# A Space-Borne Ka-Band Tile-Type Phased Array Transmitter Module Based on HTCC Technology
## 1 Introduction  
With the increasing demand for flexible payloads, phased array antennas are developing rapidly [1; 2; 3; 4]. Traditional active phased array antenna systems consist of radiating units, transmit/receive (T/R) modules, and beam-forming networks. The interconnection between each functional module is achieved via radio frequency (RF) and low-frequency connectors, which shows the disadvantages of high loss, large footprint, and low integration density [5; 6]. With the rapid development of semiconductor technology and micro-packaging technology, highly integrated T/R modules using micro-packaged chips have become the core of active phased array systems [7; 8; 9; 10; 11]. Advanced transceiver components mostly use system-in-package (SiP) packaging technology to integrate the chips into one package, which can greatly reduce the size, increase integration density, and reduce interconnection losses [12; 13; 14]. With a high-density dielectric substrate as the core, SiP integrates and packages various active and passive components such as RF, analog, and power supply components to build high-performance modules. SiP technology can achieve chip interconnection, heat dissipation, and environmental adaptability protection. Most used high-density substrates include multi-layer printed circuit board (PCB) boards [15] and multi-layer ceramic substrates [16; 17; 18; 19; 20]. Due to the unique requirement of space applications, the PCB processing technology cannot achieve flexible signal interconnection between layers. However, ceramic materials, such as low-temperature co-fired ceramic (LTCC) [16; 17; 18; 19] and high-temperature co-fired ceramic (HTCC) [20], can achieve multi-layer substrate stacking through multi-layer co-firing technology, enabling flexible interconnection and layout between layers. In the meantime, stacking high-density substrates in the vertical direction and realizing inter-board interconnection through a ball grid array (BGA) can further increase integration density and reduce interconnection length, leading to reduced parasitic capacitance, inductance, and improved RF performance [21]. Plenty of works have been proposed to reduce the footprint of the T/R modules while maintaining good electrical performance, as the size of the T/R module strongly confinesthe spacing of radiating elements and the geometry of the active array, which influence the gain and scanning range of the phased array system [2; 6]. [PERSON] et al. [9] proposed a T/R front end based on a gallium nitride (GaN) monolithic microwave integrated circuit (MMIC), which achieved a more compact size compared to traditional T/R modules [7]. However, the proposed MMIC needs to be packaged with a multifunction chip for phase and amplitude control to fully satisfy the requirement of a phased array antenna. [PERSON] et al. [10] proposed a compact T/R module with phase and amplitude tuning ability based on 3D packaging technology. However, it consists of two LTCC submodules connected through a metallic interposer board. An additional assembling procedure is needed in the fabrication. [PERSON] et al. [19] reported a Ka-Band T/R module that integrated four T/R channels into one SiP. This multi-channel T/R module is suitable for large-scale, high-density phased arrays. Currently, most of the T/R modules are designed in a single-sided layout. To further reduce the footprint, designing the SiP in a double-sided way is a promising solution. In this work, we propose an HTCC-based tile-type four-channel transmitter module for Ka-band phased array antennas. The multi-layer HTCC substrate facilitates signal interconnections, enables self-packaging, and creates cavities for chip assembly. Kovar metal frames are welded on the HTCC substrate for hermetical sealing and signal shielding. The four-channel T/R component features a hermetic metal-ceramic package with a footprint of 12.2 mm \(\times\) 12.2 mm and a thickness of 4.3 mm, utilizing 169 BGA pins for signal and DC power interconnection and shielding.