# Design of Multifunctional Mesosphere-Ionosphere Sounding System and Preliminary Results
Although MF radar has many advantages, but at a lower operation frequency, the large mechanical dimensions of the commonly used standing-wave antennas also means a greater difficulty for construction. Moreover, due to the prevalent monopulse working mode, a quietly large transmission peak power is required, which makes the cost and power consumption huge. For instance, the length of the dipole antenna employed by Wuhan MF radar built in 2000 reach 75 m, with a peak power as high as 64 kW [18]. As a special type of radar, the development of ionospheric sounder has a long history and many mature devices have been developed [19]. Through continuous hardware improvements and the upgrades of the software, Dynasonde, developed by the National Oceanic and Atmospheric Administration (NOAA), and Digisonde, developed by University of Massachusetts Lowell, have become the currently most advanced ionosonde systems [20; 21]. As early as the 1990s, the Ionospheric Laboratory of Wuhan University also began work on the development of the Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS) to research the large region of the ionosphere in real-time [22]. By now, it has become a highly integrated, multi-functional platform with the abilities of the vertical, oblique, backscattering sounding and multi-station networking [23; 24; 25]. When some spaceborne methods are employed to probe the atmosphere, ionospheric observations can also be carried out using satellite networks. [PERSON] detected midlatitude Sporadic-E (Es) relaying on the interferometric synthetic aperture radar (InSAR) in 2017, which clarified the spatial structure with unprecedented resolution [26]. [PERSON] et al. also investigated the influence of the perturbed (by a solar X-ray flare) ionospheric D-region on the global navigation satellite systems (GNSS) and synthetic aperture radar (SAR) signals in 2019 [27]. Although the observation range is large in this way, the establishment of satellite networks is difficult. And mainly from the perspective of the total electron content (TEC), it is not easy to obtain the real-time ionospheric electron density profile of a specific location. Some other networks such as automatic packet reporting system (APRS) and automatic dependent surveillance broadcast (ADS-B) can also be used for ionospheric studies [28]. However, the same problems still remain. At present, the ionosondes are still difficult to replace for ionospheric sounding. Compared with MF radar, the ionosonde's transmitting power and the size of the antennas are rather small. However, usually working in high frequency (HF) band, the vast majority of the existing ionosondes can only study the ionosphere above the E layer, which is usually higher than 100 km. This makes it applicable only to a relatively narrow mission scope, which may lead the observation and research to be unilateral. In this paper, we propose a novel multi-functional system to satisfy the sounding of the mesosphere and ionosphere simultaneously, which is referred to as the middle atmosphere-ionosphere (MAI) system in this paper. The functions of MF radar and ionosonde are integrated on the same hardware platform and antenna array to achieve the complementarity with each other. Different from the traditional MF radars, the pseudo-random (PRN) phase-coded modulation technology is employed. Due to the extra gain generated by the pulse compression, the peak power required for transmission is greatly reduced. The excellent anti-jamming performance is also very suitable for ionospheric sounding. For the mesospheric sounding MAI system adopts a one-transmitting-and-six-receiving mode, which is unusual. While omitting the transceiver switches, the possible coupling interference may also be avoided. Moreover, innovatively, miniaturized two-wire progressive-wave antennas are employed on the MAI system to achieve the functions of MF echoes' receiving and ionospheric sounding simultaneously [29].