Null Forming in Circularly Polarized Antenna Patterns Using Reactive Loading of Multi-Arm Archimedean Spiral Antenna

Abstract

A multi-arm spiral antenna, of N arms, can have N modes of operation. The integer represents the operating mode which is determined by the signal phase increment between adjacent arms as fed from the antenna terminals. For the antenna to radiate effectively, the active region must be enclosed by a circumference of mode number (n) times the operating wavelength. Each mode generates a different radiation pattern. Modes, with between 2 and , are capable of forming radiation pattern nulls. This paper shows a way to excite noninteger modes along with integer modes of radiation, which combined, can create a null which can be steered away from the antenna vertical bore sight. Furthermore, variable reactive loading of spiral arm ends offers additional steering control and positioning of nulls in a 2D angular hemispherical space.Index Terms-Active region, Archimedean spiral, multi-arm, nulls in circularly polarized patterns, reactive loading, spiral arm, spiral array.

Triple‐mode resonant null frequency scanning antenna with positive scanned slope

“…Finally, Table 2 systematically compares the proposed antenna and other null frequency scanning antennas in terms of operation principle, the number of radiators/ resonant modes, configurational complexity (number of design parameters), null frequency scanning functionality, available radiation bandwidth, requirement of additionally external feed accessories, and antenna size. Compared to the most of the reported null frequency scanning designs, [12][13][14][15][16][17][18][19][20][21][22][23][24][25]40,41 the proposed antenna can be directly fed by a coaxial probe, without incorporating any additional external feed accessories. Compared to the latest triple-mode resonant counterparts, the proposed antenna can continuously scan a wider angular range with a positive scanned slope.…”

“…Alternatively, the radiation null can also be steered by modifying the shape of the array 10,11 . The second way should be the mode‐reconfiguration technique 12–18 . To enable a continuous null scanning functionality, multiple PIN diodes, reactively loaded ports and varactors may be felicitously integrated into the antenna 12–14 .…”

“…[12][13][14][15][16][17][18] To enable a continuous null scanning functionality, multiple PIN diodes, reactively loaded ports and varactors may be felicitously integrated into the antenna. [12][13][14] Accordingly, narrow band null scanning functionality has been attained by varying the relative phase between four loaded capacitive exciters (CCEs) 15 or two external parasitic elements. 16,17 A square patch antenna under hybrid "fixed-tunable" loading 18 can also offer similar functionality.…”

Amplitude Control Null Steering in a Multi-Mode Patch Antenna

“…To steer a single null in such array antennas, amplitude and phase control of only the edge elements of a linear configuration [5,6] or a planar configuration [7] is required. Another common method of null steering is the use of diodes [8], varactors [9,10], and reactive loading [11] or capacitive exciters [12] in the antenna design. However, the dc control circuits make the overall system complex and introduce more loss.…”