## 1 Introduction  
Pattern reconfigurable antennas received considerable attention owing to its attractive performance, as they can switch radiating patterns while keeping other operating parameters unchanged, such as operating frequency and polarization. In spacecraft, satellite, and missile applications, antenna constraints include weight, size, cost, and aerodynamic profile. Thus, the implementation of a pattern reconfigurable antenna with a low profile can alleviate those constraints. To date, many pattern reconfigurable antennas [1; 2; 3; 4; 5] have been developed, and reconfigurable antennas are commonly implemented using variodes [6; 7] and PIN diodes [1; 2]. Compared with the variodes, PIN diodes, and other technologies, radio frequency (RF) micro-electromechanical systems (MEMS) switches possess many attractive advantages, such as high linearity, high quality factors, and almost no Please check the sections highlight in yellow in \"the whole text\" as we have made little modification. direct current (DC) power consumption [8]. Many reconfigurable antennas have been developed by employing MEMS switches [9; 10; 11; 12]. However, most of those reconfigurable antennas operate at a low frequency and do not have process consistence, namely, the RF MEMS switches were mounted on circuitry after the antenna patch was implemented, instead of the integrated manufacture of the antenna patch and the RF MEMS switches. In addition, with the various superiorities such as a wide bandwidth, a compact device structure, and a high data throughput capacity, devices in a Ka-band have many advantages.  
A pattern reconfigurable antenna that consisted of a driven patch (active element) and two assistant radiated patches (passive elements) was designed [6], but the proposed method to design and analyze the assistant patches was severely dependent on full-wave simulation, which is time-consuming. A beam-steering antenna was designed in [1], and the antenna was comprised of active patch and passive patch elements, but the analysis of the passive patch elements was rough and had no quantified calculations. In [13] an antenna using parasitic coupling was designed, but the analysis of the parasitic coupling function was insufficient, and the antenna only had simulated results. The active element pattern method integrated with the signal flow diagram needs to be shown to be effective in analyzing the passive antenna patches (parasitic coupling) [14; 15]. The active element pattern of an element is defined as its radiation pattern when all other elements terminate in matched loads [16], and an antenna can be fully described by the its active element pattern and scattering parameters. This method is employed to design and analyze the proposed RF MEMS pattern reconfigurable antenna in this study.  
In this paper, a pattern reconfigurable antenna operating at 35 GHz is proposed by employing RF MEMS switches. By changing the two RF MEMS switches operating modes, the proposed antenna can switch among four different kinds of operating states and obtain three kinds of reconfigurable patterns (because two operating modes possess the same pattern). The proposed pattern reconfigurable antenna is analyzed using an active element pattern method and a signal flow diagram. Comparing the calculated and simulated results with the measured ones, good agreement is acquired.  
This paper is divided into five sections: Section 2 illustrates the design of the pattern reconfigurable antenna, Section 3 analyzes the operating mechanism of the proposed pattern reconfigurable antenna, Section 4 displays the measurement and results, and Section 5 summarizes the paper.