies that can be used for communication and other terahertz systems. Although there are multiple ways to address the problem of interconnect and packaging solutions at these frequencies, such as system-on-package (SOP), multi-chip modules (MCM), substrate integrated waveguide (SIW), liquid crystal polymer (LCP) based multilayer technologies, and others, we show that deep reactive ion etching (DRIE) based silicon micromachining with vertical integration allows the most effective solutions at terahertz frequencies.

The development at 1.9 THz of a microlens antenna consisting of a leaky-wave waveguide feeding and a silicon microlens is presented in this paper. The antenna has excellent performances compared to horn antennas and can be fabricated entirely using silicon micromachining. Two antenna prototypes were developed: one with a 2.6-mm-diameter microlens and a directivity of 33.2 dB and the other with a 6.35-mm-diameter microlens and a directivity of 41.2 dB. Both prototypes were fabricated and measured, obtaining good agreements with simulations. The fabrication, assembly, and measurement process are explained and detailed in this paper.

We designed and microfabricated a (2×2) silicon platelet horn antenna at 560 GHz, which is the highest frequency ever among silicon corrugated horn antennas. This was enabled by a silicon compression pin alignment technique of which inaccuracy is less than ± 2 μm in layer-to-layer. The simulation results show that the return loss and gain across the operation frequency of 490-600 GHz are approximately 25 dB and 22 dBi, respectively. The cross-polarization level is below -40 dB. The feature of batch processing will enable us simultaneously to build hundreds or thousands of horn antennas.

Using newly developed silicon micromachining technology that enables low-mass and highly integrated receivers, we are developing state-of-the-art terahertz spectrometer instruments for space-based planetary and astrophysics orbiter missions. Our flexible receiver with integrated antenna architecture provides a powerful instrument capability in a light-weight, low-power consuming compact package which offer unprecedented sensitivity performance, spectral coverage, and scalability to meet the scientific requirements of multiple missions.

Increasingly, terahertz systems are being used for multi-pixel receivers for different applications from mapping the star-forming regions of galaxies to stand-off radar imaging. Since microstrip patch antennas are too lossy and corrugated horn antenna arrays are difficult to machine at terahertz frequencies, suitable antenna array designs have been one of the key area of research for this field. Moreover, silicon micromachined waveguide housing for front-end integration is becoming very popular for multi-pixel terahertz instruments. This paper describes multi-pixel terahertz instruments with silicon-micromachined front-end and discusses design challenges for integrating terahertz antennas with such systems.

In this paper, we have microfabricated a 6.4 mm diameter silicon lens array on a 4 inch silicon wafer using silicon micromachining technique. The goal of this lens array is to build a 2×2 lens antenna array for 1.9 THz receiver application. It requires multiple thick photoresist coatings and long selective etching of silicon and photoresist after thermal reflow process. To the authors' knowledge, this is the biggest silicon lens ever microfabricated by semiconductor process.