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A 256-element planar phased array is designed and measured, operating between 24.25 GHz and 27.5 GHz. The low-cost array architecture is based on a quad-channel beamforming Radio Frequency Integrated Circuit (RFIC) and multilayer stacked PCB technology. Measured results achieved show that the proposed phased array antenna is efficient in achieving good radiation characteristics with a simple structure. The antenna has a gain of 27.2 dB, 3-dB beam-width of 5.2° and SLLs of −12 dB with uniform-distribution at Ka band.

An X-band metal-only reflectarray, which consists of three parallel metallic dipoles loaded by split square loop units, is investigated in this paper. Enough phasing range and nearlylinearly reflected phase curve benefit from the outer split square loop, which adds a resonantstructure and controls the reflected characteristic. The reflectarray is designed and simulated, which covers an aperture of $200 \times200$ mm $^{2}$. The proposed reflectarray has a lower cross-polarization, and its simulated gain, side-lobe levels, and cross polarization levels are 24.7 dB, -15.8 dB, -35dB at the center 10 GHz respectively. Its 1-dB gain bandwidth is about 20% at X-band.

The design of a tri-band dual-polarization (TBDP) shared-aperture microstrip array antenna for synthetic aperture radar (SAR) applications is presented. It operates at L-, Sand X-bands with a frequency ratio of 1:2.8:8. This TBDP shared-aperture array is assembled by two L/S and L/X DBDP shared-aperture sub-arrays with one L-band dual-polarized sub-array. A prototype array has been fabricated and measured, which exhibits wide impedance bandwidth (VSWR ≤ 2) of 13.4%, 14.8%, and 16.8% in L-, S-, and X-bands, respectively. The measured array isolation is better than -27 dB in all three bands. The measured radiation patterns agree well with the simulation, confirming the cross-polarization level of below dB within the main lobe region, and the array scanning capability of ±27° in S- and X-bands. This array design approach can be further extended to shared-aperture arrays with more than three bands.

Utilization of true-time-delay (TTD) is an important approach for improving the beam-pointing accuracy of wideband phased arrays. This paper studies the side lobe properties as the true-time-delay are equipped at subarray level. The study shows that side lobe levels increase because of periodic phase error. And then, an element-level TTD line scheme is proposed for effective reduction of side lobe levels.

A method of extracting waveguide slot admittance based on the simulated results of the commercial software HFSS is presented. The formula of calculating self-admittance of a single slot in waveguide is derived from transmission line theory, and that of calculating active admittance of a slot in array is given, simultaneously. With the proposed method, a waveguide slot antenna array can be designed easily and economically.